الفهرس 
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Abstract
Heat transfer plays an important role in numerous applications so augmentation of heat transfer is a subject of considerable interest to researchers as it leads to saving in energy and cost. Achieving higher heat transfer rates through the various augmentation techniques can result in substantial energy saving and more compact and less expensive equipment with higher efficiency. In the present work, the turbulent convective heat transfer and friction factor behavior of Al2O3/water nanofluid with various concentrations in a circular tube have been studied experimentally. The effect of using Al2O3 nanofluid with different volume fraction of the nanoparticles at different Reynolds number was investigated. Al2O3 nanofluid used at different concentration mainly 0.3%, 0.5%, 0.7% and 1% and Reynolds number ranged from 2,670 to 17,000. The working fluid flow (Pure water or Al2O3/water) is heated under uniform heat flux by means of an electric heater wrapped around the wall of the sample tube, The measurements showed that Nusselt number considerably increases with increasing Reynolds number, the average heat transfer coefficient for Al2O3/water nanofluid with concentration of 1% was found to be 1.5 time of that for pure water. The friction factor is noticed to be increased by 1.2 time to that given by using pure water. The Nusselt number is improved with the increase of nanofluid concentration. Higher heat transfer enhancement ratios and friction factor are found with using Al2O3/water nanofluid with concentration of 1%. The results show that the friction factor for 0.3% concentration of Al2O3/water is lower than that used at concentration of 1%. The maximum thermal performance factor which is 5.66 is found with the using Al2O3/water nanofluid of 1% concentration at Reynolds number of 13,000. Based up on experimental measurements
a generalized correlation is deduced for estimating the friction factor, Nusselt number and thermal performance with using water and Al2O3/water nanofluid for flow in circular tube under constant heat flux valid in the range of 2,670 < Re < 18,000, and the concentration range of nanofluid 0 < ɸ < 1%, 3.72 < Pr < 6.50.