R. Anandalakshmi

Numerical Simulations for the Analysis of Entropy Generation During Natural Convection in Porous Rhombic Enclosures

Entropy generation analysis has been introduced to investigate the effectiveness in heat transfer during natural convection within porous rhombic enclosures of various inclination angles ϕ for differential (case 1) and Rayleigh Benard (case 2), heating situations. The results are presented in terms of streamlines (ψ), isotherms (θ), and entropy generation maps (S θ and S ψ ). Entropy production on the basis of various heating patterns and geometrical orientations have been reported based on the relation between total entropy generation (Stotal) and average Nusselt number via Bejan Number, which relates the available thermal energy to irreversibilities.

Analysis of Convective Heat Flow Visualization within Porous Right Angled Triangular Enclosures with a Concave/Convex Hypotenuse

Analysis of natural convection in porous right angled triangular enclosures with a concave/convex hypotenuse has been carried out using the Bejans heatlines approach. A generalized non-Darcy model without Forchheimer term is employed for fluid flow in a porous matrix and the governing equations are solved by the Galerkin finite element method. The cavity is subjected to a thermal boundary condition of an isothermal cold left wall, isothermal hot curved right wall, and adiabatic bottom wall. Due to intense closed loop heatlines, thermal mixing is higher in convex cases compared to the concave case for all parameters. Average heat transfer rate is found to be largest in the concave hypotenuse case.

Heat Flow Visualization for Natural Convection in Rhombic Enclosures: Bejan’s Heatline Approach

The phenomena of natural convection within a rhombic enclosure filled with air (Pr = 0.71 ) for (a) isothermally (case 1) and (b) non-isothermally (case 2) heated bottom walls with various aspect-ratios has been studied numerically. In all the cases, top horizontal wall is maintained adiabatic and side walls are maintained cold. Galerkin finite element method with penalty parameter is used to solve non-linear coupled partial differential equations for flow and temperature fields. Poisson equation of streamfunction and heatfunction is also solved using Galerkin method. Simulations are carried out over a range of Rayleigh numbers and numerical results are presented in terms of streamfunction, heatfunction and temperature contours. Streamlines are useful to visualize the fluid flow whereas heatlines are used to study the heat energy distribution within the rhombic cavity. Heatlines are further used to visualize the trajectories of heat flow and zones of high thermal mixing. At lower Ra, heatlines are smooth circular arcs with low magnitude streamfunctions and heatfunctions and thus the heat transfer is conduction dominant. Asymmetric flow is observed for all the cases due to geometrical asymmetry. As Ra increases, buoyant force starts dominating and the magnitudes of streamfunctions and heatfunctions are found to be greater due to enhanced convection effect. Heatlines are distorted greatly showing complex heat distribution inside the cavity. It is observed that primary heat circulation cell is larger for greater tilt angles and thus thermal mixing is high. Heat transfer rates are also studied via local and average Nusselt numbers as functions of Ra and Pr on bottom, left and right walls. Various quantitative and qualitative features of Nusselt numbers have also been explained based on heatlines.© 2011 ASME