Análise numérica do desempenho termodinâmico de regeneradores barocalóricos ativos utilizando borracha PDMS para aplicações em refrigeração

Abstract

This dissertation focuses on the Active Barocaloric Regenerators (ABR's) that use elastomers as solid state coolant. This technology, not yet tested experimentally and also little explored through theoretical models, is considered to have great potential to be an alternative to vapor compression refrigeration. This research aimed to develop a model capable of simulating the thermodynamic performance of an ABR using PDMS rubber as coolant, to then evaluate the real potential of this device to operate as a refrigerator, as well as to identify the factors that contribute to its performance. A transient 2D model of a parallel plate regenerator was proposed, in which each plate is composed of a layer of PDMS confined between two stainless steel or aluminum walls. An oscillating flow of the heat transfer fluid (water) between the plates cools a cold heat exchanger and heats a hot heat exchanger. The flow was modeled by the mass conservation and Navier-Stokes equations decoupled from the thermal problem and, with a series of simplifications, an analytical solution could be applied to the hydrodynamic problem. The heat transfer was modeled by the energy equation and solved by the finite volume method using the analytical flow solution as an input. After a mesh refining study and model verification, the thermodynamic performance of the RBA was simulated with different working fluid flow rates, periods, temperature ranges, geometric parameters and material properties. When metallic walls thick enough to withstand the pressure that activates the BCE are used, no positive cooling capacities for the ABR are observed in the the results. This is mainly due to the high thermal inertia of these walls, the low thermal conductivity of the PDMS and an unfavorable characteristic of the experimental measurement curves of the BCE for PDMS. Therefore, this study shows that important advances related to the properties of the materials and the type of geometry of the regenerator are still necessary to motivate the experimental study of the ABR's.