Improving elastocaloric cooling performance by applying novel thermodynamic cycle

Utilizing the old and relatively inefficient vapor-compression refrigeration / air-conditioning has depleted the ozone layer in the past and is worsening the global warming today. Consequently, natural refrigerants, which could be less efficient, toxic or inflammable, would replace the current refrigerants in near future. This in turn, allows for developing alternative non-vapor-compression cooling/heat-pumping technologies among which elastocalorics have a considerable potential.

Shape memory alloys such as NiTi, can be used as recyclable, nontoxic, nonflammable and environmentally friendly solid refrigerants in elastocaloric cooling / heat-pumping. Thin wires under tension and thin-walled tubes under compression that would allow for fast and efficient heat transfer are ideal candidates to be applied in elastocaloric regenerators and are therefore selected for this study.

In this study, multiple thermodynamic cycles have been studied with an emphasis on the parameters of the holding segment of the cycle. The results reveal that the applied thermodynamic cycle significantly affects the thermomechanical response and thus the cooling/heating efficiency of the material. Applying isostrain or isostress cycles leads to significantly different thermomechanical and elastocaloric responses. An isostress cycle results in a Carnot-like thermodynamic cycle that significantly improves the heating/cooling efficiency. Moreover, it allows for reaching larger adiabatic temperature changes in smaller stress/strain ranges that is beneficial for reducing the probability of buckling under compression, increasing the tensile fatigue life and reducing the total required forces in elastocaloric regenerators and other multielement cycles in both tension and compression.