Effects of step height and particle diameter on the heat transfer and fluid flow of water-nanoencapsulated phase change material over the backward step

Abstract

In this work, effects of step height and particle diameter on the average heat transfer coefficient, pressure drop and thermal performance index of mixture of water and nanoencapsulated phase change material (NEPCM) over the backward step is examined numerically at different values of Reynolds number, wall heat flux and particle concentration. To validate numerical model, comparisons were made with experimental and other available works in the literature and good agreements were observed. Results show that an increase in the step height causes the heat transfer to decrease and increase thereafter. It is shown that addition of NEPCM to the pure water could enhance the heat transfer rate at high step height. Numerical findings declare that an increase in the particle diameter causes the heat transfer rate to increase and this increase is of little significance at low particle concentration. It is found that the increase in the step height dramatically results in the increase in the pressure drop while an increase in the particle diameter has nearly no effect on the pressure loss. Results indicate that the thermal performance index is a strong function of particle concentration and the best thermal performance index is obtained at low particle concentration.