Papers by Keyword: Cavitation

Abstract: The source of micro bubbles within the haemodialysis extracorporeal circuit is currently unknown. If micro bubbles enter the body they may result in several health issues. Micro bubbles may be formed near the needles if the local pressure drops below the vapour pressure of blood, causing cavitation. Cavitation has been hypothesised to occur at the arterial needle due to the lower local pressures from the suction forces created by the peristaltic blood pump. A CFD model was developed to study the possible inception of cavitation from various options. Variations in needle flow rate and needle orientation were studied using a transient waveform, to determine the clinical conditions in which cavitation might occur. Cavitation may occur within the needle bore when the flow rates are temporarily elevated in the waveform. Needle orientation was also found to have no effect on cavitation potential.

Abstract: The one of technical key of the convergence-divergence nozzle is extend Angle. To use applies continuity equation, momentum equation and Rayleigh-Plesset equation, bubbly liquid through different extend angles of converging-diverging nozzle were simulated. The results show that it is helpful to increase the vibrating width of cavitate bubble when enlarge appropriately the exit taper of nozzle, that is the convergence-divergence nozzle with extended angle is more conducive to cavitation.

Abstract: In order to reduce the production cost of biodiesel, the transesterification process under ultrasound-assisted condition is studyed in this paper by using heterogeneous solid base catalyst NaAlO₃/Al₂O₃ instead of the traditional homogeneous catalyst. Through one-factor experimentation, ultrasonic frequency, oil-alcohol molar ratio, catalyst amount and reaction time on the yield of biodiesel are examined. Transesterification conditions are optimized through orthogonal experiment and the effect order of four factors is as follows: ultrasonic frequency >molar ratio of methanol to oil > reaction time > the amount of catalyst. Results show that the amount of catalyst and reaction time are reduced under ultrasound-assisted condition, and the optimum preparation conditions are: 20min of reaction time, 28KHz of the ultrasonic frequency, molar ratio of methanol to oil 9:1 and 2% catalyst. Under above conditions, the yield of biodiesel reaches 95.21%.

Abstract: Four kinds of cavitations suppression schemes on the basis of cavitations theory of control valve were designed in this paper. The fluid dynamic characteristics parameters under the above schemes was obtained by using RNG k-ε turbulence model respectively, which is composed with the velocity vector of internal fluid, pressure and cavitations distribution contours of numerical simulation. The results show that the design of straight-through porous structure has a lot of advantages compared with other structures in terms of its good fluid dynamic characteristics that fluid flow is uniformly in the valve cartridge, the loss of pressure is lower, the impaction in expansion cartridge is smaller and impact noise of it can be reduced. Therefore, the straight-through porous structure could suppress the initiation and development of the cavitations.

Abstract: This paper aims to bring an organized overview of the damper malfunction due to the cavitation and aeration phenomena, which are normal problems for all kinds of hydraulic dampers. The object of this report is to describe, detect and simulate these damper failures.

Abstract: To reduce the cavitation occurring on valve plate of typical Swashplate piston pump, an optimization design method was introduced to quantitively analyse the accurate relationship between structural jet grooves parameters and cavitation.Using the CFD method, the sunking and discharging process in piston pump was simulated dynamically.The damp grooves structure effect on both jet angle and pressure shock were analysed visually with a series of different parametrical grooves.By establishing parametrical damp groove model, the piston pumps dynamic analysis was integrated with the technologies of CFD analysis, experimental design and approximation model, etc.The mathematical model of plunger pressure in oil back period, jet angle and structural parameters of damp groove were established in the form of second-order RSM model. The damp groove structure of valve plate was optimized on the basis of the RSM model.Test data show that the anti-cavitation performance of optimized valve plate was increased obviouslyAnd this method provided theoretical foundation for the structure design of damp groove.

Abstract: A new cavitator-choking cavitator is designed on the basis of analyzing the choking cavitation phenomena that occurs in gas-liquid mixed flow of straight pipe ,in jet pump under operating limits and in steady adiabatic flashing flow of stepped circular tube as well as in a cylindrical pipe with a sharp edged-corner for the steady and unsteady flows. The feasibility preliminary research of choking cavitator is carried out with analysis the signals of cavitation noise and treating simulated wastewater (phenol solution). The results offers a new approach in cavitator development field at home and abroad because of the effect that treating simulated wastewater with choking cavitator is preferable,and the cavitation per energy produced by choking cavitator is higher than that by self-oscillated chamber nozzle.

Abstract: Cavitation is a complicated multiphase phenomenon which leads to turbulence in fluid flows. The presence of cavitation and turbulence in a diesel injector nozzle has an effect on the subsequent spray characteristics. However, the mechanism of the flow dynamics is unclear because of the complexities of the nozzle flow. Meanwhile, there is few data exist about injector-body temperatures representative of diesel engine operation which can lead to phase change due to fuel flash boiling upon injection. Therefore, it is important to study the effect on internal nozzle flow characteristic. This paper mainly analyzed results of temperature and pressure conditions on internal nozzle flow characteristic. Diesel was simulated at 300,340,360,380,390K temperature for inlet pressure of 0.2 and 0.3MPa while the back pressure is 0.1MPa. Mass flue rate and the average velocity were also performed, and the Weber and Ohnesorge number were considered in the analysis.

Abstract: With reference to cavitation phenomena in the feed-oil pump of aero-engine, a numerical method is presented in this paper to analyze operating performance of pump. Local re-meshing model is introduced to update the computational mesh when the gear teeth in mesh depart each other. Also, the full cavitation model is applied to simulate the flow field, the mass transfer between oil and vapor at low pressure producing region. The performance of a typical feed-oil pump is predicted to evaluate the altitude influence. Results show that more oil vapor is produced at higher altitude. Meanwhile, the leakage mass is mainly depended on the pressure drop.

Abstract: Through analyzing and comparing the treatment of fracturing fluid flowback at home and abroad, it can be found that fluid derived organic waste water can be handled by micro electrolysis economically and efficiently. But there are also some shortages of traditional micro electrolysis. So this paper discusses a new micro-electrolysis technology, namely cavitation-impinging stream electrolysis technology which has several advantages in high concentration organic wastewater treatment. The technology can not only solve the problems that the passivation of process and the plugged equipment in the treatment of fracturing fluid flowback fluid by traditional micro electrolysis, but also can better promote the reaction from the reaction kinetics with the help of Coupling application about cavitation and impinging stream technology, so as to realize the purpose of improving the reaction rate and efficiency.