Absence Of Porous Medium Research Articles

Numerical analysis of the flow dynamics in Maxwell hybrid nanofluid flow with gyrotactic microorganisms over a permeable stretching surface with convective and zero-mass flux conditions: A comparative analysis

This study observes the 2-D flow of a Maxwell hybrid nanofluid flow on a permeable stretching surface containing Cu and CuO nanoparticles and gyrotactic microorganisms. The thermal convective and zero-mass flux constraints are adopted by incorporating a hot working fluid with a heat transfer coefficient and zero mass flow at the permeable sheet’s surface to investigate the heat transfer rate. This study is designed to present a comparative analysis of the nanofluid (Cu–water) as well as hybrid nanofluid (Cu–CuO/water) flows on a stretching sheet. Examining activation energy in water-based hybrid nanofluid flow offers important insights into the kinetics of chemical reactions, which in turn helps to optimize the features of the nanofluid and build more effective systems that use nanofluids for a variety of applications. The problem formulated initially is converted to dimension-free notation using appropriate variables for finding the numerical solution by incorporating the bvp4c MATLAB function. From the obtained results, it is found that the higher magnetic and porosity factors have declined the velocity profiles. Also, in the absence of porous media and magnetic field effects, the velocity distribution is highly affected when compared with the existence of these effects. It is observed that the velocity profiles of both nanofluids are dominant for Newtonian fluid in comparison to non-Newtonian fluid. Also, the thermal profiles of both nanofluids are dominant for non-Newtonian fluid in comparison to Newtonian fluid. The friction force of hybrid nanofluid is significantly influenced by the magnetic factor, porosity factor, and volume fractions of the solid nanoparticles when compared to nanofluid.

Visualization of thermo-magnetic natural convective heat flow in a square enclosure partially filled with a porous medium using bejan heatlines and Hooman energy flux vectors: Hybrid fuel cell simulation

The aim of the article is to study the magneto-convective laminar incompressible flow within a differentially heated square enclosure partly filled with porous medium saturated with ionized helium gas in the presence of a transverse magnetic flux, as a model for emerging fuel cell designs. A Darcy model is utilized for porous medium bulk drag effects. Visualization of heat line and energy flux vectors is computed via Bejan's heat line approach and the Hooman energy flux vector method. The horizontal (i.e., bottom and top) wall boundaries are considered adiabatic and impermeable, while the side walls (cold and hot walls) are maintained at different but constant temperatures. The nonlinear coupled conservation equations under prescribed boundary conditions are solved with a finite difference-based vorticity-stream function approach. Appropriate convergence criteria factors are deployed. Furthermore, validation with earlier studies for the purely fluid, non-magnetic case i. e. in the absence of porous medium (Da) and Hartmann number (Ha) effects, is included. A parametric examination of the impact of Rayleigh number (Ra), Darcy number (Da) and Hartmann number (Ha) on temperature contours, heat lines, energy flux vectors and streamline patterns for ionized helium gas (Prandtl number, Pr = 0.71) is conducted. An increment in Hartmann magnetic number decreases the magnitudes of heat lines, suppresses heat transmission in the enclosure and curtails flow circulation. Enhancing the magnetic parameter and Rayleigh number however boosts the average heat transfer rate. Average Nusselt number at the left hot wall is elevated with increasing permeability of the porous medium and Rayleigh number. Mid-section velocities are enhanced in the porous layer but depleted in the non-porous layer of the enclosure with greater Rayleigh number. The simulations find provide some insight into applications in emerging hybrid electromagnetic fuel cells enabling better visualization of the thermal/fluid characteristics via the novel heat flow visualization heat-function and energy flux vectors analogy.

Novel hybrid thermal management for Li-ion batteries with nanofluid cooling in the presence of alternating magnetic field: An experimental study

Lithium-ion batteries' dependability, efficiency, and security significantly rely on thermal management systems. This paper aims to design a novel battery thermal management system consisting of metal foam-paraffin PCM composite, nanofluid cooling, and heat sink, which all were subjected to a magnetic field. The battery surrogate was utilized to experimentally simulate the battery heat generation, where the occurrence of the thermal runaway was considered as the most crucial criterion for battery performance. The combined effect of various conditions on the paraffin wax melting process and maximum battery temperature was also investigated. Furthermore, the battery's temperature uniformity was also measured in the presence and absence of porous media. Compared to the base case, the maximum temperature of the battery in the best scenario was reduced by about 7.5 °C, while the working time of the system is increased by 179% at Re = 1250. Likewise, this improvement on battery cooling was 151% when the Reynolds number was 890. Further, the temperature difference of the proposed hybrid battery thermal management system (BTMS) was mainly below 4 °C. The experimental results revealed that the proposed hybrid BTMS has a striking cooling effect on eliminating the generated battery's heat and transferring it to the surrounding environment.

Structural dependence of effective mass transport properties in lithium battery electrodes

Scanning electrochemical microscopy (SECM) has recently been reported as a convenient technique to characterize the apparent diffusion coefficients in porous media (D⋆) such as lithium-ion battery electrodes. The technique relies on hemispherical diffusion at the probe in the presence and absence of porous media. However, transition towards cylindrical diffusion follows as the diffusion layer becomes comparable to the media thickness, gradually limiting direct correlation between D⋆ and the SECM probe steady state current. In this work, we examine the experimental parameters that define this transitional frontier using simulations. A best practice thickness criterium is derived that ensures that the measured steady state current is ≳ 90% of that found in the ideal hemispherical case. Below this thickness limit the response was found to follow an empirical formulation with only two variables. Fundamentally, this quantifies diffusion in the transition regime between hemispherical and cylindrical transport. Practically, this correction formulation may be included into standard steady-state current expression to account for the deviation from hemispherical transport in “thin” electrodes. The analysis consolidates SECM as a reliable tool to characterize liquid phase mass transport within porous films over wide range of thicknesses, including films supported on blocking substrates, like lithium-ion battery electrodes.

Visualization of Chemical Heavy Oil EOR Displacement Mechanisms in a 2D System

This study aims to develop a visual understanding of the macro-displacement mechanisms associated with heavy oil recovery by water and chemical flooding in a 2D system. The sweep efficiency improvements by water, surfactant, polymer, and surfactant-polymer (SP) were evaluated in a Hele-Shaw cell with no local pore-level trapping of fluids. The results demonstrated that displacement performance is highly correlated to the mobility ratio between the fluids. Surfactant and water reached similar oil recovery values at similar mobility ratios; however, they exhibited different flow patterns in the 2D system—reductions in IFT can lead to the formation of emulsions and alter flow pathways, but in the absence of porous media these do not lead to significant improvements in oil recovery. Polymer flooding displayed a more stable front and a higher reduction in viscous fingering. Oil recovery by SP was achieved mostly by polymer rather than due to the effect of the surfactant. The surfactant in the SP slug washed out residual oil in the swept zone without increasing the swept area. This shows the impact of the surfactant on reducing the oil saturation in water-swept zones, but the overall oil recovery was still controlled by the injection of polymer. This study provides insight into the fluid flow behavior in diverging flow paths, as opposed to linear core floods that have limited pathways. The visualization of bulk liquid interactions between different types of injection fluids and oil in the Hele-Shaw cell might assist in the screening process for new chemicals and aid in testing the production process.

Nonlinear electrohydrodynamic instability through two jets of an Oldroydian viscoelastic fluids with a porous medium under the influence of electric field

In the light of the viscous potential theory, a nonlinear instability of the surface waves propagating through two jets of viscoelastic fluids is scrutinized. The flow is jetting through porous media under the action of a uniform axial electric field. The Oldroyd B model is employed to characterize the rheological behavior of the viscoelastic fluid. A weakly nonlinear theory of wave propagation is deemed. A general dispersion relation and neutral curves are addressed and plotted for the different parameters. The Routh-Hurwitz criterion is utilized to determine the stability criteria. Several special cases are reported. It found that, in absence of porous media, the stability happens for large relaxation time and small retardation time. In addition, small retardation time leads to increase the elasticity of the fluid. Therefore, the stability is determined due to the elasticity of the fluid. However, in the presence of porous medium, the elasticity of the fluid decreases with the increase of relaxation time. Thus, the elasticity has a destabilizing effects. Furthermore, fluid viscosity has showed dual role of the stability diagram. Also, the case of Maxwell fluid is illustrated graphically. It is observed that Maxwell model is less stabilizing than Oldroyd model. The method of multiple time scale with the Taylor’s expansion is employed to conduct the well-known Ginzburg-Landau equation, which governs the nonlinear stability of the system. New several regions of stability and instability are identified due to the nonlinear effects.

Numerical investigations on convective heat transfer enhancement in jet impingement due to the presence of porous media using Cascaded Lattice Boltzmann method

The present numerical study using the Lattice Boltzmann method investigates the convective heat transfer characteristics in impinging jets due to the inclusion of porous media. A cascaded collision model is employed in the present study, and the comparison with BGK collision model shows that the cascaded collision model is more stable and computationally efficient. The local thermal non equilibrium model (LTNE) or the two energy equation model is used in the present study to account for the local thermal non-equilibrium arising between the fluid and solid phase temperatures due to the high solid to fluid thermal conductivity ratios associated with metallic porous foams saturated with air. Two jet impingement configurations with porous media are modeled: jet impingement over a porous heat sink and jet impingement through a porous passage. Jet impingement over a porous heat sink is observed to be deteriorating the convective heat transfer whereas jet impingement through a porous passage showed enhancement. A parametric study is carried out for the porous passage configuration by varying the porous passage width from twice the jet width (2W) to once the jet width (W) and varying the Darcy number from 2.75e-2 to 2.75e-4. Jet impingement through a porous passage of width equal to the slot jet width is found to enhance the stagnation Nusselt number by 60.7% and the average Nusselt number by 53.7% compared to the jet impingement configuration in the absence of porous media. Similarly, lowering the Darcy number helps in augmenting the stagnation Nusselt number, however, it did not show any influence on the Nusselt number in the wall jet region.

Experimental Investigation and Three-Dimensional Numerical Analysis of Ferroconvection Through Horizontal Tube Under Magnetic Field of Fixed Parallel Magnet Bars

This study includes experimental and three-dimensional numerical analysis of conjugate steady-state laminar forced ferroconvection of Newtonian incompressible ferrofluid through a horizontal circular pipe under constant heat flux and in presence of transverse magnetic field. The magnetic field was applied by two fixed parallel magnet bars at the beginning of the tube. To validate the thermohydrodynamic characteristics obtained by numerical results, appropriate experimental setup with accurate instrumentations was conducted. Based on presence and absence of porous media and solid rod inside of pipe, six conditions were compared for quantifying the heat transfer enhancement and effectiveness. Governing equations were discretized by finite volume method (FVM) and solved using the semi-implicit method for pressure linked equations (SIMPLE) algorithm and computational fluid dynamic (CFD) techniques. It was found that magnetic field, porous media, and solid rod increase heat transfer and pressure loss in the pipe such that solid rod has the best effect on heat transfer and worst effect on effectiveness.

EFFECT OF VARIABLE POROSITY ON COMPOSITE HEAT TRANSFER IN A BOUNDARY LAYER FLOW

The effects of variable porosity and thermal conductivity of a medium, and also the emission, absorption, and scattering of radiation, are studied in this paper. A comparative study has been made for three different situations, namely, (1) variable porosity; (2) constant porosity; and (3) absence of porous medium. In carrying out the solution, as a first step the temperature profile within the radiation layer is determined and hence the heat transfer in the presence as well as in the absence of radiation parameter is obtained. The momentum and energy equations are coupled and they are solved simultaneously by the Runge-Kutta-Gill method in conjunction with the Newton-Raphson iterative scheme. The results of the analyses show that in the cases of variable porosity and absence of porous medium the velocity profiles possess very small curvature at the wall, whereas in the case of the constant porosity situation the velocity profile is almost zero up to a certain distance and then increases. Nevertheless, it reaches unity asymptotically in all three cases. The temperature profile becomes linear as the value of the ratio of the thermal conductivity of a solid to a fluid, λs/λf , increases. Another important result of the analyses is that the rise in temperature in a variable porosity medium is about 25% more in comparison with the absence of porous medium. Furthermore, the results show that the total heat flux in a variable porosity medium is about 79% more compared to a constant porosity medium, and the variable conductivity enhances the total heat flux by about 33% compared to the constant conductivity of the medium. The results also show that as the radiation parameter increases the total heat flux decreases in all three cases.

Gravitational Instability of Thermally Conducting Fluid in a Variable Magnetic Field Through Porous Medium with Hall Current

The flow of an infinitely extending homogenous self-gravitating thermally conducting fluid permeated through porous medium by a variable magnetic field has been investigated. The combined effect of several physical parameters, namely Hall current, finite conductivity, kinematic viscosity, thermal conductivity, nonextensive parameter as well as the porosity and permeability of porous medium on the system instability is studied in the framework of Tsallis statistics. The stability of the system is discussed both analytically and numerically. It is found that the Hall current and Alfven velocity have destabilizing effects while the medium permeability and porosity of porous medium have slightly destabilizing and stabilizing effects, respectively, and all other physical parameters have stabilizing effects, and also that the system has more stabilizing effect in the presence of porous medium than its effect in absence of porous medium. Keywords. Hydromagnetic stability; Tsallis'nonextensive theory; Jeans'instability; Thermal conductivity; Self-gravitating system; Hall current, Porous media.

The Determination of Effective Diffusivity Coefficients in a Solvent Gas Heavy Oil System for Methane

In this investigation, an accurate high pressure and temperature diffusion setup was applied to measure the diffusion coefficients of methane in Iranian heavy oils in presence and absence of porous media by using the pressure-decay method. The solvent diffusivity in heavy oil was determined by both graphical and numerical methods. In addition, the effects of the porous medium and the temperature on the molecular diffusion coefficient of the solvent gas in the liquid phase were discussed and finally, using experimental data, a functionality dependence of molecular diffusivity on temperature and porous medium characteristics was proposed.

Effects of radiation and magnetic field on the mixed convection stagnation-point flow over a vertical stretching sheet in a porous medium

This paper is concerned with the two-dimensional mixed convection boundary layer magnetohydrodynamic (MHD) stagnation-point flow through a porous medium bounded by a stretching vertical plate with thermal radiation. The stretching velocity and the surface temperature are assumed to vary linearly with the distance from the stagnation-point. The coupled partial differential equations are reduced into ordinary differential equations by using similarity transformations. The series solutions of the coupled non-linear system is obtained using an analytical technique namely the homotopy analysis method (HAM). Both cases of assisting and opposing flows are taken into account. The convergence, salient features of the flow and heat transfer characteristics are analyzed and discussed in detail through graphs. The values of skin friction coefficient and the local Nusselt number are tabulated in both cases of assisting and opposing flows. Comparison of the obtained results with the known numerical results (Ishak et al. (2006) [25]) of hydrodynamic flow in absence of porous medium and thermal radiation is made and an excellent agreement is noted.

Nonlinear Study of Stratified Fluid Through Porous Media

An analysis is presented to describe the effects of Darcy resistance, fluid inertia, and horizontal density gradient on a heterogeneous Boussinesq fluid saturated porous medium in the presence of the vertical gravitational field using the Forchheimer-Lapwood extended Darcy (DLF) equation. The fluid is initially at rest, and sets in motion owing to two forms of the initial density gradients. One is the constant initial horizontal density gradient and the other is the piecewise constant density gradient. In the case of the uniform initial horizontal density gradient a purely horizontal motion develops satisfying the nonlinear Forchheimer extended Darcy (FD) equation. Analytical solution of this equation is obtained and limiting solutions valid for the Darcy regime and for a nonviscous fluid in the absence of porous media are derived. A measure of the stability of the flow is discussed briefly using the Richardson number. A comparison between the nature of solutions satisfying the nonlinear and linear initial value problems is made. We found that the vertical density gradient varies continuously both with space z and time t but the horizontal density gradient remains unchanged. In the case of a piecewise constant initial density gradient with continuous distribution of density, stream function formulation is used and the solutions are obtained using time-series analysis. In this case the solution shows crowding of the density profiles in the lower half of the channel, reflecting an increase in density gradient and incipient frontogenesis there, because of the increase in circulation of the flow due to the piecewise initial density gradient. Copyright © 2001 by Begell House, Inc.

Convection in a porous medium with velocity slip and temperature jump boundary conditions

The onset of convection in a rarefield gas saturating a horizontal layer of a porous medium has been investigated using both Darcy and Brinkman models. It is assumed that due to rarefaction both velocity slip and temperature jump exist at the boundaries. The results show that (i) when the degree of rarefaction increases the critical Rayleigh number as well as the critical wave number for the onset of convection increases, (ii) stabilizing effect of temperature jump is more than that of velocity slip, (iii) Darcy model is seen to be the most stable one when compared to Brinkman model or the pure gaseous layer (i.e. in the absence of porous medium).

Composite heat transfer in a variable porosity medium bounded by an infinite flat plate

Heat transfer by simultaneous radiation and convection in a variable porosity medium bounded by an infinite flat plate is determined by solving momentum and energy equations. The problem is investigated for two different cases, viz., presence of porous medium and absence of porous medium. In the presence of porous medium both variable and constant porosity situations are studied. Similarity solutions are obtained for an isothermal and impermeable wall. The Kozeny-Blake expression connecting porosity and permeability is incorporated in the analysis for unified treatment. A parameter survey is made to study the effect of optical thickness, porous parameter, albedo scattering and ratio of conduction to radiation using Runge-Kutta-Gill method. The heating and cooling cases are considered for variable porosity situation. The results show that both convective and radiative components decrease with increase in porous parameter, and the inhomogeneity of the medium enhances heat transfer rate. The increase in optical thickness leads to decrease in both convective and radiative fluxes. For a particular value of wall emissivity (e w =0.5932116) the radiative flux is reduced to zero.

Water absorption by swelling seeds. II. Surface condensation boundary condition

The previously developed model of water absorption by a swelling seed has been applied to imbibition and germination of wheat seed with the limiting supply condition of purely water vapour transport both with and without the presence of a porous medium. Experimental imbibition and germination data show that with vapour transport, the rate of imbibition and germination of wheat decreases with increasing distance from the supply source and that competition for water vapour occurs between seed. This competition effect was verified by values of the flow pathway shape factor for vapour transport to seed, measured in a three-dimensional electrical analogue. After accounting for heat production and losses with vapour absorption and using appropriate values of the flow pathway shape factors, the equilibrium seed absorption isotherms were used to derive surface condensation boundary conditions for several imbibition situations. These calculations suggest that in the absence of porous media a significant temperature rise of the seed retards the rate of imbibition. By comparison, with a close-packed porous medium around the seed, the large thermal conductivity of the medium should maintain nearly isothermal conditions. Using a finite difference approximation, the swelling seed model and condensation boundary conditions are analysed to give predicted imbibition data which can be compared with experimental data. These results show good agreement between predicted and experimental imbibition in the absence of a porous medium. For seed embedded in a porous medium, the predicted imbibition rate significantly exceeds the experimental rate, but no account could be taken for restriction of seed swelling by the porous medium. The results are discussed in terms of their relevance to the sowing of seed in 'dry' seed bed conditions.