Two Dimensional Simulation of Heat Transfer and Fluid Flow in a Rectangular Natural Circulation Loop Containing PCM Suspensions

A two-dimensional numerical simulation, via a finite difference method, of fluid flow and heat transfer in a rectangular natural circulation loop is presented to explore efficacy of using solid-liquid phase change material (PCM) suspensions as a heat transfer medium. A continuum mixture flow model is used for the buoyancy-driven circulation flow of the PCM suspensions together with an approximate enthalpy model to describe the solid-liquid phase change (melting/freezing) process of the PCM particles in the loop. Parametric simulations have been conducted for the pertinent physical parameters of a loop with fixed geometrical configuration in the following ranges: the modified Rayleigh number Ra* = 10⁹ ∼ 10¹³, the modified Stefan number Ste* = 0.05 ∼ 0.5, the particle volumetric fraction c_v = 0 ∼ 20%, and the modified subcooling factor Sb* = 0∼2.0. The melting/freezing processes of the PCM particles at the heated/cooled sections of the loop are closely interrelated in their inlet conditions of the suspension. Closer examination of numerical results reveals that there could be a flow regime in the parametric domain where heat transfer performance of the suspension circulation loop is significantly enhanced, due to contribution of the latent heat transport associated with melting/freezing of PCM particles.