Enhancement of the Elastocaloric Performance of Natural Rubber by Forced Air Convection

We study the enhancement of the elastocaloric effect in natural rubber by using forced air convection in order to favour heat extraction during the elongation stage of an stretching-unstretching cycle. Elastocaloric performance is quantified by means of the adiabatic undercooling that occurs after a fast removal of the stress, measured by infrared thermography. To ensure accurate measurements, spatial averages on thermal maps of the sample surface are performed since undercooled samples display heterogeneities caused by various factors. The influence of the stretching velocity and the air velocity is analysed. The results show that, given the fact that the stretching velocities should be high enough to improve the cooling power, there is an optimal air velocity that provides maximum adiabatic undercooling. Our experiments have also allowed us to characterise the dependence of the Newton heat transfer coefficient on the air convection velocity. We have shown that this coefficient may show an enhancement up to 600% for air velocities around 4 m/s.