The aim of the present investigation is to analyze the effect of the motion of horizontal walls on the entropy generation and heat transfer rates in an entrapped triangular porous cavity during mixed convection. Two different thermal boundary conditions are considered as follows: (i) hot inclined walls and cold horizontal walls and (ii) cold inclined walls and hot horizontal walls. Overall, Re = 100 may be recommended at Prm = 0.026, 7.2, Gr = 105, and Dam = 10−4 to 10−2 within the upper and lower cavities for cases 1 and 2. © 2017 Taylor & Francis.

Satyajit Roy

Department of Mathematics

Tanmay Basak

Department Of Chemical Engineering

Pratibha Biswal

entropy

Mixed convection

entropy generation

Heat transfer rate

HORIZONTAL WALLS

INCLINED WALLS

LOWER CAVITY

POROUS CAVITIES

Thermal boundary conditions

TRIANGULAR CAVITIES

Heat transfer

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Role of various moving walls on entropy generation during mixed convection within entrapped porous triangular cavities

Numerical Heat Transfer; Part A: Applications

The aim of the present investigation is to analyze the effect of the motion of horizontal (cases 1a–1d) and vertical walls (case 2a–2c) on the entropy generation and heat transfer in a porous square cavity during mixed convection. The cavity is subject to the thermal boundary conditions such as the hot bottom wall, cold side walls, and thermally insulated top wall. Analysis has been done for various fluids with Prandtl number, Prm = 0.026–7.2, Grashof number, Gr = 105, Reynolds number, Re = 10–100, and Darcy number, Dam = 10−4–10−2. Numerical results are presented using streamfunction (ψ), local entropy generation due to fluid friction (Sψ), isotherms (θ), and local entropy generation due to heat-transfer (Sθ) contours. In addition, the total entropy generation (Stotal), average Bejan number (Beav), and overall heat-transfer rate at the hot bottom wall (Formula presented.) are analyzed and discussed. © 2016, Copyright © Taylor & Francis Group, LLC.

Analysis of entropy generation for mixed convection within porous square cavities: Effects of various moving walls

Entropy generation analysis is carried out during natural convection within entrapped porous triangular cavities for two cases based on the heating or cooling of the inclined and horizontal walls (case 1: hot inclined walls with cold horizontal walls and case 2: cold inclined walls with hot horizontal walls). The results are plotted in terms of the isotherms (θ), streamlines (ψ), and entropy generation maps (Sθ and Sψ). The total entropy generation (Stotal), average Bejan number (Beav), and average Nusselt number (or) as a function of Darcy number (Dam) at a high Rayleigh number (Ram = 106) have been studied for both cases 1 and 2 and the optimal case is recommended based on least Stotal and largest or. © 2016 Taylor & Francis Group, LLC.

Analysis of entropy generation during natural convection within entrapped porous triangular cavities during hot or cold fluid disposal

Computational studies on entropy generation during laminar mixed convection in porous square enclosures have been carried out based on Darcy-Brinkman-Forchheimer model using the penalty finite element method. Finite element simulations are performed for the isothermally hot bottom wall, adiabatic top wall, and isothermally cold side walls (case 1) or linearly heated side walls (case 2) or linearly heated left wall with isothermally cold right wall (case 3) for a wide range of modified Darcy numbers (10-5 ≤ Dam ≤ 10-2), Grashof numbers (Gr = 103-105), and modified Prandtl numbers (Prm = 0.026 and 7.2). Further, the effects of Dam on the total entropy generation (Stotal), average Bejan number (Beav), and average Nusselt number are discussed. It is found that Re = 100 is preferred over Re = 1 based on larger heat transfer rate with minimum entropy generation for Prm = 0.026 and 7.2, 10-5 ≤ Dam ≤ 10-2 at Gr = 105 for all the cases. © 2015 Taylor and Francis Group, LLC.

Analysis of entropy generation during mixed convection in porous square cavities: Effect of thermal boundary conditions

The strategic application of entropy generation concept for optimization of the natural convection process has been studied in the present work. The wall, AB is isothermally heated and walls, BC and DA are cooled in presence of adiabatic wall CD. The numerical results are presented in terms of isotherms (θ), streamlines (ψ) and entropy generation maps for heat transfer (S<inf>θ</inf>) and fluid flow (S<inf>ψ</inf>) for various modified Prandtl numbers (Pr<inf>m</inf>=0.015 and 1000), modified Darcy numbers (Da<inf>m</inf>=10-5--10-2) and modified Rayleigh numbers (Ra<inf>m</inf>=103 and 106). The maximum value of the entropy generation due to heat transfer (S<inf>θ, max</inf>) is observed at hot and cold junction points (A and B), due to high temperature gradient, irrespective of Da<inf>m</inf>, Pr<inf>m</inf> and inclination angles (ϕ). The active regions of S<inf>θ</inf> occur at top portion of the walls, BC and DA at high Da<inf>m</inf>(Da<inf>m</inf>=10-2) and high Pr<inf>m</inf>(Pr<inf>m</inf>=1000). The maximum value of entropy generation due to fluid flow (S<inf>ψ, max</inf>) is found at various locations on the walls of the cavity whereas significant S<inf>ψ</inf> is also observed in the interior regions due to the friction between counter rotating circulation cells. The heat transfer rate along the wall AB (Nu<inf>AB</inf>) and the total entropy generation (S<inf>total</inf>) are found to be constant for the conduction dominant regime (10-5≤Da<inf>m</inf>≤10-3) whereas non linear increasing trends are observed for convection dominant regime (10-3≤Da<inf>m</inf>≤10-2). The inclination angle ranges, 30° ≤ ϕ ≤ 50° and 25° ≤ ϕ ≤ 75° are optimal tilt angles for Pr<inf>m</inf>=0.015 and 1000, respectively based on minimum entropy generation and reasonable heat transfer rate at high Da<inf>m</inf>(Da<inf>m</inf>=10-2) with Ra<inf>m</inf>=106. © 2015 Taiwan Institute of Chemical Engineers.

Journal of the Taiwan Institute of Chemical Engineers

Role of entropy generation on thermal management during natural convection in tilted porous square cavities

Abstract Current work attempts to study the heatline patterns during natural convection for different types of Dirichlet heatfunction boundary conditions. The enclosures with various shapes (square, curved, trapezoidal, tilted square and parallelogrammic) are considered with various thermal boundary conditions such as (a) case 1: hot left wall, cold right wall and adiabatic horizontal walls, (b) case 2: hot bottom wall, cold left and right walls and adiabatic top wall and (c) case 3: hot bottom wall with other cold walls. Traditionally, the reference of heatfunction (Π=0) is assumed at the adiabatic wall and the implementation of reference (Π=0) may be non-trivial for the case with zero or multiple adiabatic wall(s). Various heatfunction boundary conditions have been formulated based on locations of Π=0 for systems with more than one adiabatic walls (case 1) or no adiabatic wall (case 3). As test problems, Π=0 is considered at the junctions of isothermal walls (cases 2 and 3) or on the isothermal wall (case 3). The governing equations are solved via the Galerkin finite element method at various Rayleigh numbers (103 and 105) and Prandtl numbers (Pr=0.015 and 7.2). The magnitudes of the heatfunctions change drastically with the location of the datum of Π (Π=0) whereas, the heat flow patterns remain same irrespective of the heatfunction boundary conditions. The gradients of heatfunctions or the heat flux along the active walls (hot/cold) are invariant of the choice of the reference (Π=0). The local and average Nusselt numbers are also independent of the choice of Π=0 and the Nusselt numbers are found to be identical with heatfunction gradients obtained with various locations of Π=0. Current work may be useful for heat flow visualization in various thermal systems involving complex thermal boundary conditions. © 2015 Elsevier Ltd.

Journal	Data powered by TypesetNumerical Heat Transfer; Part A: Applications
Publisher	Data powered by TypesetTaylor and Francis Ltd.
ISSN	10407782
Open Access	No