Sunday, 23 November 2014

Homework Help: The coefficient of performance for refrigerators....

Q) The coefficient of performance for refrigerators is defined as K = qc / w. It is also known as Tcold / Thot - Tcold.

What happens to K reversible as Tc (temp cold) goes to 0k?

Sol:
K = Tcold/(Thot-Tcold)
K reversible means 1/K
Hence 1/K= (Thot-Tcold)/ Tcold
              = (Thot/ Tcold)-( Tcold/ Tcold)
         =  (Thot/ Tcold)- 1
By neglecting 1, which is a small value, we get
1/K directly proportional to 1/ Tcold

Hence as Tcold goes to 0k, K reversible tends to infinity, a very large value.

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