Refrigerator / Heat Pump

Refrigerator: device that EXTRACTS heat from a cold reservoir and DUMPS it to a hot reservoir, using work INPUT.

Reverse of heat engine — runs the cycle counter-clockwise.

Work IN, heat OUT to atmosphere. Q_h = W + Q_c (energy conservation).

Coefficient of Performance: COP = Q_c/W = heat extracted per unit work input.

Carnot refrigerator COP: COP_max = T_c/(T_h − T_c). Can exceed 1.

Heat pump: same machine but operated for HEATING. COP_heat = Q_h/W = 1 + COP_ref.

Real refrigerators: COP ~ 2-4 for household, 3-5 for AC. Heat pumps: 3-5 for heating.

Clausius statement (2nd law): Cannot transfer heat from cold to hot without work input.