Coolant for -25¦C
Coolant for -25¦C
(OP)
Hello everyone,
We are working in a project where we need to cool a volume to -25ºC, Let's say the minimum temperature in the system is -40ºC (-40ºF). A special cooling plant (with pump, heat exchanger...) is being prepared; it will work underpressure to avoid leakage inside the system. Insulation, calculations... are being carried out.
But the coolant to be used has not been chosen yet. There are mainly 4 ideas:
- Methanol (in principle water methanol mixture, 60-40%)
- Ethanol (in principle pure, but it could be also combined with water to increase the specific heat)
- Glycol (also mixed with water)
- Perfluorohexane, C6F14 (pure)
Each one has its own advantages and disadvantages.
Ethanol and Methanol are cheap and have pretty good properties, but they corrode the metal and are flammable.
Glycol is non-flamable but very viscous; on the other hand the Perfluorohexane has low viscosity but it's expensive. Both are non flammable.
We don't want to use silicone oils because they are very dirty (difficult to clean in case of leakage).
Does anyone have experience with cooling for a system in this temperature range?
Attached a comparison with the properties
http://files.engineering.com/getfile.aspx?folder=7...
Thank you in advance
Regards,
We are working in a project where we need to cool a volume to -25ºC, Let's say the minimum temperature in the system is -40ºC (-40ºF). A special cooling plant (with pump, heat exchanger...) is being prepared; it will work underpressure to avoid leakage inside the system. Insulation, calculations... are being carried out.
But the coolant to be used has not been chosen yet. There are mainly 4 ideas:
- Methanol (in principle water methanol mixture, 60-40%)
- Ethanol (in principle pure, but it could be also combined with water to increase the specific heat)
- Glycol (also mixed with water)
- Perfluorohexane, C6F14 (pure)
Each one has its own advantages and disadvantages.
Ethanol and Methanol are cheap and have pretty good properties, but they corrode the metal and are flammable.
Glycol is non-flamable but very viscous; on the other hand the Perfluorohexane has low viscosity but it's expensive. Both are non flammable.
We don't want to use silicone oils because they are very dirty (difficult to clean in case of leakage).
Does anyone have experience with cooling for a system in this temperature range?
Attached a comparison with the properties
http://files.engineering.com/getfile.aspx?folder=7...
Thank you in advance
Regards,





RE: Coolant for -25¦C
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RE: Coolant for -25¦C
RE: Coolant for -25¦C
I believe there was a Dowtherm product that had a similar viscosity to EG though. But, it has been years since I've looked at this and I hope I am not leading you off in the wrong direction.
RE: Coolant for -25¦C
My one comparison chart shows 50:50 EG having ~1/4 the viscosity of 50:50 PG at -34ºC. Obviously, one has to weigh the toxicity and handling constraints imposed by EG vs PG.
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RE: Coolant for -25¦C
They have little viscosity change with temperature.
= = = = = = = = = = = = = = = = = = = =
Plymouth Tube
RE: Coolant for -25¦C
If you're worried about silicone oils leaking, forget about ethanol or methanol- either will leak much worse, with consequences far worse than merely being a mess to clean up. Both have flash points below room temperature.
I'd build a tight, leak-free system and use a thin silicone oil designed for low temperature, such as Syltherm XLT.
RE: Coolant for -25¦C
PS Sorry for my english ))
RE: Coolant for -25¦C
So the OP needs to stipulate how much heat needs to be rejected.
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RE: Coolant for -25¦C
RE: Coolant for -25¦C
First of all, thank you for all the answers.
We don't have any problem about toxicity so we can forget about the PG.
I haven't mentioned we are going to use a leakless system where we work under atmospheric pressure, so if there is a leak inside the important parts, air will come in and not the coolant out.
The problem of working below atmospheric pressure is we must check carefully the pressure drop along the system, since there is not much room low viscosity is very important; that's why perfluorinated is being considered.
Cheers,
RE: Coolant for -25¦C
I agree completely with being prudent, and with your caution of "expanding" your operating temperature zone past the expected minimum of -25 deg C .... But the difference in brittle fracture and coolant behavior between -25 deg C and -40 degrees C is very, very significant.
Are you really, really sure you want to go that far below the expected -25 degrees? Even using -30 deg C will let you use several different options that are less expensive in the long run costs of operation and fabrication. Very few places on earth get below -30 C for long periods of time, so you should be able to control the environmental temperature to safely maintain the "outside" operating temperature above -30 deg C, but only you - after all- actually know your client's conditions. (Said he who has had to use frozen outdoor portable-toilets in -10 deg F weather ...)