Thermal Switch Based on an Adsorption Material in a Heat Pipe

For many applications, the possibility of controlling heat flow by “thermal switching” could be very beneficial. Several concepts for heat switches were already proposed and tested, however, many drawbacks of these concepts are evident. In this work, we present 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. The first part of this work concentrates on the adsorbent characterization by analyzing the adsorption isobars and isotherms and thus understanding the behavior of the system. Furthermore, a model to predict the release of water from the adsorbent in dependence of temperature was developed. Subsequently, the adsorbent was integrated into an actual heat pipe demonstrator to verify these predictions and demonstrate the thermal switching ability. Overall results revealed a very good agreement between the predictions concerning water release and the heat pipe’s thermal behavior. The obtained thermal switching ratio depends on the heating power and temperature range that is considered. Depending on whether evaporator/condenser or the adiabatic zone are considered, average switching ratios of circa 3 and 18 were found, respectively.