Venturi design question?

Would I need to increase the flow thru in order to increase the vacuum proportionally?

I believe the answer to this is... yes,

Be aware that you can't get more and more vacuum...you can only ever 'suck' to 1 atmosphere.

Are you sure you want 'more' vacuum...what are you sucking?

I am "sucking" a foamer chemical into a water stream. The output is desirable for what we want as far as velocity is concerned, but I need to draw in more chemical. It currently measures 14 in/Hg which I believe is about half what you say I can "suck" at max. Again, are there any basic principle equations that you might be able to assist me with? Thank you.

Bernoulli principle deals with the effect, but it's tons of maths.

Venturi eductors usually have interchangeable nozzles to provide different ratios of product to water. It's probable easiest to make up a set of nozzles with different orifice sizes and do some tests.

These devices are available reatively cheaply.. are you designing one or are you a user? Often the chemical supply companies can provide a system, sell you one or point you at a supplier of these things.

(I work in chemical dosing, but we don't use these..we use peristaltic pumps.)

I am using one of our current designs for a different application and trying to make it work with as little modification as possible. We also use peristaltic, but this application requires a venturi. I have experimented with many different orifice configurations (started small and slowly enlarged) that made a pretty big difference with velocity, but it seems the more velocity, the less suction. I found a happy medium, but I need slightly more suction. Velocity is very important in this application, as it must "throw" a fair distance from the end of the barrell, and like I said, I have gotten good velocity, I now need to draw a better vacuum.

If you have done the experimentation and got the results...

Draw the logical conclusion...

You aren't going to increse the suction therefore you need to increase the 'strength' of the chemical product you are sucking up!

I would also suggest the positioning, aperture size and feed tube will be critical for best delivery.

I have also observed that many products are made with high viscosity to 'feel/apperar' better to the end user. Obvoiusly you want as low a viscosity as possible.

If anyone can figure out why I'm offering gratuitous advice to a competitor please let me know.

Maybe I'm hoping for strokies? Prrrrr prrr rub.

Yes, part of the issue may be the viscosity. Strength of chemical is not an option as it will vary with different products and would need to be varied with metering tips to suit specific needs. The chemical I am working with in the lab is pretty viscous, I don't have the actual number but when compared with water there is a HUGE difference. Feed tube size is also something I'm working with, currently waiting for a sample to come in. Also, thank you for the input, even though you may be a competitor.

That makes me think of pre-mixing it to get the viscosity down, then shoot it!

good discussion. This is my first time looking at one of these sites and find this topic interesting. i was going to suggest.The material you wish to inject is obviously in a container, can you simply pressurise the container thus actually forcing the material out at a controlled rate. If you are using compressed air you will need to install a pressure regulator to ensure the container will not inflate and burst. This may be another route you may decide to travel. I myself have been trying to use the venturi system to draw sand into a nozzle . its working but not as good as i had hoped. i would love to be able to have full control over the amount of sand being sucked in . I have many different theories but its just getting the time. Keep on talking folks .... great for the mind and we can progress faster by learning from other peoples mistakes.

"If anyone can figure out why I'm offering gratuitous advice to a competitor please let me know."

It is because you are a nice guy and do not mind helping someone that has a clue as to what they are doing.

A few suggestions:

Add another eductor upstream.A certain minimum spacing between the eductors will be required to avoid an overall loss.Another option, is to add another eductor to the intake, in parallel with the present eductor.A "Y" configuration. Alternatively, inject the material on the suction side of the pump, if materials are compatible with the foam.This will aslo insure a better mixing of the carrier and the foam component.IMHO

HTRN

hi sir

please dend mi th principal of the system that can liquid to pipe line of water

your senscerly

ebrahimzadeh .

gh2_2006@yahoo.com

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Increasing the water flow will increase the vacuum. It's questionable which way the mixture ratio will go. Would think that if the mixture was that critical they would provide a needle valve to increase the mixture.

Increasing the water flow will increase the vacuum. It's questionable which way the mixture ratio will go.

Nicely put...

That's why you need to increase the water velocity...but not the flow...therefore a smaller orifice.

A smaller orifice? I didn't even consider that. I'll have to give it a try. Makes sense for increasing velocity.

You might also want to try moving the nozzle back, this could increase the suction/entrainment ratio. Conversely, moving it forward will help you overcome higher back pressures. Is there any way to pre-pressurise the the liquid under suction ?

des-eng

Another possibility is restrictions and limitations in the suction line.

• Consider eliminating bends, valves, etc.
• Consider duplicating the injection points.
• Consider eliminating lift lines from the injection fluid storage vessel; jack the vessel up a few metres!

Also, be aware that the maximum suction is limited to the vapour pressure of the injection fluid at whatever temperature it is at. At this level of suction, the fluid is boiling and cannot be lifted further as a liquid.

Earlier you stated you can draw 14 in. Hg. In my opinion, that is not a bad suction from a venturi. However you want more chemical into the mix.

1. Increase the suction tube for larger flow of chemical.

2. Elevate the chemical container to reduce suction required (let gravity help with your work).

Simple ideqas from a simple mind.

Del the cat is right, the fundamental rules for flow dynamics would help you for analysing your problem. Different to Del I am not thinking these rules/theories (Bernoulli Equation, continuation principle) are tons of maths, but frankly spoken it is work to dig through.

You are asking for formulas. It is too much to give a full approach here, but a lot of literature had been published. For sure the internet will provide basic literature as well. Recently I found the site www.pipeflowcalculations.com and they are referring to different topics. One offer is a calculator for venturi tubes (but without lifting a second media). Nevertheless it might be useful to go for modelling your primary flow, and see what suction can be archieved in the small section of the Venturi tube. This calculator holds you free from formulas and knowledge of rules - you simply typing in the geometry and media data.

By the way: what to do with an orifice in conjunction with a venturi tube? You may control the mass-flow through a well designed Venturi tube by an orifice in the supply line (or downstream the venturi), but in sufficient distance to the venturi tube (not disturbing the venturi-tube with turbulences from the orifice. placing an orifice in or close to a venturi tube is turning the venturi principle over head (in the suction pipe for the second media an orifice might be allowed).

good luck, Albert

Thank you for the website. I am currently just learning fluid dynamics through literature, online study materials, and trial and error in the lab (best method in my opinion). My experience is all electrical/mechanical equipment that has nothing to do with flow dynamics. So this is a new area for me and I'm enjoying learning I'm not too concerned with formulas I guess as I would rather have general principles to take into consideration. These things have been around long enough so there is no need to re-invent the wheel, just slightly modify it. Thanks for the input.

You're welcome. Become a member, we all learn from each other.

concentric reducer at orifice

Del the Cat & all other guys are going well with you.

Please check up Croll Reynolds.

They are pioneers in this thing and their technical books with formulas can help you alot. Also you can ask them to help you ot.

Well, I connected a larger diameter tube on the suction port and wow, huge difference, 7X more chemical entrailement. The larger diameter tube, coupled with some minor orifice dimensional changes and a shorter barrel have together increased performance ten fold. Thank you guys for the ideas and information provided. Yea, I think it's about time I sign up on the site as well now. Iv'e been using it for about 6 months a s a guest. Again, thank you.

Ha excellent .. great to get the feed back!

Saucers of milk for everyone !

Bravo and a great achievement for you as well as for the Guest.

OK, I finally signed up to the sight so now you guys have a name to associate with my sometimes ridiculous questions. Like I stated before, I am just learning fluid mechanics so, I'll probably have many basic questions. Bare with me through the learning process. And again, Thank you.

Welcome but all credits goes to Del the Cat.

Absolutely

Prrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrr

use Q(flow rate m^3/sec)=area (m^2)*velocity(m/sec) this is basic continuity equation based on which you will get all the diameters and use standards to find angles in converging and diverging portion and then by geometry you will get the lengths in converging and diverging portion