Experimental analysis on rheological and heat transfer characteristics of paraffin/water emulsion.

Paraffin in water emulsions used as PCSs can theoretically provide an increase of the thermal storage capacity and high heat transfer characteristics. The aim of the present article is to report experimental results concerning both the rheological and heat transfer behavior of a paraffin/water emulsion. The results were obtained in a specific test bench: mainly consisting in a pair of symmetric cooled rectangular channels whose sizes are typical of plate heat exchangers. The local heat transfer coefficients along the fluid path during the crystallization of the paraffin are determined. The results demonstrate that an emulsion containing 30 %wt. paraffin has a Newtonian behavior. For laminar flow, the heat transfer coefficients of the emulsion are comparable to those for the single-phase fluid (water). Particular attention was given to the heat transfer phenomena: this led to the development of correlations for the local and overall Nusselt numbers that can be of practical interest when comparing the performances of a variety of fluids.