Accurate prediction of work and coefficient of performance of elastocaloric materials with phase transformation kinetics

Elastocaloric cooling is a novel solid-state cooling technology based on the latent heat associated with martensitic phase transformation in shape memory alloys. The work associated with elastocaloric cooling cycle is determined based on the material physical properties as well as the operating temperatures. To predict the work accurately under common practical conditions, a 1-D dynamic model for the shape memory alloys with phase transformation kinetics for polycrystalline is developed in this study. The model is discretized and then implemented in MATLAB Simulink. Based on the physics of the phase transformation free energy, the model is capable to predict whether or not the local material would undergo transformation under the given stress and temperature condition. To validate the model, series of compressive loading-unloading tests for super-elastic Ni-Ti alloys were conducted under different temperatures. The test results and data from literature were compared to the model prediction, and the deviation is within 10%. The cycle work and coefficient of performance is demonstrated for a two-bed active elastocaloric regenerator system as an example and then compared with the conventional single-stage system.