Filter Porosity Research Articles

Use of Nuclepore filters for ambient and workplace nanoparticle exposure assessment—Spherical particles

Nuclepore filter collection with subsequent electron microscopy analysis for nanoparticles was carried out to examine the feasibility of the method to assess the nanoparticle exposure. The number distribution of nanoparticles collected on the filter surface was counted visually and converted to the distribution in the air using existing filtration models for Nuclepore filters. To search for a proper model, this paper studied the overall penetrations of three different nanoparticles (PSL, Ag and NaCl), covering a wide range of particle sizes (20–800 nm) and densities (1.05–10.5 g cm−3), through Nuclepore filters with two different pore diameters (1 and 3 μm) and different face velocities (2–15 cm s−1). The data were compared with existing particle deposition models and modified models proposed by this study, which delivered different results because of different deposition processes considered. It was found that a parameter associated with flow condition and filter geometry (density of fluid medium, particle density, filtration face velocity, filter porosity and pore diameter) should be taken into account to verify the applicability of the models. The data of the overall penetration were in very good agreement with the properly applied models. A good agreement of filter surface collection between the validated model and the SEM analysis was obtained, indicating a correct nanoparticle number distribution in the air can be converted from the Nuclepore filter surface collection and this method can be applied for nanoparticle exposure assessment.

Simultaneous Reduction of Particulate Matter and NOx Emissions Using 4-Way Catalyzed Filtration Systems

The next generation of diesel emission control devices includes 4-way catalyzed filtration systems (4WCFS) consisting of both NOx and diesel particulate matter (DPM) control. A methodology was developed to simultaneously evaluate the NOx and DPM control performance of miniature 4WCFS made from acicular mullite, an advanced ceramic material (ACM), that were challenged with diesel exhaust. The impact of catalyst loading and substrate porosity on catalytic performance of the NOx trap was evaluated. Simultaneously with NOx measurements, the real-time solid particle filtration performance of catalyst-coated standard and high porosity filters was determined for steady-state and regenerative conditions. The use of high porosity ACM 4-way catalyzed filtration systems reduced NOx by 99% and solid and total particulate matter by 95% when averaged over 10 regeneration cycles. A "regeneration cycle" refers to an oxidizing ("lean") exhaust condition followed by a reducing ("rich") exhaust condition resulting in NOx storage and NOx reduction (i.e., trap "regeneration"), respectively. Standard porosity ACM 4-way catalyzed filtration systems reduced NOx by 60-75% and exhibited 99.9% filtration efficiency. The rich/lean cycling used to regenerate the filter had almost no impact on solid particle filtration efficiency but impacted NOx control. Cycling resulted in the formation of very low concentrations of semivolatile nucleation mode particles for some 4WCFS formulations. Overall, 4WCFS show promise for significantly reducing diesel emissions into the atmosphere in a single control device.

NOx storage capacity of yttria-stabilized zirconia-based catalysts

A NOx chemisorption study was performed on yttria-stabilized zirconia (YSZ), an O2− ionically conducting ceramic. NO2 chemisorption on YSZ as well as NO+O2 interactions on Pt/YSZ catalyst were clearly correlated to the presence of surface oxygen vacancies. A remarkable NOx storage capacity was obtained on Pt/YSZ powdered catalysts, by combining nitrates formation and NO2 adsorption on oxygen vacancies. Under cycling conditions (lean phase/rich phase: 3min/2min) and using propene as a reductant, powdered Pt-Rh catalyst exhibited overall NOx abatement conversion of around 75% at 250 and 300°C. Pt/Rh/YSZ catalysts were finely dispersed in the porosity of SiC mini diesel particulate filters (DPFs). Quite reproducible and stable NOx conversions were achieved in cycling conditions with values around 50% between 250 and 400°C. In addition, YSZ-based catalysts have shown high thermal resistance and sulfur tolerance.

Porosity, Flow, and Filtration Characteristics of Frustum-Shaped Ceramic Water Filters

AbstractThis paper presents the results of an experimental study of the effects of porosity on the flow rate and Escherichia coli (E. coli) filtration characteristics of porous ceramic water filters (CWFs) prepared without a coating of silver. Clay-based CWFs were fabricated by sintering composites of redart clay and fine woodchips (sawdust) in three different proportions by volume, viz: 50∶50, 65∶35, and 75∶25. Sintering the greenware below 1,000°C produced reddish colored pot of three different degrees of porosity and micro- and nanoscale pores, which are the key to efficient filtration. The porosities and pore size distribution frequencies of the sintered clay ceramics were characterized using mercury intrusion porosimetry (MIP). The porosity of the CWFs ranged from ∼36% to ∼47% and increased with increasing sawdust content in a linear fashion, and the pore size varied from ∼10 nm to ∼100 μm. The volume flow rates of water through the CWFs were investigated by measuring the cumulative amount of water...

Effects of Sol-Gel Treatment and Plating on the Electrical Properties of Multilayer Filters

The effects of sol-gel treatment and plating on the electrical properties of multilayer filters were investigated. The results showed that the sol-gel treatment process can effectively lower the apparent porosity of multilayer filters, preventing the penetration of electroplate liquid into the filters. The mean insertion loss rise for the sol-gel-treated components was 0.171 dB, which increased up to 0.811 dB for the filters without sol-gel seal treatment. Microstructural studies revealed that the sol-gel seal treatment is an effective preplating treatment to diminish the insertion loss of multilayer filters.

Inverse Estimation of the Effective Diffusion of the Filter in the In Situ Diffusion and Retention (DR) Experiment

Porous filters are often used in laboratory and in situ diffusion and retention experiments. The proper interpretation of these experiments requires knowing the effective diffusion, De, of the filter which is commonly determined from laboratory diffusion experiments or estimated from the filter porosity. The De of the filter in the in situ experiment may differ from the De of the filter measured in the laboratory due to pore clogging. Here, we present an inverse method to estimate the De of the filter of in situ diffusion experiments. The method has been tested for several sampling schemes, numbers of synthetic data, N, and standard deviations of the noise, σ. It has been applied to the following tracers used in the in situ diffusion and retention (DR) experiment performed in the Opalinus clay at Mont Terri underground research laboratory: HTO/HDO, Br−,I−, 22 Na+,133 Ba2+,85 Sr2+, Cs+/137Cs+, and 60Co2+. The estimation error increases with the standard deviation of the noise of the data and decreases with the number of data. It is smallest for sorbing tracers. The De of the filter can be properly estimated from 12 data collected within the first 3 days for conservative tracers as long as σ ≤ 0.02 and for sorbing tracers as long as σ ≤ 0.05. The estimate of De for conservative tracers is poor when data are collected from a 10-day experiment with daily sampling. The convergence of the estimation algorithm for conservative tracers improves by starting with a value of the De smaller than the true value. The choice of the initial value of De does not affect the convergence of the estimation algorithm for sorbing tracers. Filter clogging and vertical flow though the filter can influence the tracer transport through the filter. The use of the De of the filter obtained from a laboratory test for the in situ experiment may result in large errors for strongly sorbing tracers. Such errors can be overcome by estimating the equivalent De of the filter with the proposed inverse method which will be useful for the design of in situ diffusion experiments.

Measurement of Diesel Exhaust Particles by LII and Evaluation of DPF

In this study, we measured PM concentration in diesel exhaust gas by laser-induced incandescence (LII). To evaluate the diesel particulate filter (DPF), the measurement was conducted at the point right after DPF exit. Four filters of different porosity and wall thickness were tested. In addition, EEPS system was used to examine the particle number concentration and calibrate LII signals. Based on the time-variation of PM concentration, an initial PM filtration efficiency and soot cake formation in DPF were discussed. The LII technique can be potentially applied to find the location of PM leakage through the filter and evaluate the after-treatment system.

Septic AKI in ICU patients. diagnosis, pathophysiology, and treatment type, dosing, and timing: a comprehensive review of recent and future developments.

Evidence is accumulating showing that septic acute kidney injury (AKI) is different from non-septic AKI. Specifically, a large body of research points to apoptotic processes underlying septic AKI. Unravelling the complex and intertwined apoptotic and immuno-inflammatory pathways at the cellular level will undoubtedly create new and exciting perspectives for the future development (e.g., caspase inhibition) or refinement (specific vasopressor use) of therapeutic strategies. Shock complicating sepsis may cause more AKI but also will render treatment of this condition in an hemodynamically unstable patient more difficult. Expert opinion, along with the aggregated results of two recent large randomized trials, favors continuous renal replacement therapy (CRRT) as preferential treatment for septic AKI (hemodynamically unstable). It is suggested that this approach might decrease the need for subsequent chronic dialysis. Large-scale introduction of citrate as an anticoagulant most likely will change CRRT management in intensive care units (ICU), because it not only significantly increases filter lifespan but also better preserves filter porosity. A possible role of citrate in reducing mortality and morbidity, mainly in surgical ICU patients, remains to be proven. Also, citrate administration in the predilution mode appears to be safe and exempt of relevant side effects, yet still requires rigorous monitoring. Current consensus exists about using a CRRT dose of 25 ml/kg/h in non-septic AKI. However, because patients should not be undertreated, this implies that doses as high as 30 to 35 ml/kg/h must be prescribed to account for eventual treatment interruptions. Awaiting results from large, ongoing trials, 35 ml/kg/h should remain the standard dose in septic AKI, particularly when shock is present. To date, exact timing of CRRT is not well defined. A widely accepted composite definition of timing is needed before an appropriate study challenging this major issue can be launched.

The performance of electropositive nanofibrous filter media

Four types of nanofibrous filters, EPN-1, EPN PAC-2, EPN-3, and EPN PAC-4, were investigated in this trial, respectively. The microstructures of nanofibrous filters were analyzed through a scanning electron microscope (SEM), while their elements were determined by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The Zeta potential, specific surface area, porosity and permeation flux of nanofibrous filters were measured in this study. The isoelectric point and pure water permeability coefficient were also calculated. The result shows that the nanofibers are less than 5 μm and are made up of γ-Al 2O 3, silicate and polyester. The electropositive filter is that the nanofiber contains γ-Al 2O 3. The nanofibers have different positive and negative charge at different pH. The specific surface areas of nanofibers are 625.58, 509.13, 850.27 and 780.23 (m 2/g), respectively. The porosity of nanofibrous filters are less than 70%. Pure water permeability coefficients of filters are 80.84, 64.03, 119.17 and 100.26 (L·m − 2 ·s − 1 ·MPa − 1 ), respectively. The performances of nanofibers without nano powdered activated carbon (PAC) are better than those with nano PAC.

Use of Impedance Probe for Estimation of Porosity Changes in Saturated Granular Filters under Cyclic Loading: Calibration and Application

Gravimetric and volumetric sampling techniques are reliable for the measurement of porosity in fully saturated granular filters. However, both methods require a significant effort to gather and prepare samples, are time intensive to process, and do not capture real-time changes. Portable impedance probes serve as a valuable alternative to these destructive and laborious sampling methods. These probes measure the dielectric properties of the soil-water mixtures from which the porosity of filters may be inferred. This study demonstrates that generalized calibrations can result in large errors for porosity estimation when using diverse and small-scale filter types. By comparing with gravimetric and volumetric based porosity measurements for saturated granular filter porosity, impedance probes with filter-specific calibration offer the reliability and confidence owing to its reduced error in a quick, nondestructive fashion. This paper also presents the results of a laboratory investigation using an impedance probe to monitor real-time changes in the porosity of saturated granular filters subjected to cyclic train loading.

Interpretation of Electrokinetic Measurements with Porous Films: Role of Electric Conductance and Streaming Current within Porous Structure

It is shown that in tangential electrokinetic measurements with porous films the porous structure makes contribution not only to the cell electric conductance (as demonstrated previously) but also to the observed streaming current. Both of these contributions give rise to dependences of streaming-potential and streaming-current coefficients on the channel height. However, due to the combined contribution of two phenomena, the dependence of streaming-potential coefficient on the channel height may be rather complicated and not allow for simple extrapolation. At the same time, the dependences of streaming-current coefficient and cell electric conductance on the channel height turn out linear and can be easily extrapolated to zero channel heights. This enables one to determine separately the contributions of external surface of porous film and of its porous structure to the streaming current and of the channel and porous structure to the cell electric conductance. This procedure is illustrated by the measurements of tangential electrokinetic phenomena and electric conductance with Millipore mixed-cellulose membrane filters of various average pore sizes (from 0.025 to 5 mum) in the so-called adjustable-gap cell of SurPASS electrokinetic instrument (Anton Paar GmbH). The design of this cell allows for easy and quasi-continuous variation of channel height as well as accurate determination of cell electric conductance, streaming-current coefficient, and channel height (from the cell hydraulic permeability). The quality of linear fits of experimental data has been found to be very good, and thus, the extrapolation procedures were quite reliable and accurate. Zeta-potentials could be determined of both external film and internal pore surfaces. It is demonstrated that the porous structures make considerable contributions to both streaming-current coefficient and cell electric conductance especially in the case of filters with larger pores. It is also found that, rather surprisingly, in filters with smaller pores the reduction in the filter electric conductivity turns out essentially stronger than could be expected proceeding from the filter porosity.

Full-Scale Removal of Arsenate and Chromate from Water Using a Limestone and Ochreous Sludge Mixture as a Low-Cost Sorbent Material

The oxyanions arsenate (AsO4(3-)) and chromate (CrO4(2-)) are major freshwater contaminants. Arsenate is a problematic contaminant in drinking water reservoirs, and chromate limits the use of urban stormwater runoff. High-capacity, low-cost, energy-efficient treatment technologies are required for the removal of these toxic anions from freshwater sources. Using a 50-m-long dual porosity filter, with limestone as filtering grains, treating stormwater runoff from Copenhagen, Denmark, we tested if addition of the waste product ochreous sludge can improve the removal of arsenate (As) and chromate (Cr) without compromising the calcite's removal affinity fowards metallic cations. Upon on-site embedding of the ochreous sludge, removal of arsenic and chromium was improved greatly, and copper (Cu) removal remained high. Steady-state effluent concentrations were reduced from 31 to 2 microg As/L, 127 to 1.5 microg Cr/L, and 18 to 9.6 microg Cu/L upon mixing with the ochreous sludge. Limestone-ochreous sludge represents a promising low-cost oxyanion and cation sorbent operating at neutral pH without pH control.

A critical review on granular dam filter behaviour – from particle sizes to constriction-based design criteria

Over emphasis on tests results involving base soils with increasing coefficient of uniformity (Cu ) makes the reliability of an empirical particle-based criterion for effective filters questionable. Extra measures such as regrading of base soil are then necessary in order to capture the effectiveness of filter constriction sizes in trapping eroding fines. Recent studies which focused on the role of the sizes of filter voids on overall filtration behaviour have deployed constriction size approaches that were shown to be equally acceptable methods for distinguishing between effective and ineffective filters. This paper examines the evolution of this approach, starting from past empirical and mathematical investigations and proceeding to the eventual development of geometric-probabilistic methods with special reference to embankment dams. Models based on dominant and controlling constriction sizes are introduced, and subsequently the constriction-based retention criteria for granular filters are presented. The proposed retention criteria were verified based on extensive experimental data taken from small- and large-scale filtration tests carried out by various authors. The integration of filter compaction, porosity and Cu , together with the incorporation of analytical principles, provides alternative and rigorous design approaches that remove most limitations of the conventional particle-based criteria, thus making the models essentially more comprehensive and quantifiable.

Batch and Size-Exclusion Chromatographic Characterization of Ultra-high Molar Mass Sodium Hyaluronate Containing Low Amounts of Strongly Scattering Impurities by Dual Low Angle Light Scattering/Refractometric Detection

It is shown that very pure sodium hyaluronate (HA) contains small amounts of strongly scattering impurities not detectable on mass scale by refractometric detection, but clearly detectable using low angle light scattering detection during a static bulk light scattering experiment. Size filtration of its solutions does not remove these impurities, only reduces their amount depending on filter porosity. Complete removal of these particle impurities, independent of filter porosity, is achieved by hydrophobic adsorption on hydrophobic filter membranes. Using 0.1 M NaCl as a mobile phase, size exclusion chromatography (SEC) column removes the impurities by hydrophobic adsorption as well; molar masses obtained from both techniques thus agree when hydrophobic filters are used in bulk light scattering experiments. Diverse hydrodynamic flow retardation effects including slalom chromatography behavior are shown to substantially bias molar mass distributions obtained for ultra-high molar mass (UHM) HA, unless the flow rate in SEC analysis is reduced below 0.1 mL/min. Too high injected concentration (c inj ) is shown to introduce the onset of HA on column degradation. Correct polydispersity indices and molar mass distributions of UHM HA are obtained from SEC at a flow rate of 0.09 mL/min and optimized c inj .

Effects of substrate moisture content, log weight and filter porosity on shiitake ( Lentinula edodes) yield

Production costs for shiitake ( Lentinula edodes) are on the rise in the United States due to increasing expenses including materials, labor and energy. Increased yield and improved bioconversion of raw materials may improve grower profit margins and may help reduce the cost of shiitake to the consumer. Two crops (Crop 1 and 2) of shiitake were grown to evaluate effects of three substrate moisture contents (50%, 55% and 60%), two log weights (2.7 and 3.2 kg) and three porosities of bag filter (low, medium and high) on mushroom yield (g/log) and biological efficiency (BE). Yield data were collected under controlled environmental conditions for two breaks. The formulation with 55% substrate moisture gave the highest yield and BE. Higher mushroom yields were produced from heavier logs (3.2 kg), but BE was not significantly affected. Filter porosity significantly affected yield and BE in Crop 1 but not in Crop 2. Significant interactions were observed for log moisture content × filter porosity for both crops. There were no significant two-way interactions observed for filter porosity × log weight or three-way interactions observed for moisture content × filter porosity × log weight. Maximum yields were obtained from 3.2 kg logs with a substrate moisture content of ca. 55% using medium or low porosity-filtered bags. This study may provide growers with additional information to better optimize production practices and become more efficient and competitive.

Design Analysis of Polymer Filtration using a Multi‐Objective Genetic Algorithm

Filtration of particle debris is an important component of the polymer fiber melt‐spinning process. The filter lifespan is determined by the pressure drop across the filter, which increases as debris accumulates inside the filtration medium. The cost of filter replacement is high, as is the cost of a loss of the finished fiber product due to debris inclusion in the spun fiber. We use a multiobjective genetic algorithm to examine the trade‐off curve that evolves from these competing goals. A “blackbox” simulator models the debris deposition, and we choose filter porosity and pore diameter as the design variables. We provide numerical results and analysis for two sets of competing objectives.

Prediction of air filter efficiency and pressure drop in air filtration media using a stochastic simulation

In this paper, we discussed the relationship of filter efficiency and pressure drop with the porosity, fiber diameter and filter thickness by Geodict®. We found that filter efficiency has exponential relationship with filter porosity, fiber diameter and thickness. Furthermorethe pressure drop has a linear relationship with filter thickness and exponential relationship with filter porosity and fiber diameter, respectively. The influence of electrostatic charge on the particle deposition has been investigated. Simulation results were compared with the actual test results by TSI 3160.

Particle deposition in random fibrous porous materials: effect of acoustic fields, fibres distribution and porosity

Porous filters are widely used to control air pollution and have different industrial applications since they constitute a reliable and low cost solution to separate particulate matter from an air stream. In this study, the particle deposition within 3D porous filters subjected to low-frequency acoustic fields is studied following a numerical approach. Findings demonstrate that the application of acoustic waves enhances the deposition of particles, which in turn improves filter performance. It is shown that frequencies ranging from 200 to 1000 Hz (intensity 120 dB) increase particle deposition up to 2.5 times. Besides, the manner in which fibres are distributed in the porous material and the filter porosity affect considerably the number of particles deposited, for filters subjected to the same filtration velocity.

Simulation on Soot Oxidation with NO2 and O2 in a Diesel Particulate Filter

Although diesel engines have an advantage of low fuel consumption in comparison with gasoline engines, exhaust gas has more particulate matters (PM) including soot. As one of the key technologies, a diesel particulate filter (DPF) has been developed to reduce PM. When the exhaust gas passes its porous filter wall, the soot particles are trapped. However, the filter would readily be plugged with particles, and the accumulated particles must be removed to prevent filter clogging and a rise in backpressure, which is called filter regeneration process. In this study, we have simulated the flow in the wall-flow DPF using the lattice Boltzmann method. Filters of different length, porosity, and pore size are used. The soot oxidation for filter regeneration process is considered. Especially, the effect of NO2 on the soot oxidation is examined. The reaction rate has been determined by previous experimental data. Results show that, the flow along the filter monolith is roughly uniform, and the large pressure drop across the filter wall is observed. The soot oxidation rate becomes ten times larger when NO2 is added. These are useful information to construct the future regeneration system.

Structural Evaluation of Phospholipidic Nanovesicles Containing Small Amounts of Chitosan

In this study we present a full characterization of nanovesicles containing soybean phosphatidylcholine and polysaccharide chitosan. The nanovesicles were prepared by the reverse phase evaporation method, including the preparation of reverse micelles followed by the formation of an organogel, which is dispersed in water to yield the final liposomal particles. Structural changes as a function of the chitosan amount and the filter porosity used in the nanovesicles preparation were studied employing Static and Dynamic Light Scattering as well as Small Angle X-ray Scattering. The hydrodynamic radius of the nanovesicles ranged between 106 and 287 nm, depending on the chitosan contents and the filter porosity. A comparison with nanovesicles free of chitosan indicates the existence of higher contents of multilamellar structures that depends on the chitosan concentration in the vesicles containing chitosan. Typical spherical vesicles having nanometric diameters with polydispersity mostly desired in the biomedical area could only be achieved by filtration through a 0.45 microm porous filter.