Experimental Investigation of Natural Convection Heat Transfer Through Rectangular Enclosure Filled with TiO2-Water Nanofluid. (Dept. M. ( Power ))

Abstract

Experimental investigations on natural convection heat transfer have been carried out inside rectangular enclosures filled with TiO2water nanofluid. Two enclosures are used with two different aspect ratios of 1 and 2 and the modified Rayleigh number based on the enclosure height in the range 9 * 5 10 Ra 10   . The bottom surface of the enclosure is heated using a constant heat flux in the range from 40 to 6600 W/m while the upper surface is cooled by forced air stream, and side walls are insulated. The heat transfer rate for aspect ratio, AR=2, is higher than that for the aspect ratio A= 1. The average temperature of hot surface decreases with the increase of nanoparticles volume concentration,  , up to minimum values at  =0.8 % and then increases with further increase in  . The average hot surface temperature increases with the increase in the modified Rayleigh number. The heat transfer rate increases with the increase of the modified Rayleigh number up to maximum values of about 8 * 10  Ra and then decreases with further increase in * Ra . The highest value of the average Nusselt number is located at  = 0.8%. A general correlation is obtained for calculating the average heat transfer rate as a function of modified Rayleigh number and nanoparticles volume concentration.