Study of heat transfer in oscillatory flow for a Stirling engine heating tube inserted with spiral spring

The heater of Stirling engine transfers heat from external heat sources to working gas. Improving its heat transfer performance is favourable to save external heat sources and decrease dead volume of engine. In this study, the flow and heat transfer characteristics of reciprocating oscillatory flow in a tube inserted with spiral spring in a Stirling engine heater were investigated. The results indicate that the Nusselt number (Nu), friction factor (f) and performance evaluation criterion (PEC) increased with spiral height (h) and decreased with spiral pitch (p) for enhanced tube within the range of parameters in this study. For the optimal enhanced tube, the PEC was equal to 1.22 and the outlet temperature was significantly improved compared to smooth tube. The maximum improvement was 115 K in entry process and 94 K in return process, and the average improvement was 64 K in entry process and 34 K in return process. The extra pressure consumption in the optimal enhanced tube was less than 0.0013 MPa compared to smooth tube, which could be negligible contrasting to the overall pressure in heating tube (1.5 ∼ 2.5 MPa). Thus, the benefits are apparent for heating tube inserted with spiral spring in Stirling engine.