Comparative Numerical Investigation on Effect of Characteristic Parameters on Thermal Energy Enhancement by Alumina-Water and Cupric-Oxide-Water Nanofluids

摘要

Heat transfer forms the basis of conversion of one form of energy to another. Increasing heat transfer area by using conventional methods of geometry design can increase the output temperature but this leads to a bulky and costly thermal system. Passive techniques can decrease the cost. The research presented revolves around enhancement of heat transfer using nanofluids. Nanofluids are colloidal suspensions of nanoparticles in a base fluid (thermal fluids) such as water with excellent thermal characteristics. They enhance heat transfer by increasing the convective heat transfer and thermal conductivity of nanofluid as compared to base fluid by increasing heat transfer area. An analysis of hydrodynamically and thermally developing or simultaneously developing laminar forced convection of nanofluids in circular pipes subjected to a constant wall heat flux boundary condition has been performed by numerical method. The numerical analysis was conducted using parametric three dimensional (3D) computational fluid dynamics (CFD) simulation code ANSYS CFX. Alumina (Al_2O_3) and copper oxide (CuO) nanoparticles were employed in water as base fluid in a liquid single-phase constant thermophysical properties model. The effect of design factors of concentration, diameter, Reynold (Re) number, and type of nanofluid on heat transfer coefficient (h), Nusselt (Nu) number, and pressure drop (ΔP) is investigated for different axial locations. Results reveal that increasing particle concentration from 1% to 5% increases the heat transfer coefficient for Al_2O_3-water by more than 5% similar to that by Re number. CuO shows little heat transfer enhancement due to high density and low thermal conductivity. Velocity increases along the length of the pipe. Moreover, the results were validated with empirical/theoretical and experimental correlations and agreed with an error less than 5%.