Two phase flow simulation of conjugate natural convection of the nanofluid in a partitioned heat exchanger containing several conducting obstacles

In this paper, numerical results for conjugate natural convection flow and heat transfer in a heat exchanger divided by a partition with finite thickness and thermal conductivity are presented using Buongiorno's two phase model. A series of numerical simulation is carried out using the finite volume method over a wide range of the Rayleigh number (104 ≤ Ra ≤ 107), volume fraction (0 ≤ φ ≤ 0.05), diameter (25 nm ≤ dp ≤ 145 nm) and type of the nanoparticles (Cu, Al2O3 and TiO2). In addition, the effects of three types of influential factors such as: thermal conductivity ratio (0.1 ≤ Kr ≤ 25), orientation of conductive partition and segmentation of the conductive obstacle on fluid flow and heat transfer characteristics are investigated. Results show that at low Ra, by dividing the conductive obstacle into the nine small segments, the heat transfer rate and absolute values of stream function decrease significantly. It is also observed that by increasing the Ra and thermal conductivity ratio (Kr) the heat transfer rate increase. Moreover, it is found that by changing the orientation of the conductive partition from vertical to horizontal mode, the heat transfer rate alters significantly. Finally, the results demonstrate that the effect of the thermophoresis force for solid particles with high thermal conductivity (like Cu) is negligible.