A 2nd order regenerator model including flow dispersion and bypass losses [heat engines]

The reliability of second order computer codes for the the simulation of regenerative cycles, such as the Stirling or the Vuilleumier cycle, is strongly dependent on the quality of the models that are used to describe the various losses. Particularly, the thermal regenerator losses can severely affect the performance, and so an accurate modeling of these is essential in order to obtain realistic results. Nevertheless most present approaches are based on the assumption of a strictly one-dimensional, ideal plug flow. In this paper, this theory is reviewed, and it is suggested to additionally include losses due to both microscopic and macroscopic flow inhomogenities. For this purpose, simplified equations are derived, which can easily be handled in a second order code.