Thermal rectification of solid-liquid phase change thermal diode under the effect of supercooling

Abstract

Solid-liquid phase change thermal diode (SL-PCTD) is potential for thermal rectification, however the unsustainable thermal rectification ratio of the SL-PCTD hampers its practical application, demanding a reasonably compatible design. Herein, a SL-PCTD composed of calcium chloride hexahydrate (CaCl2·6H2O) and paraffin wax is investigated, where the supercooling effect of CaCl2·6H2O plays a significant role in thermal rectification. In the forward direction, natural convection sustains in the SL-PCTD below the melting temperature (30 °C) due to the supercooling, leading a robust heat transfer within a temperature bias range of 10–40 °C. In the reverse direction, heat flux should be inhibited for effective thermal rectification, thus supercooling is dislodged via manual supercooling release (MSR) within a large temperature range of 30–7 °C. As a consequence, thermal rectification ratio of 2.95 is achieved, which is competitively sustainable at large temperature bias compared to the SL-PCTD without supercooling effect. Furthermore, a theoretical model base on thermal resistance approach is proposed to analyze the supercooling effect on thermal rectification comprehensively, and the theoretical and experimental results find a great agreement. According to the theoretical analysis, the SL-PCTD with supercooling works at a large thermal rectification ratio of around 2.8 within a wide temperature bias range of 33–87 °C, indicating the significant role of supercooling in thermal rectification.