吹氩模式对钢包内多相流流动行为影响的数值模拟研究

以某钢厂150 t钢包为对象,通过数值模拟手段研究了吹氩模式和吹氩流量对钢包流场、钢渣界面行为和壁面剪应力分布的影响。结果表明:单孔吹氩模式下,钢包内环流远端流速低,钢渣界面流动不活跃,易导致此处渣层冷凝结壳;双孔等流量吹氩模式下,随着吹氩流量增大,钢渣界面流速增加,但其流动活跃性降低;双孔差流量吹氩下,大吹氩流量时钢渣界面能维持一定范围的活跃流动。当吹氩流量在120~240 L/min范围,单孔吹氩所形成的渣眼面积大于两种双孔吹氩模式;当吹氩流量超过240 L/min,双孔等流量吹氩下渣眼面积最大,双孔差流量吹氩对应的渣眼面积最小。另外,单孔吹氩下壁面剪应力最大,应力面积较小,双孔等流量吹氩下剪应力虽然显著降低,但分布区域面积增大。综上所述,双孔差流量吹氩模式可以在提高钢液精炼效率的同时,降低对钢包内衬耐火材料的流动侵蚀。

基于粒子系统与纹理映射的空气分离可视化模拟

空气分离工艺流程复杂,导致流体在机械装备内的流动难以模拟与表达。为实现空气分离系统吸附、换热与精馏等工艺过程的可视化,提出了一种基于粒子流源与纹理映射的空气分离可视化模拟方法:采用关键帧间坐标系递推变换,描述运动部件位置及运动的变化;采用自定义粒子流源,模拟流体的传热传质属性;采用多尺度纹理映射,描述流体的流动迹线。开发了基于虚拟现实技术的可视化系统,实现了空气分离的性能模拟与可视化。

Numerical Simulation of Gas Holdup Distribution in a Standard Rushton Stirred Tank Using Discrete Particle Method

The discrete particle method was used to simulate the distribution of gas holdup in a gas-liquid standard Rushton stirred tank. The gas phase was treated as a large number of bubbles and their trajectories were tracked with the results of motion equations. The two-way approach was performed to couple the interphase momentum exchange. The turbulent dispersion of bubbles with a size distribution was modeled using a stochastic tracking model, and the added mass force was involved to account for the effect of bubble acceleration on the surrounding fluid. The predicted gas holdup distribution showed that this method could give reasonable prediction comparable to the reported experimental data when the effect of turbulence was took into account in modification for drag coefficient.

Advances in Studies on Turbulent Dispersed Multiphase Flows

Dispersed multiphase flows,including gas-particle(gas-solid),gas-spray,liquid-particle(liquid-solid) ,liquid-bubble,and bubble-liquid-particle flows,are widely encountered in power,chemical and metallurgical,aeronautical and astronautical,transportation,hydraulic and nuclear engineering. In this paper,advances and re-search needs in fundamental studies of dispersed multiphase flows,including the particle/droplet/bubble dynamics,particle-particle,droplet-droplet and bubble-bubble interactions,gas-particle and bubble-liquid turbulence interac-tions,particle-wall interaction,numerical simulation of dispersed multiphase flows,including Reynolds-averaged modeling(RANS modeling),large-eddy simulation(LES) and direct numerical simulation(DNS) are reviewed. The research results obtained by the present author are also included in this review.

Gas–liquid two-phase flow in serpentine microchannel with different wall wettability

Gas–liquid flow in serpentine microchannel with different surface properties exhibits drastically different flow behavior. With water and air as working fluids, the method of numerical simulation was adopted in this paper based on CLSVOF(coupled level set and volume of fluid method) multiphase model. After verifying the reasonability of the model through experiment, by changing wall properties and Re number(Re<1500), the influences of contact angle and surface roughness on flow regime and Po number were discussed. Moreover, the difference of pressure drop between curve and straight microchannel was also calculated. Beyond that, the combined effect of curve channel and wall properties on flow resistance was analyzed. This paper finds that wall properties have great influence on gas–liquid flow in microchannels not only on flow regime but also flow characteristics. Meanwhile, the pressure drop in curve microchannels is larger than straight. It is more beneficial for fluid flowing when the straight part of microchannel is hydrophilic smooth wall and curve part is hydrophobic with large roughness.

Effect of particle loading on heat transfer enhancement in a gas-solid suspension cross flow

Heat transfer between gas-solid multiphase flow and tubes occurs in many industry processes, such as circulating fluidized bed process, pneumatic conveying process, chemical process, drying process, etc. This paper focuses on the influence of the presence of particles on the heat transfer between a tube and gas-solid suspension. The presence of particles causes positive enhancement of heat transfer in the case of high solid loading ratio, but heat transfer reduction has been found for in the case of very low solid loading ratio (M s of less than 0.05 kg/kg). A useful correlation incorporating solid loading ratio, particle size and flow Reynolds number was derived from experimental data. In addition, the k-ε two-equation model and the Fluctuation-Spectrum- Random-Trajectory Model (FSRT Model) are used to simulate the flow field and heat transfer of the gas-phase and the solid-phase, respectively. Through coupling of the two phases the model can predict the local and total heat transfer characteristics of tube in gas-solid cross flow. For the total heat transfer enhancement due to particles loading the model predictions agreed well with experimental data.

Numerical Simulation of Enhanced Oil-Water Separation in a Three-Stage Double-Stirring Extraction Tank

Numerical simulation of enhanced fluid flow characteristics in a three-stage double-stirring extraction tank was conducted with the coupling of an Eulerian multiphase flow model and a Morsi-Alexander interphase drag force model. Results show that the addition of a stirring device into the settler can efficiently reduce the volume fraction of out-of-phase impurity in the outlet, and accelerate the settling separation of oil-water mixture. Such addition can also effectively break down the oil-water-wrapped liquid droplets coming from the mixer, inhibit reflux from the outlet, and improve the oil-water separation. The addition of a stirring device induces ignorable power consumption compared with that by the mixer, and can thus facilitate the commercialized promotion of this novel equipment.

Numerical investigation of confined swirling gas-solid two phase jet

This paper presents a \%k\|ε\|k\-p\% multi\|fluid model for simulating confined swirling gas\|solid two phase jet comprised of particle\|laden flow from a center tube and a swirling air stream entering the test section from the coaxial annular. A series of numerical simulations of the two\|phase flow of 30 μm, 45 μm, 60 μm diameter particles respectively yielded results fitting well with published experimental data.

A Preliminary Study on Hydrate Anti-agglomerant Applied in Multiphase Flow Pipeline

When new types of hydrate chemical inhibitor （such as hydrate anti-agglomerant） are used in offshore fields, some difficulties will be encountered in the pipe transportation processing design. In view of these difficulties, a horizontal flow experiment pipe loop of transparent polypropylene pipe （25.4 mm inner diameter, 20 m long） was constructed, and some experiments were conducted. The working fluids were the mixed paraffin hydrocarbons, water and condensate oil mixtures obtained from offshore oil field. Analyzing the experimental results and adopting relevant theories of liquid-solid two-phase flow, the computational method of hydrate slurry transportation in pipe was developed. For the operating conditions of a certain multiphase pipeline, by using OLGA software, this method can be used to calculate pressure drop of the multiphase flow pipelines using anti-agglomerant, which can provide support for hydrate anti-agglomerant application.

Second-order moment modeling of dispersed two-phase turbulence——Part 1:USM,k-ε-k_p,and non-linear k-ε-k_p two-phase turbulence models

Turbulent dispersed multiphase flows,including gas-particle,gas-droplet and bubble-liquid flows,are widely encountered in various engineering facilities.Modeling of two-phase turbulence,in particular the dispersed phase turbulence,is the key problem in the Eulerian-Eulerian simulation of practical dispersed multiphase flows.Although different models were developed and used,the experimental validation shows that they cannot always give satisfactory prediction results.In this paper the present author give a detailed review of the unified second-order moment (USM),k-k p and nonlinear k-k p two-phase turbulence models,proposed by him.The derivation and closure of these models are described in detail and the experimental validation and application of these models are extensively discussed.

Computer Simulations and Measurements of RadialSolid Flow Distribution in a Riser

Comparisons between the numerical predictions from a two-phase model and the experimental hydrodynamic data have been performed in fully developed gas-solid flows for FCC catalysts. The resultssuggested the existence of self-similar solid flux profiles at low solid fluxes. Non-uniformity in theradial solids fluxes was found with a high solid flowing mainly downward near the wall. The modelpredictions were reasonably caught up the experimental trends.

The impact of interphase forces on the modulation of turbulence in multiphase flows

The modulation of turbulence by particles has been rigorously investigated in the literature yielding either a reduction or an enhancement of the turbulent kinetic energy at different spatial length scales.However,a general description of the turbulence modulation in multiphase flows due to the presence of an interphase force has attracted less attention.In this paper,we investigate the turbulent modulation for interfacial and fluid-particle flows analytically and numerically,where surface tension and drag define the interphase coupling,respectively.It is shown that surface tension and drag appear as additional production/dissipation terms in the transport equations for the turbulent kinetic energies(TKE),which is of particular importance for the turbulence modelling of multiphase flows.Furthermore,we study the modulation of turbulence in decaying homogenous isotropic turbulence(HIT)for both types of multiphase flow.The results clearly unveil that in both cases the energy is reduced at large scales,while the small-scale energy is enhanced compared to single-phase flows.Particularly,at large scales surface tension works against the turbulent eddies and hinders the ejection of droplet from the corrugated interface.In contrast,at the small scales,the surface tension force and the velocity fluctuations are aligned leading to an enhancement of the energy.In the case of fluid-particle flows,particles retain their energy longer than the surrounding fluid increasing the energy at the small scales,while at the large scales the particles do not follow exactly the surrounding fluid reducing its energy.For the latter effect,a considerable dependence on the particle Stokes number is found.