Experimental study of the heat transfer characteristics of a paraffin-in-water emulsion used as a secondary refrigerant

A Phase Change Material Emulsion (PCME) is a multifunctional fluid consisting in a Phase Change Material (PCM) as paraffin, dispersed in an aqueous surfactant solution, usually water. PCMEs stand out as potential latent thermal fluid in comfort cooling applications. This article reports experimental results concerning the heat transfer behavior of a 30 wt% paraffin in water emulsion for a temperature range of 0-20 °C. Thermophysical properties of the emulsion were investigated. Then an experimental study of laminar forced convection heat transfer was performed. The convective heat transfer coefficient of the emulsion during cooling was determined in a specific experimental set-up. The setup consists mainly of two heat exchangers, having rectangular sections (80 × 6 mm2) of 1 m lengths. The results show that the emulsion is an attractive candidate for air conditioning applications. It has a heat capacity of 5894 kJ/kg, which is two times higher than water in the same temperature range. Furthermore, convective heat transfer performance for the studied PCME is improved with respect to water due to the use of paraffin. Correlations giving the local and global Nusselt numbers, depending on Reynolds and Prandtl numbers, were established.