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Cavitation - Science topic

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As it is noticeable, there are several research projects with regard to using of cavitation and the production of bubbles for friction reduction in ship movements. I want to understand the mechanism thoroughly for this process. Also, how much is it practical for decreasing fuel consumption?
Best regards,
Hossein Pouresmaeil
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This is an inescapable fundamental review (one of the oldest but most quoted) on drag reduction by bubbles on an external flow; Whether injected or created using cavitating flows, the physical phenomenon is fundamentally the same: a dispersed gas-liquid flow that has often been tackled using two-fluid models.
Ceccio, S.L. (2010). Friction drag reduction of external flows with bubble and gas injection. Annual Review of Fluid Mechanics, 42, 183-203.
Abstract
The lubrication of external liquid flow with a bubbly mixture or gas layer has been the goal of engineers for many years, and this article presents the underlying principles and recent advances of this technology. It reviews the use of partial and super-cavities for drag reduction of axisymmetric moving objects within a liquid. Partial cavity flows can also be used to reduce the friction drag on the nominally two-dimensional portions of a horizontal surface, and the basic flow features of two-dimensional cavities are presented. Injection of gas can lead to the creation of a bubbly mixture near the flow surface that can significantly modify the flow within the turbulent boundary layer, and there have been significant advances in the understanding of the underlying physical process of drag reduction. Moreover, with sufficient gas flux, the bubbles flowing beneath a solid surface can coalesce to form a thin drag-reducing air layer. The current applications of these techniques to underwater vehicles and surface ships are discussed.
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I am performing shadowgraphy imaging of laser-induced cavitation bubbles. I want to know the optimum value of optical density for a NDF in my experiment which can provide me the best image.
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Start with higher OD values that you have and then keep reducing the OD values in small steps.... You will notice that images will improve... Stop reducing the OD when you see the image is bright enough, otherwise your CCD sensor will get saturated... If the intensity is high enough the sensor may get damaged as well... Hope this helps....All the best!!
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Hello all,
Source terms have been known to cause reliability issues in numerical methods affecting therein convergence and accuracy. I am currently facing a similar challenge when trying to solve a Poisson equation with a non-zero divergence velocity field. The source term that I am working which is a cavitation source term dependent on local value of pressure.
For the most part, linearizing that source term seems to solve the issue in the literature however even with linearization my Poisson equation does not converge, and even when it does, the solution is inaccurate and often oscillatory.
Any input from the experts would be helpful
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Noted professor Stam Nicolis , I will keep that in mind. Thanks for your time and help!
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Dear Colleagues. We investigate the process of sawdust activation in the cavitator. The results obtained show high physical and mechanical properties of materials from activated sawdust. The question arose whether there is a cavitation effect when grinding in water? cavitator. The results obtained show high physical and mechanical properties of materials from activated sawdust. The question arose whether there is a cavitation effect when grinding in water?
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Sorry for the delay u need more help contact me +256781661909 whatsapp
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I am using 2 ultrasonic assembly for cleaning purpose and I want to increase cavitation intensity.
(1) a ceramic transducer with a diameter of 30 mm and a horn with a end diameter of 8 mm.
(2) a ceramic transducer with a diameter of 40 mm and a horn with a end diameter of 8 mm.
Since the input power of (2) is higher than that of (1), I expected that the sound pressure of (2) is higher than that of (1), but it was not.
I think it is because the acoustic impedance of (2) is much lower than that of (1) (even though the power is high, sound pressure can be lower since Z=p/v is lower).
1. Am I misunderstanding something??
2. If not, how to increase the acoustic impedance of the ultrasonic assembly??
3. How can I estimate the acoustic impedance of the ultrasonic assembly??
4. What is the best?? the acoustic impedance of the ultrasonic assembly should be equal to the acoustic impedance of the media (water in my case) or as high as possible?
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However, If you look up matching layers in general, you will find that they are quarter wave (in the matching layer material) thick and of impedance (Zh*Zw)^.5, where Zh is the acoustic impedance of the horn material and Zw the acoustic impedance of the water (1.5 MRayls). Ideally, you should also have a matching layer from the transducer into the horn as well, same formula but using the impedances of the ceramic and horn material. The matching layer is designed for one frequency (where the matching layer is a quarter-wave thick) so will not help a lot for high bandwidth (very short) pulses.
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When the proposed water-lubricated textured groove thrust bearing is under high speed, the initial cavitation number will increase, so the cavitation effect should be considered when modelling.
The previous research has established that cavitation obviously exists in the textured bearing, including thrust bearing under hydrodynamic lubrication and mechanical seals.
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Please go through the link and find your required answer.
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Heavy fuel oil is a combenation of a large number of different hydro carbon chains. I no the difference between boiling and flash point. I am reasearching cavitation of pumps and valves on heated fuel oil systems and would like to find a chart or table where different fuel would start to boil. This is difficult since the different hydro carbon chains boil at dirrerent temperatures. But I am intrested where the first hydro carbon chains would start to boil and have the potential to lead to pump or valve cavitation?
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A pressure gauge is located in the suction side of a water pump. It shows 25 inches of Hg. Lot of bubbles are present in the pipe. Does it mean that there is presence of cavitation in the pipe due to negative pressure? What is the relation between vapor pressure of water and negative pressure?
For eg., 9500 Pa is vapor pressure of water at 45 deg C.
If pressure is negative 25 inch Hg at 45 deg C, what does that mean?
How to identify presence of cavitation with a pressure gauge located in the suction side of pump?
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Nagalingam,
I was about to offer an idea but just read that you designed this with a restriction to enhance cavitation. Instead of asking us to guess...Please explain the design so we can offer appropriate help.
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I'm working on an industrial wastewater mainly composed by DMF and alcohols. I'm treating samples with hydrodynamic cavitation, hydrodynamic cavitation/H2O2 or hydrodynamic cavitation/O3 but at the end of each process the COD value is slightly higher than the wastewater one. I tried to remove excess of H2O2 by heating the samples at 90°C or adjusting pH to 10-11 and then heating at 45°C because of its interference, but also other samples have same problem Hannah Instrument COD kits are used to determine COD values.
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Hi Federico Verdini,
For the said industrial wastewater, determine or (repeat) the COD by varying dilution factors
(1:10, 1:50, 1:100, 1: 200). After that you may get average range of COD.First confirm intial value of given sample. For more accuracy you can correlate with BOD value.
However you can more details about interference and its limitations in APHA Standard method 5220, SECTION 5-11)
Reg
Prashant. B.B
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Hi,
I am doing a sonication study to dissolve Extracellular matrix proteins in PBS to induce gelation. I came up with a strategy to reduce heat produced by sonication and cavitation affecting proteins but I was wondering if anyone knows if cavitation itself can lead to ECM protein denaturation. Besides, ultrasonic frequencies (20kHz) can neither damage ECM proteins right?
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Dear Gabriela Sanchez,
Please see the link below.
With my best regards
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A few years ago I and my colleague Peter Wall wrote a short summary for Switch Function and and Complementarity Problem based formulations in a chapter which is available Open Access:
Andreas Almqvist and Peter Wall (October 26th 2016). Modelling Cavitation in (Elasto)Hydrodynamic Lubrication, Advances in Tribology, Pranav H. Darji, IntechOpen, DOI: 10.5772/63533. Available from: https://www.intechopen.com/books/advances-in-tribology/modelling-cavitation-in-elasto-hydrodynamic-lubrication
Since there are many more models for cavitation in lubrication flows it would be interested to hear from the community which ones you think are the most suitable ones and in which situations they should/could be applied.
Cheers, Andreas
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Great question Andreas Almqvist! One which I've debated a lot!
The complementarity problem is an excellent and effective way of solving the problem of hydrodynamic cavitation. Have you (or someone else) applied this method to highly-loaded contacts (GPa pressures) such a line and point contact geometries out of interest? Great to see answers already from authors adapting the approach for their specific problems here too.
I see the expected pressure magnitude being one of the main drivers behind the choice of model for this phenomena. I have reviewed (a little) the modelling approaches to hydrodynamic cavitation with the late, great Duncan Dowson as part of this publication: . In this article we developed a 'moving mesh' type of approach for modelling the onset of cavitation but did not consider film reformation. This method can be applied to low pressure (MPa) and high pressure (GPa) problems without any difference in the implementation.
For lower pressure environments (MPa) the Elrod-Adams algorithm is still widely used as the baseline method for simulating cavitation including papers published by my group this year: . There are several publications optimising and adapting this method with varying degrees of success in the literature, too many to list here.
More recently this method has been combined with the complementarity condition to formulate the problem as described by Andreas and others. This also links to recent improvements in the solution approach by Woloszynski and the use of the Fischer-Burmeister equation to formulate the complementarity problem (see very recent work by Ron van Ostayen at TU Delft).
The complementarity method is a more stable than Elrod-Adams approach numerically because of the lack of switching functions and more robust mathematical formulation, but this does require a LCP solver which may be prohibitive to some. This is likely why Elrod-Adams remains widely used given it can be used with a standard PDE solver and setup readily with commercial codes, albeit with switching functions included making the problem numerically stiff.
There is also the issue of the change of variable approach from pressure to a derived field used explicitly for the cavitation problem, which then conflates the solution to the lubrication flow in terms of one variable. Therefore several authors use a pressure-only type approach such as that which I explored with Andreas here: . This article uses the Söderfjäll model to create a blending function reducing the density and viscosity of the lubricant rapidly to almost zero in the presence of negative pressure. This simulates the effect of cavitation solely on the lubricant properties and produces the required pressure distribution efficiently with rupture and reformation included. A similar but different approach was used by Gao et al in this paper: . The approach is very useful for where there are many regions of cavitation occurring within the domain.
Note that all the applications discussed so far are conventionally developed for low pressure (MPa) environments, and that in the classic high pressure (GPa) contact problems cavitation is managed with less rigour of the pressure profile shape/value. This is because of the large separation in magnitude between the max pressure and the vapour pressure in such contacts, with the requirement only being to resolve the pressure and pressure gradient to zero at the location of the onset of cavitation (JFO conditions).
For GPa problems the JFO conditions are conventionally achieved either with the use of a free boundary problem (see the classic multilevel solutions of Venner) or with the penalty approach of Wu (see more recent solutions by Habchi). Neither of these approaches fully resolve the problem of cavitation and this has led to several two-phase type models being developed which require very fine grids to resolve the flow. Multi-phase CFD simulations have also been developed recently by Imperial College London to investigate cavitation in much more depth for highly-loaded contacts and resolving all the flow (see Hartinger et al. and Hajishafiee et al.). These two- or multi- phase models also allow variance in the film thickness direction and are therefore not necessarily based on the Reynolds equation, making them more complex descriptions of the flow that are harder to solve numerically.
So the question comes down to whether resolving the full pressure shape/value is of importance to the outcome required, which itself is connected to the magnitude of the expected pressure. There is also the question of what type of solver you have readily available, whether a change of variable doesn't conflate the problem formulation, and if you're interested in very fine detail about the flow features.
Personally I would be in favour of the ALE or complementarity approaches for any problem/geometry but this certainly needs more development, hence my question at the start. I also think a review paper on the topic is well overdue!
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Dear Colleagues,
I’m pleased to inform you that open access journal /Catalysts/ (ISSN 2073-4344, Impact Factor: 3.444) is planning to publish a Special Issue on the topic of "Trends in Catalytic Advanced Oxidation Processes". The submission deadline is 31 July 2020.
Detailed information regarding this issue, please follow the link below to the Special Issue website at:
This Special Issue is dedicated to novel achievements in the field of catalytic advanced oxidation processes. The contributions should be related to the listed topics:
· Catalytic processes in water and wastewater treatment
· Developments in Fenton-like AOPs
· Activation of Persulfates for AOPs
· Formation of sulfate radicals
· Catalytic cavitation-based AOPs (hydrodynamic cavitation and acoustic cavitation)
· Sonocatalysts
· Catalytic ozonation
· Photocatalysts—including visible light and UV applications
· Catalytic wet air oxidation (CWAO)
· Catalytic–electrochemical AOPs
· Carbon catalysts for AOPs
· Nanocatalysts
· Risk of by-product formation during water and wastewater treatment
· Developments in process control of catalytic AOPs (analytical methods, chromatographic, and spectroscopic techniques)
· Methods of catalysts characterization
· Post-process assessment of effluents toxicity
· Application of nanobubbles in AOPs
· Economic analysis of catalytic AOPs application and catalysts life cycle assessment (LCO)
· Industrial catalytic wastewater treatment
· Modelling and optimization of catalytic processes
· Green chemistry aspects in catalytic water and wastewater treatment
Detailed information regarding this issue, please follow the link below to the Special Issue website at:
Sincerely hope this invitation will receive your favorable consideration.
Best regards,
Guest Editor
Prof. Grzegorz Boczkaj, PhD. Sc. Eng. Assoc. Prof.
Department of Process Engineering and Chemical Technology, Faculty of
Chemistry, Gdansk University of Technology, 80-233 Gdansk, Poland
Caroline Zhan
Assistant Editor
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Dear Prof.
Looking forward to hear if any special issue under your editorship.
Thanks
Siddhartha
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What is the best mesh is recommended in order to use for modelling cavitation conditions by using multiphase investigation in FLUENT (CFD)?
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IMHO the type of mesh and the simulated physics are not very closely related to each other.
What matters with no regard to the mesh type, is that you obtain a mesh independent CFD solution in the limit of dx-->0. This applies to all possible mesh types and to all possible CFD physics.
Best regards,
Dr. Th. Frank.
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I run simulation by putting BC in fluent with cavitation model and got the result but when i plot the XY graph with an expression acos(X/radius) and keeping the X as geometry variable. the graph i got is till 200 degree. i need to plot till 360 degree. how this can be done in CFD post?
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can not plot in Fluent
try in CFD Post
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Dear Colleagues,
I’m pleased to inform you that open access journal /Catalysts/ (ISSN 2073-4344, Impact Factor: 3.444) is planning to publish a Special Issue on the topic of "Trends in Catalytic Advanced Oxidation Processes". The submission deadline is 30 March 2020.
This Special Issue is dedicated to novel achievements in the field of catalytic advanced oxidation processes. The contributions should be related to the listed topics:
· Catalytic processes in water and wastewater treatment
· Developments in Fenton-like AOPs
· Activation of Persulfates for AOPs
· Formation of sulfate radicals
· Catalytic cavitation-based AOPs (hydrodynamic cavitation and acoustic cavitation)
· Sonocatalysts
· Catalytic ozonation
· Photocatalysts—including visible light and UV applications
· Catalytic wet air oxidation (CWAO)
· Catalytic–electrochemical AOPs
· Carbon catalysts for AOPs
· Nanocatalysts
· Risk of by-product formation during water and wastewater treatment
· Developments in process control of catalytic AOPs (analytical methods, chromatographic, and spectroscopic techniques)
· Methods of catalysts characterization
· Post-process assessment of effluents toxicity
· Application of nanobubbles in AOPs
· Economic analysis of catalytic AOPs application and catalysts life cycle assessment (LCO)
· Industrial catalytic wastewater treatment
· Modelling and optimization of catalytic processes
· Green chemistry aspects in catalytic water and wastewater treatment
Detailed information regarding this issue, please follow the link below to the Special Issue website at: https://www.mdpi.com/journal/catalysts/special_issues/catalytic_aop
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First decision provided to authors approximately 13.4 days after submission; acceptance to publication is undertaken in 5.5 days (median values for papers published in this journal in the second half of 2018).
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In order to plan for the whole paper project, I appreciate you could inform me within three weeks as to whether you would be willing to contribute. I also encourage you to send a short abstract to me (grzegorz.boczkaj@pg.edu.pl) or to Caroline Zhan (caroline.zhan@mdpi.com) in advance.
Sincerely hope this invitation will receive your favorable consideration.
Best regards,
Guest Editor
Prof. Grzegorz Boczkaj, PhD. Sc. Eng. Assoc. Prof.
Department of Process Engineering and Chemical Technology, Faculty of
Chemistry, Gdansk University of Technology, 80-233 Gdansk, Poland
Caroline Zhan
Assistant Editor
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Thanks for your invitation. We can contribute if publication charges are waived.
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I have been trying to read up a bit and find a plausible explanation to link of higher ultrasound frequency to the cavitation phenomenon and its effect on sono-chemical reactions. Does it promote the rate of reaction in any way or degrade it?
Also, one thing I am not clear is whether the stable cavitation aids in these reactions or not. I am aware that transient caviation helps in disruptive phenomenon so probably it helps in preventing aggregations and destroying weak bonds. But does the frequency of ultrasound increase the threshold to reach the transient cavitation?
Any help would be appreciated. Thank you in advance.
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I think the answer is YES. however, it is very difficult to describe the relationship between ultrasound and chemical reaction with a clear rule or math model.
see
Optimization of solid food waste oil biodiesel by ultrasound-assisted transesterification
Kinetic Model of Biodiesel Processing Using Ultrasound
Synthesis of Biodiesel Using Microwave Absorption Catalysts
Kinetics for the Synthesis of Biodiesel Based on the Calculation of Hot Spot Temperatures in the Catalyst.
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  • When the effects of non condensable gas, surface tension and viscosity are negligible, as it is the case for big enough bubbles, the Rayleigh-Plesset equation reduces to the simple Rayleigh equation(Fig.1).Furthermore, if the applied pressure p is constant, the Rayleigh equation can be integrated once to give the bubble interface velocity(Fig.2)
Those content above are from the book,here is the thing I can't figure out :How to integrate the equation to get the velocity?
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We can get its solution by Homotopy Analysis method(《Beyond Perturbation...》 by Liao Shi Jun).
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What are the design parameters for the  hydrodynamic cavitation reactor for biodiesel production?
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@ Master Naseem Ahmad ,
Thanks for your kind suggestion.
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I am working to simulate cavitation model in an axial flow pump can anybody provide me any tutorials in this field please. Thanks
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Many thanks Taimoor
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I am working to simulate single and cavitation model in an axial flow pump can anybody provide me any tutorials in this field please. Thanks
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...because this is one of the best validated 2-equation turbulence models with a good balance between accuracy and computational effort. In particular more sensitive to flow separations.
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I am simulating injector nozzel to see cavitations and want to validate Winklhofer results using Mohan's paper(attached in files). I simulated flow for simple geometry (attached in files) with sharp edge and validated the resultes successfuly, when i made little change in geometry 20 micro meter round edge at throat of nozzel, results changed drastically and vapors vanished even with same boundary condition and flow modle. Can any one help me in solving this?
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flash extraction, better yield, ultrasonic cavitation, Flash extractor, Herbal Blitzkrieg extractor
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Please look at the following below links which may help you in your analysis:
Thanks
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Hi all,
I'm trying to get a cell distruption vessel such as this one (Parr Instrument 4635, https://www.parrinst.com/products/sample-preparation/cell-disruption/4639-cell-disruption-vessel/applications/).
Are there other good companies that sell this sort of equipment that you recommend?
Thank you so much!
Gloria
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Cultured cells are useful for studying the subcellular distribution of proteins, including peripheral membrane proteins. Genetically encoded fluorescently tagged proteins have revolutionized the study of subcellular protein distribution. Nitrogen cavitation is well suited for mammalian and plant cells and fragile bacteria, but is less effective with yeast, fungi, spores, or other cell types with tough cell walls
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Hello,
Background
I'm attempting to refine the design of my sonicator horn. I currently have two prototype horns, one is made of aluminum, the other is made of stainless steel. I made the aluminum version as a proof of concept, it has a tip diameter of 11mm and has a resonant frequency of ~26KHz. My stainless horn has a tip diameter of 9.5mm and operates at ~30KHz. I'm powering these with a 100W variable frequency ultrasonic driver, and a 100W transducer. My horns are both stepped horns that are 1 wavelength long. I will happily post my horn designs if need be, nothing I'm doing is confidential.
My aluminum horn, gives me the typical stream of cavitation bubbles going straight down from the tip. I'd show a picture, but this is surprisingly hard to photograph. This is good. Though I can't keep using the aluminum horn because the tip ablates due to the cavitation and leaves metal in what ever liquid it's being run in.
My Question
Because of this I developed my second horn which is made of stainless steel and has an interchangeable titanium tip which is threaded in. Now, this horn doesn't have the typical cavitation stream down from the tip. Instead, there are some downward streams, but they're not stable, the steam tends to move around on the tip. There are also steams of bubbles that come off of the edges of the tip. Does anyone have an ideas as to why?
Thank you for any information or suggestions, I will happily provide more details if you ask for them.
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Hello!
This is because, in the second case, the assembling by threading causes failures in transmission of the oscillation down to the tip. You should adopt other solutions that imply larger surfaces in contact between those two parts: horn and tip.
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Hi guys, Maybe someone can tell me about the current state of interpreting sonoluminescence as dynamical Casimir effect? Recently I came across two older theoretical papers from the 90s on this topic. One paper (actually as series) is from Julian Schwinger with the title "Casimir light", the other paper is from Claudia Eberlein "Sonoluminescence as Quantum Vacuum Radiation".
If I understand correctly, these papers say that the rapidly changing bubble wall converts virtual photons, which constitute the field of the cavity as quantum electrodynamic vacuum, into the real ones. However, it is shown that there is significant deviation between the theoretical expectation and experimental observation.
So, are there any new experiments or new theoretical calculations after the 90s on this topic? Thanks a looooot!
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There's this unfortunate tendency to stick the words ``Casimir effect'' everywhere.
Sonoluminescence is the emission of electromagnetic waves by sound waves-it's a classical effect and doesn't depend on the ability to resolve either the photons or the phonons, whose superpositions the corresponding waves are.
The Casimir effect regards the fluctuations of the intensity of some field about its average value in the vacuum, in the presence of boundaries. This doesn't have anything to do with sonoluminescence beyond pertaining to the shot noise of the photons and/or the phonons involved in sonoluminescence, when these can be resolved, in the presence of boundaries.
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Referring to an ultrasound device (sonica 2200 soltec, ultrasound frequency:40 kHz) we know the efficiency of cavitation of 300 mL water placed in 1 becker inside the sonication bath (3 L volume). The device has two specific position for 300 mL beckers. Hence we can assume same efficiency inside a second Becker, i.e: treating 600 mL instead treating 300 mL. Hence, the ratio energy consumed:volume treated would be half. Could we approximately assume the same applied to 3 L solution placed directly in the sonication bath, or the cavitation efficiency would be significantly reduced?
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If I understand your question you want to have a ultrasonicated volume within a bath. The ultrasound field is not uniform over volume it is designed for utility cleaning. Your use of the bash for cavitation will need to be graded on the results of your beaker position in the bath. A short discussion from Heilsher details this in a more complete fashion. The link is https://www.hielscher.com/probe-type-sonication-vs-ultrasonic-bath-an-efficiency-comparison.htm
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What can lead to higher yield of cavitational reactor adopted for biodiesel production?
Can the types of alcohol: methanol, ethanol affect the cavitation reavtor
Can the types of catalyst affect the reactor?
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Thank you for your contribution, Dr. Rachan Karmakar for your wonderful contribution.
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Dear researchers,
I have been trying to simulate cavitation in Venturi device to study the evaporation in it. But I cannot find a way to do it. I do not know which module is capable of understanding the evaporation of the water when the pressure drops in venturi throat. Can anybody help me?
Regards,-MF
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if you will use fluent you can see below link.
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A 52/F professional from high socioeconomic status reported with low-grade irregular fever for 20 days and night-sweat only. No cough/sputum, no enlarged LNs, no coexisting disease. CXR> a consolidation with a satellite one in Rt upper lobe. CECT> a lesion with a small cavity on the base of anterior segment (RUL). Slight neutrophilic leukocytosis. Procal> normal. BAL culture> Delftia acidovorans + Streptococcus. All other reports are within normal limits. Leads a healthy family life, has no H/O I/V drug use (IDU). What should be the line of treatment, please?
# You may please redirect this to any renowned microbiologist/ID specialist you know.
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Alhamdullah 🙏
Excellent Dr. Rabiul Alam and your team
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Since Bisphosphonates produce mandible deterioration resulting in cavitations ("dead jaw") will this side effect be monitored?
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@ OPG is used for detecting bone metabolism changes such as myelitis. Bisphosphate efficacy is making bone ageless that inhibits bone metabolism. Therefore, precisely monitoring the level of jaw bone deterioration in cavitations maybe need using other adjunctive methods.
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The factors that increased or decreased Cavitation
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Cavitation is what to do with suction line. A number of parameters include; pipe length, diameter, and roughness, fluid density and viscousity, flow speed and temperature, upstream pressure, elevations.
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Dear RG,
How can you justify variation in the cavitation yield of biodiesel adopting various alcohol, catalyst and reactors?
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You may find answer to your question in this article
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I want to use the solvents for treating wastewater
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Hello, what really you want to find out? What solvent you mean?
Acoustic cavitation can be done directly with waste water which normally called hydrodynamic cavitation.
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There is a micro Kaplan hydro plant:
Flow rate: 0.58 mc/s Head: 4.85 m RPM: 625 Max electrical power: 16.5 kW Generator+gearbox efficiency: 0.89 Maximum Turbine efficiency: 0.67 Draft tube: vertical/conical, 1.5 m high
The problem is the decrease in electrical power (measured during operation) with the time up to an asymptotic value, although all the external conditions (head, flow rate, rpm, blades configurations) remain constant.
I summarize here better, by using a picture (in attach). The picture depicts the power in kW versus the time in minutes.
Let's suppose that the turbine is switched off. Then it is switched on and the ELECTRICAL power reaches in few seconds 16.5 kW. But, as you can see from the picture, then it starts to decrease approaching, over three days, 13.65 kW, and remains at 13.65 kW. Then, suppose that it is again switched off and switched on (process that last few minutes, not again plotted in the figure),  again the ELECTRICAL POWER reaches 16.5 kW as at the beginning, but then it decreases approaching 13.65 kW (after 3 days) and remains 13.65 kW. If we repeat again the switch on/off (process done in few minutes), again it reaches 16.5 kW, and then decreases up to 13.65 kW. If the turbine is not switched on/off, the power remains 13.65 kW “forever” ….. until a new switched off/on is made. Therefore, the switched off/on process last few minutes, while the decreasing trend until the lowest power value of 13.65 kW lasts few days.
Have you got general ideas?
1) Formation of a big vortex in the draft tube. If this would occur, the decreasing trend should last few minutes (the time needed for the vortex development), and the power would immediately approach 13 kW. This phenomenun should last few minutes, not days. Furthermore, by CFD simulations, the vortex in the draft tube is not powerful, and at the outlet of the draft tube flow velocities are vertical.
2) Possible inclusion of air from the conical (vertical) draft tube towards the turbine. The draft tube is immersed of slightly more than 1.1 D into the downstream water level (D is maximum turbine diameter), as recommended by engineering practice. From CFD simulations flow velocities are downward, so this point should be ok.
3) Possible electro-mechanics/electrical load problem.
4) Cavitation: during operation there are not noise, neither appreciable vibrations, but there is hub erosion due to cavitation. But cavitation should reduce the maximum power output, not generate a decreasing trend during the time.
Thanks
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If there is a guide blade, maybe their attack angle changed in 3 days and set in steady angle. If this problem cause is electrical, transient time is less than a minute. if it causes is hydrodynamic, transient time is less than a hour. so I think cause of that is mechanical mechanism.
Good Luck
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For cavitation that is produced from the face of an ultrasonic horn (sonotrode) -- If I know the cavitation power intensity (say 100 watt/cm^2) at frequency f1 and I want to estimate the power intensity at a second frequency f2, what is the relationship? In order to establish the relationship, either the driving amplitude or driving velocity must be specified as constant (i.e., effect of frequency at constant amplitude or effect of frequency at constant velocity). See http://www.ultrasonic-resonators.org/applications/cavitation/cavitation.html#effect_of_frequency
Is the frequency relationship affected by the fluid? If so, what fluid properties? (I'm particularly interested in cavitation in water.)
Thanks,
Don C.
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Jochen --
If we assume a constant velocity (resulting in halving the amplitude in going from 20 kHz to 40 kHz), it remains unclear to me if the power intensity then remains constant. Using an electrical analogy, the power developed in a linear resistor is P = I^2 R where I is the current and R is the resistance. If the current I is held constant (analogous to constant mechanical velocity) then the power P remains constant; however, this is only true if R is independent of frequency. (As a further analogy, the hysteresis losses in an electrically-driven magnetostrictive material increase rapidly with frequency. This is why most magnetostrictive transducers are limited to an upper frequency of about 30 kHz.) Thus, this gets to my basic question -- is the acoustic resistance of the cavitating fluid actually independent of frequency since both the bubble size and the bubble density (the cavitation cloud) depend on the frequency? (I'm looking for a reference study with verifiable results.)
Regards.
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Hi! We are isolating mitochondria from platelets using nitrogen cavitation via a Parr bomb apparatus. Has anyone had experience isolating mitochondria from blood or other culture cells using this technique? Is there an optimal cell number or cell number range to be loaded? We are able to load 300 microliter aliquots of cells into our apparatus. Thank you for any assistance you may be able to provide.
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Hi, there has not been consensus on the cell numbers to load but most authors used 300 like you. I think you are in order but more cell optimal loading test should be done to ascertain the optimal cells to load for the best results.
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The final target is to study the fundamental physical processes involved in bubble dynamics and the phenomenon of cavitation. Develop a new bubble dynamics CFD model to study the evolution of a suspension of bubbles over a wide range of vesicularity, and that accounts for hydrodynamical interactions between bubbles while they grow, deform under shear flow conditions, and exchange mass by diffusion coarsening. Which commercial/open source CFD tool and turbulence model would be the most appropriate ones?
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It would be a highly educational experience if you could try to develop your own solver using MATLAB then write it in a low-level programming environment like Fortran.
But OpenFOAM should be sufficient if you want to get a bit better at programming CFD, and ANSYS/Fluent would be best if you plan on proceeding as a CFD user.
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I am culturing cells in a microfluidic device for several days. Before the experiment, I am performing a Nitrogen cavitation procedure in order to expose the intracellular compartments of the cells to the fluid flow. During Nitrogen cavitation (N2 bomb) you place the microfluidic device in a high pressure chamber and allow Nitrogen to fill the chamber. After a few minutes, you quickly release the pressure effectively breaking the cells apart.
Obviously there will be lots of bubbles in the device after the experiment. However, even if I get rid of them (using a vacuum chamber as suggested in another thread), more bubbles come out from what seems to be within the PDMS itself. PDMS is very permable to gases but it seems that even after 10 minutes the Nitrogen keeps seeping out from the PDMS. This effectively ruins the experiment as the bubbles destroy the cell remnants.
Any suggestions to stop this?
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I don't have a solution for your problem, but some of the following comments may help:
1. PDMS is hydrophobic. Bubble problems are much worst when the surface is hydrophobic. Plasma treatment may render the PDMS hydrophilic, but the effect lasts some hours. You need days. There are other treatments, more complicated, to modify the PDMS surface properties. If you are interested look in the literature. Surface modification may also reduce the amount of gases that permeate the PDMS.
2. When you compress the fluid inside the microfluidic device with N2 a large amount of it will dissolve in the liquid. If you immerge your microfluidic device under water during the pressurization, maybe you can protect your liquid inside the device from N2 (it will take time for the N2 to diffuse to your liquid of interest).
3. Even liquid at 1 atm, before your experiment, will have gases dissolved so your vacuum treatment will remove those gases also. So, to minimize bubbles maybe you should try to use liquids that have been under vacuum before the experiment. Since your experiment takes days maybe you should also immerge your device on degassed water to avoid dissolving gases from the atmosphere.
4. You probably need a small amount of dissolved gases to break the cells, so 2 and 3 may not help.
5. Other possible solutions:
a) use traps to confine the cell debris and inject bubble free fluid
b) break the cells with other methods that do not require massive pressurization (e.g. ultrasonics)
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Is your code capable of predicting propeller cavitation? if yes, what types of cavitation it can predicts and how accurate the predictions are?
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Hello Mounir,
Thank you for your feedback. I was actually referring to the particular code base that Mohammed is using in his project. Thank you.
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Dear all, I am trying to model cavitation using Abaqus CAE. The problem is assigning the cavitation pressure. Abaqus CAE doesn't allow to define the pressure. It can be defined in input file using following command (according to abaqus user manual).
*Acoustic Medium, Cavitation Limit
0,
But then again abaqus doesn't read it and gives a warning. Can anyone please suggest me a way to define this limit? The same thing happens for defining initial pressure condition for cavitaiton.
Thanks in advance.
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For anyone who is facing such problem. While modeling cavitation, a cavitation limit has to be defined. We can define it in input file. Once the input file is saved, it has to be run from abaqus command. Abaqus/CAE can not rut the file.
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Even ultra low vacuum grease evaporates near absolute vacuum.
Cavitation takes place when pressure drops near absolute zero pressure, near -100 kPa, -1 atm... when the "vapor pressure" limit is crossed.
But that applies only to materials with relatively weak bonds, as far as I know. Water, oil... so, what is the closest thing to non-cavitating fluid? How low can the pressure go, before it is pulled apart?
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A gel is a two-phase system: dispersant/external phase is a solid and dispersed/internal phase is a liquid. Size of liquid particles range roughly from 1 to 1000 nm. The gel migth flow (non-newtonian fluid), depending on the relative proportion of phases. During flow, cavitation may occur, governed mainly by the liquid phase vapour pressure, which is highly dependent on temperature. Again, you’ll have to find/develop a gel using a liquid of very low vapor pressure, so as to minimize the chances of cavitation.
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I am simulating a 3D cavitation model with 2 Way FSI coupling in ANSYS Fluent 18.1.
The simulation is succesful but as I open CFD post for post processing, I get this error.
Variable 'Pressure' does not exist on 'symmetry_minus_middle'
'symmetry_minus_middle' is one of my many named selections. However, I am unable to check values for pressure at any location.
Is anyone familiar with this kind of an error? If so, how did you solve it?
Any help would be greatly appreciated!
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Dear sir,
I had this problem many times so I open the CFD POST individually and load the FLUENT results, this will make all of results important to the CFD POST and you can run FLUENT many times in different boundary conditions l.
Note that you have to export the results by (case and data) from the FLUENT program.
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Hi
I have human placental cells JEG-3 in culture and some cavitations have appeared in them (see pictures). It has occurred several times in different thawed vials during the year. Does anyone know why this is happening?
Thank you.
Eli
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Hello Elisabet,
This question showed up in my home feed and I found it interesting. So let me take a crack at it.
I know that hydrodynamic cavitation occurs when local pressure decreases below vapor pressure of the liquid at that temperature. Generally, this phenomenon is associated with high speed flows of incompressible or slightly compressible liquids. I googled and found that the JEG-3 cells you are using are stored in liquid nitrogen. So I think this phenomenon might have something to do with the gas being used. I again googled and found saturated N2's vapor pressure at different temperatures (https://www.bnl.gov/magnets/staff/gupta/cryogenic-data-handbook/Section6.pdf). I says that at temperatures lower than STP or room temperature, the vapor pressure is significantly greater than 1 atm. Thus the local pressure (assuming 1 atm) satisfies the condition for cavitation to occur resulting in the pictures you have posted. From the pics it seems that liquid N2 were hidden in the channels (?) where cavitation was seen.
My follow up questions / comments are:
1. Is my assumption about storage in liquid nitrogen correct?
2. Are the cells completely thawed when kept outside? How do you judge complete thawing?
3. Cavitation results in small bursts of these gas bubbles as the local pressure increases around the bubble. Will this potentially damage the cells you are trying to observe?
4. What is the length scale of the cells we are looking in the picture. I do not have a biology background so please pardon my lack of knowledge.
I hope my reasoning makes sense and this answer is helpful. I will be happy to hear or discuss what the experts have to say.
Regards,
Pranab
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I am trying to simulate effects of cavitation and air entrainment. My intention is to simulate effects of cavitation on a nozzle due to water vapour and air trapped in water (air entrainment).
I have been so far succesful in simulating 2 phase flow of water and water vapour and cavitation due to it. But I am unable to add a third phase of dispersed air in water and its effect.
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which model did you use for 3 phase flow, and which software are you using for you modeling?
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 design of high energy centrifugal pump impelles
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- By increasing the diameter of the impeller eye can add less space for liquid to boil or vaporize.
- By adding a impeller inducer. Pump inducers are designed to prevent significant cavitation by adding a smoother inlet for pumped liquids or materials.
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Who knows the number of cavitation bubbles that can be generated in one second when applying ultrasound. Is there exact data? or order?
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Acoustic cavitation—the formation and implosive collapse of bubbles—occurs when a liquid is exposed to intense sound. Cavitation can produce white noise, sonochemical reactions, erosion of hard materials, rupture of living cells and the emission of light, or sonoluminescence1, 2. The concentration of energy during the collapse is enormous: the energy of an emitted photon can exceed the energy density of the sound field by about twelve orders of magnitude3, and it has long been predicted that the interior bubble temperature reaches thousands of degrees Kelvin during collapse. But experimental measurements4, 5 of conditions inside cavitating bubbles are scarce, and there have been no studies of interior temperature as a function of experimental parameters. Here we use multi-bubble sonoluminescence from excited states of metal atoms as a spectroscopic probe of temperatures inside cavitating bubbles. The intense atomic emission allows us to change the properties of the gas–vapour mixture within the bubble, and thus vary the effective emission temperature for multi-bubble sonoluminescence from 5,100 to 2,300 K. We observe emission temperatures that are in accord with those expected from compressional heating during cavitation.
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Hello everyone,
I am trying to simulate cavitating flow over the NACA66(mod) hydrofoil by interPhaseChangeFoam solver. SST k-w turbulence model and Kunz model is applied. The initial setting of k and w is small when I use the calculator by setting the turbulence length scale 7%  of the hydraulic diameter.
Boundary conditions in nut file are:
nut —> nutUSpaldingWallFunction
inlet —> calculated
outlet —> calculated
The simulating goes well but the unexpected cavity shedding appears  since attached cavitation is expected.Bounded variables omega_max has great value during the simulation.
However when I change the k and w to a great number,there is no cavity shedding and the bounded value seems good to me.
Does anyone know  why k and w have such influence on the simulation?
Attached files are the residuals plotted by pyFoam and fvSchemes, fvSolutions files.
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Hello, Ziming Zhu 
I'm not an expert in turbulence also, but i guessed several reasons which can lead to behaviour, described by you. So i can't say which turbulent viscosity ratio more realistic, but i can ask you to change intensity at inlet whithout changing ratio. And if results are same for both cases then the reason in eddy viscosity ratio.
Regarding Q.2 - yes, you need time varying B.C. Also, if you have initial velocity internal field with value, equal to inlet, then flow "hits" the hydrofoil with dynamic pressure rho*w*w/2 and this can create large pressure drop and vapor generation term, Try to increase velocity field from 0 to 2.1m/s.
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Dear all, 
Myself and a fellow collaborator are interested to model the hydrolysis of fatty oils based on the cavitation phenomenon. Could you all please direct us to some data sources to sufficiently model the systems. 
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We have a system in which we are reducing pressure from about 250 bar to 10 bar. according to the valve sizing calculations, the maximum allowable pressure drop is less than the required pressure drop. However, system volume is very low and the max. allowable flow rate (from valve design calculations) is much higher than the required flow.
deltaPmax<deltaPrqd
deltaFlowmax>deltaFlowrqd
Will there be choked flow in the system or will it just lead to cavitation?
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Such a large pressure drop across a valve is destructive to  the valve with vibration, ultrasound, erosion, and recoil. Unstable control and excess noise are the common complaints.
Best remedy is to let down in two stages or more, one setting a down stream pressure and the other setting a flow through. To avoid interference I prefer a spring operated pressure control and an instrument operated flow control. This is a common configuration that usually contains a safety pressure relief valve to protect down stream against failures. 
Other remedies are possible. The petroleum industry uses calibrated chokes to deliver small flow at high pressure drop. They are just precisely made short lengths of metal cylinders with a small passage drilled and machined  through the center.
If you had more flow a work engine might be possible.
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I know cfd-online.com but I need something more specific about simplefoam, turbolence application, and then cavitation simulations
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I recently finished an MSc project on cavitation over a 3d hydrofoil. While running a DES simulation for cavitation on NACA 0015 in Star-ccm+, I observed vapours near the outlet developing after the bubble diminished from the trailing edge. The pic attached shows the volume fraction of vapour at 100ms. The vapours downstream start developing at 90ms, would be great if you could shed some light as I am still an amateur, could this be flashing or cavitation inception in the vortices developed?. The conditions are at σ = 1, inlet velocity 6m/s and outlet pressure 20.9 kPa.
Thank you.
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The structure close to the trailing edge could be physical, but the rest are spurious. Looks a bit like it could be in proximity to a mesh coarsening if you have a refinement wedge around the foil?
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I know that both in cavitation and flash boiling are driven by same flow physics i.e., when ambient pressure drops below the saturation vapor pressure of the liquid at respective temperature the phase changes occur.
The difference between these process to my knowledge is:
In cavitation the pressure drop is relatively so the diff. between the temp. of liquid and saturation temp. @dropped pressure is low so there is no much heat transfer. But in case of flash boiling the pressure drop is relatively higher so the temp. effects cant be neglected.
please let me is this understanding about these process is right?
and I have 2 more basic doubts
1) In a cavitating bubble what will be the pressure, will be the saturated vapor pressure, or the pressure of liquid (which is less than saturated vapor pressure)
2) In flash boiling what will the temp. & press. of vapor formed. Will it be same as the superheated liquid?
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Hi Bavan
  • Cavitation is the process of rupturing a liquid by decrease in pressure at roughly constant liquid temperature. If the liquid at constant temperature undergoes to a decreasing pressure, p, which falls below the saturated vapor pressure, pv. The value of (pv -p) is called the tension, and the pressure you mean will be the pressure of the liquid which is compared with saturated vapor pressure. The cavitation phenomenon to occur the pressure must be raised again to high value than the vapor pressure to lead cavity collapsing.
  • Flashing is the process of rupturing a liquid by decrease in pressure at roughly constant liquid temperature but differ from cavitation that the decreased pressure eventually remains lower than the vapor pressure and doesn't  recover again.
  • Boiling is a rupturing of the  liquid by increasing the temperature at roughly constant pressure. A liquid at constant pressure may be subjected to a temperature, T, in excess of the normal saturation temperature, Ts. The value of dT=T-Ts is the superheat, and the point at which vapor is formed, DTC, is called the critical superheat.
For more information I suggest
CAVITATION AND BUBBLE DYNAMICS book by Christopher Earls Brennen
With regards
Thanks
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Dear All,
keeping in mind the fact that during the molecular dynamics simulation at lower temperature below certain density, the system (bulk liquid) may cavitates, how can I recognize the fact that my system is cavitating or has gone into the unstable region( ie below liquid spinodal line) ?. Even if we take snapshot of the system and visualize, how do i know that it is cavitated and not inhomogeneous ?    
Any help regarding this will be very much appreciated
Thanks in advance
Debdas
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Hi Atreyee,
Thanks for your answer. You are right but i have something to add. Negative pressure doesn't always mean a signature of liquid gas coexistence. A liquid in metastable state may also show negative pressure in simulation. Any-ways I wanted to know  about how to calculate exact cavitation line not the liquid-gas spinodal line.
Thanks again
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Generally wear occurs on the bearing surface due to the phenomenon of cavitation. I am planning to do Phd in this topic. So i need a test rig to measure cavitation.
Cavitation is the formation of vapour cavities in a liquid – i.e. small liquid-free zones ("bubbles" or "voids") – that are the consequence of forces acting upon the liquid. It usually occurs when a liquid is subjected to rapid changes of pressure that cause the formation of cavities where the pressure is relatively low. When subjected to higher pressure, the voids implode and can generate an intense shock wave
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If you are looking for physical rig to observed the formation of cavitation in journal bearing, then you can construct your journal bearing from tranparent materials such as perspex or any tranparent materials that willnot be corroded or reactive to the lubricant.. Your rig should allow for variable ecentricity and rpm. You need only to construct the lower journal from transparent material. With high speed camera and some form of computer imaging  you should be able to observe the formation of cavities in the lubricant. 
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After sonication tips get mangled from cavitation, can I grind them down flat again with no ill effects to their performance, or the generator? 
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For the following, I assume that you mean the threaded replaceable tips. Then there are three considerations for renewing sonication tips -
1. Frequency. As the eroded material is removed, the frequency of the ultrasonic stack will increase. Ultrasonic power supplies (generators) typically have a frequency band within which they will operate properly. This will depend on the design of the power supply. However, you should typically expect at least +/-1% of the nominal operating frequency (e.g., +/- 200 Hz at 20 kHz) or more. You can get the exact spec from the equipment manufacturer although the equipment may still operate well outside the specified band. You can simply remove tip material until the frequency falls outside this band at which point the power supply should no longer start due to its internal protection circuitry.
2. Amplitude. As the frequency increases the output amplitude may change. If the amplitude is critical then you should measure the amplitude with a new tip. Then when the renewed tip is installed the amplitude should be adjusted via the power supply to get the desired amplitude. These measurements can be taken in air.
3. Heating. You should be able to run a new tip for some time (say 30 seconds) in air without appreciable heating of the tip. If you run the same test with a renewed tip and find appreciable heating then this means that the stiffness across the tip's surface is not adequate to support the tightening load. Then the renewed tip should be discarded.
If you are making your own tips then you can try machining the tips somewhat longer than normal to give extra wear length. The frequency will then be below nominal (for instance 19.8 kHz instead of 20 kHz). However, the added weight will put additional stress on the tip-horn joint so you should avoid this method if you find any extra heating at this joint.
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Does anybody know where to find data for validation of RPeq code. Sure, one can find many results in the papers, but nobody lists the values of ALL variables which are need to be included in the code (pressure evolution, initial bubble radius, surface tension, vapor pressure, liquid and vapor density, polytropic constant, viscosity... ).
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You can find such data in Table 1 of this paper:
S. A. Mohammadein and K. G. Mohamed, Growth of a gas bubble in a supersaturated and slightly compressible liquid at low Mach number, Heat and mass transfer 47 (12), 1621-1628, (2011)
I can also help you to find any missed data.
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from the view cavitation induced damage to the creep, does anyone have any suggestion about whether the cavity formation and development is induced by creep strain or the applied stress and what is the dominant mechanisms behind?
I am really appreciated for your help!
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Mostly micro cavity chains , which are nothing but growing vacancy clusters  are observed along those grain boundaries subjected to the applied uniaxial tensile stresses, and  aligned  almost normal to the direction of the stress axis. Theoretically one can't image to have creep strain without having applied stress unless one deals with the relaxation stage that takes place after one  turns off the applied stress.  With the acception of   high temperature Herring-Nabarro creep,  there is a large amount  of dislocation climb  occurs due to the vacancy flow to the compression sides of  the dislocations having edge or mixed characters.  This  temperature dependent  process especially enhanced very much under the applied high stresses, and the creep rate shows almost  sin- hyperbolic dependence  on the stress. (Barrett & Nix). 
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I am wondering what will be the effect of decreasing the number of blades in case of Francis turbine or high discharge machine on cavitation performance.
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P = ωΤ . Lower number of blades means lower angular mass i.e torque. If the speed remains the same, then the output power should be lower. Something has to change. Either the speed, or the power. If the speed remains the same, then the turbine produces less power, it is "weak" and it will  "see" more motion resistance i.e cavitation. If the power remains the same, then the speed will be higher for a lower number of blades, but higher speed leads to cavitation. 
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Let's say we made an experiment with 2 cavitation bubbles. One is very big and the other is very small. They both collapse near a wall in a form of a microjet (nonspherically). Now we want to make a simulation and we are lazy and simply take the Rayleigh-Plesset equation for the spherical bubble dynamics. For the comparison to the experiment we measure the real bubble volume and recalculate how big the radius would be if the bubble would be spherical. Now the big question... which bubble would follow the prediction by the Rayleigh-Plesset equation more closely - the big one or the small one, and why?
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Dear Matevz, late answer, just joined RG.
The volume dynamics is very well captured with RP, thus RP should work for midly deformed bubbles. This is the case for gamma>1.5 near a surface, the jet forms only in the late phase prior collapse. The rebound with jet can't be captured with RP, because you loose energy during the impact (water hammer pressure) and the formation of a vortex ring. Thus the question remains, RP better for smaller than larger bubbles? It works very well for small (SL type bubbles) and for large ones (under water explosions), yet when the bubble is too large, buoyant effects can came in as the pressure head between top and bottom is large and the oscillation time is larger, thus more time to develop instabilities. My guess therefore is that RP is good for volume dynamics for gamma>1.5 and sufficiently small bubbles.
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Xylem cavitation appears to be a major cause of tree mortality during droughts. If a tree is not killed, to what extent can this cavitation be reversed when the drought ends? There is quite a lot of indirect evidence for this, but there are also suggestions in the literature that indirect methods exaggerate the extent of embolism, and thus, by implication, the extent of recovery. I am confused about what the current state-of-knowledge is!
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Hi,
we did quite a number of experiments in the recent years to address specifically these questions. We have not worked with tropical trees, but I think the processes are quite generic (see or global review paper in Nature Choat et al 2012). 
There is actually two questions:
1- Are trees able to refill embolised vessels? There is a lot of confusion in the literature on this point because many previous observations are biased by faulty methodologies. X-ray micro-CT is probably the most reliable technique available today to study these processes and we have used it intensively recently (through Synchrotron facilities, or with our lab based systems). So far, our conclusion is that trees can refill embolised vessels only if they can generate positive root pressures. In other words, we have not been able to confirm the so called 'novel' refilling with these robust techniques. This means that embolism can be reversed only when transpiration is null (at night) and when soil is fully hydrated. I've seen this phenomenon on temperate trees only during spring on few species. A point that should be made clear is that cavitation is not routine in trees. Cavitation forms only under extreme drought conditions, typically after stomata have closed and leaves loos their turgor. We have never been able to confirm daily cycles of embolism/refiling with our new technologies (micro-CT). 
2- Are trees able to recover once embolism has formed? How resilient are they ? We have addressed this question experimentally by exposing trees so increasing levels of drought, measuring embolism and quantifying mortality. We have data for about 10 species and if we can generalize from this small data set we can say that the lethal level of embolism is around 90% for angiosperms and 50% for gymnosperms. Above these levels tree never recovered (=death). Below, they were able to regrow, but their growth was impaired and they would have eventually die in the field (less competitive).
There is of course a lot of experiments that need to be done to confirm these preliminary conclusions. The real world is probably more nuanced and several species probably behave different (especially in the tropics!). However, the key point is that you should be extremely critical about the methods you use and it is essential to confirm your findings with robust techniques such as micro-CT. Very sadly there is a lot of confusion in the literature, so please do not bring more confusion ! 
Here is a list of recent papers from our group addressing these questions. You can find them here on Resarchgate or on my website: http://herve.cochard.free.fr/publi.htm
Torres-Ruiz JM, Jansen S, Choat B, McElrone A, Cochard H, Brodribb TJ, Badel E, Burlett R, Bouche PS, Brodersen C, Li S, Morris H, Delzon S. 2015 Direct X-ray microtomography observation confirms the induction of embolism upon xylem cutting under tension. Plant Physiology 167: 40-43.
Cochard H, Delzon S, Badel E. 2015 X-ray microtomography (micro-CT): a reference technology for high-resolution quantification of xylem embolism in trees. Plant Cell and Environment. 38: 201-206
Martin-StPaul N K, Longepierre D, Huc R, Delzon S, Burlett R, Joffre R, Rambal S, Cochard H. 2014 How reliable are methods to assess xylem vulnerability to cavitation? The issue of “open vessel” artifact in oaks. Tree Physiology 34: 894-805.
Torres-Ruiz JM, Cochard H, Mayr S, Beikircher B, Diaz-Espejo A, Rodriguez-Dominguez CM, Badel E, Fernández, JE. 2014 Vulnerability to cavitation in Olea europaea current-year shoots: more support to the open-vessel artefact with centrifuge and air-injection techniques. Physiologia Plantarum. 152: 465-474 doi: 10.1111/ppl.12185
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I am unable to download EDTSurf from the site. The windows executable file does not run. Is there an online site which takes the PDB file as input and gives appropriate output in form of data/figure as Depths and cavites?
Any help will be appreciated.
Thanks!
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Dear Khawar,
I suggest that you go to the online service of "Zhang Lab On-line Service System", they can help you.
Good luck,
Regards
Abel
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I have been working with ILES in OpenFOAM for numerical simulation of partial sheet cavitation. I would like a backup of your opinions about the subgrid model and subgrid dissipation.
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Dear Dr. Thornber and Dr. Bensow,
Thank very much for your answers.
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I'm wondering if there is any research work which has already aimed to measure the gas content of cavitation bubbles occurring inside nozzles (geometrical induced cavitation) ? 
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Hi again,
A cavitation bubble normaly consists of combination of dissolved gas (O2, N2 etc..) and vapour. (For further explanation, you can look at 1st and 2nd chapters of Brennen's book 1995)
Mostly, i am interested in the numerical simulation of cavitation based on bubble dynamics models. Therefore, i could say that, due to easy treatment, most of cavitation models based on bubble dynamics ignores the dissolved gas and assumes only vapour inside of cavitating bubbles. Thats, why physically we assume that when the pressure in the local region falls below the Pv (vaporisation pressure) bubbles (which are already existed inside liquid) start to grow up. This phenomena is called as cavitation. In other words, the small micro bubbles are already dispersed inside liquid, which result in the phase change by growing up within low pressure region.
Hope it helps for you.
Baris. 
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Are there any analytical equations or theories that relate the final droplet's SMD to the mechanism by which cavitation bubbles improve the spray emerging from plain orifice nozzles into still air?
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I complete Mr Bicer's answer : the bubble collapse is due to inertial phenomena and lead sometimes to implosion which results in the splitting of the main bubble in various smaller ones tha t can have the size of a spray particle.
Regards!
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I am trying to simulate nozzle cavitation and using interphasechangeFoam. When I check the quality of mesh gives following error about concave mesh. Is there anyone who can advise me how can I correct this error? And is this error really important or ignorable?
checkMesh -allTopology -allGeometry
Mesh stats
points: 654382
faces: 1596014
internal faces: 1412748
cells: 471322
boundary patches: 3
point zones: 0
face zones: 0
cell zones: 0
Overall number of cells of each type:
hexahedra: 410213
prisms: 0
wedges: 0
pyramids: 0
tet wedges: 0
tetrahedra: 0
polyhedra: 61109
Checking topology...
Boundary definition OK.
Cell to face addressing OK.
Point usage OK.
Upper triangular ordering OK.
Face vertices OK.
Topological cell zip-up check OK.
Face-face connectivity OK.
Number of regions: 1 (OK).
Checking patch topology for multiply connected surfaces ...
Patch Faces Points Surface topology Bounding box
wall 182766 183793 ok (non-closed singly connected) (-0.006 -0.008 -2.71051e-20) (0.00194 0.007 0.00194)
outlet 100 121 ok (non-closed singly connected) (0 -0.008 0) (0.00194 -0.008 0.00194)
inlet 400 451 ok (non-closed singly connected) (-0.006 0.007 0) (0.00194 0.007 0.00194)
Checking geometry...
Overall domain bounding box (-0.006 -0.008 -2.71051e-20) (0.00194 0.007 0.00194)
Mesh (non-empty, non-wedge) directions (1 1 1)
Mesh (non-empty) directions (1 1 1)
Boundary openness (2.22526e-14 -1.42534e-17 -2.50737e-15) OK.
Max cell openness = 2.06795e-16 OK.
Max aspect ratio = 2.5 OK.
Minumum face area = 3.75e-11. Maximum face area = 1.6e-07. Face area magnitudes OK.
Min volume = 7.03125e-16. Max volume = 6.4e-11. Total volume = 1.37934e-07. Cell volumes OK.
Mesh non-orthogonality Max: 29.0546 average: 10.3431
Non-orthogonality check OK.
Face pyramids OK.
Max skewness = 1.6129 OK.
Coupled point location match (average 0) OK.
Face tets OK.
Min/max edge length = 5e-06 0.0004 OK.
All angles in faces OK.
Face flatness (1 = flat, 0 = butterfly) : average = 1 min = 1
All face flatness OK.
Cell determinant (wellposedness) : minimum: 0.821136 average: 13.565
Cell determinant check OK.
***Concave cells (using face planes) found, number of cells: 58628
<<Writing 58628 concave cells to set concaveCells
Failed 1 mesh checks.
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Thanks Franco,
As you said, i already used blockMesh and refineMesh utulities and solved problem. I saw that if you just check mesh quality by typing only checkMesh, you cant see this message. On the other hand, It is just seen in the case of typing checkMesh -allTopology -allGeometry, and found that it is ignorable.
Thanks for your answer.
Baris
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Any suggestions, and or possible solutions for the following.
Decreasing maintenance intervals: Turbine component materials in relation to cavitation decay and wear of high friction areas. Bearings etc.
Increasing overall efficiency: Exotic turbine compressor blades. High steam press and low steam press expansion-contraction zones to increase vacuum pressures and stable boundary layer effects.
Designing modular components: Speed up the unscheduled repair time. IE rapid prototyping techniques and processes.
Thank you,
Ben
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I believe that steam turbines should only be taken from service and dismantled for overhaul if there is a good economical or technically compelling reason.  I recall two machines that operated for 17 years before overhaul.   A close watch was kept on internal condition by regular performance and vibration  monitoring. OEM advice should of course be taken into account if they have experience of any particular issue with similar designs or components. 
To speed up the outage period, steam forced cooling can enable a turbine to be stopped inside a day rather than taking a few days by natural cooling.  Air forced cooling has been used to further reduce cooling time but that needs some equipment and minor turbine modification 
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Usually the effect of cavitation appears with a lowered pressure of liquid, for example, in water. However, this effect can be observed and at an elevated pressure. This effect was found by my research supervisor G. Askar'yan 50 years ago. I confirmed it experimentally. Without knowing this effect it is difficult to understand up to the end the cavitation phenomenon. These researches are published.
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Dear James F Peters, the answer of this question you could find in Sov. Phys. JETP 01/1990; 70(6):997 - 1002.
Dear James F Peters, and Sergey Sukhinin the answer of this question you could find in Sov. Phys. JETP 01/1990; 70(6):997 - 1002.
Dear James F Peters, and Sergey Sukhinin I'll give the answer with all explanations and drawings after one answer another my question.
Dear colleagues, I would like to ask the Bible question connected with numbers. Can seem that this question is far from interests of pure scientists, but my researches showed that all scientists anyway faced this question therefore I couldn't ignore it. For everything two "bad" numbers are known. The first is "13", the unhappy number or "baker's dozen", and the second is "666", this number of an animal or the devil. From here question: "How in old editions of the book of the Bible pages 13 and 666 were numbered?"
Sincerely yours,
Alexander
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