The effects of exothermic catalytic reactions upon combined transport of heat and mass in porous microreactors

Karimi

Nourbakhsh

2019

J Therm Anal Calorim

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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.

“…The volumetric rate of local entropy generation in the porous region of the problem can be expressed by the following relation [44][45][46][47][48]:…”

Section: Entropy Generationmentioning

confidence: 99%

Effects of radiation and magnetic field on mixed convection stagnation-point flow over a cylinder in a porous medium under local thermal non-equilibrium

Karimi

Nourbakhsh

2019

J Therm Anal Calorim

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“…The problem outlined in Section "Theoretical and numerical methods" was solved using various non-dimensional and dimensional parameters that are presented for quantitative analysis by the default values in Tables 2 and 3, respectively. It is noted that the values of parameters in Table 2 were chosen in a way that the results become comparable with the existing data in the literature for Newtonian fluids [1,3].…”

Section: Description Of the System Configurationmentioning

confidence: 71%

“…Catalytic porous microchannels, where catalytic channels of small sizes filled with porous media, have received increased interest in traditional and advanced chemical and energy technologies in the last decade. Featuring high surface-tovolume ratios, catalytic porous microchannels can readily achieve the desired performance on transport and chemical reactions [1][2][3]. Therefore, extensive studies have been reported in recent years on applications of catalytic porous microchannels [4][5][6][7].…”

Section: Introductionmentioning

confidence: 99%

Heat and mass transfer and thermodynamic analysis of power-law fluid flow in a porous microchannel

Sarafan

Fattahi

et al. 2020

J Therm Anal Calorim

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Transfer of heat and mass and thermodynamic irreversibilities are investigated in a porous, parallel-plate microreactor in which the working fluid is non-Newtonian. The investigated microreactor features thick flat walls with uneven thicknesses, which can be subject to different thermal loads. The dimensionless governing equations of the resultant asymmetric problem are first derived theoretically and then solved numerically by using a finite volume technique. This results in two-dimensional solutions for the velocity, temperature and concentration fields as well as the distributions of Nusselt number and local and total entropy generations. The results clearly demonstrate the significance of the numerical value of the power-law index and departure from Newtonian behavior of the fluid. In particular, it is shown that by increasing the value of power-law index the Nusselt number on the wall decreases. This leads to the intensification of the temperature gradients in the system and therefore magnifies the local and total entropy generations. Also, it is shown that the wall thickness and thermal asymmetry can majorly affect the heat transfer process and thermodynamic irreversibility of the microreactor. It is noted that the current work is the first comprehensive study of heat transfer and entropy generation in porous micro-chemical reactor with non-Newtonian, power-law fluid.

“…Considering a strongly temperature-dependent reaction rate and thermal diffusion of mass (Soret effects), the conservation of chemical species becomes [39,41,42]…”

Section: The Studied Configuration Governing Equations and Assumptionsmentioning

confidence: 99%

Application of Machine Learning to Investigation of Heat and Mass Transfer Over a Cylinder Surrounded by Porous Media—The Radial Basic Function Network

Journal of Energy Resources Technology

Abad

Fattahi

et al. 2020

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This paper investigates heat and mass transport around a cylinder featuring non-isothermal homogenous and heterogeneous chemical reactions in a surrounding porous medium. The system is subject to an impinging flow, while local thermal non-equilibrium, non-linear thermal radiation within the porous region, and the temperature dependency of the reaction rates are considered. Further, non-equilibrium thermodynamics, including Soret and Dufour effects are taken into account. The governing equations are numerically solved using a finite-difference method after reducing them to a system of non-linear ordinary differential equations. Since the current problem contains a large number of parameters with complex interconnections, low-cost models such as those based on artificial intelligence are desirable for the conduction of extensive parametric studies. Therefore, the simulations are used to train an artificial neural network. Comparing various algorithms of the artificial neural network, the radial basic function network is selected. The results show that variations in radiative heat transfer as well as those in Soret and Dufour effects can significantly change the heat and mass transfer responses. Within the investigated parametric range, it is found that the diffusion mechanism is dominantly responsible for heat and mass transfer. Importantly, it is noted that the developed predictor algorithm offers a considerable saving of the computational burden.