The numerical simulation and experimental study of heat release in a heat storage system with various diameters of aluminum tubes

Phase change materials (PCMs) can be used to store solar energy. The heat released from PCMs is directly influenced by the efficiency of thermal energy storage and the scope of application. In this study, paraffin was used as the PCM, and was encapsulated in an aluminum tube. The temperature of the inner PCM was measured, and the heat release process of the PCM was simulated. The results indicate that the melt temperature of the PCM ranged from 45 °C to 60 °C, and the latent heat was 177 J/g. The heat release processes of the PCM in different aluminum tubes included three stages: 1) the stage during which no phase change occurred at temperatures above the melt temperature and at a rapidly decreasing temperature; 2) the stage during which phase change occurred at very slowly decreasing temperatures; 3) the stage during which no phase change occurred at temperatures lower than the melt temperature. The temperature of the PCM decreased when the radius of the aluminum tube increased. The temperature results obtained via simulation were similar to the actual temperature data. The total energy released from the PCM increased linearly with the time required to complete the energy release process of the PCM in aluminum tubes with different diameters, as well as with the increase in the aluminum tube diameter. The diameter of the PCM exerted no significant influence on the energy release rate. The relationship between the tube diameter and the time required to complete heat release, and the relationship between the amount of heat released, the diameter of the aluminum tube, and the release time, were established. These equations could predict actual values and provide theoretical guidance for heat release in heat storage systems. They could also be used as a guide in practical production.