Modelling and Simulation of Heat Transfer Enhancement Using Nanofluids

Abstract

Enhancement of heat transfer is possible through many techniques. One of the technique is to improve the properties of heat transfer fluid by adding nanoparticles into it called nanofluids. Numerical investigation of heat transfer enhancement in nanofluids is carried out in this work using the Fluent software. This study is carried out using single phase and multiphase approach and their results are compared. For numerical investigation of heat transfer enhancement, effective thermal conductivity and viscosity of nanofluid needs to be determined. Various researchers proposed different models for it. To identify appropriate model a study is carried out with widely used four models of thermal conductivity and dynamic viscosity. The property values predicted by these models are compared with experimental results for different fluid temperature, nanoparticles size and concentration for water-Al2O3 nanofluid. The result shows that amongst the four models of thermal conductivity and dynamics viscosity, thermal conductivity model proposed by Chon et al. [37] and dynamic viscosity model proposed by Maiga et al. [41] gives better results. When nanoparticle diameter is less than 20 nm prediction of the nanofluid thermal conductivity using Yu and Choi [33] model found to be better than other models. Numerical investigation is done for flow through a pipe in developing and fully developed flow regimes with constant heat flux boundary condition. The simulation results are validated with the existing experimental results. Parametric study is carried out by varying Reynolds number (laminar flow regime), nanoparticles size, base fluid material, nanoparticle material and nanoparticle concentration. Results show that heat transfer increases with lowering particle size, increasing Reynolds number and increasing particle concentration. Out of these three parameters, it is found that the effect of change of Reynold number is more dominant and increment in heat transfer ratio is more when nanoparticles are added to less viscous fluid compared to viscous fluid. As thermal conductivity of Cu is more than CuO and Al2O3 it is obvious that heat transfer enhancement is better when that is used in base fluid and similar results are obtained in the present study. Study shows that for developing flow, both single phase and multiphase approach works well. However, for fully developed flow, results differs significantly even at very low particle concentration (< 0.3%) of water-Al2O3 when single phase approach is adopted. For fully developed flow, two-phase mixture model predicts better results. Thus based on present study it can be concluded that for developing flow single phase approach works well. However, there is need to use two-phase approach for fully developed flow.