Peculiarities of propagation of the dispersed phase in a gas-droplet flow downstream of a pipe sudden expansion

The results of numerical simulation of the propagation of the dispersed phase in a gas-droplet flow downstream of a pipe sudden expansion for small initial mass concentrations of particles (M _L1 = 0–0.1) are presented. Fine-dispersed droplets with the Stokes numbers Stk < 1 are entrained by a separated flow and are present in the whole cross section of the pipe. The near-wall region of the pipe is free of fine particles due to intense evaporation. Heavy particles (Stk > 1) do not get in the recirculation flow region and are present only in the mixing layer and in the flow core. It is shown that the addition of fine-dispersed droplets suppresses the energy of the gaseous phase turbulence in the separated flow. The results are compared with the experimental data for two-phase separated flows and are found to be in the conformity with these data.     

贴壁风对脱硫反应器内液滴粘壁的影响

反应器内液滴粘壁对半干法烟气脱硫效率和运行稳定性具有重要影响.本文采用数值方法研究了不同贴壁风风速和风口高度对反应器内液滴粘壁现象的影响规律.结果表明,贴壁风对减轻液滴粘壁具有一定作用.贴壁风风速越高,液滴贴壁数量越少.贴壁风衰减较快,其风口高度存在最佳值,贴壁风风口与液滴喷射口的高度距离是按照液滴直线运动粘壁时液滴高度行程的1.2倍.     

Techniques for increasing the film cooling efficiency by means of the vortex near-wall jets

Experimental results on the effect of the methods of gas cooling arrangement on thermal efficiency are presented. The swirl cooling is considered at both injecting along the axis and co-axial supply of the cooling gas. The influence of swirling degree, density ratio of both flows and flow regimes on the efficiency of near-wall cooling is considered.     

脉冲功率3 kW二极管激光器叠阵的相变冷却

针对二极管激光器叠阵的高效散热冷却开展了研究,设计了基于R134a制冷剂的相变冷却系统和以节流式微通道相变冷却方式工作的冷却器,完成了脉冲功率3 kW叠阵的封装,并分析了制冷剂在热沉进出口的温度对叠阵出光波长的影响。实验测试结果表明:在20%的高占空比下,电流197 A时叠阵的输出功率达到3 030 W,插座效率为39%,光谱宽度小于3.8 nm,冷却器内R134a的气化率约为50%。制冷剂R134a的流量为0.60 L/min,仅为水系统的1/5,大幅减小了冷却液流量和热管理系统的体积。     

高重复频率水冷Nd:YAG激活镜放大器的温度特性

为解决高重复频率大能量激光放大器的热管理问题,采用数值模拟与实验分析的方法,对背面水冷Nd:YAG激活镜放大器的流体散热进行了研究.基于低雷诺数k-ε湍流模型,建立了流-固共轭传热多物理场藕合分析模型,对比分析了近壁面处理方法对流体流动、对流扩散和热传导过程及温度分布的影响,分析研究了不同冷却液流量和泵浦参数对流场特性、激光介质温度和波前分布的影响.数值模拟表明:激光介质的温度分布与固液边界层内的黏性作用密切相关,且冷却液的热扩散主要发生在100μm范围内;激光介质的热沉积分布中心对称,而温度分布沿水流方向不对称,最大温升位于出水口端且基本保持不变;增益介质前表面的温度分布与介质的波前分布随冷却液流量非线性变化,而随泵浦参数线性变化;实验结果与数值模拟符合较好.     

PIV measurement of mean and pulsating velocities in a gas-droplet jet with low concentration of dispersed phase

A Particle Image Velocimetry (PIV) system was used to perform an investigation into the effect of low concentration of dispersed phase on time-average and pulsating characteristics of the flow over the self-similar part of a two-phase jet emanating into ambient space filled with the same fluid. A phase discrimination procedure based on reflected intensity was introduced into routine practice. Distributions of mean and pulsating velocities in the carrier and dispersed phases of the gas-droplet jet were obtained. In spite of low concentration of the dispersed phase, large droplets present in the flow were found to reduce the intensity of velocity pulsations in the gas phase.     

Concentration model based on movement model of powder flow in coaxial laser cladding

The structure below the coaxial nozzle is critical since the spatial distribution of metal powder particles determines the laser attenuation as well as catchment efficiency. It is difficult to simulate the powder concentration distribution, because the complex phenomena involved in the two-phase turbulence flow. In this paper, the air-powder flow is studied along with powder properties, nozzle geometries and shielding gas setting. A Gaussian model is established to quantitatively predict the powder stream concentration in order to facilitate coaxial nozzle design optimizations. An experimental setup is design to measure the powder concentration for this process. The simulated results are compared with the experimental results. This study shows that the powder concentration mode is influenced significantly by powder properties, nozzle geometries and shielding gas setting.     

基于局部非热平衡模型的发汗冷却过程的数值模拟

本文对水平槽道内发汗冷却建立了包括主流区、多孔壁面区和致密壁面区在内的完整的物理模型和数学描述, 对耦合传热过程开展了数值模拟,对平板发汗冷却的机理进行了深入的研究。研究表明:发汗冷却减小了壁面处的速度梯度,使下壁面边界层明显增厚;随着冷却流体的注入,壁面处的湍流应力明显增大;湍流应力的最大值向没有发汗冷却的壁面一侧偏移,并且增加了最大湍流应力;边界层的增厚使得发汗冷却区域壁面摩擦阻力系数降低。随着冷却剂流量的增大,壁面温度也随之下降;数值模拟结果与实验结果较好地吻合。     

Thermoelectrical regime of a vertical electrolyzer. Part 2: Numerical modeling of two-phase electrolyte convection

The results of numerical modeling of two-phase electrolyte thermo-and hydrodynamics in the working space of a separate electrolyzer cell with vertical electrode arrangement are presented. The problem is solved in a self-consistent formulation taking into account the electric current, Joule heat evolution, gas evolution, gas and liquid flows, and electric conductivity of the disperse phase. Within the framework of the proposed two-liquid approach, near-wall bubbly flow is calculated using a model of expanding gas plume, which is based on the introduction of an effective force acting upon the gas phase. The results of several variants of such calculations are compared. The numerical solution is also compared to approximate analytical solutions of the problem. The results of this study can be used to calculate estimations of the electrical and thermal regimes of vertical electrolyzers.     

基于PET基底透明屏蔽膜的制备研究

为满足光学器件透红外屏蔽电磁波的要求,在PET柔性基底上制作了金属网栅透明屏蔽膜.分析网栅参数对其屏蔽效率及透过率的影响,选取结构参数.针对PET基底的柔性特点及其热稳定性,经试验研究优化光刻工艺中的提拉速度、烘烤时间及温度等参数,从而得到高质量的图形结构.采用磁控溅射法制备透明屏蔽膜,通过优化溅射功率、溅射气压等参数使膜/基结合更牢固.最后得到线宽为3μm、周期为250μm的金属网栅透明屏蔽膜.采用分光光度计测得其在300~2 200nm波段的平均透过率为77%;采用屏蔽室法测得其在2~18GHz频段的电磁屏蔽效率为12dB以上.     

Peculiarities of evolution of shock waves generated by boiling coolant

Simulation of compression wave generation and evolution at the disk target was performed for the case of explosive-type boiling of coolant; the boiling is initiated by endwall rupture of a high-pressure pipeline. The calculations were performed for shock wave amplitude at different times and modes of pipe rupture. The simulated pressure of a target-reflected shock wave is different from the theoretical value for ideal gas; this discrepancy between simulation and theory becomes lower at higher distances of flow from the nozzle exit. Comparative simulation study was performed for flow of two-phase coolant with account for slip flow effect and for different sizes of droplets. Simulation gave the limiting droplet size when the single-velocity homogeneous flow model is valid, i.e., the slip flow effect is insignificant.     

蒸发器出口状态热式测量的实验研究

根据热式感应原理,专门设计热式感应传感器,用于测量蒸汽压缩制冷循环中干式蒸发器出口的气液两相流动状态;热式感应传感器的测量数据与蒸发器出口流型、过热度等参数的综合比较分析表明:热式感应传感器可以辨识出蒸发器出口过热蒸汽、雾状流和二者交替三种流动状态.同时,实验数据表明蒸发器出口处于过热蒸汽、雾状流二者交替的过渡区时其换热效率最佳,因此热式感应传感器可以用于作为膨胀阀-干式蒸发器调节回路的反馈信号.应用热式感应传感器对蒸发器出口状态的随机性和周期性波动的测量证明:热式感应传感器动态性能良好,可以实时反映蒸发器出口状态变化.     

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 d...     

轴流压缩机叶栅内固体微粒沉积的数值研究

本文针对轴流压缩机叶栅内固体微粒沉积的问题,采用计算流体动力学(CFD)软件对压缩机叶栅内的气固两相流动进行了模拟。文中首先采用不同的湍流模型和不同的壁面处理方法计算了垂直圆管内固体微粒的沉积,并与实验数据进行了对比。在此基础上,研究了轴流压缩机叶栅内不同直径粒子在叶片压力面和吸力面的沉积规律;且研究了不同工况对粒子沉积的影响。     

Optimum convective heat transfer coefficient for diode-pumped laser slabs

It is important for laser designers to study the characteristics of heat transfer from the laser crystal slab to the coolant in high-power DPSS laser operations. We have simulated and obtained the optimum heat transfer coefficient and coolant flow rate for our cavity design, in which the circulating coolant is maintained at a constant temperature. It has been determined that the coolant temperature and the convective heat transfer coefficient (h) are important parameters in the thermal analysis. The coefficient h is affected by the coolant flow rate, the physical properties of the laser slab and the coolant and the pumping cavity geometry. Using analytical heat transfer equation, for cooling water temperature of 300 K, the optimum flow rate for our cavity geometry is found to be 390 cm³/s, corresponding to h=5 W/cm² K.     

直流非转移弧热等离子体喷枪加热效率分析

利用计算机模拟技术,采用有限容积方法,针对自制的低能耗、高效率内送粉等离子喷涂设备,对喷枪内部影响喷涂热效率的因素进行了分析。研究结果表明通过适当提高进气流量、提高混合气体中的氮气或氢气含量和减少喷枪通道长度,均能提高等离子喷枪热效率。而电流的大小以及喷枪的通道直径对热效率无显著影响。     

动态细水雾的最佳热辐射消光粒径

研究了细水雾遮蔽衰减热辐射过程中,取得最佳遮蔽效果的动态雾滴初始粒径问题。综合考虑雾滴的光学特性和动力学特性,定义了热遮蔽指数作为度量动态雾滴消光能力的指标。在模型构建中,用索特粒径将多分散性的细水雾等效成单分散系;用Planck平均法获取水雾的灰体辐射特性参数;并采用数组调用、线性插值的方法提高大量计算Mie氏消光因子的效率。研究发现,基于遮蔽指数的最佳消光粒径要远大于基于光学特性的最佳消光粒径。     

New numerical algorithms in SUPER CE/SE and their applications in explosion mechanics

The new numerical algorithms in SUPER/CESE and their applications in explosion mechanics are studied. The researched al-gorithms and models include an improved CE/SE (space-time Conservation Element and Solution Element) method,a local hybrid particle level set method,three chemical reaction models and a two-fluid model. Problems of shock wave reflection over wedges,explosive welding,cellular structure of gaseous detonations and two-phase detonations in the gas-droplet system are simulated by using the abov...     

卧式螺旋管内汽液两相流不稳定性试验研究

本文在中、低压汽水试验台上对卧式螺旋管内汽液两相流动不稳定性进行了详细的试验研究，获得了各类脉动发生的界限及各主要参数对脉动的影响规律，并在无固次分析的基础上，给出了密度波脉动起始边界的预报关系式。