Numerical Study of a New Solar Vacuum Tube Integrating with Phase Change Material

In this work, a new solar vacuum tube (SVT) integrating with phase change material is introduced and numerically investigated. The mathematical model and the numerical solution of phase change heat transfer is introduced. The heat transfer of the solar energy collection system during the energy storage process is simulated. Solid-liquid phase change characteristics of the SVT with paraffin inside is analyzed. Optimization analysis of fin structure parameters (fin thickness and fin spacing) in the vacuum tube is conducted. The results showed that the metal fin has a great effect on the phase change heat transfer of paraffin in SVTs. The closer the paraffin is to the fins, the more uniform the paraffin temperature is and the sooner the paraffin melts. As the fin thickness increases and the spacing between the fins decreases, the melting time of the paraffin decreases. Meanwhile, the effect of fin spacing on the overall heat transfer performance of the phase change energy storage tube is larger than the effect of the fin thickness. When the fin thickness is 2 mm, the melting time of paraffin with a fin spacing of 80 mm is 21,000 s, which is almost three times of that with a fin spacing of 10 mm (7400 s). Therefore, decreasing fin spacing is an effective way of enhancing phase change heat transfer. When the total fin volume is constant, a SVT with small fin space and small fin thickness performs better in heat transfer performance.