Flexible phase change materials with photothermal conversion properties as pipe insulation for improved thermal stability

Long-distance district heating pipelines exposed to the ground for extended periods experience significant heat loss. The application of flexible phase-change composite materials with a photothermal conversion function offers a novel approach to coupling heating pipes with phase-change heat storage, utilizing solar energy for insulation. In this study, melamine foam serves as the supporting skeleton, erythritol as the phase change material, and polydopamine as the light-absorbing material. The composite phase change material exhibits a thermal conductivity of 0.04574 W/m·K, an enthalpy of 357.6 J/g, a melting peak at 121.9 °C and an average photothermal conversion efficiency of 63.82 %. The simulation results show that the thermal insulation layer formed by the photothermal conversion material effectively slows the cooling rate of water within the pipe. The results of the evaluation show that if photothermal conversion material is used as insulation in the long-distance district heating pipeline in Taikoo and Lvliang cities, the daily operating cost savings would be 1,226.5 CNY/d and 2,147 CNY/d, respectively. The long-distance district heating pipeline in the two cities could offset the additional cost of photothermal conversion material over an ordinary insulation layer in 698.92 days and 886.31 days, respectively. This study provides technical support for the application of solar energy in heating pipe insulation.