Thermal Performance of Microencapsulated Phase Change Material Slurry in a Coil Heat Exchanger

Abstract

An experimental study has been carried out to investigate the convective heat transfer and pressure drop characteristics of microencapsulated phase change material (MPCM) slurry in a coil heat exchanger (CHX). The thermal and fluid properties of the MPCM slurries were determined using a differential scanning calorimeter (DSC) and a rotating drum viscometer, respectively. The overall heat transfer coefficient and pressure drop of slurries at 4.6% and 8.7% mass fractions were measured using an instrumented CHX. A friction factor correlation for MPCM slurry in the CHX has been developed in terms of Dean number and mass fraction of the MPCM. The effects of flow velocity and mass fraction of MPCM slurry on thermal performance have been analyzed by taking into account heat exchanger effectiveness and the performance efficiency coefficient (PEC). The experimental results showed that using MPCM slurry should improve the overall performance of a conventional CHX, even though the MPCM slurries are characterized by having high viscosity.

Performance characteristics of microencapsulated phase change material slurry in a helically coiled tube

“…The experimental results clearly showed that the viscosity of MPCM slurry is independent of shear rate and the coefficient of variation r X of the viscosity is less than 1.2%. Therefore, it can be concluded that MPCM slurries behaves as Newtonian fluids at the tested mass fractions, ranging from 2.1% to 10.9%, which is consistent with previous experiments and observations [1,3,8,9]. Using the temperature-dependent viscosity data, the Andrade equation was used for estimating fluid viscosity as a function of fluid temperature, which is defined as follows:…”

“…For similar rheological properties of MPCM slurry, a higher latent heat of fusion of PCM can considerably lead to enhanced heat transfer performance. Relevantly, Kong et al [8] reported that the overall heat transfer coefficient of MPCM slurry, having a latent heat of fusion of 152 J/g, was higher than that of water when using an industrial coil heat exchanger. Fig.…”

“…In addition, the latent heat of fusion of the PCM (88 J/g) used in the study was relatively low to enhance Nusselt number. Recently, Kong et al [8] used methyl stearate microcapsules with a latent heat of fusion of 152 J/g and observed that PEC value for a 4.6% MPCM slurry was higher than one. It is evident that using MPCM slurry can enhance the overall performance of CHX by increasing heat transfer, even though the higher viscosity of MPCM slurry leads to a higher pressure drop (i.e.…”

“…In addition, the latent heat of fusion of the PCM (88 J/g) used in the study was relatively low to have any considerable effect on Nusselt number. Organic phase change materials with latent heat of fusion values in the range of 150-200 J/g had been used in previous studies [1,3,[6][7][8][9], which are approximately 1.7-2.3 times greater than the one used in this study. For similar rheological properties of MPCM slurry, a higher latent heat of fusion of PCM can considerably lead to enhanced heat transfer performance.…”

“…Their experimental results showed that the pressure drop for the MPCM slurry at 5.9% mass fraction was less than that for water. Kong et al [8] measured pressure drop of a MPCM slurry flowing through a coil heat exchanger (CHX). Experimental results showed that the pressure drop of the MPCM slurry increased with increasing MPCM concentration and fluid velocity.…”