Numerical study of natural and mixed convection heat transfer between differentially heated cylinders in an adiabatic enclosure filled with nanofluid

The problem of natural and mixed convection in an adiabatic enclosure containing several pairs of hot and cold cylinders is studied numerically. Surface of the cylinders is maintained at the constant temperatures while walls of the enclosure are thermally insulated. The present study considered the effects of pertinent parameters such as; position and number of the cold cylinders, location and rotation direction of the heat source/sink, Rayleigh number, Richardson number, volume fraction, size (25nm <= d(p)<= 145nm) and type (Cu,Al2O3, TiO2) of the nanoparticles on fluid flow and heat transfer rate. The results indicate that heat transfer rate may increase or decrease by changing rotation direction of the hot and cold cylinders. Moreover, it is found that by changing the location of the heat source/sink from bottom-top to top-bottom configuration the heat transfer rate decreases significantly. Finally, the results show that by changing the position of the cold cylinder from vertical to horizontal mode, the average Nusselt number reduces dramatically. (C) 2015 Elsevier B.V. All rights reserved.