Turbulent forced convection of nanofluids in a circular channel

The heat transfer coefficient and pressure drop for the turbulent flow of nanofluids based on distilled water with differently sized particles of aluminum oxide and silicon are measured in a circular duct. The volume concentration of these particles ranged from 0.25 % to 2 %. Dependence of the heat transfer coefficient on the concentration of nanoparticles, as well as their size and material, is investigated. It is shown that the heat transfer coefficient is determined by the size of nanoparticles and their material. Therefore, there are certain situations when the heat transfer coefficient of nanofluids may be lower than that of the base fluid. Conditions, under which it occurs, are revealed. It is experimentally shown that the coefficient of nanofluids depends not only on the size of nanoparticles, but also on their material.