Study On The Heat Transfer Characteristics In Stirling Engine Regenerators Under Unidirectional And Oscillating Flows

As one of the three main heat transfer components in the Stirling engine,regenerator has a significant impact on the output power and thermal efficiency.However,correlations derived from unidirectional flow are usually used in Stirling cycle analysis method,which causes deviations between analysis results and practical operation results and influences design and optimization.In this study,the heat transfer characteristics of regenerator under unidirectional flow and oscillating flow are analyzed by numerical simulation and experiment method.The heat transfer phenomenon under unidirectional flow is characterized in the conditions of different kinds of gas,pressures,temperatures,velocities and meshes.And a new Nu-Re correlation is derived from the numerical results as Nu=-9.74+3.78 Re0.36.Temperature contours and streamline charts are further qualitatively analyzed based on pore-scale.The process of heat transfer is considered to be influenced by the temperature drop and velocity disturbance when gas goes through the wire-mesh.Unidirectional flow test-rig is buit and the single-blow method is improved to verify the fitted correlation.And the deviation between experimental result and numerical simulation is less than 2.09%,which verifies the accuracy of the correlation derived from the pore-scale simulation.By means of non-thermal equilibrium model,the temperature distribution of the regenerator along axial and radius direction is discussed and it is found that the proportion of heat conduction loss increases with the heating time.The pore-scale simulation is further extended to oscillating flow field and instantaneous heat transfer characteristics are analyzed at different hot end temperatures,inlet velocities and frequencies for a single cycle of oscillating flow.The heat transfer characteristics are much different between heating and cooling processes.As to the same Reynolds number,the maximum deviation of Nusselt number is 22%between the cooling and heating periods.In general,the heat transfer rate of oscillating flow is usually 20%more than that of unidirectional flow.Two Nu-Re correlations(Nu=3.56+0.36Re0-66 and Nu=17.67+0.37Re0.64)are obtained for heating and cooling processes,respectively,and the deviation is less than 7%between the simulation and experimental results.Finally,the simulation result is verified through oscillating flow experiment and the average relative error is 6.57%.