Thin Porous Plate Research Articles

Numerical simulation of the gas flow through the rectangular channel with perforated plate

The perforated plates are commonly used for gas flow control in the wide-angle diffusers of electrostatic precipitators of large power plants. Many studies dealt with the investigation of the effects of the perforated plate?s geometry on flow parameters in the cases where incoming flow is perpendicular to the plate and the plate is covering the whole cross-section of the flowing channel. These results are partially applicable in cases where flow is inclined on the plate or when the plate is not occupying the whole cross-section of the channel. The subject of this work is a numerical investigation of flow through the rectangular channel with a perforated plate in various positions in the cross-section of the channel. The aim was to investigate the effect of the plate position on the flow. The perforated plates were modeled as thin porous media of finite thickness by using the directional loss model. Numerical experiments are carried out by using Computational Fluid Dynamics software Ansys CFX. Results of pressure drop and velocity distribution behind the plate are compared to the results of CFD simulation of the full 3D plate model. In order to obtain a reasonable agreement both of the pressure drop and velocity distribution behind the plate when using a simplified thin porous plate model, the value of streamwise permeability of the plate had to be adjusted. The level of adjustments has determined iteratively and it depends on the plate position in the channel?s cross-section.

A numerical approach for simulating flow through thin porous media

In this study we develop a formulation to model the effect of a thin porous plate of arbitrary geometry in a fluid flow. This underlying model is based on the 1D pressure drop in the normal direction to the plate and is easily used for 2D and 3D flows. Our primary interest lies in perforated plates for use in ocean wave damping applications, although other porous media such as woven gauze or slotted screens can be handled in an identical manner. We implement the model in a Smoothed Particle Hydrodynamics (SPH) framework which is an intrinsically suitable method for the interaction between complex geometries and ocean waves. We compare predictions of the method to theory and available experimental data in a set of simulations including 2D steady-state flow normal and inclined to a screen. In all cases the results from the SPH implementation are in very satisfactory agreement. The method is then demonstrated on solitary wave interaction with a porous barrier and the transmission, reflection and absorption of wave energy is predicted as a function of permeability.

Wave interaction with dual circular porous plates

In this paper we investigated the reflection and the transmission of a system of two symmetric circular-arc-shaped thin porous plates submerged in deep water within the context of linear theory. The hypersingular integral equation technique has been used to analyze the problem mathematically. The integral equations are formulated by applying Green’s integral theorem to the fundamental potential function and the scattered potential function into a suitable fluid region, and then using the boundary condition on the porous plate surface. These are solved approximately using an expansion-cum-collocation method using the behaviour of the potential functions at the tips of the plates. This method ultimately produces a very good numerical approximation for the reflection and the transmission coefficients and hydrodynamic force components. The numerical results are depicted graphically against the wave number for a variety of layouts of the arc. Some results are compared with known results for similar configurations of dual rigid plate systems available in the literature with good agreement.

Scattering of water waves by a pair of vertical porous plates

The two-dimensional problem of scattering of small-amplitude surface water-waves by two symmetric vertical thin porous plates is investigated here assuming the linear theory. The problem is formulated in terms of two hypersingular integral equations of the second kind involving the discontinuities in the unknown symmetric and antisymmetric potential functions describing the motion in the fluid across one of the plates. Exploiting the conditions at the two tips of the plate, the discontinuity is approximated by expanding it in terms of a finite series involving Chebyshev polynomials of the second kind multiplied by an appropriate weight function, and then the integral equations are solved numerically by a collocation method. Using the solutions, the reflection and the transmission coefficient are computed numerically. The numerical results for the reflection and the transmission coefficients, amount of energy dissipation and the hydrodynamic forces are depicted graphically against the wave number. Known results for the reflection coefficient for two impermeable plates are recovered when the porous-effect parameter is set to be equal to zero. An energy identity for the permeable plates is determined.

Review on gas–liquid separations in microchannel devices

Separations are indispensable to most chemical processes, regardless of operational scale. In the field of chemical microprocess engineering, separations have so far attracted rather limited attention compared to reactive processes, although increasingly more research is directed towards this area. Microstructured devices offer the opportunity of intensifying transport processes associated with separation operations by providing high ratios of contact areas to volume, short transport distances and high driving force gradients. These attributes have so far been exploited for various microseparations. In this review, we focus on separations where gas and liquid phases are present, and in particular on absorption, stripping and distillation. Two main approaches for contacting the two phases have been employed: continuous and dispersed phase contactors. Removal of components from gas mixtures by absorption and stripping of volatiles from liquid mixtures have been achieved in falling film devices, thin porous plate microcontactors, as well as in dispersed flow systems. Distillation has been performed in microchannel devices, utilizing capillary, centrifugal and gravity forces, vacuum or carrier gas.

Thermal stability problems in a thin porous plate

Some numerical and analytical aspects of the stability of the formal solution for the dynamical problem associated with the governing equations in a thin porous plate under a constant thermal source are discussed.

Wave absorbing system using inclined perforated plates

The interaction of oblique monochromatic incident waves with horizontal/inclined/dual porous plates is investigated in the context of two-dimensional linear potential theory and Darcy's law (the normal velocity of fluid passing through a thin porous plate is linearly proportional to the pressure difference across it). The developed theory is verified by both small-scale and full-scale experiments. First, matched eigenfunction expansion (MEE) solutions for a horizontal porous plate are obtained. The relationship between the plate porosity and the porous parameter is obtained from systematic model tests by using six porous plates with different sizes and spacing of circular holes. Secondly, a multi-domain boundary-element method (BEM) using simple-sources (second-kind modified Bessel function) is developed to confirm the MEE solutions and to apply to more general cases including inclined or multiple porous plates. The BEM-based inner solutions are matched to the eigenfunction-based outer solutions to satisfy the outgoing radiation condition in the far field. Both analytical and BEM solutions with the developed empirical porous parameter agree with each other and correlate well with both small-scale data from a two-dimensional wave-tank test and full-scale measurement in a large wave basin. Using the developed predictive tools, wave-absorption efficiency is assessed for various combinations of porosity, water depth, submergence depth, wave heading, and plate/wave characteristics. In particular, it is found that the performance can be improved by imposing the proper inclination angle near the free surface. The optimal porosity is near porosity P=0.1 and the optimal inclination angle is around 10° as long as the plate length is greater than 20% of the wavelength. Based on the selected optimal parameters (porosity=0.1 and inclination angle=11.3°), the effective wave-absorption system for MOERI's square basin is designed.

Simplified analytical solutions for wave interaction with absorbing-type caisson breakwaters

Simplified analytical solutions are presented to model the interaction of linear waves with absorbing-type caisson breakwaters, which possess one, or two, perforated or slotted front faces which result in one, or two, interior fluid regions (chambers). The perforated/slotted surfaces are idealized as thin porous plates. Energy dissipation in the interior fluid region(s) inside the breakwater is modelled through a damping function. Under the assumption of potential flow and linear wave theory a boundary-value problem may then be formulated to describe wave interaction with the idealized structure. A solution to this simplified problem may be obtained by an eigenfunction expansion technique and an explicit analytical expression may be obtained for the reflected wave height. Using the experimental work of previous authors, damping coefficients are determined for both single and double chamber absorbing-type caisson breakwaters. Based on the damping for a single perforated-wall breakwater, a methodology is proposed to enable the estimation of the damping coefficients for a breakwater with two chambers. The theoretical predictions of the reflection coefficients for the two-chamber structures using the present model are compared with those obtained from laboratory experiments by other authors. It is found that the inclusion of the damping in the interior fluid region gives rise to improved agreement between theory and experiment.

On the effect of the bending vibration on the acoustic properties of thin poroelastic plates

An experimental study on the effect of bending vibration on the acoustic properties of thin porous plates is presented. Poroelastic plates are tested in a large impedance tube in the lower frequency range. It is shown that bending vibration can be excited by the incident sound and detected by measuring the acoustic impedance of a plate. This effect together with the effect of the flow resistivity on the values of the acoustic impedance of the plate are shown. The data from the large and small impedance tubes illustrate how these effects are reduced with the reduced size of the plate.

Analysis of the transpiration cooling of a thin porous plate in a hot laminar convective flow

This paper deals with the asymptotic and numerical analysis for the steady-state transpiration cooling of a thin porous flat plate in a laminar hot convective flow, taking into account the streamwise heat conduction through the plate. For high conductivity plates, a regular perturbation analysis has been carried out, yielding a three-term asymptotic solution for the distribution of plate temperature. In the limit of a very poorly conducting plate, a singular perturbation technique, based on matched asymptotic expansions, is employed to solve the governing equations. We also solved the equations numerically using a quasilinearization technique. The numerical results are in good agreement with the asymptotic solution close to the asymptotic limits studied.

Stress and strain in a plate subjected to intensive drying

The study was carried out to investigate the development of a stress-strain state in a thin porous plate subjected to intensive drying. A narrow evaporation zone (an evaporation front) divides the plate into two regions with different structures and rheological behavior. The complete saturation area is described by Kelvin-Voigt's viscoelastic model, and the dry area, by Hooke's elasticity law. Shrinkage is suggested to be a function of the evaporation zone velocity. The influence of variable shrinkage on the stress distribution across the plate is studied.

Multiporous plate sensilla in antennae of the chalcidoidea (Hymenoptera)

The ultrastructure of one sensillar type in one group of insects is described so that comparisons of this structure with similar structures in different groups of insects might be made. The ultrastructure of multiporous plate sensilla (MPS) in antennae was studied in 13 species from 7 families of Chalcidoidea. The cuticle of the MPS consists of an elongated, porous plate elevated above the antennal surface. Two cuticular invaginations form 3 channels, a median channel and 2 lateral channels that extend through the length of the sensillum. The MPS are innervated by numerous neurons, more than 50 in some species. The dendrites extend towards the median channel at the proximal end of the sensillum. When the dendrites reach the median channel, they branch and turn towards the distal end of the sensillum, traversing its longitudinal axis. Pore tubules, which occur in the pore chambers, come in contact with the membranes of the dendritic branches. There are 2 types of MPS: (1) with a relatively thin porous plate and many pores occurring in females and males; (2) with a thicker porous plate and fewer pores occurring in females only. The MPS in the Chalcidoidea are compared with the MPS in other Hymenoptera and the functional significance of the 2 types of MPS in the Chalcidoidea is discussed.

Typology of ephemerid chloride cells.

The tracheal gills of 16 species of mayfly larvae were studied with regard to the chloride cells. The ephemerid chloride cells occur as two main types: single cells and cell complexes. The single chloride cells are characterized by deep tubular or slit-like infoldings of the apical cell membrane, whereas the chloride cell complexes show numerous intercellular channels resulting from cellular interdigitation at the basolateral side. According to the structural organization of the apices, the ephemerid chloride cells may be classified into caviform, coniform, bulbiform and filiform types. In the caviform type (single chloride cell), the apex retracts to form an apical cavity similar to teleost chloride cells. In the other types (chloride cell complexes), there is a progressive extension of the central cell apex into or beyond the cuticle in the form of cones, bulbs or filaments. The common feature of all types is the differentiation of the cuticle into thin porous plates or envelopes covering or surrounding the various forms of apices. Histochemical precipitation of sodium and chloride in the apical region suggests that all types have basically the same function of salt absorption. The population of the various types differs with the species. However, there seem to be some taxonomic regularities with respect to the families. No relation was found between the types of chloride cells and habitat of the species.

I. On the molecular mobility of gases

The molecular mobility of gases is here considered in reference chiefly to the passage of gases, under pressure, through a thin porous plate or septum, and to the partial separation of mixed gases which can be effected, as will be shown, by such means. The investigation arose out of a renewed and somewhat protracted inquiry regarding the diffusion of gases (depending upon the same molecular mobility), and has afforded certain new results which may prove to be of interest in a theoretical as well as in a practical point of view. In the diffusiometer, as first constructed, a plain cylindrical glass tube, rather less than an inch in diameter and about ten inches in length, was simply closed at one end by a porous plate of plaster of paris, about one-third of an inch in thickness, and thus converted into a gas receiver.

XVII. On the molecular mobility of gases

The molecular mobility of gases will be considered at present chiefly in reference to the passage of gases, under pressure, through a thin porous plate or septum, and to the partial separation of mixed gases which can be effected, as will be shown, by such means. The investigation arose out of a renewed and somewhat protracted inquiry regarding the diffusion of gases (which depends upon the same molecular mobility), and has afforded certain new results which may prove to be of interest in a theoretical as well as in a practical point of view. In the Diffusiometer, as first constructed, a plain cylindrical glass tube, about 10 inches in length and rather less than an inch in diameter, was simply closed at one end by a porous plate of plaster of Paris, about one-third of an inch in thickness, and was thus converted into a gas-receiver. A superior material for the porous plate has since been found in the artificially compressed graphite of Mr. Brockedon, of the quality used for making writing-pencils. This material is sold in London in small cubic masses about 2 inches square. A cube may easily be cut into slices of a millimetre or two in thickness by means of a saw of steel spring. By rubbing the surface of the slice without wetting it upon a flat sand-stone, the thickness may be further reduced to about one-half of a millimetre. A circular disc of this graphite, which is like a wafer in thickness but possesses considerable tenacity, is attached by resinous cement to one end of the glass tube above described, so as to close it and form a diffusiometer (fig. 1). The tube is filled with hydrogen gas over a mercurial trough, the porosity of the graphite plate being counteracted for the time by covering it tightly with a thin sheet of gutta percha (fig. 2). On afterwards removing the latter, gaseous diffusion im­mediately takes place through the pores of the graphite. The whole hydrogen will leave the tube in forty minutes or an hour, and is replaced by a much smaller proportion of atmospheric air (about one-fourth), as is to be expected from the law of the diffusion of gases.