Why does the yellow dot move backward compared to the engine page?

The same four processes form the loop, but a refrigerator consumes work to pump heat uphill. Traversing the loop in the opposite sense swaps which legs absorb or reject heat relative to the engine animation.

Can COP be less than 1?

For cooling, COP_R can be below 1 when the temperature lift T_H − T_C is large relative to T_C. That does not violate thermodynamics; it means more work is needed per joule removed from the cold side.

Is this how my kitchen refrigerator is drawn in textbooks?

Real appliances use a vapor-compression cycle with a valve or capillary instead of an isentropic expander, and property charts for the refrigerant. This page isolates the Carnot limits and sign conventions.

Refrigeration Cycle (Reverse Carnot)

This lab presents the **reversible Carnot cycle** as an ideal **refrigerator** (or heat pump): the same ideal-gas **P–V** closed curve as the Carnot engine simulator, but the state point moves **in the opposite direction**. Heat **Q_C** is absorbed on the **cold isotherm** (evaporator analogy), heat **Q_H** is rejected on the **hot isotherm** (condenser), and **work W** is supplied by the compressor. The Carnot **coefficient of performance** for cooling is **COP_R = T_C/(T_H − T_C)** and for heating **COP_HP = T_H/(T_H − T_C)** with temperatures in **kelvin**. A simple schematic suggests a household fridge layout; it is not a full vapor-compression cycle with a throttle and refrigerant tables.

Who it's for: Introductory thermodynamics after the Carnot engine; links energy balance to COP and real appliance intuition.

Key terms

Carnot refrigerator
COP
heat pump
reverse Carnot
isothermal heat transfer
kelvin temperatures

How it works

Reverse Carnot refrigerator: heat pumped from cold to hot with work input. Carnot COP limits and a simple fridge schematic beside the PV loop.

Key equations

COP_R = Q_C / W · COP_R,Carnot = T_C / (T_H − T_C) · COP_HP = Q_H / W

Q_H = Q_C + W (energy balance) · T in kelvin for Carnot limits

Frequently asked questions

Why does the yellow dot move backward compared to the engine page?: The same four processes form the loop, but a refrigerator consumes work to pump heat uphill. Traversing the loop in the opposite sense swaps which legs absorb or reject heat relative to the engine animation.
Can COP be less than 1?: For cooling, COP_R can be below 1 when the temperature lift T_H − T_C is large relative to T_C. That does not violate thermodynamics; it means more work is needed per joule removed from the cold side.
Is this how my kitchen refrigerator is drawn in textbooks?: Real appliances use a vapor-compression cycle with a valve or capillary instead of an isentropic expander, and property charts for the refrigerant. This page isolates the Carnot limits and sign conventions.