NATIONAL BUREAU OF STANDARDS REPORT

9499

SNOWMELTING SYSTEMS FOR HANGAR DOORS

By

J. C. Davis and P. R. Achenbach

Environmental Engineering Section

Building Research Division

Institute Applied Res-ea-rch / GLC.hn: ! 0 C/ cj

t

/ /

Final Report

to

Naval Facilities Engineering Command

Office of Chief of Engineers

United States Air Force

II. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
THE NATIONAL BUREAU OF STANDARDS

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NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

42100-12-4212401 November 21, 1967 9499

SNOWMELTING SYSTEMS FOR HANGAR DOORS

By

J. C. Davis and P. R. Achenbach

Environmental Engineering Section

Building Research Division

Institute erf Applied He-s-eare-h— Oddii/oo

if"

Final Report

to

Naval Facilities Engineering Command

Office of Chief of Engineers

United States Air Force

IMPORTANT NOTICE NATIONAL BUREAU OF ST

for use within the Government,

and review. For this reason, th whole or in part, is not author Bureau of Standards, Washingt

the Report has been specifically

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST) on October 9, 2015

ss accounting documents intended

subjected to additional evaluation

listing of this Report, either in

i Office of the Director, National

the Government agency for which

opies for its own use.

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

Snow-melting Systems for Hangar Doors

J. C. Davis and P. R. Achenbach

I. Introduction

The agencies of the Department of Defense employ snow-melting systems in cold climates for the area under and adjacent to the large sliding

doors of aircraft hangars to expedite snow removal and thus facilitate

rapid movement of aircraft into and out of these structures. These

systems usually are installed in areas where the winter design temperature

is 10 °F or lower, and in any climate where the average annual snowfall

is 20 inches or more.

A typical snow-melting system, as used by the U.S. Air Force for

this purpose, consists of a heat exchanger with steam at 40 to 100 psig,

or high-temperature water circulating through the primary circuit of the

exchanger; with an antifreeze heat- transfer fluid circulating through the

secondary circuit; pipe coils embedded in the concrete under and adjacent

to the doors; one or more circulating pumps; and automatic controls for

regulating the flow rate and temperature of the antifreeze liquid in

response to the need for heat in the embedded pipes. The antifreeze heattransfer fluid is usually a glycol solution, although special oils have

been used in some cases. A few installations have used two stages of

heat exchange between the primary heating fluid and the antifreeze heattransfer medium. The Bureau of Yards and Docks makes considerable use of

electric heating elements embedded in concrete for snow melting at hangar

doors. The U.S. Air Force also uses similar systems to provide floor

panel heating in some of their aircraft hangars.
At the request of the Tri-Service Defense Agencies, the National

Bureau of Standards made an investigation of corrosion and sludge formation, which have created serious operating and maintenance problems in

glycol systems. A concurrent study also was made of the properties of a

number of other heat-transfer liquids to determine their suitability for

snow-melting and panel-heating systems.

1.1 Scope and Purpose

The U.S. Air Force has experienced operating problems related principally to the formation of sludge and to corrosion in the antifreeze

pipe circuit in snow-melting systems using glycol solutions. These

problems were particularly serious at Minot Air Force Base. In the Minot

system, where sludge formation was excessive, the high- temperature water

at an inlet to the heat exchanger was 380 ®F, and the temperature of the

ethylene glycol solution at the supply to the pipe grid in the concrete

was as high as 160 ®F. Furthermore, the spigot water used for making

the ethylene-glycol-water solution had an abnormally high percentage of

dissolved solids. Purchase specifications for the glycol solutions have

not provided for any specific grade of glycol for this application, and

the operating practices have not prevented mixing of different proprietary

products, nor provided for periodic analysis and control of the corrosion

inhibitors in the system at any of the Air Bases employing snow-melting

systems. Apparently, spigot water has typically been used at these Air

Bases, rather than making any attempt to use water with a smaller amount

of dissolved solids.

2
The first objective of this study, was (a) to evaluate the present

state of knowledge on the chemical, physical, and engineering properties

of glycol solutions, special oils that have been used in snow-melting

systems, certain halogenated hydrocarbons, silicate esters and related

derivatives, organo silanes and disiioxanes, and other fluids that possess

many of the desired characteristics for this application. Snow-melting

systems that do not employ liquid antifreezes were also investigated.

Further objectives were (b) to prepare a specification for the purchase

of heat-transfer media, and (c) to describe the operating conditions

under which glycol solutions and oils could be used in snow-melting systems.

Included in the third objective was the description of procedures for

monitoring the depletion and for replacement of the corrosion inhibitor

in glycol solutions, or for replacement of the solution itself; finding

methods fnr monitoring oil ; determining what modifications in the heatexchange apparatus and controls might improve the application of various

hea t- transfer media to snow-melting; and determining whether laboratory

work in this field was needed or appeared desirable. These objectives,

in the main, have been reached.

Information on the design and construction of snow-melting systems

was not requested originally, but a number of important factors, which

might lead to Improved operation, were investigated. These are discussed

as an aid to engineers, designers, and maintenance personnel. Many of

the findings would be applicable to floor radiant-heating systems employing

ethylene glycol. Some of the reported data were taken from these radiant

systems

3
Only a limited amount of experimental work, which was on the study

of the use of ion-exchange resins for producing de-ionized water in a

snow-melting system, was done by the National Bureau of Standards. Information was obtained largely through literature search, visits to the

chemistry or engineering departments of the manufacturers of hea t- trans f er

media, to Government agencies such as Aberdeen Proving Ground, to snowmelting systems in office buildings or plants, and through discussions

with staff members of the National Bureau of Standards.

2. THE ETHYLENE GLYCOL SYSTEM

2.1 Description of Air Force Base Snow-Melting Systems Visited

by the National Bureau of Standards Personnel

Personnel of the National Bureau of Standards visited Westover

Air Force Base, Mass., the Plattsburg Air Force Base at Plattsburg, N.Y.

,

and the Minot Air Force Base at Minot, N. Dak.

At these three Bases, the source of heat at the primary circuit of

the snow-melting or floor radiant-heating systems was either steam or

high-temperature water (HTW) . Plattsburg AFB and Minot AFB used only HTW,

while Westover AFB used both heating media. The temperature of the water

at the supply to the heat exchanger (converter) in the HTW systems was

about 380 °F at all three Bases. At Westover AFB and Plattsburg AFB,

the temperature of the glycol solution at the supply to the pipe grids

within the concrete was about 110 °F; but at Minot AFB, the antifreeze

temperature at the supply to this grid was in the range from 125 to 160 °F,

4
Typical temperatures of the HTW or steam in the primary circuit of

the heat exchanger, and the ethylene glycol solution in the secondary

circuit, for snow-melting or radiant-heating systems at all three Bases

are shown in table 1.

During the 1962-63 winter season at Minot Air Force Base, it was

reported by the office of the Civil Engineer at that Base that the use of

automotive types of inhibited ethylene glycols produced sludge at the

strainers in a number of snowmelting systems. All of the glycols were

purchased on the open market v?ithout specification. It was also reported

that conversion to a product designed especially for snow-melting systems

and known as Dowtherm SR-1 was tried on an experimental basis in one

building with good results. In the following thirty-day period no plugged

strainers were evident in that building. It was reported finally in April

1954 that conversion to the new material was made in almost all of the snowmelting systems and radiant heating systems with the same good results.

The Dowtherm SR-1 was mixed with water in the ratio of 40 parts

of Dowtherm to 60 parts of water. Untreated spigot water was used with

the 40/60 solution. The Dow Company has assisted in the monitoring of

the Dowtherm solution, but no significant addition of the inhibitors or

replacement of the antifreeze had been made by 1965.

Investigations revealed that two factors contributed to the formation of the sludge when the commercial types of automotive antifreezes

were used: (1) the large proportion of dissolved solids in the spigot

water and (2) the high temperatures encountered in the systems.

5
TABLE 1

FLUID TEMPERATURES OF PRIMARY AWD SECONDARY SYSTEMS IN THE HEAT EXCHANGER

ROR SNOW-MELTING OR RADIANT-HEAT SYSTEMS AT WESTQVER,

PLATTS BURG, AND MINOT AIR FORCE BASES, °F

We stover Air Force Base

Multipurpose Hangar Nose Dock, 23 (HTW)

Primary Secondary

Supply 377 119

Return 181 108

Multipurpose Hangar Nose Dock, 32 (Steam)

Supply 240 98

Return Not available 87

Multipurpose Hangar Nose Dock, 34 (Steam)

Supply 233 118

Return Not available 103

D .C . Hangar System (Snow-Me It ing System) (HTW)

Supply 383 123

Return 245 104

Plattsburg Air Force Base

Building 2763 (M.A.B. Hangar) (HTW)

Supply 370 113

Return 150 97

Building 2763 (Radiant Heating, Floor ) (with HTW control valve closed)

Supply 385 102

Return 150 98

Building 2763 (with HTW control valve open)

Supply 382 111

Return 135 98

Nose Dock 2808 (with HTW control valva open)

Supply

Return

Minot Air Force Base

Nose Docks (HTW)

Supply

Return

352

330

380

Not available

88

Not available

135 - 140

Not available

6
The ethylene glycol used at Westover AFB and Plattsburg AFB, where

less corrosion occurred in the system, was also purchased without specifications,

and was of the type commercially available for automotive antifreeze solutions.

No attempt was made to consistently use one brand in the same system from

season to season, and there was evidence that brands were mixed in several

of the systems. In some cases there had been no clean-out and recharging

of the systems for 6 or7 years. Despite these deviations from good practice,

deterioration of the antifreeze solutions was not excessive, although

replacements have been recommended in some cases. Samples were obtained

from three systems from each base and analyses made later at NBS . Tables

2 and 3 give identification and results of the analyses of the samples

from the three systems at Westover AFB, and tables 4 and 5 provide similar

information for the samples from the three systems at Plattsburg AFB.

Plattsburg AFB and Westover AFB are in a northern area of the

United States, but do not experience the extreme cold temperatures and

high winds that occur at Minot AFB in North Dakota.

The snow-melting system at Westover AFB was an open type, and those

at Plattsburg AFB and Minot AFB were closed types. There was an expansion

tank in the system in each case; at Westover AFB it was about 50 feet above

ground level and 15 or 20 feet above ground level at the other two Bases.

The high level of 50 feet at Westover AFB prevented overflow of the tank

if air became trapped in the system or if boiling of the solution occurred.

Each of the snow-melting systems at the three bases used a branched

pipe grid in the concrete near the rails for the sliding doors. In each

system there were balancing cocks to equalize the rate of flow in the

different branches.

7
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of

Antifreeze

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solutions

for

systems 1

and 3

were

recommended

by

NBS,

due

to

the

large

amount

of

sediment.
Heat exchange between the steam and glycol solution, or the HTW

and the. glycol solution, was accomplished with the use of heat exchangers,

the high- tempera ture media flowing through the tubes of the heat exchanger

and the glycol between the tubes and the shell. All systems used modulating

valves to control the flow of the steam or water into the heat exchanger,

and ultimately the delivered temperature of the glycol solution. Pneumatic

or electronic controls were used for the valves, which responded to the

outdoor temperature or the temperature of the glycol solution in the heat

exchanger. In nearly all cases, the modulating valve was "normally closed",

so that when a power outage occurred, or the circulating pump was otherwise

automatically shut off, the primary medium would not overheat the glycol

solution lying stagnant in the heat exchanger. At Westover AFB, however,

one floor radiant-heating system employed an electronically-controlled

valve which was "normally open". However, according to the engineers, power

failure or mannual shut-down did not occur frequently at this Base.

At Plattsburg AFB, a by-pass around the heat exchanger was part of

the control system for one floor radiant-heating system. When the outdoor

temperature was high, a large proportion of the HTW by-passed the heat

exchanger, keeping the temperature of the glycol solution in the heat

exchanger at a relatively low temperature. Modulation of the flow of HTW

through the heat exchanger was regulated pneumatically by a 3-way valve.

There was an orifice in this valve so there could be no positive shut-off

to allow the temperature in the heat exchanger to become excessive. In a

snow-melting system in one nose dock at this Base, the modulating valve

was by-passed with a manual valve, to be used if the modulating valve failed.

10
Steam and HTW were used as a heat source in different systems at

Westover AFB. Where steam was used, the heat exchangers were about 2

- 1/2

feet long. Pressure of the steam at the input to these heat exchangers was

about 10 pounds, with a saturation temperature of about 240 e F. The heat

exchangers used with the HTW at the other two Bases were about 5 feet long.

Most were manufactured by the Old Dominion Iron and Steel Corporation.

There were no strainers in the systems at Westover AFB and Plattsburg

AFB. The spigot water used for the ethylene glycol solutions at these two

bases was relatively low in dissolved solids. Analyses of water samples

from Westover, Plattsburg, and Minot Air Force Bases were obtained from

the Geological Survey and the Hall Co., of Pittsburgh, with the following

results. The low concentration of ions at Westover AFB will be noted.

Table 6

Analysis of Water

(Concentrat ion of ions in ppm)

Westover AFB*

Feb 1, 1965)

Plattsburg AFB

Chlorides 2 .8 6

Sulfates 6.9 10

Bicarbonates 6.0 55

Carbonates 0 -- Iron 0.2 -- Copper

Calcium plus

--

magnesium 4 5 21

pH 6 .4 7.0

* Conductivity at 70 °F, 35 punhos .

Minot AFB

105

180

230

10

0.1

0.3

150

9.0

11
Although most of the systems at Minot AFB eventually used Dowtherm

SR-1 as the heat- transfer medium, one system was filled with a clear solution,

slightly green in color, which contained globules of black material having

diameters of 1/4 to 1/2 inch. Tnese were analyzed at NBS with following

results :

Table 7

Analysis of Black Deposit in Sample

From Minot AFB

Weight of the deposit in. sample, 16.7 g.

Volume of liquid in sample, 400 ml.

Percentage by weight of materials in sample:

Organic Material 16%

FegOg, 80%

Material not soluble in HG£ , 1%

Not determined, 3%

100%

It is generally recognized in the literature [1,2,3] and by investigators,

that the temperature of the older types of inhibited ethylene glycol for

automotive use should be maintained at 300 °F or less. When these types

of glycol were used at Minot AFB and the temperature of the medium in

the primary system was about 380 °F, it is probable that the ethylene

glycol in areas of the heat-exchanger where the glycol was stagnant or in

other areas where sludge had collected, was subjected to temperatures in

excess of 300 'F. The analysis of the spigot water used for the solutions

showed a high concentration of chloride, bicarbonate, sulfate, and carbonate

ions, all of which will accelerate corrosion, according to the principal

manufacturers’ literature.

12
At the Westover and Plattsburg AFB's, where the water had a low

percentage of dissolved solids, and where the temperatures in the system

were well below 300 °F , sludge was generated at a much slower rate. The

NBS representatives were advised that the solution had not been changed,

except for make-up, for from 5 to 7 years. Make-up was reported to be

about 10 percent a year.

Further information on installation and maintenance practices at

Grand Forks Air Force Base was supplied by letter from Mr. John J. Kotalik,

Deputy Civil Engineer, Grand Forks AFB, North Dakota. Information from

this Base was significant because of its northern climate, and because this

Base had experienced some sludge at the strainers in one system. Table 8

shows an analysis of the water at the Grand Forks AFB.

Table 8

Concentration of ions in ppm

Chlorides 3

Sulfates 16

Bicarbonates 128

Carbonates 0

Iron 0.2

Copper

Calcium plus

magnesium 38

pH 7.6

Conductivity at 70 °F, 293 p,mhos

It is interesting to note the marked difference in amounts of dissolved solids between the water at Grand Forks AFB and at Minot AFB,

which is less than 200 miles away.

13
3. GLYCOLS AND THEIR INHIBITORS

3.1 Aqueous Glycol Solutions

Glycols can be defined as those compounds which have two hydroxyl

(OH) groups attached to separate carbon atoms in an aliphatic carbon chain.

They are known as polyhydric alcohols, and sometimes as diols. The simple

glycols are stable, odorless, water-white liquids when pure. They have

higher boiling points than water, and those used most often in antifreeze

solutions freeze at temperatures below 32 °F. Aqueous glycol solutions

of selected proportions have been used extensively throughout the world as

heat-transf er liquids, because of their low freezing point, low viscosity,

and good hea t- trans f er properties. Ethylene glycol is used most often in

antifreeze systems. Propylene glycol is used where it is believed that

food might be exposed to the solutions.

Until a few years ago snow-melting systems employing ethylene glycol

as the heat transfer media used automotive ethylene glycol solutions entirely.

Solutions for sncw-melting systems are typically 40 percent by weight of

ethylene glycol, with a freezing point of -11 °F, or 50 percent by weight

of ethylene glycol, with a freezing point of -32 °F. Federal Specification

No. 0-A-548a is available for use in purchasing ethylene glycol for automotive purposes. Two types are covered: type I, based on a fixed formulation

with borax as the chief inhibitor, and type II which allows the use of any

type inhibitor, and which must pass certain qualification tests. The

automotive ethylene glycols, however, are designed principally for use in

automobile systems where the glycol is subjected to different conditions

and sometimes different materials than those encountered in snow-melting

systems. Specifications for their purchase allow marginal products

14
according to present-day standards. Further, the inhibitors in these

glycols vary from one manufacturer to another, and mixtures of different

types of inhibitors can lead to difficulty.

Two proprietary products were found by the NBS investigations to be

satisfactory and designed specifically for snow-melting systems: Dowtherm

SR-1, manufactured by the Dow Chemical Co., of Midland, Mich., and UGAR 17

Thermofluid, manufactured by the Union Carbide Chemicals Co., a division

of the Union Carbide Co. , of New York, N Y. The UCAR 17 Thermofluid

material is similar to its predecessor, PM 1717, made by the same company.

Both products consist largely of ethylene glycol with inhibitors. All

additives in these products are not known; however, analyses performed at

NBS revealed that both products contain mercaptobenzothiazole and either

sodium hydrogen phosphate or potassium hydrogen phosphate. The investigation

also showed that an ethylene glycol solution developed by the Coatings and

Chemical Laboratory of the U.S. Army at Aberdeen Proving Ground was satisfactory for snow-melting systems.

Dowtherm SR-1 does not contain borax. Tie buffering agent in

Dowtherm SR-1 is not known. The UGAR-17 Thermofluid contains borax, which

belongs to a class of anodic inhibitors and acts as an agent to neutralize

the action of contamina tion products [4], as well as a buffering agent to

maintain a high pH [5]. The use of a buffering agent is a technique employed

in many commercial products in which, for a considerable range, relatively

large additions of acidic products have very little effect on pH. A good

exposition of the chemical theory of the buffering action is given by

Koltoff and Sandell [6].

15
The purpose of the mercaptobenzothiazole (MBT) is to inhibit

corrosion of copper, and certain of its alloys, in water and aqueous solutions [7]. A water solution of sodium MBT is sometimes known by the

proprietary name of "Nacap". The purpose of the potassium hydrogen phosphate or sodium hydrogen phosphate is to provide anodic protection, and

protection for ferrous and certain non-ferrous metals [5,7]. This inhibitor

also serves as a buffer. Both of these inhibitors are relatively new to

the industry and their use has contributed to the greatly increased life

of ethylene glycol solutions.

The NBS was informed by a technical representative of the Union

Carbide Chemicals Co. that UCAR 17 has approximately the same formulation

as the ethylene glycol product developed by the Chemical Coatings Laboratory of the U.S. Army Aberdeen Proving Ground. Analysis of the UCAR 17

material at NBS showed this to be essentially true, except that potassium

hydrogen phosphate is used instead of sodium hydrogen phsophate, and the

amount of MBT is considerably less.

The inhibited ethylene glycol developed by the Chemical Coatings

Laboratory has shown long life, both in simulated service tests in the

laboratory, and in actual automotive service tests at the Proving Ground.

The simulated service test consists of a mechanical unit arranged to

permit the test solution to be circulated in a closed system at a controlled

circulation rate and temperature. In these simulated service tests, using

a 50/50 mixture of ethylene glycol and water, good performance was obtained

for 7000 hours. (The old type I glycol with borax of Federal Specification

0-A-548a had an average life of about 2000 hours). Good performance also

16
was obtained for about 20,000 miles of service for staff cars, and about

50,000 miles of service for private cars. Information on the development

and testing of the Chemical Coatings Laboratory formulas can be found in

Aberdeen Proving Ground CCL Report No. 156 f_ 8 J

. In bench-corrosion tests

described in this report, a set of six metal test specimens known as

coupons were immersed in a glass flask containing the test solution. The

solution is aerated and refluxed at 180 °F for 192 hours, after which the

metal specimens are examined for extent of corrosion. The report states

that in almost every instance use of the Coatings and Chemical Formula

(Formula B by their designation) lessened the weight-loss of metal coupons

,

including aluminum, over other formulas tested. The formula also performed

satisfactorily with water containing 100 ppm of Cl , SO*

-

, and HC03

.

Results relating to protection against solder corrosion were not conclusive,

however. The laboratory stated that a harmless white flocculent precipitate

consisting of undissolved MET is suspended in the solution for reserve

purposes. This precipitate will pass through the strainers and will not

deposit anywhere in a snow-melting system.

To purchase Dowtherm SR-1, or equivalent material manufactured by

a company other than the Dow Chemical Co., it is suggested the specification

given in Table 9 for Type A inhibited ethylene glycol be used. To purchase

UCAR 17 or equivalent, it is suggested the specification in Table 10 for

Type B material be used.

17
TABLE 9

SPECIFICATIONS

FOR

TYPE A INHIBITED ETHYLENE GLYCOL FOR SNOW-MELTING SYSTEMS

(For use in the purchase of Dowtherm SRTM 1 or equivalent material)

Property

pH (50% solution by volume)

Limits Test Method

8.0 - 9.5 ASTM Designation D1287

Reserve alkalinity

(ml 0.1 N HC/10 ml), minimum

Phosphate ion content,

% by weight, minimum

10 ASTM Designation D1121

1 . 0 Paragraph A a

Mercaptobenzothiazole ion

content, 7a by weight, minimum

Total glycols having hydroxyls

on adjacent carbons, % by

weight, minimum

0.04 Para. 4. 4. 3.1. of Federal

Specification 0-l-490a,

Inhibitor Corrosion, LiquidCooled System

92 Para. 4.6.4. of Federal

Specification 0-A-548a, Antifreeze, Ethylene Glycol,

Inhibited

Water, % by weight, maximum 3.0 ASTM Designation D1123

Vf Glycols other than ethylene

glycol, % by weight, maximum

Chlorides

3.0

To pass

test

Obtained by calculating the

difference between the total

of percentages for all other

items and 100 percent.

_ , b

Paragraph B

Ash, % by weight, maximum

Arsenic, % by weight, maximum

Reagent Chemicals, Am. Chem.

Soc . Specifications, 1955

3.0 ASTM Designation D1119

100 ppm Gutzeit method. Described in

* Glycols can be defined as those compounds which have two hydroxyl

(OH) groups attached to separate carbon atoms in an aliphatic carbon

chain

.

(a) Shown on page 20

(b) Shown on page 21

18
TABLE 10

SPECIFICATIONS

FOR

TYPE B INHIBITED ETHYLENE GLYCOL FOR SNOW-MELTING SYSTEMS

(For use in the purchase of UCAR-17 Therraof luid or equivalent material)

Property Limits Test Method

pH (50% solution by volume) 8.3 - 9.8 ASTM Designation D1287

Reserve alkalinity 20 ASTM Designation D1121

Phosphate ion content,

%, by weight*, minimum

0.45 Paragraph A

a

> Mercaptobenz&thiazole ion

content, %> by weight, minimum

0.07 Para. 4. 4. 3.1 of Federal

Specification 0-l-490a,

Inhibitor Corrosion, Liquid

Cooled System

Borax, % by weight, minimum 1.3 Para. 4. 4. 3. 2 of Federal

Specification 0-l-490a,

Inhibitor Corrosion, Liquid

Cooled System

Total glycols, having hydroxyls

on adjacent carbons, % by

weight, minimum

93 Para. 4.6.4 of Federal

Specification 0-A-548a, Antifreeze, Ethylene Glycol

Inhibited

Water, other than water of

hydration in borax % by weight,

maximu^D

3.0 ASTM Designation D1123

Glycols ' other than ethylene

glycol, % by weight, maximum

3.0

To pass

Obtained by calculating the

difference between the total

of percentages for all other

items and 100 percent

b

Ch lor ides test Paragraph B

Ash, Yo by weigl t, maximum 3.0 ASTM Designation D1119

Arsenic, % by weight, maximum 100 ppm Gutzeit method. Described in

Reagent Chemicals, Am. Chem.

Soc . Specifications, 1955

* Glycols can be defined as those compounds which have two hydroxyl

(OH) groups attached to separate carbon atoms in an aliphatic carbon

chain

.

(a) Shown on page 20

(b) Shown on page 21

19
Paragraph A. Phosphate (P0^ 3 “

)

A weighed 5-ml sample is diluted to 1 liter in a 1-liter volumetric flask

and a 2-ml aliquot of this is used. Twenty-five ml of 0.5 N hydrochloric

acid is added, followed by 1 ml of ammonium molybdate reagent and 1 ml

of p-methylaminophenol sulfate reagent. The color is allowed to develop

for 2 hours and then the volume is made up to 50 ml with 0.5 N hydrochloric acid. The transmittance of the solution is read at 650 m|i .

Standards containing 0, 10, 25, 50, and 100 p,g are colored in a similar

manner for a standard curve. The amount of phosphate present in the

aliquot is determined from the curve.

Ammonium molybdate reagent solution . 50 grams of ammonium molybdate

reagent (NH4, )6 Mo? *4^ 0 are dissolved in one liter of 1 N sulfuric acid.

p-Methy laminophenol sulfate solution . 2 grams of p-methy laminophenol sulfate are dissolved in 100 ml of water. To 10 ml of this solution, add

90 ml water and 20 grams of sodium bisulfite.

Standard phosphate solution (1 ml = 1 |j,g P04

3 ~

) . 0.143 grams of KH2 PO4

are dissolved in water and diluted to 1 liter. 10 ml of this solution are

diluted to 1 liter.

Alternate Method for Determination of Phosphate (PO^ 3 "

) . Para. 4. 4. 3.

3

of Federal Specification 0-l-490a, Inhibitor Corrosion, Liquid-Cooled

System, except that for the calculation of the weight of the phosphate

94.97

ions use the mi] li-equivalent of P04 which is equal to 0.004129 = (

~2

"3

~x ]_qq

' q

) •

20
Paragraph B. Chlorides

To 10 ml of concentrated inhibited ethylene glycol add 10 drops of concentrated nitric acid and agitate. Add 1 ml of a 3 percent aqueous

Solution of silver nitrate and filter. Discard the filtrate. Wash the

residue with concentrated ammonium hydroxide, recovering the filtrate.

Acidify the filtrate with concentrated nitric acid. No precipitate shall

form within 30 minutes. A slight turbidity is allowed.

Paragraph C.

The undiluted glycol shall be shipped to the user in containers made of

steel and which do not contain tin.

21
To obtain the gLycol solution recommended by the Coatings and

Chemical Laboratory at Aberdeen Proving Ground, the purchaser buys the

relatively inexpensive Type I borax inhibited ethylene glycol under

Federal Specification 0-A-548a, then adds packaged inhibitors in

accordance with the weight requirements shown below. The inhibitors are

added at the optimum rate of 1 oz . of the inhibitor to each two quarts

of the water used. The Type I borax inhibited ethylene glycol can be

procured through the military supply system. The packaged inhibitors

are covered by Federal Specification 0-I-490a and can be procured from

the General Services Administration stock No. 6850-5842707.

Table 11

Weight Requirements for 6 and 8-1/2 oz Packages of Formula B

6 oz (170 gm) 8% oz (242 gm)

package weight, package weight,

in grams in grams

Units

Composition Min

.

Max

.

Min

.

Max

.

Mercaptobenzothiazole 24.8 26.6 35.3 37.7

NagB^Qy, anhydrous 67.0 68.8 95.5 97.9

NagHPQi, anhydrous 14.7 16.5 21.1 23.5

Specification 0-I-490a also lists methods for testing for the

three chemicals in the package.

A further advantage of the new inhibitors is their ability to

recondition the solution with the addition of small amounts of inhibiting

ma teria 1

.

22
Type A, Type B or the Coatings and Chemical Laboratory Solution

can be stored satisfactorily in large steel drums, but precaution must be

taken not to expose them to a temperature of less than 10 °F, since the

freezing point of undiluted ethylene glycol is +9 °F. In all cases, the

glycol should be throughly stirred and mixed before use in the system.

None of the three types should be stored in tin-lined containers. Mercaptobenzothiazole , an organic compound, will react with the tin.

As a result of the findings at Minot Air Force Base and of discussions

with the Coatings and Chemical Laboratory, the Dow Company and Union Carbide

Company, there is some evidence to show that Dowtherm SR-1, UCAR 17, and

type I borax - inhibited glycol with formula B material added, can be used

for somewhat higher temperatures than the borax-inhibited glycols purchased

under specification 0-A-548a.

3.2. MONITORING AND MAINTENENCE OF

ETHYLENE GLYCOL SYSTEMS

3.2.1 Importance of Water Quality

It is well known that water high in dissolved solids, when used in

aqueous glycol solutions, will speed corrosion of the metals in an automotive or sncw-meltLng system. Chlorides and sulfates have been long established as water contaminants that aggravate corrosion |_9], and also

bicarbonates and carbonates. Some indication of the effect of water quality

on auto-coolinj'-system corrosion is presented in a paper by Boehmer and

Compton [10]. These effects should apply, in some measure, to snow-melting

sys terns

.

23
Several ways to obtain de-ionized water were investigated. Distilled

water is satisfactory, but expensive. The use of steam condensate offers

another satisfactory method, and the use of de-ionization systems with

exchange resins, another. The latter method is too expensive generally

for the production of water for new systems containing 500 to 2000 gallons,

but shows some promise for the production of make-up water. To quantitatively determine the feasibility of their use for make-up water in a system,

the National Bureau of Standards performed special laboratory tests on a

number of de-ionizing cartridges purchased from the Illinois Water Treatment Co., of Rockford, 111. They were all of the same type, known as the

Universal Model, commonly used in laboratories to convert spigot water into

de-ionized water at a rate of about 5 gal/hr. The cost per cartridge was

about $10 in 1963.

Each cartridge was essentially a transparent plastic cylinder with

two end pieces, the cylinder containing resin crystals through which the

water ran from top to bottom and out through a spigot. The crystals were

initially lavender in color. With time, as water passed through them and

was de-ionized, they turned yellow, the change in color slowly moving from

top to bottom. According to the manufacturer , when the yellow color reached

a point about 2 inches from the bottom, the cylinder was expended.

The cartridge is a mixed-bed de-ionizing type. This designation

signifies the mixing of a quantity of a strongly basic anion exchanger with

an equivalent quantity of a strong cation exchanger, such that complete

de-ionization of a solution may be accomplished and a neutral pH maintained

throughout the entire exchange process [llj. This technique surpasses

older techniques in existence only a few years ago.

24
For the first two laboratory tests , the water to be neutralized was

placed in a 55-gallon drum, supported near the ceiling of the laboratory

by a wooden structure, and allowed to run through a cartridge. During the

first test, distilled water with a known amount of dissolved solids, approximating that in the spigot water at Minot AFB, was used. The amounts used

are shown in Table 12. This charge of dissolved solids was known as charge

No. 1. The synthetically ionized water passed through the filter and collected in 5-gallon jars, then the conductivity of the water in each jar

was determined. The flow of water was continued until its conductivity

reached a value in the range from 100 to 200 p,mhos . By totaling the volumes

of collected water in the jars, a determination of the useful life of a

cartridge was obtained. The test was repeated four times, four cartridges

being tested sequentially. Performance of the four cartridges was essentially

the same.

Table 12

Dissolved solids,

ions Parts /mil 1 ion

Chlorides 105

Sul fa tes 180

Bicarbonates 230

Carbonates 10

Ca Icium-Hnagnes ium 600*

*By NBS analysis, the water at Minot AFB showed 150 ppm for the com- bination of calcium and magnesium ions. It was impossible to obtain a smaller concentration of calcium and magnesium ions than the above, when

easily available and reasonably priced calcium carbonate and magnesium

sulfate were used. The Water Resources Board of the Geological Survey

advised that finished spigot water at Minot, N. Dak., often showed a con- centration of 600 ppm for these two types of ions to obtain the level of

bicarbonate and sulfate ions shown in Table 6.

25
For the second test, the dissolved solids were in the same proportion, but the amount of each was one-half that in charge No. 1. The charge

for this solution was designated as charge No. 2, and roughly represented

the dissolved solids found in a number of localities in the United States.

Two cartridges were used sequentially in the test and the performance of

both cartridges was essentially the same.

A third test was performed with Washington, D.C. city water. This

de-ionized water ran from the cartridge into a metal drum, and samples were

collected periodically for determination of conductivity. Two cartridges

were used sequentially in this test, and their performance was essentially

the same. An analysis of Washington city water is shown in Table 13.

Table 13

Concentration of Ions

Washington City Water (May 1964)

Dissolved solids,

ions Parts/ million

Chlorides 9.8

Sulfates 35.0

Bicarbonates 45.0

Carbonates 0.0

Iron 0.05

Copper 0.01

CalciurrH-magnesium 30.6

pH 7.5

Before each test, determinations were made of the conductivity of

the synthetically ionized water in the 55-gallon drum, and of the city water.

The rate of flow of water for all tests was 5 gal/hr. Results of the three

tests are shown in Table 14.

26
TABLE 14

Conductivities of Samples of De-Ionized Water

Test No. 1 (Charge No. 1)

i

f

i

1st Cartridge 2nd Cartridge 3rd Cartridge 4th Cartridge

Conduc r y

(pmhos ) Gal/sample

Conduc 'y

i \ (pmhos ) Gal/3 ample

jConduc ’y

j (pmhos )

Gal / sample

Conduc ’y

(pmhos )

Gal/

sample

Initial j Conduc ’ y j 883 1 883 831 831

Sample 1 No. i

\ 1 2.0 5 3.4 5 2.6 5 1 .2 5

2 6.0 5 7.5 5 9.7 5 5.6 5

3 15.0 5 15.8 5 16.7 5 13.3 5 4 18.9 5 25 .5 2 22 J 5 17.1 5 5 177.0 5 580 5 15.7 5 6 1035 5

| 1075 5 237 5

7 1500 3 1500 2 1500 5 Total 33 J IT i i

32 33

Test No. 2 Test No. 3

(Washington, D.C.

(Charge No. 2) City Water)

1st Cartridge 2nd Cartridge 1st Cartridge 2nd Cartridge

Conduc’y Gal/ f Conduc 'y Gal/ IConduc y Cum. ;Conduc y Cum.

(p.mhos ) sample (p.mhos ) sample (p.mhos ) (gal . ) (pmhos ) (ga 1 .

)

Initial

Conduc ' y 430

p 398 319 370

Sample s No.

1 1.3 5 1.4 5 1.5 15 8.8 25

2 1.6 5 1.3 5 10.7 50 136 60

3 1.0 5 ; i.3 5 10.9 65 970 104

4 2 .5 5 j 2,1 5 35.3 75

5 5,0 5 5.4 5 240 85

6 7.1 5 6.7 5 682 95

7 7.5 5 9.7 5 812 103

8 7.7 5 1 10.0 5

9 8.1 5 10.0 5

10 12 .2 5 9.7 5

i

11 13.6 5 | 11.5 5

f 12 30 5 33 5 13 316 5 108 5 l 14 880 5 670 5

l

i 15 12 00 5 j 1070 5 } 16 1300 5 1200 5

i

i 17 1360 2 910 2

*

\ Total

_j 82 82

- 103

i

.

.

T04

27
One cartridge of the 12 purchased for the tests failed to allow

a sufficient flow rate of 5 gal/hr and was discarded. For some cartridges,

water was allowed to wet the crystals from top to bottom, the entire

cartridge turned upside down momentarily to remove the air, returned to

its normal vertical position, and then the spigot opened. Tests showed

there was no significant difference in performance between this operation

and when the cartridge remained upright.

Figure 1 shows curves of conductivity with respect to amount of

\«ter da-ionized as determined from the tests. The curve marked (a) was drawn

from the data of Table 14 for Test No. 1, first cartridge ; (b) from data

of the same table Test No. 2, first cartridge; and (c) from that of the

same table for Test No. 3, first cartridge. It will be noted that the

cartridges exhibited a quick deterioration at a certain point. Once a

conductivity of about 20 p,mhos had been reached, a rapid increase occurred

for subsequent samples.

Analyses of two samples of water taken during the second test

with charge No. 2 at about the 30 pmho point are given in table 15.

These two samples are identified in Curve (b) of Figure 1.

TABLE 15

PARTS PER MILLION OF DE- IONIZED WATER HAVING A CONDUCTIVITY OF

ABOUT 30 p,mhos , SECOND TEST, CHARGE NO. 2 (Beginning of test - conductivity 430 p,mhos)

Sample a~ SO* c£fe HgCOa HCOa CQa ph

Conduc 'y

(umbos)

1st Cartridge 2 <2 4 4 5to6 30

2nd Cartridge 2 <2 5 5 5 to6 33

28
1300

1200

1 100

sooo

900

800

70 0

GOO

50 0

<00

300

200

SCO

0

(

* t

GALLONS OF WATER USED BY l ON

EXCHANGER

.. S. 29
Table 15 shows a very light ion concentration. About 60 gal of

water had been de-ionized when the samples were taken.

An analysis of each of the two samples of Washington city water taken

during test 3 is shown in table 16. These two samples are identified in

Curve (c) of Figure 1.

TABLE 16

PARTS PER MILLION OF DE-IONIZED WATER, THIRD TEST,

WASHINGTON CITY WATER

(Beginning of test - conductivity 319 (j,mhos)

Conduc 'y

Sample Cl S© 4 CO^ HgCOg" HC03 C03 pH (p,mhos)

1st Cartridge 27 25-30 20 - 19 1 8.1 Approx. 240

2nd Cartridge 23 <2 6 6 - - 3.3 Approx. 240

Table 16 shows a moderate ion concentration. About 85 gal of

water had been de-ionized when the samples were taken .

The results of these two analyses show that at 30 p,mhos (charge

No. 2), the parts per million of chloride, sulfate, bicarbonate, and

carbonate ions were very small, but at 250 p,mhos (when city water was

demineralized), the concentration of chloride ions had increased;

chloride ions, for example, were about 25 ppm. This performance is consistent with the expected behavior of the mixed-bed type of de-ionizer,

where the ion content is insignificant for the first few gallons of

operation and remains small until the de-ionizer is nearly spent. At

this point, the negative ions are produced from the mixed bed in increasing

numbers and the conductivity rises sharply, as shown for all curves of

Figure 1.

30
As shown in Table 15 the pH at the SO-p.mho point is 5 to 6. It

was found during the study that it was very difficult to make a positive

determination of pH for samples of de~ionized water, which had conductivities

of less than 30 p,mhos. Unless extreme care is taken the results will be

low. For the determination made during this study, a pH meter was employed

by which two electrodes were placed in the sample under test and the pH

reading was observed by a dial reading on the face of the meter. To calibrate the pH meter, a given buffer solution was used, and an adjustment was

made in the electrical circuit of the meter so that the dial reading was

exactly 40. After calibration, the electrodes were rinsed thoroughly with

distilled water and the sample tested, but it was virtually impossible to

remove all traces of contaminants left on the electrodes from previous tests

and traces of the buffer used during calibration. For water which had a

low conductivity, the traces of contaminants and the buffer had a relatively

large effect, thus removing some accuracy from the determination. Reference

is made to Section 3.1, where some explanation is made of the buffering

action by ethylene glycol inhibitors.

After extremely careful measurement techniques had been followed

and comparisons were made of pH readings where different buffers were used,

the meter indicated, that the pH for samples having conductivities in the

range 1 to 20 p-mhos was between 5,5 and 6, which is satisfactory for makeup water in a snow-melting system. Distilled water will show a pH

of about 7 and will drop in a very short time to about 5.7, due to the

formation of carbonic acid from the C0g in the air. Cases have been

reported where de-ionized water is highly corrosive. This is true

because of the complete lack of a buffer. However , for inhibited

ethylene glycol solutions where a buffering material is always present,

appreciable corrosion will not occur.

The pH values of 5 to 6 for water having a conductivity of from 1 to

3 0 p,mhos appears to be in agreement with chemical theory. Assuming that

31
all the anions are chloride ions, and all the cations are hydrogen ions, a

conductivity of 30 p.mhos will be equivalent to a pH somewhere between 5 and 6.

Based on considerations of conductivity and pH, it is reasonable to

establish 20 p,mhos as a limit for conductivity of water de-ionized by a

cartridge of the type used during the test. Referring to Fig. 1, it is

feasible to use only about 20 gallons of water with dissolved solids similar

to those in charge No. 1, about 55 gallons with dissolved solids similar to

those in charge No. 2, and about 65 gallons for city water similar to that

in Washington, D. C. for each deionizer cartridge of the type employed in

this study.

The manufacturer's advice that the cartridges may be used until the

yellow coloring in the crystals reaches a point 2 inches from the bottom of

the cartridge was found to be inappropriate for the present application.

During the study of pH it was found that after 62.5 gallons of water had

been de-ionized, the crystals were yellow to a point 10 inches from the

bottom of the cartridge; after 103 gallons, when the conductivity was 32

p.mhos and the pH 4.2, a point 6-1/2 inches from the bottom; and after 120

gallons, when the conductivity was 441 |amhos and the pH 3 , a point 4 inches

from the bottom. It is probable that not only would the de-ionized water be

highly acidic when the yellow coloring reached a point 2 inches from the

bottom, but there would be a high concentration of mineral ions, many of

which have been shown to be detrimental to inhibited ethylene glycol solutions.

There is no absolute assurance that the performance of cartridges

from other manufacturers will be similar to those tested. However, staff

members of the National Bureau of Standards have been advised that the resins

used in the mixed-bed type of filters are manufactured by only one or two

chemical companies. Therefore similar performance would be expected.

32
Large de-ionizers of other types might profitably be used at certain installations, especially de-ionizers in which the crystals can be

re-activated and re-used. Water de-mineralization costs for four types

of systems, including the mixed-bed type, are compared in a paper by

Kahler and Reents [12],

3.2.2 Determination of Water Quality

The following methods are suggested for determining if local water

requires de-ionizing because of chloride and sulphate ion concentration.

If the concentration of these ions is less than 20 ppm and 30 ppm, respectively, it probably will not be necessary to use condensate or de-ionized

water.

3. 2. 2.1 Chloride Ion Concentration

Reagents : The following test can be used for determining the chloride

ion concentration of the water:

Standard Methods for the Examination of Water and Wastewater r 13] ,

11th Edition, 1960, American Public Health Association, Inc., Test

for Chloride, pp. 78 and 79.

33
3.2. 2. 2. Sulfate Ion Concentration

For determination of the sulfate ion concentration of the water, use

the test specified on pages 237-243 of Standard Methods for the Examination of Water and Wastewater [13].

3.2.3. Determination of Amount of Depletion of the Inhibitors of

an Ethylene Glycol Solution During Service

Without special apparatus, there is no easy and certain method for

monitoring inhibitor effectiveness of the aqueous ethylene glycol solution

in a snow-melting system. For Dowtherm SR-1, the Dow Company offers a

monitoring service whereby the customer sends representative samples of

the solution from its snow-melting system for analysis. After analysis

and without charge, the Dow Company recommends whether the additives

should be increased or whether the solution has reached a point where a

complete change is necessary.

The Union Carbide Company does not offer this service for UCAR 17,

but an advertising brochure suggests a set of criteria for maintaining

the quality of the solution, which includes tests and limits for

appearance, pH, phosphate ion content, sodium MBT content, chloride content, and freezing point. This brochure can be obtained by writing to

Union Carbide Corp., Chemicals Division, 270 Park Ave . , New York, N. Y.,

10017. A test for reserve alkalinity also should be added. Reserve

alkalinity as a partial means for monitoring will be discussed later in

further detail.

34
If one of the three newer types of inhibited ethylene glycol described in this report is used in the system, usually only tests for reserve

alkalinity, freezing point, and pH are necessary. Reserve alkalinity is

defined as "the number of milliliters of 0.1 N hydrochloric acid required

to titrate 10 milliliters of concentrated glycol to a pH of 5.5." The tests

should be performed at least once a year for the first two years, and every

six months thereafter, either by the manufacturer, if a testing service is

supplied, or by the engineering staff at the site of the snow-melting system.

If the test values for reserve alkalinity, freezing point, and pH approach

the following minimum limits, further tests, as enumerated below, should be

performed to determine the need either for reconditioning or placing a new

charge in the system. Some of the limits shown were supplied by the manufacturer .

Dowtherm SR-1

Reserve alkalinity, minimum, ASTM Designation D1121 8.0

pH, minimum, ASTM Designation D1287 7.0

Phosphate ion content, %by weight of concentrated

ethylene glycol , 54

No limits are given for the mercaptobenzothiazole ion content.

However, the Dow Company states f 14] , that "if the phosphate ion level drops

below 0.54 percent, based upon 100 percent Dowtherm SR-1 , the solution should

be re-inhibited. Addition of the Dowtherm SR-1 inhibitor will replenish both

sodium mercaptobenzothiazole and dipotassium phosphate in proper ratio and

to the required levels". This inhibitor can be obtained from the Dow Company.

35
UCAR 17 Thermofluid

Reserve alkalinity, minimum, ASTM Designation D1121 7.0

pH, minimum, ASTM Designation D1287 7.8

Mercaptobenzothiazole ion content, % by weight, minimum 0.01

Phosphate ion content, % by weight, minimum 0.1

If the values fall below the minimum limits, it is suggested that

the Union Carbide Chemicals Company be contacted for methods of reconditioning

the solution.

Type I Inhibited Ethylene Glycol with Formula B Inhibitors

Reserve alkalinity, minimum, ASTM Designation D1121 7.0

pH, mimimum, ASTM Designation D1287 7.8

Mercaptobenzothiazole ion content, % by weight, minimum 0.01

Phosphate ion content, % by weight, minimum 0.1

It is highly improbable that the value for the mercaptobenzothiazole

ion will fall below 0.01 percent, because of the heavy reserve amount in the

material (approx. 0.25% when the solution is new); however, should either

the value for the MBT ion content, or the phosphate ion content fall to the

specified minimum values, new formula B inhibiting material should be used

to recondition the solution, or the solution should be discarded if there is

evidence of heavy amounts of rust, foreign deposits, crystalline material, or

amorphous material other than the white flocculant precipitate of mercaptobenzothiazole normal for the solution. Federal Specification 0-I-490a gives

information on the size package of the formula B inhibiting material to use.

36
3.2. 3.1 Discussion of Applicable Tests

a. Reserve Alkalinity . The test for reserve alkalinity is one of

the most positive methods to determine the amount of inhibitor depletion.

This determination gives an indication of the buffering agent remaining in

the solution. A value greater than 20 is common for the new and unused

automotive antifreeze solutions. Of 91 samples of new ethylene glycol automotive antifreeze products tested by the State Laboratories Department of

North Dakota, only 7 had values for reserve alkalinity that were lower than

20 1_ 15] , of which 5 had values greater than 15. Most of these contained

borax. For solutions which have been in the snow-melting system for some

time, the amount of change from year to year is a better criterion for renewal than a lower limit.

ASTM D1121 specifies that the test be performed on a sample of undiluted material. In making a test for reserve alkalinity in accordance

with ASTM D1121, the analyst must consider the amount of water in the solution. For example, if a sample of 50/50 ethylene glycol and water is tested

he must use a 20 ml sample instead of the 10 ml sample specified by D1121.

To obtain an approximate indication of the ratio of glycol to water in a

used solution, determine the freezing point of the solution.

37
b . Determination of the Freezing Point of the Solution . The desired

freezing point at a given site depends upon the weather conditions at the

Base where the snow-melting system is under use. The hydrometer method

can be used. Cleanliness is important. The hydrometers can be washed

with soap and water, dried, and wiped with a cloth moistened with alcohol

to remove any residual soap film [16]. However, even with a clean

hydrometer, certain precautions should be taken to insure correct

readings. In order that a hydrometer may indicate correctly the density

or strength of a specified liquid, it is essential that the liquid be

uniform throughout, and at the temperature specified on the instrument [l6].

The influence of surface tension of the liquid is another important factor [l6]. This liquid adhering to the stem above the general level of

the liquid in which the instrument is floating has the same effect as

adding to the mass of the hydrometer, thus increasing the depth of

immers ion

.

A much simpler and more accurate device for measuring the freezing

point is the type which measures this point directly. A small amount of

the aqueous glycol solution is placed in a small cup, then carbon dioxide

is released from a capsule and directed on the exterior of the cup. Because

of the expansion of the gas, the solution freezes. The cup and solution are

then allowed to warm up. The point at which the solution melts can be

readily observed on an a lcohol -in-glass thermometer, whose bulb is fixed

in the solution in the cup.

The NBS laboratory has used this kind of device and found it to be

very satisfactory. The only commercially available tester of this type

known to the National Bureau of Standards is the Cold Cup Antifreeze Tester,

38
made by Rolf Darbo , Box 2158,, University Station, Madison, Wisconsin, USA.

One of the Cadillac agencies in Washington, D. C „ , has used this device

for a number of years and recommended it highly in preference to the

hydrometer

.

c. Determination of pH of a Solution . In an article describing

research of the British Cast Iron Research Association, it was stated that

the pH value of an antifreeze solution is probably not an adequate criterion

of its corrosivity in a snow melting system, since a solution of pH value

as high as 7.5 had been found to be associated with very rapid corrosion;

whereas, it previously had been assumed that all solutions of pH value

greater than 6,4 were safe F 1 7 ] » The article also states that a better

criterion of renewal is reserve alkalinity. The test specified by ASTM

Designation D1287 requires the use of a pH meter. If circumstances make

use of a pH meter impracticable, the Union Carbide Company advises the use

of a Taylor Model T-0 pH slide comparator, with a slide covering the range

7.8 to 9.2, Catalog No. 1000L. If necessary, suitable pH test papers that

change color over a narrow pH range are also recommended by the Union

Carbide Company.

d . Determination of Amount of MET in Solution;

Weigh 25 to 30 g of the antifreeze info a 250 ml beaker and dilute to

100 ml with water.

Add 15 ml of copper sulfate solution (10 g of CuS0^ o 5H

? 0 in 100 ml of

water) and let the mixture stand for one hour.

Add 5 ml of N hydrochloric acid and stir. Digest the mixture at approximately 50 °C for 30 minutes and then allow to cool to room temperature.

Filter the precipitate of copper mercaptobenzothiazole through a fared

Gooch or sintered glass crucible, wash once with 0.5 N hydrochloric acid

solution and then with water until the washings are free from chloride. Dry

in oven at 100 °C . Cool and weigh.

Mercaptobenzothiazole ion, percent by weight =

84 x weight of copper mercaptobenzothiazole

weight of sample

This specification is from British Standard Specification 3150:1959 r 18"'.

39
The Union Carbide Company specified the following qualitative test

for MBT, which is easy to perform:

Fill a 4- to 6-inch test tube 1/3 to 1/2 full with the sample test

solution. Add 10 to 15 drops of a 50-percent ammonium hydroxide

solution, NH^OH; stopper the tube and shake. Add a few drops>-of a

1.5- to 2.0-percent silver nitrate, AgNO^, solution to the test tube,

and examine visually. The immediate formation of a white precipitate

indicates the presence of MBT.

e. Determination of Phosphate Content . The Union Carbide Company

recommends that the phosphate ion concentration in UCAR 17 should be not

less than 1000 ppm. The following method of analysis for phosphate ion content in UCAR 17 is recommended by that company*. The same limit should apply

for the ethylene glycol developed by the Coating and Chemical Laboratory

purchased under Federal Specification 0-I-490a.

Equipment and Reagents

(1) Taylor Slide Comparator for phosphate ion content;

Catalog No. 1100.

(2) pH base, Catalog No. 531

(3) Low phosphate comparator slide, 0- to 25-ppm, Catalog

No. 1105.

(4) Reagent vial with 0.1-ml pipette (3 ea . ) ; Catalog No. 502A.

(5) Low phosphate mixing tubes (6); Catalog No. 516.

* Brochure on UCAR-17 Thermofluid published by the Union Carbide Company.

40
(6) Test tubes, 5-ml capacity (12 ea,); Catalog No. 500.

(7) Molybdate reagent for phosphate determination, 32 oz;

Catalog No, 601.

(8) Stannous chloride reagent for phosphate determination,

4 oz; Catalog No. 602.

Sample Dilution

UCAR Thermofluid 17 contains 4800 ppm phosphate ion and antifreeze

solutions made by mixture with water normally would be expected to

fall in the 1000“ to 3000-ppm range. Using the specified equipment,

an appropriate dilution of the sample soultion from the system can

be made to facilitate evaluation on the low phosphate comparator

slide (0- to 25-ppm) . For example, if the sample solution is

diluted 1:100, and the phosphate ion content upon examination is

found to be 10 ppm for this dilution, than simply multiplying 10

by 100 will give 1000 ppm as the phosphate ion content of the

original sample system solution.

Procedure

Add the diluted sample solution from the system to the first line

on the low phosphate mixing tube; addition is equal to 10 ml. Then

add molybdate reagent to the second line on the tube; addition is

equal to 4 ml. Stopper the tube and shake. Now add 1 ml of the

stannous chloride solution prepared by following the directions on the

reagent > ial, using the marked pipette. Transfer this blue-colored

solution to a 5-ml test tube and place it in the base of the Taylor

Slide Comparator. Place two 5-ml test tubes, filled with water, on

either side. Using the 0- to 25-ppm, low phosphate, comparator slide,

41
compare the various color intensities, and select the one best

matching the color intensity of the blue-colored solution.

Adjusting of System Solution

When an adjustment in the phosphate ion content of an antifreeze

solution is necessary, the addition should be based on the fact that

adding 1.5 lb of potassium hydrogen phosphate K^HPO^ , to each 100

gallons of system solution is equivalent to adding approximately 1000

ppm of phosphate ion to the system solution. A good grade phosphate,

low in chloride and sulfate ion content, should be employed and be

pre-dissolved in water, or a portion of the glycol coolant apart from

the system.

3.2.4. Importance of Cleanliness

Cleanliness of a system is very important. A letter received from the

Chief Engineer of the Torrington Company, Torrington, Connecticut, who has

had success for a number of years with an ethylene glycol snow melting system, says: "One point that cannot be emphasized too strongly is the desirability of using new pipe when installing such a system, and being sure that

it is thoroughly clean and free of scale and rust before introducing the

solution in the system" £19].

If a system has been used for some time and contains water-formed

deposits, and the solution requires changing, it is necessary that it be

washed thoroughly before recharging. The following suggested instructions

were sent to the NBS by the Union Carbide Company:

a. Flush the system thoroughly with water to remove previously

used coolant.

42
b. Purge the flush water from the system, using air or nitrogen.

c. The system should be filled with a solvent formulated to efficiently remove corrosion products and scale. A 15- to 25-percent

solution of inhibited hydrochloric acid is suggested. The system

should be filled with the solvent and the solvent allowed to

remain in the system for a period of 6 hours at ground temperature.

d. Following the contact time of 6 hours, the cleaning solvent

should be displaced from the system, using water containing 0.05-

percent citric acid (4 lb/1000 gal). This flushing procedure

should be continued until the chloride content of the effluent

flush water is less than 50 ppm. To test for chloride content

of the water, follow the procedure outlined in section 3.2.1.,

Importance of Water Quality.

e. Purge the remaining flush water from the system, using nitrogen.

This will prevent after-rusting of the metal surfaces. The system is then ready for installation of the heat transfer media.

NOTE: If the system is to remain empty for any period of time,

it might be advisable to maintain a positive nitrogen pressure.

The Dow Company recommends the use of Vertan 690, one of their own

products, especially if sweated joints are used; or Vertan 675 Compounded

Chelant, if there is copper in the system.

The Oakite Products Corp., 46A Rector St., New York, N. Y., 10006,

offers a service for cleaning snow-melting systems.

43
3.2.5. Importance of Using Only

One Type of Antifreeze Solution in the Snow-Melting System

It is important that only one type of inhibited ethylene glycol

solution be used in a snow melting system. Manufacturers of antifreeze

fluids advise that mixtures of certain types of inhibitors can cause the

formation of precipitates. There is no certainty that one mixture of any

two types of the three ethylene glycol products recommended in this report

will cause difficulty and if the UCAR-17 Thermofluid Type product and the

Type I Borax inhibited product which have essentially the same chemicals but

in different proportions are mixed, it is probable that no difficulty will

occur. Nevertheless, it is strongly recommended that advice be obtained

from the Union Carbide Company (or manufacturer of equivalent material),

the Coatings and Chemical Laboratory of Aberdeen Proving Ground, or another

qualified labora tory, before such a mixture is made.

3.3. Toxicity of the Inhibited Glycols

Toxicological information on the various glycols is summarized in

Patty’s Industrial Hygiene and Toxicology f 20] . Di-ethylene glycol, small

amounts of which usually appear in a drum of new ethylene glycol, is regarded

as toxic for applications where there is a possibility of ingestion. Toxicity

is greater at high temperatures. In some ethylene glycol products small

amounts of arsenites are used as inhibitors. Because of the toxicity of

these compounds and their inhibitors, it is suggested that working personnel

wash their hands upon completion of their work. Reference is made to

section 5.2.8, which discusses safeguards for keeping the main water supply

pure when applying make-up water to the snow-melting system.

44
Propylene glycol is considered safe for use near foods and is used

for certain applications in restaurants and food-handling installations.

According to Patty [20j, tri-ethylene glycol is not as toxic as

ethylene glycol on ingestion.

4.0 Other Types of Heat Transfer Media

During the investigations a search was made for satisfactory heat

transfer media other than ethylene glycol. Among those investigated were

fluorinated hydrocarbons , silicate esters and their related derivatives,

organo silanes and disiloxanes, oil and water. Only the oil seemed to be

entirely practicable for use in snow melting systems for hangar doors.

Discussions of each of these media investigated are given below.

4.1. Fluorinated Hydrocarbons

Of the fluorinated hydrocarbons used conventionally in refrigeration

systems, R 11, (CCl^F) , and R 113, (CCI 2F - CCIF 2

) appeared to be the most

promising for use in snow-melting systems. The more commonly used types

such as R 12 and R 22 have critical temperatures of 233.6 °F and 204.8 °F

respectively, indicating that a change of state would be likely to occur in

the range of temperature normally encountered in a snow-melting system.

R 11 and R 113, like most of the fluorinated hydrocarbons, have an

absolute viscosity of approximately 0.5 centipoise at 86 °F and densities

30 to 40 percent higher than that for aqueous solutions of the glycols.

They both have specific heats of about 0.22 Btu/lb (deg), however, as compared to about 0.81 for a 50 percent solution of ethylene glycol. The

freezing points of R 11 and R 113 are -168 °F and -31 °F, respectively.

R 11 has a boiling point of 75 °F whereas R 113 has a boiling point of 118 °F

at atmospheric pressure. All the conventional ferrous and non-ferrous metals

45
except zinc, magnesium, and aluminum alloys can be used with both liquids.

None of the fluorinated hydrocarbon materials is flammable or explosive.

The low order of toxicity of these materials is well-known.

4.2. Silicate Esters and Related Derivatives;

Organo Silanes and Disiloxanes

The silicate esters, developed primarily for use as lubricating fluids

in systems such as aircraft hydraulic systems, are another group of possible

heat- transfer media, but are relatively expensive. Certain esters of this

type exhibit good viscosity- tempera ture character is itcs and hydraulic stability in the temperature range of -65 °F and 400 °F. They have low freezing

points, low vapor pressure at elevated temperatures, a high specific heat,

high thermal conductivity, high flashpoint, and a low order of toxicity.

Viscosity at 32 °F is generally about 3 to 20 centipoise; at 100° , it is

less than 10.

Conversations with technical personnel and sales representatives revealed that these organic materials, unless they are specially treated tend

to hydrolyze slowly under prolonged contact with even small amounts of water.

The hydrolytic instability of the silicate esters was once considered a severe

limitation. This property has been suppressed considerably by utilizing

branch chained or higher alcohols for the synthesis of these hydraulic fluids.

The organo-silanes and disiloxanes composed of both alkyl- and alkoxysubstituents he ^e approximately the same characteristics as the silicate

esters, but are more stable and are highly resistant to hydrolysis. R. L.

Peeler and S. A. Kovacich [2Xl, showed that silanes and disiloxanes of this

type could be prepared having hydraulic stability markedly superior to

currently available silicate esters at a temperature of 400 °F. Tert-Alkoxy

46
and long alkyl groups were particularly effective in providing steric protection to the molecule. These materials are more difficult to synthesize

than the silicate esters or require more expensive starting materials and

are consequently more expensive than the silicate esters. Peeler and Kovacich

[21], report the following two materials with high hydrolytic stability:

(1) Ethyl-tert-butoxydi ( 2 - e thy Ihexoxy ) silane

(2) 1, 3-Diethyl-l, 3-di (tert-pentoxy) 1, 3-di (2-ethylbutoxy)

The lubrication properties of these liquids with respect to their effects

on circulating pumps also need investigation before they are considered for

use in snow-melting system.

4.3. Oil

Oil as the heat-transfer media in a snow-melting system is reported

to have good stability when properly applied [22]. The vapor pressure of

some heat-transfer oils is below atmospheric pressure at 400 °F; used with

most metals other than copper.. The oils are not corrosive and are not toxic.

Heat-transfer characteristics of the material are not as good as those of

ethylene glycol, consequently, the heat exchangers must be larger. Oil has

a relatively high viscosity at low temperatures; however, at a temperature of

100 °F, the pumping head of a light oil will be only 20 percent higher than for

a system using water [22]. Because many installation leave their snow-melting

systems operating continuously night and day once the outdoor temperature is

below a certain level, the pumping head will usually be in this range.

Viscosity values for satisfactory oils at 100 °F are about 40-60SUS. Pourpoint for heat-transfer oils is well below 0 ®F; a pour-point of -20 °F is

readily attained, while some oils have a pour-point as low as -50 °F.

47
A description of a toll-road plaza snow-melting system which employs

oil appears in Heating, Piping and Air Conditioning, March 1957 [23]. Public

Building Services Specification No. 304-15 [24], contains requirements for

a complete snow-melting system using heat- transfer oil. Other literature is

available on the use of oil in snow-melting systems. The technical bulletin

published by the Mobiltherm Company might be helpful [25*1.

4.3.1. Oil Requirements

Petroleum oils are made up of carbon atoms in aromatic and naphthenic

rings and paraffinic chains [26], The oils are not pure chemical compounds,

but heterogeneous mixtures of many molecular structures. Petroleum fluids

deteriorate at elevated temperatures as a result of two separate processes -

thermal cracking and oxidation [25]. Therefore, it is important that the

new oil which is to be placed into a system shall have certain characteristics

that minimize such deterioration. Oils known as aromatic oils, which have a

high percentage of aromatic hydrocarbons, are relatively resistant to cracking and thermal decomposition. However, viscosity is high for some oils of

this type.

The GSA Specification No. 304-15 for a complete snow-melting system

using oil as the hea t- trans fer medium requires the tests in Table 17 and

approximate limits for new oil.

Table 17

Va lue

ASTM

Test Method

API. gravity 12.0 D287

Maximum pour point -20 °F D97

Flash point, minimum 250 °F D92

Initial boiling point 450 °F D445

48
A value for viscosity at 100 of 40-60 SUS is also recommended if

the above limits are to be used for purchasing oil for snow melting systems.

The limit- of 12.0 for API gravity apparently allows only the aromatic type oil. One aromatic type oil designed specifically for snow-melting

systems that meets these requirements is Mobiltherm Light Oil, produced by

the Mobil Oil Company.

There is not sufficient evidence to disallow the naphthenic type oil

even if it does not meet the requirements shown above. One naphthenic oil

Circosol 306 (sometimes known as CIRCO XXX Lt . ) , produced by the Sun Oil

Company, has shown good performance in a snow-melting system at the Museum

of History and Technology, Smithsonian Institution, Washington, D. C., for

the two winter seasons. The API gravity number for this oil is about 24.

Results of monitoring the condition of this oil will be discussed in a later

section of this report.

Mobiltherm Light and CIRCO XXX are the only two heat transfer oils,

with a sufficiently low pour point and suitable for snow melting systems, for

which the National Bureau of Standards has any information. In discussions

with manufacturers' representatives consideration was given to the use of

ordinary fuel oil for snow-melting systems, but investigations showed that

this oil was not stable enough, with respect to oxidation and cracking. It

also contains too many impurities in the form of sulfur , water, and other

residue

.

49
4.3.2. Monitoring Procedures for an Oil System

In order to effectively maintain close control of the quality of the

oil in the system, it is necessary to perform certain periodic tests on

samples of the oil. Sometimes these tests are performed by the company

producing the oil, other times it will be necessary to perform them at the

installation.

In reply to an inquiry by the National Bureau of Standards, the

Customer Service Laboratories of the Mobil Oil Company sent the following

suggestions for monitoring the oil in the system, regardless of the manufacturer. At the time the letter was written, these tests were used by the

company for monitoring oil for their customers. Tney are basic petroleum

tests, easily performed by technicians (intially under the supervision of a

chemist) and do not require elaborate equipment. In general, these tests

are employed to monitor fluids in moderate to severe service, involving

continuous operation at temperatures up to 400 °F. Under such conditions,

the fluid must be evaluated for evidence of cracking, as well as oxidation.

Snow-melting systems operate intermittently at lower temperatures. Consequently in such a system evidence of deterioration as indicated by the tests

may not develop for a number of years.

a. API Gravity . Significant changes in the API gravity of the oil

indicate the presence of large quantities of foreign materials,

or that the oil has undergone a substantial amount of molecular

change, such as cracking or oxidation that tends to decrease the

API gravity value. The reduction may amount to several degrees

API.

50
b

.

Viscosity . The viscosities of heat-transfer oils show increases

during oxidation. In addition, experiments show that the viscosity

of fluid subjected to cracking at any one temperature decreases

at first. This can be attributed to the production of low molecular weight materials. However, as time progresses, a certain

well-defined point of minimum viscosity is reached, then the

viscosity increases. In this latter stage, polymerization of

molecules is the dominating feature. As the viscosity increases

due to oxidation, polymerization, or a combination of the two, a

point is reached where the oil is too viscous to allow for efficient heat transfer. Experience by customers of the Mobil Oil

Company has demonstrated that efficient heat transfer for most

systems can be maintained at viscosities up to twice that of the

original oil. Thus, it is evident that viscosity is a critical

parameter, whose behavior over a regulated time period gives an

indication of the chemical, as well as the physical, state of the

oil

.

c. Neutralization Number . The oil's neutralization number is affected

by oxidation. As the oil undergoes oxidation, the neutralization

number rises quite rapidly. Experience by the Mobil Oil Company

has shown that oils possessing neutralization numbers up to 1.0

mgm ROH/gm can give efficient service. The neutralization number

shows virtually no change during cracking.

d. Water Content . If substantial quantities of water are present

in the system when it is operating at temperatures exceeding the

boiling point of water, steam will form. During periods of heat51
up, this may result in bumping and sudden increases in volume.

This, in turn, will back up the fluid into the expansion tank,

a problem that can be minimized by slowly bringing up the temperature. However, water can be easily removed from the oil, completely

eliminating this problem, by simple oil-water separating procedures.

In addition, since substantial quantities of water can be present

before its presence has any effect on the system, simplified

water determination tests, such as the hot-plate test, can be

utilized. (The procedure outlined in ASTM. Standard 1965, part 17,

Designation D1796 [27], has been found to be inexpensive and

effective for tests made at NBS. Tests on six samples were performed in about 4 hours by a technician having no chemical analytical experience. A centrifuge is required for this test),

e. Flash Point . The flash point is lowered as cracking proceeds.

The formation of light products in cracking is responsible for

the lowering of the flash point. Determination of this point will

not be as indicative as other tests; however, it is not a complicated test and it might give some indication of deterioration.

To gain some insight into the procedures for monitoring of oil, two

samples, one of new, unused Mobiltherm Light Oil, and the other of used Mobiltherm Light Oil, were tested at the National Bureau of Standards or by an

approved testing laboratory in accordance with those tests enumerated above.

The test results are shown in Table 18.

52
Table 18

Mobiltherm Mobiltherm

Light, New Light, Used

API gravity at 60 °F 12.8 13.3

Pour point -5 °F -10 °F

Flash point, C.O.C. 265 °F 270 °F

Viscosity at 100 °F

,

SUS 40.8 44.2

Neutralization No. (acid number) 0 . Img KOH/gr of sample Unknown

These results show no significant change. The neutralization number

for the used oil was not determined, however. These samples were probably

from different batches and furnished by the Socony Mobil Company, and it is

not known how long the used oil had been in a system.

The same tests also were made on the oil in the snow-melting system

at the Museum of History and Technology of the Smithsonian Institution, which

used the CIRCO XXX Oil (Circosol 306). The values obtained for the used oil

were compared with the values claimed by the Sun Oil Company for new , unused

oil, with the following results in Table 19.

Table 19

API gravity at 60 °F

Pour point

Flash point

Viscosity at 100 °F

,

Neutralization No. (. Wa ter

CIRCO XXX, New

24.1

-50 °F

300 °F

SUS 58.0

cid number) Unknown

CIRCO XXX, Used

24.5

-65 °F

305 °F

57.6

0 . 2mg KOH/gr of sample

Usually <0.01 %*

*0.4% and 0.16% of water in 2 out of 9 samples. These two samples

were taken from a drain (or drains).

Again the results show no significant change.

5J,
4.4. Water

Water has most of the desirable characteristics listed earlier in

this report for a heat transfer medium for snow-melting systems. The principal

disadvantage of water for such applications is that it freezes at 32 °F. This

would not be a serious disadvantage, if automatic temperature control devices

could be relied upon to maintain a minimum water temperature of 40 °F regardless of whether or not snow-melting was required. In a two-stage heat

transfer system water might well be the fluid used in the higher temperature

circuit

.

From heat transfer and hydraulic considerations water has some advantage as compared to ethylene-glycol-water mixtures and considerable advantage

with respect to light oil as a heat transfer medium. The specific heat,

specific gravity, thermal conductivity, and viscosity of these fluids are

listed in Table 20 for a range of temperature.

Water has higher specific heat and thermal conductivity at any temperature than either the water-glycol mixture or the heat transfer oil. Water

also has a lower viscosity than the two fluids so it would require less

power to pump it through a given size pipe at a given rate. The product

of the specific heat and specific gravity for water at each temperature

in Table 20 is higher than that for the water-glycol mixture, and very

much higher thar that for oil. For example, in cooling 1 °F from 200 to

199 °F, the relative magnitude of the heat given up by one gallon of water,

water-glycol, and oil would be 2.13 to 2.03 to 1, respectively. Amount of

heat transfer from the pipe to the fluid inside the pipe would usually follow

the laws of forced convection. For a given mass velocity (lb/hr) and tube

diameter the heat transfer by forced convection would be proportional to

54
(k^'^C^' \i [28 a, p 92] where k is the thermal conductivity, C the specific

heat at constant pressure, and p. the viscosity (in. lb/ft. hr., i.e., the

viscosity in centistokes x specific gravity x 2.42) of the medium. For a

given mass velocity and pipe size, calculations indicate that the heat transfer between a fluid and the pipe surface would be, for water, 1.8 times that

for a water-40-percent-glycol mixture and 6.6 times that for Mobiltherm Light

Oil at a temperature of 200 S F.

Ta b 1 e 20

Properties of Possible Heat Transfer Fluids

Fluid Temperature

Specific

Heat

Specific

Gravity

Thermal

Conductivity Viscosity

' *F Btu/lb °F Btu/(hr)(ft)(°F) Centistokes

Wa ter 100 0.998 0.993 0.363 0.681

200 1.005 0.963 0.395 0.306

300 1.007 0.918 0.390 0.185

Wa ter

,

40% 100 0.86 1.05 0.240 1.90

Glycol 200 0.90 1.02 0.242 0.54

300 0.94 0.98 0.244 0.35

Mobiltherm 100 0.434 0.984 0.066 3.80

Light 200 0.480 0.944 0.064 1.40

300 0.524 0.905 0.060 0.80

Technical Report 58-175 , AD No.. 151168 [28a] of the Wright Air

Development Center states that 2.6 times as much heat exchanger surface is

required to transfer a given amount of heat to oil as for a water-glycol

mixture with other conditions being the same.

4.5. Comparison of Properties of Heat Transfer

Media for Snow-Melting Systems

A comparison of the properties of different types of heat transfer

media used in snow-melting systems, and types which could possibly be used

in these systems is shown in Table 21 at the end of the report.

55
5.0, DESIGN AND CONSTRUCTION FOR SNOW -MELTING

SYSTEMS USING ETHYLENE GLYCOL OR OIL

5.1. Literature on Construction Methods

The literature has many references related to design and construction of s now -me 1 ting systems . One good discussion appeared

in Heating, Piping and Air Conditioning In March 1959 [3]

.

Some of the

points that are emphasized in this reference are protection of concrete

slabs from ground water, proper support and encasement of piping, the danger

of electrolytic action between dissimilar metals and materials, proper

allowance for venting and balancing, and proper mixing and placement of

concrete. Another excellent reference is a series of 12 articles that

appeared for 12 consecutive months in Air-Conditioning, Heating and

Ventilating during 1956 and 1957 [ 29J » containing general information on

snowfall, and design data for determining operating characteristics of

snow-melting systems. Included are climatic data, with snowfall data,

classified into 11 regional areas of the United States. For each area

design information and operating data are provided for three classes of

snow-melting systems, the class rating being essentially dependent upon

the desired rate of snow-melting; information is given on climatic peculiarities and recommendations related to economic feasibility for idling

the systems.

An article appearing In Air Conditioning, Heating and Ventilating,

November 1955 [ 30] gives a comparison of fluid properties of two aqueous

ethylene glycol solutions, two heat-transfer oils, and two organic

fluids. Values for kinematic viscosity, specific heat, and specific

weight (density) are given for temperatures from -20 °F to 160 °F.

56

t
Other considerations discussed are the effect of these physical properties on operation, such as pumping requirement and on coil resistance;

and chemical conditions such as corrosivity and flammability. An example

of calculations for selection of a pump is given. A discussion of thermal stresses in snow-melting systems appears in Heating, Piping and Air

Conditioning, June and August 1955 [31].

Other sources of information on design and construction are the

Guide and Data Books of the American Society of Heating, Refrigerating

and Air Conditioning Engineers [32]. Much of the material in reference

29 can be found in condensed form in the Guide and Data Books

.

5.2. Recommendations for Design, Construction, and Maintenance

During the study many recommendations, based on experience', for

improving the operation of the snow-melting system in regard to construction, design, and maintenance, were made by engineers and other technical

staff members of office installations, manufacturers of ethylene glycol,

and, particularly, Air Force Bases. These are presented in the following

paragraphs, together with some references to the literature relating to

the recommendations

.

5.2.1. Expansion Tank

A closed system is generally recommended for both ethylene glycol

and oil systems. This type of system subjects the heat -trans f er media to

less air, and the attendant oxygen that contributes to deterioration of

both types of media. The Dow Chemical Company recommends the use of a

closed system with Dowtherm SR-1, and other large manufacturers of ethylene

glycol made the same recorramendation for their products. Most of the

Air Force Base engineers showed a preference of the closed system over

the open. General Services Administration Specification No. 304-15 for Snow57
Melting Systems for Heat Transfer Oil [24] specifies that the expansion

tank shall be of the closed type. In this type it is important that the

air space in the tank be large enough to accommodate the expansion of the

heat transfer fluid without creating pressure in the system, and that a

relief valve be provided, to discharge the fluid if excessive pressure

should occur under abnormal conditions. Both of these features are required

in the GSA specification.

5.2.2 Piping and Gridwork

Welded steel or wrought iron piping and pipe grids usually are

recommended for ethylene glycol systems. A study by Agnew and his associates

[33] showed that the corrosion rates of cast iron, steel, copper, brass,

aluminum, and solder were all fairly constant for pH values between 6 and 9

in an uninhibited 40-percent ethylene-glycol-water mixture, whereas the

corrosion rate of all these materials increased at pH values below 6 and the

corrosion rate of aluminum and solder increased rapidly when the pH value

for the solution was above 10.

Sensitivity of an aluminum alloy to corrosion in a 30:70 glycolwater mixture was reported by Dempster [34]. Twiss and Guttenplan [35]

have shown the relation of corrosion of aluminum to the velocity of the

moving solution, and to the impurities of the water used to make up the

glycol solution Caplan and Cohen [36] have shown that corrosion rates of

some metals may be accelerated at low temperatures in certain inhibited glycol

systems. Their study showed that the phenomenon was particularly true for

zinc when glycol solutions with a borax inhibitor were used. A representative

of the Dow Chemical Company advised the National Bureau of Standards that

galvanized metals should not be used above room temperature with ethylene

glycol solutions.

58
In the past few years , due to the increased use of aluminum in automobile engines, and of necessity, the automotive ethylene-glycol

products have improved in resistance to corrosion when used with aluminum.

Conley, from the Coating and Chemical Laboratory of Aberdeen Proving

Ground, for example, reports good performance of Formula B material when

used with aluminum [ 8J • There still appears to be some difficulty with

solder, but the problem is not important in snow-melting systems because

of the small amounts involved.

It is imperative that no copper be used in a system using oil. The

oil reacts with copper to produce sludge in the system.

Normally, piping or pipe grids made of wrought iron, steel, or copper

in concrete is protected from external galvanic action and corrosion,

because any small amount of moisture in the concrete that might be around

the metal would carry a pH of about 12, which is alkaline. If water gets

to the metal via the expansion joints of the sidewalk above the metal

pipe grids, rapid corrosion can occur. One office building installation

in the New York area using an oil heat transfer medium has experienced

a number of serious failures and a heavy loss of oil because water leaked

through the expansion joints of a sidewalk. Finding the source of the

oil leaks was difficult, and at one time 15 drums were lost before the

leaks were found. In this installation, a polyethylene vapor barrier was

placed under the pipe grids but not over itj a vapor barrier over the

pipe grids might have protected the. metal. Other instances of this type of

failure were reported to a representative of NBS . In the article, "How

to Prevent Failures in Snow-Melting Systems" f 3 ] , methods for eliminating

this difficulty are described.

59
Another possible remedy for exterior corrosion of ferrous piping is

the use of a plastic-coated steel tubing wrapped with coal-tar tapes. A

snow-melting system using this polyethylene-coated material j_ 37^ recently

was installed in a basement- level clothing store in West Hartford, Conn.,

but no information on the effectiveness of this treatment has been obtained.

Piping of a 3/4-inch diameter or larger on 12-inch centers is recommended for oil by the ASHRAE Guide [38]. For ethylene glycol, designers

space the piping from about 8 to 18 inches, depending on conditions. In

the past, some contractors have spaced piping up to 24 inches apart. However,

an engineer of a large engineering firm specializing in the installation of

heating, air-conditioning, and snow-melting equipment stated that under these

conditions the snow partially melts and refreezes, causing a line of refrozen

snow that is more difficult to cope with than the original condition. The

same engineer recommended that there be balancing cocks for all loops.

In the September 1963 issue of Air Conditioning, Heating and Ventilating, ai article on piping for snow-melting systems discusses the reason

for choosing series coils over pipe grids for a large installation [39].

The author states that coils give continuous uniform circulation throughout

the entire system, it is easier to eliminate air pockets, the heating is

more uniform, and there is a minimum number of welds.

Smith, o

f the American Iron and Steel Institute, describes a steelpipe system using oil that has given satisfactory performance since 1958 [ 40]

Extensive precautions were taken to protect the piping at hidden locations

against external attack by seepage of rainwater and melted snow. All piping

that passes through a sleeve or is buried in earth or gravel was protected

by a coat of bitumastic enamel primer followed by one coat of high-melt enamel.

60
The latter was applied simultaneously with a single wrap of glass-fiber

pipe covering, followed by a second coat of enamel and a wrap of 15-pound

coal- tar-saturated asbestos pipe-lining felt.

The use of dissimilar metals in the piping of a system can induce

galvanic action and corrosion. Tnis is discussed in the article in Materials

Protection, May 1964 [41],

5.2.3, Meat Exchangers

Most of the heat exchangers in the systems at the Air Force Bases

visited were manufactured by the Old Dominion Company and were of the tubein-shell type. The primary side of these exchangers is supplied with either

high- tempera ture water or steam. The tubing, which is removable and fits

snugly into the shell, was usually made of No, 18 BWG Admiralty metal and

has the following approximate analysis.

Table 22

Percent

Copper 71

Zinc 28

Tin 1 100

This metal was used to retard dezincif ication , which in effect is selected

corrosion of the alloy with redeposition of copper. The metal has been

used successfully for condenser tubes and for salt-water applications for

a number of years. The Old Dominion Company advised that the tubing sometimes was made of No. 20 BWG 90-10 copper-nickel. According to the company,

the tube supports and baffles are of inhibited Muntz or non-ferrous metals.

The shells were made of steel. The HTW or steam of the primary flows

through the tubes, and the aqueous ethylene glycol flows in the space between

the tubes and the shell. If sediment deposits in the shell, low velocity or

61
62

stagnant areas in the ethylene glycol or oil could accelerate the deterioration. Large deposits of sludge had been found in the converters at Minot

AFB before Dowtherm SR-1 was employed. There was little sludge in the systems

of the other Bases.

stagnation. A study has shown that there would be little loss of heat-trans

The Old Dominion Company was approached about this change . Although

they agreed to the feasibility of the design, they pointed out that the

shells now used will not withstand the pressures exerted by HTW or steam

and that considerable expense would be involved. A further requirement

would be increased insulation. Nevertheless, it is recommended that such

a design be considered for the future. A pertinent discussion of the

economic considerations of heat exchangers by Flaxbart and Schumer [43]

might be helpful in studying the possibilities of a new design.

Control of the temperature of ethylene glycol in the heat exchanger was

accomplished at the Air Force Bases visited and the Grand Forks AFB by

regulating the flow of either HTW or steam at the primary side of the

converter .

Regulation was accomplished in some systems by a controller with a

fixed temperature setting and a sensing element placed within the ethylene

glycol in the heat exchanger, and in other cases within the glycol line leaving

the exchanger. The controller, in turn, adjusted the flow automatically

by actuation of a modulating valve in the circuit of the HTW or steam.

In at least one case, the modulating valve was by-passed by a hand valve

The opposite arrangement, in which the antifreeze media traveled

would cause a rapid flow of media and would not allow

fer efficiency under this arrangement [42].

5.2.4. Controls

that could be used in case the controller circuit became inoperative.
This system, with a fixed setting at the controller, was one of three

types at the Grand Forks AFB. The controller for the system was not interlocked with the motor pumps and there were times when the ethylene glycol

was not flowing in the heat exchanger when the primary side was heated.

Experience at that Base, with a fan-coil heating system using ethylene glycol

as the heat transfer medium, indicated that the resulting high temperature

can cause difficulty and glycol deterioration. The greatest difficulty was

when the 3-way valves in the ethylene glycol lines were closed by the room

thermostat override. Under this condition of no-flow, and with the control

set at a temperature of 230 °F , actual tests revealed that the glycol

temperature rose to 273 °F in the heat exchanger and the actual tube surface

could be higher, because the glycol boils violently for a short period of

time. A discoloration of the glycol was noted, and a 45 PSI safety relief

valve was activated and the entire quantity of antifreeze was discharged.

In more satisfactory snow-melting systems at Grand Forks, Restover,

and Plattsburg AFB's the HTW was regulated pneumatically by a 3-way valve

and controlled by the outdoor temperature (the lower the temperature, the

greater the flow allowed through the heat exchanger), and usually there was

continuous flow in the ethylene glycol lines. The only difficult feature

in the system at Grand Forks AFB, according to operating personnel, is that

the pumps are on a separate outdoor control and start only when the temperature drops below 65 °F. It is possible that the controller may call for

heat in the heat exchanger at outdoor tempera tures above 65 °F when the pumps

are inoperative. Re were advised that an override should be installed to close the

pneumatic control valve in the primary circuit at any time the pumps are not

operating. The type of control system at Minot AFB is not known.

63
Engineers advised at. one Base that when the temperature of the ethylene

glycol was sensed in a bulb in the glycol solution inside the heat exchanger

there was a marked unsteadiness in this temperature causing erratic control

of the flow in the primary circuit. A more satisfactory location for sensing, we were advised, is in the glycol line leaving the exchanger where

the flow is more consistent.

At Westover AFB, the modulating valve controlling the supply of hot

water was controlled electrically and was motor driven. Unlike a pneumatic

control, this control would stop the valve at whatever position it was in if

a failure of the electrical system occurred, possibly allowing the flow of

hot water when the glycol flow had stopped.

A failure of this type actually occurred during the visit; the glycol

supply at the heat exchanger was about 200 °F instead of the 120 °F normally

encountered. Data taken for this system when the valve was malfunctioning are shown below:

Table 23

High Temperature Water

Supply Return

Temperature (°F) 383 233

Pressure (PSIG) 232 228

Ethylene Glycol

Temperature (°F) 200 170

When the control was repaired, the glycol temperature lowered rapidly.

In light of the considerations enumerated, it is recommended that

(a) the sensing element regulating the controller for the HTW be located in

the glycol line leaving the heat exchanger, (b) in order to insure that there

64
will be a flow of ethylene glycol in the heat exchanger , there should be

an interlock between the circulating pumps in the glycol circuits and the

control valve for the high temperature water circuit or steam circuit, so

that at least one pump is operating before the hot water or steam can be

admitted to the converter, and (c) as a further precaution, the control valve

in the hot water supply shall be normally closed on electrical or pneumatic

failure

.

These recommendations still apply, even if the new types of inhibited

glycol are used. Conformance would not be expensive; and it is probable

that temperatures greater than these new glycol types can tolerate would

otherwise be encountered occasionally under certain conditions.

5.2,5. Pumps

The pumps for most of the systems in the three Bases had mechanical

seals. The engineers at each base advised that this type of seal was important; pumps with packing glands had exhibited a number of leaks, and

had increased the exposure of the glycol to the oxygen of the air.

The Chief Engineer at the Smithsonian Institution advised that teflon

seals were considerably more satisfactory than the neoprene seals first used

in the pumps in their oil system. The oil system installed at the H. J.

Heintz Company, Cereal Building and Research Center in Pittsburgh, uses

teflon seals in their pumps [40], This system has given satisfactory service

since 1958.

The engineers at Minot AFB suspected the ethylene glycol-water

solution in the pumps was causing the neoprene to break down.

65
5.2.6, Hours of Operation for the Ethylene Glycol

Snow-Melting System

All three Air Force Bases that were visited operated their snowmelting systems continuously throughout the winter. There are two principal

advantages in this procedure: (a) the snow-melting system is certain to be

in operation during a heavy snowfall, and (b) there is much less chance

someone might turn it off inadvertently if it is well known that it is to

be kept in operation full-time. One Air Force Base pointed out that, even

then, on occasion inexperienced personnel would pull the wrong switch in

the belief he was turning off lights or other machinery. Short of using

padlocks, no method had been found to keep this from happening.

At installations visited in private and Government buildings, the

systems were either turned on automatically when outdoor temperatures fell

below a certain temperature (50 °F at one installation), or manually when

there was threat of a snowfall. However , a chief engineer at one installation

stated that a manually controlled system must have a large snow-melting

capacity in case heavy snow fell during the night when no one was on duty.

He cited one instance in which there was already 2-1/2 inches of snow when

he turned on the system at 6 a.m. and by 8:30 a.m. the walks and driveways

of the large building that it served were free of snow. There were 1500

gallons of oil in the system and it served about 10,000 square feet of area.

The oil supply had a temperature of 160 to 180 °F , and the return was about

100 to 120 °F

66
Detect or -switches for automatically turning the snow-melting system

on are mentioned frequently in the literature. One switch on the market

today for this purpose is the Sno-Melter, Model EZ-AS-1, sold by the

Climate Control Division of the Singer Co., Auburn, N.Y. This detector is

equipped with a snow-melting funnel. The temperature of the surface of the

collecting funnel is always kept above 32 °F by means of a small heater.

When the first snowflakes start to fall they are converted into water which

is used for unbalancing an electrical bridge so that the snow-melting electrical switch is closed. No other switches of the type were found during

the investigations.

A simple method that has been used successfully, but has some disadvantages, is to place a mirror face up on the slab to be heated. Whenever the outdoor temperature falls below about 40 °F, a light is directed

onto the mirror from a fixed source and is reflected to a photocell.

When snowfall begins and flakes fall on the mirror, the light is

attenuated and the photocell cuts of ^activating the heating circuit below

the slab. When the slab is heated, the snow on the mirror melts and the

photocell cuts on. However, it is important to keep the mirror polished;

otherwise the snow-melting system could cut on when not needed. This

could be overcome by a pilot-light inserted into the system to show when

it is on.

If a detector fails to cut on, or if for any other reason it is

necessary to start a snow-melting system at temperatures as low as -40 °F,

it is important to remember that the viscosity of aqueous ethylene glycol

solutions is high at low temperatures: for a 50 percent solution the

viscosity is about 100 centipoises at -40 °F and about 2 centipoises at

100 °F . Should the pumps and motors in the system not be designed for this

67
contingency, it might not be advisable to start the system. For some oils,

such as Mobiltherm Light, the pour point is as high as -20 °F.

Two pumps are often installed in a system to operate in parallel

during the heat-up period. When the hea t- trans fer media, either glycol or

oil, have warmed up sufficiently, operation of one pump is sufficient.

5.2.7. Charging the New System with

Ethylene Glycol or After Cleaning

One of the engineers at Westover AFB recommended that the solution

of ethylene glycol and water be mixed in drums with mechanical mixers before

charging the system. He said contractors sometimes put the glycol in the

system, add water, and expect the pumping and circulation to mix the solution

thoroughly, but that such mixing does not occur. Air pockets form and parts

of the solution remain stagnant with excessively large proportions of either

water or glycol. Ross [ 44~| , in an article describing a system at the Garden

City Tollway Plaza, St. Catherines, Ontario, Canada, also recommends prior

mixing of the antifreeze and water.

5.2.8. Application of Make-up Water to System

At one of the Bases visited, make-up was fed directly to the snowmelting system from the main water supply system by means of a fixed piping

arrangement. This procedure is dangerous. A direct cross connection between

potable and unpotable water supply sometimes results in a back flow of unpotable water. Ethylene glycol is regarded as toxic when ingested, and in

some cases, small amounts of arsenites are included as an inhibitor. A

better procedure, is to feed the make-up water to a system through a hose

which is disconnected when not in use; or to feed water into the air space

of the expansion tank by gravity flow when the system is not under pressure.

68
5.2.9.

Strainers

The systems at Westover AFB and Plattsburg AFB did not use strainers.

They were used at Minot AFB and Grand Forks AFB, however. Strainers are

used in a system principally to catch sludge and other impurities, but they

are also recommended as a means for detecting unexpected deposits in the

system between analyses.5.2.10.

Possible Thermal Shock

In Hot Water Boiler

The following statement by Ross relating to the operation of large

ethylene glycol systems was taken from Heating, Piping and Air Conditioning

[44], Tliis information might be useful in the design of a new system.

"With large load variations and large volumes of water

pumped through hot water boilers, precautions must be taken

to prevent thermal shock.. Serious damage can result if large

quantities of water are circulated with a large difference

between return and supply water temperatures of the boiler. A

snow-melting system of this size, with the load variations expected,

necessitated extra precautions.

"In this case, the boiler controls are wired to prevent

either boiler from running unless the boiler water pump is

running. A differential temperature controller with bulbs in

supply and return boiler water connections to the antifreeze

solution heat exchanger overrides all other controls. The

controller starts to close the 3-way valve supply connection

to the heat exchanger if the supply-return water temperature

difference exceeds 20 °F. This control also insures that the

administration building's heating system will not be starved

when the snow-melting system is on full pickup load."

5.2.11.

Removal of Water from a Snow-Melting System Area

For any type of snow-melting system, it is important that drains be

provided for removal of the water which forms from the melted snow. Not

only does the presence of water dissipate energy for heating, but it can

lead to icy surfaces. The Michigan State Highway Department

69
reports [45] in a study of an experimental electrical highway system where

drains could not be provided, that there was an added burden to the system

due to a layer of water and that at low temperatures of about 5 ®F, ice

ridges formed on the lanes of the highway.

6.0 Electrical Systems

Electrical systems normally consist of insulated electrical cables

buried in concrete or asphalt areas used for driveways, sidewalks, roadways,

or parking lots. The insulation for the cables can be made of a mineral

material such as magnesium oxide, of silicone or neoprene rubber, or of

polyvinyl chloride. The General Electric Company makes an insulation

known as Vulkene which, according to their literature, is a thermosetting

material designed for emergency overload. Typically, this insulation is

covered with copper tubing for protection against water and against heavy

traffic. According to catalog information, the Climate Control Division

of the Singer Co. , manufactures a cable in which the inner conductors are

completely surrounded and insulated with highly compressed magnesium oxide.

The outer sheath is copper tubing. Lead cable is sometimes used, in which

case the heating element is insulated with asbestos or glass fiber. The

lead is covered by vinyl for protection of the lead from salts present in

the concrete.

Sometime , pre-wired and assembled mats made up of a mesh of wiring

are used instead of cables, to help the contractor cut labor costs on installation. He puts the units into place, encased in asphalt or

concrete and connects the leads to the electrical distribution and timing

equipment

70
According to one manufacturer's catalog information, the cables can

be designed for a 120, 208, 240, 277, 440, or 600 volt supply, and are rated

in wattage per lineal ft. The designer selects cable wattage in accordance

with design conditions of temperature, wind velocity, humidity, amount of

snowfall expected, spacing of the cables, and other conditions, such as

depth of cables, type of paving material, and the heat loss downward. A low

value is 5 watts and a high value is 30 watts per lineal foot. Design

information for electrical systems can be found in a General Electric publication on Heating Cable [46], and in publications by Mayer F47] and Potter T48].

Included in these publications are tables on snow-melting system effectiveness

and the number of watts per square foot required for various climates, under

various conditions of snowfall and amount of snow removal desired. Suggestions

for installation techniques, spacing of coils, and electrical controls are

also given. An article appearing in Actual Specifying Engineer magazine, July

1964, T49], is another good source of information that gives some admonitions

and suggested specifications based upon experience in the field of electrical

snow melting. One suggestion is the absolute need for waterproof junction

boxes. On a visit to one Government installation, a junction box at driveway level was covered by a metal plate that was neither secure or well-gasketed.

The box was half-full of water, the electrical junctions were buried in water,

and the snow-melting system was almost ineffective, and dangerous when in

operation. The system was restored in good working order by re-gasketing

the box and fastening the top down more firmly; nevertheless, the placement

of the box was at fault and repeated trouble is likely. Engineers have advised

keeping the junction boxes at a high level. Some design, construction, and cost

71
information on an experimental electric system can be found in the Michigan

State Highway Department Research Reports [45].

A specification for the furnishing and installation of a complete

electrical sncw-melting system by the Public Buildings Service, General

Services Administration [ 50j is near completion and, as it now stands, it

includes requirements for the heating cable, panelboards, branch heating

circuits, conduits, junction boxes, circuit breakers, expansion fittings,

and wattage limitations.

There are several other types of electrical systems under consideration or in the experimental stage. Impedance heating is a term used loosely

to describe energization of regular or additional steel reinforcing members

within the pavement [5l] . Low voltage/high current power is required for

this system. Another low voltage/high current system is one in which a

heavy iron-core cable, covered directly with PVC, is buried in the pavement.

The advantage claimed by the Electraradiant Corporation, one manufacturer

who markets the components of this system, is ease of installation. Both

the impedance heating and the Electraradiant type heating systems require

transformers and some auxiliary equipment. Infra-red heating stems also

have been used successfully for snow-melting. If an overhead infra-red

radiating snow-melting system is used, loss of heat to the surrounding

environment is a factor as well as reflection of the radiant heat from the

snow

72
7.0. Ethylene Glycol Systems

For Aircraft Runways

As discussed in the foregoing pages, conventional snow-melting systems

generally have been designed to use liquids circulated at temperatures from

100 to 130 °F, with temperature drops of from 20 to 30 °F , and pipes placed

from 8 to 18 inches apart. When large areas are contemplated, such as

aircraft runways, these systems become impracticable, due to the excessive

volume of fluid which must be circulated, and the larger pipe sizes and

great distances over which the fluid must be transported.

As a consequence, experimental systems with high temperature liquid

and pipe spacing as great as 4 feet have been developed, making it possible

to reduce pumping costs, and installation and operating costs [28].

During a 2-year test program at Loring Air Force Base on an experimental

installation of this type, coil temperatures were greater than 300 °F without apparent ill effects [28]. Socony Heat Transfer Oil Light and an

aqueous solution of triethylene glycol were the two types of media used

during the tests. It has not proved feasible to continue operation of

these experimental systems at Loring AFB.

8.0. Discussion and Conclusions

The following conclusions can be made as a result of the study

described in this report:

(a) The sludge and precipitate experienced in the snow-melting systems at the Minot Air Force Base, before Dowtherm SR-1 was used, were due

primarily to (1) excessive temperatures in the heat exchangers, and (2) a

high concentration of dissolved solids in the water used in the aqueous

solution of ethylene glycol.

73
(b) Tne relatively better performance of the snow-melting systems

at Westover and Plattsburg Air Force Bases was due to the lower temperatures

in the heat exchangers and the lower concentra tion a£ dissolved solids in

the water used in the aqueous ethylene glycol solution.

(c) The control value of the HTW or steam supply to the primary

system should be normally closed so that when a failure occurs in the control

system and the pumps for circulating the antifreeze are inoperative,

heated water or steam cannot flow into the primary circuit and cause excessive

heating of the stagnant antifreeze.

(d) It is advisable to design a control system so that the controls

of the antifreeze pumps are interlocked with the rest of the system so that

the pumps will always be in operation when there is a heated medium in the

primary system. If in present installations the control for the pumps is

separate, there should be an override to close the control value in the

primary circuit anytime the pumps are not operating.

(e) When the temperature of the ethylene glycol is sensed for control of the flow in the primary circuit, it is recommended that it be

sensed in the glycol line leaving the exchanger and where the glycol flow

is consistent.

(f) The water used in an aqueous ethylene glycol solution should

be either steam condensate or de-ionized water. A small cartridge of the

mixed-bed, exchange type, was found by laboratory tests at NBS to be

satisfactory for use in obtaining de-ionized make-up water, providing

certain precautions are taken.

74
(g) According to the literature, the older types of automotive

inhibited ethylene glycols, which depended principally on borax, usually

suffer breakdown when they are subjected to temperatures of 300 °F or

higher. Studies performed at Grand Forks AFB in one system showed that when

solutions with these older types of inhibitors were subjected to about

257 °F in the heat exchanger, deterioration and breakdown began to occur.

At Westover and plattsburg Air Force Bases when the temperature of the

glycol in the supply to the grid system was about 120 °F there was little

deterioration. At Minot Air Force Base, where the temperature of the

glycol at the supply to the grid system sometimes reached 160 °F, there

was serious breakdown. This trouble, however, may have been due in part

to the high percentage of dissolved solids in the water used in the antifreeze solution.

(h) The newer types of inhibited ethylene glycols, which make use

of mercaptobenzothiazole , disodium- or dipotassium-phosphates, and sometimes

borax, show promise of much longer life than the older automotive types.

Experience at Minot Air Force Base indicated that Dowtherm SR-1 (one of these

types) can tolerate water which has a high concentration of dissolved solids.

It is not recommended that water with a high concentration of dissolved

solids be used, however.

(i) It is recommended that one of the following types of ethylene

glycol antifreeze materials be used for snow-melting systems:

Dowtherm SR-1 or equivalent covered by the specification

given in this report for Type A inhibited ethylene glycol.

75
UCAR-17 Thermofluid or equivalent covered by the specification

given in this report for Type B inhibited ethylene glycol.

The Coatings and Chemical Laboratory Formula B with Type I

Borax Inhibited Ethylene Glycol. The CCL formula is covered

by Federal Specification 0-X-490a and the Type I glycol by

0-A-548a

(j) It is recommended that these antifreeze solutions not be mixed.

Since the UCAR-17 Thermofluid or equivalent has very nearly the same inhibiting materials as the Coatings and Chemical Laboratory formula but in different proportions, it might be permissible, under emergency conditions, to mix

these two fluids. It is further recommended that the Union Carbide Laboratory, the Coatings and Chemical Laboratory or another qualified laboratory,

be consulted before the mixture is made.

(k) Monitoring of the types of ethylene glycol recommended in this

report for snow-melting systems usually can be accomplished by performing

tests for reserve alkalinity, freezing point, and pH. If the values for the

tests for reserve alkalinity approach minimum values specified in the text

of this report, tests usually should be performed for mercaptobenzothiazole

ion content and phosphate ion content, and if the values for these tests

fall below certain minimum values, reconditioning can be made by adding

small amounts of inhibitors, or the solution should be changed if serious

deterioration has occurred. Monitoring tests should be made once a year

for the first two years, and every six months thereafter.

76
(l) Systems using oil as the heat transfer medium are also recommended.

Heat-transfer oils such as Mobiltherm Light and CIRCO XXX (Circosol 306),

manufactured by the Sun Oil Company, appear to be satisfactory for use.

The General Services Administration recently has published GSA Specification

No. 304-15 for a complete snow-melting system using oil. This specification

is available for use by other Government agencies.

(m) A closed system is desirable for either an ethylene glycol or

oil system. Other design procedures are recommended in Section 5.0.

(n) Electric snow-melting systems are not used by Government Agencies

as often as ethylene glycol or oil systems. A GSA Specification for electric

snow-melting systems is near completion and will be available for use by

other Government agencies.

9.0. Acknowledgements

Acknowledgement is given to Dr. J. K. Taylor and Mr. R. A. Paulson

of the Chemistry Division of the Institute for Materials Research of the

National Bureau of Standards for their analytical work on the inhibited

ethylene glycol products and oil products supplied to them, for their

suggestions and advice in formulating the specifications and test methods

for these products, and for their review of large sections of the report

pertaining to the chemical phases in snow melting systems. Acknowledgement

is also made to Mr. Cyrus Malmburg of Institute for Materials Research of

the Analytical Chemistry Division of the National Bureau of Standards for

his helpful suggestions relating to the experimental work on the de-ionization of water and to Mr. Virgil Hatch and Mr. Charles Jordon of the Coatings

and Chemical Laboratory of Aberdeen Proving Ground, for their valuable

assistance in the study of the properties of Formula B inhibitors and

77
advice on the expected performance of the glycol solution with Formula B

when installed in a snow melting system. The consultative help given by

Dr. R. D, Stiehler and Mr, Hugh Logan of the Institute of Materials Research

of the National Bureau of Standards is also appreciated.

78
REFERENCES CITED IN THE REPORT

[ l] P. B . Gordon, Antifreeze protection for snow-melting systems,

Official Bui. of Heating, Piping and Air Conditioning Contractors

Assoc. 52, 21-22 (Feb. 1950).

[2J A. F. Gallaugher and H. Hilbert, Studies on reactions relating to

carbohydrates and polysachar ide s , LV . Vapor pressures of polyethylene

glycols and their derivatives, J. Am. Ghem. Soc . 2521 (Dec. 1937).

[3] How to prevent failures in radiant heating and snow-melting systems,

Heating, Piping and Air Conditioning [3] 3J_s 153-168 (Mar. 1959).

14] C. W. West, Notes on corrosion inhibitors, Technological Series No.

GI-8, Techn. Service Lab., Union Carbide Chemicals Co., Tarrytown,

N. Y.

[5] J. Dulat of Borax Consolidated, Ltd., Comments at a symposium on the

protection of motor vehicles from corrosion, Soc. Chem. Indus. Monog.

4^ 79 (Mar. 1958), London.

L6J I. M. Kbit off and E. B. Sandell, Quantative Inorganic Analysis,

43-45, McMillan Co.

[7] L. C. Rowe, Corrosion JL3, 750t (1957).

[8] J. H. Conley, The development of an improved cooling system corrosion

inhibitor, Coating and Chem. Lab. Report No. 156, Aberdeen Proving

Gr ound , Md

[9] T. E. Larson and R. V. Skold, Corrosion 14_, 285t (1958).

[10] M. A. Boehmer and J. W. Compton, Soap and Chem. Specialties (June and

July 1959).

[11] R. Kimin and R. J. Myers, Ion Exchange Resins, 109 (1952), John

Wiley and Sons, Inc., New York, N. Y.

[12] F. II. Kahler and A. C. Reents, Water demineralization costs, Chem.

Eng. 64, 206-210 (Jan. 1957).

[ 13] Standard methods for the examination of waste and waste water. Am.

Publ. Health Assoc., Inc., 11th ed . (1960).

[ 14] Private communication between the Dow Chemical Co., and J. C. Davis

of NBS , July 8, 1965.

[15] Petroleum products and anti-freeze report, Bui. No. 140, May 1964,

State Lab. Dept., Oil Inspection Dlv., Bismarck, N. D.

[16] Standard method for inspection, test and standardization of

•hydrometers, ASTM Designation: E126-62, Am. Soc. for Testing

Materials, 1916 Race St., Philadelphia, Pa. 19103
2

[17] Antifreeze and corrosion, Metallurgia [361] LX, 212 (Nov. 1959)

[18] British Standard Specif ica t Lon 3150: 1959. Corrosion Inhibited

ethanediole Antifreeze for Water-cooled engines, Type A, British

Standards Inst., British Standards House, 2 Park St., London Wl

England

,

[19] Private communica tion from the Torrington Co., Torrington, Conn.,

by J. H. Thompson, Chief Engineer, to J. C. Davis, NBS , (Dec. 11,

1962)

[20] Patty's Industrial Hygiene and Toxicity _2, 1497-1526, Interscience

Publ., Div. of John Wiley Co., London and New York City.

[21] R. L. Peeler and S. A. Kovacich, Alkyl-silicate Aviation Hydraulic

Fluids with Excellent Hydrolytic Stability, Industrial and Engineering Chemistry, 51 , pp. 749-752 (June 1959).

[22] R. B. Purdy, How to use heat transfer petroleum fluids for snow- melting systems, Heating, Piping and Air Conditioning [12] 32_

(Dec. 1960).

[23] R. Shuttleworth, Melt snow at toll road plazas, Heating, Piping and

Air Conditioning _3 , 95-98 (Mar. 1957).

[24] Guide Specification 304-15, Snowmelting system heat transfer oil.

This specification can be obtained by Government Agencies from

General Services Administration, Public Building Services, General

Services Administration Building, 19th and F St., N. W., Washington,

D. C. 20405.

[25] Heating with Mobil therm, Techn. Bui., Socony Mobil Oil Co,, Inc.,

150 E. 42nd St., New York 17, N. Y.

[26j Technical Bulletin Process Oils No. 86, Sun Oil Co., Philadelphia,

Pa. 19103.

[27] ASTM Standard 1965, part 17, Designation D1796, Petroleum Products,

fuels, solvents, engine tests, lubricating oils, cutting oils, grease,

hydraulic fluids. American Standards for Testing Materials, 1916 Race

St., Pniladelphis , Pa. 19103

[28] (a) Report on aircraft runway snowmelting tests using high temperature

fluids, Wright Air Development Center Techn. Rep. No. 56-348, (b) Report

on aircraft runway snowmelting tests using high temperature liquids,

Wright Air Development Center Techn. Rep. No. 58-175.
3

[ 29 J W. P. Chapman, Calculating the heat requirements of a snow-melting

system, Air Conditioning, Heating and Ventilating, a series of 12

articles (Sept. 1956 through Aug. 1957).

[ 30] W. P. Chapman, Snow-melting hydraulics, Air Conditioning, Heating

and Ventilating 52_ (Nov. 1955).

[31] W. P. Chapman, Are thermal stresses a problem in snow-melting

systems, Heating, Piping and Air Conditioning, 93-94 (June & August 1955).

[32] Guide and Data Book, American Society of Heating, Refrigerating and Air

Conditioning Engineers, Applications Edition, 989-1000 (1966)

[33] R. J. Agnew and J. K. Truitt, Corrosion of metals in ethylene glycol

solutions, Industrial and Engineering Chemistry [4] 50, 649-656 (1958).

[34] N. B. Dempster, Corrosion of aluminum alloy in glycol-water cooling

systems, Corrosion [8] L5, 13-16 (Aug. 1959).

[35] S. B. Twiss and J. C. Guttenplan, Corrosion testing of aluminum,

Corrosion 12_, 263-311 (June and July 1956).

[36] D. Caplan and M. Cohen, Accelerating effect of decreasing temperature

on corrosion of glycol solutions, Corrosion [9], 284 (Aug. 1953).

[37] A. First, Snow-melting installation uses plastic-coated steel pipe.

Domestic Engineering, 68-69 (Jan. 1964).

[38] Guide and Data Book, American Society of Heating, Refrigerating, and

Air Conditioning Engineers, Application Edition, 989-1000 (1966).

C 39 j W. J„ Cullen, Piping for a snow melting system, Air Conditioning,

Heating and Ventilating _60, 69-76 (Sept. 1963).

[40] E. H. Smith, Snowmelting steel pipe system, Actual Specifying

Engineer, 74, 75, 118 (July 1964).

[41] Problems in the use of corrosion inhibitors in automobile engine

cooling systems. Materials Protection, 37-41 (May 1964).

[42] C. J. Dobratz, Put the viscous fluid in the shell, Chem. Eng. [ 6J

66, 179-180 (Mar. 23, 1959).

C 43 j E. W. Flaxbart and D. E. gchirmer, Economic considerations on shell

and tube heat exchanges selection, Chem. Eng. Progress 5

, 98-105

(Dec. 1961).

[44] J. Ross, Snowmelting system keeps Skyway 1 s toll plaza clear, Heating,

Piping and Air Conditioning, 99-104 (Mar. 1964).
[45] Michigan's experiment in snow and ice removal on highways by radiant

heat, Research Lab., Testing and Research Div., Reports No. 152, 165,

and 192 (Aug. 1950, Dec. 1951, and July 1953).

|_46j Heating cable, General Electric Co., Wire and Cable Dept., Bridgeport,

Conn.

[47] J. R. Mayer, Melt ice and snow off your driveway - electrically,

G. E. Review, 1-4 (Nov. 1958).

[48] Potter, W. G., Electric Snow Melting Systems, Journal of the American

Society of Heating, Refrigerating and Air Conditioning Engineers, 35-45,

October 1967.

[49] L. M. Watson, Snowmelting electric system. Actual Specifying

Engineer, 76, 77, 104-108, 136 (July 1964).

[50] GSA Specification, Snowmelting system (electrical). Under preparation.

When completed, may be obtained by Government Agencies from General

Services Administration, Public Building Services, General Services

Administration Building, 19th and F St., N. ¥., Washington, D. C.

20405.

[51] K. E. Hodges, Snow melting, various types of snowmelting systems.

Actual Specifying Engineer, 73, 98-100, 116 (July 1964).
LITERATURE NOT CITED IN REPORT

1. British Standard Specification, Corrosion inhibited ethanediol antifreeze for water-cooled engines, Type C, sodium tetraborate

inhibited, B.S» 3152:1959, British Standards House, 2 Part St.,

London, Wl

2. The protection of motor vehicles from corrosion, S.C.I. Monog. No. 4,

Soc, Chem. Industry, 14 Belgrave Square, London, SW1, (1958).

3. F. H. Bridges and J. Bricker, The effect of ethylene glycol on pipe

friction and heat transfer. Heating and Ventilating [7] 48., 61 (1951).

4. W. P. Chapman and S. Katunich, Heat requirements of snow melting

systems, ASHAE Trans. [1577] 62 359 (1956).

5. W. P. Chapman, Design of snow melting systems, Heating and Ventilating

[4] 49, 95 (1952) and [11] 49, 88 (1952).

6. ASTM standards on engine antifreezes. Methods of Testing Specification, 4th ed . (Dec. 1961), Am. Soc. for Testing and Materials,

1916 Race St., Philadelphia, Pa.

7. Highway snow melting, from Report No. 152 of Research Laboratory

Testing and Research Div., Mich. St. Hgwy. Dept., Heating and

Ventilation [ l] 4.8, 64 (1951),

8. P. T. Gilbert, Some factors affecting the performance of condensers

and heat exchanger tubes, Chem. and Industries 44_, 1424-1425 (Nov. 1,

1958).

9. G. C. Vincent, J. 0 Haugen, and G. E. Dreifke, Fluid mixing in shell

and tube heat exchangers, Chem. Eng. Progress [7] 5_7, 48-52 (1961).

10. G. 0. Curme, Jr., and F. Johnston, Glycols Monog. Series, No. 114,

Chap. 4, p. 64, Re inhold Publ. Corp., New York, N. Y.

11. D. H. Green, H. Lamprey, and E. E. Sommer, Properties vs. performance

of present-day antifreeze solutions. Jour, of Chem. Education f 10]

18, 488 (1941).

12. Standard method of test for pH of concentrated engine antifreeze,

Am. Soc. for Testing and Materials, D1287-58.

13. Reserve alkalinity of concentrated engine antifreeze, Am. Soc. for

Testing and Materials, D1121-54.

14. Private communication from N. R. Cooper, Union Carbide Chemicals Co.,

to J. C. Davis, NBS , Dec. 11, 1962,

15. P. H. Miller, L. Pierce, Jr., G. M. Goodale, and J. M. Cole,

Silicate esters as functional fluids and synthetic lubricants,

Union Carbide Chemicals Co., New York, N. Y.
16. Private communication from P. E. Peterson, Union Carbide Chemicals

Co., to J. C. Davis, NBS, with enclosed unpublished technical information.

17. Development of high temperature aircraft hydraulic fluic, WADC Technical Report 54-191 (Dec. 1954),

18. R. L. Peeler and S. A. Kovarich, Alkyl-silicate aviation hydraulic

fluids with excellent hydraulytic stability, Industrial and Eng.

Chem. 51, 749-752 (June 1959).

19. T. N„ Ad lam, Snow melting by embedded pipes, Radiant Heating , Radiant Cooling, and Snow Melting , Chap. 15, Industrial Press, New

York, N. Y.

20. C. S. Craqoe , Properties of ethylene glycol and its aqueous solutions

National Bureau of Standards Report No. 4268 (Aug. 1958). (Not

available at Supt . of Documents. Request information from the report

from P. R. Achenbach or J. C. Davis, NB&)

21. A. D. Abbott, J. R. Wright, A. Goldschmidt, W. T. Stewart, and R. 0.

Balt, Silicate esters and related compounds [3] 6 (July 1961).

22. Antifreeze battle looms, Chem. and Eng. News [46] _33 , 4976 (Nov.

14, 1955).

23. Antifreeze turnabout, Chem. Weekly [6] ji9, 39 (Aug. 11, 1951).

24. D. A. Barsness, Extreme temperature range of organic coolants,

ASTIA Techn. Abst . Bui. No. AD258-597 (July-Sept. 1961).

25. I. Baumel, Determination of 1 , 2-propylene glycol In ethylene

glycol, Analytical Chem. [5] 26 , 930-931 (1954).

26. J. C. Cessna, Electrical resistance method for studying corrosion

inhibitors in automotive antifreezes. Corrosion JL5, 67-72 (Nov. 1959)

27. C. E. Cole, How to Install piping for high temperature heat transfer,

Heating, Piping and Air Conditioning [3] i29, 99-101 (1957).

28. New clue to corrosion, Chem. Eng. News [ 24j _36, 48 (June 16, 1958) „

29. H. L. Craig, Jr., and P. H. Woods, Inhibition of corrosion of

hyperertef tic aluminum-silicon alloys in antifreeze solutions,

Corrosion [9] _16, 457t-460t (1960).

30. Does antifreeze in a heating system affect heat transfer?. Heating

Piping and Air Conditioning [2] 22_, 97 (1950).

31. Dump your antifreeze, Diesel Power and Diesel Transportation [4] 35,

53 (1957).
32. Electric snow removal adds 13.4 KW to load, Electric World [24] 146 , 162 (Dec. 10, 1956).

33. M„ B. Glasser and G. Thados , Recovery of ethylene glycol from spent

antifreeze solutions, Chem. and Eng. Progress [3] 52, 94M-96M (1956) u

34. Indirect heating methods for snow-melting systems. Actual Specifying

Engineer (Dec. 1961).

35. J. L. Koffman, Ehtylene glycol, Automobile Eng. [557] XLII , 365-367

(Sept. 1952).

36. G. D. Lain, Heat transfer in snow-melting systems depends on conditions around pipes, Heating, Piping and Air Conditioning [6] 2_8

70 (1956).

37. M. Levy, Corrosion inhibitors in auto cooling media, Industrial and

Eng. Chem. [4] 50, 657-662 (1958).

38. Miscellaneous heating and cooling media. Heating and Ventilating

Reference Data [3] 50., 163 (1953).

39. Now about antifreeze, Diesel Power and Diesel Transportation [ 1] 31 , 36-38 (1953).

40. 0, 0. Oaks, The application of high temperature liquid as a heat or energy transfer medium for domestic and industrial uses, Trans.,

Am. Soc. Heating and Ventilating Eng. 52_ t 65-67 (1946)„

41. Byers wrought iron for radiant heating, A. M. Beyers Co., 6th and

Bingham St., Pittsburgh, Pa.

42. Byers wrought iron pipe for snow-melting systems, Ibid.

43. Design data for radiant panel heating, Suppl. to Bui. No. 19,

National Tube Co., Pittsburgh, Pa.

44. Dowtherm SR-1, heat transfer fluid, The Dow Chemical Co u , Midland,

Mich .

45. Freon, Techn. Bui. B-2 , Properties and applications of the "Freon"

fluorinated hydrocarbons. I„ E. du Pont de Nemours and Co., Inc.,

"Freon" Products Div., Wilmington, Del.

46. General Catalog, National Tube Div., U 0 S. Steel, 525 William Penn

Place, Pittsburgh, Pa.

47. Glycols, Union Carbide Chem. Co., Div. of Union Carbide Corp.,

270 Park Ave . , New York, N. Y.

Physical properties data, "Prestone" antifreeze solution. Union

Carbide Consumer Products Co., 270 Park Ave., New York, N. Y.

48 .
Steel pipe sx\ow melting and ice removal system, Committee on Steel

ripe Research, Arm Iron and Steel Inst., 150 E. 42nd St., New York,

N. Y.

A. T. P. B, Squires, Corrosion inhibitors for ethylene glycol-water

for; piston engines, the protection of motor vehicles from corrosion,

Soc. Chem. Indus. Monog. _4 , 51-68 (1958), Soc . Chem. Indus., 14

Belgrave Square, London.

British Standard Specification 3150:1959, Corrosion inhibited ethanediole antifreeze for water cooled engines, type A, British Standards

Inst., British Standards House, 2 Park St., London, W1

military Specification MIL- 11-5559A , Hydraulic fluid, arresting gear,

(Apr. 25, 1964) (Hdqs)

MANUFACTURERS' ADVERTISING LITERATURE

Ion exchange with the amberlite resins, Rohm and Haas Co.,

Washington Square, Philadelphia, Pa.

2. If you use water, Ibid.

Amberlite ion exchange resisn laboratory guide, Mallinckrodt Chem.

Works, 2nd and Mallinckrodt St., St. Louis, Mo., Industrial Chem.

Div.

Cold -cup antifreeze tester, Rolf Darbo, Box 2158, Univ. Sta .

,

Madison, Wise.

Republic X-TRU-CQAT plastic -coated steel pipe, Republic Steel Corp.,

General Offices, Cleveland, 0.

Heating cable, G. E. Co., Wire and Cable Dept., Bridgeport, Conn.

7 Dowtherm handbook, The Dow Chem. Co., Midland, Mich.

Nalcite, ion exchange materials, Bul u Z-12 and Z-13, Nalco Chem. Co.,

Bon Exchange Div., 6216 W. 66th Pl„, Chicago, 111.

9, 1961 information and field service manual on the use of glycols for

refrigeration and moderate temperature heat transfer applications,

M. A. Boehmer, Industrial Applications Manager, Product Development

Dept., Research Div., Wyandotte Chem. Corp., Wyandotte, Mich.

8CX»*MIBS*0C


TABLE 21

PHYSICAL AND CHEMICAL PROPERTIES OF SELECTED LIQUIDS FOR HEAT TRANSFER IN SNOW-MELTING SYSTEMS

Liq. Vapor

Name of Material General Sp- Heat

Dens . at

Viscosity at Freezlng b

Boiling

b

Pressure

Selected Crit. Suitable Chemical Trade Class. at 100 F 86 °Fa 100 0 F

3 Point Point Temp. Temp. Flash Point Toxicity with metals Btu/lb deg lb/ft centi- poises

U F °F psia °F °F

Ethylene Glycol H0CH

pCHp0H

Diol 0.581 69.0 10.4 +9 388 0.9 at 250 °F

c 245 Slightly

toxic

See Report

Text

Diethylene

Glycol

Diol 0.56 69.0 18.0 +18 473 0.14 at 250

0 F

c 290 Lower than

for Ethylene

Glycol (See Remarks)

c

Triethylene

Glycol

Diol 0.53 70.0 20.0 + 19 550 0.03 at 250 °F

c 330 Lower than

for Diethylene Glycol

(See Remarks)

Ethylene Glycol 40Z Solution

(By weight) hoch

2ch2oh

Diol 0.86 65.0 1.7 -11 221 25.1 at 250 °F

114.0 at 350 °F

c d Slightly

toxic

See Report

Text

Ethylene Glycol

507. Solution

(By weight) hoch

2ch2oh

Diol 0.81 66.0 2.2 -32 225 23.3

0 at 250 °F

106.0 at 350 °F

c d Slightly

toxic

See Report

Text

Ethylene Glycol

607. Solution

(By weight)

HOCHpCHpOH

Diol 0.77 67.0 2.89 Pro- bably

below

-50

230 21.0 at 250 °F

96.1 at 350 °F

c d Slightly

toxic

See Report

Text

Proprietory

Ethylene Glycol

Product

Dowtherm

SE-1

Diol 0.59 67.0 12.0 -56 for

607. 330 c 0 240 Low acute

oral toxi- city

Suitable for

steel, copper, aluminum, wrought iron

Propriety UCAR-17

Bthylene Glycol

Product

Methylene Chlo- R-3®

ride CH

2C12

(Footnotes on

Diol

Chlorohydrocarbon

page 3 of Table

h

Approx. 0.30

21)

h h

0.37

Page

h h

-142 104

1 of Table 21

h

!3.3

0 at 100 F

h

458.6

h

i

h

500 ppm by volume MAC

for successive 8 hr

days. Some- what less toxic than group 4 Underwriters.

h

Suitable for

use with copper, steel and cast

q iron up to 140 Reacts with alu- minum and zinc.

Remarks

Low vapor pressure would

tend to lessen danger from inhalation

Extensive tests on animals

have shown little ill effect after long exposure.

Do not use with galva- nized metals over room temperature .

Contact of the fluids with

the skin should be avoided.

(CONTINUATION) TABLE 21

PHYSICAL AND CHEMICAL PROPERTIES OF SELECTED LIQUIDS FOR HEAT TRANSFER IN SNOW-MELTING SYSTEMS

Dens . Name of Ma teria

Genera 1 Sp , Hea t a t Chemical Trade Class

a t 100 °F

a 86 °F

a Btu/lb deg lb/ft

Monochlorodif 1 tiorome thane chcif

2

B-22 Fluo r inated Hydrocarbon0.335

at 86 °F

73.4

Dichlorodif luoromethane

CC1

2 F2

B-12 Fluorinated Hydrocarbon

0.24

a t 86 °F

80.7

Tr ichlorotrif 1 uoromethane

cci

2f-ccif

2

B-113 Fluorinated Hydrocarbon

0.22

at 86 °F

97.0

Trichloromonof luoromethane

cci

3f

B- 11 Fluorina ted Hydrocarbon

0.21

at 86 °F

91.4

Dichlorotetra- B-114 Fluorinated 0.24 89.9

fl rethane Hydrocarbon at

c2ci

2f4 86 °F

Tetra (2- Ethylbutyl)

Silicate

PM 3189 (Union

Carbide)

Silicate c Ester

56

at

68 °F

Tetra (2- Ethylboxyl) Silicate

PM 3190 (Union

Carbide)

Silicate 0.48 Ester at 104 *F

55at

68 °F

Aromatic Oil Mobiltherm Light

Petroleum 0.434

Oil

60

at 100 °F

(Footnotes on page 3 of Table 21)

Liq

Viscosity at

100 °F

a

Freezln« b PointBoiling , Point

Vapor Pressure Selected

Temp

Crit. Temp

Flash Point centi- poises

°F °F psia °F °F

0.23

at 86 °F

-256 -41 716, cr itica

pressure

204.8 Non-flammable

0.25

at 86 °F

-252 -22 597, critical pressure

233.6 Non-flammable

0.62

at 86 °F

-31 118 101.8 at 250 °F, 283.3 at 350 °F

417.4 Non-flammable

0.41

at 86 °F

-168 75 182.0 at 250 °F, 468.0 at 350 °F

388.4 Non-flammable

0.36

at 86 °F

-137 38 310.0 at

250 °F

294.3 Non-flammable

3.6 Below

-148

c <.005 Lq. at wide range

of temp.

335

6.0 Below -130

680 <.005 Lq. at wide range

of temp.

390

4.5 -20 Above

400

.20 at 250 °F .64 at 300 °F

c 300 - 350 f

Page 2 of Table 21

Toxicity

Group 5A Underwriters

Group 6 Underwriters

Much less than Group 4, but more than Group

5 Underwriters

Group 5A Underwriters

Group 6 Underwriters

Low order

(See Remarks)

Low order

(See Remarks)

Non- toxic

Suitable with metals

All standard

ferrous and non-ferrous

metals can be used

All standard

ferrous and non-ferrous

metals can be used

All standard

ferrous and

non- ferrous metals can be used

All standard

ferrous and non-ferrous

except zinc Mg & A1 alloys

can be used.

All standard

ferrous and non-ferrous

except zinc Mg & A1 alloys

can be used.

c

c

Can be used with

steel, but not copper

Remarks

Ltr . to J.C. Davis, NBS

of 4/3/62 stated that toxicity was low order.

Ltr. to J.C. Davis ,NBS of 4/3/62 stated that toxicity was low order

Footnotes for Table 21

PHYSICAL AND CHEMICAL PROPERTIES OF SELECTED

LIQUIDS FOR HEAT TRANSFER IN SNOW-MELTING SYSTEMS

Unless otherwise shown at individual entry,

b

At atmospheric pressure.

c Information not readily available.

^ Solutions containing less than 85% glycol by weight actively on heating

and the flame was extinguished during test cited in reference [ 1 73

e Pour point.

^ Fire point.

® AIHA Hygienic Guide Series, December 1956.

^ Essentially ethylene glycol.

Practically non-flammable at ordinary temperature. Forms a weekly com- bustible mixtures at high concentrations of solvent in air.

Page 3 of Table 21