Towards idealized thermal stratification in a novel phase change emulsion storage tank

Energy storage density and charging/discharging speed are crucial performance indices for an energy storage unit. Phase change materials (PCMs) have been perceived to improve the energy storage density in thermal energy storage, but the relatively low charging/discharging speeds have been a bottleneck to their application. In building cooling storage applications using ice, the energy efficiency is compromised as the working temperature of ice storage is far below that required for air dehumidification and building cooling, which ranges between 7 and 17 ?. In this study, both experimental and numerical studies were carried out to demonstrate a novel stratified storage tank of PCM-in-water nano-emulsion for cold storage in building radiant cooling applications. A 20 wt% PCM-in-water nano-emulsion was utilized as both the storage medium and heat transfer fluid. The experimental results showed that the cooling capacity of a cooling panel was increased by 60% with phase change emulsion circulating in the loop. The effective energy storage capacity of the stratified storage tank was 1.6-1.7 times that of water in a wide range of discharging flow rates/speeds. Validated with the experimental data, the numerical simulation showed that installing baffle plates in the storage tank could effectively reduce the fluid mixing and significantly increase the effective energy storage capacity, especially at high discharging flow rates/speeds. In comparison with other PCM thermal energy storage designs, the stratified storage tank of PCM-in-water nano-emulsion has the advantage of a lower temperature difference between the cooling source and the demand, and thus raising the overall system energy efficiency.

Automated summary

This study demonstrates a novel stratified storage tank of PCM-in-water nano-emulsion for cold storage in building radiant cooling applications, through experimental and numerical studies. The experimental results show that the cooling capacity of a cooling panel increases by 60% with phase change emulsion circulating in the loop, while the effective energy storage capacity of the stratified storage tank is 1.6-1.7 times that of water.