A novel thermomechanical energy conversion cycle

This paper presents a new power cycle for direct conversion of thermomechanical energy into electrical energy performed on pyroelectric materials. It consists sequentially of (i) an isothermal electric poling process performed under zero stress followed by (ii) a combined uniaxial compressive stress and heating process, (iii) an isothermal electric de-poling process under uniaxial stress, and finally (iv) the removal of compressive stress during a cooling process. The new cycle was demonstrated experimentally on [001]-poled PMN-28PT single crystals. The maximum power and energy densities obtained were 41W/L and 41J/L/cycle respectively for cold and hot source temperatures of 22 and 130°C, electric field between 0.2 and 0.95MV/m, and with uniaxial load of 35.56MPa at frequency of 1Hz. The performance and constraints on the operating conditions of the new cycle were compared with those of the Olsen cycle. The new cycle was able to generate power at temperatures below those of the Olsen cycle. In addition, the new power cycle can adapt to changing thermal and mechanical conditions.