الفهرس 
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Abstract
Storing solar energy in the form of latent heat using phase change materials (PCMs) such as paraffin wax is an effective way of storing solar energy. PCMs have been widely used in solar water heating systems to store solar energy in the form of latent heat during day light and to give that heat back during night when there is no solar radiation available, and there is a demand for hot water. Unlike sensible heat storage methods, latent heat storage provides much higher storage density, with a smaller temperature difference between storing and releasing heat. However, paraffin wax has a low thermal conductivity, i.e. 0.25 W/m.K, which lowers the rate of heat transfer from the wax to the pipes of water heaters, especially when it solidifies over the pipes.
The objective of this research is to improve the thermal performance of solar water heaters that contains a heat storage material, i.e. paraffin wax. In this research, an innovative and cheap technique is examined to improve the heat transfer across the phase change material (PCM), paraffin wax, which is embedding copper strips or thermal fins inside the PCM. An experimental setup has been designed and developed to investigate the influence of using (1) unfinned pipes i.e. normal solar water heaters, (2) finned pipes and (3) metallic strips, on the performance of solar water heaters. 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 exchanger pipes. Also, adding fins and metallic strips has enhanced the temperature homogeneity in the molten wax. The time of getting hot water has increased by more than 36% in case of using finned pipes than the normal solar water heaters, and by 154% in case of using metallic strips. It can be concluded from the performed experiments that adding fins or metallic strips to solar water heaters using a heat storage material improves the heating capability of the water heater.