Mixed convection nanofluid flow in a non-Darcy porous medium with variable permeability: entropy generation analysis
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ORIGINAL PAPER
Mixed convection nanofluid flow in a non-Darcy porous medium with variable permeability: entropy generation analysis L Tlau and S Ontela* Department of Mathematics, National Institute of Technology Mizoram, Aizawl, Mizoram 796012, India Received: 13 September 2019 / Accepted: 13 April 2020
Abstract: The study discusses the issue of entropy generated in a mixed convection Cu–water nanofluid flow in an inclined channel filled with a non-Darcy porous medium with variable permeability taking into account the Navier slip and convection at the boundary. The equations of momentum and temperature are highly nonlinear and coupled, and these are solved using the homotopy analysis method after converting to the dimensionless form. The flow velocity and temperature expressions as required during the entropy generation analysis are obtained. Bejan number is also obtained which indicates the role of heat transfer and viscous dissipation in the entropy generation process. The consequences of the relevant flow parameters are discussed, and the results are shown graphically. It was observed that entropy is minimum just above the center of the channel width. Keywords: Entropy; Variable permeability; Nanofluid; Navier slip; Convective boundary
1. Introduction Ever since nanofluids were introduced to the world by Choi and Eastman [1], the subject of nanofluids has been constantly expanding. The nanofluids have augmented the thermal conductivity of the base fluid by up to 20% as reported by Lee et al. [2], which is considerably higher than other modes of heat transfer enhancement like extended surfaces. The interest in this topic was inflamed by promising and encouraging results in the field of automation, machining, electronics, biomedicine, etc. The recent developments and reviews of nanofluids and its applications were reported in the following literature [3–5]. The Darcy model for flow in a porous medium was extended by Brinkman and Forchheimer. This was done due to the failure of Darcian model at high velocity fluid flow and high porosity porous medium. Thus, for high porosity medium and fluid flows with high velocity, the Darcy model was extended to incorporate the inertial drag term. Accordingly, many researchers have incorporated the Darcy–Brinkman–Forchheimer model to study fluid flow in a porous medium embedded in different flow geometries. A numerical study was conducted by Al-Odat and Al-Ghamdi
*Corresponding author, E-mail: [email protected]
[6] on the unstable 2D MHD free convection flow past a perpendicular surface integrated into a non-Darcy porous media. They found that the increase in magnetic parameter lowered the boundary layers of both velocity and temperature, respectively. The magnetic effect of a thermally stratified free convection nanofluid stream past an upright plate embedded in a non-Darcy porous media was explored by Murthy et al. [7]. The thermal conveyance in the flow was significantly affected by the stratification. Rosca and Rosca [8] numerically solved a steady, mixed convec
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