Experimental comparison of latent thermal energy storage units with different metal macro-additives

The inherent low thermal conductivity of phase change materials hinders the industry's deployment of practical latent heat storage systems. Adding macro-additives into PCMs is the most economical way to overcome this problem. This study experimentally compares three mid-temperature shell-and-tube LTES units with macro-additives of fins, copper foam, and shavings under the same conditions. The heat transfer mechanism of three macro-additives is investigated by analyzing the temperature evolution curves and comparing their structural characteristics. Experimental results show that the charging time of the fin unit is 68.4% shorter than the copper foam unit and 59.5% shorter than the copper shaving unit. Although the three heat storage units have the same compactness factor, the fin unit has the best thermal conduction performance for two reasons. One is that the local porosity of the fin unit decreases as the radius increases, achieving a higher effective thermal conductivity in the regions with a larger temperature gradient. The other is that the fins have a concentrated thermal energy flow pathway in the radial direction, which aligns the primary effective thermal conductivity direction with the heat flux direction. In addition, the larger pore size in the shaving unit is the main reason for its better performance than the foam unit.