Question 6.6: A Questionable Claim for a Refrigerator An inventor claims t...

An extraordinary claim made for the performance of a refrigerator is to be evaluated.
Assumptions Steady operating conditions exist.
Analysis The performance of this refrigerator (shown in Fig. 6–52) can be evaluated by comparing it with a reversible refrigerator operating between the same temperature limits:

\begin{aligned}COP _{ R , \max } &= COP _{ R , rev }=\frac{1}{T_{H} / T_{L}-1} \\&=\frac{1}{(75+460 R ) /(35+460 R )-1}=12.4\end{aligned}

Discussion This is the highest COP a refrigerator can have when absorbing heat from a cool medium at 35°F and rejecting it to a warmer medium at
75°F. Since the COP claimed by the inventor is above this maximum value, the claim is false.