[superschan]

I am doing an investigation on vapour-compression refrigeration cycle where the refrigerant used is R141b (1,1-Dichloro-1-fluoroethane) one of the assenments I have to do is to calculate the coefficient of performance (C.O.P.) and compare this figure to literature values. I am unable to find the C.O.P. of this refrigerant anywhere. Specifically the commercial name of the refrigerant used is Forane 141b made by Elf Atochem (now Arkema Inc.)

[eugenedakin]

Hello superschan,

This looks like a very interesting question. 

Could you help me out by letting me know more of the parameters for determining the C.O.P.?  If you can show me the work that you have completed, it may help me figure out where I can help you.

From the information I have, R141B has the chemical formula CH3CCl2F or also as 1,1-dichloro-1-fluoroethane (HCFC - 141b).

Thanks, and I look forward to your next post.

Sincerely,

Eugene

[Montemayor]

I presume that we agree that the Coefficient of Performance for a mechanical refrigeration cycle (COP) is defined as the desired heat transferred divided by the work done by the compressor.  Expressed in other terms it is equivalent to the amount of heat energy removed in the evaporator divided by the electrical energy consumed by the electric motor driving the compressor.  The energy terms should be in the same units so that the COP is dimensionless.

The COP is a means used to compare different configurations of refrigeration cycles as well as cycles using different refrigerants.  When this is done, all the cycles have to be analyzed at the same datum plane: The condensing temperature of the refrigerant has to be the same for all cycles – in other words, the heat sink for the compressor’s discharge has to be the same.  When this is done, Ammonia is found to be the best performer or right at the top of the list.  The higher the COP, the better the efficiency results.

What you have to do is calculate the brake horsepower required for your evaporator load using the condensing medium that you have.  You do these calculations by resolving the various cycle flow streams in your refrigeration cycle.  I always do this in Excel and form a process flow diagram complete with a heat and material balance table.  For an example of how this is done, you can visit

http://www.cheresources.com/invision/index.php?s=0635769b153e99b9e0816bd7c1bb0c31&act=idx

and see various examples of how this is done using the NIST thermodynamics database for the refrigerants.  For example, if you go to

http://webbook.nist.gov/chemistry/fluid/

you will find complete thermodynamic values for your refrigerant, R 141B.  You can download this information and easily calculate all the information in a refrigeration cycle.  I have done it quite a bit and it is very accurate.  Plus, it is absolutely FREE.

If you are a knowledgeable Chemical Engineer or ChE student, you should be able to calculate your COP very easily by this method.

I hope this helps you out in your project.