Thermal conversion efficiency of an ideal thermoelastic marmem cycle

The thermal conversion efficiency of an ideal stress-strain-temperature cycle based on the mechanical shape memory effect associated with a thermoelastic martensite transformation (thermoelastic marmem cycle) has been studied. A relationship between the upper limit of the thermal efficiency and a set of materials properties has been derived. It is shown that a higher thermoelastic marmem efficiency and a closer approach to the corresponding Carnot efficiency are favoured by: (1) higher yield stress of the high-temperature phase, (2) larger recoverable strain, (3) smaller transformation temperature range and thermal hysteresis associated with the transformation, and (4) smaller transformation latent heat. The thermal efficiency has been calculated for a cycle utilizing a Ti-50.4 at % Ni alloy. The highest efficiency for this particular alloy was found to be about 9%; this amounts to 45% of the corresponding Carnot efficiency. Thus it is concluded that efficiencies can be obtained which are comparable with those of cycles operating at small temperature differences with fluids as working media.Marmem is derived from martensite memory 21].