Porous Bed Research Articles

Numerical and analytical investigation of the possibilities to enhance the thermal conductivity of core-shell particle packed beds

We report on a numerical study of the thermal conductivity of core-shell particle packed bed columns. Covering a variety of packing structures and a broad range of mobile phase and porous zone conductivities, it was in all cases found that switching to particles with a highly conducting core (e.g., with a gold or copper core instead of a silica core) would produce a much smaller increase of the effective heat conductivity of the bed (keff) than previously expected in literature. We found maximal increases on the order of some 20–70%, which is much lower than the potential increases up to 2000% assumed in literature. The overestimation in literature could be attributed to the fact that this literature was based on an incorrect extrapolation of the Zarichnyak-model which was the heat conductivity model predominantly used up till now. On the other hand, the computed relationships between keff and the core conductivity obtained in the present study are in good agreement with an analytical solution derived from the effective medium theory, a theory which is physically much more relevant for the case at hand than the Zarichnyak-model. The results also show that the observed increase in effective bed conductivity between fully porous and core-shell particle beds frequently observed in literature is not only due to the presence of the core, but that differences in the shell layer conductivity can play an equally important role. In addition, it could also be demonstrated that, if ways could be found to increase the conductivity of the shell layer, this would produce a much stronger increase of the overall bed conductivity than will ever be possible by increasing the conductivity of the cores.

Reducing polycyclic aromatic hydrocarbon and its mechanism by porous alumina bed material during medical waste incineration

In this paper, porous alumina was used as an alternative bed material to reduce polycyclic aromatic hydrocarbon (PAH) and monocyclic aromatic hydrocarbons (MAH) emission during medical waste incineration in a fluidized bed combustor (FBC). In order to understand the reduction mechanisms of MAH and PAH, porous alumina, nonporous alumina, and silica sand (180–250 μm and 250–320 μm) were used as the bed materials. In comparison to the silica sand (180–250 μm) bed material, the reduction efficiencies of ∑MAH, ∑PAH and ∑PAH toxic equivalent (TEQ) by porous alumina bed material were in sequence as 91.57%, 58.90% and 73.23% during medical waste incineration under 800 °C. There were three mechanisms for the reduction of PAH under porous alumina bed materials. Firstly, the evolution rate of hydrocarbon was reduced by porous alumina due to its low heat transfer coefficient. Secondly, porous alumina bed materials could absorb more gaseous hydrocarbon and prolong the residence time of hydrocarbon in the diluted zone of FBC due to its higher BET. Lastly, the oxidization of the gaseous hydrocarbon was accelerated by porous alumina due to its catalytic effect. Thus, less light hydrocarbon, MAH and PAH were formed during medical waste incineration. The experimental results also indicated that the heat transmission, catalytic effect, and adsorption effect of porous alumina bed materials respectively accounted for 22.8%, 29.2% and 20.9% of the ∑PAH reduction.

Angular multiscale statistics of turbulence in a porous bed

The physics of turbulent flow in porous media is explored in the Lagrangian frame. The evolution of curvature angles along the fluid trajectories reveals the multiscale nature of turbulence. The asymptotic value of the curvature angle quantifies the effect of geometric confinement on turbulence.

Porosity variation within a porous bed composed of multisized grains

We capture the interfacial region of randomly packed porous layers composed of multi-sized spherical or arbitrarily-shaped granules using X-ray computed tomography to explore the porosity-depth variation below a porous media interface. In the case of uni-sized spherical beads, we found in our previous study that the porosity varies from 1 to it's bulk value within a depth of the order of one grain diameter. In this study, we show that for the multi-sized spherical and randomly-shaped granules the porosity reaches it's bulk value within a depth equal to a multiple of the median diameter of the mixture. All multiplication factors for the samples examined here were between 2.6 and 3.8 and mimicked the experimental data with reasonable precision. A direct consequence of this observation is that the diffusion coefficient below the interface can not be considered as a constant. The effect of depth-dependent porosity on the the diffusion coefficient below the porous media interface was examined. It was found that the difference between a constant and a depth-dependent diffusion coefficient in the porous layer is significant and reaches up to 65% for sandy sediment (φb = 0.35) and 20% for highly porous media (φb = 0.90) immediately below the interface. This finding is of great significant when no experimental data of porosity as a function of depth is available. Such situations arise frequently in heat and mass transfer exchanges across fluid-porous or solid wall-porous boundaries.

Comparison between experimental and numerical results of a packed-bed thermal energy storage system in continuous operation

This paper reports the comparison between the results obtained by experimental tests made on a thermal energy storage (TES) system of sensible heat type under continuous operation with numerical simulations performed with a CFD model. TES system consists of a packed bed of spherical particles of alumina and air used as heat transfer fluid. The study concerns the time-dependent behaviour of the temperature field inside the bed, highlighting the thermocline evolution and its deterioration after repeated charge/discharge cycles due to the thermal hysteresis with a consequent progressive reduction of the recoverable energy. It is demonstrated that this effect is reduced by loosening the temperature constraints set at the end of each phase, increasing the amount of recovered energy and reducing the number of cycles needed to obtain the steady state. The CFD model was carried out considering a two-dimensional axisymmetric computational domain with the porous bed coupled to the wall. The governing equations are solved for incompressible viscous turbulent flow and fully developed forced convection based on the two-phase transient model equation to calculate both fluid and solid temperatures. Satisfactory agreement between detailed experimental and numerical results is reached when inlet air temperature follows that measured during experimental tests during both charge/discharge phases. CFD model used is reliable for predicting the whole temperature field of the TES during continuous operation.

Experimental study of transient heat transfer characteristics of single-phase natural convection in multidimensional porous bed with volumetric heat generation

ABSTRACTNatural convection in an internally heated porous bed of height and diameter of 450 mm and 500 mm, respectively, and superposed with the fluid layer has been experimentally investigated. The onset of natural convection in the bed is indicated by change in the rate of temperature rise within the bed. An empirical model based on local Nusselt number and local Rayleigh number has been developed. A comparison of the present model with the models in literature is made to draw out the differences between the local heat transfer of large multidimensional beds and the average heat transfer of small beds.

Development of a projection-based SPH method for numerical wave flume with porous media of variable porosity

The paper presents a numerical wave flume with porous media of variable porosity. A fully-Lagrangian computational method is developed for simulation of fluid flow interactions with porous media based on a projection-based (or Incompressible) SPH (Smoothed Particle Hydrodynamics) method. The continuity and Navier-Stokes equations are reformulated with incorporation of volume fraction, based on two-phase mixture theory. The proposed method benefits from a set of enhanced schemes and is therefore referred to as Enhanced Incompressible SPH (ISPH). The effect of porous media is represented by considering linear and nonlinear resistance force terms as well as incorporation of a newly-derived source term of PPE (Poisson Pressure Equation). The results are characterized by smooth and continuous pressure fields, as well as regular particle distributions at the fluid-porous media interface in absence of any artificial smoothing schemes. Since the local volume fraction of fluid phase particles is consistently calculated based on the volume fraction of surrounding porous phase particles, the method is capable of accurately reproducing fluid flow interactions with spatially varying porous media. Validations are made through a set of benchmark tests including fluid flow in a U-tube with uniform and multi-layered porous media, rapid seepage flows in rockfill dam, solitary wave attenuation over a porous bed, solitary wave interaction with a submerged porous structure and wave propagation over a submerged triangular permeable bar.

Simulation and experimental investigation of fluid flow in porous and non-porous solar air heaters

The porous absorber in the solar air heater gives considerable temperature increment which is shown by computational fluid dynamic simulation and verified experimentally. Experimental analysis on porous (wire screen) and non-porous solar air heaters were carried out to study the heat transfer and friction factor characteristics. The analysis encompasses the investigation on effect of mass flow rate on air temperature increment, thermal efficiency and pressure drop across the test section. The heat transfer parameter is established in terms of Colburn (Jh) factor for porous bed solar air heaters. The effect of friction factor on different geometries for a range of operating Reynolds number (194–591) is presented. Two wire screen matrix (WSM) solar air heater WSM-I and WSM-II were investigated which has different diameter, pitch and porosity. Thermal efficiency increased on introducing the packed wire-screen matrix diagonally in the air flow path. The increase in thermal efficiency for WSM-I and WSM-II were found to be 5–17% and 5–20% respectively with the mass flow rate ranging from 0.01 kg/s to 0.055 kg/s. The collector heat removal factor was found to be 0.95 ± 0.021 for wire mesh absorber and 0.72 ± 0.0073 for conventional type. The pressure drop across the length of the duct was studied to be in the range of 15 ± 0.28 Pa to 17 ± 0.28 Pa and 7 ± 0.16 Pa to 11 ± 0.28 Pa for WSM-I and WSM-II respectively and for conventional type it was between 5 ± 0.20 Pa and 10 ± 0.28 Pa.

Extended wind wave model (WWM) incorporating the effect of submerged porous media with high permeability

In this study, the phase–averaged wave action equation (WAE) is extended to incorporate the effect of submerged porous media with high permeability. The wave dissipation coefficient for submerged porous media is incorporated into the WAE of the wind wave model. The coefficient of turbulent flow resistance is obtained from the work by taking the imaginary part of a mathematical model of wave transformation over a submerged porous medium under the mild–slope assumption. A method to estimate the characteristic parameter of turbulent frictional resistance in porous media is proposed in this study. Comparisons with experiments and other numerical results showed that the proposed model could be applied to waves propagating over porous beds and reefs. Practical simulations were used to investigate wave damping due to porous seabeds in nearshore areas.

An experimental study on two-phase flow resistances and interfacial drag in packed porous beds

Abstract Motivated by reducing the uncertainties in quantification of debris bed coolability, this paper reports an experimental study on two-phase flow resistances and interfacial drag in packed porous beds. The experiments are performed on the DEBECO-LT (DEbris BEd COolability-Low Temperature) test facility which is constructed to investigate the adiabatic single and two phase flow in porous beds. The pressure drops are measured when air-water two phase flow passes through the porous beds packed with different size particles, and the effects of interfacial drag are studied especially. The results show that, for two phase flow through the beds packed with small size particles such as 1.5 mm and 2 mm spheres, the contribution of interfacial drag to the pressure drops is weak and ignorable, while the significant effects are conducted on the pressure drops of the beds with bigger size particles like 3 mm and 6 mm spheres, where the interfacial drag in beds with larger particles will result in a descent-ascent tendency in the pressure drop curves along with the fluid velocity, and the effect of interfacial drag should be considered in the debris coolability analysis models for beds with bigger size particles.

Reduction of mild-dehydrated, low-grade iron ore by ethanol

Low-grade iron ore with high combined water (CW) content (e.g., goethite) has been first dehydrated at low temperatures mildly to be slit-shaped nano-order pore, then has been reduced by ethanol (C2H5OH) charging under the heating conditions. Bioethanol as derived from biomass, regarded as a renewable and carbon-neutral resource, is a promising candidate as a reducing agent for ironmaking. In the experiments, ethanol was dropwise added to the mild-dehydrated, porous iron ore beds at heating conditions using the temperature-program. As a result, the ethanol was soon decomposed to CO and H2, which then reduced the iron oxides. Porous iron ore acts as a good catalyst for ethanol decomposition as it simultaneously reduces to metallic iron. Interestingly, iron oxides were reduced at a lower temperature, compared to conventional coal-based ironmaking in the blast furnace. Metallic Fe was obtained at only 750 °C, showing a reduction degree of 81%, due to the contribution of hydrogen reduction. The longer charging time of ethanol promotes the higher reduction degree as well as sufficient compositions of reducing gas (H2-CO) for the reduction process. The results of experiments using different iron ores revealed the general rule that the higher CW content in ore makes the larger surface area of the iron ore by mild-dehydration, causing higher reactivity in the reduction process. The results appealed that mild-dehydrated iron ore is good raw materials of bioethanol ironmaking, due to its nanopores.

Modeling and Simulation of Local Thermal Non-equilibrium Effects in Porous Media with Small Thermal Conductivity

The two-equation model in porous media can describe the local thermal non-equilibrium (LTNE) effects between fluid and solid at REV scale, with the temperature differences in a solid particle neglected. A multi-scale model has been proposed in this study. In the model, the temperature differences in a solid particle are considered by the coupling of the fluid energy equation at REV scale with the heat conduction equation of a solid particle at pore scale. The experiments were conducted to verify the model and numerical strategy. The multi-scale model is more suitable than the two-equation model to predict the LTNE effects in porous media with small thermal conductivity. The effects of particle diameter, mass flow rate, and solid material on the LTNE effects have been investigated numerically when cryogenic nitrogen flows through the porous bed with small thermal conductivity. The results indicate that the temperature difference between solid center and fluid has the same trend at different particle diameters and mass flow rates, while the time to reach the local thermal equilibrium is affected by solid diameter dramatically. The results also show that the temperature difference between solid center and surface is much greater than that between solid surface and fluid. The values of $$ \rho {\text{c}} $$ for different materials have important influence on the time to reach the local thermal equilibrium between solid and fluid.

Effect of a Floating Elastic Plate/Membrane on the Motion Due to a Ring Source in Water With Porous Bed

The velocity potentials due to the presence of a horizontal circular ring of wave sources of timedependent strength in water of finite constant depth with a floating elastic plate or a floating membrane are determined. The uniform bottom is composed of non-dissipative porous medium. The problems are formulated as the initial value problems and the Laplace transform method is used to solve these. For time-harmonic source strength, the steady-state analysis of the potentials reveals the existence of outgoing progressive waves. Graphs for the surface profiles are presented for different values of the tension parameter for the membrane, flexural rigidity of ice and the porous-effect parameter.

Polymer Flooding in Artificial Hydrate Bearing Sediments for Methane Gas Recovery

Polymer flooding has been one of the most promising methods used for enhanced oil recovery from matured crude oil reservoirs across the globe due to its distinct advantages over simple water flooding. However, the use of polymer flooding has not yet been investigated for methane recovery from hydrate reservoirs. In our earlier work, we have investigated the effect of various molecular weights and concentrations of polyethylene glycol (PEG) polymer on the phase stability and kinetics of methane hydrate. This information has been explored for successful use of PEG as a chemical agent for polymer flooding from hydrate reservoirs. In this work, detailed experimental investigations on methane production from hydrate bearing sediments have been carried out using PEG polymer flooding in a three-dimensional hydrate reactor. Initially, methane hydrate formation has been investigated using two silica sand porous beds (viz., 0.16 and 0.46 mm), and pure water at an initial hydrate formation pressure of 8 MPa and 277....

An Experimental Study on the Interaction between Oscillatory Flow and Idealized Porous Bed

Shigematsu, Sota Nakajo, and Yuya Okada, 2018. An Experimental Study on the Interaction between Oscillatory Flow and Idealized Porous Bed. In: Shim, J.S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 981–985. Coconut Creek (Florida), ISSN 0749-0208.The microscopic structures of over and inside flow of a porous medium placed in oscillatory flow was measured by the Particle Tracking Velocimetry with the refractive index matching method in order to investigate interaction between them. The strong shear flow was observed over the surface of the porous medium and the thickness of shear flow varied with the phase of the oscillatory flow. It was found that the thickness of non-dimensional shear flow was almost constant and that it did not depend on the Reynolds number. It was found that the thickness of non-dimensional shear flow was almost constant and it independented with the Reynolds number. Besides, it was also found that the phase difference between flows over and inside the porous bed occurred. The characteristics of the spatial variance of velocity components were shown in detail with the time phase variance. Further, the flow properties around the particle constitutes porous body were measured and investigated in detail.

Hazard Assessments of Energetic Systems, A Field Still in Development

Hazard Assessments of Energetic Systems, A Field Still in Development

Oblique wave scattering by a floating elastic plate over a porous bed in single and two-layer fluid systems

An analytical study is presented in this paper for oblique wave scattering by a floating elastic plate in a one or two-layer body of water over a porous seabed of infinite depth. The solution procedure adopted, under the assumption of small-amplitude surface waves and structural response, is the eigenfunction expansion method. The study aims to look into the interaction between oblique waves and a floating elastic plate that serves as an effective breakwater. Effects of three types of edge conditions, viz. (i) free edge, (ii) simple-supported edge, and (iii) clamped edge are analyzed. Numerical results for the reflection and transmission coefficients are computed and examined for various values of the wave, porous bed and structural parameters. Results for wave interaction with an elastic plate over a non-porous bed are obtained as special cases and compared with results available in the literature. The study reveals that for various combinations of wave and structural parameters, zero reflection and full transmission may occur in case of rigid bottom and real porous-effect parameter of the porous bed. However, for complex porous-effect parameter, zero reflection and full transmission do not occur. Moreover, due to the energy dissipation by porous bed, wave transmission decreases significantly with increase in length of the floating plate in case of complex porous-effect parameter. The results will be useful in the design of breakwaters for the protection of harbors, inlets and beaches against attacks from surface waves.

Chemostratigraphy and sedimentary facies analysis of the Permian Lucaogou Formation in the Jimusaer Sag, Junggar Basin, NW China: Implications for tight oil exploration

The middle Permian Lucaogou Formation (P2l) in the Jimusaer Sag of the southeastern Junggar Basin, NW China hosts China’s first commercial tight (shale) oil production. Two tight-oil sweet spot intervals have been identified within the P2l formation. Coupled chemostratigraphic and sedimentary facies analysis reveals that the sweet spot intervals were deposited in deep–shallow saline lacustrine to nearshore environments under an overall dry climate setting. The sweet spot intervals in the P2l formation comprises several chemostratigraphically and lithologically distinct units deposited under the influence of subtle climatic and environmental changes that have previously not been recognized. A total of 11 depositional units have been identified within the two sweet spot intervals based on an Integrated Prediction Error Filter Analysis (INFEFA) of Gamma Ray logs and environmental parameters derived from chemostratigraphic data. The tight oil reservoir sweet spot intervals were found to be controlled by the spatial and temporal distribution of total organic carbon (TOC) and reservoir properties (e.g., porosity and permeability) and source-reservoir coupling. Two potential tight oil exploration plays are recognized, including those depositional units with porous reservoir beds interbedded with high-TOC source beds (a self-generation play), and those units with porous reservoir beds adjacent to high-TOC source beds (a near-source play).

Investigation of thermal performance of unidirectional flow porous bed solar air heater using MLP, GRNN, and RBF models of ANN technique

In the present work, Multi-layer perceptron (MLP), Generalized regression neural network (GRNN), Radial basis function (RBF) and Multiple linear regression (MLR) models has been used to predict the thermal performance of unidirectional flow porous bed solar air heater. These four models have been constructed on the basis of actual experimental data and calculated values. Total 96 experimental data sets have been used in the present work. In GRNN, RBF and MLP models, six input parameters such as mass flow rate, wind speed, atmospheric temperature, inlet fluid temperature, fluid mean temperature and solar intensity were used in input layer, and one variable, the thermal efficiency was used in output layer. Same parameters were used in MLR model. It is observed that GRNN model is the best model due to lowest error and highest value of R2 as compared to MLP, RBF and MLR model performances. It is found that the value of MAE, RMSE and R2 for GRNN model are 1.1128E−03, 5.9284E−06 and 0.99758 respectively, and the model efficiency is 0.99760, which is the highest value as compared to other model. These results confirmed that the GRNN model is appropriate model to predict the thermal performance of solar air heater.

Squeeze-film flow between a flat impermeable bearing and an anisotropic porous bed

We consider a theoretical model of the squeeze film in the presence of a porous bed. The gap between the porous bed and the bearing is assumed to be filled with a Newtonian fluid. We use the Navier-Stokes equation in the fluid region and the Darcy equation in the fluid filled porous region. Lubrication approximation is used to derive the corresponding evolution equation for the film thickness. We use G. S. Beavers and D. D. Joseph [“Boundary conditions at a naturally permeable wall,” J. Fluid. Mech. 30, 197–207 (1967)] and M. Le Bars and M. G. Worster [“Interfacial conditions between a pure fluid and a porous medium: Implications for binary alloy solidification,” J. Fluid. Mech. 550, 149–173 (2006)] condition at the liquid porous interface and present a detailed analysis on the corresponding impact. We assume that the porous bed is anisotropic in nature with permeabilities K2 and K1 along the principal axes. Accordingly, the anisotropic angle ϕ is taken as the angle between the horizontal direction and principal axis with permeability K2. We show that the anisotropic permeability ratio and the anisotropic angle make a significant influence on the contact time, flux, velocity, etc. Contact time to meet the porous bed when a bearing approaches under a constant prescribed load is estimated. We present some important findings (relevant to the knee joint) based on the anisotropic properties of the human cartilage. For a prescribed constant load, we have estimated the time duration, during which a healthy human knee remains fluid lubricated.