Filtration Permeability Research Articles

The fiber‐coating model of biopharmaceutical depth filtration

AbstractDepth filters are often used in biotechnology processes to remove cell debris from cell culture solutions. A model of filter plugging was developed to allow predictions of required filter area from limited amounts of initial data. The filter microstructure was idealized as an assembly of randomly oriented, straight, cylindrical fibers. It was assumed that filters plug as solids coat the surfaces of fibers, making them thicker and reducing filter porosity and permeability. The Carman–Kozeny equation was used to allow calculation of filter permeability as a function of filter fiber radius, filter solid fraction, and volume filtered. An explicit equation for filtrate volume as a function of time during constant pressure operation was derived, and an explicit equation for pressure as a function of time during constant flow rate operation was derived. A second model that accounted for the combined effects of fiber coating and surface caking was also derived. The models were tested on data from a replica cell culture fluid filtered through a glass fiber based depth filter and data from E. coli lysate filtered through glass fiber and diatomaceous earth based depth filters. The fiber coating model provided good fits of the volume vs. time data and good predictions of filter capacity from limited initial data. The combined cake‐fiber coating model provided improved performance over the fiber coating model. The models are useful tools for sizing of depth filters for fermentation and cell culture applications and may be useful for other liquid and gas filter applications. © 2005 American Institute of Chemical Engineers AIChE J, 2005

Modeling of Porous Filter Permeability via Image-Based Stochastic Reconstruction of Spatial Porosity Correlations

A methodology for producing a pore-scale, 3D computational model of porous filter permeability is developed that is based on the analysis of 2D images of the filter matrix and first principles. The computationally reconstructed porous filter model retains statistical details of porosity and the spatial correlations of porosity within the filter and can be used to calculate permeability for either isotropic or 1D anisotropic porous filters. In the isotropic case, validation of the methodology was conducted using 0.2 and 0.8 microm ceramic membrane filters,forwhich it is shown that the image-based computational models provide a viable statistical reproduction of actual porosity characteristics. It is also shown that these models can predict water flux directly from first principles with deviations from experimental measurements in the range of experimental error. In the anisotropic case, validation of the methodology was conducted using a natural river sand filter. For this case, it is shown that the methodology yields predictions of filtration velocity that are similar or better than predictions offered by existing filtration models. It was found for the sand filter that the deviation between observation and prediction was mostly due to swelling during the preparation of the sand filter for imaging and can be reduced significantly using alternative methods reported in the literature. On the basis of these results, it is concluded that the computational reconstruction methodology is valid for porous filter modeling, and given that it captures pore-scale details, it has potential application to the investigation of permeability decline underthe influence of pore-scale fouling mechanisms.

An Experimental and Numerical Analysis of Puff Hydrodynamics

Abstract The permeability of a tobacco rod in a cigarette increases as it converts into char and ash in the coal. The hot coal introduces a significant resistance to the air flow when air passes through. Through a series of experiments, the cigarette burn line and burn rate, the centerline temperature, and the pressure drop were measured for continuous puffing conditions. The gas viscosity was calculated from the temperature distribution inside the cigarette and applying Sutherland's law. Then, the experimental setup was mathematically modeled from a commercially available CFD (Computational Fluid Dynamics) code and, by matching the numerical and experimental results, the changes in coal and filter permeability during puffing were estimated. The numerical simulation successfully reproduced the results of experiments on the air flow through the coal, ventilation holes and paper wrapper.

Thermal effects on CR-39 detector response and permeability of some membranes used in radon measurements

Passive technique based on a diffusion chamber fitted with permeable membrane and CR-39 detector is applied in the present study. The detector response and the filter permeability for radon were measured as a function of exposure temperature. The combined effects on the detector and membrane are studied in the temperature range from 27 to 58 °C. Two membrane categories, the paper-type and the polymer-type, are used. The obtained results show advantages of paper-type membranes over polymer-type, where the permeability of paper filter is temperature independent. As a result, the detector response is increased with temperature by a higher rate in case of polymer membrane. Consequently, the using polymer type in radon measurement at unusual temperature needs corrections. The measurements were taking into consideration the effect of temperature on the radon source emanation power which increased from 0.518 to 0.724 in the studied temperature range. The combined uncertainty for all measured parameters is calculated and discussed.

Particle transport characteristics and filtration of granitic residual soils from the Korean peninsula

Weathered granitic residual soils, which are found in much of the Korean peninsula, pose unique challenges in terms of internal stability and filtration. The particle transport and filtration behavior of two extreme soil types, named Shinnae-dong and Poi-dong, are investigated in this paper. The erodibilities of the two soils are evaluated using constant flow-rate experiments on both undisturbed samples and samples with cylindrical holes. A comparison of the results from these experiments revealed the extent of particle redeposition and self-filtration in the internal erosion process. In spite of the differences in the mineralogical properties and engineering characteristics of the two soils, the size of the eroded particles from the two soils fell within the same range of 1–100 µm. The two soils were coupled with filters, chosen according to the US Bureau of Reclamation's (USBR) filter criteria, to determine the efficiency of filters in minimizing erosion. It was found that the filters significantly minimized the erosion of the two base soils. However, the associated reductions in filter permeability are greater than one order of magnitude. Experiments using filters alone with particulate suspensions as the influents enabled the evaluation of a coefficient, λ, which could be used to characterize the particle retention capacities of the filters.Key words: particle transport, residual soils, filtration, drainage, Korean peninsula, soil filter criteria.

Effect of filter permeability on the release of captured dust from a rigid ceramic filter surface

Accumulation and release mechanisms of captured dust from a ceramic filter element were tested using five elements made of different materials and structures. Increase of the pressure drop due to the accumulation of dust was continuously monitored until it reached a predetermined value. Captured dust was then removed from the element surface by injecting a high-pressure pulse cleaning air. The behavior of the dust detachment was monitored by several means, such as pressure change at various locations along the element, movement of released dust and their high-speed video images.As a result, pressure drop of dust on the element was found to increase quickly at the beginning because of the formation of a dense dust layer on the filter surface and then a slowdown in the increase in rate due to the formation of a coarse layer. A similar trend was observed for all tested elements; however, quantitatively, it strongly depended upon the filter material and structure. To reach a predetermined pressure drop, the filtration time of each filter is different and increases with filter permeability. Furthermore, the calculated dust porosity at a large dust-load condition also indicated that it increases as filter permeability increases. These obtained results indicate the dependence of filter permeability on the structure of the accumulated dust layer. In the cleaning process, it is found that pressure traces after the injection of cleaning air also have different behaviors, depending on the filter permeability. In case of a high-permeability filter, the cleaning process starts almost immediately after injection of cleaning air. For a low-permeability filter, cleaning air is stored before the cleaning process occurred. Based on the experimental observation, the detachment behavior of captured dust from a filter surface is related to the filtration condition and filter properties.

Time-Dependent Particle Transport through Granular Filters

This paper describes an analytical model of filtration for granular media, based on the mechanics of particle migration under hydraulic loads. A new equation to predict the probability of particle movement through a 3D network model of the filter voids has been developed. Void constriction sizes are determined based on the particle-size distribution and relative density of the filter. An important new development is the differentiation between particles that form part of the filter structure and fine particles that are loose within the filter voids, or coarse particles that are enmeshed in a matrix of fines. The rate of particle erosion and transport is governed by the consideration of mass and momentum conservation. The model describes the time-dependent change of flow rate and base and filter particle-size distribution, porosity, and permeability. The model has application in the design of granular filters for noncohesive uniform, well-, and broadly graded base and filter materials.

Changes in pressure loss and face velocity of ceramic candle filters caused by reverse cleaning in hot coal gas filtration

Hot coal gas filtration using ceramic candle filters with off-line cleaning showed rapid changes in pressure loss and face velocity during filter cleaning, due to the injection of cleaning gas and the decrease of filtration area. These changes had the capacity to affect facilities which are sensitive to pressure change and filter durability. From this point of view, on-line pulse jet cleaning was thought to be preferable to off-line cleaning but still caused some changes. Numerical calculations showed that a smaller system pressure loss before cleaning and a short pulse duration were most effective in reducing those changes. Some properties of the pulse jet cleaning were also investigated both experimentally and by numerical calculations. In a long candle, the cleaning pressure, which is the pressure difference in the filter and residual dust layer, varied along the filter, and a diffuser or an entrance region was necessary to accomplish cleaning throughout the filter. A onedimensional numerical model could estimate the cleaning pressure as a function of reservoir pressure, filter permeability, etc. © 1998 Elsevier Science S.A. All rights reserved.

Feasibility of warable artificial kidney using presently commercially availble hollow-fiber membrane

On the assumption that continuous treatment is effective in preventing β2-microglobulin deposition in a patient without kidney function, a wearable artificial kidney device was theoretically designed on the basis of using presently commercially available hollow-fiber membrane for hemodialysis. The device was assumed to be connected between an arteriole and a large vein. The device, with an optimal dimension consisting of the membrane with an appropriate filtration permeability, was capable of carrying out continuous hemofiltration using the blood pressure of the patient only and of preventing β2-microglobulin deposition. If dialysate was fed into the device for an appropriate time every day, concentrations of urea nitrogen and creatinine were also maintained at a lower level than that of conventional intermittent hemodialysis. Because the dimension and technical data of the device giving these results are comparable to those of commercially available hemodialyzers, we should reconsider whether the wearable artificial kidney can be put into clinical use.

C013 Different effects of calcium blockers on large arteries fluid filtration and albumin permeability in hypertensive rats

C013 Different effects of calcium blockers on large arteries fluid filtration and albumin permeability in hypertensive rats

Electrochemical filters for oxygen sensors with improved surface properties

Oxygen sensors based on YSZ (yttria stabilized zirconia) are best known for high temperature measurements. The protection of such oxygen sensors with dense electrochemical filters is an effective way to increase their life time in aggressive industrial atmospheres. This work reports on the performance of sensors protected by composite or single phase mixed conducting filters. The first group includes materials based on GCO (Gd2O3 doped CeO2)+LC (LaCoO3), and on YSZ+LCM (La(Mn,Co)O3). Sensors protected with GCO+LC composites showed the best performance amongst the composite filters already evaluated. Electroded single phase GCO filters were also tested to check on the role of surface reaction kinetics on the overall oxygen transport process across the filter. The fastest sensor responses to a sudden decrease in oxygen partial pressure were obtained with deposited electrodes either on both surfaces of the filter or on the filter cathode side. These preliminary results suggest that the cathodic process is more relevant than the anodic one in determining the filter permeability (and protected sensor performance), which fulfils the logical requirement of electrode free surfaces in contact with the furnace atmosphere.

Mechanism of Cake Buildup in Crossflow Filtration of Colloidal Suspensions

Experimental results are presented for the crossflow filtration of concentrated bentonite suspensions. It is proposed that the hydrodynamic forces acting on the suspended colloids determine the rate of cake buildup and, therefore, the fluid loss rate. A simple model is proposed that predicts a power law relationship between the filtration rate and the shear stress at the cake surface ( q γ τ 1/n w). This is found to be consistent with experimental data at different filtration times at various suspension flow rates using three different suspensions. The model shows that the cake formed will be inhomogeneous with smaller and smaller particles being deposited as filtration proceeds. An equilibrium cake thickness is achieved when no particles small enough to be deposited are available in the suspension. The cake thickness as a function of time can be computed from the model. It is also shown that for a given suspension rheology and flow rate there exists a critical permeability of the filter below which no cake will be formed. This critical permeability has been computed for our experiments. The model suggests that the equilibrium cake thickness can be precisely controlled by an appropriate choice of suspension flow rate and filter permeability. These observations have important implications in cross-flow filtration and in slip-casting of inorganic membranes.

Convection of macromolecules is the dominant mode of transport across horizontal 0.4- and 3-μm filters in diffusion Chambers: Significance for biologic monolayer permeability assessment

The purpose of the present study was to evaluate the permeability characteristics of fluorescein-labeled hydroxyethyl starch (FITC-HES, 20 < molecular radius, a E < 111Å) across large pore (0.4- and 3-μm polycarbonate) filters used in endothelial cell monolayer diffusion studies. Although the apparent permeability ( P) of the FITC-HES macromolecules across these filters declined as the molecular radius increased, this decline was less than that associated with each solute's free diffusion ( D 0). Thus, the P D 0 anomalously increased as a E increased, a pattern not seen for free diffusion (flat P D 0 with increased a E) or restricted diffusion (decline in P D 0 with increased a E). Substantial natural convection across the porous filters produced the anomalous P D 0 curve for the following reasons: (1) this effect was elevated with positive pressure and ameliorated by zero driving pressure, and (2) the effect was much greater across filters with large (3 μm) vs small (0.4 μm) pore sizes. In addition, we estimated that less than half of macromolecular transport above 50 Å probe radius at zero transmural pressure arrives by diffusion. The findings suggest that the property of restricted diffusion of biologic layers on these filters will be artifactually exaggerated when the measured resistance of the filter is subtracted from that of the filter plus biologic monolayer. Remedies for this problem may include using smaller pore filters, filters layered with extracellular material, or structural methods to determine true filter permeability.

Interfacial Transport in Large and Small Blood Vessels

In this paper we shall review some recent mathematical models which have led to new conceptual views of the ultrastructural pathways by which water, solutes and large molecules cross the endothelial interface between tissue and blood. In particular, we shall show how a sequence of models for the endothelium and underlying tissue in large arteries have finally led to the experimental discovery of the large pore via which LDL and other large molecules enter the artery wall and how a new three-dimensional model for the interendothelial cleft in capillaries might reconcile the several long standing paradoxes relating to the measured filtration and solute permeability coefficients in the transcapillary exchange of water and hydrophilic solutes in the microcirculation.

Characteristics of mole drainage as a major ameliorative technique for surface-waterlogged soils

The equation of water-exchange in the filtration area has been used as a basis for describing the filtration and hydraulic regime in mole draining. It has been found that the depression curve of the steady-state and nonsteady-state subsoil flux provides the most adequate characterization of the major processes associated with the drainage of soils which become surface waterlogged because of their having a second horizon (from 20 or 50 cm below the surface) with low permeability. The roles of the space between drains, the depth of drains and the water permeability of the mole slit have been differentiated and assessed. Mole drainage ought to be made within the upper permeable horizon. In case this is impossible for static and field management reasons, a part of the mole drain may be burrowed through the second, low-permeable horizon but this penetration should be as small as possible and high geometric and filtration permeability of the mole slit should be ensured, especially of the portion extending into the low-permeable horizon.

The osmotic permeability of isolated calf pulmonary artery endothelial cells

Osmotic permeability coefficients, P F , for water in isolated calf pulmonary artery endothelial cells determined over the temperature range 41 to 20°C are 311 · 10 −5 cm · s −1 at 37°C and 159 · 10 −5 cm · s −1 at 20°C. The value at 37°C is close to that reported earlier for the diffusional permeability coefficient, P D . The P F /P D ratio is 1.0 at 37°C. The P F values are within the range of values extrapolated for filtration permeability in pulmonary endothelium. The temperature dependence expressed as the activation energy is 7.2 kcal · mol −1. The product of hydraulic conductivity, L p (or P F ) and of viscosity changes in water is not constant from 37 to 20°C. These results can be interpreted to indicate a similar pathway for water whether under diffusional or osmotic gradients.

Single kidney function: Effect of acute protein and water loading on microalbuminuria

The hyperfiltration induced by an acute response to an oral protein and water load was investigated to ascertain whether it can modify the urinary albumin excretion (UAE) in the microalbuminuric range by further increasing the glomerular filter permeability. To this end, six patients with a single kidney selected as having microalbuminuria on a regular diet without the clinical or laboratory data of overt renal disease and eight healthy subjects received a short-term protein and water load (150 g of meat-derived protein and 1 liter of water). In patients with one kidney, mean basal UAE values were significantly higher than in control subjects (p <0.006), whereas endogenous creatinine clearance values were only slightly lower (p >0.05). One hour after the protein and water load, an abrupt increase in microalbuminuria levels was found in patients with one kidney and mean UAE values were significantly higher than in control subjects (p <0.002), whereas mean creatinine clearance values were significantly lower in patients than in control subjects (p <0.01). High UAE (p <0.002) and low creatinine clearance (p <0.002) values were maintained over the following four hours in patients with one kidney. These data suggest that in the single kidney with reduced renal functional reserve, an oral protein and water load magnifies the pre-existing loss of glomerular permselective properties due to chronic hyperfiltration as manifested by a further increase in microalbuminuria.

The simulated motion of a loose revetment block

The equations of motion are developed for an unrestrained revetment block lying on a free-flowing filter layer, subject to harmonic base pressure during wave downrush. The resulting trajectories are calculated numerically and depicted at discrete time intervals. The influence is then estimated of progressive decreases both in the spacing of adjacent blocks and in the filter layer permeability. Some consideration is also given to small-amplitude, continuous oscillations. It is suggested that reductions in filter thickness and permeability are more effective in reducing block uplift than are increases in block thickness.

Vascular reactions to perfusion fixation.

Vascular reactions to fixation with a 2 x 5% w/v glutaraldehyde fixative were studied in a constant flow perfusion system on isolated rabbit intestines and hind limb preparations. Reactions induced by the fixative were compared to reactions induced by noradrenaline in each single preparation. Changes in vascular resistance were assessed from continuous recordings of arterial and venous pressures and perfusion flow. Changes in vascular filtration and macromolecular permeability during fixation were approximated from recordings of flow and measurements of concentrations of dextran in the perfusate at the arterial inlet and at the venous outlet. Our results indicate that the vascular bed of the preparations studied can be reliably fixed in a high resistance state of smooth muscle activity induced by noradrenaline as well as in a low resistance state in the absence of noradrenaline, provided that hydrodynamic parameters are strictly controlled. The vascular filtration decreases during fixation. In optimally perfused preparations 5-10 min are required to fully saturate the binding capacity of the tissue for glutaraldehyde. Data on viscosity and colloid osmotic pressure of Tyrode solution containing dextran T-70 in various concentrations, and of various aldehyde-containing fixatives in 0 . 1 M sodium phosphate buffer with and without dextran added, are given.

Pathophysiology of the acutely failing kidney.

The term “acute renal failure” (ARF) describes a curtailment of glomerular function and tubular reabsorptive and secretory processes. The kidneys loose their ability to concentrate the urine and to lower the urinary sodium concentration to values below approximately 40 mmol per 1. Glomerular filtration rate (GFR) is always considerably reduced, which leads to an accumulation of creatinine and urea in the blood. The impairment of cellular metabolism, either through oxygen deprivation or nephrotoxins, is the causal event in the generation of ARF. Each etiological factor leading to the phenomenon of ARF will initially affect different individual cellular functions; for example, ATP formation during anoxia, the formation of membrane characteristics by metal ions, or DNA synthesis by toxic peptides. Although their initial effects differ, the final changes in overall cellular function induced by anoxia or nephrotoxic substances are similar and reflect the inherent function of the tubular cells. In the kidney it is the diminished reabsorptive and secretory functions of the tubular cells which determine the excretory function of the kidney during ARF. Because of the different etiological factors different intrarenal pathophysiological reactions follow and dominate, such as intratubular cast formation, increased tubular permeability, reduced filtration area or filtration permeability of the glomerular capillaries, stimulation of the tubuloglomerular feedback system, and renal vasoconstriction. A specific combination of the various abnormalities becomes typical during ARF and the significance of the various pathogenetic factors may differ during its course over time.