A novel thermal dispersion model to improve prediction of nanofluid convective heat transfer

摘要

This study numerically investigates the hydrothermal characteristics of the nanofluid in a laminar flow inside a straight tube. A new model is proposed for dispersion thermal conductivity while a theoretical approach is adopted to predict the particle distribution at the tube cross section considering the effects of non-uniform shear rate, Brownian diffusion and viscosity gradient on particle migration. It is observed that nanoparticles are not distributed uniformly at the tube cross section such that the values of concentration are higher at central regions of the tube and this non-uniformity intensifies at higher mean concentrations and Reynolds numbers. The particle distribution is applied in the proposed dispersion model. The findings show that this dispersion model presents more accurate results than traditional homogenous one. For dispersion model, the velocity profile is flatter than that obtained from the homogenous model. In addition, in the vicinity of the wall, the value of temperature and its gradient obtained from the dispersion model are respectively lower and higher than those from the homogenous model. Increasing the mean concentration results in convective heat transfer enhancement, while causing not much penalty in pressure drop. This indicates that application of nanofluids can result in energy efficiency improvement. (C) 2014 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.