Heat transfer and entropy generation analysis of HFE 7000 based nanorefrigerants

摘要

In this study, two dimensional numerical simulations of forced convection flow of HFE 7000 based nanofluids in a horizontal circular tube subjected to a constant and uniform heat flux in laminar flow were performed by using single phase homogeneous model. Four different nanofluids considered in the present study are Al_2O_3, CuO, SiO_2 and MgO nanoparticles dispersed in pure HFE 7000. The simulations were performed with particle volumetric concentrations of 0, 1,4 and 6% and Reynolds number of 400,800,1200 and 1600. Most of the previous studies on the forced convective flow of nanofluids have been investigated through hydrodynamic and heat transfer analysis. Therefore, there is limited number of numerical studies which include both heat transfer and entropy generation investigations of the convective flow of nanofluids. The objective of the present work is to study the influence of each dispersed particles, their volume concentrations and Reynolds number on the hydrodynamic and thermal characteristics as well as the entropy generation of the flow. In addition, experimental data for Al_2O_3-wa-ter nanofluid was compared with the simulation model and high level agreement was found between the simulation and experimental results. The numerical results reveal that the average heat transfer coefficient augments with an increase in Reynolds number and the volume concentration for all the above considered nanofluids. It is found that the highest increase in the average heat transfer coefficient is obtained at the highest volume concentration ratio (6%) for each nanofluids. The increase in the average heat transfer coefficient is found to be 17.5% for MgO-HFE 7000 nanofluid, followed by Al_2O_3-HFE 7000 (16.9%), CuO-HFE 7000 (15.1%) and SiO_2-HFE 7000 (14.6%). However, the results show that the enhancement in heat transfer coefficient is accompanied by the increase in pressure drop, which is about (9.3-28.2%). Furthermore, the results demonstrate that total entropy generation reduces with the rising Reynolds number and particle volume concentration for each nanofluid. Therefore, the use of HFE 7000 based MgO, Al_2O_3, CuO and SiO_2 nanofluids in the laminar flow regime is beneficial and enhances the thermal performance.