Cake Porosity Research Articles

Fabrication of submicron powders and nanostructured NiAl-based granules by the SHS method from a mechanically activated mixture

The influence of parameters of mechanical activation (MA) on the structure and phase composition of the Ni–Al reaction mixtures, as well as the products that are formed from them during the subsequent self-propagating high-temperature synthesis (SHS), is investigated using optical and electron microscopy, X-ray structural analysis, electron probe microanalysis, and laser diffraction. Optimal MA modes of reaction mixtures and optimal synthesis conditions of porous cakes are determined. Special functional additives of Al2O3, BN, and WC powders, which increase the cake porosity and facilitate the subsequent grinding, are selected and their amount is determined. It is revealed that boron nitride and tungsten carbide additives most efficiently promote the destruction of NiAl particles. Submicron powders with an NiAl-based nanoblock structure are prepared.

Fabrication of Submicron Powders and Nanostructured NiAl-Based Granules by the SHS Method from a Mechanically Activated Mixture

The influence of parameters of mechanical activation (MA) on the structure and phase composition of the Ni–Al reaction mixtures as well as the products that are formed from them during the subsequent self-propagating high-temperature synthesis (SHS) is investigated using optical and electron microscopy, X-ray structural analysis, electron probe microanalysis, and laser diffraction. Optimal MA modes of reaction mixtures and optimal synthesis conditions of porous cakes are determined. Special functional additives of Al2O3, BN, and WC powders, which increase the cake porosity and facilitate the subsequent grinding, are selected; and their amount is determined. It is revealed that boron nitride and tungsten carbide additives most efficiently promote the destruction of NiAl particles. Submicron powders with the NiAl-based nanoblock structure are prepared.

Nanocolloid cake properties determined from step‐up pressure filtration with single‐stage reduction in filtration area

A sophisticated method was developed for evaluating simultaneously and accurately both the average specific resistance and average porosity of the filter cake formed in unstirred dead‐end ultrafiltration of nanocolloids such as protein solution and nanosilica sol. In the method, a step‐up pressure filtration test was conducted by using a filter with a single‐stage reduction in the effective filtration area. The influence of the pressure drop across the cake on not only the average specific cake resistance but also on the average cake porosity of highly compressible filter cake was evaluated using only flux decline data in one dead‐end filtration test, taking advantage of the decrease in the cake thickness caused by the pressure increase. As a result, the cake properties were easily determined for a variety of nanocolloids. Constant pressure dead‐end ultrafiltration data obtained under various pressures and concentrations were well evaluated based on the method proposed. © 2015 American Institute of Chemical Engineers AIChE J, 61: 4426–4436, 2015

Nonuniform External Filter Cake in Long Injection Wells

Buildup and stabilization of external filter cake is a well-known phenomenon in several environmental and industrial applications. Significant decline of the tangential rate along thick intervals in lengthy vertical wells yields a nonuniform external filter cake profile. We derive the mechanical equilibrium equations for the stabilized cake profile accounting for electrostatic particle–rock interaction, varying permeate factor, applying the torque balance to describe cake equilibrium, and calculating the lever arm ratio using Hertz’s theory for contact deformation of cake and particles. An implicit formula for the cake thickness along the well is derived. Two regimes of the stabilized cake buildup correspond to low rates, where the cake starts from the reservoir top, and for high rates, where the cake is formed in the lower well section only. The sensitivity analysis shows that the drag and permeate forces are the competitive factors affecting cake thickness under varying Young’s modulus, rate, and salinity. The main parameters defining external cake profile are injection rate, cake porosity, water salinity, and Young’s modulus.

Cake porosity analysis using 1D-3D fractal dimensions in coagulation-microfiltration of NOM.

Fouling during coagulation-ceramic microfiltration of natural organic matter was investigated. Two process configurations (inline coagulation (IC) and tank coagulation (TC)) and two process conditions (types of coagulants-aluminum-based PAX and iron-based PIX-and G-values) were studied. The rate of irreversible fouling corresponding to the increase of initial transmembrane pressure after backwash of IC-PAX was lowest followed by TC-PAX and TC-PIX, while the performance of IC-PIX was found worst. The 1D and 2D fractal analysis revealed that flocs from IC were morphologically different from those of TC, leading to different filtration characteristics. The 3D fractal analysis revealed two groups of morphologically similar flocs: one led to successful filtration experiments, whereas the other led to unsuccessful ones. Cake porosity was found dependent on the floc morphology. Thus, such an approach was found complementary with fouling analysis by means of a membrane fouling model and minimization of fouling phenomenon was achieved by combining the two approaches.

Effect of compressibility of synthetic fibers as conditioning materials on dewatering of activated sludge

Efficient solid–liquid phase separation of excess sludge from the mixed-liquor suspended solids in wastewater treatment is difficult to achieve without prior sludge conditioning. Several physical conditioners have been assessed as skeleton builders or filtering aids to reduce sludge compressibility; however, little is known about how the properties of the physical conditioner affect sludge compressibility and dewaterability. In this study, synthetic poly(ethylene terephthalate) (PET), polypropylene, and viscose rayon (VR) fibers were used as physical conditioners for activated sludge, and the effects of the fiber compressibility on the dewaterability of activated sludge collected from a laboratory-scale reactor were assessed. Based on expression experiments using a laboratory-scale apparatus, it was found that: (1) the rate of consolidation of sludge cakes increased after incorporation of synthetic fibers, particularly at the primary stage. (2) The porosity of the sludge cake was maintained only with fibers that required high pressures for compaction (i.e., PET and VR); thus, high dewaterability of the cakes was achieved with these fibers. It is proposed that the compressibility of the physical conditioner may be one of the more important factors for improving sludge dewaterability.

Effect of ionic strength and permeate flux on membrane fouling: Analysis of forces acting on particle deposit and cake formation

In Cross-Flow Microfiltration (CFMF), suspended particles deposit to form a cake layer on the membrane surface, which provides a resistance to permeate flow. The cake resistance, which plays an important role on the performance of CFMF, is mainly determined by the packing porosity of the cake and, the physical and chemical properties of particles. This study aimed at understanding the porosity and the specific filtration resistance of the cake for a given condition. These properties have been studied using experiments under a constant permeate flux. Factors such as permeate flux and ionic strength were investigated in terms of the particles deposition and cake formation. This study also adopted a force balance model to predict the deposit rate of particles and then compare with the experimental results. Inter-particle forces (electric double layer repulsion force and Van der Waals attraction force) were incorporated into the calculation of cake structure (cake porosity and specific resistance) together with the equilibrium condition of hydrodynamic forces. The experimental results showed that the higher the permeate flux led to the greater amount of particles deposit and the denser structure of cake. The porosity of cake decreased with the increase in ionic strength (0∼0.01M) and then increased sharply afterwards (0.01∼0.1M). The hydrodynamic force balance model estimated well the tendency of variation in cake structure depending on the ionic strength.

Pressure drop model for nanostructured deposits

This study presents a new pressure drop model developed for cakes composed of nanostructured particles. The cake structure is understood as a tangle of chains composed by juxtaposed primary particles with (aggregates) or without (agglomerates) a partial overlap. Since cake porosity is one of the main parameters determining aeraulic resistance, an experiment protocol based on the changes in deposit thickness as a function of the cake mass per surface area has been developed to accurately determine this parameter. To this end, the pressure drop and the porosity of the cakes created by the filtration of carbon nanoparticles aggregates and agglomerates on PTFE membrane were measured. The aggregate and agglomerate count median mobility diameters range from 91nm to 170nm and from 48nm to 62nm, respectively. The associated Peclet numbers range from 0.19 to 53 for filtration velocities of 0.01, 0.05 and 0.09m/s. Initial experimental results indicate that the porosity of the cakes ranges from 0.94 to 0.984 in correlation with the Peclet number of the aggregates or agglomerates. The agreement between experimental results and the pressure drop model is fairly good. Of the experimental values, 95% are within plus or minus 25% of the theoretical value.

Cake properties of nanocolloid evaluated by variable pressure filtration associated with reduction in cake surface area

A potential method has been developed for evaluating simultaneously both the average specific resistance and average porosity of the filter cake formed in unstirred dead‐end ultrafiltration of nanocolloids such as bovine serum albumin solution and silica sol. The method consists of variable pressure filtration followed by constant pressure filtration. The relation between the average specific cake resistance and the pressure drop across the cake was determined from the evolution of the filtration rate with time in the course of the variable pressure filtration period, based on the compressible cake filtration model. The average porosity was evaluated from the significant flux decline caused by a sudden reduction in the cake surface area in the middle of the constant pressure filtration period. The pressure dependences of both the average specific cake resistance and average cake porosity were obtained from only two runs which differed from each other in the pressure profiles. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3869–3877, 2014

Modelling of particle deposition in a submerged membrane microfiltration system

In this study, microfiltration of a concentrated suspension of kaolin clay was performed in an aerated tank with submerged flat sheet membranes. Particle deposition was correlated with cake resistance based on experimental results. The effects of air flow rate and permeate flux on transmembrane pressure (TMP) and on membrane resistance were studied. The experimental results show that the filtration resistance due to cake formation plays a dominant role in the total filtration resistance. An increase in permeate flux caused higher TMP development due to an increased amount of particle deposition. Conversely, an increase in air flow rate reduced TMP by detaching deposited layers back into suspension. The particle deposition under different filtration flux and air flow rates was correlated to establish an empirical formula. Based on the experimental results, a general relationship between the cake resistance, permeate flux and particle deposition was derived as Rc=1.01×1012J·wc that suggests that the cake resistance is proportional to the multiplication of flux and cake deposition. Moreover, the effect of air flow on cake porosity was observed to be more significant at low permeate flux.

Investigation into the parameters of influence on dust cake porosity in hot gas filtration

The development of robust and cost-effective hot gas filtration technologies is crucial to facilitate the implementation of advanced coal-based power systems. Understanding the structural characteristics of the dust cake, such as porosity, in relation to the pressure drop evolution is a subject of interest to improve the filtration process. This paper focuses on the study of dust cake compaction and its influence on cake porosity. A semi-empirical model based on Kozeny–Carman equation has been applied to experimental data from the operation of four types of commercial filters (two bag filters and two rigid filters) in a hot gas filtration experimental facility. The method proposed calculates the cake porosity from the specific dust cake resistance coefficient and dust properties. Cake porosity values obtained have been analysed to determine the effect of the operating parameters (filtration velocity, temperature and filtering media). Results show that filtration velocity is the variable that most affects the dust cake porosity. In addition, a correlation between filtration velocity and dust cake porosity has been established.

High-level deliquoring of activated sludge by ultrahigh-pressure expression combined with flocculation

The efficient deliquoring process has been developed for achieving high-rate and high-degree deliquoring of municipal excess activated sludge, which exhibits relatively low dewaterability. In the method developed, low-pressure filtration combined with flocculation led to high-rate deliquoring of sludge due to the formation of large flocs. Subsequently, ultrahigh-pressure expression combined with water permeation through the filter cake which promoted the re-dispersion of flocs in the cake resulted in high-degree deliquoring of the cake. It should be noted that the moisture content in the compressed cake was finally reduced to 31wt% by expression operation under action of an ultrahigh pressure of 15MPa. This extremely low value of the cake moisture content implies that the liquid contained within the microorganism cells was partially removed by the mechanical pressure when the ultrahigh pressure is applied to the cake in the course of expression. The relation between the equilibrium porosity in the compressed cake and solid compressive pressure was empirically represented by a power function. The kinetics of ultrahigh-pressure expression such as the time variation of the moisture content in the compressed cake was accurately described by combining the multi-stage creep model with the modified Terzaghi model describing the primary consolidation.

Fabrication of surface-treated SiC/epoxy composites through a wetting method for enhanced thermal and mechanical properties

• SiC/epoxy composites is prepared by the wetting method. • The surface treatment of SiC particles results in an enhanced wettability of epoxy. • The measured thermal conductivity is correlated with theoretical models. • Storage modulus reveals that the wetting process results in enhanced mechanical properties. Silicon carbide (SiC)/epoxy composites were prepared by a wetting method. To increase the dispersion of dropped epoxy resin on top of the SiC cake, a surface oxidation treatment was applied to the SiC particles. The surface treatment of the SiC particles was applied for an enhanced wettability of the epoxy resin due to a secondary interaction between SiC and epoxy. The thermal transport properties of the composites were maximized at 70 wt.% of SiC during the wetting process because of the limited porosity of the SiC cake. The measured thermal conductivity as a function of the filler concentration correlated with Agari’s model. The results, based on the coefficient obtained by Agari’s model, indicated that the wetting method for the production of the composites combined with a surface treatment of SiC particles facilitates the formation of conducting paths. Storage modulus results also revealed that the wetting process results in enhanced mechanical properties of the composites.

Visualization of the Particle Dendrite Deposition Phenomenon by Using Computer Technology

The phenomenon of dust particles surface deposition in the fibrous medium showed the dendrites structures, which had been confirmed and could be visualized by using computer technology for better understanding particle deposition behavior on filtration process of fibrous media. The pseudo-random movement model was used and the impact of particle inertia movement and diffusion movement on the dust cake growth process in the fibrous filtration media surface were studied by simulation. The simulation method and programs were introduced in detail in the paper, and the result simulation of particle deposition was in good agreement with experimental test result. The results showed that more irregular the dust cake morphology structure was, the greater the dust particles dispersion was and the greater dust cake porosity was.

Seawater ultrafiltration: role of particles on organic rejections and permeate fluxes

The role of natural compounds of seawater and added particles on mechanisms of membrane fouling and organic matter rejection has been investigated. Ultrafiltration (100 kDa) has been conducted in both dead-end (out/in) and tangential (in/out) modes on polysulfone hollow fibre membranes. The permeate fluxes are approximately three times higher for tangential ultrafiltration than for dead-end ultrafiltration without differences between settled and non-settled seawaters (NS-SWs) (51–55 L h−1 m−2 for tangential and 17–22 L h−1 m−2 for dead-end ultrafiltration). Adding bentonite or kieselguhr from 0.13 to 1.13 g L−1 of suspended solids to NS-SW does not act significantly on permeate fluxes of dead-end contrary to tangential ultrafiltration. For the latter, an addition of particles induces a slight drop of permeate fluxes. Original particles of reconstituted seawater could increase the cake porosity, whereas bentonite and kieselguhr, compounds smaller than original particles, could participate in the formation of a compact cake. The total organic carbon removal was equal to approximately 80% whatever the mode of ultrafiltration may be and the suspended solid concentration ranged from 0.13 to 1.13 g L−1. Dissolved organic carbon (DOC) and colloidal organic carbon rejection rates were greater for tangential ultrafiltration (37–49%) compared with dead-end ultrafiltration (30–44%) at different concentrations of added particles. Bentonite or kieselguhr addition induced a slight decrease of DOC removal. In the case of particles addition, the worst DOC rejection is found for bentonite.

Performance Study of Nonionic Filter Aid on Wet-Process Phosphoric Acid

A non-ionic copolymer PAMA which has two functions of flocculation and surface activity was synthesized in aqueous solution. The copolymer was also characterized by means of infrared spectroscopic and unclear magnetic. The application performance of PAMA were studied, and the results show that the filtration rate of the phosphoric acid can be increased by about 3.8 times,the water content of the filter cake can be reduced by about 9.8%. Meanwhile, PAMA may increase the cake porosity by 25.82%,increase the mean void area about 7 times ,increase the surface contact angle of phophogypsum by 9.8°and decrease the surface tension by 7.4 mN·m-1 according to the SEM photos and hydrophobic experiment. All this confirms that PAMA is useful for vacuum filter system of wet process phosphoric acid.

CFD analysis of tracer response technique under cake-enhanced osmotic pressure

A cake-layer mass transfer model applicable for RO, that incorporates the cake-enhanced osmotic pressure (CEOP) effect of a particulate fouling layer, is presented. This model includes the effect of a variable dissolved solute concentration on the specific cake resistance and porosity of the cake layer. The model is based on one-dimensional diffusion of the dissolved solute through the cake layer, and uses the solute concentration at the cake surface and the cake mass per unit area to calculate the solute concentration at the membrane surface and the trans-membrane osmotic pressure. The cake-layer mass transfer model is incorporated into a commercial Computational Fluid Dynamics (CFD) software package. Simulations are validated against experimental data, and the model predictions are within ±7% for permeate fluxes and within ±14% for measured concentration polarisation.The model is used to interpret and assess tracer response test results for estimating concentration polarisation and fouling resistance. Model predictions confirm the assumption for the tracer experiment that the average concentration polarisation along the membrane wall does not change significantly after a step change in the feed concentration of the tracer solute. However, it was found that the tracer experiment over-estimates the concentration polarisation index and under-estimates the fouling resistance, particularly under fouled conditions. The sources of error are discussed and a multiple tracer response test is proposed to minimise estimation error.

Filter Cake Properties of Water-Based Drilling Fluids Under Static and Dynamic Conditions Using Computed Tomography Scan

Previous studies considered the water-based drilling fluid filter cake as homogenous, containing one layer with an average porosity and permeability. The filter cake was recently proved to be heterogeneous, containing two layers with different properties (thickness, porosity and permeability). Heterogeneity of the filter cake plays a key role in the design of chemical treatments needed to remove the filter cake. The objectives of this study are to describe filter cake buildup under static and dynamic conditions, determine change in the filter medium properties, and obtain the local filtration properties for each layer in the filter cake. A high pressure high temperature (HPHT) filter press was used to perform the filtration process at 225 °F and 300 psi. A CT (computed tomography) scanner was used to measure the thickness and porosity of the filter cake. The results obtained from the CT scan showed that under static conditions, the formation of filter cake changed from compression to buildup; while under dynamic conditions, the filter cake was formed under continuous buildup. The CT results explained the changes in the thickness and porosity of each layer of the filter cake with time. The CT scans showed the change in the properties of the ceramic disk, such as porosity and permeability, which affect the calculation of the filter cake permeability. The change of the properties of the filter medium was ignored in previous studies.

Effect of Hydraulic Retention Time on Sludge Properties, Cake Layer Structure, and Membrane Fouling in a Thermophilic Submerged Aerobic Membrane Bioreactor

Sludge properties, cake layer structure, and membrane fouling in a membrane bioreactor were studied under various hydraulic retention times (HRT). A decrease in HRT resulted in an increase in extracellular polymeric substance production in bulk sludge and changes in cake layer structure from gel layer to one or two cake layers. Particle size distribution in cake sludge changed with respect to HRT. An evolution in cake layer thickness and porosity was observed with trans-membrane pressure (TMP) jump. The change in cake layer structure might bear more responsibility for the TMP jump than the quantity of cake layer.

Modelling and simulation of stamp-charged coke making by 2-D discrete element method

Coking of coal blends using high-volatile coals with poor caking properties can be achieved by densifying the coal prior to carbonisation. In stamp-charged coke making, the coal charge is compacted to one large cake before entering the coke oven. A coal cake density of approximately 80% of the coal solid density is needed to produce a high-quality coke. Also, sufficient mechanical strength is required when transferring the cake from the stamping machine to the oven. To gain insight into the densification process and cake structure a 2-dimensional computational model based on the discrete element method (DEM) was set up. The model was validated against force and displacement patterns from laboratory stamping tests. Stamper movement in response to cake properties could be reproduced. The approach also enables tracking of cake porosity, particle rearrangement, stress and strain rates, etc. This offers additional possibilities for studying the densification process and understanding mechanical strength development.