Thermodynamic optimization of a regenerator heat exchanger

This paper introduces a general computational model for regenerators fed by a hot fluid stream on one side, whereas the other side is a fluid mixture, in which one of the components (refrigerant) undergoes a phase change. A simplified physical model, which combines fundamental and empirical correlations, and principles of classical thermodynamics, mass and heat transfer is developed and the resulting three-dimensional differential equations are discretized in space using a three-dimensional cell centered finite volume scheme. The proposed model is used to simulate numerically the behavior of the regenerator working under different operating and design conditions. Mesh refinements are conducted to ensure the convergence of the numerical results. The proposed methodology is shown to allow a coarse converged mesh for all simulations performed, therefore combining numerical accuracy with low computational time. The model was then used to determine optimal parameters for a specific geometric configuration of the regenerator, finding that the two-way maximized efficiency operating with optimal porosity and dimensionless mass flow rate of liquid ammonia, is ηmax,max = 45.5% for the optimal pair (ϕ,m˜s)opt=(0.5,0.01). As a result, the model is expected to be a useful tool for simulation, control, design, and optimization of regenerators for heat driven refrigerators.

► We introduce a general computational model for regenerator heat exchangers.
► A simulation and optimization study was conducted with the model.
► The existence of optimal porosity and ammonia mass flow rate was investigated.
► Efficiency was maximized up to 45.5%.
► Model could be a tool for simulation, design, and optimization of regenerators.