Effect of droplet characteristics on liquid-phase distribution in spray zone of internal mixing air-mist nozzle

In continuous casting production,droplet characteristics are important parameters for evaluating the nozzle atomization quality,and have a significant impact on the secondary cooling effect and the slab quality.In order to study the behavior of atomized droplets after reaching the slab surface and to optimize the spray cooling effect,the influence of droplet diameter and droplet velocity on the migration behavior of droplets in the secondary cooling zone was analyzed by FLUENT software.Results show that the droplets in the spray zone and on the slab surface are mainly concentrated in the center,thus,the liquid volume fraction in the center is higher than that of either side.As the droplet diameter increases,the region of high liquid volume fraction on the slab surface becomes wider,and the liquid phase distribution in the slab width direction becomes uneven.Although increasing the droplet velocity at the nozzle exit has little effect on droplet diffusion in the spray zone,the distribution becomes more uneven due to more liquid reaches the slab surface per unit time.A prediction formula of the maximum water flow rate on the slab surface for specific droplet characteristics was proposed based on dimensionless analysis and validated by simulated data.A nozzle spacing of 210 mm was recommended under the working conditions in this study,which ensures effective coverage of the spray water over the slab surface and enhances the distribution uniformity of water flow rate in the transverse direction.

Study on Venturi nozzle for gas-liquid two-phase flow metering

Experiments were carried out to study gas-liquid two-phase flow through a horizontally mounted Venturi nozzle. The inner diameter of pipe is 25 mm and the throat diameter of Venturi nozzle is 5. 1 mm. The pressure difference and pressure loss across the nozzle were measured. It was found that the degree of pressure fluctuation strongly depends on the gas quality. However,the relationship between the standard deviation of pressure difference and the gas quality is not monotonous. Multiple solutions may occur when the relationship was used to determine gas quality. On the other hand,the standard deviation of pressure loss was found to be monotonously correlated to X. This phenomenon was applied to measured gas quality. Also a modified Lin's equation is proposed to calculate the two-phase flow rate. The experimental measurements agree well with the predicted values.

Experimental Analysis of the Flow Characteristics of an Adjustable Critical-Flow Venturi Nozzle

The response of an adjustable critical-flow Venturi nozzle is investigated through a set indoor experiments aimed to determine the related critical flow rate,critical pressure ratio,and discharge coefficient.The effect of a variation in the cone displacement and liquid content on the critical flow characteristics is examined in detail and it is shown that the former can be used to effectively adjust the critical flow rate.The critical pressure ratio of the considered nozzle is above 0.85,and the critical flow control deviation of the gas flow is within±3%.Liquid flow can reduce the gas critical mass flow rate accordingly,especially for the cases with larger liquid volume and lower inlet pressure.The set of results and conclusions provided are intended to support the optimization of steam injection techniques in the context of heavy oil recovery processes.

Comparison of One-Dimensional Analysis with Experiment for CO₂Two-Phase Nozzle Flow

The aim of this study is to investigate CO2 two-phase nozzle flow in terms of both experimental and analytical aspects for the optimum design of two-phase flow nozzle of CO2 two-phase flow ejector. In the experiment, it is measured that the temperature profile in the stream-wise direction of a divergent-convergent nozzle through which CO2 in the supercritical pressure condition is blown down into the atmosphere. In the analysis, a one-dimensional model which assumes steady, adiabatic, frictionless, and equilibrium is proposed. In the convergent part of the nozzle the flow is treated as single-phase flow of liquid, whereas in the divergent part the flow is treated as separated two-phase flow with saturated condition. The analytical results indicate that the temperature and the pressure decrease rapidly in the divergent part, and the void fraction increases immediately near the throat. Although this analysis is quite simple, the analytical results can follow the experimental results well within this study.

Numerical Study on the Effects of Contraction Ratio in a Two-Phase Flow Injection Nozzle

The Euler-Euler numerical method was used to investigate the effects of contraction ratio on twophase flow mixing with mass transfer in the flow injection nozzle. The geometric shape of the nozzle was modified to improve carbonation efficiency. A gas inlet hole was created to increase the flow mixing of CO2 with water. A nozzle throat was also introduced to increase the gas dissolution by increasing flow rates. Various contraction ratios of nozzle throat, inlet gas and liquid velocities, and gas bubble sizes were employed to determine their effects on gas hold-up, gas concentration, and mass transfer coefficient. Results revealed that the flow injection nozzle with high contraction ratios improved carbonation because of high gas hold-up. Gas concentration was directly related to contraction ratio and gas flow velocities. Carbonation reduced when high liquid velocities and large gas bubbles were employed because of inefficient flow mixing. This study indicated that flow injection nozzle with large contraction ratios were suitable for carbonation because of their ability to increase gas hold-up, gas concentration, and mass transfer coefficient.

Numerical simulation of the gas-solid two-phase flow inside the multi-channel nozzle for the surface nanocrystallization induced by the ultrasonic particulate peening

Using a gas-solid two-phase model(a discrete phase model),the authors investigated the flow field inside the multi-channel nozzle for surface nanocrystallization(SNC)induced by the ultrasonic particulate peening(USPP).By computation,the velocity fields of both the gas and the solid phases were simulated and the track of the solid phase was analyzed in detail.It can be found that the velocities of the two phases are able to reach an ultrasonic level;meanwhile,the dispersion width of the solid phase at the nozzle exit is less than that of the gas phase.When particle diameters are less than 5 μm,there is a decreasing trend in the dispersion width of the solid phase with an increase in particle diameters.The trend becomes stable as the particle diameters are greater than 5 μm;in the meantime,the distribution of solid particles is near the axis of the jet flow.The optimal standoff distance between the nozzle and the substrate in the process of USPP is about 120 mm.Simulation results can help improve the design of mass-production-oriented multi-channel nozzles for SNC induced by USPP.

AN IMPLICIT ALGORITHM OF THIN LAYER EQUATIONS IN VISCOUS，TRANSONIC，TWO－PHASE NOZZLE FLOW

Omitting viscosity along flow direction, we have simplified the dimensionless N-Sequations in arbitrary curved coordinate system as the thin layer equations. Using theimplicit approximate-factorization algorithm to solve the gas-phase governing equ-ations and the characteristic method to follow the tracks of particles, we then obtainedthe full coupled numerical method of two-phase.transonic, turbulent flow. Here, par- ticle size may be grouped, the subsonic boundary condition at entry of nozzle is ireatedby quasi-characteristic method in reference plane and the algebraic model is used forturbulent flow. These methods are applied in viscous two-phase flow. calculation of ro-cket nozzle and in the prediciton of thrust and specific impulse for solid propellant ro-cket motor. The calculation results are in good agreement with the measurerment va-lues. Moreover, the influences of different particle radius, different particle mass frac-tion and particle size grouped on flow field have been discussed, and the influences of particle two-dimensional radial velosity component and viscosity on specific impulse ofrocket motor have been analysed.The method of this paper possesses the advantage of saving computer time. More important, the effect is more obvious for the calculation of particle size being grouped.

Experiment and Numerical Simulation of Free Water Jet by a Central-body Nozzle

The recent research about cavitation jet mainly focuses on the organ-pipe nozzle and triangular nozzle. The research content mainly includes the optimized design about the structure of nozzles, the observation and flow analysis about the cavitation jet in the water, and the theory of rock attacked by the cavitation jet, while the energy characteristic of the free jet is not studied yet. In China, the research about the central-body nozzle is almost empty. For the purpose of studying the energy characteristic and the structure of free water jet discharged from central-body nozzle, an experiment with phase Doppler particle anemometry（PDPA） technology is carried out to measure the free water jet flow, which is produced by a central-body nozzle under the jet pressure of 15 MPa. While five sections with different axial distances from the nozzle outlet are selected for data process and analysis, the axial and radial velocity and the droplets of the particle size are studied. Meanwhile, numerical calculation of corresponding flow field is conducted by using volume of fluid（VOF） multiphase model, and the jet flow feature is discussed. The experimental and calculating results show that the axial velocity of high speed jet flow dissipates slowly in the air, and the core area and diffused area are discovered. The diameter of droplet in the core area is small, and jet energy is concentrated, while in the diffusion area, water is mingled with ambient air and radial velocity is relatively large. Obvious low-pressure area exists behind the central body and potential cavitation may occur in that area. The proposed research reveals the energy characteristic of free jet discharged from central-body nozzle, provides the theoretical basis for preestimating erosion feature of the central-body nozzle and also the theoretical foundation for revealing the mechanism of erosion.

Influence of Self-excited Vibrating Cavity Structure on Droplet Diameter Characteristics of Twin-fluid Nozzle

It is a great challenge to find effective atomizing technology for reducing industrial pollution; the twin-fluid atomizing nozzle has drawn great attention in this field recently. Current studies on twin-fluid nozzles mainly focus on droplet breakup and single droplet characteristics. Research relating to the influences of structural parameters on the droplet diameter characteristics in the flow field is scarcely available. In this paper, the influence of a self-excited vibrating cavity structure on droplet diameter characteristics was investigated. Twin-fluid atomizing tests were performed by a self-built open atomizing test bench, which was based on a phase Doppler particle analyzer(PDPA). The atomizing flow field of the twin-fluid nozzle with a self-excited vibrating cavity and its absence were tested and analyzed. Then the atomizing flow field of the twin-fluid nozzle with different self-excited vibrating cavity structures was investigated.The experimental results show that the structural parameters of the self-excited vibrating cavity had a great effect on the breakup of large droplets. The Sauter mean diameter(SMD) increased with the increase of orifice diameter or orifice depth. Moreover, a smaller orifice diameter or orifice depth was beneficial to enhancing the turbulence around the outlet of nozzle and decreasing the SMD. The atomizing performance was better when the orifice diameter was2.0 mm or the orifice depth was 1.5 mm. Furthermore, the SMD increased first and then decreased with the increase of the distance between the nozzle outlet and self-excited vibrating cavity, and the SMD of more than half the atomizing flow field was under 35 μm when the distance was 5.0 mm. In addition, with the increase of axial and radial distance from the nozzle outlet, the SMD and arithmetic mean diameter(AMD) tend to increase. The research results provide some design parameters for the twin-fluid nozzle, and the experimental results could serve as a beneficial supplement to the twin-fluid nozzle study.

Influence of Diesel Nozzle Geometry on Cavitation Using Eulerian Multi-Fluid Method

Dependent on automatically generated unstructured grids, a comprehensive computational fluid dynamics(CFD)numerical simulation is performed to analyze the influence of nozzle geometry on the internal flow characteristics of a multi-hole diesel injector with the multi-phase flow model based on Eulerian multi-fluid method.The diesel components in nozzle are considered as two continuous phases, diesel liquid and diesel vapor respectively.Considering that both of them are fully coupled and interpenetrated, separate sets of governing equations are established and solved for each phase.The geometric parameters mainly include the length and exit diameter of nozzle, the rounded radius at inlet of nozzle orifice and the angle between axis of injector and axis of nozzle orifice, and they are individually taken into account to analyze the impact on the cavitating flow in nozzle.The results show that the geometrical characteristics of nozzle have a strong influence on the volume fraction of diesel vapor in nozzle and the outlet flow velocity of injector.So cavitation in nozzle orifice should not be neglected for the in-cylinder fuel atomization process, especially for the primary break-up of liquid jet.

Effect of carrier gas pressure on vapor condensation and mass flow-rate in sonic nozzle

Non-equilibrium vapor condensation of moist gas through a sonic nozzle is a very complicated phenomenon and is related to the measurement accuracy of sonic nozzle.A gas-liquid two-phase model for the moist gas condensation flow was built and validated by moist nitrogen experiment of homogeneous nucleation through a transonic nozzle.The effects of carrier gas pressure on position and status of condensation onset in sonic nozzle were investigated in detail.The results show that condensation process is not easy to occur at lower carrier pressure and throat diameter.The main factors influencing condensation onset are boundary layer thickness,heat capacity of carrier gas and expansion rate.All of results can be used to further analyze the effect of condensation on mass flow-rate of sonic nozzle.

Branch Quality Control of Gas-Liquid Two-Phase Flow Using a Novel T-Junction Type Distributor

In order to eliminate mal-distribution and ensure the side arm to produce desirable gas quality a special distributor is proposed. The experimental distributor mainly consists of a straight through section,a gas extraction line,a liquid extraction line and a side arm branch. A gas orifice and a liquid orifice are mounted at the gas and liquid extraction line respectively to control the outlet gas quality. The diameter of the liquid orifice was set to 2. 50 mm and three gas orifices with different size( dG= 2. 65,5. 00,10. 00 mm) were tested. The experiments were carried out at an air-water two-phase flow loop. The gas superficial velocity ranged from 6. 0 to 20. 0 m /s and the liquid superficial velocity was in the range of 0. 02- 0. 18 m /s. Flow patterns such as wave flow,slug flow and annular flow were observed. The gas quality of the side arm branch was found mainly determined by the flow area ratio of the gas orifice to the liquid orifice and independent of gas and liquid superficial velocity,flow patterns and extraction flux.

PERFLUOROOCTANESULFONIC ACID CATALYZED FRIEDEL-CRAFTS ALKYLATION WITH OLEFINS IN GAS-LIQUID PHASE

Solid superacid perfluorooctanesulfonic acid(POSA)catalyzed Friedel-Crafts alkylation of aromatic hydrocarbons with olefins in gas-liquid phase.The alkylations gave good yields with simple operation and easy work up.The amount of the catalyst used in the reactions was small and could be reused.The optimum temperature of the reactions and the effect of the amount of the catalyst used in the reactions are also discussed.

喷嘴位置对轴承腔内油气润滑两相流的影响

基于气液两相流理论,采用多重坐标系法构建角接触球轴承数值计算模型,分析不同喷嘴位置和转速下轴承腔内油相体积分数、保持架表面及轴承内外圈的油气分布特性。结果表明:在轴承低转速下,正面供油时轴承腔内油相体积分数及其周向分布的波动大于背面供油;正面供油时保持架下表面会产生润滑油的积聚,造成润滑油无法及时通过出口排出,而背面供油时润滑油在保持架表面的油相分布更均匀;正面供油时内圈左面油相体积分数较高,外圈油相分布变化较大,而背面供油时内圈右面、中间面及外圈中间面油相体积分数较高。不同转速下喷嘴位置对腔内油相分布的影响也不同,低转速下正面供油时腔内油相体积分数更高,高转速下喷嘴位置对轴承腔内油相分布的影响较小,润滑油在轴承腔内分布较为均匀,保持架下侧未见明显的润滑油积聚。

板坯宽度方向非均匀冷却条件下凝固模拟

利用多物理场仿真软件COMSOL模拟板坯连铸宽度方向非均匀冷却状态下的凝固过程的数值模拟。通过将各冷却区设定的铸坯表面目标温度作为约束条件代入傅里叶传热微分方程,反向推算板坯内弧表面中线上各冷却区的换热系数。在此基础上,根据二冷区喷嘴的布置及喷嘴喷雾分布试验数据将该换热边界条件沿铸坯宽度方向进行拓展,计算出板坯从MD弯月面开始到最末扇形段出口的整个铸流区间的3D温度场。通过该方法可模拟出相同冷却条件下不同铸坯宽度在厚度中性层剖面两相区区间范围的区别,并且也可以清晰地反映出喷嘴的布置对铸坯表面温度及凝固终点的影响,从而为生产中的凝固末端压下策略和喷嘴布置的设计提供有力的数据支撑。

喷管两相湍流数值模拟及湍流模型性能评估

研究固体火箭发动机喷管中颗粒质量流率对两相流的影响规律以及不同RANS模型对该问题的预测性能,可为喷管设计等工程应用提供重要参考。在欧拉-拉格朗日(Euler-Lagrange)框架下,通过3D大涡模拟(3D LES)研究了颗粒质量流率对喷管两相流场的影响规律,以3D LES结果作为参考依据,分析了不同RANS模型针对喷管两相流在2D轴对称和3D模拟中的性能。结果表明:由于扩张段内颗粒集中在中轴线附近区域,颗粒质量流率越大,该区域马赫数越低,温度越高;壁面附近存在无颗粒区,故边界层内流动几乎不受颗粒影响。另外,采用不同湍流模型计算得到的颗粒分布与LES基本相同。在2D轴对称RANS模拟中,发现RNG k-ε模型所预测的气相质量流率和喷管比冲与LES结果吻合最好;在高颗粒质量分数下(约30%),不同湍流模型预测的相对比冲损失差别可超过3%。在3D RANS模拟中,发现Realizable k-ε模型表现出最佳的综合性能,所预测的物理量沿中轴线分布的准确性均优于其他模型。当颗粒质量分数约为31.2%时,Realizable k-ε模型所预测的比冲为与LES结果相比误差仅1.56%。

矩形喷管出口宽高比对流场与声场的影响

为探究矩形喷管出口宽高比对喷流流场和声场的影响规律,采用DES/FW–H混合算法对出口宽高比为3和1.5的矩形喷管超声速完全膨胀喷流开展研究,分析出口宽高比对喷流流动与噪声的影响。针对多个流场变量进行对比分析,以验证数值模拟方法的可行性,发现喷管出口宽高比不同,靠近出口内壁面上的压力变化也有所不同:喷管出口宽高比越大,压力变化越快。结合已有噪声实验数据和计算数据,验证了噪声模拟的准确性。对不同出口宽高比下剪切层厚度的变化进行了分析,研究了这种变化对喷流噪声的影响,发现随着宽高比增大,剪切层厚度增大,且剪切层快速扩张位置和高频噪声源位置向上游方向移动。对比了不同宽高比下出口唇线上特定频率噪声的相速度,研究发现:喷管宽高比不同,同样频率的近场噪声有着不同的相速度,这决定了近场噪声向下游传播的最大角度;相速度对应的马赫角越大,近场噪声向下游传播的最大角度越大;宽高比增大,长轴唇线上的相速度显著降低,近场噪声向下游的辐射角度减小。

闪沸喷雾孔几何形状对孔内流动特性影响的数值模拟

研究了汽车直喷汽油机喷嘴的几何形状对于闪沸喷雾孔内流动以及相变过程的影响机理。基于热不平衡假设建立了一维的两相相变流动模型,对于具有不同喷孔流道长度、直径、入口处圆角以及流道锥角的结构,分析了闪沸喷雾孔内流动的特性。将该模型结果与作者团队先前的实验结果进行了精度比对,验证了模型的准确性。结果表明:喷孔流道长度越长,孔径越小,从而孔内相变越剧烈。流道入口处圆角会减少喷孔内部蒸汽的生成。收缩型喷孔压降较小,孔内蒸汽相的生成也相应减少,从而扩张型喷嘴增大蒸汽产生速率。不同的喷孔结构,改变了流道内的压力以及速度分布;压力分布影响了气泡的生长速率,速度分布影响了气泡的生长时间,而两者共同作用影响了孔内的相变特性。

A New Distribution Method for Wet Steam Injection Optimization

A new approach and a new related distribution system are proposed to address the issue of uneven steam injection caused by the different suction capacities of the used wells during the application of steam“stimulation”methods for enhanced oil recovery.The new distribution system consists of a swirler,spiral dividing baffles,and critical flow nozzles.Numerical simulations are used to analyze the flow-field and degree of steam homogeneity obtained with such an approach.The results indicate that a higher inlet pressure leads to better results.Additionally,the internal flow field becomes more stable,and the deviation from an even distribution reduces to±4.0%even when the resistance of each branch is inconsistent.Furthermore,field tests have yielded satisfactory results.