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Nanofluids as Heat Transfer Fluids for High-efficiency Caloric Heat Pumps

Received: 18 February 2019 Accepted: 26 April 2019 Solid-state is the new frontier of Not-In-Kind technologies arisen as possible future replacement of vapor-compression-based systems. Caloric cooling and heat-pumping found their operation on caloric effect; a class of thermo-physical effects detected in caloric materials following an adiabatic change of the intensity of an applied external field, that results in a variation of the temperature in the material itself. A Brayton-based thermodynamical cycle, called Active Caloric Regenerative cycle, is used to build caloric cooling systems or heat-pumps. In ACR cycle the caloric material acts both as refrigerant and as regenerator and an auxiliary Heat-Transfer Fluid (HTF) is employed to vehiculate heat fluxes between the cold and hot environments. The most common HTF is water but advanced solutions could be adopted to enhance the heat exchange coefficients, like nanofluids. Nanofluids are suspensions consisting of solid high-thermal-conductivity nanoparticles dispersed in a base fluid to enhance the global thermal conductivity of the fluid. In this paper we investigate, numerically, the energy performances of a caloric heat pump employing water-based Al2O3 nanofluids as HTF. The analysis is perpetuated changing both the nanofluid volume concentrations and the caloric materials employing electrocaloric, elastocaloric and barocaloric ones.