The thermal response of heat storage system with paraffin and paraffin/expanded graphite composite for hot water supply

The low thermal conductivity of phase change material (PCM) leads to low heat storage/retrieval rates. The expanded graphite (EG) was used to enhance the thermal conductivity. EG/paraffin composite with the 7% mass fraction of EG was prepared as a good candidate for the latent thermal energy storage (LTES) system. A shell and tube LTES system built for room heating and hot water supply in a family was experimentally investigated. The paraffin and paraffin/EG composite were used as the heat storage material, respectively. The experimental results indicated: The utilization of EG/paraffin composite PCM greatly improved the heat storage/retrieval rates of the LTES system. The LTES system with paraffin/EG composite showed a 44% reduction in heat storage duration and a nearly 69% reduction in the retrieval duration, respectively, compared to those for the system using pure paraffin. The most outstanding advantage, for the LTES system filled with paraffin/EG composite, was that the outlet temperature of water can be maintained at a higher level for a longer term than that with paraffin. However, the LTES system filled with EG/paraffin composite did not show an obvious advantage in the step-by-step heat retrieval mode, compared with paraffin.