Experimental investigation on thermodynamic performance of a copper foam-based cascaded latent heat storage tubes

Cascaded latent heat storage (CLHS) systems offer an effective means for energy storage from moderate to medium and low temperature heat sources (100-200℃). In this study, a three-stage shell-and-tube cascaded latent heat storage system was designed and fabricated. Three types of paraffin wax with distinct melting points were employed as phase change materials (PCMs), and foam copper was utilized to enhance heat transfer. By adjusting the inlet temperature and flow rate of heat transfer fluid (HTF), the thermodynamic performance of each LHS stage and the entire system under different operating conditions were investigated. Exergy analysis, entransy analysis, and sensitivity analysis were employed to study the primary influential factors on system performance and the impact weights of diverse operating conditions. Experimental results highlighted the crucial significance of maintaining consistency in the physical parameters of PCMs across different stages in the CLHS system for its thermodynamic performance. The high thermal conductivity and low latent heat of PCM#2 in the second stage result in substantial energy losses during the heat storage process, reducing the efficiency of energy cascaded utilization within the system. With an increase in the HTF inlet temperature and flow rate, the energy storage capacity and rate increase, while the energy storage efficiency exhibits a decreasing trend. Moreover, the effect of varying inlet temperature on the energy storage efficiency is much smaller compared to that of inlet flow rate. This study emphasizes that heat dissipation is a critical factor affecting the thermodynamic performance of the cascaded latent heat storage system. For CLHS systems targeting high-temperature and high-flow rate heat sources, enhancing insulation is crucial for ensuring the sustained high-efficiency operation.