Effect of the particle injection position on the performance of a cyclonic gas solids classifier

This study investigates the effect of the particle injection position on particle classification performance of a cyclonic classifier. The Rankine-type vortex flow in the cyclonic classifier is divided into three characteristic regions from the wall to the center according to the tangential and axial velocity distribution. Three representative particle injection positions are selected within those regions. The particle flow and the particle residence time are investigated via the Reynolds stress and discrete phase models. The simulation result shows that particles injected in the near-wall region provide the highest separation efficiency but the lowest classification accuracy. The residence time of particles injected within the region of maximum tangential gas velocity is shorter, facilitating a rapid and efficient particle classification. The powder classification experiment result confirms the simulation result and the feasibility of this method to enhance the separation degree of particles in the vortex flow.     

The temperature recovery factor in a boundary layer on a permeable plate

A numerical investigation of the boundary layer on a permeable wall in a supersonic gas flow is performed using a differential turbulence model. Temperature recovery factors are obtained for a series of Prandtl numbers and gas suction or injection in a wide range of the permeability factor from critical injection to asymptotic suction. With the example of air injection into a supersonic air flow, two methods for determining the temperature of a heat-insulated permeable wall are considered. The first is to solve the problem with a boundary condition of zero heat flux to the wall. The second is similar to an experimental method when the temperature of the gas injected at a section along the plate length becomes equal to the wall temperature. The heat-insulated wall temperatures and temperature recovery factors obtained by these two methods for injection below the critical one are close to each other. In case of critical injection, these two methods yield different results.     

圆形金属腔旋流二氧化碳激光器

现有的工业ＣＯ２激光器,主要为横流,纵流和扩散冷却三种,章提出一种新型激光器,即圆形金属腔ＣＯ２激光器,该激光器的腔体由多个等距,同轴安装的空腔单元组成,每个腔单元有多个流道,放电在流道与腔体接口处产生,气流将放电及被其激活的粒子吹入腔内,形成增益,输电激光,章研究了电极结构,金属腔壁对工作气体的冷却作用和胺内的增益分布,研究结果表明,多通道放电吹入和腔内旋流,有利于腔内的均匀放电,金属腔壁有利于腔内对流冷却,降低对气速度的要求,从而缩小激光器的体积,相邻的腔单元相对转动适当角度,可以提高腔内增益分布的圆周均匀性,从而获得光束质量好的激光束。     

A decrease in the effective cross section of a cooling stream caused by hot air penetration into the blowout channel

The phenomenon of penetration of a hot air stream into a channel of finite depth by which a cooling stream is injected was revealed and studied by numerical methods. The penetrating stream decreases the effective cross section of the cooling stream, increases the velocity of this stream, and reduces the near-wall gas screen cooling efficacy.     

Load-carrying ability of large-diameter pipes

In the construction of oil and gas pipelines use is made of spiral-welded pipes with a diameter of 820–1420 mm and a wall thickness of 8–14 mm. Low-carbon hot-rolled stell produced by continuous casting is used as the material. The properties of the material produced by this relatively new method as well as the workability of structural elements under the conditions similar to the working conditions of actual structures are now a topical problem.Volga Pipe Plant, Volzhskii. Sverdlovsk. Translated from Problemy Prochnosti, No. 1, pp. 32–36, January, 1978.     

Comparison of methods for wall boundary conditions as applied to the calculation of turbulent heat exchange characteristics

Methods for setting and realizing wall boundary conditions numerically in calculating turbulent flows is considered. A method for realizing weak boundary conditions on the wall with discretization of Reynolds-averaged Navier–Stokes equations by the control volume approach is discussed. The results of calculations for a number of model problems obtained within the framework of different approaches to the near-wall modeling are compared to the data of the physical experiment and the available correlation dependences. The grid dependence of the solution in using the method of near-wall functions is compared to that in using weak boundary conditions.     

A Treatment of wall boundaries for turbulent flows by the use of a transmission finite element method

A method to connect momentum Navier-Stokes equations with the universal law of the wall using the finite element method is developed for turbulent wall flows. This method is based on a domain decomposition of the fluid into subdomains near a solid boundary where the law of the wall is valid. A transmission formulation is introduced to match these regions and a new class of boundary finite element is used. This finite element takes into account the near-wall profile of the velocity and the transmission conditions. Computational results are presented for Poiseuille flow and flow over a backward-facing step.     

基于流体体积函数模型的横板型稳压罐内气液两相流场仿真研究

针对水流量标准装置中横板型稳压罐,基于Navier-Stokes方程建立罐体计算流体动力学仿真模型。使用湍流模型、流体体积函数瞬态模型和有限体积法进行离散,并在近壁区采用标准的壁面函数法进行修正,完成横板型稳压罐内部两相流场的数值模拟。数值结果显示空罐充水流态依次经过无水状态-射流-上壅-漫流-稳定状态,同时形成掺气现象和泡状流;气液体积比1:3情况下,满罐充水流场有固定周期的晃荡现象,上侧形成逆时针转动的漩涡气腔,流场湍流粘度较小,分布较均匀,稳定效果最好。     

Effect of drag force modeling on the flow of electrostatically charged particles

In CFD simulations of two-phase flows, accurate drag force modeling is essential for predicting particle dynamics. However, a generally valid formulation is lacking, as all available drag force correlations have been established for specific flow situations. In particular, these correlations have not been evaluated for particle-laden flows subjected to electrostatic forces. The paper reports the effect of drag force modeling on the flow of electrically charged particles. To this end, we implemented different drag force correlations to the open-source CFD tool pafiX. Then, we performed highly-resolved Direct Numerical Simulations (DNS) using the Eulerian–Lagrangian approach of a particle-laden channel flow with the friction Reynolds number of 180. The simulations generally revealed a strong influence of the precise drag correlation on particles in the near-wall region and a minor effect on the particles far from the walls. Due to their turbophoretic drift, particles accumulate close to the channel walls. For uncharged particles, the simulations show large deviations of the particle concentration profile in the near-wall region depending on the drag force correlation. Therefore, the disturbance of the flow surrounding a particle by a nearby wall or other particles is important for its drag. Driven by electrostatic forces, charged particles accumulate even closer to the wall. Contrary to the uncharged cases, when the particles carry a high charge (in our case one femto-coulomb), we found minor effects of drag force modeling on particle concentration profiles. In conclusion, for the investigated conditions, we propose to account for the effect of nearby particles and walls on the drag of low- or uncharged particles.     

Scheduling continuous aluminium casting lines

This study considers the problem of scheduling casting lines of an aluminium casting and processing plant. In aluminium processing plants, continuous casting lines are the bottleneck resources, i.e. factory throughput is limited by the amount of aluminium that can be cast. The throughput of a casting line might be increased by minimizing total setup time between jobs. The objective is to minimize setup time on production lines for a given time period while balancing workload between production lines to accommodate potential new orders. A mathematical formulation for scheduling jobs to minimize the total setup time while achieving workload balance between the production lines is presented. Since the casting scheduling problem is an NP-hard problem, even with only one casting line, a four-step algorithm to find good solutions in a reasonable amount of time is proposed. In this process, a set of asymmetric travelling salesman problems is followed by a pairwise exchange heuristic. The proposed procedure is applied to a case study using real casting data.     

Mass Transfer and Friction in Near-Wall Film Flows in Conditions of High-Velocity Co-Current Gas Flow

We present the experimental research on the interaction of co-current gas flow with near-wall liquid film for gas velocities up to 300 m/s. Local parameters of near-wall liquid film are measured by using capacity-type probes. It is shown that co-current gas flow has strong influence on near-wall liquid film, leading to intensive wave formation, detachment of droplets from the film surface and their entrainment by the gas flow. Thus it is shown that the relative amount of liquid carried away by co-current gas flow is well characterized by Weber number of gas flow. A model for the motion of a film with co-current flow, connecting a thickness and velocity of the film with value of shearing stress at gas-liquid boundary, is suggested. It is shown that intensive wave formation leads to essential increase of the interphase friction value.     

Investigation on thickness of short time oxide films in Al–1Mg and Al–2Mg alloys

Abstract

The melts of aluminium alloys are very sensitive to oxidation during casting, and the surface oxide film formed during casting can be folded and entrained into the melt due to melt surface turbulence. In this research, sandwiches of oxide–metal–oxide (OMO) formed in a very short time within the cast during solidification were investigated in order to see the effect of magnesium content (i.e. 1 and 2 wt-%) on the oxide film thickness. To form OMO sandwiches within the cast, a certain amount of air was blown into the melt every 0·5 s during casting time by means of a compressor at 0·5 atm pressure. Where bubbles of air collided, they formed a sandwich which later was used for investigating purpose. Both the thickness and the surface of oxide films were studied via SEM. The results showed that the thickness of the short time oxide film varies in the range of 150–250 and 200–300 nm for Al–1Mg and Al–2Mg alloys respectively.     

The effect of electron detachment on the diffusive decay of a low-pressure electronegative plasma

There are two possible scenarios in the diffusion decay of a low-pressure electronegative plasma in a system featuring the electron detachment effect. In the case of a weak detachment, the system exhibits an initial sharp drop in the electron concentration followed by the ion-ion plasma formation. A small admixture of electrons appearing as a result of the detachment keeps all negative ions within the volume. In this stage, the densities of all charged plasma components decay according to the same exponential law with a characteristic detachment time. In the limit of a strong detachment, a principally different plasma decay regime takes place. In this limiting case, a usual (free of negative ions) rather than ion-ion plasma is formed in the second stage. This can be accompanied by paradoxical phenomena such as the growth of electron density with time, build-up of the near-wall potential jump, and a considerable decrease (up to complete vanishing) of the diffusion electron cooling usually dominating in the electron gas energy balance.     

Synergy between shear-induced migration and secondary flows on red blood cells transport in arteries: considerations on oxygen transport

Shear-induced migration of red blood cells (RBCs) is a well-known phenomenon characterizing blood flow in the small vessels (micrometre to millimetre size) of the cardiovascular system. In large vessels, like the abdominal aorta and the carotid artery (millimetre to centimetre size), the extent of this migration and its interaction with secondary flows has not been fully elucidated. RBC migration exerts its influence primarily on platelet concentration, oxygen transport and oxygen availability at the luminal surface, which could influence vessel wall disease processes in and adjacent to the intima. Phillips'' shear-induced particle migration model, coupled to the Quemada viscosity model, was employed to simulate the macroscopic behaviour of RBCs in four patient-specific geometries: a normal abdominal aorta, an abdominal aortic aneurysm (AAA), a normal carotid bifurcation and a stenotic carotid bifurcation. Simulations show a migration of RBCs from the near-wall region with a lowering of wall haematocrit (volume fraction of RBCs) on the posterior side of the normal aorta and on the lateral-external side of the iliac arteries. A marked migration is observed on the outer wall of the carotid sinus, along the common carotid artery and in the carotid stenosis. No significant migration is observed in the AAA. The spatial and temporal patterns of wall haematocrit are correlated with the near-wall shear layer and with the secondary flows induced by the vessel curvature. In particular, secondary flows accentuate the initial lowering in RBC near-wall concentration by convecting RBCs from the inner curvature side to the outer curvature side. The results reinforce data in literature showing a decrease in oxygen partial pressure on the inner curvature wall of the carotid sinus induced by the presence of secondary flows. The lowering of wall haematocrit is postulated to induce a decrease in oxygen availability at the luminal surface through a diminished concentration of oxyhaemoglobin, hence contributing, with the reported lowered oxygen partial pressure, to local hypoxia.     

Numerical Investigation of Unsteady Heat Exchange in Ignition for Reactive Channel Walls by the Flow of a High-Temperature Viscous Gas

A study is made of the process of ignition of reactive channel walls by a laminar flow of hot gases, including the stages of heating of a substance and of reacting in the surface layer with self-acceleration of the chemical reaction. The process is determined by the heat exchange between the gas and the wall, the strength of the heat source in the chemical-reaction zone, and the sink of heat due to conduction in the radial and axial directions. In the stage of self-heating, we can have heat sink not only deep into the wall and/or through its external boundary but into the gas flow as well. The problem has been solved in a conjugate formulation. The influence of the temperature, the velocity of the gas at the entrance to the channel, and the wall thickness on ignition characteristics has been studied.     

RLS耐热铸造不锈钢燃烧器精密制造

RLS燃烧器是石油高新加热装备中的最核心关建零部件,铸件材质为耐热铸造不锈钢。燃烧器的内部形为状环状,是一个有8条细长窄缝的环形封闭室的压力容器,它的结构比较特殊,铸件壁厚也不均。而使用硅溶胶精密铸造工艺铸造,受熔模精密铸造工艺的局限性,模具制造、蜡件制造、模壳制造、铸件清理的制造工艺难度太大,产品的成功率很低。本文通过对铸件的铸造工艺性分析,汽腔被分割设计成汽腔芯和汽腔体,巧妙设计了汽腔芯的8条细长窄缝模具和制模工艺。通过先分后合工艺方法,解决了耐热铸造不锈钢燃烧器环形封闭汽室的细长窄缝蜡件和铸件的制造问题,使产品满足了要求。     

Influence of the rates of gas flows through the smoke-removal and input-ventilation systems on the height of the smoke-free zone in a fire within a building

Integral, zonal, and empirical methods of calculating the mass rate of the gas flow through the smoke-removal system in the case of fire in a building were considered. Numerical experiments on investigation of the influence of the flow rates of the smoke removed and the cold air supplied by the input-ventilation system on the height of the smoke-free zone in a model fire within a building have been carried out. It is shown that, in the case where cold air is blown into the near-ceiling layer zone, to prevent the propagation of smoke to the adjacent rooms it is necessary to substantially increase the rate of gas flow through the smoke-removal system. It has been established that the simulation of a combustion region in the form of a point heat source positioned lower relative to the combustion surface gives incorrect results. It is shown that, in the integral and zonal models, account must be taken of the fact that air is entrained from the cold-air zone through the lower boundary of the near-ceiling layer by the smoke-removal system.     

Analysis of flux flow and the formation of oscillation marks in the continuous caster

In the industrial process of continuous steel casting, flux added at the top of the casting mould melts and forms a lubricating layer in the gap between the steel and the oscillating mould walls. The flow of flux in the gap plays an essential role in smoothing the casting operation. The aim of the present work is to better understand the mechanics of flux flow, with an emphasis on such problems as how the flux actually moves down the mould, the physical parameters governing the consumption rate of the flux and the geometry of the lubricating layer. The problem considered is a coupled problem of liquid flow and multi-phase heat transfer. In the first part of the paper, the formation of the lubricating layer is analysed and a set of equations to describe the flux flow is derived. Then, based on an analysis of the heat transfer from the molten steel through the lubricating layer to the mould wall, a system of equations correlating the temperature field in the steel and flux with the geometry of the lubricating layer is derived. Subsequently, the equations for the flux flow are coupled with those arising from heat-transfer analysis and then a numerical scheme for the calculation of the consumption rate of flux, the geometry of the lubricating layer and the solidification surface of the steel is presented.     

Dissipative heating under conditions of shear flow of liquid in a flat channel of finite length in view of temperature dependence of viscosity

A steady-state process of heat transfer is considered under conditions of Couette-type shear flow in a flat channel of finite length. The problem is solved in view of dissipation of mechanical energy and of temperature dependence of viscosity under symmetric boundary conditions of the third kind on the channel walls. A number of simplifying assumptions are made, and approximate solutions are obtained within two formulations of the initial problem. In the first case, the constant velocity of the moving channel wall is assigned. This problem is conventional and leads to quite predictable results. In the second case, it is assumed that it is the resultant force applied to the moving channel wall which is assigned. The wall velocity in the steady-state mode is not known in advance. It is found that, in this case, the dependence of kinematic and thermal characteristics of the process on Froude number exhibits a hysteretic pattern.     

模具定量精确成形技术在挤铸生产中的应用 研究

目的解决小型铝合金挤压铸件在浇铸过程中,存在的浇铸质量误差大、铸件组织的一致性较差、热节区出现组织缩松的问题,同时提高材料利用率。方法将模具定量精确成形技术引入到实际生产。结论模具定量精确成形技术的应用,能够有效解决小型铝合金挤压铸件在浇铸过程中因浇铸质量误差大的问题,铸件的总体质量误差能够控制在±0.02 kg范围以内,有效解决了因铸件质量误差大造成的铸件壁厚误差大,解决了铸件组织的一致性较差、热节区出现组织缩松的问题,提高了材料的利用率。