Extraction into a flow of a fluid with a velocity gradient

Unsteady extraction from a system of semi-infinite capillaries to the flow of a fluid with a linear velocity gradient is studied. An assumption that the diffusion in the flow is a quasi-steady-state process is taken to obtain a linear equation for the local mass flux from the pore space, which involves fractional derivatives with respect to time and flow coordinate. Limiting solutions for the total diffusion flux at small and large times that cover the entire time interval are found.     

Propagation of a burning front over a condensed material from a focus

Measured propagation speeds are given for the combustion front in a blind gap in a condensed substance, which are related to gap height and mean pressure. The front may propagate monotonically, which is characteristic of relatively high pressures and wide gaps, or as a result of additional burning foci arising at a certain distance from the main front. At low pressures and particularly with small gap heights, the front propagates in an unstable fashion over the surface.Moscow. Translated from Fizika Goreniya i Vzryva, Vol. 28, No. 4, pp. 49–53, July–August, 1992.     

Interaction of a Shock Wave with a Cloud of Aluminum Particles in a Channel

Interaction of an incident shock wave (with a rectangular or triangular profile behind its front) with a finite-width semi-infinite cloud of aluminum particles located in a channel along the plane of symmetry is numerically simulated. Shock-wave interaction with the leading edge of the cloud results in the formation of a vortex that leads to cloud dispersion. Reflection of the curved shock wave from the plane of symmetry may be regular or may include the formation of the Mach stem. If the cloud is loaded by a rather strong shock wave, a detonation wave is formed in the cloud. In this case, the flow is periodic, which is caused by passing of transverse waves and their reflection from the walls.     

Detonation of a Column of a Chemically Active Bubbly Medium in a Liquid

The problem of a detonation wave propagating in a cylindrical column of a chemically active bubbly medium screened by a liquid from the tube walls is formulated and numerically solved within the framework of the Iordanskii–Kogarko two-phase model with allowance for energy dissipation due to acoustic radiation of bubbles. The wave structure of the reaction zone and the detonation velocity of the bubbly medium column are calculated. It is found that the self-sustaining wave can propagate with a velocity greater than the velocity of one-dimensional bubble detonation by a factor of 1.5–2.5.     

Separation of mixtures and distribution of a liquid on a structured packing in a large-scale model of a distillation column

A large-scale experimental setup is designed to study the hydrodynamic parameters and the mass-transfer efficiency in a countercurrent flow of mixtures of Freon R21 and Freon R114 on structured packings in a column 0.9 m in diameter. The study deals with the local and integral parameters of separation of the mixture, the degrees of nonuniformity of the flow rates and concentration distributions of the liquid and vapor phases over a cross section and on the column wall, and the pressure difference while varying the number of packing layers and their rotation angle. The mass-transfer processes while independently varying the liquid and vapor flow rates over wide ranges are also investigated. Experimental data are presented to illustrate the effect of the operating parameters on the height of an equivalent theoretical plate, the relative pressure difference, and the distributions of the local parameters of the flows.     

Transient Outflow of a Liquid from a System of Holes in a Horizontal Tube

The transient outflow of a liquid from a perforated horizontal tube as a result of abruptly applied constant pressure is studied theoretically and experimentally. Equations and a computer program are developed for estimating the parameters of such transient processes. Retardation of the liquid outflow is observed, and its mechanism is discussed.     

Laminar flow deformation of a droplet adhering to a wall in a channel

We study the deformation of oil droplets of varying viscosity adhering to a solid, rigid wall in a rectangular channel induced by a pressure-driven, laminar flow of water. Our experimental investigation involves the systematic study of the effects of initial droplet volume, flow rate and viscosity ratio on the various modes of droplet motion and deformation; this is performed via direct visualisation of the flow in a glass cell using a high-speed camera. Our results are used to construct flow maps that delineate the critical conditions for droplet ‘sliding’, ‘crawling’ and detachment from the channel wall as a function of system parameters. Comparisons of our experimental results with numerical predictions obtained using a procedure based on the diffuse-interface method yield reasonably good agreement for certain flow regimes.     

Effect of a hydrodynamic cleaning of a cross-flow membrane system with a novel automated approach

The effect of different hydraulic cleaning methods was investigated in terms of flux decline and resistance using the cross-flow UF unit. The use of varied production intervals, varied ratios of periodic relaxation and the use of a periodic high-rate crossflow were investigated.This cleaning method of relaxation followed by high-rate crossflow mainly removed the resistances of the concentration polarization and gel layer compared with weak adsorption resistance. The cleaning protocol utilizing a periodic relaxation step and/or a periodic increased cross-flow rate at a decreased pressure can lead to productivity improvements and an increase in the operational lifetime of the membrane. If the optimal frequency and duration of the cleaning step (1 h production–60 s relaxation–60 s crossflow) is used, a net productivity increase of 14.8% is achievable and a significant extension to the membrane's life results. However, a critical point of different cleaning intervals did exist. Utilizing the optimized periodic cleaning techniques developed in this study allows higher recovery rates for ultrafiltration to be achieved, without the problems of increased flux decline normally experienced when operating with high recovery rates.     

Mixing of a lateral gas stream in a two-dimensional riser of a circulating fluidized bed

A cold model of a circulating fluidized bed having a two-dimensional riser, with a 12 × 120 mm section and a 6.4 m height, was equipped with a device to inject a lateral gas stream along the riser. The apparatus was operated under conditions ranging from those characteristic of combustors to those of gas-conversion processes. Flow structures in the interaction region between the rising gas—solids suspension and the lateral gas stream were studied by means of a motion analysis system. Three main configurations were identified. The ratio between the momentum of the lateral gas stream and that of the rising suspension was found to be the parameter able to discriminate among the three configurations. A satisfactory agreement was found with mixing data obtained using a cylindrical riser.     

Contact of a spherical particle with a droplet

The collection of particles by liquid drops is profoundly influenced by the contact angle of the particles with the drops and the surface tension of the drops. The present investigation was undertaken to establish an equation with reference to the force which acts on a particle by surface tension after contact of a particle with a drop, and to simplify its solution. Moreover, the approximate equations obtained can be applied as regards the arbitrary contact angle of a particle with a drop and the arbitrary ratio of the radius of the drop to the particle. The agreement between theoretical and experimental values could be verified by this experiment.It is considered from these results that the approximate equations can be utilized when it is necessary to know the behaviour of a particle after contact with a liquid drop.     

Formation of a high-velocity particle flow from shaped charges with a liner consisting of a hemisphere and a degressive-thickness cylinder

Particle flows formed from shaped charges with a combined steel liner consisting of a hemisphere and a cylinder with a hemispherical part of degressive thickness (decreasing from top to bottom) were investigated by flash radiography. It has been found experimentally that the change from a constant to a degressive thickness of the hemispherical part increases the velocity of the head part of the liner jet formed during its compression, which is subsequently separated upon collapse of the cylindrical part. The maximum particle velocity obtained as a result of separation in the experiments was 8.6 km/s.     

Passage of a Bubble-Detonation Wave into a Liquid

The passage of a detonation wave from a chemically active bubble media into a chemically inert medium (liquid) is studied experimentally. The structure of the transmitted wave and the wave reflected from the butt-end of a shock tube (post-detonation waves) is investigated, and the pressures of these waves for different liquids are measured. The evolution of the post-detonation waves is traced, their velocities are measured, and the attenuation constants of these waves are determined. The energy-dissipation mechanisms for post-detonation waves in liquids are analyzed qualitatively.     

Mesomorphic transitions in a mixture of a flexible and a semi-rigid polymer

Phase studies on a mixture of two polymers are presented, one of which is mesomorphic. We have systematically examined the influence of the molecular weight of the flexible polymer (including the oligomers) and of the semi-flexible polymer. In addition to the effect of the molecular weight, specific interactions are important for compatibility and formation of a homogeneous mesomorphic phase. The nature of this phase is demonstrated to be cholesteric and the pitch is determined.     

Analytical solution of a sink model of a two-dimensional counterwasher

Shwartz and Probstein 1 formulated a sink model of a two-dimensional flooded counterwasher operating in the Darcy flow regime. They gave a numerical solution of a special case of this model, but did not provide an analytical solution for its performance characteristics. This solution omitted a parameter which caused it to represent only a restricted case of a counterwasher having certain pressure constraints. In this paper, we repair this omission and present a completely analytical solution for the general sink model. The results are simple formulas for the performance of the counterwasher in terms of the geometric, flow and pressure parameters. Formulas for the brine crown height and shape are also given. These formulas are in good agreement with the numerical solution given by Shwartz and Probstein for their special case.     

Interaction of a shock wave with a cloud of particles

The present paper is devoted to experimental and theoretical investigation of shock-wave propagation in a mixture of a gas and solid particles with clearly defined boundaries of the two-phase region (cloud of particles). The effect of qualitative transformation of supersonic flow behind a shock wave in a cloud of particles is shown experimentally and substantiated theoretically for volume concentrations of the dispersed phase of 0.1–3%.Translated from Fizika Goreniya i Vzryva, Vol. 32, No. 2, pp. 86–99, March–April, 1996.     

Modeling of a grinding circuit with a swing-hammer mill and a twin-cone classifier

A model was formulated for a continuous, air-swept milling system, assuming the mill to be fully mixed, with all particles leaving the mill in the air stream. The air-sweeping effect was treated as an internal classification which allows fine particles to leave and returns coarse particles for regrinding. The kinetic parameters for the continuous model were estimated using experimental data from a continuous pilot-plant air-swept swing-hammer mill. Functional forms that provide information regarding the power, the internal classification action of the mill, and the action of the external classifier, were deduced for different plant conditions. It was found that the specific rates of breakage could be assumed to vary with particle size according to S_i = a(x_i/x_o)^α, where the value of α was 1.3 for the coal used in the tests. The values of a varied with mill hold-up W, giving a maximum of aW as W became large. The primary breakage distribution values were assumed to be normalized, giving a value of characteristic slope of γ = 0.60.     

Drag of a cylinder moving near a wall in a yield stress fluid

The drag of a cylindrical obstacle moving at a constant velocity in a yield stress fluid close to a wall is studied experimentally and numerically. The wall influence has been explored for gap values between the cylinder of diameter D and the wall ranging from 0.01D to 100D, which corresponds, respectively, to hydrodynamic lubrication and to unconfined domain conditions. A model yield stress fluid (Carbopol gel) is used in the experiments. The viscous and plastic drag coefficients have been calculated and measured as depending on the Oldroyd number, in conditions where the yield stress effects are more important than those of viscosity and the inertia negligible. We have performed experimental and numerical validations in the Newtonian case and provided more specifically comparisons of our measured data on yield stress materials with those resulting from viscoplastic flow simulations. © 2018 American Institute of Chemical Engineers AIChE J, 64: 4118–4130, 2018     

Break-up of a drop in a stirred tank

The drop break-up mechanism was studied in a stirred tank containing two immiscible liquids. The daughter drops formed by break-up of a single drop of known size were recorded photographically. From the experiments at constant agitator speed the following results were obtained. There is a critical drop size under which drops do not break up under given conditions. The break-up frequency increases approximately linearly with increase in drop volume. The number of daughter drops, v, is a random variable with a mean v > 2 which increases with the volume of the mother drop. The relative volume of a daughter drop has a β-distribution.     

近壁面静止圆球的尾迹特性

圆球在大空间均匀来流下的绕流特性已得到了广泛的研究,但是壁面对圆球绕流特性的影响还未清楚。通过实验方法研究了与壁面接触的静止圆球在明渠流中的绕流特性,重点关注了圆球后尾迹的特性。研究发现,圆球尾迹存在三种状态：稳定状态、非稳定对称状态和非稳定非对称状态。当Re<150时,尾迹呈稳定状态,尾迹关于垂直于壁面的平面对称;当150<Re<400时,尾迹呈对称状态,Reynolds数较高时,圆球后存在规则的、周期性的涡脱落,Strouhal 数为0.26~0.33,脱落涡关于垂直于壁面的平面对称,此时尾迹功率谱的频带分布较宽;而当Re>400时,圆球后的涡脱落不再对称,尾迹随着Reynolds数的增大呈现混沌特征。