STIRLING CYCLE

This cycle works on the principle of regeneration by using a regenerator within the engine itself which would store the rejected heat energy during heat rejection process and supply the same during heat addition process. The Stirling cycle consists of two reversible isotherms and two reversible isochors. The p − v and T − s diagrams are shown in Fig. 9.3. We note that heat addition process 2−3 and heat rejection process 4−1 cancel each other, since the energy taken from the regenerator is returned in the latter. An alternative interpretation is to consider the regenerator as a part of the system so that the heat exchange with the surroundings involves only the source at temperature T₁ and the sink at temperature T₂. The heat supplied per cycle is, therefore, during the process from 3−4 and heat rejection is during the process 1−2. For one kg of ideal gas (T₁ > T₂), we have

Heat supplied, 

Heat rejected, 

Thermal efficiency, 

But v₄ = v₃, v₁ = v₂ and  hence

Generally there is loss of heat due to radiation and poor conductivity of gas. If η_r is the efficiency of the regenerator, then

Heat supplied = RT₁ ln r + (1 − η_r) c_v (T₁ − T₂)

Heat rejected = RT₂ ln r + (1 − η_r) c_v (T₁ − T₂)

Figure 9.3 Stirling cycle: (a) p-v diagram, (b) T-s diagram