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

Rathnam, V. Mani; Roy, Monisha; Basak, Tanmay

doi:10.1080/10407782.2016.1139976

Cited by 11 publications

(6 citation statements)

References 40 publications

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“…The obtained results showed that the entropy level increased for higher Rayleigh numbers and high irreversibility ratios. Rathnam et al 21 analyzed entropy production caused by laminar natural convection inside tilted triangular enclosures with different base angles. The optimal shape and tilt angle beside the Rayleigh number were indicated in terms of minimum entropy and maximum heat transfer.…”

Section: Introductionmentioning

confidence: 99%

CFD‐based analysis of entropy generation due to mean and fluctuating fields during turbulent natural convection in a square enclosure

2022

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The current study aims to numerically investigate the entropy generation during the natural convection flow of air in a square cavity. The governing equations for the conservation of mass, momentum, energy, and turbulence are solved using a control volume‐based technique employing the commercial code Fluent. Runs have been performed for both laminar and turbulent flow regimes by varying the Rayleigh number (Ra) from 103 to 1010. On the other hand, various viscous distribution coefficients (ϕ = 10−4, 10−3, and 10−2) and constant Prandtl number (Pr = 0.71) were considered. Given the conflicting perspectives in the literature regarding the entropy generation under turbulent regimes, more research is needed to better understand the impact that the fluctuating flow has on entropy production. The four terms of entropy generation inherent to turbulent natural convection (entropy generation due to dissipation in the mean and the fluctuating velocity fields in addition to the heat flux due to the mean and the fluctuating temperature) are computed in the present work and compared to calculations based on only mean values of temperature and velocity gradients. It was found that taking into account the fluctuating terms of temperatures and velocities augment the total entropy generation by 10.10%, 14.43%, and, 17.70%, up to 32.60%, respectively, for Ra = 5 × 108, Ra = 109, Ra = 1.58 × 109, and Ra = 1010. The gain shows the tendency to increase with the Rayleigh number. Thus, the fluctuating terms cannot be neglected particularly for high Rayleigh numbers. Furthermore, unlike entropy production due to the mean flow field, numerical outcomes reveal that the generated irreversibilities due to fluctuating flow are located around the upper hot and the lower cold corners of the heated walls. In addition, a numerical relationship between the first and the second laws of thermodynamics has been derived. A promising result that emerged from this study has shown that the Nusselt number and therefore the first law of thermodynamics is sufficient to estimate the heat part of entropy generation without the necessity of using the second law.

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Section: Introductionmentioning

confidence: 99%

CFD‐based analysis of entropy generation due to mean and fluctuating fields during turbulent natural convection in a square enclosure

2022

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“…Analysis of the variation of average Bejan number with Da illustrated that the fluid friction irreversibility contributes significantly to the increase in total entropy generation. Rathnam et al [19] studied the influence of the Rayleigh numbers (Ra = 10 3 −10 5 ), the Prandtl numbers (Pr = 1.5 10 −2 −10 3 ) and the base angles (φ = 45° and 60°) on entropy generation during natural convection in isosceles triangular cavities for various base angles or tilt positions. They were able to determine the most suitable parameters as well as geometric configuration to minimize the entropy generation.…”

Section: Introductionmentioning

confidence: 99%

Prandtl Number Effects on the Entropy Generation During the Transient Mixed Convection in a Square Cavity Heated from Below

Ferroudj¹,

Köten

Kachi

et al. 2021

Period. Polytech. Mech. Eng.

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This numerical study considers the mixed convection, heat transfer and the entropy generation within a square cavity partially heated from below with moving cooled vertical sidewalls. All the other horizontal sides of the cavity are assumed adiabatic. The governing equations, in stream function–vorticity form, are discretized and solved using the finite difference method. Numerical simulations are carried out, by varying the Richardson number, to show the impact of the Prandtl number on the thermal, flow fields, and more particularly on the entropy generation. Three working fluid, generally used in practice, namely mercury (Pr = 0.0251), air (Pr = 0.7296) and water (Pr = 6.263) are investigated and compared. Predicted streamlines, isotherms, entropy generation, as well as average Nusselt numbers are presented. The obtained results reveal that the impact of the Prandtl number is relatively significant both on the heat transfer performance and on the entropy generation. The average Nusselt number increase with increasing Prandtl number. Its value varies thereabouts from 3.7 to 3.8 for mercury, from 5.5 to 13 for air and, from 12.5 to 15 for water. In addition, it is found that the total average entropy generation is significantly higher in the case of mercury (Pr«1) and water (Pr»1) than in the case of air (Pr~1). Its value varies approximately from 700 to 1100 W/m3 K for mercury, from 200 to 500 W/m3 K for water and, from 0.03 to 5 W/m3 K for air.

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“…In the same way, Erbay et al [13,14], specify values which increase linearly with the Rayleigh number (Ra), starting at 10 -13 for Ra=10 2 to reach 10 -9 for Ra=10 6 , with constant steps of 10. Rathnam et al [15], use an order of magnitude analysis of parameters to evaluate the same ratio at 10 -3 . Magherbi et al [16], Ilis et al [17], De C. Oliveski et al [18], and Bouabid et al [19], consider this coefficient as an investigative parameter in the same way as the Rayleigh, or Prandtl numbers for example in [16], φ varies from10 −4 to 10 −1 and in [17-18-19], φ varies from 10 −4 to 10 −2 .…”

Section: Introductionmentioning

confidence: 99%

New Approach to Compute Accurately the Entropy Generation Due to Natural Convection in a Square Cavity

Boudebous

Ferroudj²

2021

E3S Web Conf.

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The idea to carry out an exercise to compare the calculation of entropy generation for unsteady natural convection in a square cavity with vertical sides that are maintained at different temperatures was motived by the observation, in the literature, of inaccurate or often erroneous results concerning the values of this significant physical entity. It then appeared necessary to reconsider this problem in order to ensure its consistent assessment. The new approach that we propose allows a direct access to the value of the entropy generation by considering the exact values of the thermophysical properties of the working fluid, which depends on the Prandtl and the Rayleigh numbers.

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

Cited by 11 publications

References 40 publications

CFD‐based analysis of entropy generation due to mean and fluctuating fields during turbulent natural convection in a square enclosure

CFD‐based analysis of entropy generation due to mean and fluctuating fields during turbulent natural convection in a square enclosure

Prandtl Number Effects on the Entropy Generation During the Transient Mixed Convection in a Square Cavity Heated from Below

New Approach to Compute Accurately the Entropy Generation Due to Natural Convection in a Square Cavity

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