Shape memory effect heat engine performance

The performance of a shape memory effect heat engine has been evaluated taking into account the heat transfer to the working element, hysteresis effects, elasticity and heat losses. It is shown that there exists an optimum stress required for maximum power output. The maximum power output is found to increase with increasing cycle temperature difference, increasing cycle strain, increasing working element heat transfer coefficient and decreasing size of the working element. Calculations for Nitinol and Cu---Zn---Al working elements, operating on a 60°C temperature difference and 2% cycle strain, indicate maximum power densities of approximately 1 W/g and conversion efficiencies of approximately 1%.