Improving Wastewater Heat Recovery Using Phase Change Material Heat Exchangers: A Numerical Study of Thermal Performance

Industrial processes often generate substantial amounts of wastewater with significant thermal energy content, which is typically discarded as waste. A promising approach to increase energy efficiency and advance sustainable resource management is waste water heat recovery. Utilizing a phase change material (PCM) to extract waste heat from wastewater and transfer it to cold water is an innovative method that separates the demand and supply of heat, while also integrating storage and transmission within a single heat exchanger (HE). A 3D numerical model of PCM-based HE is developed and simulated. The thermal behavior of PCM and preheating of cold water are investigated in this study. In order to increase the thermal conductivity of the PCM, fins are strategically positioned. Around 71.13% of melting time is reduced by adding fins. Further, the 10° orientation of the fins is also numerically observed and it is found that it helps to improve natural circulation of molten PCM. Thus, melting time is reduced by 34% compared to the vertical fin. A 3.5°C–4.5°C temperature rise in cold water is obtained with the inclined fin, which is 14.28% higher than the vertical fin model.