The Future of Energy

Appendix A

The Carnot Cycle

The Carnot cycle, when acting as a heat engine, consists of the following four steps:

1. Reversible and isothermal expansion of the gas at the “hot” temperature, T_H (isothermal heat addition). During this step (A to B in Figure A.1, 1 to 2 in Figure A.2), the expanding gas makes the piston do work on the surroundings. The gas expansion is propelled by the absorption of heat, designated Q₁, from the high temperature reservoir.

Figure A.1 A Carnot cycle acting as a heat engine, illustrated on a temperature-entropy diagram. The cycle takes place between a hot reservoir at temperature T_H and a cold reservoir at temperature ...