NATIONAL BUREAU OF STANDARDS REPORT

599J+

EXAMINATION OF THE TEMPERATURE DISTRIBUTION

WITHIN THE N.B.S. FLOOR TEST FURNACE

by

J. Ve Ryan

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U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
THE NATIONAL BUREAU OF STANDARDS

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NATIONAL BUREAU OF STANDARDS REPORT

MBS PROJECT

1002-12-1029 July 25, 1958

NB8 REPORT

599^

EXAMI NATION OF THE TEMPERATURE DISTRIBUTION

WITHIN THE N.B.S. FLOOR TEST FURNACE

by

Jo V. Ryan

IMPORTANT NOTICE

NATIONAL BUREAU OF ST

Intended for use within the

to additional evaluation and

luting of this Report, either the Office of the Director, N; however, by the Government

to reproduce additional copl

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST)

on October 9, 2015.

progress accounting document*

ormally published It is subjected

:, reproduction, or open-literature

eslon Is obtained In writing from Such permission Is not needed,

y prepared If that agency wishe*

<NBS>

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

EXAMINATION OF THE TEMPERATURE DISTRIBUTION

WITHIN THE N.B. S. FLOOR TEST FURNACE

ABSTRACT

The temperatures within the NBS floor test

furnace are monitored by 12 thermocouples

distributed symmetrically with respect to the

furnace plan, and located 12 in® below the

specimen. Extra thermocouples were included

during several standard fire tests to give the

temperatures at other positions within the

furnace

„

The mean temperature variation with moderate

change in distance from the specimen surface

was determined and compared with the variations

among the individual standard thermocouples®

The horizontal and vertical temperature

distributions within the furnace chamber

during typical tests are reported®

I® INTRODUCTION

Fire endurance studies of floors and roofs are made

by the National Bureau of Standards, employing a floor

furnace in which the specimen forms the top of the

combustion chamber® The chamber height is about 6 ft but

varies with the thickness of the specimen; the chamber

width is 12 ft 8 in® and the length 17 ft 3 in® Premixed

gas and air is fed to 9 burners along each side wall®

The burners are at two levels, about 38 and 52 in® above

the furnace floor; those at 52 in® are located in ports

through the furnace wall, those at 38 in. are in brick

piers that extend about 28 in® out from the wall and 50 in®

up from the floor® The burners discharge horizontally,

in the space from about 3^ to 58 in® above the floor®

The individual fire tests are conducted in accordance

with a Standard Test Method, ASTM E119 (l) 9 that specifies

the time-temperature curve to be produced, as closely as
,• •

.'
2

feasible, in the furnace chamber, as indicated by thermocouples placed 12 in. below the exposed surface of the

specimen. The thermocouples are encased in iron pipes

of which eight are inserted through holes in the furnace

walls, and the other four extend up from a central pier.

The pipes for the latter may be cut to the necessary

length to place the thermocouple junctions at the

specified 12 in. below the specimen. However, the eight

peripheral thermocouple pipes are essentially horizontal.

The vertical distance below the specimen is adjusted in

discrete steps by the choice of one of four holes at

each location along the furnace walls. The positions of

these holes permit the initial placement of the thermocouple junctions within 1 in. of the specified distance

for specimens within the range of thicknesses normally

found in buildings. Specimens of unusual designs could

make it necessary to place the thermocouple junctions at

distances below the specimen significantly different

than 12 in.

As a means for exploring the effects of such

misplacements as well as general temperature variations

within the furnace, extra thermocouples were placed at

various locations within the chamber during four tests.

2. THERMOCOUPLE LOCATIONS

The thermocouples in the first test were placed to

permit evaluation of the effect of displacing the eight

peripheral thermocouples 4- to 6 in. farther than the

specified 12 in. from the specimen. Those in the second,

third, and fourth test were placed to sample the horizontal

and transverse temperature distributions.

The specific locations of the thermocouple junctions

are shown in Figure 1. In the first test, with two levels

of peripheral thermocouples, those at the standard 12 in.

distance were supported with nichrome wires to minimize

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sag. In the other three tests, the extra experimental

thermocouples were mounted in a manner intended to

minimize sag without introducing serious obstruction to

the normal circulation of hot gases.

3. TEST METHOD

The test method requires that specimens be exposed

to the furnace fires controlled to produce, as closely as

feasible, the temperatures of the standard time-temperature

curve (l). These include 1000°F at 5 min, 1300°F at 10

min, 1550°F at 30 min, 1700°F at 1 hr, l850°F at 2 hr,

2000° F at 4 hr, and 2300° F at 8 hr.

Fire exposure severity is defined as the ratio of

the area under the curve of average furnace temperatures

to the area under the standard time -temperature curve for

the same elapsed time, both taken above 20°C as a base

line. The severity is expressed as a percent, and variation

of ± 5 percent is allowed, in tests of over 2 hr duration.

4. TEST RESULTS

The first, second, and fourth tests were of six hourdurations; the third of only 50 min duration. Therefore,

most of the results and conclusions were derived from the

data of the former group.

Some of the individual thermocouples ceased to function

properly before the ends of the six hour tests. Hence the

data were not complete for the full duration, in all cases.

4.1 First Test

For the sake of analysis, two groups of twelve

thermocouples, and the mean values of the data therefrom

were considered. The first group was composed of the

thermocouples at the standard 12 in. from the specimen;

the mean temperature indicated by this group was

designated U. . The second group was composed of the

eight peripheral thermocouples 4 to 6 in. below the

standard position plus the four along the central pier;

this group's mean temperature was designated .
BEO
- 4 -

The four thermocouples along the central pier, at the

standard 12 in. from the specimen, were included in

both groups because the furnace design is such that

their junctions may always be placed at the standard

position.

The mean temperatures were jietermined at 10 min

intervals. The difference, a = t( - i~$ , reached a

maximum of 8 deg C at 20 min and decreased more or less

uniformly to 1 deg C at 4 hr 40 min. The root-meansquare values of the deviations from the mean among

the data from the twelve standard thermocouples were

in the range of 20 to 40 deg C over the 4 hr 40 min

period.

The effect of the difference in elevation on the

fire exposure severity was estimated by determining the

ratio of the accumulated A to the accumulated mean

from the standard thermocouples, expressed as a percent

^4 1 (T, - "Ts ) ' tfsp- A too - ~~= U

£ T5 X oo

The values of 4* ranged from 0.99 percent at 20 min to

0.42 percent at 4 hr 40 min. The effects of difference

in thermocouple location on fire exposure would thus be

less than 1.0 percent.

4.2 Second Test

The results of the second test are presented as

graphs of temperature vs distance above the furnace

chamber floor, at a given distance from the side wall

(that of the standard thermocouple positions), and of

temperature vs distance from the side wall, at two

elevations above the furnace chamber floor. Each graph

has a family of curves, each curve corresponding to a specific time. These graphs are given in Figures 2,

4, and 6.

4.3 Third Test

The floor specimen under test failed at 52 min,

much earlier than anticipated. Therefore, the data

cover a much smaller time than those from the other

' tests .vThe-y do not appear to. contradict those from the

other 'te'sts, and are not presented.
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4. A Fourth Test

The results of this test are presented as graphs

similar to those for the second test. These graphs

are given in Figures 3 ? 5? and 7«

5. DISCUSSION

The first test showed that the 12 in. spacing of

the furnace thermocouples from the specimen surface

might be exceeded by as much as 6 in. without introducing

a serious difference in the actual exposure to the

specimen. Since the peripheral thermocouple pipes at

the standard 12 in. were supported and those at greater

distance were not, the distance between increased as

the latter pipes softened and bent down under the

effects of the fire. Despite this increase in

separation, the temperature differences between the

mean values decreased. This test also indicated that

near the specimen the mean furnace temperature

decreased slightly with decrease of distance from the

specimen. This should be expected due to the heat

absorption by the specimen, plus the fact that the

direct flames from the burners are concentrated somewhat below the standard thermocouple position.

The direction of the temperature gradient near

the specimen was confirmed by the other tests. This

may be seen in Figures 2 and 3? showing the vertical

temperature distribution in the second and fourth

tests.

Figures b and 5 show the horizontal temperature

distribution at a level $b in. above the floor, and

slightly above the burners. As expected, the curves

are reasonably flat. Figure A, covering distances

from 12 to 77 in. from the furnace wall, (the latter

distance being at the centerline) shows the cooling

effect of the furnace wall to be fairly slight. The

temperature observed at the centerline (77 in. ) was

consistently lower than that at 60 in. for the same

time. This may have been due to overheating at the

latter distance due to a feature of the furnace

geometry. The temperature difference was more pronounced for the lower pipe and the cause is discussed

in coniiec tion^with Figure 6.

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Figures 6 and 7 show the horizontal temperature

distribution at a level 36 in. above the furnace floor.

Here the geometry of the furnace causes significant

interference in the circulation of the furnace atmosphere. Figure 6 indicates a high temperature condition

persisting at about 60 in. from the furnace wall. This

is believed due to the deflection of the flames from

one burner by the support for one of the thermocouple

pipes from the central pier. This appears to be born

out by Figure 7* In the later test, the thermocouple

junctions were on the opposite side of the centerline,

and no localized hot spot is indicated by the data.

6. CONCLUSIONS

The graphs indicate that: The horizontal temperature distribution near the specimen is fairly uniform.

The piers in the furnace chamber cause some local hot

spots but the overall temperature distribution is still

reasonable at about 3 ft above the furnace chamber

floor.

The vertical temperature distribution is much less

nearly uniform than the horizontal distributions.

The temperature gradient within 18 in. of the

specimen is such that the temperature decreases as the

specimen surface is approached.

The deviations from uniformity, both horizontal

and vertical, decrease significantly as the test

duration increases.
*
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REFERENCES

1. "Standard Method for Fire Tests of Building

Construction and Materials", American Society

for Testing Materials, designation E119»

NORTH

WEST

PLAN \RESTRAINING

A- 52 STANDARD THERMOCOUPLES 36“FR0M D*“ THERMOCOUPLES IN SPECIAL TUBES

WALLS AND IN CENTER PIER. ALL 32" 1 2”

> 36“60“AND77" FROM WEST WALL

BELOW SPECIMEN IN TEST NO. 2

B” 8 THERMOCOUPLES I6”T0 18" BELOW

SPECIMEN IN TEST NO. I C" THERMOCOUPLES IN SPECIAL TUBES G“ 4 THERMOCOUPLES 16“ ABOVE FLOOR

32“ 4 4“ 50“A N D 62“ FROM EAST WALL 36" FROM WALL IN TEST NO. 4

SN TEST NO. 4

E- 4 THERMOCOUPLES 16“ ABOVE FLOOR

36“ FROM WALL IN TEST NO. 2

FIG.I -THERMOCOUPLE LOCATIONS
'
TEMPERATURE,

FIG.2-TEMPERATURE DISTRIBUTION

ABOUT 36 INCHES FROM SIDE WALL

(TEST NO. 2)

SPECIMEN

SURFACE

TEMPERATURE

DISTANCE ABOVE FLOOR, INCHES

FIG. 3-TEMPERATURE DISTRIBUTION

ABOUT 36 INCHES FROM SIDE WALL

(TEST NO. 4)

SPECIMEN

SURFACE

TEMPERATURE,

FIG.4- TEMPERATURE DISTRIBUTION

54 INCHES ABOVE FLOOR

(TEST NO. 2)

TEMPERATURE,

FIG. 5-TEMPERATURE DISTRIBUTION

54 INCHES ABOVE FLOOR

(TEST NO. 4)

TEMPERATURE,

FIG.6 -TEMPERATURE DISTRIBUTION

36 INCHES ABOVE FLOOR

(TEST NO. 2)

TEMPERATURE,

1200

o

©

1100

1000

900

800

700

600

500

400

300

200

100

0.

5HRS 0

3HRS°-

2HRS°:

I HR40M!N°-

20 MIN o-

-O Y -O

-O

LU

cr

UJ

UJ

o

LUO

<

cr3

Li_

) 10 20 30 40 50 60 70 80

DISTANCE FROM EAST WALL, INCHES

FIG. 7 -TEMPERATURE DISTRIBUTION

36 INCHES ABOVE FLOOR

(TEST NO. 4)

U. S. DEPARTMENT OF COMMERCE

Sinclair Weeks, Secretary

NATIONAL BUREAU OF STANDARDS

A. V. Astin, Director THE NATIONAL BUREAU OF STANDARDS

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