Empirical equation to estimate viscosity of paraffin

Thermal energy storage (TES) systems using phase change materials (PCM) are nowadays widely developed to be applied in solar power plants or cooling and domestic comfort services. The design of a TES system does not only rely on the energy density that a PCM can provide, but also on other important material properties such as its rheological behavior when the PCM is melted. Viscosity varies with temperature, but the lack of an empirical equation predicting its value has lead researchers to simulate the system performance taking constant viscosity values which, consequently, have led to errors on the designs. As paraffin are one of the most common PCM types used, the present paper evaluates the rheology of four commercial paraffin with different phase change temperatures in order to find out an empirical equation for the whole paraffin family. A polynomial 3 model type equation has been found as the best one to predict paraffin viscosity.