Feasibility assessment of water as a means of constructing a novel contact melting method: A numerical study

This study proposes a novel contact melting mode based on the incompatibility of water and paraffin. This mode involves filling a small amount of water at the bottom of the unit to expedite paraffin melting through the high thermal conductivity of water while also utilizing water as a heat storage medium. A 2-D numerical model is developed using the enthalpy-porosity method to account for natural convection between paraffin and water and to verify the relevant model. The study compares the impact of varying water filling heights on the melting performance (liquid phase distribution, velocity distribution, temperature distribution, total melting time, heat storage rate, and rate of different heat storage media) of the phase change heat storage unit. The results indicate that the contact melting mode, achieved by filling water at different heights at the bottom of the unit, gradually enhances heat transfer with increasing water height. However, increased water volume negatively impacts total heat storage. Specifically, compared to a pure paraffin structure, it is found that when water occupies 10% of the total volume, the melting time is reduced by 8.60%, and the overall heat storage rate (PCM + water) is increased by 4.05%, yet overall heat storage is reduced by 5.16%. Furthermore, when the volume of water is 5%, an increase in initial water temperature is advantageous for the heat storage rate of PCM at the initial melting stage, resulting in a shortened total melting time. However, this comes at the expense of the heat storage and heat storage rate of water. Moreover, an increase in the heat source temperature from 342.15 K to 357.15 K reduces melting time by 36.83%, an increase in the average heat storage rate of PCM by 73.20%, and a substantial improvement in overall heat storage.