A Numerical Study on Heat Transfer of High Efficient Solar Flat-Plate Collectors with Energy Storage

The integrated solar collector is considered to be a promising direction for increasing the economic feasibility of low-temperature solar systems for heating water in domestic and industrial applications. Phase change material (paraffin) energy storage can be used in solar water heaters. The paraffin-integrated solar collector eliminates the need of conventional storage tanks, thus reducing cost and space. But a negative aspect of paraffin is that the materials suffer from inherent low thermal conductivity. In this paper, new aluminum foams filled with paraffin were presented to solve this problem. Local thermal equilibrium between the solid filler and the matrix is not ensured in such systems since their thermal diffusivities are very different. A two-temperature model was used for the aluminum frame and liquid paraffin respectively in this paper. A general momentum equation, which includes the Brinkman-Forchheimer extension to Darcy flow, was employed when the paraffin was melted. Apparent heat capacity method was used to simulate the phase change heat transfer of the paraffin melting process in the aluminum foams. The results indicated that the heat transfer ability is significantly improved by using paraffin with aluminum foams and the temperature difference between the frame and liquid paraffin cannot be ignored during the melting/solidifying process.