Abstract
Heat transfer enhancement and entropy generation are investigated in a nanofluid, stagnation-point flow over a cylinder embedded in a porous medium. The external surface of cylinder includes non-uniform transpiration. A semi-similarity technique is employed to numerically solve the three-dimensional momentum equations and two-equation model of transport of thermal energy for the flow and heat transfer in porous media. The mathematical model considers nonlinear thermal radiation, magnetohydrodynamics, mixed convection and local thermal non-equilibrium in the porous medium. The nanofluid and porous solid temperature fields as well as those of Bejan number are visualised, and the values of circumferentially averaged Nusselt number are reported. The results show that thermal radiation significantly influences the temperature fields and hence affects Nusselt and Bejan number. In general, more radiative systems feature higher Nusselt numbers and less thermal irreversibilities. It is also shown that changes in the numerical value of Biot number can considerably modify the predicted value of Nusselt number and that the local thermal equilibrium modelling may significantly underpredict the Nusselt number. Magnetic forces, however, are shown to impart modest effects upon heat transfer rates. Yet, they can significantly augment frictional irreversibility and therefore reduce the value of Bejan number. It is noted that the current work is the first systematic analysis of a stagnation-point flow in curved configurations with the inclusion of nonlinear thermal radiation and local thermal non-equilibrium.
Highlights
Convective-radiative heat transfer in porous media is of growing importance in a wide range of technological applications [1, 2]
Heat transfer enhancement and entropy generation are investigated in a nanofluid, stagnation-point flow over a cylinder embedded in a porous medium
The results show that thermal radiation significantly influences the temperature fields and affects Nusselt and Bejan number
Summary
Convective-radiative heat transfer in porous media is of growing importance in a wide range of technological applications [1, 2]. The increasing use of porous media in radiative energy systems such as solar collectors, solar reactors and porous burners has raised a pressing need for further understanding and modelling of this combined mode of heat transfer [3,4,5]. The use of magnetic effects in advanced energy technologies (e.g. cooling of nuclear fusion reactors) necessitates inclusion of magnetohydrodynamic effects in heat transfer analyses. The current work aims to respond to these needs through conduction of a numerical analysis on a generic configuration including a vertical cylinder covered by a porous medium and subject to an impinging flow. The primary objective is to understand the influences of pertinent parameters on this complex multiphysics problem
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