Improving Heat Transfer Through Paraffin Wax, by Using Fins and Metallic Strips

Abstract

Phase change materials (PCMs) such as paraffin wax are used to store solar energy in the form of latent heat of melting, which can be used later when no solar radiation is available. However, paraffin wax has a low thermal conductivity, i.e., \(0.25\, \hbox {W/m}\,\hbox {K}\), which lowers the rate of heat transfer from the wax to the pipes of water heaters, especially when it solidifies over the pipes. An experimental setup was developed to investigate the influence of (1) finned pipes and (2) metallic strips on the performance of solar water heaters that contains a heat storage material, i.e., paraffin wax. It has been found that the presence of fins and metallic strips inside the wax is acting as channels of heat transfer across the wax, such that the heat transfer process continues even if the wax solidifies over the heat exchange pipes. Also, adding fins and metallic strips has enhanced the temperature homogeneity in the molten wax. The amount of heat energy released by the wax to the flowing water has increased by 47% in case of using finned water pipes than unfinned pipes, and by 304% in case of using copper strips. It can be concluded from the performed experiments that adding fins or metallic strips to solar water heaters that contain paraffin wax improves the heating capability of the water heater.