两阶段悬浮液超音速火焰喷涂传热和流动模拟

两阶段悬浮液超音速火焰喷涂过程中的悬浮液溶剂的蒸发、固体颗粒沉积于基板时的温度和速度对最终形成涂层的性能有着至关重要的影响,因此有必要对悬浮液液滴和固体颗粒在流场中的换热和运动过程加以研究。在分析两阶段悬浮液超音速火焰喷涂原理的基础上,建立了两阶段悬浮液超音速火焰喷涂过程的传热和流动模型,通过使用DPM模型采用双向耦合的方式对TiO_2悬浮液液滴注入超音速流场过程进行数值模拟。研究了不同掺混气体质量流量对液滴以及TiO_2固体颗粒粒径、温度、速度的影响。模拟结果表明,氮气质量流量越高,沿轴线相同位置液滴粒径越大,液滴水分蒸发越慢,TiO_2固体颗粒温度下降越明显,TiO_2固体颗粒速度越大。     

两相流超音速流动_激波及其应用研究

从两相流体的音速特点出发 ,研究两相超音速流动 ,分析超音速流动导致的激波状况 ,并利用两相激波加速凝结和增压的特点 ,设计了增压换热器。两相流的音速受其压缩性的影响而呈现出与单相流不同的特点 ,其较小的音速值使得两相超音速流动更易实现。两相流激波与波前马赫数密切相关 ,波后汽相凝结、压力升高 ,利用该特点设计的汽水直接接触式换热器 ,具有高效换热和增压的特点     

两相流超音速流动、激坡及其应用研究

从两相流体的音速特点出发，研究两相超音速流动，分析超速流动导致的激波状况，并利用两相激波加速凝结和增压的特点，设计了增压换热器。两相流的音速受其压缩性的影响而呈现出与单相流不同的特点，其较小的音突起独两相超音速流动更易实现。两相流激波与前马赫数密切相关，波后汽相凝结、压力升高，利用该特点设计的汽水直接接触式热器，具有高效换热和增压的特点。     

喷枪结构对低温超音速火焰喷涂颗粒飞行特性的影响

建立了低温超音速火焰喷涂传热和流动模型,对喷涂过程的焰流和颗粒的运动加热历程进行了模拟分析.研究了三种不同结构的喷枪对焰流速度与温度分布、不同粒径颗粒飞行特性的影响.模拟结果表明,粒径为20μm的Cu颗粒在撞击基板时能达到临界速度,且温度低于熔点,有利于沉积并减少了颗粒氧化;枪管的扩张率对喷涂颗粒的速度影响不大,而对颗粒温度的影响较大;延长扩张段的长度代替平直枪管有利于在保证颗粒速度的同时提高颗粒的温度.     

微米沙尘高温气-粒两相流平板沉积特性研究

基于微米沙尘高温弹塑性碰撞理论及沙尘-壁面碰撞沉积模型和两相流理论，研究了不同温度下1~5 μm沙尘与镍基单晶材料壁面碰撞沉积特性，分析了气流流动特性、颗粒运动轨迹和碰撞沉积结果等，研究了粒径和温度对微米沙尘碰撞率、沉积率和捕捉率的影响。结果表明：微米沙尘在通道输送过程中不同出口位置处运动轨迹差异较大；温度为1 323 K时，直径1~5 μm沙尘碰撞率随粒径减小而减小，1 μm沙尘沉积率和捕捉率最大，分别为37.86%和6.049%，2 μm以上沙尘沉积率和捕捉率相对较小；直径1 μm沙尘在1 273，1 323和1 343 K 3种温度下沉积率和捕捉率随温度升高而增大。     

超音速等离子喷涂技术与装备

超音速等离子弧喷涂技术是重要的表面工程技术之一。与其它的喷涂技术相比较,它具有生产效率高、涂层质量好的特点。可以熔化金属、碳化物陶瓷和氧化物陶瓷等材料。乌克兰科学院巴顿电焊研究所研究开发的超音速等离子喷涂技术与装备具有显著的技术优势,其最大工作电流达400A;粉末颗粒飞行速度达到750m／s;各种材料涂层的结合强度大于55MPa;沉积率大于60％;金属粉末的送粉速度高达50kg／h。     

循环流化床锅炉管防磨喷涂

本文对循环流化床锅炉燃烧室卫燃带上部锅炉管采用火焰喷涂防磨层与采用超音速电弧喷涂复合涂层的使用效果进行了对比 ,提出了采用超音速电弧喷涂复合防磨涂层是解决循环流化床锅炉磨损问题的有效途径。     

汽轮机叶片防水蚀超音速现场喷涂技术研究及应用

基于便携式超音速喷涂设备,采用超音速火焰喷涂(HVOF)技术制备抗水蚀涂层,测试涂层的金相组织、孔隙率、硬度、结合强度和耐盐雾腐蚀等性能,筛选出最优化工艺,用于叶片喷涂试验乃至最终投产。结果表明:超音速火焰喷涂制备的NiCr-Cr_3C_2金属陶瓷涂层均匀致密,孔隙率小于1.5%,硬度为700HV～1200HV0.3,结合强度大于50MPa;叶片喷涂试验各项指标与试片一致,涂层封孔后耐盐雾腐蚀性能优异。该技术已经应用于机组改造项目叶片现场喷涂。     

催化裂化烟气轮机级叶栅内气固两相运动特性的数值研究

基于欧拉-拉格朗日模型,对催化裂化烟气轮机叶栅内烟气流动特性进行数值研究.采用可压缩流体的k-ε双方程湍流模型,对流道内压力、温度、速度以及水蒸气含量变化进行研究;研究结果表明:级叶栅流道低压区会导致超音速流动,增加流动的不均匀性;二次流使5μm颗粒向动叶压力面底部移动,且压力面处分子黏度大、温度低,易造成颗粒沉积结垢;10μm以上大颗粒容易造成叶顶出气边磨损.模拟结果为烟气轮机长周期安全运行提供理论基础.     

超音速喷涂防磨的应用及质量控制

水冷壁管磨损是循环流化床锅炉受热面磨损删中最突出的问题,采取炉膛内热喷涂或补焊后热喷涂的方法,在水冷壁管磨损区域或部位喷涂金属耐磨层来提高耐磨性。选择喷涂方法与耐磨涂层、喷涂质量检查验收,是炉内热喷涂质量控制的关键。实践表明,在炉膛内进行超音速喷涂金属耐磨层,使水冷壁管因磨损漏泄、爆管得到有效控制。     

基于图像处理的小通道内气液两相流含气率的实验研究

采用高速摄像机对水力直径为1.15 mm的正三角形小通道内气液两相流流型进行实时拍摄和图像采集,提出一种利用数字图像处理技术检测小通道内气液两相弹状流体积含气率的方法。针对小通道内两相流型中气泡间相互无遮掩的优势,利用图像处理技术对各流型图像进行消噪、边缘提取、二值化、区域标记和填充等处理,根据提出的三维气相体积计算模型得到体积含气率。最后与漂移流模型计算结果进行比较,比较和实验结果都表明:对于弹状流,该方法得到的含气率与真实值的误差在±15%以内,具有较高的测量精度;并对实验数据进行回归分析得到了截面含气率公式,可用于微小通道内气液两相流参数的在线检测,为今后微小通道内的两相流动特性研究提供参考。     

气固两相Y型分支管网流量分配特性的试验研究与数值模拟

在水平Y型分支管道中,采用压缩空气作为输送动力,小米作为输送介质进行气力输送试验,对分支管道的固体流量分配特性进行了研究.试验表明,变动支管与主管中轴线夹角与气体表观速度对固相分配特性具有较大影响.同时,采用Euler-Lagrange两相流研究方法,固相采用离散相(DPM)模型,采用Fluent软件对3种不同夹角的Y型分支管内气固两相流动进行了数值模拟.模拟结果较好地预估了颗粒在分支处的流动形态、颗粒在分支管内的运动轨迹,以及重新实现颗粒相流场均匀分布所需的距离.通过对分支管内固体颗粒质量分配的数值模拟结果与试验结果比较,发现两者之间相对误差较小.     

Contributions concerning quasi-steady propagation of thermal detonations through dispersions of hot liquid fuel in cooler volatile liquid coolants

The two-phase flow model of 1-dim. propagation of thermal detonation is reformulated to permit isolation of both new and existing conclusions which are independent of fragmentation kinetics data. The two-phase flow model is found to be necessary for making quantitive predictions of detonation strength in hydrodynamic fragmentation. A wide spectrum of kinetics-independent permissible Chapman-Jouguet states is found possible for any specific intitial condition in calculations for the UO₂-sodium system, with sensitivity of these (C-J) states found to initial sodium (coolant) vapor blanket volume fraction. Arguments are presented which suggest our use of an equilibrium sonic velocity for C-J wave termination. The abrupt decrease of sonic velocity due to the presence of vapor or gas is found to be sufficiently severe as to render vaporization unlikely either in the steady detonation zone or at the C-J plane, and further identifies a lower threshold for thermodynamically permissible C-J propagations which occurs at coolant saturation.     

Two-phase flow distribution in multiple parallel tubes

This work is focussed on the development of a numerical simulation model that predicts the thermal and fluid-dynamic behaviour of the two-phase flow distribution in systems with multiple branching tubes like manifolds. The geometry of a simulated branching system is represented as a set of tubes connected together by means of junctions. On one side, the in-tube evaporation/condensation phenomena are simulated by means of a one-dimensional two-phase flow model, and on the other side, the splitting/converging flow phenomena occurring at junctions are predicted with appropriate junction models obtained from the technical literature. The global flow distribution is calculated using a semi-implicit pressure based method (SIMPLE-like algorithm) where the continuity and momentum equations of the whole domain are solved and linked with both the in-tube two-phase flow model and the junction models.In the present paper, the flow distribution model is described and its most significant aspects are detailed. Furthermore, the model is validated against experimental and numerical data found in the open literature. The numerical predictions are compared against an adiabatic single-phase flow manifold system working with water and also against a two-phase flow upwardly oriented manifold system working with carbon dioxide. In addition to this, a numerical comparison of a manifold system with two different orientations is carried out. Concluding remarks about the possibilities that this kind of model offers are presented in the last section.     

600MW超临界CFB垂直并联内螺纹管两相流压力降不稳定试验研究

在600 MW超临界CFB水冷壁变负荷实际运行条件下,以水冷壁实际采用的Φ28.6×5.8 mm的4头内螺纹管为研究对象,在高压汽水两相流回路上对垂直并联管中汽液两相流压力降型不稳定进行了试验研究.确定了压力、质量流速、进口过冷度以及上游可压缩容积对垂直并联内螺纹管两相流压力降型脉动的影响.结果表明,随压力增大,发生脉动的临界热负荷增加,界限干度逐渐升高,系统稳定性增强,脉动周期先变长后变短,脉动的振幅逐渐减小.本试验中,当压力P＞6 MPa时,就不再有压力降脉动发生;随着质量流速的增加,脉动发生的界限热负荷升高,而脉动的周期减小;进口过冷度对密度波脉动呈现单值性影响,随进口过冷度增加,界限热负荷单调增加,界限干度的变化表现出不同的趋势,在较低的质量流速下,随着过冷度的增加,界限干度单调下降;在较高的质量流速下,随着过冷度的增加,界限干度单调上升;上游可压缩容积对界限热负荷的影响较小,随充气比的增大,脉动的周期和幅值逐渐增大.     

Numerical investigation on the effects of re-organized shock waves on the flow separation for a highly-loaded transonic compressor cascade

This paper presents a detailed numerical investigation of the influence of re-organized shock waves on the flow separation for a highly-loaded transonic compressor cascade. The boundary layer suction (BLS) was used to control the location and strength of shock waves, with the aspirated slot locating at 49% chord, where is just downstream of the impingement point of shock wave at the leading edge. The numerical simulation is based on NUMECA, a commercial software, where the cell-centered control volume approach with third-order spatial accuracy is used to solve the 3-D Reynolds-averaged Navier-Stokes equations under the Cartesian coordinate system. Several conclusions can be made through the observation of the numerical results. (1) Multiple shock waves in cascade passage leaded the velocity deficits of boundary layer on suction surface downstream of shock wave, resulting in seriously separated flow on the suction side of blade, especially when the front shock wave is much stronger than the rest of the shocks. (2) BLS with small mass flow rate can not effectively improve the boundary layer. When the impingement point of oblique shock wave coming from cascade leading edge is bled to downstream of the passage shock wave by BLS, the boundary layer flow is greatly improved. However, if the BLS mass flow rate exceeds a critical value (1.2%), the boundary layer downstream of shock wave would separate from suction surface. (3) At the blade mid-span, the aerodynamic performance of compressor blade is improved as BLS mass flow rate increases. The optimum BLS is about 1.2%. Compared with the baseline case, the BLS with flow rate of 1.2% increases the total pressure recovery coefficient by 12%, and decreases diffusion factor by 18% and deviation angle to 7 ° while keeping the pressure rise constant. (4) The three dimensional flow structure of the compressor cascade ranged from 25% span to 75% span was improved greatly with the 1.2% BLS flow rate. However it could not control the development of the corner boundary layer effectively.     

Interaction of a moving shock wave with a two-phase reacting medium

The flow field, that develops when a moving shock wave hits a two-phase medium of gas and particles, has a practical application to industrial accidents such as explosions at coal mine and in grain elevator and furthermore to solid propellant combustion in rocket engine. Therefore, a successful prediction of the thermo-fluid mechanical characteristics development of gas and particles is very crucial and imperative for the successful design and operation of rocket nozzles and energy conversion systems. This paper describes an interaction phenomenon when a moving shock wave hits a two-phase medium of gas and particles with/without chemical reaction. A particle-laden gas is considered to be located along a ramp so that numerical integration is accomplished from the tip of ramp for a finite period. For the numerical solution, a fully conservative unsteady implicit second order time-accurate sub-iteration method and the second order Total Variation Diminishing scheme are used with the finite volume method for gas phase. For particle phase, the Monotonic Upstream Schemes for Conservation Laws as well as the solution of the Riemann problem for the particle motion equations is also used together with the schemes above. Transient development of thermo-fluid mechanical characteristics is calculated and discussed by changing the particle mass density and particle specific heat. For the case of the reacting particle-laden gas flow, a carbon particle-laden oxygen gas is considered to be located along a ramp. The results are discussed by comparison with the cases of the pure gas and the inert particle-laden gas. Major results reveal that when the particle mass density is smaller, there is a stronger interaction between two phases so that the velocity and temperature differences between two phases more rapidly decrease. When the particle specific heat is varied, only a thermal effect is observed while the other effects are minor. The case with reacting particles yields significantly different results due to chemical reaction such that the gas density does not monotonously but rapidly decrease due to the slip line in the relaxation zone, while the pressure and temperature become higher in comparison with the non-reacting case. But the dynamic variation would be only secondary to the thermal one.     

Two—phase Flow of Liquid—gas in Diesel Fuel Injection System and Their Effect on Engine Performances

IntodcttonThe inveshgation of liquldgas tWo-phase flow uP todate indicates the the stUdy is not ouly in ndhaldeveopment period, but also will be a sphere of lwtwith twt views, for itS changeability andcomPlealty[']. For diesel fuel injechon system withW-Pipe-nozale system, liquld-gaS tWo-phaSe fiowPhenom ekistS, will influenee engine PerfOnnanCes,such as fuel economy, stability of engine OPeraon,regUlarity of fuel injection, and Pmpagation velocity ofPressare wave of the fuel injection…