Arul K Prakash

The heat transfer characteristics of nanofluid produced by mixing nano titania with transformer oil, facilitated by addition of surfactants are analyzed. A 2D model is used to analyze the heat transfer and fluid flow characteristics of nano fluid for understanding the formation of hot spots in the chamber filled with nanofluid. Governing equations for conservation of mass, momentum and energy for capturing the above characteristics are described. The temperature along the vertical mid line from the hot spot are measured experimentally and compared with simulation results. Temperature distribution obtained for nanofluid and transformer oil under both steady and transient state has revealed high rate of heat dissipation in nanofluid. Streamlines have shown the presence of press board affects flow in the bulk of the cavity. Nusselt number estimated across the edges of the hot spot has shown higher convective heat transfer in nanofluid.

The present study investigates the fluid flow and heat transfer characteristics in a 180∘ bend domain with a bypass in the divider section using an in-house code based on Streamline Upwind Petrov-Galerkin Finite Element Method. The ratio of the inlet height to outlet height (IOR), location of the bypass (Lbyp) and Reynolds number (Re) are the parameters considered to assess the effects of heat transfer in a 180∘ bend. Flow in three IOR geometries i.e., IOR 1:2, 1:1, 2:1 with three Lbyp (−7, −5, −3) and Re in the range of 100–900 is investigated. IOR and Lbyp significantly affect the flow transitions from steady-state to periodic unsteady and finally to chaotic unsteady state. In this study, it is established that the IOR-bypass combination augments the heat transfer and decreases the pressure drop, which has been quantified using Thermal Performance Factor (TPF) and Nusselt number distribution (Nu). The increase in Nu and TPF for IOR 1:2 and 2:1 domains is higher than IOR 1:1 domains. A three-dimensional unsteady state investigation at Re=300 is also performed for IOR 1:2 with Lbyp=−7 to understand the convection of 3D vortices in the span-wise direction and its influence on heat transfer. From the 3D study, it is concluded that though the vortex shedding in the streamwise direction is similar to the 2D case, the spatial arrangement of 3D vortices along the span-wise direction is irregular at any given instant, which results in variable temperature and Nu distribution in the domain.

In the present study, fluid flow and thermal characteristics associated with forced convection cooling of an array of discrete protruding heat sources mounted on impingement plate of channel by an impinging laminar jet is investigated for various Reynolds number (Re) and channel height (H/L). It is observed that, the magnitude of average Nusselt number for all heat sources increases with increasing Re and decreasing H/L, except the regions of heat sources covered by recirculation bubbles which may be due to accumulation of heat resulting in hot spots. In order to eliminate these hot spots, a porous layer is attached to the impingement plate. A parametric study is conducted to predict the performance of porous layer on fluid flow pattern, heat transfer and entropy generation for various values of Darcy number (Da), Reynolds number (Re), channel height (H/L), porosity (∈) and porous layer thickness (h/H). For the purpose, equations governing two-dimensional, time-dependent, incompressible and laminar flow are solved in a Cartesian framework by using Streamline Upwind Petrov-Galerkin (SUPG) Finite Element (FE) method. The generalized Darcy-Forchheimer-Brinkman model is adopted to model the flow in porous medium. The recirculation bubbles on heat sources are completely eliminated with the inclusion of porous layer at Darcy number, Da=10-2. The magnitude of overall Nusselt number and global entropy generation due to heat transfer (Sθ,Ω¯) and fluid friction (Sψ,Ω¯) increases with increasing Da,Re,h/H and decreasing ∈ and H/L. The optimum configuration for maximum heat transfer and minimum entropy generation is observed at Da=10-2,Re=1000,H/L=1.0,h/H=0.75 and ∈=0.5.

In this paper, fluid flow and heat transfer characteristics are analyzed numerically for fluid flow past two elliptic cylinders arranged in a tandem manner. The numerical computation was performed using an in-house code based on the SUPG - FEM algorithm. Isothermal boundary condition is imposed on the surface of both the elliptic cylinders. Parametric studies are carried out by varying the axis ratio of the elliptic cylinders (AR = 0.5, 0.8, and 1.0) and distance between the two cylinders (L/D = 1.5, 2.0, 2.5, 3.5, and 5.0) for different Reynolds numbers (Re = 50, 100, 150, and 200). Parameters such as pressure coefficient, drag coefficient, lift coefficient, Strouhal number, and Nusselt number are calculated for all the cases. It is observed that the critical spacing ratio (distance between the cylinders at which the mean drag coefficient shows a sharp increase) of the cylinders shifts toward a lower value at Re = 200 for AR = 0.5 and 0.8. It is also found that for both the cylinders, convective heat transfer increases for elliptic cylinders with lower axis ratio (AR = 0.5 and 0.8). Finally, correlations are derived for mean drag coefficient and average Nusselt number as a function of Reynolds number, spacing ratio, and axis ratio.