Yin-Yang heat flow rate converter: Based on Guar Gum composite phase change materials with controllable thermal conductivity

Solid-liquid phase change materials (PCMs) have broad potential but suffer from leakage problems and unreasonable thermal conductivity, resulting in low utilization efficiency. In this study, using Guar Gum (GG) as large frame and graphene oxide (GO) or SiO2 aerogel microchip as small frame, thermal conductivity strengthening PCMs (GG-C-PEG) and thermal conductivity weakening PCMs (GG-I-PEG) were prepared after loading polyethylene glycol (PEG). In-depth characterizations turned out that the phase change enthalpy retention was close to 100% of PEG. In particular, the composites achieved 0.94 W/(m·K) of enhanced thermal conductivity and exhibited a reduced thermal conductivity of 0.11 W/(m·K). Simultaneously, the mass of the PCMs remained above 94.08% when heated at 80 °C for 45 min and the loss of melting enthalpy was less than 6.11% after 100 cycles, indicating outstanding stability in shape and performance during the heating–cooling cycles. To further utilize of solar energy, GG-C-PEG exhibited great photothermal conversion efficiency reaching 83.67%. Moreover, inspired by Tai Chi culture, a novel device that could control the heat flow rate from minimum to maximum by utilizing different thermal conductivity properties of the two types of PCMs was designed, taking composite PCMs further into practical scenarios.