Investigation of the effects of shell geometry and tube eccentricity on thermal energy storage in shell and tube heat exchangers

In this research, the combined effects of the shell geometry and downward eccentricity of the heat transfer tube on the melting behavior of the paraffin wax in shell and tube heat exchangers (HXs) are parametrically investigated. Different shell geometries with a wide range of eccentricity factors are studied while the mass of paraffin in all geometries is kept constant. Transient numerical simulations using the enthalpy-porosity method have been carried out to explore the melt interface evolution, streamlines, heat transfer rates, average velocities, as well as thermal energy storages for all the considered cases. Results reveal that the melting rate accelerates by increasing the eccentricity of the HTF tube. Nevertheless, there is an optimum eccentricity factor for each geometry beyond which the melting rate reduces. The maximum melting time reduction compared to the concentric tube HX with circular shell (base case) was 50.4% obtained by the HX with circular shell at an eccentricity factor of 0.5. It was also concluded that increasing the eccentricity factor prolongs the convection-dominated melting time and shortens the conduction-dominated melting, and results in a more uniform heat transfer rate over the whole charging process which is important for the industrial deployment of the thermal storage units.