Numerics Applied Nanofluid Analysis in a Square Array Subchannel

Abstract

This dissertation treats the thermohydrodynamic performance of alumina (Al2O3) nanofluid in a square array subchannel featuring pitch-to diameter (P/D) ratio of 1.25 and 1.35 to check its applicability in a typical Pressurized Water Reactor (PWR) rod bundle under single phase turbulent flow condition. Two fundamental aspects of thermal hydraulics viz. augmentation of convective heat transfer coefficient and accompanied pressure drop have been discussed using pure water and different volume concentrations (0.5%, 1.5% and 3.0%) of water/alumina (Al2O3) nanofluids as coolant. A widely used and commercially available CFD package STARCCM+ (ver. 9.06.011) has been utilized to carry out numerical simulation by setting up flow as single phase, incompressible and turbulent for different inlet Reynolds number, Re spanning from 3×105 to 6×105. The realizable k-ε model is implemented to simulate turbulence inside subchannel. Despite the results of a simulation performed in a single subchannel may not be reliable for analyzing the entire rod bundle, however, their quantitative and qualitative similarity can readily be utilized as a preliminary step in fixing thermohydrodynamic parameters of a rod bundle. The numerical results revealed that convective heat transfer coefficient, h (W/m2.K) is augmented with increasing nanoparticle volume concentration in the subchannel geometry. While for the same inlet Re, maximum heat transfer increment of about 22% is achieved for 3.0% particle volume concentration of alumina nanofluid, using same mass flow rate at inlet boundary and for same vol.% it is observed that convective heat transfer coefficient of nanofluid is slightly lower compared to pure water. The pressure drop is found to be increased significantly with the augmentation of particle volume concentration of alumina nanofluid due to increased viscosity and density and in case of 3.0% volume concentration pressure drop increment is about 56% compared to that of pure water. Finally, a multiple regression analysis has been performed to propose a new correction factor for an existing correlation of square array subchannel to obtain Nusselt number, Nu more accurately for nanofluids in such geometry.