Experimental Study on Concentration Effects on the Supercooling of Phase Change Material-in-Water Nanoemulsions.

In energy storage, energy transfer and thermal management applications, phase change material (PCM) nanoemulsions are promising; however, supercooling has always been an important issue in the research and application of PCMs. When supercooling occurs, the efficiency of energy storage applications may possibly be reduced. In this study, n-octadecane and n-eicosane (as core materials), and nonionic surfactants (hydrophile-lipophile balance value = 8) were used to prepare n-octadecane and n-eicosane emulsions with a mass concentration of 1–9%. The effects of particle size and operation temperature on emulsion viscosity were investigated, and the relationships between supercooling and the PCM particle size, PCM concentration and process cooling rates were analyzed. The results showed that small PCM particles could form a 2nd freezing point far from the melting point, resulting in a large supercooling degree. As the process cooling rates increased, the supercooling became more pronounced. However, when the high-concentration emulsion was mainly composed of small particles and subjected to low cooling rates, the concentration effect was significant, thereby decreasing the supercooling effect. [ABSTRACT FROM AUTHOR]