Study of oscillating flows through a novel constructal bifurcation Stirling regenerator

High flow resistance in conventional porous regenerators has been an important factor for limiting the overall performance of Stirling engines. Herein, a novel constructal bifurcation regenerator based on constructal concept was developed to reduce the flow resistance in the Stirling regenerator. First, the pressure drop and transient conjugate heat transfer characteristics of oscillating flows through the constructal bifurcation regenerator with various geometrical parameters were investigated by the CFD approach. The results showed that the fluid flow and heat transfer between the acceleration and deceleration phases, as well as the discharge and suction phases, were varied significantly. These differences should be resulted from the local acceleration effect, the formation of eddies in the acceleration phase, and different windward surfaces generated by the regenerator matrix to the fluid in the discharge and suction phases. Additionally, the flow characteristics between the oscillating and steady flows were compared and the local acceleration effect was proven to be the main cause of the difference between them. Then the three-parameters correlation equations of friction factor and Nusselt number for each structure and four master correlation equations with geometrical parameter dependence were built to predict the regenerator performance. Thereafter, the constructal bifurcation regenerators were converted to equivalent porous media, and thus the main porous parameters were obtained for the full Stirling engine simulation in the next studies. Finally, the friction factor and Nusselt number of the constructal bifurcation regenerator were compared with those of other commonly used regenerators. It showed that the constructal bifurcation regenerator had a low flow resistance and moderate heat transfer, thus obtaining a high comprehensive performance. The superior comprehensive performance of the regenerator makes it possible to improve the performance of Stirling engines.