Autonomous Heat Switch With Limit Cycle Behavior Based on a Shape Memory Elastomer

We explore the use of actuation in shape memory elastomers as a route to establish limit cycle temperature responses, and thereby, the realization of a heat switch. Temperature-dependent force generation on a small magnetic widget due to the thermomechanical response of liquid crystal elastomer is coupled with distance-dependent magnetic attraction of the widget for a fixed warm surface. The resulting motion is time-dependent, and exhibits limit cycle behavior, under appropriate conditions, with heat periodically transferred to a nearby cold surface. We examine the dynamics of the system and parameterize the stability of the oscillation in terms of substrate heat flow, thermal transport coefficients, and relevant thermophysical properties of the elastomer. A lumped heat transfer model is developed to investigate the optimal parametric conditions for maximum heat transfer efficiency by exploring the associated dimensionless variable space. We anticipate that self-sustained cyclical thermal transport of this variety will have application in waste heat harvesting. In particular, the thermal oscillator realized here is of interest for waste heat recovery using pyroelectric devices.