Elastocaloric Cooling: The Energy Performances of Possible Solid-State Refrigerants in a Rotary Air Conditioner

Elastocaloric is a promising cooling technology in the scenario of the solid-state cooling alternative to vapor compression. The elastoCaloric Effect (eCE) is defined as the reversible adiabatic temperature change (∆Tad) and the reversible isothermal entropy change (∆ST) in Shape Memory Alloy (SMA) materials when applying or removing an external mechanical load (tensile, compressive, or torsional). To date, the benchmark of elastocaloric materials that offers the best thermal and mechanical performance is represented by the binary alloy nitinol (NiTi).In this paper, different elastocaloric materials have been compared with nitinol to identify the best material to use for the construction of an experimental device. The developing experimental device is a novel rotating device that ensures a continuous flow of hot or cold air for air conditioning applications based on the Active elastocaloric Regenerative refrigerant (AeR) cycle. The elastocaloric material is composed by 600 wires (diameter 0.5 mm and length 300 mm). The elastocaloric device is made by means of two concentric cylinders (Dinner = 250 mm and Dexternal = 280 mm), inside which the elastocaloric material is rotated by varying the frequency in the range of 0.3 Hz and 0.7 Hz. The device has two inlet sections and two outlet sections, ensuring fluid flow along two opposite directions so that the hot and cold useful effect can be had simultaneously. The temperature of the elastocaloric material is the same along its entire length, therefore a simplified two-dimensional rotary problem is modelled and solved through the COMSOL code. A comparison between the different elastocaloric materials (Ni50.8Ti49.2, Ni55.9Ti44.1, Ni45Ti47.2Cu5V2.75, (Ni50Mn31.5Ti18.5)99.8B0.2, Ni50Mn30Ti20) have been carried out in terms of: outlet air and air temperature variation in the cold and hot side of the regenerator, cooling/heating power, and COP.