Prelecture 31: Slide 1

In this prelecture, we will introduce the concept of the heat engine. That is, we will look at systems in which the working substance of an engine, usually a gas, extracts heat from a hot reservoir, does some useful work and then exhausts any remaining heat to a cold reservoir.

We begin by defining the efficiency of the engine as the ratio of the work done by the engine to the heat extracted from the hot reservoir. We will find that the second law of thermodynamics places an upper limit on this efficiency that is determined by the temperature difference of the reservoirs.

We will then introduce the Stirling cycle as our standard example of a heat engine. This cycle consists of two isothermic transitions (that is, at constant temperature) and two isochoric transitions (that is, at constant volume). We will calculate the efficiency of this engine when the working substance is an ideal gas.

Let's get going!