Measurement on Nusselt number of regenerator wire meshes by cylindrical probe

The regenerator is an important element in Stirling engines. As a regenerator element, a fire-hardened layer of wire mesh became popular for Stirling engines. However, such a mesh is expensive. Recently, a packed wire mesh has been used widely in Japan, but its basic performance, such as flow resistance and heat transfer ratio, has yet to be clarified. In the present study, a new method to estimate the Nusselt number of wire meshes in oscillating flow is proposed and reported. This method employs a cylindrical probe having two thermocouples in the axis symmetry direction. The present method has a feature that temperature variation in oscillating flow conditions can be estimated without expensive instruments for unsteady measurements. It became clear that the measured Nusselt numbers of usual meshes are from 45% lower to 30% higher than the empirical equations of previous studies. The Nusselt number of the packed wire mesh became about 1/6 of the equivalent layer of a usual mesh. These results shows that a rough estimation of performance of heat transfer is possible by the present method