scholarly journals Cavitating Flow through a Micro-Orifice

Micromachines ◽  
2019 ◽  
Vol 10 (3) ◽  
pp. 191 ◽  
Author(s):  
Zhi-jiang Jin ◽  
Zhi-xin Gao ◽  
Xiao-juan Li ◽  
Jin-yuan Qian
Keyword(s):  
Pressure Difference ◽  
Rapid Development ◽  
Cavitation Number ◽  
Cavitating Flow ◽  
Hydrodynamic Cavitation ◽  
Apparent Difference ◽  
Microfluidic Systems ◽  
Vapor Cavity ◽  
Exit Pressure ◽  
Flow Through

Microfluidic systems have witnessed rapid development in recent years. As one of the most common structures, the micro-orifice is always included inside microfluidic systems. Hydrodynamic cavitation in the micro-orifice has been experimentally discovered and is harmful to microfluidic systems. This paper investigates cavitating flow through a micro-orifice. A rectangular micro-orifice with a l/d ratio varying from 0.25 to 4 was selected and the pressure difference between the inlet and outlet varied from 50 to 300 kPa. Results show that cavitation intensity increased with an increase in pressure difference. Decreasing exit pressure led to a decrease in cavitation number and cavitation could be prevented by increasing the exit pressure. In addition, the vapor cavity also increased with an increase in pressure difference and l/d ratio. Results also show the pressure ratio at cavitation inception was 1.8 when l/d was above 0.5 and the cavitation number almost remained constant when l/d was larger than 2. Moreover, there was an apparent difference in cavitation number depending on whether l/d was larger than 1.

Assessment of Tandem Venturi on Enhancement of Cavitational Chemical Reaction

2008 ◽  
Vol 131 (1) ◽  
Author(s):  
Hoseyn Sayyaadi
Keyword(s):  
Chemical Reaction ◽  
Oxidation Process ◽  
Flow Characteristics ◽  
Chemical Oxidation ◽  
Cavitation Number ◽  
Cavitating Flow ◽  
Hydrodynamic Cavitation ◽  
Operating Pressure ◽  
Local Pressures ◽  
Second Category

The collapsing phenomenon of cavitation bubbles generates extremely high local pressures and temperatures that can be utilized for the chemical oxidation process. This process is carried out in cavitation reactors. A Venturi tube is one of the most common forms of hydrodynamic cavitation reactors, which is suitable for industrial scale applications. In this work, the hydraulic performance and efficiency in chemical reaction of a new form of hydrodynamic cavitation reactors, which is called “tandem Venturi,” were studied and compared with the conventional type of the single Venturi. The tandem Venturi is used for enhancement of the chemical reaction of hydrodynamic cavitating flow. The reaction enhancement is useful especially for the reaction of aqueous solutions not containing volatile organic compounds (VOCs). The operating pressure, inlet pressure, flow rate, and consequently the cavitation number were controlled and systematically varied for both single and tandem Venturis. Moreover, a specified amount of H2O2 was injected into the flow as required. The effects of operating pressure and the cavitation number on cavitating flow characteristics for single and tandem Venturis were experimentally observed and the results were compared. In addition, the performance of the tandem-Venturi reactor for degradation of non-VOC contaminants (2-chlorophenol) was studied. Its performance was compared with the performance of a conventional Venturi reactor. Two different categories were conducted for the experiments. In the first category, the effect of the net cavitating flow on degradation of non-VOC for the single and tandem Venturis was compared. In the second category, the effect of H2O2 injection into the cavitating flow on degradation of non-VOC (“cavitation-oxidation” process) was studied. The performance of the single and tandem Venturis for the cavitation-oxidation process was compared. Further investigation was performed to assess the advantage of utilizing the tandem Venturi from the viewpoint of efficiency of the oxidation process. The results of the energy efficiency were compared with the corresponding efficiency of the single Venturi. Finally, the relationship between the main parameters of cavitation reaction flow with the chemical performance was discussed.

Hydrodynamic Cavitation in Flow Through Micro-Constriction Elements Entrenched in Rectangular Microchannels

2005 ◽  
Author(s):  
Chandan Mishra ◽  
Yoav Peles
Keyword(s):  
High Speed ◽  
Scale Effects ◽  
Flow Patterns ◽  
Cavitating Flow ◽  
Pressure Effects ◽  
Hydrodynamic Cavitation ◽  
Experimental Investigations ◽  
Mems Devices ◽  
Microfluidic Systems ◽  
Macro Scale

Hydrodynamic cavitation, the explosive growth and catastrophic collapse of vapor bubbles, has immense impact on the design and performance of hydraulic machinery in the macro world. However, cavitation in high-speed microfluidic systems has received scarce attention and hardly been reported. This article reports the presence of hydrodynamic cavitation in the flow of de-ionized water through 11.5–40micron wide rectangular slot micro-orifices entrenched inside 100–200micron wide microchannels. Pioneering experimental investigations on hydrodynamic cavitation in rudimentary microfluidic configurations such as slot micro-orifices has been presented and unique cavitating flow patterns have been identified. Assorted cavitating (two-phase) flow patterns including incipient, choking and supercavitation have been detected. Designers of high-velocity microfluidic systems, especially Power-MEMS devices, need to be aware of the deleterious effects of cavitation as it can significantly affect device performance. The effects of micro-orifice and microchannel size on cavitation have been discussed and results indicate the existence of strong scale effects. Incipient and choking cavitation numbers are observed to increase with increasing micro-orifice size, while the orifice discharge coefficient plummets once cavitation activity erupts. In addition, inlet pressure effects on several cavitation parameters have been discussed and compared with established macro-scale results. The cavitating flow patterns encountered are significantly influenced by the micro-orifice and microchannel size. Flow rate choking occurs irrespective of the inlet pressures and is a direct consequence of cavitation inside the micro-orifice. Cavitation hysteresis is observed but its effects are more marked for the smallest micro-orifice.

scholarly journals PIV Analysis of Cavitating Flow Behind Square Multi-Orifice Plates

10.29007/fhdg ◽  
2018 ◽  
Author(s):  
Zhiyong Dong ◽  
Wenqian Zhao
Keyword(s):  
Conventional Technique ◽  
Disinfection Byproducts ◽  
Cavitating Flow ◽  
Water Disinfection ◽  
Hydrodynamic Cavitation ◽  
Pathogenic Microorganisms ◽  
Turbulence Structures ◽  
Image Velocimetry ◽  
Piv Analysis ◽  
Mutagenic Effects

Currently, in water supply engineering, the conventional technique of disinfection by chlorination is used to kill pathogenic microorganisms in raw water. However, chlorine reacts with organic compounds in water and generates disinfection byproducts (DBPs) such as trihalomethanes (THMs), haloacetic acids (HAAs) etc. These byproducts are of carcinogenic, teratogenic and mutagenic effects, which seriously threaten human health. Hydrodynamic cavitation is a novel technique of drinking water disinfection without DBPs. Turbulence structures of cavitating flow were observed by the Particle Image Velocimetry (PIV) technique in a self-developed hydrodynamic cavitation device due to square multi- orifice plates, including effects of orifice number and orifice layout on velocity distribution, turbulence intensity and Reynolds stress, which aimed at uncovering mechanism of killing pathogenic microorganisms by hydrodynamic cavitation.

Reverse Flow Pressure Limiting Aperture

2000 ◽  
Vol 6 (1) ◽  
pp. 21-30 ◽  
Author(s):  
Gerasimos D. Danilatos
Keyword(s):  
Pressure Difference ◽  
Gas Flow ◽  
Reverse Flow ◽  
Gas Jet ◽  
The Third ◽  
The Core ◽  
Annular Aperture ◽  
Flow Through ◽  
Flow Pressure ◽  
Gas Molecules

The reverse flow pressure limiting aperture is a device that creates and sustains a substantial gas pressure difference between two chambers connected via an aperture. The aperture is surrounded by an annular orifice leading to a third chamber. The third chamber is maintained at a relatively high pressure that forces gas to flow through the annular aperture into the first of said two chambers. The ensuing gas flow develops into a supersonic annular gas jet, the core of which is coaxial with the central aperture. A pumping action is created at the core of the jet and any gas molecules leaking through the aperture from the second chamber are entrained and forced into the first chamber, thus creating a substantial pressure difference between the first and second chamber.

Cavitating Flow Simulation in a Closed Pump Sump by Two-Fluid Model and Its PIV Verification

2003 ◽  
Author(s):  
Yu Xu ◽  
Yulin Wu ◽  
Shuhong Liu ◽  
Yong Li
Keyword(s):  
Fluid Model ◽  
Flow Simulation ◽  
Cavitating Flow ◽  
Governing Equations ◽  
Two Phase ◽  
Averaged Equations ◽  
Flow Through ◽  
Pump Sump ◽  
Two Fluid Model ◽  
Two Fluid

In this paper, the two-fluid model was adopted to analyze the cavitating flow. Based on Boltzmann equation, governing equations for two-phase cavitating flow were obtained by using the microscopic kinetic theory, in which the equation terms for mass and momentum transportations can be obtained directly. Then the RNG k–ε–kg turbulence model, that is RNG k–ε model for the liquid phase and kg model for the cavity phase, was used to close the Reynolds time-averaged equations. According to the governing equations above, the simulation of the two-phase cavitating flow through a closed pump sump has been carried out. The calculated results have been compared with a PIV experiment. Good agreement exhibited.

Unsteady Cavitating Flow Around an Inclined Rectangular Cylinder

Volume 3 ◽  
2004 ◽  
Author(s):  
Terukazu Ota ◽  
Isao Tsubura ◽  
Hiroyuki Yoshikawa
Keyword(s):  
Separation Bubble ◽  
Fluid Dynamic ◽  
Flow Characteristics ◽  
Low Frequency ◽  
Cavitation Number ◽  
Cavitating Flow ◽  
Dynamic Force ◽  
Unstable Flow ◽  
Rectangular Cylinder ◽  
Cavity Configuration

Unsteady characteristics of cavitating flow around an inclined rectangular cylinder with a width to height ratio of 8.0 were experimentally investigated for various angles of attack and cavitation numbers. Measurements of fluid dynamic force and surface pressure were made and the cavity configuration was observed with a camera. Especially considered are the self-oscillating unstable flow characteristics along with the time variation of cavity configuration. It is found that a severe vibration occurs at some cavitation number, in which the attached cavity is formed in the separation bubble. As the cavitation number further decreases, the low frequency fluctuation of flow occurs.

scholarly journals Fluid dynamics of acoustic and hydrodynamic cavitation in hydraulic power systems

2017 ◽  
Vol 473 (2199) ◽  
pp. 20160345 ◽  
Author(s):  
A. Ferrari
Keyword(s):  
Power Systems ◽  
Acoustic Cavitation ◽  
Vapour Phase ◽  
Cavitation Number ◽  
Homogeneous Mixture ◽  
Hydrodynamic Cavitation ◽  
Hydraulic Power ◽  
Two Phase ◽  
Advantages And Disadvantages ◽  
Propagation Of Waves

Cavitation is the transition from a liquid to a vapour phase, due to a drop in pressure to the level of the vapour tension of the fluid. Two kinds of cavitation have been reviewed here: acoustic cavitation and hydrodynamic cavitation. As acoustic cavitation in engineering systems is related to the propagation of waves through a region subjected to liquid vaporization, the available expressions of the sound speed are discussed. One of the main effects of hydrodynamic cavitation in the nozzles and orifices of hydraulic power systems is a reduction in flow permeability. Different discharge coefficient formulae are analysed in this paper: the Reynolds number and the cavitation number result to be the key fluid dynamical parameters for liquid and cavitating flows, respectively. The latest advances in the characterization of different cavitation regimes in a nozzle, as the cavitation number reduces, are presented. The physical cause of choked flows is explained, and an analogy between cavitation and supersonic aerodynamic flows is proposed. The main approaches to cavitation modelling in hydraulic power systems are also reviewed: these are divided into homogeneous-mixture and two-phase models. The homogeneous-mixture models are further subdivided into barotropic and baroclinic models. The advantages and disadvantages of an implementation of the complete Rayleigh–Plesset equation are examined.

scholarly journals Experimental Investigation on Cavitating Flow Induced Vibration Characteristics of a Low Specific Speed Centrifugal Pump

2017 ◽  
Vol 2017 ◽  
pp. 1-12 ◽  
Author(s):  
Bo Gao ◽  
Pengming Guo ◽  
Ning Zhang ◽  
Zhong Li ◽  
Minguan Yang
Keyword(s):  
Frequency Band ◽  
Low Frequency ◽  
Local Maximum ◽  
Cavitation Number ◽  
Cavitating Flow ◽  
Vibration Characteristics ◽  
Vibration Energy ◽  
Stable Operation ◽  
Centrifugal Pumps ◽  
Number Range

Cavitating flow developing in the blade channels is detrimental to the stable operation of centrifugal pumps, so it is essential to detect cavitation and avoid the unexpected results. The present paper concentrates on cavitation induced vibration characteristics, and special attention is laid on vibration energy in low frequency band, 10–500 Hz. The correlation between cavitating evolution and the corresponding vibration energy in 10–500 Hz frequency band is discussed through visualization analysis. Results show that the varying trend of vibration energy in low frequency band is unique compared with the high frequency band. With cavitation number decreasing, vibration energy reaches a local maximum at a cavitation number much larger than the 3% head drop point; after that it decreases. The varying trend is closely associated with the corresponding cavitation status. With cavitation number decreasing, cavitation could be divided into four stages. The decreasing of vibration energy, in particular cavitation number range, is caused by the partial compressible cavitation structure. From cavitation induced vibration characteristics, vibration energy rises much earlier than the usual 3% head drop criterion, and it indicates that cavitation could be detected in advance and effectively by means of cavitation induced vibration characteristics.

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