泵内压降和水力损失耦合诱导泵内液氮空化研究

为了研究泵内压降和水力损失耦合诱导泵内液氮空化,采用Zwart空化模型和RNG k-ε湍流模型,并使用CEL语言将饱和蒸气压随温度变化函数关系式导入CFX软件中进行求解,对不同流量下低温泵的空化特性曲线进行分析。研究结果表明,低温泵内压力、温度和空泡体积分数分布与空化的发展程度有关,由于水力损失的作用,小流量工况下,泵内会出现涡状流,从而对叶轮内空化产生影响。     

Überlastgrenzen bei Hochvakuumpumpen

High-vacuum pumps have a limited inlet pressure above which they cannot function. Recognizing and dealing with the approaching overload conditions is an important aspect of vacuum system operation. This paper outlines the basic considerations for selecting the pressure at which the high vacuum pumps are started, emphasizing the importance of mass flow (throughput) limits rather than the pressure as such. Some basic parameters, such as the ratio of pumping speeds of the roughing pump and the high vacuum pump are associated with the choice of the cross-over pressure. Practical engineering recommendations are offered for system design and operation. Adverse system effects (e.g., backstreaming and oil loss) resulting from pump overload are noted for momentum transfer pumps (diffusion pumps and turbomolecular pumps) and capture pumps (sputter-ion pumps and cryogenic pumps). To prevent any adverse effect, normally, the transient pressure rise during switching should not be longer than a few seconds.     

叶轮空蚀状态下离心泵振动特性分析

空蚀是指空化过程中产生的空泡溃灭引起过流表面材料损坏的现象。为研究离心泵叶轮空蚀后的振动信号特征,选用IS-50-160-00单级单吸离心泵为试验对象,基于虚拟仪器技术搭建试验泵系统。测得离心泵空蚀条件下的振动信号,采用均方根(RMS)分析、峭度(K)分析两种统计方法对发生空蚀后的离心泵振动信号的平均能量、冲击波能量进行分析,采用短时傅里叶变换(STFT)分析了振动信号的时频域特性。分析结果表明:空蚀条件下整体来看基座方向和轴向方向振动幅值较大且都是无规则振动,而横向方向和纵向方向上的振动信号振幅相对较小;振动信号的能量随着流量的增大呈现先减小后平稳再增加的趋势,空蚀增加了振动信号的能量值;空蚀加剧了液体对离心泵的冲击使得振动信号峭度值增加,且基座方向峭度值大于3可作为空蚀故障的诊断参考标准;通过时频谱分析可知空蚀发生后流体可能对离心泵存在冲击波及冲击波导致的脉冲信号,且空蚀后产生了高频振动信号,高频带的振动信号可为离心泵空蚀故障诊断提供参考。研究叶轮空蚀后离心泵振动信号的特征有助于及时发现离心泵空蚀故障的发生,从而调整运行参数,以免造成严重后果。     

Study on Failure Analyses and Material Characterizations of a Damaged Booster Pump

Pumps are a key and crucial part of many industrial units which usually are endangered by metallurgical, mechanical, and chemical damages. The most important mechanisms of failure in pumps are cavitation, erosion, and corrosion which directly are influenced by pump’s materials, type of fluent, and operation condition. The aim of this study was to investigate the role of material selection in the main failure mechanisms of a power plant booster pumps. To observe the kind and micro structure of pumps optical microscopy and image analyses software were used. Morphology of the pumps’ body is investigated by scanning electron microscopy. Electrochemical tests and water analyses are done for measurement of corrosion rate as well as amount of particles in feed water. Moreover, tensile testing was carried out to compare the mechanical properties of body alloy with standard alloy. The results revealed that cavitation and erosion were the most significant mechanisms. On the other hand, the data from analyses and observations clarified that the material which chosen for pumps alloy was improper which was accompanied with lack of fabrication technology.     

LNG接收站低温罐内潜液泵水力研发设计

低温罐内潜液泵是LNG接收站必不可少的关键设备之一。为浙江宁波LNG接收站用户研发的大型罐内潜液泵,现场一次开车成功,各项水力性能指标满足设计要求,高汽蚀性能诱导轮及其它主要水力部件运行稳定,可完全替代进口。     

超空泡航行器三维流场仿真及性能分析

提出了带进水管路超空泡航行器基本结构和性能评价方法.基于三维Reynolds平均N-S方程、Mixture 多相流模型和完全空化模型,建立了超窄泡航行器内外流仿真模型.开展了不同航行状态和空化器攻角下流场仿真,分析了航速、航行攻角和空化器攻角对空泡形态、航行器水动力特性和进水管路性能等影响规律.研究表明:航行攻角严重影...     

Resonance of torsional vibrations of centrifugal pump shafts due to cavitation erosion of pump impellers

Selected results were gathered during investigation of centrifugal pumps used in a sea water cooling system of one of Diesel power stations are presented in the paper. The main goal of research was to explain the reason of occurring fractures in pump shafts. The investigation has shown that the fractures were caused mainly by the resonance between pump shaft torsional natural vibrations and those following from the pressure fluctuations related to the frequency of the shaft rotational speed and the number of impeller blades. The resonance occurred as a result of intense erosion of pump impellers derived mainly from cavitation phenomenon that caused about 20% of the impeller mass decrease. The scope of the investigation has covered among others: erosion damage recognition, tests of the investigated pumps operating conditions, spectral analysis of pressure fluctuation generated by the pump blade system as well as strength analysis of the pump shaft and the frequencies of its natural bending and torsional vibrations.     

内置式深冷泵抽速计算及数值模拟研究

基于全舱布泵概念设计的内置式深冷泵是真空羽流效应实验中维持真空舱内动态真空度的关键设备.对基于麦克斯韦速度分布假设的内置式深冷泵抽速计算公式分析发现,该式不适用于带喷流的空间发动机羽流实验舱内的动态真空度和冷板面积计算.采用直接模拟蒙特卡罗(DSMC)方法对所设计的内置式深冷泵的抽速和真空舱内的动态真空度进行了数值模拟研究,结果表明DSMC方法在给定条件下能更准确地计算带喷流的空间发动机羽流实验舱内的动态真空度和冷板面积,计算结果与国外同类实验中空间发动机喷流流量与所需冷板面积的计算结果一致.     

超空泡流下壳结构模型动态特性实验研究

首次采用首部钢丝绳牵引方式进行了超空泡流下壳结构模型实验。实验模型壳体部分采用聚碳酸酯材料,锥部采用铝合金材料,首部空化器则采用不锈钢制作,最后各部分通过螺纹或者胶水粘结而成。三种不同速度下的超空泡实验结果表明：采用首部钢丝绳牵引方式进行超空泡实验是可行的。位于壳体上相对位置相同的部位其应变曲线趋势一致,超空泡形成后轴向的减阻效果是非常明显的,尾拍振动引起的应变则呈现出周期性的特征。在一定速度下,超空泡形成后轴向力引起的应变和尾拍振动引起的应变处于同一个水平上。随着速度的提高,超空泡减阻的效果更加明显,尾拍振动引起的应变幅值也相应增大。实验结果可为超空泡水下航行体的结构设计提供依据。     

低温推进剂火箭发动机泵出口密度、温度计算的一种新方法

对补燃循环和使用低温推进剂的液体火箭发动机，需要考虑泵出口温度、密度变化对发动机动、静态特性的影响，目前计算泵出口温度、密度的方法存在一定的局限性，本文提出了一种新的计算方法，它根据泵出口推进剂的压力和比焓，利用推进剂的有关热力状态方程来迭代计算泵出口推进剂的密度与温度，具有使用方便，适用范围广和计算精度高的优点，采用最小二乘法拟合了低温推进剂火箭发动机泵出口温度、密度计算所需的热力状态方程，利用本文的方法对低温发动机泵出口密度、温度进行了计算，计算结果与实测值吻合很好。     

气液两用槽车设计制造中应着重考虑的一些问题

根据某型高压低温充氧车的研制实践,对氧、氮气液两用槽车的贮槽与贮气瓶的配置、低温液体贮槽蒸发率的要求及控制、低温液体泵的安装及工作条件的保障以及槽车安全性设计等方面应重点考虑的问题进行了探讨。     

我国主要容积式真空泵质量状况浅析

本文对容积式真空泵－旋片泵，滑阀泵，罗茨泵的总体情况进行了介绍，重点对其质量状况进行了分析，阐述了近几年容积真空泵的质量改进情况和目前仍存在的主要问题以及问题产生的原因和改进措施，并对真空泵普遍存在的共性问题进行了分析。     

Numerical simulation of cryogenic cavitating flow by an extended transport-based cavitation model with thermal effects

Thermodynamic effects on cryogenic cavitating flow is important to the accuracy of numerical simulations mainly because cryogenic fluids are thermo-sensitive, and the vapour saturation pressure is strongly dependent on the local temperature. The present study analyses the thermal cavitating flows in liquid nitrogen around a 2D hydrofoil. Thermal effects were considered using the RNG k-ε turbulence model with a modified turbulent eddy viscosity and the mass transfer homogenous cavitation model coupled with energy equation. In the cavitation model process, the saturated vapour pressure is modified based on the Clausius-Clapron equation. The convection heat transfer approach is also considered to extend the Zwart-Gerber-Belamri model. The predicted pressure and temperature inside the cavity under cryogenic conditions show that the modified Zwart-Gerber-Belamri model is in agreement with the experimental data of Hord et al. in NASA, especially in the thermal field. The thermal effect significantly affects the cavitation dynamics during phase-change process, which could delay or suppress the occurrence and development of cavitation behaviour. Based on the modified Zwart-Gerber-Belamri model proposed in this paper, better prediction of the cryogenic cavitation is attainable.     

A Comparative Study on the Performance Characteristics of Centrifugal and Progressive Cavity Slurry Pumps with High Concentration Fly Ash Slurries

Slurry pumps are extensively used in the hydraulic transportation of fly ash slurries through pipes in thermal power plants. Today, a wide range of slurry pumps are available and the most commonly used pumps are broadly classified into two main categories, namely, positive displacement and centrifugal pumps. These two types of pumps differ considerably in construction as well as in operating principle compared to the conventional pumps. The aim of the present study is to compare the performance characteristics of these two different types of pumps operating with high concentration fly ash slurries. For each type, the performance characteristics have been experimentally evaluated at the rated speed with water as well as with fly ash slurries in the concentration range of 50 to 70% by weight. The pump total head, overall efficiency, and pump input power as a function of the flow rate have been measured. The results obtained from the centrifugal slurry pump performance show that at rated speed, the head and efficiency of the pump decrease with an increase in solid concentration and the effect is strongly dependent on slurry properties. The pump input power also increases monotonically with an increase in solid concentration. In the case of progressive cavity screw pump, pump performance characteristics and behavior were completely different compared to the centrifugal slurry pump. At rated speed, the head developed and the efficiency of the pump improved with an increase in solid concentration for progressive cavity screw pump.     

Geräuschberechnungen zur Gestaltung kavitationsarmer Flüssigkeitsringpumpen

A model for calculating the cavitation noise is presented and applied to water ring pumps. The results reveal the influence of hydraulic and constructional parameters. The constants in the semi-empirical equations are derived from experimental data of selected pumps. These equations allow to predict the noise for different operating conditions and geometrically similar pumps. The results provide guidelines for a substantial reduction of cavitation and cavitation-related noise by proper constructional measures.     

Möglichkeiten und Grenzen der Vorausberechnung von Kavitationsschäden in Kreiselpumpen

The cavitation damage in centrifugal pumps can be estimated quantitatively if the cavity length is measured or calculated. Erosion rate, implosion pressure and erosion inception can be derived also from fluid- or solid-borne noise measurements in a consistent manner — albeit with a large scatter. Measuring cavity length, fluid- or solid-borne noise and carrying out paint erosion tests al-low a sound assessment of the risk of cavitation damage in critical cases. Nearly one hundred measurements in various installations, in completely different pump types from different manufacturers corroborate the empirical damage correlations in a statistically relevant manner. Three measurements in plants and one experiment on the test bed demonstrate the application of the methods developed in real life and show their limitations.     

Operation and Improvement of Liquid Nitrogen Pumps with Radial High- Temperature Superconductor Bearings

This paper reviews the advantages of replacing the mechanical bearings of low-temperature pumps by radial high- temperature superconductor (HTS) bearings. Radial HTS bearings have the advantage of being non-abrasive, so that the working life is increased significantly. In this article, two types of liquid nitrogen pump with radial HTS bearings are proposed. To reduce heat leakage, one pump uses a permanent magnet (PM) coupling and the other uses a long hollow pipe coupling. Successful stable operation of these two pumps means that radial HTS bearings have the potential to be applied in liquid nitrogen pumps. Test results show that the flow rate is influenced mainly by rotational speed but not by the coupling component. Further designs of the two types of pump for practical applications are described, and their characteristics are analyzed: the pump with a PM coupling has lower heat leakage, whereas the pump with a long hollow pipe coupling can solve the force creep problem of the HTS bearing. The design of the pump with a long hollow pipe coupling is based on the pump that is already in practical use, and therefore has greater feasibility for practical applications. Finally, improvements of the liquid nitrogen pump by improving the structure of the pump and the performance of the radial HTS bearing are discussed.     

Inversion of the source and vorticity equations for supercavitating hydrofoils

The problem of a supercavitating hydrofoil of general shape with leading edge cavity detachment is addressed in linear theory in terms of unknown source and vorticity distributions on the foil and cavity. The related singular integral equations are inverted analytically and the cavitation number, the source and vorticity distributions are expressed in terms of integrals of quantities which depend only on the hydrofoil shape and the cavity length. Numerical algorithms for computing these integrals accurately and efficiently are given.     

Contributions to some cavitation problems in turbomachinery

In the present article, three problems associated with cavitation in turbomachinery are discussed. The first one deals with the potential application of recent understanding in cavitation inception to similar problems in turbomachinery. The second considers the thermodynamic effects in developed cavitation. This has relevance to turbopump operation using fluids other than water. Old correlations to predict the above effect are summarized and a new correlation is proposed. Lastly, the possible methodology to predict pump cavitation noise is outlined. This section relies heavily on similar developments in propeller cavitation noise research. The article has been prepared with financial support from the Department of Education, Ministry of Human Resource Development through a project on “Marine Propeller Analysis”.     

Selbsttrocknende Membran‐ Vakuumpumpen für feuchte Gase

Diaphragm vacuum pumps have proved their superiority as dry‐running systems over other types of vacuum pumps in many applications, and in particular in the medical, analysis, and process engineering sectors, as well as in the chemical industry. These pumps deliver the media without any contamination of content, have a high gas tightness, and can be designed as chemically resistant with regard to those parts which come in contact with the media. Although they are in principle relatively insensitive towards condensates which may be formed or conveyed with the media, liquids in the vapor or gas flow may be the cause for the prolongation of a vacuum process, which can be considerable and is certainly undesirable. This applies in particular to applications involving multi‐user vacuum systems in chemical laboratories, which under certain circumstances may contain very substantial volumes of condensates, and to the use of pumps in steam sterilizers (autoclaves) and vacuum drying cabinets. These examples of applications will be considered in greater detail hereinafter. The condensates which occur in the pump head of a diaphragm vacuum pump cause interference in that — due to re‐evaporation during the suction cycle — they incur a substantial reduction in the usable suction capacity of the pump. This problem can be resolved by means of a drying system for diaphragm vac uum pump heads. The drying system makes use in this case of the pressure differential which pertains between the pump chamber and the atmosphere outside the pump. The function of the drying system can be described as follows: A solenoid valve vents the pump head in a cyclic manner, with the result that liquid in the pump head will be blown out, while the process vacuum in the process engineering system will continue to be maintained. Diaphragm vacuum pumps equipped with this drying system have provided excellent results, for example in the chem ical laboratory, both in individual diaphragm vacuum pumps as well as in multi‐user vacuum systems. Extremely good experience has also been gained in the evacuation of sterilizer autoclaves and vacuum drying cabinets with the use of diaphragm vacuum pumps fitted with the drying system. When using the drying system on steam sterilizer autoclaves, another favorable effect is also encountered: The vapor fraction in the pumping medium is cooled in the diaphragm pump head to below the evaporation or boiling temperature, with the result that the vapour condenses. This reduces its volume to a fraction of the initial value, which is the equivalent of an additional suction capacity, in the same manner as with a condenser. The condensate which occurs with this process is blown out of the pump heads by the drying system, and, as a result, can no longer cause interference due to re‐evaporation.