ABSTRACT
Properties such as density, specific heat, thermal conductivity, and viscosity of nanofluids are important parameters that quantify the transfer capability of a heat exchange process. The different values of a property reported by investigators can be due to the different stability criteria employed, in addition to particle distribution. The heat transfer coefficient (HTC) is dependent on flow velocity, base fluid and nanofluid properties, and volume fraction. It is observed that nanofluid forced convection HTC is greater than that of the base fluid for laminar and turbulent flows under similar operating conditions of flow and temperature. The ratio of nanofluid convection HTC to that of base fluid decreases with an increase in the Reynolds number. 2It attains an optimum value for a particle size and temperature, which is dictated by the ratio of viscosity to thermal conductivity enhancement. When working with nanofluids, a number of investigators reported higher values of pressure drop that increased with concentration.
The conventional equations for the estimation of the average Nusselt number under laminar flow deviate by more than 52% from the experimental data. In turbulent flow, equations reported in the literature predict the Nusselt number with a maximum deviation of 10%. However, the influence of material properties such as thermal conductivity, density, and specific heat on nanofluid forced convection heat transfer has not been investigated.
