Numerical modeling of convective heat transfer of thermally developing nanofluid flows in a horizontal microtube

In this study, forced convection heat transfer of alumina-water nanofluid (1-3 vol%) flows was investigated inside a microtube for Reynolds numbers ranging from 500 to 2000 using the Eulerian multiphase model. In the Eulerian model, the Brownian motion, thermophoresis effect and particle-particle interactions were taken into account. The single phase (homogeneous) model was also congruently implemented to compare with the implemented two-phase (suspended particle) model. In the single phase model, four sets of the most used correlations (viscosity, conductivity) were utilized to study the effect of different correlations on convective heat transfer. Convective heat transfer in a microtube with a length of 12 cm and inner and outer diameters of 500 and 700 μm, respectively, was modeled with relevant boundary conditions. The inlet temperature was set as 293 K, the atmospheric pressure was maintained at the outlet, and constant heat flux ranging from 25 to 300 kW/m2 was imposed on the channel walls. Having validated the model, the effects of volume fraction on heat transfer and flow characteristics were discussed in detail. The velocity and temperature profiles of two phase model were obtained. The results of numerical modeling indicated that adding nanoparticles to the base fluid significantly changed velocity profiles and enhanced heat transfer. While the addition of 3 vol% alumina nanoparticle to the base fluid at Reynolds number of 2000 led to an enhancement in convective heat transfer up to 50%, the single phase model resulted in an enhancement of about 15%. It was observed that the homogeneous (single-phase) model underestimated thermal and hydrodynamic results of nanofluid flows.