Analysis of the performance of a sintered stainless steel wire mesh filter for cryogenic liquid purification

As a traditional and mature solid-liquid separating technique, filtration has been adopted in cryogenic liquid purification system owing to its low energy cost, simplified system, long lifetime and high purifying efficiency. Whereas, few data or result of filtration performance at low temperature is put forward in literatures, most of which are related to room and high temperatures applications. Furthermore, as an excellent cryogenic material, stainless steel medium is suitable for cryogenic liquid filtration, which is also seldom reported. In this paper, we propose a filtration system for purifying CO₂ particles from liquid nitrogen using a sintered stainless steel wire mesh filter with a nominal filtration degree of 0.5 μm, and characterize the separation behavior of this kind of filter medium at cryogenic temperature. Experimental results show that the whole filtration process can be divided into three stages with sufficient particle concentration in the feed slurry according to the evolution of pressure drop. Differences between surface filtration and depth filtration are demonstrated, and the influence of growth of filter cake is characterized. Pressure drop increases with increasing feed slurry flow and CO₂ concentration, and evolution tendency of filtration efficiency is affected by its calculation method. By comparison with the filtration at room and high temperatures, the effects of temperature on the fluid and media are emphasized.     

Influence of pulse-jet cleaning pressure on performance of compact dust collector with pleated filter operated in clean-on-time mode

To operate a bag filter continuously, pulse-jet cleaning of dust particles from the filter medium is commonly required, and the pulse-jet pressure significantly affects the filter performance. In this study, the accumulation structure of residual dust particles inside and on the surface of a filter medium at different pulse-jet pressures was investigated by constructing a simple model, and the influence of the dust structure on the filter performance was clarified. Using a simple model, we determined the effective ratio of filtration area β, which represents the ratio of the filterable area to the total filtration area, the true resistance coefficient due to the primary dust layer ζ_p’ thinly deposited on the filter surface, and the true resistance coefficient inside the filter media itself ζ_f’_. The effective ratio of filtration area β decreased with operation time for all pulse-jet pressures; however, it maintained a high value when the pulse-jet pressure was high. The validity of β analyzed by the model was verified using two different methods, and the results showed good agreement, indicating that the model is effective in identifying real conditions. The true resistance coefficient due to the primary dust layer ζ_p’ decreased as the pulse-jet pressure increased; however, the true resistance coefficient inside the filter media itself ζ_f’ was the highest at 0.5 MPa. In addition, the dust collection efficiency was different at each pulse-jet pressure, which was considered to be caused by the difference in the dust particle accumulation structure.     

Influence of Physicochemical Interactions on the Properties of Suppositories. III. Reeological Behaviour of Fatty Supfository Bases and its Effect on Spreading in Rats

Abstract

The viscosity and other rheological properties of the molten base at rectal temperature can markedly affect the rate of release and absorption of drugs' from fatty suppositories. The rheograms of pure mono-acid triglycerides, their mixtures and triglyceride suppository bases were determined at various temperatures using a rotational rheometer. Completely molten systems gave Newtonian behaviour, while incompletely molten mixtures, containing a suspension of higher melting triglyceride, exhibited plastic behaviour with thixotropy which reverted to Newtonian behaviour on removal, dissolution or melting of the higher melting component, The plastic yield values (67 Nm^?2) were less tnan the reported rectal pressure (300 Nm^?2), suggesting that they exert little effect on spreading in the rectum.     

EXPERIMENTAL STUDY OF DUST FILTRATION IN SURFACE-TYPE NONWOVENS

ABSTRACT

Surface type nonwovens are widely used in industrial dust control. Recently, they have been utilized in some engine air filtration applications as automotive filters, heavy-duty engine self-cleaning filters or safety filters. Because of their mechanical strength and regenerative ability they are a perfect material for applications where filter replacement is a problem. On the other hand, the random distribution of fibers and needle punching may result in pinhole formation during dust loading, especially at high aerosol velocities. As a result, the seepage mechanism is common in applications involving fine solid aerosols.

In the inertia dominated region, the collection efficiency of particles depends on the adhesion probability. When particle momentum increases, the efficiency decreases. In general, there is no agreement between filtration theory and experiment when the Stokes number is greater than one.

Filter efficiency increases with dust loading when the filter medium is a good dust cake supporter. In this case, dust reentrainment, causing seepage, may occur at high aerosol velocities and pressure drops. In contrast, reentrainment in nonwovens can take place even at lower aerosol velocities and dust loadings. It is difficult to predict conditions favorable for dust reentrainment and pinhole formation. This process depends on media geometry, dust particle size distribution, and aerosol flow parameters.

This paper discusses filter performance of surface-type nonwovens exposed to polydisperse dusts. Filter efficiency and pressure drop are discussed as functions of aerosol velocity, dust loading, and dust particle size distribution.     

Plate and Frame Filtration in Photographic Gelatin Manufacturing—Some Practical Considerations

Abstract

Gelatin filtration is a required operation in all photographic gelatin manufacturing facilities. For lime-processed bovine bone gelatin, many different filtration methods can be used, one of which is plate and frame filtration. The successful operation of plate and frame equipment depends on a good working knowledge of, and careful adherence to, good filtration practices. Careful choice of a filter medium is also important. This paper outlines many of the practical considerations gelatin manufacturers should think about when setting-up and operating plate and frame equipment, and choosing filter media.     

NON-PARABOLIC FILTRATION BEHAVIOR

ABSTRACT

In this paper, the multiphase equations of change are used as a theoretical hasis for analyzing constant pressure, non-parabolic filtration behavior. This theory, verified by experiment, predicts that the medium resistance is the dominant factor influencing filtrate rates and that septum selection, relative to the particulate phase, is the key variable affecting non-parabolic behavior.

Experimental data also shows that non-parabolic behavior is more energy efficient than parabolic and that non-parabolic behavior cannot be attributed to non-Darcian effects.     

Modelling of filtration processes of fibrous filter media

This work presents a stochastic approach, based on Monte Carlo method, to simulate liquid filtration processes through non-woven fibrous materials. The real filter material is represented as a multilayer medium with a network of multiply connected pores. To describe the deposition and resuspension of particles on and from the filter medium, the following four mechanisms were considered: particle capture by sieving, patricle capture by fibers; particle capture by blocked pores; and particle re-entrainment. The particle capture by fibers and blocked pores, and particle re-entrainment depend on the balance between the adhesion and removal forces. The adhesion forces for particles of diameter smaller than 20 μm were determined through the concept of London-Van Der Waals forces. For particles of diameter greater than 20 μm, gravitational forces were considered. Three-dimensional random flow was assumed to stimulate the particles motion through the multilayer medium. The pressure drop across the filter medium was calculated as the sum of the pressure drop across the clean filter plus the pressure drop due to the deposited particles.A FORTRAN Program was developed to implement the filtration process model. For a wide range of typical filtration conditions, the calculated filter efficiencies predicted the experimental results with a percent difference between 0.5 and 19.3 depending on the particle size. The filter material capacities were predicted with an average discrepancy of 23.0%     

GENERAL PRINCIPLES OF VEHICLE CAB FILTRATION

ABSTRACT

The basic requirements to be satisfied by cab filters are discussed, and the behaviour of fibrous filters with respect to airflow resistance and the capture of particles by mechanical and electrostatic means are outlined. Optimisation of filter performance by means of pleating, to increase the area, is briefly reviewed, and the behaviour of both mechanical and electrically charged filters on loading is discussed. Finally, the requirements for tests of cab filter performance, both in the field and in the laboratory, are considered.     

STOKES FLOW THROUGH A SYSTEM OF PARALLEL INFINITE CYLINDERS WITH AXES ORIENTED AT AN ANGLE TO THE DIRECTION Of MEAN FLOW

Abstract

Theoretical models based on Stokes flow of air through a fibrous filter predict a significantly higher pressure drop than experimentally measured values. This discrepancy persists even when the interaction of the flow between) neighboring fibers is accounted for. Various authors have attributed this discrepancy to the inhomogeneity of the fiber distribution within the filter and to the possibility that some fibers are partially orientation in the directon of mean flow. It has been shown that fiber density inhomogeneity does indeed contribute to this discrepancy

In this paper, the effect on the flow and subsequent pressure drop when the fibers are oriented at an angle to the directon of mean flow is studied. The solution of the three dimensional equation for creeping, incompressible flow in a doubly periodic, infinite lattice of infinite circular cylinders when there is a constant mean flow whose direction makes an acute angle with the axes of the cylinders is given. If the volume fraction of fibers is small, the periodic boundary conditions can be replaced by requiring zero vorticity at the outer boundary of an imagined cylindrical cell of fluid surrounding one of the cylinders. The resulting parallel and transverse problems have known solutions and give an approximate solution to the flow through the periodic lattice. The resulting drag is used to compute the dimensionless pressure drop across a filter for several values of the volume fraction of fiber and is compared to the experimentally determined formula of Davies. It is shown that the average drag over a uniform distribution of fiber orientations yields a pressure drop which is significantly closer to the experimental values of Davies than that resulting from strictly transverse flow.     

PRELIMINARY PERFORMANCE TESTS OF A PULSED JET PLEATED PAPER CARTRIDGE FILTER SYSTEM

ABSTRACT

A pulsed jet pleated paper cartridge filter system was tested for particle removal efficiency and operating stability using agricultural limestone as the test dust. The test system consisted of 6 pleated paper filter units arranged in parallel, each unit having an effective filtration area of 18.1 square meters. The system was operated at constant pressure drops of 6.25, 7.50 and 8.75 kPa (2.5, 3.0 and 3.5 inches of water), with face velocities of 0.78 to 1.04 m/ min (2.5 to 3.4 feet per minute) and dust loadings ranging from 0.5 g/ m to 2.5 g/ m³. Penetration through the media appeared to be relatively independent of dust loading, and efficiencies were in the 99.95 + % range. Slightly lower efficiencies were found for particles having diameters of 0.3 to 1.0 micrometers. A measure of the redeposition of dust pulsed from the filter was required to describe the effects on the pulse rate caused by changes in system flow and pulsing set point. Increased redeposition was found to occur with increasing flow rate, causing an increase in the pulse rate required to maintain operation of the system at a pulsing set point. Overall, the reverse pulse jet pleated paper cartridge filter system displayed extremely high particle removal efficiency in a compact unit that operated with low differential pressure.     

CFD-DEM analysis of internal packing structure and pressure characteristics in compressible filter cakes using a novel elastic–plastic contact model

Cake-forming filtration is a proven method for separating particles from suspensions. Most filtration models are based on the simplification of incompressible and homogeneous cake structures. However, most filter cakes are in fact unevenly compressed by e.g. the high transmembrane pressures, leading to dense structures with high flow resistance at the filtration membrane. Experimental investigations of these inhomogeneous cakes are challenging due to mostly invasive procedures after filtration has already taken place. In contrast, numerical methods can provide extensive information about fluid flow, particle separation and cake formation during filtration. However, this requires that both elastic and plastic particle deformation and forces are modeled correctly. To achieve this, the present study implemented a novel elastic–plastic DEM model that only requires measurable material parameters and therefore does not need any fitting. Subsequently, previously measured material parameters for elastic–plastic cellulose-lactose pellets (MCC) were used to investigate the packing density, fluid pressure levels and contact forces inside compressible filter cakes using CFD-DEM coupling. A comparison with incompressible and elastically compressible filter cakes showed a significant difference in the filtration behavior. Due to plastic deformation, a strong increase of the packing density when nearing the filtration membrane was found, leading to higher flow resistance for the filtration process. For cyclic filtration events, only the plastically deformed cake showed reduced height recovery in a relaxed state.     

Influence of slip length on filtration performance of fine particles

Fine particle filtration has been known to become progressively inefficient as the filter cake builds up owing to restricted movement of liquid through the small cavities formed in the cake. In different chemical industries, this restricts higher throughput rates and also results in higher transportation costs due to increase in moisture content. This paper discusses the influence of using a surfactant, DAH (dodecylamine hydrochloride), in enhancing the filtration rate of a finely ground particles and the reduction of moisture content in the cake. The observed enhanced filtration rate has been attributed to a reduction in the resistance to liquid flow due to the increase in hydrophobicity at the particle surface. The resulting enhanced filtration rate has been modelled by superimposing a slip velocity at the boundary of the capillaries formed in the cake. The model evaluates the cake and medium resistances by incorporating a slip length into the filtration equation which varies with the concentration of hydrophobic reagent and the effective size of capillaries. The increase in filtration rate is more pronounced for finer particle slurries. Also, it has been observed that the moisture content of the filter cakes formed was reduced.     

Dual phase vitreous enamels Part 1 Preparation,application, and properties

Abstract

Vitreous enamel coatings are prone to impact damage as a consequence of their low toughness. Previous attempts to improve this situation by adding fine aluminium powder particles have not been entirely successful because of the very high levels of contiguous porosity that result from the reaction of molten aluminium with hydroxyl ions. A new processing route is described that overcomes this problem and leads to high quality coatings having greatly improved impact resistance, excellent adhesion to steel substrates, and enhanced high temperature oxidation behaviour.

MST/1015     

异丙醇处理对熔喷聚丙烯驻极体空气净化材料性能和结构的影响

本文通过测试过滤效率和阻力、热刺激放电谱、X射线衍射谱以及扫描电镜观测,研究了异丙醇浸泡和熏蒸对材料驻极体性能及微观结构的影响。结果表明,异丙醇浸泡与熏蒸都可以使材料中的电荷完全消失,但不会影响材料的晶相结构。浸泡后材料的剩余过滤效率比熏蒸后的高。浸泡与熏蒸对材料过滤阻力的影响不大。     

A MATHEMATICAL MODEL FOR THE DYNAMIC PARTICIPATE FILTRATION IN DIESEL FOAM FILTERS

ABSTRACT

Diesel Particulate Filters (DPFs) are probably the most effective means for trapping the exhaust-emitted participate from diesel engines. Foam type filters become a promising alternative to the common wall flow filters, since they are effective in filtering small size particles and provide a larger specific surface area for catalytic coatings. A mathematical model taking into account the significant phenomena during the dynamic filtration of foam filters is developed. The model predicts the filtration efficiency and the induced backpressure as function of the geometric filter properties and operating conditions. Due to the particular structure properties of the foam filters it is necessary to employ a tunable parameter, which accounts for the influence of non-Stokes flow in foam filters. This parameter is easily derived by simple measurements. The model is employed to identify and understand the critical parameters of the filtration in foam filters. Indicative parametric runs are presented, which illustrate the applicability of the model in system optimization procedures.     

Corrosion and wetting behaviour of metals and steels with molten alkali carbonates

The corrosion and wetting behaviour of metals and steels with molten alkali carbonates is of particular interest for the design of molten carbonate fuel cells. Such cells, operating at 650 °C with a lithium and potassium carbonate electrolyte, offer a very corrosive medium for fuel cell components.Static corrosion tests under simulated anode conditions have shown that rhodium, ruthenium, platinum, palladium, silver, gold, Nickel 200 and Monel 400 exhibit no measurable corrosion over a 100 h period. Copper, Kanthal and Fecralloy exhibit good resistance with thin protective oxide layers. Stainless steels show less resistance to attack with thicker more permeable oxide coatings being formed.In addition, contact angle measurements indicate that copper, gold, silver and ruthenium demonstrate appreciable non-wetting under a H₂-CO₂ atmosphere. Steels are substantially wetted.     

Flow Properties of Compressible Lactose Containing Small Quantities of Drug Substances

Abstract

The flow behaviour of direct compressible lactose after addition of small quantities of drug substances was studied by different laboratory methods. Determination of the limiting unconfined yield pressure, [f_c], in an annular shear cell was found to be a material saving technique suitable for use in early formulation work. Estimation of the flow behaviour in a multiple punch machine by means of coefficient of tablet weight variation at high tabletting speed in a multiple punch machine was also performed with a material saving technique and was found to reflect the differences in flow behaviour as measured with the shear cell technique and also angle of repose. Water adsorption to the added drug substances was found to be an important factor for explaining the sometimes significant changes in flow behaviour.     

Effect of Surface Modification on Flow Properties and Pressure Filtration of Alumina Slurries

ABSTRACT

The purpose of this research is to evaluate the effectiveness of various dispersants in fine particle processing. The surface of alumina in aqueous solution was modified by using both non-ionic and ionic surfactants. The rheological properties of highly loaded alumina suspensions were studied as a function of surfactant concentration. Pressure filtration experiments were also carried out in order to evaluate the dispersion properties and consolidation behavior. The pressure filtration results could be used to distinguish between well-dispersed and flocculated slurries. The results of rheology measurements and pressure filtration experiments are interpreted using suitable models. To assist the analysis, electrokinetic sonic amplitude (ESA) technique was used for characterization of electrical double layer.     

THEORETICAL STUDY OF A NEW MATERIAL FOR FILTERS: AEROGELS

Aerogels are highly porous materials made by removing the liquid phase of a dilute suspension of solids by taking off the vapor under super-critical temperature and pressure conditions. The aerogel structure has a skeleton of nanometer-size elements forming pores that are tens of nanometers in dimension. In some cases the structure of the aerogel arises from clusters having fractal geometry. The collection efficiency and pressure drop for such material is predicted here from models in the literature. A quality factor is used to compare aerogel material with other filter materials. The quality factor relating gas filtration efficiency with pressure drop is predicted to be unusually high for these materials in comparison with other common fibrous filter media, predicting lower flow resistance for aerogels at equivalent particle collection efficiency levels.     

Nickel base wide gap brazing with preplacement technique Part 2 - Forl11ation mechanisms of macrovoids

Abstract

Microstructural inhomogeneities and variations in the extent of erosion of base metal in nickel base wide gap brazed joints produced by the preplacement technique with braze mixes of different gap filler contents were investigated, from which the flow behaviour of the braze mix constituents and the formation mechanisms of the various types of macrovoid were deduced. The results show that the formation of various types of macrovoid is closely related to the flow behaviour of the constituents of braze mixes during brazing, the latter in turn being strongly influenced by the braze mix ingredients, the brazing temperature, and the gap depth. For a wide gap brazed joint to be free from macrovoids, the braze mix must be sufficiently viscous to bridge the gap faying surfaces and must flow as a whole into the gap. Braze mixes with gap filler contents of 30–40% are ideal for such requirements. With too Iowa gapfiller content, the molten filler would flow preferentially ahead of the mass-of braze mix, leading to the formation of irregularly shaped macrovoids at the tail end of the joint. With too high a gap filler content, the molten filler metal available was insufficient to completely fill the interstices among the gap filler particles, leading to near spherical macrovoids in the braze mix deposit and adjacent joint area. At too Iowa brazing temperature, the braze mix would be too viscous to penetrate into the gap freely and local premature solidification would occur, leading to large, irregularly shaped macrovoids throughout the longitudinal section of the joint.

MST/3132