Flow and heat transfer performance of reciprocating oscillatory flow in a Stirling engine compared to steady unidirectional flow

The driving force of a Stirling engine comes from the thermal expansion and cold compression of working gas under reciprocating oscillating flow, the flow and heat transfer performance of which is significantly different with that of steady state unidirectional flow. In this work, the performance differences in a heating tube for a Stirling engine under steady state unidirectional and reciprocating oscillating flows were studied. The results indicate that the temperature distribution was mainly dependent on the inlet velocity for a steady unidirectional flow. For a reciprocating oscillatory flow, the temperature distribution was greatly affected by the working gas state in the previous period besides the inlet velocity. Furthermore, a slightly weaker of heat transfer was obtained for reciprocating oscillatory flow, accompanying with a slightly stronger pressure consumption. The change time of pressure difference, velocity and heat transfer for the reciprocating oscillatory flow were earlier than, substantially equal to, and later than that of the steady unidirectional flow. Finally, the entry-return asymmetric insert was suggested to prioritize the heat transfer enhancement in entry process of a heating tube under reciprocating oscillatory flow to achieve the excellent overall performance for a Stirling engine.