Question

The cycle of a Stirling engine has two isothermal processes and two isochoric processes. The isochoric processes do not use any external heat, instead the heat is passed back and forward between different parts inside the system. Will such processes play any role in determining the efficiency of the engine? Justify your answer.

Answer 1

Figure shows the thermodynamic path of Sterling Cycle. From state-a to state-(b) is isothermal expansion, heat is absorbed from hot reservoir. From state-(b) to state-(c) is isochoric process , heat is transferred to internal system. From state-(c) to state-(d) is isothermal process , heat is released to cold reservoir . From state-(d) to state-(a) is isochoric process , heat is absorbed from internal system.

Quantity of heat absorbed or released in isochoric process will be same because these isochoric processes are occuring at constant volume between same temperature difference. Hence whether heat is absorbed from environment and released to environment or absorbed and released internally does not make any difference to determine the efficiency