Classical Filtration Theory Research Articles

Clariant and Lummus awarded contract for one of the world[StQuote]s largest PDH units

Nanoparticles (NPs) are particles of less than or equal to 100 nm in diameter. Due to their size, they have a significant effect on health and safety of people. Capture of these NPs in general ventilation systems by filters remains one of the most widely used means of protection due to its relative simplicity of implementation and its effectiveness for capturing various size of particles. In North America, filters used in general ventilation systems are tested by the ANSI/ASHRAE Standard 52.2 and are graded according to their efficiency, which is a function of particle diameter. However, the current standard limits the filtration efficiency assessment for particles between 0.3 and 10.0 µm. There is therefore a significant lack of knowledge about the behavior of these filters with respect to the particle diameter below 0.3 µm considering the overall filter used in general ventilation. The main objective of this study was to develop a measurement procedure to evaluate the effectiveness of mechanical filters used in general ventilation systems against NPs. In this regard, a small setup was designed, build and qualified. Then measurement procedure was validated by comparing the penetration measurements with those obtained on qualified big loop setup for nanoparticles, which was inspired by ASHRAE. One type of mechanical filter rated (MERV 8) in three depth sizes (2.54, 5.08 and 10.16 cm) was used to compare the penetrations. The obtained results are consistent with the classical filtration theory for mechanical media and with previous experimental measurements on media. The data presented in this study show that the penetration range of 0.7–1.0 obtained for particle range 22.1–294.3 nm and at 1.00 and 0.75 m/s gives a fairly good correlation (R2 = 0.898) between the two setups. The outcome results validate the methodology used to evaluate the effectiveness of one mechanical filter used in general ventilation systems against nanoparticles by using the small setup.

Albemarle undertakes strategic review of catalyst business

Nanoparticles (NPs) are particles of less than or equal to 100 nm in diameter. Due to their size, they have a significant effect on health and safety of people. Capture of these NPs in general ventilation systems by filters remains one of the most widely used means of protection due to its relative simplicity of implementation and its effectiveness for capturing various size of particles. In North America, filters used in general ventilation systems are tested by the ANSI/ASHRAE Standard 52.2 and are graded according to their efficiency, which is a function of particle diameter. However, the current standard limits the filtration efficiency assessment for particles between 0.3 and 10.0 µm. There is therefore a significant lack of knowledge about the behavior of these filters with respect to the particle diameter below 0.3 µm considering the overall filter used in general ventilation. The main objective of this study was to develop a measurement procedure to evaluate the effectiveness of mechanical filters used in general ventilation systems against NPs. In this regard, a small setup was designed, build and qualified. Then measurement procedure was validated by comparing the penetration measurements with those obtained on qualified big loop setup for nanoparticles, which was inspired by ASHRAE. One type of mechanical filter rated (MERV 8) in three depth sizes (2.54, 5.08 and 10.16 cm) was used to compare the penetrations. The obtained results are consistent with the classical filtration theory for mechanical media and with previous experimental measurements on media. The data presented in this study show that the penetration range of 0.7–1.0 obtained for particle range 22.1–294.3 nm and at 1.00 and 0.75 m/s gives a fairly good correlation (R2 = 0.898) between the two setups. The outcome results validate the methodology used to evaluate the effectiveness of one mechanical filter used in general ventilation systems against nanoparticles by using the small setup.

Relation of the Modern Theory of Disperse Systems with the Classical Filtration Theory

Relation of the Modern Theory of Disperse Systems with the Classical Filtration Theory

Filtration of Submicron Soot Particles, Oil Droplets, and their Mixtures on Single- and Multi-layer Fibrous Filters

The dynamics of filtration efficiency and pressure drop during the simultaneous filtration of soot and oil aerosols on single- and multi-layer filters were investigated, and the determined filtration efficiency was compared with the theoretical efficiency obtained via the classical filtration theory. Additionally, the influence of liquid-phase aerosols on the morphology of the formed deposits was investigated. It was concluded that the addition of oil aerosols decreased the filtration efficiency and lowered the pressure drop increase rate for multi-layer filters. Additionally, for the filtration of aerosols containing soot and high oil concentrations, once maximum filtration efficiency was reached, an efficiency decrease occurred. The system imperfection factor was proposed as a mean to predict the efficiency of multi-layer filters. The modified version of the single fibre efficiency method was used to calculate filter mass change with reasonable accuracy.

Probing the Effective Diffusion Coefficient and Filtration Performance of Micro/Nanofibrous Composite Layered Filters

Diffusion is an important filtration mechanism of fibrous filters for removing fine particles from gas streams. An analytical model is proposed in this work, based on fractal theory, to quantify the effective diffusion coefficient (EDC) across micro/nanofibrous filters with a layered structure. To show the influence of macroscopic parameters of fibrous filters on EDC, the present models are expressed in terms of fiber diameter. Polyacrylonitrile (PAN) nanofibers were prepared by electrospinning on melt-blown polypropylene (PP) microfiber filter materials to form micro/nanofibrous filters. To validate this model, a three-dimensional (3D) fiber model with physical parameters of the samples was reconstructed using the GeoDict code, and the Brownian movement of nanoparticles was simulated to calculate the EDC. Two kinds of pore size distributions for the layer-structured fibrous filters have been identified, which also shows the internal heterogeneity of the filter media. With decreasing fiber diameter, the tortuosity of the pore channel increases, while the EDC decreases. Compared with the numerical simulation and the experimental data reported in the literature, the current model gives a better theoretical prediction. In addition, the diffusion mechanism in classical filtration theory was modified to reduce the deviation between theoretical prediction and experimental results.

Particle Track and Trace during Membrane Filtration by Direct Observation with a High Speed Camera.

A methodology was developed for direct observation and analysis of particle movements near a microfiltration membrane. A high speed camera (1196 frames per second) was mounted on a microscope to record a hollow fiber membrane in a filtration cell with a transparent wall. Filtrations were conducted at varying pressure and crossflow velocities using synthetic core–shell particles (diameter 1.6 μm) of no and high negative surface charge. MATLAB scripts were developed to track the particle positions and calculate velocities of particle movements across and towards the membrane surface. Data showed that the velocity of particles along the membrane increases with distance from the membrane surface which correlates well with a fluid velocity profile obtained from CFD modelling. Particle track and trace was used to calculate the particle count profiles towards the membrane and document a higher concentration of particles near the membrane surface than in the bulk. Calculation of particle velocity towards and away from the membrane showed a region within 3–80 μm from the membrane surface with particle velocities higher than expected from the velocity of water through the membrane, thus the permeation drag underpredicts the actual velocity of particles towards the membrane. Near the membrane, particle velocities shift direction and move away. This is not described in classical filtration theory, but it has been speculated that this is an effect of particle rotation or due to membrane vibration or change in flow pattern close to the membrane.

Micro-scale layered structural filtration efficiency model: Probing filtration properties of non-uniform fibrous filter media

Motivated by modeling of the filtration of non-uniform fibrous filter media, a micro-scale layered structural based single fiber filtration efficiency (SFFE) model is developed to calculate filtration efficiency of clean fibrous filter media. A new methodology based on fractal theory, statistical theory and classical flow field theory is developed in the SFFE model. The microstructure of the four fibrous samples are resolved by the GeoDict code and included in the model. With the non-uniform SFFE model, evolution of the microscopic characteristics of the samples (fiber diameter, fiber orientation, pore size distribution, and permeability) can be probed. Based on analysis of the SEM image of the sample showed that the fiber diameter and orientation distribution were Gaussian. Results from four kinds of fibrous filter media are analyzed and compared with the simulated and theoretical values. The pore size distribution was independent of the grammage. The air permeability decreased with sample thickness, and the fluid had a fast flow velocity for large pores in the porous material. Compared with classical filtration theory, the non-uniform SFFE model show good agreement with the experimental and simulated values.

Permeate flux hysteresis with transmembrane pressure in the gel controlling membrane filtration

The formation of the gel layer occurs during the clarification of any plant extract in membrane filtration processes. This study was aimed at investigate the impact of the increasing and decreasing transmembrane pressure cycle on the permeate flux of ultrafiltration (UF) and nanofiltration (NF) membranes when a clarified extract of olive mill solid wastes (OMSWs) is used as feed mixture. A hysteresis effect was observed for the selected membranes with molecular weight cut-off in the range 150–3500 Da. This phenomenon was studied by using a combination of the classical filtration theories in the context of two component filtration. Further, the mathematical theory was categorised depending on the cut-off of the membrane, having separate physical scenarios. The proposed model can track both the flux and the permeate concentration profile within a reasonable accuracy, explaining the underlying physics of gel formation as well as the system behaviour.

Procedure to measure the penetration of one mechanical filter for nanoparticles – Validation by comparison

Nanoparticles (NPs) are particles of less than or equal to 100 nm in diameter. Due to their size, they have a significant effect on health and safety of people. Capture of these NPs in general ventilation systems by filters remains one of the most widely used means of protection due to its relative simplicity of implementation and its effectiveness for capturing various size of particles. In North America, filters used in general ventilation systems are tested by the ANSI/ASHRAE Standard 52.2 and are graded according to their efficiency, which is a function of particle diameter. However, the current standard limits the filtration efficiency assessment for particles between 0.3 and 10.0 µm. There is therefore a significant lack of knowledge about the behavior of these filters with respect to the particle diameter below 0.3 µm considering the overall filter used in general ventilation. The main objective of this study was to develop a measurement procedure to evaluate the effectiveness of mechanical filters used in general ventilation systems against NPs. In this regard, a small setup was designed, build and qualified. Then measurement procedure was validated by comparing the penetration measurements with those obtained on qualified big loop setup for nanoparticles, which was inspired by ASHRAE. One type of mechanical filter rated (MERV 8) in three depth sizes (2.54, 5.08 and 10.16 cm) was used to compare the penetrations. The obtained results are consistent with the classical filtration theory for mechanical media and with previous experimental measurements on media. The data presented in this study show that the penetration range of 0.7–1.0 obtained for particle range 22.1–294.3 nm and at 1.00 and 0.75 m/s gives a fairly good correlation (R2 = 0.898) between the two setups. The outcome results validate the methodology used to evaluate the effectiveness of one mechanical filter used in general ventilation systems against nanoparticles by using the small setup.

The effect of pH and ionic strength on the transport of alumina nanofluids in water-saturated porous media

Alumina nanofluids are one of the most useful nanofluids, especially for increasing the thermal conductivity. Due to importance of porous media in the improvement of heat transfer, this study investigates the transport and retention of gamma alumina/water nanofluid in the water-saturated porous media. For this purpose, alumina nanofluids were introduced to the porous media consisting of water-saturated glass beads possessing various pH values (4, 7 and 10) and different ionic strengths (0.001 M of KCl, CaCl2, AlCl3, K2SO4, CaSO4, Al2(SO4)3, K2CO3 and CaCO3). Then the break through curve of each experiment was drawn and modeled by combining classical filtration theory with advection–dispersion equation. Single collector efficiency (η0) and attachment efficiency (α) were calculated by classical filtration theory. Also curve fitting of experiments and modeling was achieved by minimizing the sum of squared residuals, to calculate retardation factor (R) and hydrodynamic dispersion coefficient (D) of each experiment. According to the results, in general, increase in pH and ionic strength will enhance the removal rate coefficient, retardation factor and retention while decreasing the steady-state break through concentration and the hydrodynamic dispersion coefficient. The opposite of this rule was observed and analyzed for aluminum salts. The lowest retention of nanoparticles at 31.04% can be related to their transport in background solution with pH = 4 [α = $$3.87 \times 10^{ - 2}$$ , Katt = $$3.33 \times 10^{ - 3}$$ (min−1), R = 3.93, D = 0.91 (cm2 min−1)], and the highest retention in nanoparticle content of 94.29% was observed in background solution containing CaCO3 [α = $$14.33 \times 10^{ - 2}$$ , Katt = $$137.82 \times 10^{ - 3}$$ (min−1), R = 12.02, D = 0.62 (cm2 min−1)]. Therefore, chemistry of water plays an important role in transport and retention parameters. The classical filtration theory and the advection–dispersion model are able to perfectly model and quantify the parameters of the alumina nanofluid transport in saturated porous media.

Fine and ultrafine particle deposition in packed-bed catalytic reactors

In this work we have performed an extensive CFD simulation campaign with the purpose of studying particle transport and deposition in different catalytic systems and under different conditions. Two types of geometric models representing different porous media were created. The first is a number of random packings of spheres created via rigid body simulations: this approach was tested in previous studies and was proved to result in realistic packings, validated in their geometric features and fluid dynamic behaviour. The second is a regular arrangement of spheres, which was also successfully employed in previous works to study fine particles dispersion.Using these random packings, simulations of particle deposition have been performed at different operating conditions. In the first part we calculated values of particle deposition efficiency and compared our results with the classical filtration theory, highlighting the criticalities in the use of the simplified models upon which the theory is based. In the second part we have studied the effect of polydisperse particle populations: this is also missing in the classical filtration theory, which always considers the transport of particles with uniform diameter. Thus, we have performed population balance modelling simulations for particle deposition, employing the quadrature method of moments (QMOM): as an accompanying technical addition, a study on the accuracy of the application of EQMOM in these systems is offered. Even more clearly in this case, the results show that the description of polydisperse populations has a very noticeable effect on the macro-scale description, which would dramatically improve the understanding of particle transport and deposition in filtration and catalytic processes.

Effect of work of adhesion on deep bed filtration process

PurposeThe purpose of this work was to study the influence of particles and fiber material properties on the deposition efficiency. Collection of aerosol particles in the particular steps of their production, and purification of the air at the workplace and the atmospheric environment requires the efficient method of separation of particulate matter from the carrier gas. There are many papers published in the past years in which the deposition of particles on fibrous collectors is considered. Most of them assume that collisions between particles and collector surfaces are 100% effective.Design/methodology/approachFor the purpose of this work, the lattice Boltzmann model was used to describe fluid dynamics, whereas the solid particles motion was modeled by the Brownian dynamics. The interactions between particles and surfaces were modeled using an energy-balanced oscillatory model.FindingsThe results show significant impact of material properties on filter performance.Practical implicationsObtained results may provide useful information for the proper design of a filtration process and the production of filters with long service life.Originality/valueIn addition, the results presented in this work show that some assumptions of the classical filtration theory lead to an overestimation of deposition efficiency.

PROBLEMS OF NONSTATIONARY FILTRATION

he article deals with the classical hydrodynamic theory of filtration. Discusses models of soil, fluid and nature of fluid flow that formed the basis for the creation of the classic filtration theory. Also discusses the assumptions made for the linearization of the equations. Evaluated the scope of the classical filtration theory. Proposed a new model of filtration through a porous medium, based on the application of the laws of theoretical mechanics. It is based on the classical model of soil: the soil is composed of capillaries with ..parallel axes, in which the liquid moves. For tasks of infiltration equations of motion. Considered special cases of unsteady motion of a finite volume of liquid. Numerical example a machine experiment.

Nanoparticle aerosols filtration using nonwoven filter media – separation mechanisms and experimental results

This paper presents the mechanisms of nanoparticles retention on nonwoven filter media during depth aerosol filtration and the influence of parameters such as particle size, linear velocity and gas temperature, fibre diameter and packing density and surface charge of particles and fibres on retention efficiency of particles according to the classic filtration theory. Based on a review of literature sources, a comparison of filtration efficiency results obtained on the basis of classic filtration theory and experimental results is presented.

In Situ Investigation on the Nanoscale Capture and Evolution of Aerosols on Nanofibers.

Aerosol-induced haze problem has become a serious environmental concern. Filtration is widely applied to remove aerosols from gas streams. Despite classical filtration theories, the nanoscale capture and evolution of aerosols is not yet clearly understood. Here we report an in situ investigation on the nanoscale capture and evolution of aerosols on polyimide nanofibers. We discovered different capture and evolution behaviors among three types of aerosols: wetting liquid droplets, nonwetting liquid droplets, and solid particles. The wetting droplets had small contact angles and could move, coalesce, and form axisymmetric conformations on polyimide nanofibers. In contrast, the nonwetting droplets had a large contact angle on polyimide nanofibers and formed nonaxisymmetric conformations. Different from the liquid droplets, the solid particles could not move along the nanofibers and formed dendritic structures. This study provides an important insight for obtaining a deep understanding of the nanoscale capture and evolution of aerosols and benefits future design and development of advanced filters.

A binomial modeling approach for upscaling colloid transport under unfavorable attachment conditions: Emergent prediction of non-monotonic retention profiles.

We used a recently developed simple mathematical network model to upscale pore-scale colloid transport information determined under unfavorable attachment conditions. Classical log-linear and non-monotonic retention profiles, both well-reported under favorable and unfavorable attachment conditions, respectively, emerged from our upscaling. The primary attribute of the network is colloid transfer between bulk pore fluid, the near surface fluid domain (NSFD), and attachment (treated as irreversible). The network model accounts for colloid transfer to the NSFD of down-gradient grains and for reentrainment to bulk pore fluid via diffusion or via expulsion at rear flow stagnation zones (RFSZs). The model describes colloid transport by a sequence of random trials in a 1D network of Happel cells, which contain a grain and a pore. Using combinatorial analysis that capitalizes on the binomial coefficient, we derived from the pore-scale information the theoretical residence time distribution of colloids in the network. The transition from log-linear to non-monotonic retention profiles occurs when the conditions underlying classical filtration theory are not fulfilled, i.e., when a NSFD colloid population is maintained. Then, nonmonotonic retention profiles result, potentially both for attached and NSFD colloids. The concentration maxima shift downgradient depending on specific parameter choice. The concentration maxima were also shown to shift downgradient temporally (with continued elution) under conditions where attachment is negligible, explaining experimentally-observed down-gradient transport of retained concentration maxima of adhesion-deficient bacteria. For the case of zero reentrainment, we develop closed form, analytical expressions for the shape and the maximum of the colloid retention profile.

Dynamic Heterogeneous Multiscale Filtration Model: Probing Micro- and Macroscopic Filtration Characteristics of Gasoline Particulate Filters.

Motivated by high filtration efficiency (mass- and number-based) and low pressure drop requirements for gasoline particulate filters (GPFs), a previously developed heterogeneous multiscale filtration (HMF) model is extended to simulate dynamic filtration characteristics of GPFs. This dynamic HMF model is based on a probability density function (PDF) description of the pore size distribution and classical filtration theory. The microstructure of the porous substrate in a GPF is resolved and included in the model. Fundamental particulate filtration experiments were conducted using an exhaust filtration analysis (EFA) system for model validation. The particulate in the filtration experiments was sampled from a spark-ignition direct-injection (SIDI) gasoline engine. With the dynamic HMF model, evolution of the microscopic characteristics of the substrate (pore size distribution, porosity, permeability, and deposited particulate inside the porous substrate) during filtration can be probed. Also, predicted macroscopic filtration characteristics including particle number concentration and normalized pressure drop show good agreement with the experimental data. The resulting dynamic HMF model can be used to study the dynamic particulate filtration process in GPFs with distinct microstructures, serving as a powerful tool for GPF design and optimization.

Analysis and Modelling of an Industrial Pressure Filtration using Process Data

In order to understand a series of pressure leaf filters located in the downstream line of a bio-based production site, historical process data have been analysed. In general, changing raw materials induce variability into the pressure profiles and thereby cycle durations of the manually reinitialised dead-end filtrations. The absence of a true steady state results in uncertainty about the optimal way of running the filters, and staff members alter the operational specifications frequently. It appears that, in some cases, this propagates disturbances rather than ameliorate them. Statistical analyses are carried out to illustrate the current situation and especially allow quantifying the extent of the uncertainties. Furthermore, significant correlations between process variables are revealed and economically motivated operational objectives are identified. Secondly, working towards on-line predictions of filtration performance, a model is presented. It is based on classical filtration theory and requires only commonly available measurements (pressure, flow, viscosity). The generated predictions are found to be acceptable for many cycles, but in some cases fail due to non-modelled effects, motivating further work.

Slow migration of detached fine particles over rock surface in porous media

Fines migration involving particle detachment in natural reservoirs usually exhibits significant permeability damage. This occurs due to mobilization and migration of detached colloidal or suspended fines that were strained in thin pore throats. Numerous laboratory coreflood tests show that the time for permeability stabilization accounts for hundreds of injected pore volumes. However, classical filtration theory assumes that the released fines are transported by the bulk of the carrier fluid, thus stabilizing the permeability after the injection of one pore volume. The current paper attributes the stabilization delay to the slow drift of the mobilized fines near the pore walls. We propose basic flow equations for single-phase particle transport in porous media with velocity lower than the carrier fluid velocity. We derive an analytical model for one dimensional flow with particle release and straining under piecewise-constant increasing velocity. The laboratory data are in high agreement with the results of mathematical modelling. The effective particle speed is 500–1000 times lower than the water velocity.

Enhanced retention of bacteria by TiO2 nanoparticles in saturated porous media

The simultaneous transport of TiO2 nanoparticles and bacteria Pseudomonas aeruginosa in saturated porous media was investigated. Nanoparticle and bacterium size and surface charge were measured as a function of electrolyte concentration. Sand column breakthrough curves were obtained for single and combined suspensions, at four different ionic strengths. DLVO and classical filtration theories were employed to model the interactions between particles and between particles and sand grains. Attachment of TiO2 to the sand was explained by electrostatic forces and these nanoparticles acted as bonds between the bacteria and the sand, leading to retention. Presence of TiO2 significantly increased the retention of bacteria in the sand bed, but microorganisms were released when nanomaterial influx ceased. The inclusion of nanomaterials in saturated porous media may have implications for the design and operation of sand filters in water treatment.