A comprehensive numerical study on entropy generation during natural convection is studied in a square cavity subjected to a wide variety of thermal boundary conditions. Entropy generation terms involving thermal and velocity gradients are evaluated accurately based on the elemental basis set via the Galerkin finite element method. The thermal and fluid irreversibilities during the conduction and convection dominant regimes are analyzed in detail for various fluids (Pr=0.026,988.24) within Ra=103-105. Further, the effect of Ra on the total entropy generation and average Bejan number is discussed. It is observed that thermal boundary conditions significantly affect the thermal mixing, temperature uniformity, and the entropy generation in the cavity. A case where the bottom wall is hot isothermal with linearly cooled side walls and adiabatic top wall is found to result in high thermal mixing and a higher degree of temperature uniformity with minimum total entropy generation. Copyright © Taylor &amp; Francis Group, LLC.

Tanmay Basak

Department Of Chemical Engineering

Ram Satish Kaluri

Arcot R. Balakrishnan

Basis sets

Bejan number

BOTTOM WALL

entropy generation

FLUID IRREVERSIBILITY

GALERKIN FINITE ELEMENT METHODS

HIGH THERMAL

HIGHER-DEGREE

Numerical studies

SIDE WALLS

Square cavity

TEMPERATURE UNIFORMITY

Thermal boundary conditions

THERMAL MIXING

TOTAL ENTROPY

VELOCITY GRADIENTS

Boundary conditions

finite element method

Natural convection

entropy

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

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IIT Madras

Effects of Thermal Boundary Conditions on Entropy Generation during Natural Convection

Numerical Heat Transfer; Part A: Applications

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.

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

The entropy generation minimization (EGM) technique is an important tool for the optimization of the thermal systems via the analysis of the associated irreversibilities measured by the entropy generation. This article presents a detailed review of works on the entropy generation analysis during natural convection in various enclosures and processes involving different practical applications. The mathematical formulations of the fundamental governing equations for natural convection followed by the equations of the entropy generation are presented. The calculation procedure of the entropy generation for various test cases is reported briefly with the finite difference and finite volume techniques for some test cases and the detailed discussion of the evaluation of the entropy generation via the finite element method is addressed. Further, the problem formulation and results in terms of the entropy generation are discussed for natural convection in enclosures of various shapes (square/rectangular, trapezoidal, triangular, parallellogrammic/rhombic, curved/wavy). The brief discussion on the entropy generation analysis during various practical applications is also addressed. Overall, the minimum entropy generation vs enhanced heat transfer rate is the main issue in all the case studies with various enclosures involving a number of practical applications to achieve the optimal configuration with the high energy efficiency. The need of the renewable energy is increasing day by day. Thus, the conversion of the renewable energy to a useful form is one of the most challenging processes and natural convection plays an important role in the conversion. The loss of the available energy via the entropy production during natural convection is highly important for the design of suitable energy systems. This review article further provides basis for future research on the entropy generation analysis during natural convection in order to improve the energy efficiency which may be applicable for various renewable energy systems. © 2017 Elsevier Ltd

Renewable and Sustainable Energy Reviews

Entropy generation vs energy efficiency for natural convection based energy flow in enclosures and various applications: A review

This paper presents a study of entropy generation during natural convection in a triangular enclosure with various configurations (cases 1 and 2 symmetric about Y-axis, and case 3 symmetric about X-axis) for the linearly heated inclined walls. The detailed analysis and comparison for the various base angles (φ = 45° and 60°) of the triangular enclosures have been carried out for Pr = 0.015 - 1,000 and Ra = 103 - 105. The results show that, case 3 configuration with the tilt angle φ = 60° may be the optimal shape based on the minimum total entropy generation (Stotal) with the high heat transfer rate at Ra = 105, irrespective of Pr. © 2016 Taylor & Francis.

Analysis of entropy generation during natural convection in tilted triangular enclosures with various base angles

Improved heat transfer is very important for the energy efficiency, higher performance, and size reduction of a system. In this context, the paper presents an efficient way for improving mixed convection heat transfer in a grooved channel by dividing total flow into main flow and injection under the assisting flow configuration. The influences of the pertinent injection parameters (e.g., position, size, and injection flow) are investigated systematically for Richardson number 0.1-10 and Reynolds number 50-200 using an in-house CFD code. The results reveal that performance with injection is always superior and heat transfer enhancement is found to increase from 50 to 218% depending upon injection, Richardson number, and Reynolds number. © 2015 Taylor and Francis Group, LLC.

Mixed convection heat transfer in a grooved channel with injection

Finite element simulations were carried out to analyze entropy generation during mixed convection inside square enclosures with an 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 Pr = 0.015-7.2, Re = 1-100, and Gr = 103-105. Local entropy maps are studied in detail, and the dominance of thermal (Sθ,l) and frictional (Sψ,l) irreversibility is studied using Bejan number maps. In addition, variation in total entropy generation (Stotal), average Bejan number (Beav), and average Nusselt number at the bottom wall with Gr are analyzed to correlate irreversibility and the overall heat transfer rate of the system or process. It is found that, for Pr = 0.015 and 7.2, Re = 100 may be the optimal level for higher convective heat transport with minimum entropy generation in all the cases for Gr = 103-105. Copyright © 2015 Taylor & Francis Group, LLC.

Analysis of entropy generation for mixed convection in a square cavity for various thermal boundary conditions

A numerical study to investigate the steady laminar natural convection flow in a square cavity with uniformly and non-uniformly heated bottom wall, and adiabatic top wall maintaining constant temperature of cold vertical walls has been performed. A penalty finite element method with bi-quadratic rectangular elements has been used to solve the governing mass, momentum and energy equations. The numerical procedure adopted in the present study yields consistent performance over a wide range of parameters (Rayleigh number Ra, 103 ≤ Ra ≤ 105 and Prandtl number Pr, 0.7 ≤ Pr ≤ 10) with respect to continuous and discontinuous Dirichlet boundary conditions. Non-uniform heating of the bottom wall produces greater heat transfer rates at the center of the bottom wall than the uniform heating case for all Rayleigh numbers; however, average Nusselt numbers show overall lower heat transfer rates for the non-uniform heating case. Critical Rayleigh numbers for conduction dominant heat transfer cases have been obtained and for convection dominated regimes, power law correlations between average Nusselt number and Rayleigh numbers are presented. © 2006 Elsevier Ltd. All rights reserved.

International Journal of Heat and Mass Transfer

Effects of thermal boundary conditions on natural convection flows within a square cavity

Scaling of natural convection of an inclined flat plate: Ramp cooling condition

International Journal of Heat and Fluid Flow

Three-dimensional numerical study of natural convection in an inclined porous cavity with time sinusoidal oscillating boundary conditions

International Journal of Thermal Sciences

Effect of the days scrolling on the natural convection in an open ended storage silo

Unsteady natural convection induced by diurnal temperature changes in a reservoir with slowly varying bottom topography

Effects of thermal boundary conditions on entropy generation during natural convection

Journal	Numerical Heat Transfer; Part A: Applications
ISSN	10407782
Open Access	No