Improved Thermal Switch Based on an Adsorption Material in a Heat Pipe

Abstract

For many applications, the possibility of controlling heat flow by “thermal switching” can be very beneficial. In previous work, we presented a novel approach for thermal switching using a water-loaded adsorbent as part of the evaporator of a heat pipe. The basic idea is that the adsorbent releases water upon exceeding a certain evaporator temperature and thus “activates” the heat pipe by providing the working fluid for thermal transport. In this work, we present an improved version of the heat switch. We found that an ordinary copper heat pipe (i.e., thermosyphon) with outer diameters common in heat pipe applications (10 mm) can be used as a base of the heat switch. The reversibility of the switching effect was proven. The location of heat input relative to the adsorbent position was optimized, leading to improved switching ratios of up to 36 as calculated from thermal resistance change between evaporator and condenser. Furthermore, the role of the insulation on thermal resistance and switching ratio was examined and found to be significant.