An inventor claims to have developed a food freezer that at

An inventor claims to have developed a food freezer that at steady state requires a power input of 0.72 kW to extract energy by heat transfer at a rate of 3.42 kJ/s from freezer contents at 300 K. Evaluate this claim for a temperature of 350 K.

Solution

[ Q_in / W_cycle ] < [ T_c / T_H - T_c ]

[3.42 / 0.72] < [300 / 350 - 300]

4.75 < 6

The claim is in accord with second law, a more indepth analysis might reveal practical or economic short comings