Effect of nanofluid and moving wall location on the characteristics of mixed convection flow in a lid-driven square cavity

Mixed convection of a nanofluid consisting of water and Al2O3 in an inclined enclosure cavity with using variable thermal conductivity and variable viscosity hasbeen studied numerically. The left and right walls are maintained at different constant temperatures while upper and bottom insulated walls. Two different caseswere considered based on moving wall position in the square cavity. In Case I the left vertical side (hot) moving upwards and In Case II the top side (adiabatic)moving rightwards. Two-phase mixture model has been used to investigate the thermal behaviors of the nanofluid for various volume fraction of nanoparticlesfrom 0% to 9%, Richardson numbers varying from 0.01 to 100 and constant Grashof number 104. The governingequations are solved numerically using the finitevolume approach. Results are presented in the form of streamlines, isotherms and average Nusselt number. Itwas found from the obtained results that the location of moving wall had most influence on increasing of average Nusselt number. Moreover the obtained resultsshowed that average Nusselt number increased with decrease in Richardson number. Finally the resultsobtained using variable thermal conductivity and variable viscosity of Khnafer formulas were compared to the results obtained by the Maxwell-Garnett modeland the Brinkman model. Significant differences are found between the magnitudes of heat transfer enhancement in the enclosure for two employed models that these differences are relatively small for φ=0.05.

Keywords:

Al2O3–Water Nanofluid , Mixed convection , Variable properties , Square cavity , Finite volume method