Dynamic thermal characteristics analysis of microencapsulated phase change suspensions flowing through rectangular mini-channels for thermal energy storage

A numerical model of laminar forced convection heat transfer for microencapsulated phase change material (MPCM) suspensions with constant heat flux is developed. Phase change process and heat conduction in the microcapsules are solved using the equivalent heat capacity method and finite volume method (FVM). Heat convection of the flowing fluid is solved using FVM with internal heat source induced by the heat transfer resistance between the microcapsules and the working fluid. The influences of various factors are analyzed in detail. The results showed that Stefan number and mass fraction are the most basic factors influencing the heat transfer performance of the MPCM suspension. The maximum modified local Nusselts number enhancement reaches more than 190% for the 20 wt% MPCM suspension with Ste =1.5, where the tube wall temperature rises 50% slower than that of water. Sensitivity analyses of several parameters like Reynolds number, particle diameter and particle shell thickness are discussed. Effects of these parameters on heat transfer rate are not as sensitive as that of Stefan number and mass fraction. Evaluation of different aspect ratios of tube cross section with same flow rate is made, and a graphical expression with the tube aspect ratio of 3 is presented to illustrate the working mechanism of this type of heat transfer suspension. (C) 2016 Elsevier B.V. All rights reserved.