Generation,validation and application of dynamic load profiles in flow measurement using cavitating Herschel–Venturi nozzles

Today, utility meters for water are tested for measurement behavior at stable operating conditions at specified flow rates as part of the approval process. The measurement error that occurs during start and stop or when changing between flow rates may not be taken into account. In addition, there are new technologies whose measuring behavior under real-world conditions is only known to a limited extend. To take these facts into account, a new method has been developed and tested to determine the measurement behavior of water meters under dynamic load profiles as they occur in the real application. For this purpose, a test rig for flow rate measurement was extended by a cavitation nozzle apparatus and the generation of dynamic load profiles was validated. For the cavitation nozzles used, possible factors influencing the flow rate, such as temperature and purity of the water as well as the upstream pressure were investigated. Using different types of domestic water meters, the applicability of the dynamic test procedure was demonstrated and the measurement behavior of the meters was characterised.     

Vibration cavitation behaviour of selected Ni-Mn-Ga alloys

Vibration cavitation erosion tests were carried out on Ni-Mn-Ga alloys of three different crystal structures: (1) the cubic austenite, (2) the non-modulated tetragonal martensite (T) and (3) the five-layered martensite (5M). All Ni-Mn-Ga alloys exhibited cavitation behaviour characterized by a step-wise curve of mass loss versus test time. This behaviour is correlated to the microstructural nature of the alloys as well as the surface conditions of the pre-test samples. The type and concentration of the defects at the surfaces were critical to the cavitation resistance of the alloys. The best cavitation resistant alloy was of a cubic austenitic structure, followed with the alloy of a tetragonal T-martensite. The largest material loss was found in the alloy with a 5M martensite. All the studied Ni-Mn-Ga alloys had an excellent cavitation resistance compared to that of the reference stainless steel, and they even excelled some NiTi alloys found in literature. This may be due to the superelasticity of the cubic austenite and the twinning of the martensitic phases.     

Non-uniform hydrogen attack cavitation and the role of interaction with creep

Hydrogen attack (HA) is the development of grain-boundary porosity by cavities filled with high-pressure methane that originates from the reaction of carbides with hydrogen at high temperatures. The cavities grow by grain-boundary diffusion and by creep of the adjacent grain material till they coalesce with neighbouring cavities to form a microcrack. Earlier work on HA has focussed on unit cells containing a single cavity, using average cavitation properties. Here, non-uniform cavitation properties on the grain-size scale are assumed in a polycrystalline aggregate, and unit cell analyses are performed to investigate the influence of the adjacent grains on the development of the grain-boundary HA. The numerical results are explained in terms of two simplified models which highlight the key parameters governing the grain deformation-grain boundary cavitation interaction process.     

初生空化与液体抗拉强度的关系

自1983年开始以液体的抗拉强度作为其空化临界压强研究初生空化的比尺效应以来,该方法已得到进一步的应用和完善。本文就研究中遇到的一些问题,如关于空化灵敏度仪的校正,“零抗拉强度”的概念,试验设备中液体抗拉强度的动态变化以及在空化试验中使用该方法的技术和意义等作详细的阐述。     

水压节流阀口流量特性的实验研究及水压节流阀的研制

本文将介绍作者自行研制的水压阀阀口流动特性的实验装置，用该装置完成了各种典型水压阀阀口流动特性以及空化影响流动特性的实验研究，依据实验的结果完成了水压元件性能试验台所需各类水压阀的研制。     

滑动轴承两种油膜边界条件的比较

本文对滑动轴承计算中两种常用的油膜边界条件进行了比较，一种是雷诺边界条件，另一种即质量守恒边界条件。对于前者，常采用负压力归零法进行计算，对于后者，大多采用Elrod算法。本文通过改变Elrod算法中的变量θ的定义，对Elrood算法进行改进，建立一新的通用方程，可自动确定动态边界，并在稳态工况下，将两种边界条件的计算结果与实验数据进行比较，发现根据质量守恒边界条件采用本文新改进的算法计算所得结果与实验数据十分吻合，同时，计算结果表明，空穴并不总是降低轴承的承载力，在稳态工况下，当空穴压力为较大的负压力时，轴承的承载能力反而有明显提高。     

Cavitation erosion behavior of CLAM steel weld joint in liquid lead-bismuth eutectic alloy

The cavitation erosion of weld joint and base metal of China low activation martensitic(CLAM)steel in liquid lead-bismuth eutectic alloy(LBE)at 550°C was investigated to simulate the cavitation erosion of the first wall and the nuclear main pump impeller in the accelerator driven sub-critical system(ADS).A suit of ultrasonic cavitation facility was self-designed to study the cavitation erosion.By studying the surface micro topography,roughness and mean pit depth of the tested specimens,it was found that some crater clusters and large scale cracks appeared on the tested specimen surface after the formation of numerous single craters,and the base metal exhibited much better cavitation erosion resistance than the weld bead due to the difference in their mechanical properties and microstructures.In addition,by comparing the results of static corrosion and cavitation erosion,it could be concluded that the cavitation erosion and the dissolution and oxidation corrosion in liquid LBE would accelerate mutually.     

Application of intensive hydrodynamic cavitation in liquids for synthesis of hydrogen and nanoparticles

In this paper, the results of experimental studies of hydrogen and nanoparticles production using intensive hydrodynamic cavitation in liquids are presented. Physicochemical processes occurring in a cavitation bubble at the last stage of its compression are very similar to processes occurring in the explosion chamber.The values of pressure and temperature achieved in this case ensure the thermodynamic stability of the reaction products and the production of a gaseous hydrogen and nanoclusters as a result of decomposition of molecules of liquid, which is confirmed by theoretical calculations.The controlled addition of hydrogen-containing liquids and the change in the compression conditions of cavitation bubbles make it possible to control the process of hydrogen synthesis, which is an important step in the development of modern high-tech alternative energy methods.The pulsation of a spherical cavity is described by the Kirkwood – Bethe equations, which are one of the most accurate mathematical models of pulsation processes at an arbitrary velocity of the cavity boundary. The model allows to describe the process of pulsations of cavitation cavities, conduct comprehensive parametric studies and evaluate the effect of various process parameters on the collapse of cavities.This work continues with the experiments on cavitation synthesis of carbon nanostructures. With the rapid movement of chemically pure hydrocarbons along the profiled channel in the form of a Venturi nozzle, cavitation bubbles form in the liquid, which are then compressed in the working chamber, in which a sharp pressure surge is created. The pressure in the shock wave, which reaches 80–90 MPa, ensures the collapse of cavitation bubbles close to adiabatic compression. As a result of the number of rapidly occurring physicochemical processes of evaporation, heating, and thermal dissociation of hydrocarbon vapors, a solid carbon phase including graphene oxide nanoparticles and a gaseous hydrogen-containing phase are synthesized in the cavitation, which is then subjected to separation. Synthesized graphene oxide nanoparticles possess activated surface due to the cavitation action and can be subsequently used as substrates for modification with functional nanoparticles, e.g. silver nanoparticles with antibacterial properties.The article is of great help to scientists and design engineers who are engaged in the development of promising hydrogen generating facilities and hydrogen complexes.     

Failure analysis on abnormal wall thinning of heat-transfer titanium tubes of condensers in nuclear power plant Part II: Erosion and cavitation corrosion

In Part I of the failure analysis on abnormal wall thinning of heat-transfer titanium tubes used in condensers in nuclear power plant, we analyzed the causes and mechanisms of abnormal thinning that commonly happened at the contact part between the tubes and the support plates. This kind of failure was the mainstream failure type in our case and the main causes were found to be eccentric contact wear and three-body contact wear rooted in processing defect of internal borings, corrosion products deposit and sagging, and foreign particles. However, there were still some individual failure tubes with different failure sites and modes and were located under the bypass pipes at the shoulder of the tube tower instead of in its lower part, obviously telling another failure story. In Part II of the failure analysis, material analysis, metallographic examination, mechanical performance tests, macro- and microstructure analysis and composition analysis were conducted. The failure causes were found to be erosion and cavitation corrosion and the synergetic effect of them. Finally, corresponding countermeasures were suggested.     

高速离心泵油乳化分析及改进措施

针对高速离心泵P-101A/B泵油乳化,轴承损坏、机械密封泄漏等问题,剖析故障原因,分别从设备、工艺、检维修三个方面对高速泵油乳化、密封泄漏等问题对系统进行了深入的研究,并根据分析结果制定对策,实施改进措施,取得良好的结果。