In an absorption refrigerator, the energy driving the

Chapter 4, Problem 15P

(choose chapter or problem)

PROBLEM 15P

In an absorption refrigerator, the energy driving the process is supplied not as work, but as heat from a gas flame. (Such refrigerators commonly use propane as fuel, and are used in locations where electricity is unavailable.*) Let us define the following symbols, all taken to be positive by definition:

Qf = heat input from flame

Qc = heat extracted from inside refrigerator

Qr = waste heat expelled to room

Tf = temperature of flame

Tc = temperature inside refrigerator

Tr = room temperature

(a) Explain why the “coefficient of performance” (COP) for an absorption refrigerator should be defined as Qc/Qf.

(b) What relation among Qf, Qc, and Qr is implied by energy conservation alone? Will energy conservation permit the COP to be greater than 1?

(c) Use the second law of thermodynamics to derive an upper limit on the COP, in terms of the temperatures Tf, Tc, and Tr alone.