Question

If a refrigerator is a heat pump that follows the first law of thermodynamics, how much heat was removed from food inside of the refrigerator if it released 483J of energy to the room?

Answer 1

According to the second law of thermodynamics, we understand that we cannot move heat from a reservoir at a lower temperature to that of a higher temperature without providing work.

When applied to a refrigeration system, the coefficient of performance can be derived as
COPr=1/(Th/Tl-1) where
Th=high temperature reservoir (room temperature) = 20C = 293K
Tl=low temperature reservoice (freezer compartment) = -18C=255K
=>
COPr=1/(293/273-1)=6.71

But COPr is also equal to Ql/Win,
Ql=energy removed from freezer (to be found)
Win=work input, also equals heat energy transformed from work into the room
= 483J
=>
Ql=COPr*Win=6.71*483=3241J
Answer: 3241 J are removed from food inside refrigerator (through the freezer compartment).