Eductor & venturi design resources?

GlobalSpec has an area dedicated to eductors. There is a page where you can Learn More about eductors. And, there are several suppliers with web links to their products and technology.

http://process-equipment.globalspec.com/specsearch/suppliers/manufacturing_process_equipment/materials_processing_equipment/eductors?SrchItem=1&frmqry=eductor&RegEvent=login

What is your application? Do you have special needs?

I'm working on a project where we are mixing a foaming solution with water at a nozzle, then air to help create the foam. Right now the performance of the "throw" is poor. The vacuum is good, the air mixture and foam quality are good, but the output is weak. I am trying to create more velocity on the output without adversly affecting the vacuum and air mixing elements. Oh, yea, it has to function using standard wall pressures of about 45-55psi. I have reduced the nozzle tip to various sizes and increased the velocity that way, but the air ports (2 holes in the nozzle after the venturi) are no longer effective and instead of pulling air in, it forces it out. Seems to be due to the created backpressure from "nozzling down" at the end. I am trying to find a balance. We do not have time to re-design what the previous engineer made, especially considering the money already put into tooling, so I would like to just modify the current setup until we do re-design a 2nd generation. I am not an engineer, just an engineering tech and would like to learn more about this subject. If I could learn the equations and such that went into the original design, I think it would help me. Thank you.

Guest,

Two air ports after the Venturi may be the problem. Is pressure "walking" back to them? You can design these things with a CFD package but, from a practical point, you'll find there is a minimum input pressure before the thing starts to work and this will vary with actual construction dimensions. Get an air regulator and a couple of gauges and just start cranking up the input until you get a decent vacuum on the eductor. Plot this on Excel or something. Then, as you decrease the nozzle, check the same thing.

Tom

Thanks, I'll give that a try.

Well, I began working with the eductors we have and decided instead of testing with air, I would use the chemical solution. I tried to "characterize" the current design by taking a baseline volumetric of input pressure, discarge distance and volume entrained in ml/min. I then began to slightly increase to internal nozzle section, where the increase in velocity and pressure drop occurs. I did this in increments of .010 of an inch and recorded the same metrics. results were an increase in discharge velocity, but a decrease in entrained chemical. Next I started with a new eductor and this time increased the venturi port in .010 increments and recorded the same metrics. Results were that velocity was still low and entrained chemical did not change. I the determined the ratio of the internal nozzle to the venturi port and proportionally increased sized to match, in hopes that as I would increase the internal nozzle size, I would see greater discharge velocities while at the same time entraining an equal amount of chemical as the original design. This actually worked pretty well. I figured out a "happy medium" if you will, which gave me gains of 70% - 90% and a better foam consistency due to higher velocities through the barrell and mix screen. My last mod was to the barrell attached at the end, which I cut down in 1" increments and recorded results. This too aided in the overall "throw" distance. Does any of that make sense? It somehow does to me, I guess that's just how I learn, through experimentation. Well, end result is a modification that increases performance by double and would not require but a pin change in the mold (relatively cheap) to accomodate for larger orafices. needless to say, my boss is extremely happy. by the way, I'm still seeking resources on the physics and equations to be used in eductor/venturi design. thank you.