Investigation of heat transfer and rheology of a phase change material emulsion with a high concentration in surfactant.

The thermohydraulic characteristics of a secondary refrigerant consisting of a phase change material emulsion (PCME) were investigated. This PCME is a paraffin-in-water emulsion containing 30 wt.% of paraffin and a relatively high concentration of surfactant (5 wt.%). A fully instrumented 1 m long rectangular channel was used to conduct heat transfer experiments. Heat transfer coefficients during cooling inside the rectangular channel were determined. Furthermore, a specific test rig was used to perform experiments on the rheological behavior. Tests were carried out using a pipe viscosimeter at different temperatures for laminar flow. The stability of the emulsion was examined under thermal-mechanical loads. The experiments revealed a shear thinning behavior. Phase change of the PCM droplets was confirmed for high Reynolds number, while for low Reynolds number, the phase change remains uncertain. In addition, results showed a large supercooling degree and a very good stability but viscosity was found to be quite high.