Two-layer Porous Media Research Articles

Syngas production from CO2/CH4 rich combustion in a porous media burner: Experimental characterization and elementary reaction model

Methane and carbon dioxide are two major components in many biomass-derived gases such as landfill gas and biogas, which are renewable and have potential fuel cell applications. Syngas production from non-catalytic and fuel-rich combustion using a two-layer porous media burner was studied experimentally and numerically with a range of CO2 content in the CH4 fuel. With an air flow rate of 5L/min, an equivalence ratio of 1.5 and a mole ratio of CO2/CH4 of 1, the reforming efficiency was found to be 45.3%, larger than that (39.1%) without CO2 in the feed at the same air flow rate and equivalence ratio. A two-dimensional model with an elementary reaction mechanism was developed to study the influence of carbon dioxide on the reforming characteristics. The model is validated by the experimental results with good agreement. The simulation results clearly showed that the reaction process along the burner could be divided into a preheating zone, a CO2-consuming zone and a CO2-generating zone according to the net reaction rate of CO2.

Elementary Reaction Modeling and Experimental Characterization on Methane Partial Oxidation within a Catalyst-Enhanced Porous Media Combustor

In this study, the fuel-rich combustion of methane in a two-layer porous media burner consisting of dense alumina pellets of different diameters was investigated experimentally and numerically. For a fixed inlet gas velocity of 0.15 m/s, methane-rich flames were stabilized near the interface of two layers for equivalence ratios from 1.4 to 1.6. It was found that 40% of the methane was converted to syngas at the equivalence ratio of 1.6 using a reforming efficiency based on low heating values. To further increase the hydrogen yield and make the burner more suitable for applications in fuel cells, a portion of the downstream layer was coated with 0.08 wt % Ni catalyst. The reforming efficiency of methane to hydrogen increased from 18.2% to 23.9% after the catalytic enhancement. A combined homogeneous and heterogeneous elementary reaction mechanism was developed for methane partial oxidation in the porous media burner with catalytic enhancement. A one-dimensional model was explored by coupling the combined m...

Power and heat co-generation by micro-tubular flame fuel cell on a porous media burner

A flame fuel cell setup is designed and built based on a micro-tubular solid oxide fuel cell and a two-layer porous media burner. The stable operation limits of the burner are obtained by adjusting the inlet gas velocity and the equivalence ratio. Methane fuel-rich flames are stabilized inside the burner from the equivalence ratio of 1.4–1.8. The effects of the equivalence ratio and the gas velocity on the temperature distribution inside the burner and the combustion products are studied. Using a burner efficiency based on lower heating values, up to 41.1% of methane was converted to H2 and CO at the equivalence ratio of 1.7. The maximum mole fraction of H2 and CO reached 9.32% and 8.18% respectively. Flame fuel cell experiments are carried out with different equivalence ratios. The tubular SOFC is directly heated up and reduced by the fuel-rich flame. The maximum power generated by the flame fuel cell reached 0.55 W at the equivalence ratio of 1.7 and the inlet gas velocity of 0.15 m/s.

Performance study of an induced air porous radiant burner for household applications at high altitude

Porous radiant burners are presented as an alternative technology for improving the thermal efficiency of conventional burners. A performance study of an induced air porous radiant burner (IAPRB) with submerged combustion using natural gas was performed at high altitude to assess the feasibility of employing a porous burner operated with induced air in household applications. The experiments were performed in two-layer porous media. The preheating and combustion zones consisted of 400 ppi alumina honeycomb and 90% porosity silicon carbide foam, respectively. Three power per unit area levels, 370 kW/m2, 480 kW/m2 and 670 kW/m2, were evaluated. Pollutant emissions (CO and NOx), the radiation efficiency, the temperature profile along the bed, the primary air rate and the pressure drop across the porous materials were measured. A maximum burner thermal efficiency near 50% was obtained for 370 kW/m2, with a radiation efficiency of 27%. The preheating of the premix caused an increased bed pressure drop, which resulted in a reduction in ambient air entrainment and an air deficiency in the reaction zone. The CO emissions exceeded the standard allowable emissions.

Effects of material properties on heating processes in two-layered porous media subjected to microwave energy

Microwave heating of double-layer porous medium is numerically investigated using a proposed numerical model. A two-dimensional domain composed of two porous layers is considered. The two porous layers have different particle sizes, porosities, thermal and dielectric properties. The generalized non-Darcian model developed takes into account of the presence of a solid drag and the inertial effect. The transient Maxwell’s equations are solved by using the finite difference time domain (FDTD) method to describe the electromagnetic field in the waveguide and in the media. The temperature profile and velocity field within the media are determined by solution of the momentum and energy equations given by the SIMPLE (Semi-Implicit Method for Pressure Linked Equations) algorithm. This study focuses on effects of diameter, porosity, position and types of particles that have different thermal and dielectric properties. The computed results agree well with the experimental results. While the particle size and porosity mainly affect fluid flow within porous media, the thermal and dielectric properties strongly influence heat transfer mechanism in each layer of porous media.

The competition between gravity and flow focusing in two-layered porous media

AbstractThe gravitationally driven flow of a dense fluid within a two-layered porous media is examined experimentally and theoretically. We find that in systems with two horizontal layers of differing permeability a competition between gravity driven flow and flow focusing along high-permeability routes can lead to two distinct flow regimes. When the lower layer is more permeable than the upper layer, gravity acts along high-permeability pathways and the flow is enhanced in the lower layer. Alternatively, when the upper layer is more permeable than the lower layer, we find that for a sufficiently small input flux the flow is confined to the lower layer. However, above a critical flux fluid preferentially spreads horizontally within the upper layer before ultimately draining back down into the lower layer. This later regime, in which the fluid overrides the low-permeability lower layer, is important because it enhances the mixing of the two fluids. We show that the critical flux which separates these two regimes can be characterized by a simple power law. Finally, we briefly discuss the relevance of this work to the geological sequestration of carbon dioxide and other industrial and natural flows in porous media.

Studies on porous radiant burners for LPG (liquefied petroleum gas) cooking applications

This paper deals with the performance tests of a PRB (porous radiant burner) used for LPG (liquefied petroleum gas) domestic cooking stoves. The burner consists of a two-layer porous media. The combustion zone is made up of silicon carbide, and alumina balls forms the preheating zone. For a given burner diameter, the performances of the burner, in terms of thermal efficiency and emission characteristics, are analysed for different equivalence ratios and thermal loads (wattages). The water boiling test as prescribed in the BIS (Bureau of Indian Standard): 4246:2002 was used to calculate the thermal efficiency of both the conventional LPG cooking stoves and the PRB. The maximum thermal efficiency of the LPG cooking stoves with a PRB was found to be 68% which is 3% higher than that of the maximum thermal efficiency of the conventional domestic LPG cooking stoves. Unlike the conventional LPG stoves, for which the CO and NO X emissions were found in the ranges 400–1050 mg/m 3 and 162–216 mg/m 3, respectively, for the one with PRB, the same were in the ranges of 25–350 mg/m 3 and 12–25 mg/m 3. The axial temperature distribution in the burner showed that the reaction zone was close to the interface of the two zones and at a higher thermal load, it shifted towards the downstream. The surface temperature of the PRB was found to be uniform.

The engineering calculation of filtering a suspension through a two-layer medium in linear kinetics of mass exchange

We have obtained a simple approximated solution of the problem of filtrating of little concentrated suspension through a two-layer porous medium in linear kinetics of mass exchange. Its comparison was carried out with the known strict solution on numerous examples of calculating physicochemical characteristics and technological parameters, which demonstrated high accuracy of formulas proposed for the practice of water treatment.

SURFACTANT-POLYMER FLOODING PERFORMANCE IN HETEROGENEOUS TWO-LAYERED POROUS MEDIA

In this paper, simulation study was conducted to investigate the effect of spatial heterogeneity of multiple porosity fields on oil recovery, residual oil and microemulsion saturation. The generated porosity fields were applied into UTCHEM for simulating surfactant-polymer flooding in heterogeneous two-layered porous media. From the analysis, surfactant-polymer flooding was more sensitive than water flooding to the spatial distribution of multiple porosity fields. Residual oil saturation in upper and lower layers after water and polymer flooding was about the same with the reservoir heterogeneity. On the other hand, residual oil saturation in the two layers after surfactant-polymer flooding became more unequal as surfactant concentration increased. Surfactant-polymer flooding had higher oil recovery than water and polymer flooding within the range studied. The variation of oil recovery due to the reservoir heterogeneity was under 9.2%.

Performance of Surfactant Flooding in Heterogeneous Two-Layered Porous Media

In this paper, simulation study was conducted to investigate the effect of spatial heterogeneity of multiple porosity fields on oil recovery, residual oil and microemulsion saturation. The generated porosity fields were fed into UTCHEM for simulating surfactant flooding in heterogeneous two-layered porous media. From the analysis, surfactant flooding was more sensitive than water flooding to the spatial distribution of multiple porosity fields. Residual oil saturation in upper and lower layers after water flooding was about the same with the reservoir heterogeneity. On the other hand, both residual oil and microemulsion saturation in the two layers after surfactant flooding became more equal as porosity distribution standard increased. Spatial heterogeneity of multiple porosity fields had only a small effect on residual oil saturation and recovery factor. The variation of recovery factor due to the reservoir heterogeneity was under 4.2%.

Rich n-heptane and diesel combustion in porous media

Rich n-heptane and diesel flames in two-layer porous media are experimentally investigated in the context of syngas production. The stable operating points of n-heptane reforming have been determined and the mole fractions of H 2, CO, CO 2 and light hydrocarbons have been measured in the exhaust gas at an equivalence ratio of 2 for different thermal input values. The reformer performance has been assessed also from the point of view of the heat losses and the mixture homogeneity. The pre-vapouriser produces an approximately uniform vapour–air mixture upstream of the flame front. The range of flow rates for stable flames decreased with increasing equivalence ratio. Heat losses were about 10% of the thermal input at high firing rates. A 77.2% of the equilibrium H 2 was achieved at a flame speed of 0.82 m/s. The same reactor with a different porous matrix for the reforming stage demonstrates diesel reforming to syngas with a conversion efficiency of 77.3% for a flame speed of 0.65 m/s.

Tidal deformations and the electrokinetic effect in a two-layer fluid-saturated porous medium

The electrokinetically induced vertical component of the electric field in a multilayer fluid-saturated porous medium caused by tidal deformations of the Earth’s crust is calculated. Petrophysical properties change in a jumplike manner at the boundary between two media. The pore pressure gradient at the boundary abruptly reaches a maximum and then exponentially decays, forming a hydrodynamic skin layer. Due to the electrokinetic effect, the electric field behaves in the same way. Observations of the vertical electric field can be used, in principle, to determine the mechanical properties of the medium experiencing deformation. The magnitudes of the effects lie within a range accessible to measurement.

Wave interaction with a new type perforated breakwater

In this study examined is the wave interaction with a new modified perforated breakwater, consisting of a perforated front wall, a solid back wall and a wave absorbing chamber between them with a two-layer rock-filled core. The fluid domain is divided into three sub-domains according to the components of the breakwater. Then by means of the matched eigenfunction expansion method, an analytical solution is obtained to assess the hydrodynamic performance of the new structure. An approach based on a step approach method is introduced to solve the complex dispersion equations for water wave motions within two-layer porous media. Numerical results of the present model are compared with previous limiting cases. The effects of rock fill on the reflection coefficient and the horizontal wave force are discussed.

Mass diffusion through two-layer porous media: an application to the drug-eluting stent

A mathematical model for the diffusion–transport of a substance between two porous homogeneous media of different properties and dimensions is presented. A strong analogy with the one-dimensional transient heat conduction process across two-layered slabs is shown and a similar methodology of solution is proposed. Separation of variables leads to a Sturm–Liouville problem with discontinuous coefficients and an exact analytical solution is given in the form of an infinite series expansion. The model points out the role of four nondimensional parameters which control the diffusion mechanism across the two porous layers. The drug-eluting stent constitutes the main application of the present model. Drug concentration profiles at various times are given and analyzed. Also, qualitative considerations and a quantitative description to evaluate feasibility of new drug delivery strategies are provided, and some indicators, such as the emptying time, useful to optimize the drug-eluting stent design are discussed.

Microdroplet absorption by two-layer porous media

Microdroplet absorption by two-layer porous media is studied both theoretically and experimentally. A two-dimensional model for liquid flow from a droplet into a porous medium is presented and veri.ed based on a simultaneous numerical solution of the Euler equations taking into account surface tension forces and the unsteady filtration equation. The effect of the structural parameters of the two-layer porous medium (pore size in the layers, and the thickness and porosity of the layers) on the droplet absorption is analyzed. It is shown that the presence of the second layer can have a significant effect on the droplet absorption rate and the liquid distribution in the medium. The pore size is found to be the main parameter that governs the effect of the second layer.

Parameter Estimation and Contaminant Source Characterization in Horizontal Tracer Experiment in Two-Layered Porous Media

Parameter Estimation and Contaminant Source Characterization in Horizontal Tracer Experiment in Two-Layered Porous Media

Moisture Removal from a Two-Layer Porous Media: A Conceptual Model and Experimental Results

Moisture removal from a two-layer porous media in which air is circulated through one layer and moisture is removed from the second has not been well studied due to the emphasis given to single-layer systems. This two-layer configuration is common in natural and engineered systems and can be used as a means to create a barrier to downward migrating fluids and to remove liquids and gases that may be present in the finer layer. However, there is little data on moisture removal from a two-layer porous media in which air is circulated through one layer parallel to the interface and moisture is removed from the finer second layer by evaporation. A conceptual model of the moisture removal from a two-layer porous media system was developed and compared to experimental moisture removal rates from laboratory scale dry barriers. The limited experimental data agrees well with the results predicted by the conceptual model, providing an initial validation.

Analytical modeling of diffusion-limited contamination and decontamination in a two-layer porous medium

Diffusion of dissolved contaminants in multilayer porous media is an important phenomenon affecting both contamination and remediation in natural aqueous environments, including diffusion in groundwater aquitards and contaminated bed sediments. This study presents a new analytical solution for solute diffusion in a semi-infinite two-layer porous medium for arbitrary boundary and initial conditions. The solution was obtained by using the Green's function approach in the Laplace domain with the application of the binomial theorem to facilitate inversion back to the real time domain. Results based on this solution were found to be simple both in form and ease of calculation and to be in good agreement with those obtained using numerical calculations based on the Crank-Nicolson finite difference method. Applications of the solution are presented in the context of a contaminated groundwater aquitard to demonstrate how different boundary and initial conditions can greatly affect the contamination and decontamination of porous media, and to illustrate how diffusion modeling might be used in a forensic sense.

Determination of the macrodispersive parameters of a motion in a two-layer porous medium

This paper develops a method for deriving good estimates of macrodispersive transport parameters describing the asymptotic evolution of a non-reactive chemical pollutant injected into a two-layer porous medium. These parameters are extracted from the coefficients of asymptotic time-polynomial expansions of some adequately chosen integral transforms performed upon the solution of the original transport problem.

Approximate analytical solutions for solute transport in two-layer porous media

Mathematical models for transport in layered media are important for investigating how restricting layers affect rates of solute migration in soil profiles; they may also improve the analysis of solute displacement experiments. This study reports an (approximate) analytical solution for solute transport during steady-state flow in a two-layer medium requiring continuity of solute fluxes and resident concentrations at the interface. The solutions were derived with Laplace transformations making use of the binomial theorem. Results based on this solution were found to be in relatively good agreement with those obtained using numerical inversion of the Laplace transform. An expression for the flux-averaged concentration in the second layer was also obtained. Zero- and first-order approximations for the solute distribution in the second layer were derived for a thin first layer representing a water film or crust on top of the medium. These thin-layer approximations did not perform as well as the ‘binomial’ solution, except for the first-order approximation when the Peclet number,P, of the first layer, was low (P<5). Results of this study indicate that the ordering of two layers will affect the predicted breakthrough curves at the outlet of the medium. The two-layer solution was used to illustrate the effects of dispersion in the inlet or outlet reservoirs using previously published data on apparatus-induced dispersion.