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alireza
08-10-2003, 02:37 AM
Hello Friends,
Is there any one who has any experience in "Very Low Temperature Systems" ? (Under -120 F)


Regards,
Alireza

Gary
08-10-2003, 11:01 AM
There are several in here who have experience with ultra-low temp systems.

chemi-cool
08-10-2003, 04:32 PM
hello alireza,
this is cooooooold what you are looking for, try also at: http://www.revco-sci.com they deal with that enviroment.
good luck and watch your fingers, at that temperature they might fall off without you even notice!!

chemi-cool

Germada
20-10-2003, 08:47 PM
Hello there,

What do you want to know about Ultra low temperature??
I am the service technician for Revco in Europe.

Regards,

alireza
20-10-2003, 10:59 PM
Hello, Germada!
Thanks to you for your reply. I'm looking for some suppliers of very low temperature refrigeration part such as thermometer, thermostat,....compressor , TEV,.......valves and some others.

Regards,
Alireza

alireza
20-10-2003, 11:48 PM
Dear Germada,
I have many questions from you:)

I Think, using of R-23 in refrigeration systems which required evaporator space temperature less than about -80 C is not proper. Simply because the R-23's Saturated pressure in -82 C is
1.015 bar absolute.( equal to 0 bar guage in sea level).

Working of the compressor in this condition, causes to decreasing of the compressor's life time and using of the oil separators or such things are not perfect ways to prevent of the compressor failures because of its working in the condition very close to vacuum.



what is the best Refrigerant for temperature range of -100 C to -150 C ?


Regards,
Alireza

alireza
20-10-2003, 11:55 PM
......................and how it is wonderful, touching the "Extra Low Temperatures"!!!!!

You have to be very good lucky that you work in this part of refrigeration systems.:)

Germada
21-10-2003, 09:41 PM
Hello Alireza,

First of all I will provid you with the name and address from the Revco dealer in your area.

Talking about the -86C units, these are 2 stage units provid with both a Copeland compressor (1 Hp).

Gascharges from the 1e stage is a mixture from R134a and R404a.
2e stage is a gasmixture from R404a and R508b, Amount is of course depending on the size of the machine.

Yes, the compressor is running in vacuum, but these compressors are specialy designed for ultra low temperature freezers.
So this is absolute no problem.

The -140C and the -150C freezers are build with 1 Copeland scroll compressor ( 3,5 hp)

The gas inside this machine is a mixture of 5 different gasses.

R134a
R142b
R14
R508b
And the last gas is Argon.

Question: Are you working on a unit?

If you need more info please let me know and will help you out with any problem you have.
I am working now for 13 years on these units.

Best regards,
Germada

alireza
22-10-2003, 02:52 AM
Dear Germada,

Thank you very much for your wonderful answer.
You opened a new horison front of my eyes about cascade refrigeration systems, I had never thought about mixing the refrigerants together for making required properties.My questions have been twice .:)

A question :

When we mix some Refrigerants together with special percents,how it is possible to determine the compresor's characteristics, such as Refrigeration capacity, Power consumption,........etc,that we are required to know for designing a system?

Also, I don't know how much this thinking is correct :

It is possible to use a compressor of an special refrigerant [for example R-502], to compress another refrigerant [for example R-13] in a condition with same compression ratio.[if we charge it with proper oil] I have never seen the special compressors of Copeland or other companies for R-13, R-14,.... and some other special refrigerants in the list of their products and it is why I think so.

If I think correct, I'm wondred that how it is possible to guess the compressor specifications with this new Refrigerant.


The extra low temperature system is a part of AC&R industry that always makes me mad of it.
In my brain, it is the end of refrigeration engineering. I love to have a chance of working in this field, but Unfortunatelay, I have not any chance to work on this systems. I have worked on commercial AC&R systems for about 4 years and on Automotive A/C units [specially, bus A/C unit] for about 3 years.[I'm student yet.:)] But, these always have not limited me to thinking not on other applications, specially Ultra low temperatures.

Best Regards,
Alireza