HEAT TRANSFER ENHANCEMENT FOR THERMAL ENERGY STORAGE USING METAL FOAMS EMBEDDED WITHIN PHASE CHANGE MATERIALS (PCMS)

摘要

In this study the experimental investigation on the solid-liquid phase change (melting and solidification) processes have been carried out. One kind of paraffin wax is used as the PCM, in which metal foams are embedded to enhance the heat transfer. During the melting process, the test samples are electrically heated on the bottom surfaces with a constant heat flux. The PCM with metal foams has been heated from solid state to pure liquid phase. The temperature differences between the heated wall and PCM have been analysed to examine the effects of heat flux and metal-foam structure (pore size and relative density). Compared to the results of the pure PCM sample, the effect of metal foam on solid/liquid phase change heat transfer is very significant, particularly at the solid zone of PCMs. When the PCM start melting, the natural convection can improve the heat transfer performance, thereby reducing the temperature difference between the wall and PCM. Even so, the addition of metalfoam can increase the overall heat transfer rate 3 - 10 times (depending on the metal foam structures) during the melting process (two-phase zone) and the pure liquid zone. The tests for investigating the solidification process under different cooling conditions (e.g. natural convection and forced convection) have been carried out. The results show that the use of metal foams can make the sample solidified much faster than pure PCM samples, evidenced by the solidification time being reduced by more than half.