scholarly journals Entropy Generation and MHD Convection within an Inclined Trapezoidal Heated by Triangular Fin and Filled by a Variable Porous Media

2021 ◽  
Vol 11 (4) ◽  
pp. 1951
Author(s):  
Ahmad Almuhtady ◽  
Muflih Alhazmi ◽  
Wael Al-Kouz ◽  
Zehba A. S. Raizah ◽  
Sameh E. Ahmed
Keyword(s):  
Inclination Angle ◽  
Hartmann Number ◽  
Phase Transfer ◽  
Particle Diameter ◽  
Fluid Phase ◽  
Bejan Number ◽  
Computational Domain ◽  
Fluid Friction ◽  
Variable Porosity ◽  
Triangular Fin

Analyses of the entropy of a thermal system that consists of an inclined trapezoidal geometry heated by a triangular fin are performed. The domain is filled by variable porosity and permeability porous materials and the working mixture is Al2O3-Cu hybrid nanofluids. The porosity is varied exponentially with the smallest distance to the nearest wall and the permeability is depending on the particle diameter. Because of using the two energy equations model (LTNEM), sources of the entropy are entropy due to the transfer of heat of the fluid phase, entropy due to the fluid friction and entropy due to the porous phase transfer of heat. A computational domain with new coordinates (ξ,η) is created and Finite Volume Method (FVM) in case of the non-orthogonal grids is used to solve the resulting system. Various simulations for different values of the inclination angle, Hartmann number and alumina-copper concentration are carried out and the outcomes are presented in terms of streamlines, temperature, fluid friction entropy and Bejan number. It is remarkable that the increase in the inclination angle causes a diminishing of the heat transfer rate. Additionally, the irreversibility due to the temperature gradients is dominant near the heated fins, regardless of the values of the Hartmann number.

A Numerical Solution of Variable Porosity Effects on Natural Convection in a Packed-Sphere Cavity

1991 ◽  
Vol 113 (2) ◽  
pp. 391-399 ◽  
Author(s):  
E. David ◽  
G. Lauriat ◽  
P. Cheng
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Particle Diameter ◽  
Fluid Phase ◽  
Momentum Equation ◽  
Spherical Particles ◽  
Porosity Variation ◽  
Nusselt Numbers ◽  
Variable Porosity ◽  
Prandtl Numbers

The problem of natural convection in differentially heated vertical cavities filled with spherical particles saturated with Newtonian fluids is investigated numerically. The Brinkman–Darcy–Ergun equation is used as the momentum equation, and the wall effect on porosity variation is approximated by an exponential function. The effect of variable stagnant thermal conductivities is taken into consideration in the energy equation. The formulation of the problem shows that the flow and heat transfer characteristics depend on six dimensionless parameters, namely, the Rayleigh and Prandtl numbers of the fluid phase, the dimensionless particle diameter, the conductivity ratio of the two phases, the bulk porosity, and the aspect ratio of the cavity. The influences of these parameters on the heat transfer rate are thoroughly investigated. The predicted Nusselt numbers are compared with existing experimental results. It is found that the computed Nusselt numbers based on the present model compare the best with experimental data.

scholarly journals Conducting dusty fluid flow through a constriction in a porous medium

2016 ◽  
Vol 5 (1) ◽  
pp. 29
Author(s):  
Madhura K R ◽  
Uma M S
Keyword(s):  
Porous Medium ◽  
Hartmann Number ◽  
Equations Of Motion ◽  
Fluid Phase ◽  
Dust Particles ◽  
Governing Equations ◽  
Electrically Conducting ◽  
Electrically Conducting Fluid ◽  
Flow Through ◽  
Constricted Channel

<p><span lang="EN-IN">The flow of an unsteady incompressible electrically conducting fluid with uniform distribution of dust particles in a constricted channel has been studied. The medium is assumed to be porous in nature. The governing equations of motion are treated analytically and the expressions are obtained by using variable separable and Laplace transform techniques. The influence of the dust particles on the velocity distributions of the fluid are investigated for various cases and the results are illustrated by varying parameters like Hartmann number, deposition thickness on the walls of the cylinder and the permeability of the porous medium on the velocity of dust and fluid phase.</span></p>

Effects of Viscous Dissipation and Radiation on MHD Natural Convection in Oblique Porous Cavity with Constant Heat Flux

2017 ◽  
Vol 9 (2) ◽  
pp. 463-484 ◽  
Author(s):  
Ammar I. Alsabery ◽  
Habibis Saleh ◽  
Ishak Hashim
Keyword(s):  
Heat Flux ◽  
Natural Convection ◽  
Viscous Dissipation ◽  
Inclination Angle ◽  
Hartmann Number ◽  
Constant Heat Flux ◽  
Governing Equations ◽  
Constant Heat ◽  
Left Wall ◽  
Porous Cavity

AbstractEffects of viscous dissipation and radiation on MHD natural convection in oblique porous cavity with constant heat flux is studied numerically in the present article. The right inclined wall is maintained at a constant cold temperatureTcand the left inclined wall has a constant heat fluxqwith lengthS, while the remainder of the left wall is adiabatic. The horizontal walls are assumed to be adiabatic. The governing equations are obtained by applying the Darcy model and Boussinesq approximations. COMSOL's finite element method is used to solve the non-dimensional governing equations together with specified boundary conditions. The governing parameters of this study are Rayleigh number (Ra=10,100,200,250,500 and 1000), Hartmann number (0≤Ha≤20), inclination angle of the magnetic field (0° ≤ω≤π/2), Radiation (0≤R≤15), the heater flux length (0.1≤H≤1) and inclination angle of the sloping wall (–π/3≤ϕ≤π/3). The results are considered for various values of the governing parameters in terms of streamlines, isotherms and averageNusselt number. It is found that the intensity of the streamlines and the isotherm patterns decrease with an increment in Hartmann number. The overall heat transfer is significantly increased with the increment of the viscous dissipation and the radiation parameters.

Numerical Investigation of Local Entropy Generation for Laminar Flow in Rotating-Disk Systems

2010 ◽  
Vol 132 (9) ◽  
Author(s):  
Mohammad Shanbghazani ◽  
Vahid Heidarpoor ◽  
Marc A. Rosen ◽  
Iraj Mirzaee
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Laminar Flow ◽  
Entropy Generation ◽  
Generation Rate ◽  
Entropy Generation Rate ◽  
Bejan Number ◽  
Local Entropy ◽  
Fluid Friction ◽  
Local Entropy Generation

The entropy generation is investigated numerically in axisymmetric, steady-state, and incompressible laminar flow in a rotating single free disk. The finite-volume method is used for solving the momentum and energy equations needed for the determination of the entropy generation due to heat transfer and fluid friction. The numerical model is validated by comparing it to previously reported analytical and experimental data for momentum and energy. Results are presented in terms of velocity distribution, temperature, local entropy generation rate, Bejan number, and irreversibility ratio distribution for various rotational Reynolds number and physical cases, using dimensionless parameters. It is demonstrated that increasing rotational Reynolds number increases the local entropy generation rate and irreversibility rate, and that the irreversibility is mainly due to heat transfer while the irreversibility associated with fluid friction is minor.

Theoretical Study on Premixed Flames of Nano Aluminum Particles and Water Mixture

2013 ◽  
Vol 284-287 ◽  
pp. 567-571
Author(s):  
Jun Su Shin ◽  
Hong Gye Sung
Keyword(s):  
Reaction Zone ◽  
Aluminum Particle ◽  
Particle Diameter ◽  
Initial Pressure ◽  
Combustion Products ◽  
Flame Speed ◽  
Computational Domain ◽  
Water Mixture ◽  
Aluminum Particles ◽  
Preheat Zone

A theoretical model is proposed to investigate premixed combustion characteristics of Nano aluminum particles - water mixture. The effects of particle size, initial pressure, and temperature were considered as well. Computational domain is divided into 3 regions; preheat zone 1, preheat zone 2, and reaction zone. No reaction occurs in either of the preheat zones. Reaction zone, consisting of nano aluminum particles–steam mixture and the combustion products, is the region where reaction and heat-release occurs. Energy conservation is considered separately at each zones. The flame speed and temperature distribution are derived by solving the energy equation in each regime and matching the temperature and heat flux at the interfacial boundaries. Combustion time correlation of nano aluminum particle is also considered to imply complex aluminum combustion kinetics. Normalized flame speed is calculated as a function of pressure, initial particle diameter, and equivalence ratio and compared with experimental data.

A Differential Quadrature Solution of MHD Natural Convection in an Inclined Enclosure With a Partition

2008 ◽  
Vol 130 (2) ◽  
Author(s):  
Kamil Kahveci ◽  
Semiha Öztuna
Keyword(s):  
Magnetic Field ◽  
Heat Transfer ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Inclination Angle ◽  
Hartmann Number ◽  
Differential Quadrature ◽  
Flow And Heat Transfer ◽  
Inclined Enclosure ◽  
Vorticity Generation

Magnetohydrodynamics natural convection in an inclined enclosure with a partition is studied numerically using a differential quadrature method. Governing equations for the fluid flow and heat transfer are solved for the Rayleigh number varying from 104 to 106, the Prandtl numbers (0.1, 1, and 10), four different Hartmann numbers (0, 25, 50, and 100), the inclination angle ranging from 0degto90deg, and the magnetic field with the x and y directions. The results show that the convective flow weakens considerably with increasing magnetic field strength, and the x-directional magnetic field is more effective in reducing the convection intensity. As the inclination angle increases, multicellular flows begin to develop on both sides of the enclosure for higher values of the Hartmann number if the enclosure is under the x-directional magnetic field. The vorticity generation intensity increases with increase of Rayleigh number. On the other hand, increasing Hartmann number has a negative effect on vorticity generation. With an increase in the inclination angle, the intensity of vorticity generation is observed to shift to top left corners and bottom right corners. Vorticity generation loops in each region of enclosure form due to multicelluar flow for an x-directional magnetic field when the inclination angle is increased further. In addition, depending on the boundary layer developed, the vorticity value on the hot wall increases first sharply with increasing y and then begins to decrease gradually. For the high Rayleigh numbers, the average Nusselt number shows an increasing trend as the inclination angle increases and a peak value is detected. Beyond the peak point, the foregoing trend reverses to decrease with the further increase of the inclination angle. The results also show that the Prandtl number has only a marginal effect on the flow and heat transfer.

scholarly journals Formation of sediment patterns in channel flow: minimal unstable systems and their temporal evolution

2017 ◽  
Vol 818 ◽  
pp. 716-743 ◽  
Author(s):  
Aman G. Kidanemariam ◽  
Markus Uhlmann
Keyword(s):  
Pattern Formation ◽  
Channel Flow ◽  
Power Law ◽  
Particle Diameter ◽  
Migration Velocity ◽  
Box Dimension ◽  
Computational Domain ◽  
Clear Fluid ◽  
Interface Shear ◽  
The Mean

The phenomenon of sediment pattern formation in a channel flow is numerically investigated by performing simulations which resolve all the relevant length and time scales of the problem. The numerical approach employed and the flow configuration considered is identical to our previous study (Kidanemariam & UhlmannJ. Fluid Mech., vol. 750, 2014, R2), the only difference being the length of the computational domain. The latter was systematically varied in order to investigate its influence on the initiation and evolution aspects. By successively reducing the streamwise length, the minimum box dimension which accommodates an unstable sediment bed is revealed, thus determining the lower threshold of the unstable modes. For the considered parameter point, the cutoff length for pattern formation lies in the range 75–100 times the particle diameter (3–4 times the clear fluid height). We also simulate the flow in a very long streamwise box with a size of 48 times the clear fluid height (featuring well over one million particles), accommodating approximately 11 initial ripple units with a wavelength in the range of 100–110 particle diameters. The evolution of the amplitude of the patterns exhibits two regimes of growth: an initial exponential regime, with a growth rate independent of the chosen domain size, and a subsequent nonlinear regime which is strongly constrained by the domain length. In the small domain cases, after the initial exponential regime, the ripples evolve steadily, maintaining their shape and migration velocity, at a mean wavelength equal to the length of the domain. The asymmetric ripple shape is characterized by a spectrum which exhibits a power-law decay over the first few dominant non-dispersive modes propagating at the mean dune migration velocity. The rate of particle transport and the mean interface shear stress exhibited an increase with increasing ripple dimensions. Nevertheless, the relationship between the two was observed to be approximately described by the empirical power-law formula for sediment transport by Wong & Parker (J. Hydraul. Engng, vol. 132, 2006, pp. 1159–1168).

scholarly journals MHD dusty hybrid nanofluid peristaltic flow in curved channels

2021 ◽  
pp. 144-144
Author(s):  
Sameh Ahmed ◽  
Zenab Rashed
Keyword(s):  
Hartmann Number ◽  
Amplitude Ratio ◽  
Peristaltic Flow ◽  
Hybrid Nanofluid ◽  
Computational Domain ◽  
Governing Equations ◽  
Curved Channels ◽  
Runge Kutta Method ◽  
Temperature Distributions ◽  
Convective Process

This paper presents numerical simulations for a magnetohydrodynamic convective process in curved channels. The worked suspension consists of water as a based hybrid nanofluid and two types of the nanoparticles, namely, Cu and Al2O3. Two systems of the governing equations are formulated for the hybrid nanofluid and dusty phases. The hybrid nanofluid system is modeled in view of lubrication approach. The governing equations are mapped to a regular computational domain then they solved numerically using the fourth order Runge-Kutta method. The obtained findings revealed that the growing in the Hartmann number causes a reduction in both of the hybrid nanofluid and dusty velocities while the mixture temperature is enhanced. Also, the temperature distributions are supported when either the Grashof number or the amplitude ratio is altered.

Numerical Simulation of Electrochemical Reaction in Reconstructed Three-Dimensional LSM/YSZ Composite Cathode

2008 ◽  
Author(s):  
Tadahiro Nakagawa ◽  
Naoki Shikazono ◽  
Nobuhide Kasagi
Keyword(s):  
Evaluation Method ◽  
Volume Fraction ◽  
Three Dimensional ◽  
Particle Diameter ◽  
Electrochemical Characteristics ◽  
Computational Domain ◽  
Good Correspondence ◽  
Composite Cathodes ◽  
Modeling Techniques ◽  
Sr Method

In the present study, a novel computational scheme for the assessment of the activation polarization of LSM/YSZ composite cathodes is proposed. The scheme consists of modeling techniques of three-dimensional microstructures and an evaluation method of electrochemical characteristics. Two modeling techniques of microstructures are employed, i.e. the stochastic reconstruction (SR) method and the random packing model (RPM). In the SR method, the 3-D structure is reconstructed statistically from the two-point correlation function of the cross-sectional image of SEM-EDX. In RPM, on the other hand, spherical LSM and YSZ particles are randomly packed in the computational domain. This model is mainly used for the parametric survey, because control parameters used in the model have good correspondence to the parameters used in the actual cell manufacturing process. The lattice Boltzmann method coupled with the Butler-Volmer equation is employed for the detailed assessment of the electrochemical characteristics inside the constructed 3-D cathode microstructures. The oxygen diffusion and the electronic and ionic conductions are calculated simultaneously, and coupled with the charge transfer at the three-phase boundary (TPB) using the Butler-Volmer equation. As a result, potential, polarization and current density distributions are fully investigated. The results from the SR method reveal that the cathode sintered at 1150 °C shows the smaller overpotential than the cathodes sintered at 1200 and 1250 °C. The RPM results show that particle diameter and its standard deviation as well as volume fraction of species have large effects on the cathode performance.

CFD Simulation of Reaction and Heat Transfer Near the Wall of a Fixed Bed

2003 ◽  
Vol 1 (1) ◽  
Author(s):  
Anthony G. Dixon ◽  
Michiel Nijemeisland ◽  
Hugh Stitt
Keyword(s):  
Heat Transfer ◽  
Steam Reforming ◽  
Gas Flow ◽  
Cfd Simulation ◽  
Control Volume ◽  
Fixed Bed ◽  
Particle Diameter ◽  
Effect Of Temperature ◽  
Temperature Profiles ◽  
Computational Domain

Modeling of fluid flow, heat transfer and reaction in fixed beds is an essential part of their design. This is especially critical for highly endothermic or exothermic reactions in low tube-to-particle diameter ratio (N) tubes, such as are used in steam reforming and partial oxidation. In the simulations a near-wall section of an entire bed is used to create a simulation geometry that can be handled in the available computational domain. A full bed model was also available for validation of the wall-segment model. In the wall-segment approach a section of the bed is modeled in more detail, allowing for a relatively smaller control volume size and a more detailed view of the flow and heat transfer patterns. A simple model of a steam reforming process is used in the CFD simulation to incorporate the effect of reaction rate on temperature profiles in the bed. Simulations were performed under realistic industrial conditions of high temperature, pressure and gas flow rate, with gas properties corresponding to those of steam reforming. A constant wall heat flux was imposed, and various shapes of particles studied with heat sinks on the surface to simulate the reforming endothermic reaction, which is mainly confined to the surface of the pellet. Results will be presented showing the existence and effect of temperature profiles on the catalyst particles, and the effect on the local heat transfer rates of different gas compositions, corresponding to conditions at different locations along the catalyst tube. Local deactivation of catalyst particles can also lead to wall hot spots, or 'giraffe-necking' which can be well-reproduced by the simulations.

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