Evaluation of the energy storage performance of PCM nano-emulsion in a small tubular heat exchanger

PCM emulsions have attracted considerable interest as the media for thermal energy storage (TES) owing to their high thermal storage capacity, desirable fluidity and thermal conductivity. However, the direct transportation of PCM emulsions in TES systems for both charging and discharging is rarely reported. In this work, a PCM-in-water nano-emulsion was prepared with n-hexadecane and suitable surfactants for cooling energy storage at a charging and discharging temperature range of 20–5 °C and 5–15 °C, respectively. It was applied to a tubular heat exchanger system to evaluate its TES performance for a cooling panel of 0.2 m2 total surface area. The thermal storage performance was notably increased with the flow rate of emulsion through the exchanger tube. The volumetric thermal storage capacity of charging was 50% higher than that of water. The cooling energy could be rapidly released in the discharging process, 79% of the stored energy at averaging 25 W during most of the discharging period. The emulsion remained stable throughout the test period. Overall, the results demonstrated that the PCM nano-emulsion has the unique characteristics of high static stability, and high energy releasing efficiency and the promising potential for air-conditioning application in buildings.