Experimental Validation of Numerical Simulations of a Closed-Loop Thermosyphon Operating With Slurries of a Microencapsulated Phase-Change Material

Experimental validation and calibration of numerical simulations of a closed-loop thermosyphon operating under steady-state conditions with slurries of a microencapsulated phase-change material (MCPCM) suspended in distilled water are presented. The slurries exhibited a non-Newtonian, shear-thinning, power-law rheological behavior in the range of parameters considered; and the constants in the related model were calibrated using data from specially conducted experiments. The flows of these slurries in the problems of interest were laminar. Furthermore, the velocity and temperature differences between the dispersed and conveying phases of these slurries were negligibly small, so homogeneous models could be used for mathematical representations of the fluid flow and heat transfer phenomena. A hybrid numerical method was used in the simulations: detailed two-dimensional axisymmetric control-volume finite element (CVFEM) simulations of the heated and cooled sections of the thermosyphon were coupled with segmented quasi-one-dimensional finite volume (FVM) simulations of the other portions. The CVFEM and FVM used in this work are well-established. Thus, the verification of these methods is not addressed here. Rather, the details of the thermosyphon, effective properties of the MCPCM and slurries, overviews of the hybrid model and the aforementioned numerical methods, notes on the experimental calibration and validation, and some results are presented and discussed.