Design Concepts and Development of Elastomer Heat Engines/Pumps

Although ideal elastomer thermodynamics has been described by many authors, their use in heat engines/pumps remains a theoretical and pedagogical curiosity. Because elastomers can generate large forces with small temperature changes, they may be useful in low delta T heat engines for energy recovery and bottoming cycles. In addition, the greater density of solid versus gas or two-phase working substances may enable a more compact system. Elastomer heat engines described in the literature are reviewed and compared. Most designs use an eccentric wheel design presenting design problems in sealing and physically separating the hot and cold sides. In addition, a variety of designs for rotary motors using the linear contraction of a solid that have been developed for thermoelastic shape memory alloy and mechanochemical systems are also pertinent. Several heat pump prototypes were constructed where an ideally isothermal process was performed by stretching in contact with a hot and a cold heat transfer plate. However, the sliding friction on the plates prevented any measured cooling effect. Designs utilizing a continuous elastomer belt winding over various configurations of rollers or pulleys appear to be most suited to elastomer systems due to the flexibility of placement of the hot and cold reservoirs. A simplified two wheeled design is described.