Numerical and experimental investigations of solid-liquid flow with mixed convection for microPCM applications.

摘要

The present study is both a numerical and experimental investigation into the two phase flow of a microPCM fluid in a circular tube with mixed convection. The PCM was octacosane encapsulated by a polyethylene shell to form a spherical particle with an average diameter of 20 microns. The microPCM particles were suspended in a 50/50 ethylene glycol water mixture. The flow was through a 0.00775 m diameter copper tube with a length of approximately 0.75m. A constant wall heat flux was supplied by an electric resistance wire. The flow was gravity fed with a pumped circulation to maintain a constant pressure head. Experimental measurements were made of the tube outer wall at the top and bottom of the copper tube. Numerically an incompressible flow model was used with an Eulerian-Eulerian method to solve the two phase momentum and energy equations. The numerical model was verified using experimental data of single phase flow with mixed convection available in literature and was also verified by thermal results of both single phase and two phase flow from the experimental work in the current investigation.;Through a numerical investigation of the experimental conditions it was found that when the slurry was not cooled to a temperature far enough below the inlet temperature a supercooling effect did not allow a full use of the latent heat available in the octacosane microPCM, only about 50% of the total latent heat was used in one case. Further numerical investigations included tube wall material in which stainless steel was compared to the copper tubing used in the experiment. The inclusion of the solid phase buoyancy term was found to affect the thermal solution. A comparison was also made of microPCM flow rates in which the Reynolds number, the mass flow rate, and the pump power were each held constant and the solutions compared. It was then recommended that a constant pump power be used as a basis for comparison. A parametric study was also completed in which the Rayleigh number and the Stefan number were both varied to find the effects on the thermal and hydrodynamic solution.