The physics processes of a Carnot heat engine.
Carnot cycle is a four stages reversible sequence consisting of
1. adiabatic compression
2. isothermal expansion at high temperature T2
3. adiabatic expansion
4. isothermal compression at low temperature T1
5. back to stage 1 and continue.
It is moving in clockwise direction as shown in the applet.
[img]http://www.phy.ntnu.edu.tw/ntnujava/index.php?action=dlattach;topic=23.0;attach=748[/img]

The above process get [b]heat[/b] (Q[sub]H[/sub]-Q[sub]C[/sub])as input to do [b]work[/b] W.

Refrigeration cycle is reversed : get input from electric power to cool the system (heat transfer from lower temperature to higher temperature). It is moving in counter-clockwise direction.
1. adiabatic expansion
2. isothermal expansion at low temperature T1
3. adiabatic compression
4. isothermal compression at high temperature T2
5. back to stage 1 and continue.

Input Work W and reverse the direction of Heat flow T[sub]c[/sub]->T[sub]H[/sub] (W=Q[sub]H[/sub]-Q[sub]C[/sub] )