Page 137 - DJJ20063- Thermodynamics 1

DJJ20063- Thermodynamics 1

A heat engine is a system operating in a complete cycle and developing net work from a

supply of heat. The second law implies that a source of heat supply (or hot reservoir) and

a sink (or cold reservoir) for the rejection of heat are both necessary, since some heat

must always be rejected by the system.

Heat engines differ considerably from one another, but all can be characterized by the

following:

❑ They receive heat from a high-temperature source (for example solar energy, oil
furnace, nuclear reactor, steam boiler, etc.)

❑ They convert part of this heat to work (usually in the form of a rotating shaft, for

example gas turbine, steam turbine, etc.)

❑ They reject the remaining waste heat to a low-temperature sink (for example the
atmosphere, rivers, condenser, etc.)

❑ They operate on a cycle.

A diagrammatic representation of a heat engine is shown in Fig. 4.1.2-1

Figure 4.1.2-1 Part of the heat received by the heat engine is converted to work,

While the rest is rejected to cold reservoir.

Heat engines and other cyclic devices usually involve a fluid that moves to and from which

heat is transferred while undergoing a cycle. This fluid is called the working fluid.

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