What is the principle of Carnot refrigerator?

Simply put, it is Carnot inverse cycle.

This cycle includes two ideal isothermal processes and isentropic processes.

The refrigerator absorbs the heat of Q 1 from the room with the temperature of T 1 and discharges the heat of Q2 to the external environment with the temperature of T2, in which mechanical work w is needed, so the refrigeration coefficient of the refrigeration cycle.

ε= W/q 1 =(q 1-Q2)/q 1 = 1-t 1/T2

Using the second law of thermodynamics