Modelling of compressible gas-liquid flow in a convergent-divergent nozzle

A two-fluid model for compressible flow of gas bubbles dispersed in liquid moving through a convergent-divergent nozzle, which is used for a gas-assisted atomization, is presented. The model is developed for flows with high values of the gas volume fraction—up to the phase inversion values. Drag and virtual mass forces are considered. A new method is proposed to correct the virtual mass coefficient for the high bubble loadings. The mixture k-ε turbulence model is adapted for the nozzle flow. The particle number density equation is solved to calculate the distribution of the locally averaged bubble diameter. Curvilinear body fitted grids are utilized to represent the nozzle shape accurately. It is shown that for numerical stability it is necessary to discretize implicitly the virtual mass term and solve the momentum equations for two phases simultaneously in a coupled way. The comparison between the experimentally measured and the predicted pressure profiles along the nozzle wall demonstrated good overall agreement. Gravitational effects are analysed by modelling a three-dimensional case. The examination of the flow through the nozzle reveals the non-uniformities of the bubble size and volume fraction distributions. It is confirmed that the virtual mass force plays a major role in accelerating/decelerating flows with a relatively low interfacial drag.     

进出油阻尼孔对偏转板射流阀射流流场的影响

应用CFD软件对偏转板射流阀进出油阻尼孔不同参数条件下的射流流场进行数值模拟,得出偏转板射流阀内部射流速度、压力的分布特征和不同阻尼孔参数D_1、D_2、L_1、L_2对射流速度、压力的影响规律。研究发现:射流速度由喷嘴处的最大值先逐渐减小,在0.8 mm位置处又上升到仅次于喷嘴射流速度的较大值;射流压力先增大后又在0.8 mm位置处减到较小值,最后在两接收口间阀体处达到射流压力最大值。参数D_1对通过V型导流窗口的射流流量、射流压力和恢复压差起决定性作用;增大参数D_2时射流速度曲线向上平移而射流压力曲线向下平移。参数L_1对射流压力有影响而参数L_2对射流场的影响可以忽略。研究结果为高性能偏转板射流伺服阀的工程设计和优化提供参考。     

钢管表面高压水除鳞效果分析与对策

介绍了钢管表面高压水除鳞系统的工作原理;分析了影响钢管表面高压水除鳞效果的设备问题;探讨了钢管表面生红锈的化学机理。通过改进高压单向截止阀设计和曲轴进油口的密封形式,并通过实验对比选择小直径喷嘴解决了钢管表面生红锈的问题,并在保证钢管表面不生红锈的同时取得了良好的除鳞效果。     

磨削中摩擦的一些研究

讨论了冷却液和喷嘴对摩擦的影响，给出了颗磨粒磨削摩擦系数的数学模型，研究了不同速度单颗磨粒磨削的摩擦系数。试验结果表明，存在一个临界磨削速度。小于临界磨削速度时，摩擦系数随速度的增加而减小，磨削速度超过临界速度后，摩擦系数随速度的增加而略有增大，我们称之为摩擦系数的速度效应。     

零位间隙及温度变化对喷嘴挡板阀的影响

双喷嘴挡板阀的零位工作特性是衡量阀静态性能的重要指标,当喷嘴内径一定时,阀的零位系数主要与喷嘴挡板的零位间隙有关,同时油液黏度随温度变化,也会对阀性能产生影响。利用FLUENT对不同初始温度下不同喷嘴挡板零位间隙的阀内流场进行解析,通过对比分析找到适应大温度范围的最佳零位间隙。结果表明:适当增大喷嘴挡板零位间隙,可以降低油液黏度随温度变化对阀静态特性造成的影响。     

喷嘴流量系数的测试研究

通过实验测试结合理论计算的方法,详细研究了射流管式电液伺服阀不同喷嘴直径下的流量系数。结果表明：不同喷嘴直径下喷嘴流量系数有一定差异,且呈现出直径越大、喷嘴流量系数越大的趋势,为喷嘴特性的进一步研究提供了参考。     

几何结构参数对磨料水射流喷嘴磨损规律影响的模拟分析

建立了前混合磨料水射流喷嘴物理模型。基于FLUENT软件,采用颗粒轨道模型、Grant弹性恢复系数和E/CRC磨损模型对磨料水射流喷嘴内的磨损特性进行了数值模拟。结果表明:当喷嘴收缩角为20°以上时,喷嘴磨损呈现两个严重磨损区,分别在喷嘴圆柱段入口处前较短距离范围内和喷嘴圆柱段出口处前较短距离范围内;随着喷嘴收缩角的增大,磨料颗粒与喷嘴圆柱段壁面碰撞次数和速度增加,同时随着喷嘴长径比的增大,喷嘴圆柱段壁面磨损速率整体增加,严重磨损区范围扩大,结果均使喷嘴圆柱段的磨损加剧。以喷嘴壁面磨损速率的面积加权平均积分表征喷嘴整体的磨损程度。随着收缩角和长径比的增大,喷嘴壁面磨损速率的面积加权平均积分增大,喷嘴的磨损整体而言越严重。因此,从减小喷嘴磨损的角度而言,喷嘴的收缩角和长径比宜取小值。     

燃烧器摆动机构的设计和改进

四角布置燃烧器喷嘴上下摆动，改变火焰中心位置，是锅炉汽温调节和炉膛吸热控制的重要手段。燃烧器喷嘴不能摆动，再热器只能以喷水降温，降低了电厂循环效率。本文详细分析了不能摆动的各种原因并提出了改进措施。     

Characteristics of hydrostatic bearing/seal parts for water hydraulic pumps and motors. Part 1: Experiment and theory

In this paper, the load-carrying capacity, power losses and stiffness of disk-type hydrostatic thrust bearings including the case of eccentric loading are discussed theoretically. The numerical analysis method is established based on a two-dimensional elastohydrostatic problem with an elastic deformation model, which is extended to adapt it for a non-axisymmetric load acting on the thrust bearing. The bearing is made of a combination of stainless steel/stainless steel and stainless steel/plastics. For the elastic materials, the maximum stiffness derived from, i.e., minimum film thickness is, larger than that of the rigid material in the range of a large ratio of pocket pressure and a hydrostatic balance ratio of over unity, which is defined as the ratio of the load to the maximum hydrostatic load-carrying capacity. The maximum load-carrying capacity and minimum power loss can exist in the domain of the hydrostatic balance ratio over unity for the case of the bearing consisting of elastic/rigid materials, in comparison with that composed of the same rigid materials. For the case of water, the power loss due to leakage flow is slightly larger but that due to frictional torque is much smaller than that in the case of hydraulic oil. Then, the total power loss is much smaller than that of hydraulic oil.     

压电驱动微喷雾化器的研制及实验研究

作为一种重要的非注射给药途径，雾化吸入治疗方法具有起效快，药物毒、副作用小等特点，因此被越来越广泛地采用。基于压电驱动喷雾打印机工作基本原理，利用微机加工技术，研制了一种压电驱动微喷雾化器。流量、雾粒的直径和速度是微喷雾化器的重要指标，文中采用相关的仪器分别对这些指标进行了测试。由测试结果可知，微喷雾化器产生的雾粒的直径和速度分布集中，且雾粒直径和速度比较适合于雾化吸入治疗，可能成为一种重要的雾化吸入治疗装置。