Cake Structure Research Articles

Insight into filter cake characteristics of fine coal tailings assisted by CPAM and α-HH during pressure filtration

To improve the filter cake structure and efficiently dewater coal slime, CPAM and α-HH were designed for combined use in filtration experiments. The conditioned coal slime dewatering effect was measured using a newly designed pressurized dewatering device; the auxiliary mechanisms were analyzed from various perspectives, including hydrophobicity, electrostatic repulsion, coal slime composition and filter cake structure. A CCD experiment indicated that the optimal concentrations of the two additives in combination were 205.90 g/t CPAM and 56.25 mg/g α-HH. Under these conditions, the coal slime water CST decreased to 31.6 s, the filtration rate increased to 177.01 mL/(s·m2), the filter cake moisture content decreased to 16.46%. CPAM still acted as a polymer flocculant, causing the coal slime particles to form large flocs, while the addition of α-HH reduced the absolute zeta potential of the filtrate to 1.36 mV, thus decreasing the static repulsive forces between coal slime particles, promoting floc formation and increasing the floc chord length to 83–185 μm. These effects enhanced the CPAM flocculation effect. In the CPAM system, these phenomena accelerated the hydration reaction of α-HH and produced many CaSO4·2H2O crystals. These crystals formed an interwoven skeleton in the coal slime flocs, increasing the CDI increased to 1650.04, and increasing the filter cake porosity from 13.26% to 16.45% and effectively improving the filter cake pore connectivity and permeability, which improved the filtration effect. This study could provide a new method and perspective for the efficient pressurized dewatering of coal slime.

Freeze-dried nanocrystal dispersion of novel deuterated pyrazoloquinolinone ligand (DK-I-56-1): Process parameters and lyoprotectant selection through the stability study

Recently, nanocrystal dispersions have been considered as a promising formulation strategy to improve the bioavailability of the deuterated pyrazoloquinolinone ligand DK-I-56-1 (7‑methoxy-2-(4‑methoxy-d3-phenyl)-2,5-dihydro-3H-pyrazolo[4,3-c]quinolin-3-one). In the current study, the freeze-drying process (formulation and process parameters) was investigated to improve the storage stability of the previously developed formulation. Different combinations of lyoprotectant (sucrose or trehalose) and bulking agent (mannitol) were varied while formulations were freeze-dried under two conditions (primary drying at -10 or -45 °C). The obtained lyophilizates were characterized in terms of particle size, solid state properties and morphology, while the interactions within the samples were analyzed by Fourier transform infrared spectroscopy. In the preliminary study, three formulations were selected based on the high redispersibility index values (around 95%). The temperature of primary drying had no significant effect on particle size, but stability during storage was impaired for samples dried at -10 °C. Samples dried at lower temperature were more homogeneous and remained stable for three months. It was found that the optimal ratio of sucrose or trehalose to mannitol was 3:2 at a total concentration of 10% to achieve the best stability (particle size < 1.0 μm, polydispersity index < 0.250). The amorphous state of lyoprotectants probably provided a high degree of interaction with nanocrystals, while the crystalline mannitol provided an elegant cake structure. Sucrose was superior to trehalose in maintaining particle size during freeze-drying, while trehalose was more effective in keeping particle size within limits during storage. In conclusion, results demonstrated that the appropriate combination of sucrose/trehalose and mannitol together with the appropriate selection of lyophilization process parameters could yield nanocrystals with satisfactory stability.

Synergistic mechanism of CTAB and nonionic polyacrylamide on pore structure of kaolinite filter cake

Filtration rate and water content of filter cake are decisive indicators in tailings solid–liquid separation processes, with the pore structure of the filter cake playing crucial roles in determining these outcomes. This work aims to investigate the effect of different filter aids on filter cake characteristic and to elucidate the mechanism of surface wettability regulation and flocculation on the pore structure of the filter cake using X-ray microtomography (XMT) to capture the porous structure of the filter cake. The results indicated that the filtration rate of the kaolinite suspension reached 12.25 × 10 -3 mL/(s·cm2) when the dose of cetyl trimethyl ammonium bromide (CTAB) was 0.3 mmol/L and nonionic polyacrylamide (NPAM) was 40 g/t. In comparison to the case without CTAB, the water content of the kaolinite filter cake decreased from 40.21% to 34.91%. Analysis of the filter cake structure demonstrated that the percentage of isolated pores in the filter cake, obtained via CTAB pretreatment followed by NPAM flocculation, was reduced to 10.12%, with uniform pore space development, good homogeneity, and an increased pore throat coordination number. These enhancements effectively improved the connectivity of the filter cake pores and created more pathways for water migration during the filtration process. Concurrently, the pore throat radius ratio in the filter cake decreased from 1.15 to 1.10, minimizing capillary resistance during water migration, resulting in a significant increase in filtration speed and efficacy.

X-ray Computed Tomography (CT) to Scan the Structure and Characterize the Mud Cake Incorporated with Various Magnetic NPs Concentration: An Application to Evaluate the Wellbore Stability and Formation Damage

The X-ray computed tomography method has provided unrivalled data about the characterization and evolution of the internal/external structure of materials by analyzing CTN and non-destructive imaging approach. Applying this method on the appropriate drilling-fluid ingredients plays a significant role in generating proper mud cake quality to stabilize wellbore, and avoid formation damage and filtration loss by preventing drilling fluid invasion into the formation. In this study, smart-water drilling mud containing different concentrations of magnetite nanoparticles (MNPs) was used to assess the filtration loss properties and formation impairment. Conventional static filter press, non-destructive X-ray computed tomography (CT) scan images and high-resolution quantitative measurement of CT number method were used to estimate the filtrate volume and characterize the filter cake layers, hence evaluating the reservoir damage through hundreds of merged images. The CT scan data were combined with the HIPAX and Radiant viewer digital image processing. The variation in CT number of mud cake samples under different concentrations of MNPs and without MNPs concentration were analyzed, and hundreds of 3D images as a cross-sectional profile were used. This paper highlights the importance of MNPs property in terms of minimizing filtration volume and improving mud cake quality and thickness, and hence improving the wellbore stability. From the results, a notable reduction of filtrate drilling mud volume and mud cake thickness to 40.9% and 46.6%, respectively, were recorded for drilling fluids incorporated with 0.92 wt.% of MNPs. However, this study asserts that optimal MNPs should be implemented to guarantee the best filtration property. As confirmed from the results, increasing the MNPs concentration beyond the optimal value (up to 2 wt.%) increased the filtrate volume and mud cake thickness by 3.23 and 33.3%, respectively. CT scan profile images show two layers of mud cake produced from water-based drilling fluids possessing 0.92 wt.% MNPs. The latter concentration was found to be the optimal additive of MNPs as it caused a decrease in filtration volume, mud cake thickness, and pore spaces within the structure of the mud cake. Using the optimum MNPs, the CT number (CTN) shows a high CTN and density material, and uniform compacted thin mud cake structure (0.75 mm). The produced thin mud cake layer reveals the precipitation or exchange of elemental/mineral composition during fluid-solid interaction. These results confirm that MNPs could help in avoiding or reducing the formation damage, driving away drilling fluid from the formation, and improving borehole stability.

Sunflower Oil Winterization Using the Cellulose-Based Filtration Aid-Investigation of Oil Quality during Industrial Filtration Probe.

Waxes, phospholipids, free fatty acids, peroxides, aldehydes, soap, trace metals and moisture present in crude sunflower oil have a negative effect on the oil quality and are, therefore, removed during the refining process. Waxes crystallizing at low temperatures are removed during winterization by cooling and filtration. Waxes have poor filtration characteristics and an industrial filtration process must be enhanced by the use of filtration aids, which improve filter cake structure and properties, and consequently prolong the filtration cycle. Today, traditional filtration aids (diatomite, perlite, etc.) being used in the industry are frequently replaced by cellulose-based aids. The aim of this study is to examine the effect of oil filtration assisted by two cellulose-based filtration aids on the chemical parameters (wax, moisture, phospholipids, soaps, and fatty acids), oil transparency, carotenoids, and Fe and Cu content of sunflower oil obtained in an industrial horizontal pressure leaf filter. In order to investigate the mentioned parameters, the following techniques were used: gravimetric (waxes and moisture content), spectrophotometric (phospholipids and carotenoid content and oil transparency), volumetric (soaps and free fatty acids content) as well as inductively coupled plasma mass spectrometry (ICP-MS) for Fe and Cu content. An artificial neural network model (ANN) was employed for the prediction of removal efficiency based on the chemical quality, oil transparency, Fe and Cu content in oils before filtration, as well as filtration aid quantity and filtration time. Cellulose-based filtration aids had multiple beneficial effects; on average, 99.20% of waxes, 74.88% of phospholipids, 100% of soap, 7.99% of carotenoids, 16.39% of Fe and 18.33% of Cu were removed.

Evaluation of a PAT-based in-line control system for a continuous spin freeze-drying process

Continuous spin freeze-drying provides a range of opportunities regarding the implementation of several in-line process analytical technologies (PAT) to control and optimize the freeze-drying process at the individual vial level. In this work, two methods were developed to (1) control the freezing phase by separately controlling the cooling and freezing rate and (2) control the drying phase by controlling the vial temperature (and hence the product temperature) to setpoint values and monitoring the residual moisture content. During the freezing phase, the vial temperature closely followed the decreasing setpoint temperature during the cooling phases, and the crystallization phase was reproducibly controlled by regulating the freezing rate. During both primary and secondary drying, vial temperature could be maintained on the setpoint temperature which resulted in an elegant cake structure after every run. By being able to accurately control the freezing rate and the vial temperature, a homogeneous drying time (SD = 0.07–0.09 h) between replicates was obtained. Applying a higher freezing rate significantly increased primary drying time. On the other hand, fast freezing rates increased the desorption rate. Finally, the residual moisture of the freeze-dried formulation could be monitored in-line with a high accuracy providing insight on the required length of the secondary drying phase.

Predictive model of constant rate expression for dewatering of semi-solid materials

Nonlinear predictive model of constant rate expression is developed for dewatering semi-solid materials and industrial filter cakes. Nonlinear consolidation equation is expressed on the base of a power-law θ-function linearising Darcy law. Analytical solutions of consolidation equation are obtained under the constant rate condition. Presented model permits obtain the local solid and liquid pressure profiles during constant rate solid–liquid expression, as well as the internal distributions of liquid flow rate, local specific cake resistance and void ratio. Proposed analytical model and numerical simulations were used in worked examples for the highly compressible filter cakes of silica and activated sludge, as well as for the moderately compressible filter cake of CaCO3. It is shown that the value of applied expression rate is determinant for the process efficiency. Expression rate should be very low in case of highly compressible filter cakes of silica and activated sludge to avoid very rapid pressure rise and excessively high expression pressure. Obtained results permit verify and confirm Shirato’s hypothesis that internal structure of filter cake compressed under the instantaneous pressure in a constant rate operation is practically the same as that compressed under such a pressure in a constant-pressure operation.

Quantitative Analysis of Separated Impurities inside Filter Cakes with Phantom-Aided X-ray Tomography

This study presents a new approach in the quantification of the deposited amount of impurity inside a filter cake made up of filter aid material. For this purpose, three-dimensional imaging by X-ray tomography is applied. Based on the X-ray attenuation properties, a model system consisting of kieselguhr as filter aid and barium sulphate as impurity is chosen. Due to the impurity particle size being smaller than the spatial resolution of the measuring setup, a calibration approach is necessary to gain insight into subvoxel information. A so-called phantom of similar material composition is prepared. The grey values are linearly correlated with the impurity volume fraction resulting in a calibration function, which facilitates the calculation of impurity volume fraction based on grey values measured inside the filter cake. First results are presented, showing that the approach delivers valid results for the chosen material system and reveals unexpected characteristics of the filter cake structure. Challenges in the context of the phantom approach and their influence on the obtained results are discussed.

In-situ investigation of solid phase evolution during lyophilization of mannitol-based antibody formulations using an XRPD climate chamber

Crystalline mannitol is commonly used as bulking agent in antibody formulations to provide structure to the lyophilized cake and prevent collapse. Depending on the lyophilization process conditions mannitol can either crystallize as α-, β-, δ-mannitol, mannitol-hemihydrate, or transition to its amorphous state. While crystalline mannitol helps to create a firmer cake structure this is not true for amorphous mannitol. The hemihydrate is also an undesired physical form as it may reduce the drug product stability by releasing bound water molecules into the cake. Our aim was to simulate lyophilization processes in an X-ray powder diffraction (XRPD) climate chamber. In the climate chamber, the process can be carried out fast with low sample quantities to determine optimal process conditions. Insights on the emergence of desired anhydrous mannitol forms helps to adjust the process parameters in larger scale freeze-dryers. In our study we have identified the critical process steps for our formulations and then varied relevant process parameters, which were the annealing temperature, annealing time and temperature ramp rate of the freeze-drying process. Furthermore, the effect of the presence of antibodies on excipient crystallization was investigated by performing the studies on placebo solutions versus two respective antibody formulations. A comparison of the products obtained in a freeze-dryer and the simulated process in the climate chamber showed good accordance demonstrating the method as suitable tool to identify ideal process conditions on a laboratory scale.

Synergistic effect of combined sucrose substitutes and partially gelatinized oat flour on gluten-free steamed oat cakes produced only by oat flour

The role of sucrose substitutes and partially gelatinized oat flour in oat-fermented food systems needs to be studied. Therefore, the synergistic effect of sucrose substitutes and partially gelatinized oat flour on the rheo-fermentation, water distribution, and textural properties of steamed oat cakes was explored. The results showed that compared to sucrose, raffinose was more easily used by yeast, leading to the highest total gas volume. Raffinose had much stronger competitive hydration ability than xylitol and maltitol, causing reduced viscoelasticity of the batter and incomplete gelatinization of the starch. Compared to raw oat flour, roasted oat flour with 30% and 50% gelatinization degrees (G30 and G50) resulted in a collapsed structure of steamed oat cakes, ascribed to a dense packed structure formed by starch. The mixed oat flour (M30) that represents 50% raw oat flour and 50% G50 oat flour formed a more stable gas chamber structure. The steamed oat cakes made by the combination of raffinose and M30 flour showed the highest gas cell area fraction (37.75%), and moderate springiness (0.88). In conclusion, the combination of raffinose and mixed oat flour can improve the texture quality of fermented oat-based foods.

The effects of quinoa and okra incorporation on the quality of diet cake.

Producing quality products in baking industry has been facing several challenges including meeting the needs of the growing population, lack of sufficient water resources for producing enough wheat, lack of quality products made from wheat flour and high amount of waste. Recently, the quality of baking products has been improved by mixing different types of flour, which increases the nutritional value and improves the quality of the final product. This study evaluates the possibility of making a cake by incorporating wheat flour with quinoa and okra flour. Moreover, basil gum is used to improve the gluten network. The cake samples were prepared with quinoa flour at two levels (15 and 30%), okra flour at two levels (0.8 and 0.16%) and basil gum at a level of 0.4%; finally, their physicochemical, rheological, SEM, and sensory properties were evaluated. Based on the results, adding quinoa and okra flour and basil gum increases the density and consistency of the batter. Hardness, springiness, chewiness, cohesiveness, and adhesiveness of the blend Q2B1R was improved. The granule structure of the quinoa flour cakes were affected, and the gluten network was not well formed as shown in the electron microscopy images. However, the gluten network was improved in the samples with 0.4% basil gum and 0.8% okra flour. By adding okra and quinoa, better specific volume, porosity, and moisture content was obtained. Sensory evaluation of the cakes indicated that the blend Q2B1R was scored close to the control sample.

Experimental study on wall-protecting mud modification of super-long bored pile in the alluvial plain region of the Yellow River

In this study, the effect of different additives (sodium carbonate, carboxymethyl cellulose, polyacrylamide, and barite powder) on modified mud performance and microstructure has been evaluated and the optimal proportion of the modified mud was determined. The specific gravity, viscosity, sand content, colloid rate, and water loss of modified mud has been investigated. The characteristics of mud cake in microstructure of modified mud have been also analyzed and evaluated by the scanning electron microscopy images (SEM). The results showed that adding bentonite dosage increased the specific gravity, the adding carboxymethyl cellulose increased the viscosity and dropped the water loss rate, and the pH value experienced a growth with the increasing sodium carbonate content. SEM tests revealed the additives made the overall structure of the mud cake more compact and enhanced the modified mud's wall protection effect and filtration loss reduction effect. The modified mud was successfully applied to the super-long pile of a project in the Yellow River alluvial plain area, which provided support for the dynamic adjustment of the mud proportion in the field construction.

Understanding the Impact of Microstructures on Reconstitution and Drying Kinetics of Lyophilized Cake Using X-ray Microscopy and Image-Based Simulation

The drying time of lyophilization and resultant cake microstructure are dependent on each other as water and solvent leave a lyophilized cake. The drying rate affects the size, distribution, and tortuosity of the pores as these macropores evolve during the primary drying phase, which in return impact the further removal of water and solvent from the cake throughout the drying period. This interplay results in a microstructure that determines the reconstitution time for a given formulation. The current study employs advanced X-ray Microscopy (XRM) coupled with mathematical models to correlate the microstructure with the drying kinetics and the reconstitution time. The normalized diffusion coefficients, derived from the reconstructed 3D microstructure of the cake, correlate with the solid content of the pre-lyophilization solution and agree with the mass transfer coefficients from a semi-empirical drying model built with lyophilization process data. Specifically, a solution with less solid content leads to a lyophilized cake with larger pores, thinner walls, and a greater pore volume compared to a solution with more solid content. Consequently, models from the microstructure and drying experiments reveals faster mass transfer independently. While the mass transfer models from the cake structure and the lyophilization process data accurately represents the drying kinetics, both models are inadequate to describe the reconstitution process due to the significant impact from formulation ingredients that alter the mass transfer mechanism via solubility and wettability. In summary, X-ray microscopy imaging and mathematical models are powerful tools that provide insights into the lyophilization process from a new angle.

A Measurement Method for the Pore Structure of Coal Slime Filter Cake

The accurate determination of the coal slime filter cake pore structure has always been a problem in the field of solid–liquid separation. An innovative measurement method for the pore structure of filter cake after filtration dehydration of coal slime water, including the preparation of coal slime filter cake, the solidification of the filter cake, and the preparation and measurement of test filter cake, was established in this paper. Epoxy resin and curing agent can ensure the strength of the filter cake, and red colorant can realize the accurate separation of coal particles and pores. The most suitable perfusate consists of epoxy resin, red colorant, and curing reagent, and the optimal ratio is 12:3:5. The application of the method to the study of the effect of filtration time on the coal slime filter cake pores shows that the modified method is effective. At the initial stage of filtration, intergranular pores formed by coarse particles are the main pores. With increasing filtration time, the macropores formed by the coarse particles are mainly filled with fine particles, and the pore size of the filter cake rapidly decreases. These measuring results and rules are accurate. This method can be conveniently used to study the microstructure of filter cake, pore channel regulation, filtration dehydration mechanisms, etc.

Effect of relative humidity and dust moisture content on filtration performance of bag filter

Bag filters are commonly used to remove fine particulate matter from industrial flue gases. Rapid formation of dense dust cakes is a major issue in bag filters as it necessitates more frequent cleaning, leading to higher operating costs. The rate of cake resistance formation is related to the interparticle forces, which vary with the wetting state of the particle surface. To reduce the cake resistance, moisture is introduced via two methods: regulating the ambient relative humidity (RH) and dust moisture content. The results show that the introduction of moisture affects the cake thickness, mass loading, and particle size distribution on the filter bag, which are critical factors in determining cake resistance. Higher RH and conditions far from the critical dust moisture content (1.44%) contribute to low-resistance filter cakes. In addition, a non-uniform filter cake structure on the surface of the filter bag was investigated, and a correlation between the filter bag height and the filter cake structure parameters was developed. We introduced interparticle forces into computational fluid dynamics coupled with discrete phase model (CFD-DPM) simulations to simulate the wet particles. Particle agglomerates and flow field forces are attributed to the non-uniform particle distributions on the filter bag. These findings provide insights into reducing cake resistance and routes to control increasing resistance over time, as well as a more accurate prediction of cake resistance.

Mille crepe cake structure-inspired fabricating parallelly-arranged TA@Ti3C2Tx composite coating for long-term corrosion resistance under alternating hydrostatic pressure

Addition of Ti3C2Tx nanosheets into epoxy matrix is crucial for improving the mechanical and anti-corrosion properties, depending on their unique structures and properties. However, randomly-arranged Ti3C2Tx nanosheets failed to meet higher corrosion protection requirements especially under alternating hydrostatic pressure (AHP) environment. Herein, inspired by the unique structure of mille crepe cake, the tannic acid (TA)-functionalized Ti3C2Tx nanosheets were distributed parallelly in the epoxy matrix using a simple blade-coating method to form layer-by-layer (LBL) coating. Particularly, epoxy matrix incorporated with TA@Ti3C2Tx exhibited a nearly perfect internal parallel arrangement structure due to shear force during blade-coating, excellent compatibility, and higher binding force. As being immersed 60 days at 1 atm and 240 h at 20 MPa AHP in 3.5 wt% NaCl solution, the worst frequency impedance values was enhanced by 1–3 orders of magnitude for the parallel alignment in comparison to the randomly-arranged TA@Ti3C2Tx composite coating. The results were mainly due to the fact that parallelly-arranged TA@Ti3C2Tx could maximize tortuosity and got the utmost out of the barrier properties of composite coating. Moreover, electrochemical characterization of defects and Molecular Dynamics (MD) simulations results proved that TA could react with Q235 steel in three ways to form ferric-tannates, which could further prevent the corrosion of steel. Prospectively, the parallelly alignment of TA@Ti3C2Tx nanosheets in epoxy would greatly increase the corrosion resistance of composite coating, especially suitable for AHP environment.

Improving the filtration properties for manganese tetroxide mud utilizing perlite particles to drill wide-range permeability sandstone formation

A required feature of any drilling formulation is to mitigate the formation damage by having an excellent filtration and filter cake properties. The key factor for preventing and limiting formation damage is to improve the sealing qualities of the planned drilling fluid. In this study, a new novel filtration agent called “perlite” was introduced for improving the manganese tetroxide mud cake ability for better sealing features. The perlite particles were loaded to formulation containing the manganese tetroxide as weighting agent. The water-based drilling mud was designed at high densities (14.25 and 17.2 ppg). Perlite was added in varied concentrations to reach the optimum performance. The filtration test conducted at reservoir temperature of 250 °F and a differential pressure of 300 psi to form the filter cake. The tests were performed using sandstone cores with two different permeability categories (low and high permeabilities) as the filtration media. This gave the full picture of perlite performance as implemented for different formation properties and considering the drilling fluid properties. The formed filter cake structure and chemical composition was evaluated using scanning electron energy-dispersive X-ray (SEM–EDS). The presented results illustrated how the perlite was compatible to be added to the manganese tetroxide weighting agents in the same formulation. In addition, it has the capacity to improve the filter cake's sealing qualities, lowering the filtration volume by 41% and the filter cake internal and external layers permeability by 58% and 25%, respectively. Moreover, the EDS analysis showed that the perlite particles are concentrated generally in the internal layer of the filter cake.

Images and photon ring signatures of thick disks around black holes

Context. High-frequency very-long-baseline interferometry (VLBI) observations can now resolve the event-horizon-scale emission from sources in the immediate vicinity of nearby supermassive black holes. Future space-VLBI observations will access highly lensed features of black hole images – photon rings – that will provide particularly sharp probes of strong-field gravity. Aims. Focusing on the particular case of the supermassive black hole M 87*, our goal is to explore a wide variety of accretion flows onto a Kerr black hole and to understand their corresponding images and visibilities. We are particularly interested in the visibility on baselines to space, which encodes the photon ring shape and whose measurement could provide a stringent test of the Kerr hypothesis. Methods. We developed a fully analytical model of stationary, axisymmetric accretion flows with a variable disk thickness and a matter four-velocity that can smoothly interpolate between purely azimuthal rotation and purely radial infall. To determine the observational appearance of such flows, we numerically integrated the general-relativistic radiative transfer equation in the Kerr spacetime, taking care to include the effects of thermal synchrotron emission and absorption. We then Fourier transformed the resulting images and analyzed their visibility amplitudes along the directions parallel and orthogonal to the black hole spin projected on the observer sky. Results. Our images generically display a wedding cake structure composed of discrete, narrow photon rings (n = 1, 2, …) stacked on top of broader primary emission that surrounds a central brightness depression of model-dependent size. At 230 GHz, the n = 1 ring is always visible, but the n = 2 ring is sometimes suppressed due to absorption. At 345 GHz, the medium is optically thinner and the n = 2 ring displays clear signatures in both the image and visibility domains. We also examine the thermal synchrotron emissivity in the equatorial plane and show that it exhibits an exponential dependence on the radius for the preferred M 87* parameters. Conclusions. The black hole shadow is a model-dependent phenomenon – even for diffuse, optically thin sources – and should not be regarded as a generic prediction of general relativity. Observations at 345 GHz are promising for future space-VLBI measurements of the photon ring shape, since at this frequency the signal of the n = 2 ring persists despite the disk thickness and nonzero absorption featured in our models. Future work is needed to investigate whether this conclusion holds in a larger variety of reasonable models.

DEVELOPMENT OF OPTIMAL COMPOSITION OF DRILLING FLUID FILLER FOR OPEN HOLE WELL COMPLETION

Experimental studies were carried out to determine the effect of inert fillers on the filtration properties of clay cakes during their formation. The sequence of experiments corresponds to the sequence of stages: formation of the main structure of the filter cake (simulation of the opening process by drilling), treatment of the bottomhole zone to restore the initial permeability (for example, during chemical destruction of the filter cakes) and washing out of process fluid filtrates from the bottomhole zone into the well. The solid phase in the drilling fluid can be represented by both structure-forming clay particles and fillers (barite, crushed cuttings, bridging agents, etc.). Moreover, fillers can have individual particles of a size of a colloidal degree of dispersion and significantly affect the filtration performance of drilling suspensions. It is especially important to evaluate the influence of the composition of the solid phase of the clay suspension on the filtration properties at the stage of formation of the main structure of the filter cake. This stage is characterized by a non-stationary filtration process. In essence, the bulk of the studies of filtration processes is carried out in this mode. In our case, it is necessary to determine the dependence of the filtration index of solutions Пр on the composition of the solid phase. In the course of experimental studies, it was confirmed that subsequent filtration through the cakes formed at stage 1 equally depends on the magnitude and nature of the drawdown application, as in stage 1, as well as on the permeability of the filter cake and the clogging zone. Therefore, the research methodology at stage 2 required supplementing experiments with the formation and modification of filter cakes during filtration through permeable sand packs.

A Review on Freeze-drying: A Stability Enhancement Technique

Freeze-drying is effective technique used in pharmaceutical industry to increase the efficacy, shelf-life of formulations and makes easier to transport and storage. Freeze-drying applies to the product that is thermolabile and unstable in solution form, because of utilization of low temperature and pressure. Nowadays freeze-drying gained so much attention in the development of parenteral formulation especially vaccines. The selection of excipients plays a key role in development of freeze-dried product and used to improve the shelf life and makes the product cost effective. The structure of cake not only focuses on appearance of product and also provide information about issues on drying stage that impact quality of product. Tray style freeze dryer helps in development of long-term storage vaccines and labile drugs. It performs freeze drying in containers or in vials on large quantities. This makes tray style freeze dryer become most common for developing lyophilized product. The need for improve the shelf-life of protein-based drug and antibiotics formulations makes tremendous growth of freeze-dried product market. This review focuses on the lyophilization process, design of freeze dryer, role of excipients in lyophilization process, decision of selecting the excipients, importance of cake structure helps to develop stable lyophilized drug product for long-term usage and applications of lyophilization technology.