Experimental study on heat transfer of oscillating flow of a tubular Stirling engine heater

Stirling engine heaters are characterized by oscillating flows which affect heat transfer coefficients greatly. A 36-tube Stirling engine heater with a piston-link drive machine is used to study heat transfer characteristics of oscillating flows. The influences of the overall heating power, oscillating frequency and gas pressure on the heat transfer characteristics are investigated. To raise the working gas pressure is positive to decrease the wall temperature and to improve the heat transfer. When the pressure varies from 0.1 to 0.4 MPa, the wall temperature reduces 17 °C and the heat input increases 10 W. The time-averaged heat transfer coefficients reach the maximum value of 78.0 W/(m2 K) among the testing conditions when the working gas pressure is 0.4 MPa and the revolution is 420 rpm. An oscillating heat transfer correlation is derived based on the experimental data which are obtained under situations close to an actual Stirling engine's flow region, where Re and Reω are in the ranges of 740-4110 and 12-71, respectively. The estimated uncertainty for the heat transfer coefficient is usually within 7.69%, and the determination coefficient of a regression fitted correlation is 0.97. The proposed correlation is respected to predict the heat transfer coefficients of oscillating flows for practical design of tubular heaters, while the classical unidirectional steady correlations are not suitable, especially at high Re conditions.