3

Fluorochemicals in Heat Transfer Applications

Questions not answered herein may be directed to the 3M Technical Service Hotline

at 800-833-5045.

1. How Do I select a fluid for a particular application?

2. Why would I choose a NovecTM Fluid over a FluorinertTM fluid?

3. How Do NovecTM HFE fluids differ from FluorinertTM Fluids?

4. Is there a materials compatibility chart for use with FluorinertTM and

NovecTM Fluids?

a. What are the compatibility issues with FluorinertTM and NovecTM

Fluids?

b. Why is it more of an issue with NovecTM fluids than with Fluorinerts?

c. What types of materials ARE NOT an issue?

d. What types of materials MAY BE an issue?

e. What is meant by compatibility?

f. How do you approach an elastomer application?

g. What is the best way to test for compatibility of elastomers?

h. Can you recommend hose and seal materials to me?

5. What type of pump should I use with FluorinertTM or NovecTM fluids?

6. I frequently have to add fluid to my FluorinertTM or NovecTM system.

Where is the fluid going?

7. How can I detect fluid leaks?

8. How do I size a heater for use with FluorinertTM or Novec HFE fluids?

9. Will FluorinertTM or NovecTM fluids cause corrosion?

Frequently Asked Questions
The selection process depends upon whether the application is single

phase or two phase. Single phase applications are applications in which

the fluids remains a liquid. In two phase applications the fluid changes

phase (usually it boils).

Single Phase

In these applications, the fluid is most often pumped in a loop between a

heat source and a heat sink. To choose a fluid, one must consider the

temperature range of the application. Consider the following application:

Example

Cooling of Semiconductor Tester

Operating range –40 to +40°C

Which FluorinertTM to use?

Because the equipment will be operating in this range, we can reasonably

expect that fluid within the tester will not exceed 40°C while fluid in the

chiller may reach –50°C. Our goal then is to find a fluid which will function

well within this range.

Obviously we want a fluid which will not boil at 40°C. We could choose FC72 which boils at 56°C. Investigation of its low temperature properties

indicate a viscosity at –50°C of 1.5 centistokes (cSt), a little higher than

water at room temperature. Obviously the fluid will be very pumpable at

this temperature and should enter the turbulent regime easily providing

good heat transfer with relatively low pumping power demands.

Use of FC-72 could lead to excessive fluid loss however. Because this

system operates over a wide temperature range, the fluid will expand and

contract considerably (usually 1 volume % for every 10°C). Many chiller

expansion reservoirs are ventilated to take in and purge air as a means of

accommodating this expansion. Because the air which leaves this

reservoir is typically saturated with fluid vapor, the only way we can reduce

the amount of fluid carried with the air during each thermal cycle is to

reduce the vapor pressure of the fluid. This is accomplished by looking to

a fluid with a higher boiling point.

We might consider FC-84. This fluid has a boiling point of 80 deg. Its vapor

pressure at 40°C is only about 40% that of FC-72. Although the actual

vapor loss must be calculated by using a vapor pressure relation and

integrating with temperature, use of FC-84 would greatly decrease losses.

The viscosity of FC-84 at –40°C is 3.0 cSt, still very pumpable and probably

1. How Do I select a fluid for a particular application?
quite acceptable. Use of a still higher boiling fluid like FC-77, cuts the

vapor pressure at –40°C to 20% that of FC-72. The viscosity of FC-77 at –

40°C is 6.6 cSt which is still probably very workable for this application.

Unless the operating temperature range is quite narrow, the choice of a

FluorinertTM or NovecTM HFE fluid for single phase application is generally

a compromise between volatility at the high end and heat transfer or

pumping power performance at the low end.

Two-Phase

The selection of a fluid for two phase applications is generally based upon

the boiling point. For heating applications such as vapor phase soldering,

the boiling point of the fluid is chosen such that it will melt the eutectic

being used as a solder.

For cooling applications such as microelectronics cooling, the boiling

point of the fluid is chosen such that it maintains the heat generating

component at the desired temperature. Thought must also be given to the

temperature of the final heat sink. In some electronics modules for

example, FC-72 is used not because its boiling point of 56°C is an ideal

temperature for operating electronics but because this boiling point allows

the condenser to deposit its heat to ambient air without a compressor.

Keep in mind that Fluorinert or HFE fluids generally require heat fluxes of

more than 2 W/cm2 to sustain boiling. Wall superheats are generally

between 15 and 25°C during boiling and the critical heat flux is usually

about 15-20 W/cm2 for pool boiling More Info
-120 -110 -100 -90

100

60

40

20

10

8

6

5

4

3

2.5

2

1.75

1.5

.25

1

.9

.8

.7

.6

.5

.45

.4

.35

.3

.28

.26

.24

.22 -80 -70 -60 -50 -40 -30 -20 -10 0 10

Temperature (∞C)

20 30 40 50 60 70 80 90 100 110 120 130 140

Viscosity vs.Temperature

FC-87 FC-84

FC-40 FC-43 FC-70

FC-72

FC-77

FC-3283

HFE-7500

HFE-7200

HFE-7100

HFE-7000
In some cases, a NovecTM HFE fluid will be chosen because of its wider

liquid range or superior heat transfer properties. More often than not,

though, the decision is based upon the superior environmental properties

of an HFE. Although all 3M fluids, FluorinertTM and HFE alike, are nonozone depleting, the Fluorinert Fluids have long atmospheric lifetimes and

high global warming potentials (GWPs). NovecTM HFEs have very low

global warming potentials and are therefore favored by some users as the

“greener” option More Info.

The user should consider the following facts:

- Use of perfluorinated fluids like the Fluorinerts is not currently

regulated by any US regulatory agency except in CFC replacement

applications. In such applications, the US EPA’s Significant New

Alternatives Program (SNAP) permits use of perfluorinated fluids “when

no other alternative is available.” The bulk of Fluorinert applications

today never employed a CFC.

- There are a few applications for which HFEs are not suited. Generally

these are very high voltage direct contact applications. These

applications may always require the superior electrical properties of

Fluorinerts.

- Perfluorinated fluids have a long and well-documented history in direct

contact cooling of sensitive electronics. Though many scientists are

researching the use of NovecTM HFEs in these applications, a long

history is not yet available.

- The vast majority of indirect contact, dielectric heat transfer

applications which employ Fluorinert fluids could just as easily use

NovecTM HFEs. This includes: ion implanters, etchers, testers, fuel

cells, reactor cooling, freeze dryers, and others.

2. Why would I choose a NovecTM Fluid over a FluorinertTM fluid?
For practical purposes relevant to heat transfer, NovecTM HFE fluids differ

from Fluorinert fluids in the following ways: chemical structure, global

warming potential (GWP), hydrocarbon solubility and Electrical properties.

Chemical Structure

This difference is best illustrated by considering FC-72 and HFE-7100 (see

figure below). FC-72 is perfluorinated meaning that all available bonding

sites on its carbon backbone are occupied by fluorine atoms. The strength

of the carbon fluorine bond is one reason that the FluoirnertTM line of fluids

(all of which are perfluorinated) are so chemically inert. HFE-7100, on the

other hand, contains not only fluorine, but also hydrogen and oxygen.

Also, HFE-7100 and all of the NovecTM HFEs are what 3M calls “segregated”

HFEs. The molecules are segregated in the sense that a perfluorinated

portion of the molecule is “segregated” from a fully hydrogenated portion

by an oxygen or “ether” linkage. It is the presence of hydrogen on the

molecule, distributed in this way, which leads to the unique properties of

NovecTM HFEs

Global Warming Potential

The presence of the hydrogenated portion of a segregated HFE makes

these molecules susceptible, once in the troposphere, to hydroxyl radicals

that break the HFE down. This breakdown is relatively rapid so that HFEs

have very short atmospheric lifetimes and consequently low global

warming potentials. HFEs GWPs are superior to those of HFC-134a, a

refrigerant used today in many air conditioning systems.

Atm. Lifetime GWP

[years] [100 year ITH]

CFC-12 102 8500

FC-72 3200 7400

FC-77 2300 6700

HFC-134a 14.6 1300

HFE L-13791 4.9 370

HFE-7100 4.1 320

HFE L-15381 <2 <250

HFE-7200 0.8 55

The L-number designation is used by 3M to indicate

3. How Do NovecTM HFE fluids differ from FluorinertTM Fluids?
Because they contain no chlorine, all FluorinertTM and NovecTM HFE fluids

are inherently non-ozone-depleting.

Hydrocarbon Solubility

The presence of hydrogen on an HFE molecule makes that molecule a

better solvent for hydrogenated materials. Since most of the organic

additives and plasticizers used in the manufacture of elastomers are

hydrocarbon-based, NovecTM HFEs will extract these materials from

elastomers more easily more info.

Electrical Properties

The FluorinertTM fluids are excellent dielectrics. This is the primary reason

they are used in many applications. NovecTM HFEs are also very good

dielectrics but their resistivity may fall short in a very small number of

applications. The table below shows electrical properties for some typical

Fluids.

At a given relative humidity, the dielectric strengths of HFEs are

comparable to those the FluorinertTM fluids. The electrical resistivity of a

NovecTM HFE, though several orders of magnitude lower than that of a

FluorinertTM, is still higher than the best attainable DI water (about 18

Mohm-cm).

Dielectric Volume

Strength Resistivity

[kV 0.1" gap] [ohm-cm]

FC-72 40 1.0E+15

FC-77 40 1.0E+15

HFE-7100 40 1.0E+09

HFE-7200 40 1.0E+08

HFE-7500 40 1.0E+09

The L-number designation is used by 3M to indicate

a material which is developmental
Before 3M commercialized HFE-7100, the first or its Novec TM or HFE

product line, there were only the FluorinertTM Fluids. These perfluorinated

fluids are very poor solvents. For this reason, they are “compatible” with a

variety of polymeric materials. It was easy at that time to make very

sweeping statements about polymer compatibility. In other words, we

could assemble a table which listed common materials of construction

(EPDM, butyl, nitrile, nylon, etc) and tell you which perform well with the

FluorinertsTM and which did not. As a rule, most performed pretty well.

While the first HFEs were being commercialized, 3M engineers performed

exhaustive compatibility testing using standard materials and arrived at

what we thought was a well-researched table like the one described above.

As complaints from the field started coming in, it quickly became apparent

that not all materials of a given class are similar. For example, we might

test ten EPDM compounds and find that eight of them perform very well.

The other two may perform miserably. There is simply too much variability

in the formulations of various materials. This situation is compounded by

the fact that construction materials may be completely untraceable. For

example. If 3M engineers test an elastomeric O-ring from the pump used by

a chiller manufacturer and find it to perform very well, they would like to

recommend it to other OEMs. Most often though, the O-ring is known only

by the chiller manufacturer’s part number. That part number may have

another part number belonging to the pump manufacturer who may buy it

as yet another part number from the O-ring vendor. The vendor may in turn

buy the raw polymeric materials from a formulator who uses a formulation

number. It is easy to see why it becomes a very complicated matter to

gather meaningful compatibility data that can be used to make design

recommendations.

We have a dilemma. On the one hand, there is a need for a simple, easy to

understand compatibility chart which design engineers can use when

selecting materials of construction. On the other hand, such a chart

cannot be foolproof because there will always be exceptions to the rules.

Use of such a chart can and has lead to expensive field problems.

What then is the solution? One possible solution is to educate customers

on the issues involved with material compatibility and the use of NovecTM

Fluids and then to provide testing procedures and even testing services.

Simultaneously, 3M could gather test data for as many commercial polymer

formulations as is practical. Data of this type would be traceable to the

formulator’s ID numbers and permits the end user to contact the polymer

4. Is there a materials compatibility chart for use with FluorinertTM

and NovecTM Fluids?
formulator directly, order the part they need and feel certain that it will

perform well with a given NovecTM Fluid. This is what 3M is doing.

The issues are these: plasticizers, plasticizers and additives. During the

production of elastomers, or of polymers in general for that matter, it is

common to add to the polymer matrix a plasticizer or additive. Most often

the material is an oil or wax which is added to the polymer to increase its

workability during manufacture or to enhance some mechanical property in

the end use. A classic example of the latter is the addition of the

hydrocarbon plasticizer dioctyl pthalate (DOP) to polyvinyl chloride (PVC)

to make a flexible shower curtain. The amount added can range from very

little to very much depending upon the polymer matrix, the plasticizer and

the mechanical properties being sought.

So why is this such an issue? The primary issue is one of solubility,

namely, the solubility of the plasticizer in the fluid. If the plasticizer is

soluble in the fluid, it is more likely to be extracted from the polymer matrix

by the fluid. The solubility, then, can tell us something about how the

polymer and the fluid will be effected.

FluorinertTM fluids are fully fluorinated or perfluorinated molecules. An

example is the molecule C6F14 or FC-72 on which all available carbon bonds

are occupied by fluorine atoms. A fundamental observation of physical

chemistry is that “like dissolves like” and so perfluorochemicals like the

Fluorinerts do a rather poor job of dissolving anything but other

fluorochemicals. Since 99+% of plasticizers used in the polymer industry

are hydrocarbon-based compounds, few of them are very soluble in the

Fluorinerts. The NovecTM HFEs on the other hand, are a different story.

Hydrofluoroethers molecules like HFE-7100 or C4F9OCH3 contain not only

Fluorine but also hydrogen (the ether oxygen plays a relatively minor role

for the purposes of the present discussion). Because “like dissolves like,”

hydrofluoroethers are more capable of dissolving common hydrocarbon

plasticizers than are the FluorinertsTM.

As a rule of thumb, those materials which we commonly think of as hard

plastics are not an issue. These materials are rarely plasticized to a

4c. What types of materials ARE NOT an issue?

4a. What are the compatibility issues with FluourinertTM and

NovecTM Fluids?

4b. Why is it more of an issue with NovecTM fluids than with

Fluorinerts?
significant degree or in a way which causes problems in HFE systems.

Materials in this category include (there are many others):

Polyethylene Polypropylene

ABS Nylon

polyvinlychloride (PVC) Polycarbonate (LexanTM)

Acrylic (PlexiglasTM) RulonTM

PTFE (TeflonTM) polysulfone

RytonTM phenolic

polyetheretherketone (PEEK)

Thermoplastics

As a rule of thumb, any material which you would describe as “rubbery” is

suspect because it may be plasticized. All common elastomeric materials

fit into this category:

Nitrile Silicone

Butyl Fluorocarbon

Fluorosilicone Natural Rubber

Chloroprene Polysulfide

Polyacrylate Polyurethane

Styrene Butadiene Ethylene Propylene (EP or EPDM)

Of these, EP, butyl and natural rubber tend to perform quite well as a class.

However, there may be members of this class which do not perform well

just as there may polyuerethanes and others that do. Those that

perform well generally contain little plasticizer. It is worth noting that

Silicones and Nitriles are notoriously bad. Fluorocarbons generally are not

heavily plasticized but they will swell in the presence of HFEs because

once again “like dissolves like” and they are fluorinated like the fluid.

There is a natural tendency when talking about elastomer compatibility

(we’ll use the term “elastomer” from now on because we’re referring to

rubbery materials) to focus on the effects the fluid will have on the

elastomer. It is true that extraction of plasticizers from an elastomer can

cause it to harden or shrink and it may even crack. In many industrial

applications, this may be the most important consideration. However,

most people overlook the effect that plasticizer extraction can have on the

fluid.

4e. What is meant by compatibility?

4d. What types of materials MAY BE an issue?
The effects of dissolved plasticizer on the fluid’s performance can be

dramatic and this can be a critical issue in the types of sensitive, high

value applications which use a FluorinertTM or NovecTM fluid. Typical

problems caused by plasticizer in the fluid include:

- Clogging of filters or small fluid passages

- High static voltages or static discharge

- Fluid decomposition (resulting from high voltage discharge)

- Coating of desiccants or fluid conditioning reagents.

The primary considerations when selecting an elastomer for a given

application and the potential effects on elastomer and fluid are: fluid to

elastomer ratio and dimensional tolerance.

Fluid to Elastomer Ratio: Because extraction is an equilibrium process,

knowing this ratio can help you assess the potential for extraction and its

effects on fluid and elastomer. An example of one extreme is a system with

hundreds of feet of plasticized silicone rubber tubing. In such an application,

the fluid may become saturated with plasticizer before the hose degrades

in any appreciable way. Expect the fluid properties to degrade but the hose

may be just fine. The opposite extreme is an application which contains

one very small O-ring with many gallons of fluid. In such an application,

the fluid acts as an infinite sink for plasticizer. If plasticizer extraction is an

issue for the elastomer, it will be worst in this case. Because the fluid

volume is large and it will receive relatively little plasticizer, the fluid may

not be adversely affected.

4f. How do you approach and elastomer application?
Dimensional Tolerance: If the O-ring described above was a radiallyloaded seal in a quick connect, we might expect the quick connect to leak

as the plasticizer is extracted and the O-ring shrinks. If, however, the Oring was used as a face seal for pipe flanges, a little shrinkage might not be

an issue. In this latter case neither the fluid nor the O-ring is adversely

effected by the extraction.

These considerations are summarized for some typical applications in the

table below.

Elastomer Application Key Features Issues

Shaft Seal on a Pump or

Valve

-Large fluid to elastomer

ratio.

-Dimensional tolerances

may be critical.

- Extraction will be maximized, expect shrinkage if

elastomer is plasticized.

- Likely source of leak.

- Choose very compatible elastomer.

- Expect little fluid contamination. This may not be

an issue.

Quick Connect Seal -Large fluid to elastomer

ratio.

-Dimensional tolerances

may be critical.

- Extraction will be maximized, expect

shrinkage/degradation if elastomer is plasticized.

- Likely source of leak.

- Choose very compatible elastomer.

- Expect little fluid contamination. This may not be

an issue.

Face seal or gasket -Large fluid to elastomer

ratio.

-Dimensional tolerances

generally not critical.

- Extraction will be maximized, expect shrinkage if

elastomer is plasticized.

- Shrinkage may or may not be a concern.

- Expect little fluid contamination unless many such

seals are present. This may not be an issue.
Tubing - Small fluid to elastomer

ratio

- Fluid may take up a lot of plasticizer. May even

saturate or supersaturate.

- Tubing may become brittle.

- Electrical properties of fluid could alter allowing

discharge or static generation.

- Plasticizer can precipitate as solid or separate

liquid phase during temperature changes.

- Dessicant material can become coated and

inactivated.

- Filters can become clogged.

The most common method in industry is to measure volume change,

weight change and hardness change following exposure of an elastomeric

sample to a small amount of fluid at a known temperature for a given amount

of time. These changes are usually reported as a percent of the initial

value (i.e. 15% weight change). This testing is often accelerated by

performing the testing at elevated temperatures, sometimes necessitating

pressure vessels.

The method described above is a good one and the data obtained in such

tests is meaningful. Unfortunately, it can be misleading in some instances.

One such instance occurred with a quick disconnect (QD) used in

semiconductor test equipment. The QD had worked fine for years with

Fluorinert FC-77. When the manufacturer converted to HFE-7100, the quick

connect began to leak. The manufacturer of the quick connect did

thorough testing of the O-ring seals using conventional methods and they

appeared to perform quite well. Weight gain, volume swell and hardness

changes appeared acceptable.

3M tested the same O-rings and found that they performed quite poorly.

Why the difference? 3M uses a different test method which we feel is more

meaningful for the applications in which our fluids are used. The 3M

method is a Soxhlet extraction test using the fluid as a solvent. In an

extraction test the part is exposed to distilled fluid condensate which is

replenished about every 10 minutes. This condensate is at roughly the

boiling temperature of the fluid and because it is distilled, it contains no

plasticizer. This does 2 things: It provides a worst case temperature (as

most applications do not exceed the boiling point) and it maximizes

diffusion of the plasticizer out of the elastomer. Because the method

allows the extracted plasticizer to be collected and weighed, it provides a

measure of the true weight loss. Since we also measure the elastomer

mass before and after, we have a measure of both the weight lost

(extracted) and the weight gained (fluid absorbed). The 3M method, we feel,

gives more insight into the true compatibility of an elastomer.

4g. What is the best way to test for compatibility of elastomers?
As an example, consider the Norprene hose shown below. Conventional

soak testing at the fluid boiling point shows a weight gain of 4.0%. This

number is small and based on these results, one might expect the

hose to perform quite well. When tested by the 3M method, the same

hose lost 21.8% of its weight in plasticizer and it simultaneously absorbed

fluid equivalent to 3.8% of its weight. This is certainly not a good result.
Why the differences? The conventional testing is done in a closed vessel

with a fixed amount of fluid. Though plasticizer will leave the polymer, it

can only go as far as the surrounding fluid. As its concentration builds in

the fluid, eventually an equilibrium is set up at which the plasticizer in the

elastomer is in equilibrium with that in the fluid. At this point extraction

stops. This equilibrium does not represent what the elastomer experiences

in the application. When the test is over, the elastomer is weighed. A 4%

weight gain is recorded but there is no way to know how much weight gain

might have been camouflaged by the lost plasticizer which is still

unaccounted for. A hardness test would have little meaning because even

though the elastomer has lost its plasticizer, it could be plasticized by the

fluid. By baking the fluid out of the elastomer in a vacuum oven and then

re-measuring volume, mass and hardness, one could gain some additional

insight but there are still many unknowns.

The 3M method does not necessarily reproduce what the elastomer

experiences in the application but it does represent a worst case for

reasons already described. The data indicate that the elastomer lost a lot

of plasticizer (21.8%). This is plasticizer which would enter the fluid in the

actual application and this is important information in sensitive

applications. 

– Comparison of Methods - Norprene 6410 hose

• Conventional Test Data (24 hr soak in HFE at B.P.)

– 4.0% weight gain

• Indicates good compatibility

• Conclusion erroneous

• 3M test data (24 hr extraction in HFE at B.P.)

– 21.8% extracted material, 3.8% absorbed fluid

• Plasticizer was leached from the elastomer and it

would become brittle upon drying

• The polymer matrix absorbed some fluid

may be permeable or may swell

fluid may plasticize the elastomer
The data which follow were taken from a test performed for a customer.

The intended to switch from compound 1 to compound 2 for their very

critical application. Sample #1 was recommended by 3M for the

application.

Additional Notes:

Static discharge: Fluorochemicals have an enormous affinity for electric

charge. Because they are also dielectric, they tend to hold that charge very

well. For this reason, they generally absorb a charge but carry it

harmlessly through a system. Plasticizer seems to effect the chemicals’

ability to hold onto charge relative to other components. A fluorochemical

which in its pure form would hold charge in the presence of a particular

material, may give up charge to that same material when plasticizer is

dissolved into the fluid. If the material taking up charge is insulated from

another which does not, then an electric potential forms between the two.

This can lead to static discharge.

Filter Clogging: As mentioned before, some plasticizers are solids even at

room temperature. Others may be liquid at room temperature but solid

within the operating range of a heat transfer system. Plasticizer solubility

is temperature dependent drops very quickly as the melting temperature of

the solute is reached. For this reason, it is quite possible that plasticizer

will precipitate from the fluid in heat a transfer system. The precipitated

plasticizer can harden to form crystals large enough to clog fine filters or

small fluid passages.

High voltage discharge: Because they are excellent dielectrics,

fluorochemicals are often used as heat transfer fluids in direct contact with

high voltage components. The presence of plasticizer dissolved in the

fluid or in separate liquid phase may not significantly effect its dielectric

Example: Extraction Compatibility Testing of two EPDM compounds

Testing done to determine extractables and general compatibility

Fluid is HFE-7100, Boiling point 61°C

Customer: XXXXXXXXXXX

Date: XXXXXXXXXXX

Data

Sample Sample Sample Flask

No Description Mi [g] Mf [g] Mi [g] Mf [g]

1 EPDM 06270K52 4.0933 4.1171 113.6821 113.7661

2 EPDM 06280K36 4.6947 3.9235 117.4613 118.4291

Results

Sample Sample Fluid Residue

No Description %mass %mass Observations

1 EPDM 06270K52 2.6 2.05 Clear white oil extracted. Sample unchanged.

2 EPDM 06280K36 4.2 20.61 Clear white oil extracted. Sample was stiff and dry.
properties. Particulate in the fluid, however, definitely will. The plasticizer

crystal described above may allow electric discharge and thermal

decomposition.

Adhesive Deterioration: It is common in many direct contact electronics

cooling applications to have adhesives present. Electronic components

may be constructed with adhesives or waxes. Though these materials are

usually compatible with the fluid, they may not be compatible with the

plasticizer. The plasticizer can diffuse into the adhesive and degrade it.

Coating of Chemisorbent Materials: Often times a cartridge containing a

chemical reagent is put into a heat transfer system to absorb unwanted

contaminants. An example is the use of a silica gel or desiccant cartridge

to absorb water. Plasticizers will often adsorb onto the reagents in such

cartridges. They can form a coating which impedes the diffusion of

species into the reagent and may essentially deactivate the cartridge.

A note about Fluoroelastomers: Materials like Viton, Fluorel and Kalrez are

touted as the Cadillacs of elastomers and rightly so. These materials are

impervious to many process fluids and have a wide temperature range. For

this reason they’re often specified rather blindly especially for high value

applications which can afford their price tag. However, because “like likes

like,” fluorinated fluids tend to swell fluorinated elastomers. Some will gain

as much as 18 wt % fluid. For many static gasket and O-ring applications

swelling causes few problems. However, if the O-ring is tightly confined or

the O-ring seat dimensions are very critical, then swelling can be a

problem. In these instances O-rings can actually burst or fragment as they

swell outside their confines. Fortunately, much cheaper, low plasticizer

materials like EPDM and Butyl generally work much better.

The materials shown below have been found to perform well

Recommended Flex Hoses for General Use

Tubing Name Type Extraction % Weight gain % Comments

Tygon C-544-A

I.B.

Clear Braided

Polyurethane

0.09 0.3 Excellent Compatibility. Good

pressure resistance.

Temperature Range –73 to 82C.

www.tygon.com

Tygon 3370 I.B. Clear Braided

Silicone

1.47 4.8 Good Compatibility. Good

Pressure resistance.

Temperature Range –73 to 160C.

Flexfab 5521-050 Green braided

silicone hose

2.08 NA Good Compatibility. Good

Pressure resistance.

Temperature range –54 to 150C.

http://www.flexfab.com

Nalgene 290

PUR

Clear Yellow.

No Braid.

0.74 0.3 Excellent Compatibility. Little

pressure resistance.

4h. Can you recommend hose and seal materials to me?
Temperature range –56 to 80C.

Tygon Phar-Med

(65)

Brownish

opaque. No

braid.

40 4.7 SHOWN FOR CONTRAST. This

material not compatible.

C-Flex (Cole

Parmer 6425-19)

White. No braid. 26 5.3 SHOWN FOR CONTRAST. This

material not compatible.

Extraction tests conducted in HFE-7100 (HFE-8401HT) for 48 hours.

Material Name Type Extraction % Weight gain % Comments

Hytrel 4056 Opaque

Polyester rubber

0.05 1.1 Excellent Compatibility. Good

pressure resistance if braided

Temperature Range –50 to 170C

(variable)

Extraction tests conducted in HFE-7100 (HFE-8401HT) for 48 hours.

Recommended Elastomers for General Use

Elastomer Name Type Extraction % Weight gain % Comments

Stillman SR721-80 EPDM 1.2 1.8 Good Compatibility.

Stilllman SR634-70 Butyl 0.12 0.56 Excellent Compatibility.

Parker EPR 540-80 EP 1.5 2.2 Good Compatibility.

Jackson Flexible

Products EPR

E3450-80

EPR 1.2 2.3 Good Compatibility.

Parker Seal Co.

EPR E515-80

EPR 1.8 2.2 Good Compatibility.

Newman EPDM

2107

EPDM 2.2 1.5 Good Compatibility.

International Seal

E480

EP? 2.0 3.0 Good Compatibility.

Bay Seal Co.

B0612-70

Butyl 0.24 0.90 Excellent Compatibility.

EPDM 06280K36 EPDM 21 4.2 SHOWN FOR CONTRAST

??? TFE-wrapped

Viton

1.0 20 SHOWN FOR CONTRAST

Extraction tests conducted in HFE-7100 (HFE-8401HT) for 48 hours.

Of course, 3M offers free compatibility testing if you have other materials in mind.
Both FluorinertTM and NovecTM HFE fluids have very low surface tensions

and viscosities. This combined with the very low contact angles these

fluids have on most surfaces, means that they will leak very easily through

the smallest of passages. Seals which would easily hold back water at 10+

atmospheres may leak generously with a fluorochemical fluid. Though

shaft seals have been used successfully with fluorochemicals,

magnetically coupled or canned pumps are generally preferable. These

pumps are much less apt to leak.

There are many manufacturers of magnetically-coupled pumps. Below are

just a few:

Fluid-O-Tech International, Inc.

Plantsville, CT

860/620-0193

http://www.fluidotech.it

MicroPump, A Unit of Idex Corp.

Vancouver, WA

360/253-3229

http://www.micropump.com

Gorman-Rupp Industries

Bellville, OH

419/886-3001

http://www.gripumps.com

Modular Products, Inc.

Gear Pump Div.

Penn Yan, NY

800/347-6055

Integrated Designs LP

Carrollton, TX 75007

972/466-2626

http://www.integrated-designs.com

Speck Pumps

Jacksonville, FL 32256

800/223-8538

http://www.usa.speck-pumps.com

Laing Thermotech, Inc

San Diego, CA

619/575-7466

http://www.lainginc.com

Zenith Division, Parker Hannifin

Sanford, NC

919/775-4600

http://www.zenithpumps.com

Liquiflow

Garwood, NJ

908/518-0666

http://www.liquiflow.com

5. What type of pump should I use with FluorinertTM or NovecTM

fluids?
Fluid loss can generally be attributed to the following mechanisms: fluid

loss resulting from fluid expansion and contraction, fluid loss resulting

from the temperature dependence of gas solubility, leaky seals.

Fluid loss resulting from fluid expansion

As a rule of thumb, FluorinertTM and NovecTM HFE fluids typically increase

in volume 1% for every 10°C. Since the expansion reservoir in many chiller

systems is permitted to “breathe,” air will enter and leave the expansion

reservoir as the fluid expands and contracts with each thermal cycle. The

air which leaves the expansion reservoir as the fluid expands is generally

saturated with fluid vapor. This loss mechanism can be easily quantified

by assuming that the fluid and air behave as ideal gases. The fluid carried

out during a thermal cycle can then be estimated as

dV = change in system liquid volume

Pvap(T) = fluid vapor pressure

Vliq = system liquid volume

β(T) = fluid coefficient of thermal expansion

n = moles

m = mass

M = molecular weight

This assumes that the system “breathes” freely (i.e. it is at atmospheric

pressure). The temperature dependence of the vapor pressure can be

obtained from 3M technical service personnel.

Fluid loss resulting from the temperature dependence of gas solubility

Although the above leakage mechanism is intuitive, people often find that

losses in an otherwise tight system are larger than those attributable to the

it. They fail to realize that air is soluble in Fluorinerts and HFEs and that

this solubility (typically around 50 volume % far from the boiling point) is

temperature dependent. Because the solubility increases as the

temperature decreases, the fluid will hold more air at low temperatures

vapor vapor

vap

vapor

liq

dm Mdn

dV

RT

P T

dn

dV V T T dT

=

=

=

( )

( )b( )

( )

( )

* ,

,

P P T

P T

dm Mdn

dn dx n

K

dP

K

dP dx

vap

vapor air

air air liq liq

air vap

air liq

−

=

= = −

=

6. I frequently have to add fluid to my FluorinertTM or NovecTM

system. Where is the fluid going?
than at high temperatures. Therefore, as a heat transfer system warms, air

will leave the system not only because the fluid is expanding, but also

because the air solubility is decreasing in accordance with Henry’s Law.

Vapor carried with this air can be estimated as shown below

dxair,liq=change in mole fraction of air in liquid

K = Henry’s law constant for air in liquid

nliq = moles of liquid

As an example, consider a 5 gallon HFE-7100 (boiling point = 61°C) system operating

between –10 and 55°C and kept at atmospheric pressure via a “breathing” expansion

reservoir:

If HFE-7500 (boiling point 128C) is used, the picture looks much different:
Obviously, staying as far from the boiling point of the fluid can reduce the

losses from both of these mechanisms. In practice, the boiling point of the

fluid is often dictated by heat transfer properties of the fluid more info.

A system is often outfitted with a vacuum break and a positive pressure

purge. An analysis similar to that shown above can be used to calculate if

and when such a system will vent and how much fluid loss will result. In

practice, this analysis depends upon many variables and can be quite

involved. 3M engineers can provide tools for modeling such systems.

leaky seals

The low viscosity and surface tension combined with the excellent surface

wetting properties of fluorochemicals makes them very difficult to seal.

Below are some seals which, in our experience, are likely to leak:

Pipe threads – This 150 year old technology works very well for a variety of

fluids and this is probably why so many off-the-counter fluid components

are still sold with pipe thread connections. Unfortunately, common

methods of sealing pipe threads, such as PTFE tape or pipe sealants, will

not work with FluorinertTM and Novec HFE fluids. Leakage can range from

very small leaks detectable only with a sensitive halogen leak detector, to

gross leaks detectable by the large puddle beneath them. These leaks can
be avoided by using compression fittings (SwagelokTM is an example)

wherever possible. Since pipe thread connections seem to be unavoidable

in some cases, we recommend sealing them with an epoxy. Another option

is a product called “Leak Lock.” It is sold by Highside Chemicals

(www.highsidechem.com).

Pump shaft seals – Any pump with a shaft seal is suspect more info.

Shrunken or cracked O-rings – An O-ring which is not compatible with the

fluid may well shrink to the point that it is no longer able seal. This is

common in dimensionally critical applications like quick disconnects and

pump shaft seals. Even in applications which are not dimensionally

critical, such as face seals or gaskets, sufficient material (plasticizer, etc.)

may be extracted by the fluid that the O-ring will crack and allow fluid to

leak more info.

Reliance on lubricated O-rings – Some fluid couplings rely heavily on

lubricated seals. Without this lube, the coupling may be difficult to

operate or it may fail quickly due to friction. Though the particular lube

may be soluble in the fluid only at part per million levels, there is generally

a very large amount of fluid in the system relative to the amount of lube.

Even if the solubility limit of the lube in the fluid is inadequate to dry the Oring, the lube may use the fluid as a vehicle to get to a sink such as a

polymeric hose. If lubricants must be used, choose a silicone grease with

the highest molecular weight available.

Diffusive losses – Diffusion rates of FluorinertTM and NovecTM HFE fluids

though most polymeric materials will be very low. For example,

experiments indicate that diffusion of HFE-7100 through Stillman EPDM

SR721-80 is less than 0.0007 g-mm/(in2-day). This means that diffusion

through a 10 foot length of 0.5 inch I.D. hose with a 1 mm wall thickness

will be less than 0.13 g/day. Experiments with one particular PTFE

indicated diffusion rates as high as 0.002 g-mm/(in2-day).
Any halogen leak detector can be used to detect fluid leaks. These

detectors are commonly used to detect refrigerants and are available from

local refrigerant retailers in every major city.

Heaters should be sized such that their heat flux or power output does not

exceed 6-10 W/cm2. Much larger heat fluxes are possible but the safe value

for a given application depends strongly upon the geometry, flow field etc.

The decision to go beyond this level should be made by the customer.

How do we get 6-10 W/cm2? 3M performs nucleate boiling experiments

with our fluids: A 0.5 mm diameter platinum wire is immersed in a

quiescent pool of saturated liquid. The current through the wire is

gradually increased. The heat flux being dissipated is recorded as a

function of the wire superheat (the difference between the wire temperature

and the bulk fluid temperature). Typical results are shown below:

As the heat flux is increased, the wall temperature rises in the natural

convection regime until boiling begins. Boiling for both Fluorinerts and

Novec HFEs generally begins at heat fluxes of around 1-2 W/cm2 though this

“incipience” point can vary greatly depending upon surface finish, level of

7. How can I detect fluid leaks?

8. How do I size a heater for use with FluorinertTM or Novec HFE fluids?
degassing, etc. Once boiling starts, the wall superheat drops and remains

relatively low throughout the nucleate boiling regime until the critical heat

flux is reached. At this distinct and repeatable point, boiling is no longer

stable, a vapor blanket forms on the wire and the wire temperature

skyrockets. This is the condition to avoid. Keep in mind that very high

heat fluxes may be obtainable if fluid is forced over the wire. We

recommend 6-10 W/cm2 because it appears to offer a good margin of safety

for applications in which the heater is simply immersed in still fluid.

The above recommendations are based upon safety considerations.

Designers should be aware that there may be other practical reasons to

keep heat fluxes far below 6-10 W/cm2. For example, an HFE-7100

recirculating chiller system which operates between –40 and 50 C may be

expected to reach 15.5 psig assuming that it has a vacuum break and a 20

psig pressure seal. However, if a large amount of gas is liberated at the

heater surface, system pressures may exceed the purge setting and allow

vapor leakage.
No. Corrosion in fluorochemical heat transfer systems can generally be

linked to either a separate water phase or thermal decomposition of the

fluid.

Water in the fluid: By this we mean water beyond the saturation level of the

fluid. The saturation level of water in a Fluorinert or Novec HFE fluid is

usually less than 100 ppm by weight. Water present in the fluid at or below

this level has never been linked to significant corrosion. Water present

above this level means a separate water phase. If such water is entrained

into contact with metal parts, corrosion can be rapid.

This is shown in the picture below: Vial #1 contains HFE-7100 with water on

top. The water does not contact the zinc-plated iron wire. Vial #2 contains

HFE-7100 with no water and some desiccant to keep the fluid dry. Vial #3

contains HFE with water on top. Unlike vial #1, the water contacts the wire

at about mid height. Vials #1 and #2 show no corrosion whatsoever

indicating that even water-saturated HFE-7100 will not corrode the metal.

Vial #3 shows zinc and iron oxide. These samples had been aged 5 months

but the corrosion was evident in vial #3 at 1 day.

Water can enter heat transfer systems in a few different ways:

Components can be hydro-tested and never dried before installation. The

moisture contained in air which enters an expansion reservoir while the

fluid in contracting can condense if the fluid is below the dew point. Air

which enters an expansion reservoir can become saturated with water

vapor if the purge is set much higher than the inlet regulator.

Water from these sources can be removed with any common molecular

sieve or silica gel desiccant sold for refrigeration systems.

9. Will FluorinertTM or NovecTM fluids cause corrosion?
Thermal decomposition of the fluid: Fluoride ion can be generated any time

the fluid is brought above its decomposition temperature and this can lead

to corrosion. Decomposition is generally very slow below 200-300°C with

most Fluorinert and HFE products. Experience indicates that corrosion

resulting from decomposition is very rare and is only observed in systems

which have undergone a failure. Examples include: a burned out heater,

high voltage discharge in dielectric systems or a burned out electrical

component in a direct contact electrical application.