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.

Multi-scale complexity entropy causality plane: An intrinsic measure for indicating two-phase flow structures

We extend the complexity entropy causality plane（CECP） to propose a multi-scale complexity entropy causality plane（MS-CECP） and further use the proposed method to discriminate the deterministic characteristics of different oil-in-water flows. We first take several typical time series for example to investigate the characteristic of the MS-CECP and find that the MS-CECP not only describes the continuous loss of dynamical structure with the increase of scale, but also reflects the determinacy of the system. Then we calculate the MS-CECP for the conductance fluctuating signals measured from oil–water two-phase flow loop test facility. The results indicate that the MS-CECP could be an intrinsic measure for indicating oil-in-water two-phase flow structures.

Multi-relaxation-time lattice Boltzmann front tracking method for two-phase flow with surface tension

In this paper, an improved incompressible multi-relaxation-time lattice Boltzmann-front tracking approach is proposed to simulate two-phase flow with a sharp interface, where the surface tension is implemented. The lattice Boltzmann method is used to simulate the incompressible flow with a stationary Eulerian grid, an additional moving Lagrangian grid is adopted to track explicitly the motion of the interface, and an indicator function is introduced to update the fluid properties accurately. The interface is represented by using a four-order Lagrange polynomial through fitting a set of discrete marker points, and then the surface tension is directly computed by using the normal vector and curvature of the interface. Two benchmark problems, including Laplace＇s law for a stationary bubble and the dispersion relation of the capillary wave between two fluids are conducted for validation. Excellent agreement is obtained between the numerical simulations and the theoretical results in the two cases.

Implementation of a Demoisturization and Devolatilization Model in Multi-Phase Simulation of a Hybrid Entrained-Flow and Fluidized Bed Mild Gasifier

A mild gasification process has been implemented to provide an alternative form of clean coal technology called the Integrated Mild Gasification Combined Cycle (IMGCC), which can be utilized to build a new, highly efficient, and compact power plant or to retrofit an existing coal-fired power plant in order to achieve lower emissions and significantly improved thermal efficiency. The core technology of the mild gasification power plant lies on the design of a compact and effective mild gasifier that can produce synthesis gases with high energy volatiles through a hybrid system: utilizing the features of both entrained-flow and fluidized bed gasifiers. To aid in the design of the mild gasifier, a computational model has been implemented to investigate the thermal-flow and gasification process inside this mild gasifier using the commercial CFD (Computational Fluid Dynamics) solver ANSYS/FLUENT. The Eulerian-Eulerian method is employed to model both the primary phase (air) and the secondary phase (coal particles). However, the Eulerian-Eulerian model used in the software does not facilitate any built-in devolatilization model. The objective of this study is therefore to implement a devolatilization model (along with demoisturization) and incorporate it into the existing code. The Navier-Stokes equations and seven species transport equations are solved with three heterogeneous (gas-solid) and two homogeneous (gas-gas) global gasification reactions. Implementation of the complete model starts from adding demoisturization first, then devolatilization, and then adding one chemical equation at a time until finally all reactions are included in the multiphase flow. The result shows that the demoisturization and devolatilization models are successfully incorporated and a large amount of volatiles are preserved as high-energy fuels in the syngas stream without being further cracked or reacted into lighter gases. The overall results are encouraging but require future experimental data for verification.

Three-dimensional multi-relaxation-time lattice Boltzmann front-tracking method for two-phase flow

We developed a three-dimensional multi-relaxation-time lattice Boltzmann method for incompressible and immiscible two-phase flow by coupling with a front-tracking technique. The flow field was simulated by using an Eulerian grid, an adaptive unstructured triangular Lagrangian grid was applied to track explicitly the motion of the two-fluid interface, and an indicator function was introduced to update accurately the fluid properties. The surface tension was computed directly on a triangular Lagrangian grid, and then the surface tension was distributed to the background Eulerian grid. Three benchmarks of two-phase flow, including the Laplace law for a stationary drop, the oscillation of a three-dimensional ellipsoidal drop, and the drop deformation in a shear flow, were simulated to validate the present model.

Numerical simulation of complex multi-phase fluid of casting process and its applications

The fluid of casting process is a typical kind of multi-phase flow. Actually, many casting phenomena have close relationship with the multi-phase flow, such as molten metal filling process, air entrapment, slag movement, venting process of die casting, gas escaping of lost foam casting and so on. Obviously, in order to analyze these phenomena accurately, numerical simulation of the multi-phase fluid is necessary. Unfortunately, so far, most of the commercial casting simulation systems do not have the ability of multi-phase flow modeling due to the difficulty in the multi-phase flow calculation. In the paper, Finite Different Method (FDM) technique was adopt to solve the multi-phase fluid model. And a simple object of the muiti-phase fluid was analyzed to obtain the fluid rates of the liquid phase and the entrapped air phase.

Studies on absorption coefficients of dual-energy γ-rays and measur-ing error correction for multiphase fraction determination

In this article, principle and mathematical method of determining the phase fractions of multiphase flows by using a dual-energy γ -ray system have been described. The dual-energy γ -ray device is composed of radioactive isotopes of 241Am and 137Cs with γ -ray energies of 59.5 and 662 keV, respectively. A rational method to calibrate the absorption coefficient was introduced in detail. The modified arithmetic is beneficial to removing the extra Compton scattering from the measured value. The result shows that the dual-energy γ -ray technique can be used in three-phase flow with average accuracy greater than 95%, which enables us to determine phase fractions almost independent of the flow regime. Improvement has been achieved on measurement accuracy of phase fractions.

基于多特征混合与GWO-SVM的气液两相流流型识别方法

气液两相流流型识别对提高石油化工行业产能和生产效率具有重要作用。针对气液两相流电导波动信号的强非线性和非平稳特性导致特征提取困难、影响流型识别精度的问题,提出了一种基于多特征混合与灰狼算法优化支持向量机(GWO-SVM)气液两相流流型识别方法。研究中,分别采用统计分析法和熵分析法对电导波动信号的不同统计特征和归一化近似熵特征进行提取,并将两类特征混合构成数据集,再利用灰狼算法(GWO)对支持向量机(SVM)模型进行优化,以提高流型识别精度。气液两相流流型识别实验表明,所提方法比SVM、PSO-SVM和GA-SVM方法具有更高的识别精度,流型平均识别率达到98.45%。

多通道平行流扁管-紧凑式翅片相变蓄热器蓄/放热性能

工业余热浪费严重、利用率较低且实际应用过程中受到时间和空间的限制,需要高效蓄热技术和装置来解决此类问题。提出一种将多通道平行流扁管与紧凑式翅片相结合的新型相变蓄热器,以水为载热流体,月桂酸为相变材料。实验研究了载热流体注入方式、流量、入口温度对蓄热器蓄/放热性能的影响,并分析小温差下蓄热器的传热特性。结果显示,该蓄热器相变材料填充率为82.5%,紧凑式翅片的采用极大强化了相变材料侧换热过程,蓄/放热性能优良。当载热流体入口温度分别为45℃和41℃时,相变材料约在270 min和75 min完成相变,最小蓄/放热温差可达2℃,最小温差时的平均蓄热比功率为25.18 W/kg,平均取热比功率为20.23 W/kg。

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.

气-液-固三相并流体系的混沌识别

通过重构相空间、Poincare截面、分维、Kolmogorov熵和Lyapunov指数谱等混沌分析方法对气 -液 -固三相并流向上流动系统的压力波动信号进行了定性和定量研究 ,研究表明 :此类系统具有非线性混沌现象 ;计算结果显示 ,系统普遍存在 2～ 3个分维 ,其中低频大尺度波动对应的分维反映全局动力学行为 。

液-液射流雾化的数值模拟与实验研究

建立了液-液雾化机理的数值模拟平台与实验研究平台,对水在非相溶溶液中的喷射雾化机理进行了研究。应用VOF-CSF多相流模型对雾化过程进行了数值模拟,并在相同工况下进行了实验验证和对比。研究表明,所建立的数学模型能成功地模拟连续射流雾化过程,与实验结果取得了非常好的一致性。通过数值模拟和实验相结合的方法,对雾化过程中的射锥高度、射流速度、非相溶介质流速等关键因素的影响进行了探讨,获得了相应的规律:在确定的雾化条件下,雾化液滴粒径呈现出离散性;液滴的运动方式随射流速度的增加由规则逐渐过渡为紊乱;射流速度为3.5 m/s与非相溶介质流速为0.18 m/s时,雾化射锥高度变化趋势发生转变。本文的研究结果对认识液-液射流雾化机理以及相应的工程应用,具有重要的指导意义和实用价值。

四川盆地早古生代构造-热演化特征

四川盆地位于扬子板块西缘,是中国重要的含油气盆地之一,在震旦纪—早奥陶世处于裂陷特征的被动大陆边缘阶段。利用地球动力学理论在岩石圈尺度探讨盆地构造-热演化特征,恢复早古生代热历史,为盆地生烃状态、生烃期次等研究提供重要热参数。首先,利用回剥技术得到盆地构造沉降史,并作为构造-热演化模拟的目标函数;然后,基于二维多期拉张模型,分别与晚震旦世、寒武纪和奥陶纪等3个时期构造沉降量拟合得到3期拉张系数,揭示岩石圈底界和温度场的演化以及基底热流随时间的演化特征。模拟结果显示：在岩石圈拉张作用下,软流圈上涌形成热扰动,震旦纪时期基底热流值略有升高,其中高值主要分布在盆地西北与西南,而川东北受到的影响最小;热扰动在寒武纪有所减弱,至奥陶纪时期基本消失,盆地热流值呈缓慢下降趋势;盆地基底热流在早古生代始终在52～59mW·m-2范围内。

多喷嘴汽-液两相喷射性能的实验研究

提出了一种多喷嘴结构的汽-液两相喷射器,该装置由7个蒸汽喷嘴、吸入室、7个混合室和扩散室组成.通过实验研究了不同蒸汽干度下多喷嘴汽-液两相喷射器的工作特性.结果表明:由于汽羽的特性和蒸汽喷嘴与混合室的距离对喷射性能的共同影响,喷射器存在一个最佳蒸汽压力,且其数值随低温水温度的升高而减小;蒸汽干度未明显影响低温水质量流量的分布规律;喷射系数随蒸汽干度的增大而增大,随低温水温度的升高而减小.

电荷耦合器件光度检测-深通道多相层流微流控芯片分析系统

采用精密数控雕刻技术,加工用于微流控多相层流分析的深通道(深度500μm)聚碳酸酯芯片,以提高芯片进行吸收光度检测的灵敏度。建立了无需辅助光学设备的近距离CCD二维图像光度检测系统,应用于三流路并行的多相层流比色分析。该芯片分析系统的特点是芯片加工快捷,检测灵敏度高,检测光程较常规芯片增加1个数量级;系统结构简单,易于推广。

碳钢在盐水-油-气多相流中腐蚀规律的研究

借助于建立的动态水平腐蚀测试装置,研究了3％NaCl溶液中介质流速、温度、油水比、气体等因素对碳钢腐蚀行为的影响。实验表明:在实验流速范围内,碳钢的腐蚀速率随介质流速增大而增大;在30～60℃,腐蚀速率随温度升高而升高,且60℃达到最大值;在油水比为1/1000～10/100范围内,腐蚀速率随油含量增加而减小;通入N2和CO2,均会对腐蚀速率产生影响。

bubble-based EMMS／PFB模型的建立及在加压流化床浓相段的应用

基于多尺度分解和能量消耗分析方法,结合压力下锥形分布板射流床气泡直径关联式,建立了一个适于加压流化床(PFB)的能量最小多尺度模型——bubble-based EMMS/PFB模型。应用此模型模拟一个二维加压射流床,分析了操作压力、位置高度、空隙率及剩余速度对非均匀因子的影响。通过模拟结果与实验数据的对比,发现该模型相比于Gidaspow模型,能够更准确地模拟加压射流床内颗粒浓度的分布状态及颗粒靠近壁面处的速度变化;将这种曳力模型应用到流化床浓相段的模拟,预测了床内颗粒浓度瞬时分布及沿轴向的时均值分布、颗粒的速度分布等流动行为,使流化床浓相段的气固流动行为可视化,对流化床的设计、放大有一定的指导作用。

多喷嘴汽-液两相喷射器的工作特性研究

对以湿蒸汽为工作流体的多喷嘴汽–液喷射器机制进行研究,利用质量、能量及动量守恒方程建立了喷射器工作特性一维理论模型。模型求解过程中,采用两相临界流均相平衡模型计算单喷射蒸汽喷嘴的临界流速,并利用多喷射速度系数对其修正,得到多喷射蒸汽喷嘴的出口速度;综合考虑Cattadori的壁面力和Howard的喉部压损理论对流动的影响来确定混合室阻力。为验证模型的正确性,设计以湿蒸汽为工作蒸汽的实验台,并采用多喷嘴喷射器作为实验元件。研究结果表明:容积喷射系数随压力比的增大而减小,且增大喷射器的截面比可使容积喷射系数增加,但缩小了喷射器的工作范围;容积喷射系数随蒸汽干度的增大和过冷水温度的升高而减小。理论计算结果与实验值基本相符。

基于MO-PLP-ELM及电容层析成像的两相流流型辨识

提出一种基于多目标优化并行感知器的极限学习机(MO-PLP-ELM)及电容层析成像(ECT)技术的两相流流型辨识算法。首先,为保证样本具有代表性,采用随机思想生成7类流型的训练及测试样本集;其次,对样本模型的电容数据归一化处理;最后,采用MO-PLP-ELM算法进行流型辨识,并与常用的BP神经网络、支持向量机、极限学习机及并行感知器改进极限学习机算法进行比较,结果表明,提出的MO-PLP-ELM算法其辨识率明显高于其它算法,平均辨识率达96.1%。

带导流管的喷动流化床湍流气-固两相流动模型的建立

带导流管的喷动流化床其流场属于湍流气-固两相流,流场特性复杂,影响因素较多,单纯使用实验方法难以全面描述床层内的流场特性.本文以湍流气-固两相流〔1〕理论为基础,选用k--εkp-pε-Θ5参数数学模型,按多流体模型以颗粒动力学理论封闭颗粒剪应力,建立了带导流管的喷动流化床湍流气-固两相流动模型,并对带导流管的喷动流化床内的流场进行模拟计算,模拟结果与实验数据吻和较好,最大相对偏差约为20%.