Laminar Mixed Convection Heat Transfer Analysis in Horizontal Annuli using Hybrid Nanofluid

Heat transfer can be augmented by employing different methodologies and techniques, such as increasing either the heat transfer surface or the heat transfer coefficient between fluid and surface that allows high heat transfer rates in a small volume. The enhanced thermal behavior of nanofluids could supply a basis for a huge innovation in heat transfer intensification. Recently, a new type of nanofluid, known as hybrid nanofluid, which consists of a mixture of two different nanoparticles suspended in the base fluid like water. The present study deals with the analysis of laminar mixed convection heat transfer in horizontal annuli using hybrid nanofluid with the thermal boundary condition of constant heat flux at the inner wall and isothermal outer wall. The SIMPLER numerical algorithm is adopted in the present study. The hybrid nanofluid consists of water as base fluid and Ag-TiO2 as nanoparticles. The ratio of Ag to TiO2 is maintained as 1:3. Main objective of the present study is to compute numerically three-dimensional axis-symmetric, incompressible, steady, laminar flow through annular ducts to investigate the effect of the hybrid nanofluid Ag-TiO2/water on thermal-hydrodynamic characteristics. The analysis reveals that secondary flow due to the buoyancy forces plays an important role in augmenting heat transfer. The development of axial flow and temperature field are strongly found to be influenced by buoyancy. Nusselt number near the entrance region is found to be maximum, then attains a minimum value at a location slightly away from the entrance, and then starts increasing slowly due to the increased buoyancy effects. Finally, the flow becomes almost stable and a nearly constant value of Nusselt number is observed as the flow approaches fully development situation. At a given axial location Nusselt number was found to increase with increasing volumetric concentration of nanoparticle. The effect of Gr Radius ratio on the Nusselt number was also studied