Numerical Analysis of transport phenomena in a heat regenerator

Abstract

Stirling engines attracted the researchers to study their performance as they have many advantages as quiet operation, the capability to work with renewable resources or waste heat, and the high efficiency which is equivalent to Carnot. The regenerator, a vital part of Stirling engines absorbs heat during one half of the cycle and supplies the heat stored in the second half of the cycle. In this work, a 2D model of the Stirling engine was developed in which the oscillating flow in the engine was modeled using Comsol Multiphysics [1], continuity, conservation of momentum, and energy conservation equations were solved, free and porous media flow module and heat transfer in fluid and porous media were used to model fluid flow and transfer of heat respectively, boundary and initial conditions were defined, moving mesh module was defined to model the piston displacement and velocity. A Mesh independence test was performed to investigate the dependence of the solution on the number of elements of the mesh. The 2D model results were validated against the work of Almajri et al. [2] where the volume variations of the hot expansion space and cold compression space at different crank angles were made the same in the current work. The resultant indicated power for different RPMs was used for validation at two charging pressures, the cycle P-V diagram was presented. Investigations for the effects of changing charging pressure and heater wall temperature on the resultant indicated power were carried out and it was concluded that the indicated power increases as the engine charging pressure increases, the resultant indicated power also increases when the temperature of the heater walls increases. Plots for effectiveness, Nusselt number, and pressure drop against Reynolds number as the RPM increases were presented and compared with results from the literature. Plots for temperature, velocity, and pressure fields at different crank angles were presented, this gives better visualization of the flow and transfer of heat in the engine. Novel geometry was presented where the V-shape corrugated porous media introduced by W.Aboelsoud [3] was used as the engine regenerator, the novel geometry was placed in the same casing of the original geometry without changing any dimension of the casing to avoid adding any dead volume to the engine, as a result, the total area of the novel geometry in the 2D model was less than that of the original geometry, the 2D validated model was used to study the transport phenomena in the novel geometry. As in the case of the original geometry, the P-V diagrams for both the compression and expansion spaces were presented, plots for temperature, velocity, and pressure at different crank angles were presented as in the case of the original geometry.