Layer Of Porous Medium Research Articles

Heat transfer and cold energy capacity properties of crushed-rock layer in cold sandy regions

Addressing the impact of climate warming and anthropic activities, crushed-rock layer (CRL) is a zero-carbon emission technology by using natural cold air to protect infrastructures in permafrost regions. But in cold sandy environment, the issue of its cold energy capacity on account of aeolian sand clogging needs to be solved. Based novel field experiments on Tibet Plateau, the dynamic evolution law and its controlling factors of natural cold energy accumulation of the CRL are quantitatively figured out. Results show that the initially open CRL had a strong forced convection of air in the first two winters, while the cooling effect was failure after the third winter. The filling of aeolian sand caused heat transfer mode of the CRL to change from forced convection to natural convection in cold season, losing the ability of “thermal semiconductor” aimed to mitigate permafrost degradation. The closed CRL represented weak natural convection in cold season and thermal insulation in warm season, which had better long-term cooling effectiveness than other conditions in the aeolian environment. As the thickness of the aeolian sand filling increased, the maximum Rayleigh number and natural convection time of the closed CRL decreased. Accumulation of cooling energy in cold season and thermal insulation in warm season were positive correlation with thickness of porous media layer. It was not recommended to solely adopt crushed rock embankment or crushed rock revetment in aeolian sand environment and regions with higher annual average temperature. The findings solved the scientific evaluation issue of cold energy storage capacity of CRL, and provided constructive engineering implications for its efficient application.

Theoretical and Experimental Study on the Performance of Photovoltaic using Porous Media Cooling under Indoor Condition

This paper presents the theoretical and experimental investigation on performance of a photovoltaic (PV) panel cooled by porous media under indoor condition. Porous media offer a large exterior surface area and a high fluid permeability, making them ideal for PV cells cooling. The photovoltaic panel was cooled using 5 cm thick cooling channel filled with porous media (gravel). Several sizes of porosity (0.35, 0.4, 0.48, and 0.5) at different volume flow rates (1, 1.5, 2, 3, and 4 L/min) were tested to obtain the best cooling process. The theoretical analysis was performed at the optimum case found experimentally, which has a porosity of 0.35 and a volume flow rate of 2 L/min, to test various experimental results of the PV hot surface temperature, related power output, efficiency and I-V characteristic curve. The enhancement obtained in PV power output and efficiency is compared against the case without cooling and the case using water alone without porous media. Results showed that cooling using small size porous media and moderate flow rate is more efficient which reduces the average PV hot surface temperature of about 55.87% and increases the efficiency by 2.13% than uncooled PV. The optimum case reduced the PV hot surface temperature to 38.7°C, and increased the power output to 19 W, efficiency to 6.26%, and the open voltage to 22.77 V. The results showed that the presence of small porous media of 0.35 in the PV cooling process displayed the maximum effectiveness compared to the other two scenarios, because the heat loss from PV surface through porous media layer have developed a homogenous heat diffusion removed much quicker at high flow rate (2 L/min). A good agreement was obtained between experimental and theoretical results for different cases with a standard deviation from 3.2% to 5.6%.

A new method to estimate the resistance coefficients of net panels modeled as porous media

Modeling net panels as thin porous media is an effective approach to carry out computational fluid dynamics (CFD) simulations of fishing nets and aquaculture cages. Existing methods to estimate the resistance coefficients for these porous media are based on simplified analytical models that relate these coefficients to the drag and lift coefficients of the panel. We propose a new method that uses a CFD model of the flow through a layer of porous media to estimate the resistance coefficients from regression analysis with experimental data. To increase the computational performance, the CFD model response is pre-calculated and interpolated in the regression analysis. The proposed method is applied to different net panels compared with existing methods. Results show that it provides better results than previous methods. Estimating both the inertial and the viscous resistance coefficients always provides better results than estimating just the inertial coefficients and it does not complicate the regression analysis with the proposed method. The method is easy to implement, fast and it could be used to estimate the resistance coefficients of materials other than net panels, since it does not make any assumption about the geometric characteristics of the actual material.

Experimental and numerical studies of mode switching performance and water transfer in unitized regenerative fuel cells with different channel structures

Different flow channel structures of unitized regenerative fuel cells have great effects on the flow process of reactive gas, liquid product and flowing purge gas inside channels and the transport process of them in the porous media layer. In this study, the unitized regenerative fuel cell with three different kinds of channel structures are designed and manufactured based on the numerical simulation. By utilizing the unitized regenerative fuel cell testing set-up, the output electricity performance test of the single cell in the fuel cell mode, electrolytic cell mode and mode switching process are realized, and effective verification data are provided for the two-phase model verification of unitized regenerative fuel cells. The results show that different channel configurations result in various performance behaviors during different procedures of the cell. Using the channel having 1 mm square cross-section structures can perform better start-up performance, compared to the T-wide and T-narrow section channels. When entering into electrolysis cell mode, compared to the cell with T-section channels, the output performance of the cell constructed with 1 mm square section channel is decreased obviously at the initial stage of start-up because of the residual water affecting. The present experiments combined with simulation works facilitate better understanding how the performance and two-phase species changing at the operating procedures of unitized regenerative fuel cells with different flow channels.

Bi-disperse convection under the action of an internal heat source

The aim of this paper is the investigation on hydrodynamic stability of an incompressible fluid saturating a horizontal layer of bi-disperse porous medium, heated from below and internally, in order to analyse the effect of the internal heat source on the onset of convective instabilities. The principle of exchange of stabilities is proved, so convection can arise only via stationary motions. Via linear instability and nonlinear stability analyses of the conduction solution, the linear threshold and the nonlinear threshold in the L2−norm for the onset of convective motions are determined and compared.

EFFECT OF VISCOUS DISSIPATION AND INTERNAL HEAT SOURCE ON MONO-DIFFUSIVE THERMOCONVECTIVE STABILITY IN A HORIZONTAL POROUS MEDIUM LAYER

A mathematical model is developed for studying the onset of mono-diffusive convective fluid flow in a horizontal porous layer with temperature gradient, internal heat generation, and viscous dissipation effects. Darcy's model is used for the porous medium, which is considered to be isotropic and homogenous. A linear instability analysis is conducted, and transverse or longitudinal roll disturbances are examined. The dimensionless emerging eigenvalue problem is solved numerically with the Runge-Kutta and shooting methods for both cases of disturbances, i.e,. longitudinal and transverse rolls. Critical wave number and critical vertical thermal Rayleigh number <i>R<sub>z</sub></i> are identified. For higher values of Gebhart number, Ge, a significant destabilizing effect of Hadley-Prats flow is computed. Internal heat generation also strongly modifies the critical vertical Rayleigh number. Extensive interpretation of the solutions related to the onset of convection is provided. The study is relevant to geophysical flows and materials processing systems.

The combined effects of rotation and anisotropy on double diffusive bi-disperse convection

In the present paper, double-diffusive convection, taking into account Coriolis effects, in a horizontal layer of Brinkman-anisotropic bi-disperse porous medium is analysed. Via linear instability analysis, we find that convection can set in through stationary or oscillatory motions and the critical Rayleigh numbers for the onset of stationary secondary flow (steady convection) and overstability (oscillatory convection) are determined.

Analysis of the steady-state pressure profile of a double-layered porous journal bearing under turbulent regimes

This theoretical investigation presented the steady-state pressure profile analysis of a hydrostatic double-layered porous journal bearing dealing with the Newtonian lubricant, including the effect of turbulence. Based on Beavers–Joseph's criterion for slip flow, the modified Reynolds equation applicable to finite porous journal bearings lubricated with Newtonian fluids has been derived. The governing equations for flow in the coarse and fine layers of porous medium and the modified Reynolds equation are solved simultaneously using the finite difference method satisfying appropriate boundary conditions. The effect of various design parameters (namely Reynolds number, slenderness ratio, eccentricity ratio, permeability factor, bearing number, and bearing feeding parameter) on the steady-state pressure profile of bearing is presented for both slip and no-slip conditions under laminar and turbulent flow.

A study on heat transfer feature and burning-decontamination rate of porous media bed soaked by combustible liquid

This work experimentally and theoretically investigated the heat transfer feature and burning-decontamination rate of porous media environment soaked (contaminated) by leaked combustible liquid. A series of fire tests were performed employing typical combustible liquid and porous media materials. The burning rate, temperature distribution, and flame appearance, etc., were measured and identified. Results show that the variation of burning-decontamination rate of porous media bed soaked by combustible liquid can be divided into two characteristic stages, and as liquid level drops, burning rate increases rapidly and then decreases gradually. In rapid growth stage, flame thermal feedback directly could affect the burning features of top-layer combustible liquid, while in the attenuation stage, the isolation of dry porous media layer to the direct effect of flame thermal feedback and the increasing surface heat loss collectively make the burning rate attenuate. This stage-variation characteristic represents the variation of the dominant mode of heat transfer. Based on the theoretical analysis of heat transfer process in different burning stages and the empirical fitting of flame height, an explicit prediction model for burning rate is established, and the model prediction results are in reasonableagreement with most of the experimental measurements within an acceptable error range. This work provides basic data and some references for burning-decontamination technology of porous media environment (e.g., soil, sand) contaminated by combustible liquid and corresponding fire safety issues.

Effects of trace PFOA on microbial community and metabolisms: Microbial selectivity, regulations and risks

Perfluorooctanoic acid (PFOA), a "forever chemical", is continuously discharged and mitigated in the environment despite its production and use being severely restricted globally. Due to the transformation, attachment, and adsorption of PFOA in aquatic environments, PFOA accumulates in the porous media of sediments, soils, and vadose regions. However, the impact of trace PFOA in the porous media on interstitial water and water safety is not clear. In this work, we simulated a porous media layer using a sand column and explored the effects of µg-level PFOA migration on microbial community alternation, microbial function regulation, and the generation and spread of microbial risks. After 60 days of PFOA stimulation, Proteobacteria became the dominant phylum with an abundance of 91.8%, since it carried 71% of the antibiotic resistance genes (ARGs). Meanwhile, the halogen-related Dechloromonas abundance increased from 0.4% to 10.6%. In addition, PFOA significantly stimulated protein (more than 1288%) and polysaccharides (more than 4417%) production by up-regulating amino acid metabolism (p< 0.001) and membrane transport (p < 0.001) to accelerate the microbial aggregation. More importantly, the rapidly forming biofilm immobilized and blocked PFOA. The more active antioxidant system repaired the damaged cell membrane by significantly up-regulating glycerophospholipid metabolism and peptidoglycan biosynthesis. It is worth noting that PFOA increased the abundance of antibiotic resistance genes (ARGs) and human bacterial pathogens (HBPs) in porous media by 30% and 106%. PFOA increased the proportion of vertical transmission ARGs (vARGs), and co-occurrence network analysis (r ≥ 0.8, p ≤ 0.01) verified that vARGs were mainly mediated by HBPs. A comprehensive understanding of PFOA interactions with its microecological environment is provided.

Non-Darcy flows in layered porous media (LPMs) with contrasting pore space structures

Compared to single layer porous media, fluid flow through layered porous media (LPMs) with contrasting pore space structures is more complex. This study constructed three-dimensional (3-D) pore-scale LPMs with different grain size ratios of 1.20, 1.47, and 1.76. The flow behavior in the constructed LPMs and single layer porous media was numerically investigated. A total of 178 numerical experimental data were collected in LPMs and single layer porous media. In all cases, two different flow regimes (i.e., Darcy and Non-Darcy) were observed. The influence of the interface of layers on Non-Darcy flow behavior in LPMs was analyzed based pore-scale flow data. It was found that the available correlations based on single layer porous media fail to predict the flow behavior in LPMs, especially for LPM with large grain size ratio. The effective permeability, which incorporated the influence of the interface is more accurate than the Kozeny-Carman equation for estimating the Darcy permeability of LPMs. The inertial pressure loss in LPMs, which determines the onset of the Non-Darcy flow, was underestimated when using a power law expression of mean grain size. The constant B, an empirical value in the classical Ergun equation, typically equals 1.75. The inertial pressure loss in LPMs can be significantly different from it in single lager porous media. For Non-Darcy flow in LPMs, it is necessary to consider a modified larger constant B to improve the accuracy of the Ergun empirical equation.

Effect of suspended particles in a porous medium layer heated from below saturating a Jeffrey fluid: A Mathematical Theorem

In this study, the influence of suspended particles on thermal convection in a porous layer saturating a Jeffrey fluid is examined. Linear stability theory based on normal modes is employed to derive a mathematical theorem on thermal convection in a porous layer saturating a Jeffrey fluid which states that the viscoelastic thermal convection at marginal state cannot manifest as stationary convection if the thermal Rayleigh number R, the medium permeability parameter Pl, the Jeffrey parameter λ_3 and suspended particles parameter B, satisfy the inequality

The onset of double diffusive convection in a rotating bi-disperse porous medium

It is well known that when a horizontal layer of fluid is heated from below, a thermal boundary layer of less dense and hot fluid rises up. When this boundary layer becomes unstable, convective motion in the fluid above sets in. Forecasting when instabilities take place is essential. When a salt dissolved in a fluid saturating a porous medium heated from below is considered, simultaneous mass diffusion and thermal diffusion occur. Unlike the diffusion of heat, the diffusion of salt can take place only through the fluid phase, so an additional physical effect has to be considered: the Soret effect, that is the mass flux created by a temperature gradient. In the present paper the onset of convection in a rotating layer of bi-disperse porous medium saturated by a binary fluid mixture, taking into account the Soret effect, is analysed. Linear stability analysis is performed in order to determine the instability thresholds for the onset of convection via a steady state (stationary convection) and via an oscillatory state (oscillatory convection). Nonlinear stability analysis is performed to obtain the global stability threshold with respect to the L^2-norm.

Thermal convection in a rotating porous medium layer saturated by a nanofluid under a helical magnetic field

In recent years, experiments with flows of liquid metals in a helical magnetic field have been actively carried out. The study of the processes of mixing and crystallization of a liquid metal is of practical importance for metallurgy. With the development of nanotechnology, more and more new types of nanofluids (hybrid, ternary nanofluids) are being synthesized, and the thermophysical characteristics of which can compete with liquid metals. This circumstance served as a motivation for conducting this theoretical study. In this study, the criterion for the onset of convection in a Darcy–Brinkman porous medium layer saturated by an electrically conductive nanofluid under a helical magnetic field is investigated. The Brownian motion and thermophoresis effects are combined in the model for nanofluids, whereas the Darcy–Brinkman model is used for porous media. Instead of prescribing the nanoparticle volume fraction on the borders, we adopted a boundary condition in which the nanoparticle flow is considered to be zero. In the absence of a temperature gradient, a new type of instability in a helical magnetic field in a thin layer of a nanofluid is considered. The growth rate and the region of the development of this instability are numerically obtained depending on the profile of the azimuthal magnetic field (the magnetic Rossby number Rb) and the radial wave number k. In the presence of temperature, the stationary regime of nonuniformly rotating magnetoconvection is studied. The accurate analytical equation for the critical Rayleigh–Darcy number in terms of various non-dimensional parameters is determined using the linear stability theory. The results show that rotation and the axial (vertical) part of the helical magnetic field retard the onset of convection. While the azimuthal part of the helical magnetic field has a destabilizing effect at positive Rossby numbers Rb. The conditions for stabilization and destabilization of stationary convection in a helical magnetic field are determined for metal oxide, metallic, and semiconductor nanofluids.

Unsteady heat transfer in a multilayer composite cylinder containing porous media

The influence of heating equipment with low thermal conductivity, such as vacuum drying equipment and electric heating atomization systems, on the temperature distribution of heated objects is vital for structure design. The transient temperature of small heating equipment is difficult to obtain, particularly when the geometric size of the equipment is less than 0.1 m. Based on Fourier’s law, a heat transfer model for a multilayer composite cylinder with porous media is established to solve this problem. The heat transfer of the porous media is simplified by the local heat balance assumption. An experiment is designed to validate the reliability of the model. The results of this study indicated that the temperature difference between the inner and outer parts of the composite cylinder with thermal conductivity is noticeable when heated by a centralized heat source. When the temperature of the centralized heat source is approximately 190 °C, the temperature difference between the inner and outer parts of the porous medium layer in the composite cylinder is approximately 50 °C. Moreover, when the temperature of the outer part of the porous medium layer in the composite cylinder is approximately 50 ℃, the temperature increased by approximately 1 °C for every 10 % decrease in the porosity. The centralized heat source cannot be used to uniformly heat a material with low heat transfer performance. Increasing the equivalent thermal conductivity of porous media materials or changing the heating structure can effectively improve this problem. Furthermore, the temperature distribution of the composite cylinder can be easily controlled by adjusting the temperatures of the surrounding and centralized heat sources. This study proposes a simple and accurate unsteady temperature prediction method for composite cylinders containing porous media. The temperature of the heating structure and the surrounding environment of the composite cylinder are obtained through simple experiments, and a theoretical model is used to predict the transient temperature of the composite cylinder during the heating process. Moreover, the influence of various factors affecting the heat source and heated object on the unsteady temperature of the composite cylinder with porous media is clarified. This new technology can solve the difficulty in measuring the temperature field of heating structures and heated objects in small heating equipment. This work can aid in the heat source design of small heating equipment.

The effects of couple stress lubricants and surface roughness on squeeze EHL motion between porous medium layer and elastic ball

This paper investigated the effects of porous media layer (PML) and couple stress (CS) lubricants at pure squeeze action in an isothermal elastohydrodynamic lubrication (EHL) point contact with surface roughness (SRN) under constant load condition. The modified transient stochastic Reynolds equation was derived in polar coordinates by means of the Christensen’s stochastic theory and the Stokes’s CS fluid theory. The Gauss-Seidel method (GSM) and the finite difference method (FDM) were both used to solve simultaneously modified transient stochastic Reynolds, force equilibrium, elasticity deformation, and rheology equations. The simulation results revealed that the greater permeability ( K) and porous layer thickness (Φ) are, the smaller central pressures ( Pc) are, and the smaller film thicknesses ( H) are. The times required for achieving maximum central pressures (Pcmax) decrease with increasing K and Φ. Due to squeeze and elastic deformation effects, the slope values of central velocity ( Vc) change from negative to positive. The magnitude of Vc and Vmin decreased with decreasing K and Φ. The Hcmin of circular type RN are greater than that of radial type RN. The Pcmax of radial type RN are slightly greater than that of circular type RN.

On one inverse dynamic problem of poroelasticity for a layered medium

An inverse dynamic problem of poroelasticity of a piecewise-smooth shear coefficient is considered using additional information on oscillations of free surface points. It is believed that Goupill's hypothesis about the equal propagation time of perturbations through the layers of a liquid-saturated porous medium has been fulfilled. Recursive formulas for recovering the unknown shift coefficient are obtained.

Analysis of S-Wave Propagation and Resistivity Value in Porous Medium for Conjecture Potential of Groundwater in Lempuing Village, Bengkulu City

Bengkulu city is facing groundwater problems where some of the groundwater is brackish. The study aimed to determine the structure of the subsurface layer through the propagation velocity of secondary wave (Vs) in a layer of porous medium in estimating the potential for groundwater. This research supported by resistivity data ​​and will be validated based on the depth of the well. MASW data was processed using WinMASW Professional 5.0 software to obtain a 1D profile of the Vs value, and Res2dinv software was used to obtain a 2D cross-section of the resistivity value. The results showed a decrease in the value of Vs in the porous medium layer from 133 to 358 m/s in the first path, and from 149 to 314 m/s for the second path. The decrease in the value of Vs is in the range of groundwater potential which is close to the depth of the resident's well, with the type of porous medium layer being sands and intact clays. The subsurface profile from the Vs measurement shows a good agreement with the resistivity value profile from the Geoelectric method. So, secondary wave propagation can be used in determining groundwater potential for a depth of &lt; 10 m

Global implicit solver for multiphase multicomponent flow in porous media with multiple gas components and general reactions

In order to study the efficiency of the various forms of trapping including mineral trapping scenarios for CO2 storage behavior in deep layers of porous media, highly nonlinear coupled diffusion-advection-reaction partial differential equations (PDEs) including kinetic and equilibrium reactions modeling the miscible multiphase multicomponent flow have to be solved. We apply the globally fully implicit PDE reduction method (PRM) developed 2007 by Kräutle and Knabner for one-phase flow, which was extended 2019 to the case of two-phase flow with a pure gas in the study of Brunner and Knabner. We extend the method to the case of an arbitrary number of gases in gaseous phase, because CO2 is not the only gas that threats the climate, and usually is accompanied by other climate killing gases. The application of the PRM leads to an equation system consisting of PDEs, ordinary differential equations, and algebraic equations. The Finite Element discretized / Finite Volume stabilized equations are separated into a local and a global system but nevertheless coupled by the resolution function and evaluated with the aid of a nested Newton solver, so our solver is fully global implicit. For the phase disappearance, we use persistent variables which lead to a semismooth formulation that is solved with a semismooth Newton method. We present scenarios of the injection of a mixture of various gases into deep layers, we investigate phase change effects in the context of various gases, and study the mineral trapping effects of the storage technique. The technical framework also applies to other fields such as nuclear waste storage or oil recovery.

Asymptotic study of premixed flames in inert porous media layers of finite width: Parametric analysis of heat recirculation phenomena

In this paper, we present an investigation on super-adiabatic premixed flames in an inert porous medium layer of finite length. The combustion process is modeled by a one-step Arrhenius kinetics in which density variations are taken into account. The asymptotic case of large ratio of thermal conductivities of solid to gas phases and the high activation energy limit are explored. The results obtained for these limiting cases are compared to those for finite values of these parameters. The use of the flame sheet model allows us to obtain steady-state solutions in an analytical form thus facilitating the parametric analysis.The investigation focuses on the phenomenon of multiplicity of steady-state solutions. It is shown that two or three (nontrivial) steady-state solutions are possible, depending on the flow rate intensity. The critical values of the parameters for the existence of multiple solutions are also determined. The stability of the obtained solutions is finally investigated by means of time-dependent simulations.