Experimental Investigation of Mixed Convection Heat Transfer in Vertical Tubes by Nanofluid: Effects of Reynolds Number and Fluid Temperature

An experimental investigation was carried out to study mixed convection heat transfer from Al2O3- water nanofluid inside a vertical, W-shaped, copper-tube with uniform wall temperature. The tests covered different ranges of some involved parameters including Reynolds number, temperature and particles volume fraction. The results showed that the rate of heat transfer coefficient improved with Reynolds number for average wall temperatures of 50 and 60ºC. Additionally, the heat transfer coefficient increased slightly with an increase of the Reynolds number. Interestingly, the pressure drop of nanofluid was very close to that of base fluid. Besides, a new correlation was proposed to calculate the Nusselt number in W-shaped tubes.