Impacts of heated rotating inner cylinder and two-phase nanofluid model on entropy generation and mixed convection in a square cavity

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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Entropy Generation Analysis of Mixed Convection Flow in a Nanofluid Filled Porous Cavity Using a Two-Component Lattice Boltzmann Method

Volume 1: Compressors, Fans, and Pumps; Turbines; Heat Transfer; Structures and Dynamics ◽

10.1115/gtindia2019-2544 ◽

2019 ◽

Author(s):

Dhrubajyoti Kashyap ◽

Anoop K. Dass

Keyword(s):

Heat Transfer ◽

Boundary Conditions ◽

Mixed Convection ◽

Entropy Generation ◽

Lattice Boltzmann ◽

Lattice Boltzmann Model ◽

Convection Flow ◽

Mixed Convection Flow ◽

Two Phase ◽

Good Concordance

Abstract In the present work, a comprehensive analysis is made to understand the effect of velocity boundary conditions on the flow and thermal behaviour during mixed convection flow in a nanofluid-saturated porous square cavity. Two different velocity boundary conditions based on the movement of horizontal walls of the cavity are considered. The vertical fixed walls are differentially heated and the horizontal lids are thermally insulated. We have adopted the two-phase thermal lattice Boltzmann model (TLBM) for nanofluid system and modified this model to simulate nanofluid-filled porous medium by incorporating the Brinkman–Forchheimer-extended Darcy model. The current results provide good concordance with the published results computed through conventional numerical techniques. The detailed study of the heat transfer rate, entropy generation is made for discretely varying Richardson numbers (Ri) from 0.1 to 10 and Darcy numbers (Da) from 10−4 to 10−2 while maintaining Grashof number (Gr) at 104 and volume fractions of Cu nanoparticle (ϕ) less than equal to 5%. It is observed from the results that the optimal flow condition in terms of energy efficiency depends on the values of Ri and Da. From the viewpoint of both 1st and 2nd laws of thermodynamics, the performance of nanofluid is not satisfactory compared to the base fluid for current configurations as the augmentation of entropy generation with ϕ is more prominent compared to heat transfer enhancement.

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