Spray pattern out of a nozzle

[srslykeeds]

Hello,

I can't seem to find much information or any fundamentals/theory on what happens to fluid flowing from a pipe through a nozzle and entering the atmosphere. I am trying to design a water nozzle that will spray in specific patterns/ratios. I know there's general spray coverage area from nozzle type and height but I can't find anything else more detailed.

Thank you for any help!

 

[MikeHalloran]

I couldn't find anything useful, either, in years of searching.
The usual academic stuff about the vena contracta is not helpful.
Apparently whatever has been learned is too commercially valuable to reveal.

Since I no longer have any commercial interest in it, I'll reveal a little of what I have observed.

First, you get a stable cylindrical stream from a sharp-edged hole normal to the exit face. Chamfers and radii will make the stream wander. Some nozzles take advantage of this, by chamfering the exit face across a diameter of the hole, so the exit is no longer planar. This causes the exit stream to oscillate along the line where the normal and slanted faces intersect. It deviates only a few degrees, but a circular array of such holes has been in production for a while. There may be an associated patent, but I haven't found it.

Second, if your stable cylindrical stream hits a planar surface, it spreads into a nice clean fan. This is used in 'pinbar' nozzles where the stream hits the square cut end of a cylinder of roughly the same size as the stream, producing a planar sheet normal to the stream, interrupted by whatever supports the pin. It works as well if the planar impact surface is angled, too, except you don't get full circle coverage of the fan, which leaves at the same angle to the stream as the impact surface.

I haven't done much work with non-round holes, mostly because they're hard to manufacture intentionally. I think some 'air assisted' nozzles distort the liquid stream into a fan by impacting it with fast moving air.

Basically, effective water nozzles that work at easily achievable pressures do their magic by making the water hit 'something', and there is considerable variety in the somethings used.

I get the impression that things work differently at high pressures, like in fuel injectors, but I have no real experience there.


Mike Halloran
Pembroke Pines, FL, USA

 

[1gibson]

How specific are the patterns/ratios? No need to invent the entire wheel, go to mcmaster.com search for "spray tips". Square, flat, hollow cone, full cone, solid stream, etc. Should get you a starting point for the design if nothing else.

 

[Latexman]

http://www.spray.com

http://www.bete.com

Good luck,
Latexman

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[IRstuff]

Or you can go down to the local Home Depot and look at sprinkler heads and garden hose nozzles.

http://www.homedepot.com/p/Melnor-7...Trigger-Nozzle-160-442/203062312#.UXBbFh0cmV0

TTFN
faq731-376

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[srslykeeds]

The patterns and ratio of water are pretty specific. It's basically a shower with flow coming vertically straight down and we need X percentage of water to be present within areas with different diameters. Some testing has shown that water leaving the tip of the nozzle has been quite random. Figuring out what goes on with the flow within in the nozzle and how that affects it leaving has been difficult.

Thanks for the input, Mike.

I know most info available is for getting what kind of spray pattern you want and how much of an overall diameter of coverage you need, nothing more specific.

 

[btrueblood]

In addition to Mike's post, you can impinge two liquid streams, and create a fan (which in around 20 or diameters breaks up into a roughly elliptical array of droplets). Hose nozzles have a central pintle which either forces water out into the outer cone for "mist" type conical sprays, or creates a more jet-like patterns as the pintle is extended. A vertical array of simple square-edged holes has a problem in creating the "even showerhead" spray pattern due to water droplets attaching to the horizontal surface and randomly attaching to the streams from the holes and disrupting the flow. You can improve such showerheads by making the exit edge of the hole closer to a protruding tube, and slanting the exit face to give a direction for the inevitable water drops on the face to dribble away. Any hole edge treatment (square, sharp cornered, radiused, beveled) is also going to degrade over time due to erosion, corrosion, or deposition.

 

[hoffmesc]

There's a lot more to nozzle design than you'll find in any book. The technical know-how is kept close to the chest of all the nozzle mfgrs. Your best bet is to contact one of the guys Latexman suggested. With regards to patterns, you could have a solid stream, flat spray, full cone, hollow cone, square full cones, etc. Within each of these, you have a wide range of flowrates possible, multitude of spray angles, varying drop size distributions, etc. Changes in pressure, viscosity, surface tension, specific gravity, will all greatly affect how any single nozzle performs and its spray characteristics, let alone physical design aspects. Contact a rep for one of the mfgrs and tell them what you need. No sense in spinning your wheels trying to reinvent it.

 

[berkshire]

I used to buy spray nozzles from

http://spray.com/

They will make you anything you want, if they do not already have it in stock.
Will they tell you how they do it , not a snowball's chance.
B.E.