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1.
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.  相似文献   
2.
Microalgae is promising to be used as feedstock resources for hydrogen production due to its high oil and grease contents. This promotes the development of extraction technology of microalgae oil. In this study, based on the Rayleigh-Plesset equation, the effects of temperature, pressure, ultrasonic power and frequency on the bubble motion of ethanol ultrasound cavitation are investigated. Subsequently, the effects of different process parameters on the extraction rate are studied using Schizochytrium sp. as raw material by stirring or ultrasonic-assisted extraction. And the composition of algae extraction oil is analyzed. The results show that the amplitude of cavitation bubbles increases with the increase of ultrasonic power and decrease of ultrasonic frequency. The extraction rate of algae oil reaches 93.76 ± 0.48% when the ultrasonic power is 150 W, the reaction time is 30 min, the temperature is 50 °C and the liquid-solid ratio is 10:1.  相似文献   
3.
A modified mathematical model is used to study the effects of various forces on the stability of cavitation bubbles within a diesel droplet. The principal finding of the work is that viscous forces of ...  相似文献   
4.
By targeting at the high-pressure common rail nozzle of diesel engines, we put forward a curved nozzle structure, established six groups of nozzle models with different curvatures. By using the CFD software STAR-CCM+, based on the incompressible fluid volume function (VOF) multiphase flow model, applying the K-Epsilon two-layer turbulence model, combined with the Schnerr-Sauer cavitation model, we investigated the degree of influence of the curved nozzle on the cavitation characteristics in the nozzle hole. Cavitation at the inlet, middle and outlet of nozzles was observed under injection pressure of 50, 100 or 150 MPa. The effects of curvature on cavitation were analyzed in detail according to cavitation volume fraction, cavitation volume content, mass flow, turbulent kinetic energy and velocity coefficient. It was found the curved nozzle can significantly reduce the cavitation degree in the nozzle holes, and the larger nozzle bending led to a smaller cavitation degree in the holes. Meanwhile, the average turbulent kinetic energy increased obviously and the average velocity decreased in both the holes and outlet, but the mass flow did not change much.  相似文献   
5.
Sleeve regulating valve is the key component of the industrial system. As the main cause of vibration and noise inside the sleeve regulating valve, cavitation also increases the energy loss when fluid flows through the valve. In this paper, in order to quantitatively analyze the influence of cavitation in the sleeve regulating valve, the effects of throttling windows number, pressure difference, valve opening and flow direction on the resistance coefficient are investigated with the application of cavitation model. By defining the cavitation influencing factor of the resistance coefficient, the calculation formula of the resistance coefficient when cavitation occurs in the sleeve regulating valve is proposed. The results show that when the fluid flows forward and the aggravation degree of cavitation increases, the energy loss also increases. And in the backward flow, the effect of cavitation on the resistance coefficient is related to the valve opening and the throttling windows number. This work is of significance for the optimization and design of sleeve regulating valve and pipeline system.  相似文献   
6.
Hydrogen storage at high pressure is currently attained by the use of different materials, such as elastomers in sealing joints, thermoplastics and thermosetting polymers in high-pressure containers, and metallic tube connections. Hydrogen containers type IV use a thermoplastic polymer for hydrogen tightness and composite materials for mechanical resistance, usually made with thermosetting resins and carbon or glass fibre. International standards impose a wide range of operative temperatures for such containers, from −40 °C to 85 °C.Once saturated with hydrogen at high pressure, a fast depressurisation process can create stress in the polymeric materials, causing its degradation by the formation of cavities. In a previous work, we were able to make a generalization of cavitation risk by the use of non-dimensional parameters, based on a simplified mechanical failure model. We observed that for the model, material's hydrogen diffusivity and yield strength are of upmost importance. In present work, we analyse the effect of temperature on these two properties, as they have an inverse evolution with temperature. Results confirm the pertinence of considering temperature in the whole application range of technology under analyse.  相似文献   
7.
The pulsed power ultrasonic-assisted gas metal arc welding (PU-GMAW) is a new development hybrid welding method. The influences of the pulsed power ultrasonic on the microstructure evolution of the welded joint of Al-Cu alloy were investigated by using scanning electron microscopy, transmission electron microscope and electron back scattering diffraction. The results showed that the efficient heat input in the PU-GMAW was increased by above 100% compared with the traditional GMAW. The grain and eutectic of the PU-GMAW weld seam were refined compared with that of the GMAW. Cavitation and acoustic streaming induced the dendrite fragmentation (α-Al) and heterogeneous nucleation, which were the main reasons for the grain refinement. The microhardness of the PU-GMAW welded joint was improved compared with that of the GMAW owing to the change of the eutectic and grain.  相似文献   
8.
Monel合金表面激光熔覆Ni基稀土合金空蚀性能   总被引:1,自引:0,他引:1  
采用激光熔覆技术在Monel 400合金表面制备Ni基稀土合金熔覆层。利用SEM、EDS、XRD、显微硬度计及超声波金属材料空蚀仪等设备对熔覆层的组织形貌、相结构、硬度、空蚀性能及失效机制进行了系统研究。结果表明:Y_2O_3细化了熔覆层的组织,其组织主要由γ-Ni固溶体、Ni_3B和高硬度的Cr_(23)C_6和Cr_7C_3组成,熔覆层平均硬度可达9040MPa,抗空蚀性能是Monel400合金的8.7倍,熔覆层空蚀过程失效机制主要为枝晶干的冲蚀剥落,Ni基稀土合金熔覆层的细晶强化及空蚀过程中产生阻断晶界网状结构是提高其耐空蚀性能的关键。  相似文献   
9.
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.  相似文献   
10.
Cavitation phenomenon is observed during deformation in many semicrystalline polymers above their glass transition temperature. Numerous voids (cavities) both nanometer and micrometer size are formed inside amorphous phase between lamellae during deformation of a polymer. The cavitation is observed only in tension, never during compression or shearing. Most often used methods of voids detection are: microscopies (SEM, TEM, AFM and light microscopy), small angle X-ray scattering and measurements of density. Usually the voids are detected close to yielding or at yielding, strongly suggesting that yielding is often caused by cavitation. However, there is a competition between two processes: breaking of amorphous phase leading to cavitation and plastic deformation of lamellar crystals. Which process occurs first depends on the relation between compliances of those two phases. If the crystals are weak and defected their deformation occurs (mostly by chain slips mechanism) without cavitation. If the crystals in a polymer are thick and more perfect then the barrier for their deformation, represented by shear yielding stress, is increased and the cavitation sets in first and yielding is determined by the stress needed for cavitation. Further deformation involves deformation of crystals due to rapid local change of stress around voids. The influence of different morphological factors: crystal thickness, crystallinity degree, arrangement of crystalline elements (e.g. in spherulites), morphology of amorphous phase (free volume, entanglements, tie molecules) were analyzed. Experimental factors, such as temperature of deformation and rate of deformation influence remarkably the formation of cavities. Cavitation is generated at points where a high local triaxial state of stress is developed. Triaxiality of stress can be amplified by a notch, even very mild notch with large radius of curvature stimulates generation of cavities. Evolution of nano-cavities into micro-cavities and change of their shapes with increasing deformation were evidenced by SAXS. Initially voids are oriented perpendicularly to deformation direction, however, with increasing elongation they become oriented along deformation direction. Stress whitening is visual sign of cavitation and is caused be light scattering either by microvoids or by assemblies of nanovoids.  相似文献   
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