A comprehensive study on the complete charging-discharging cycle of a phase change material using intermediate boiling fluid to control energy flow

Abstract

The low melting and solidification rates of phase change materials (PCM), which traces back to their low thermal conductivity coefficient, has led the application of these materials to face limitations. This paper aims to explore the effectiveness of a novel method called intermediate boiling fluid (IBF) in speeding up the energy storage and transfer processes in PCMs during a complete charging-discharging cycle. Throughout this novel technique, paraffin and acetone are utilized as PCM and IBF, respectively. In the solidification process, there is no direct contact between the cold source and the molten paraffin, while acetone, as an intermediate fluid, is being boiled via absorbing paraffin's heat and ultimately causing paraffin to be cooled down and solidified. The melting and solidification experiments were run in a test cell with and without acetone. The experimental results indicate that utilizing this technique dramatically enhances the solidification rate and improves the melting rate to a moderate level. It is illustrated that by using this method under the optimum condition the solidification time, melting time, and the total melting and solidification time decrease by 77 times, 22 percent, and 80 percent, respectively, compared to the conventional method. It is also concluded that by adjusting the container pressure and using different amounts of intermediate boiling fluid (IBF), the freezing and melting rates of phase change materials can be controlled.