DIY Water screen

[VJ AIWAZ]

yea we were just screwing around one day with some stuff i had in the shop it was more of a proof of concept

but yea i know the rounded lip was causing most of the trouble and the pitch of the container
also the water needs some turbulence because when we projected video on it it need a lot of power to get a small image

[FourDee]

Maybe you could add a kind of rake on top of the lip to create some turbulence

[Doc]

What about a half round 6" aluminium rainwater gutter, fixed level, with an intermittent slot cut in to the bottom with a jigsaw?

Like this:


---------- ---------- ---------- ---------- --------- ---------- --------- ---------

The small sections of no slot would keep the structural integrity of the gutter and create turbulance in the falling water and a simple float swith could control the charging pump.

[liteglow]

I think you get a better result if the water is laminar before it fall out from the lip .
If there is turbulence in the water when it fall from the lip, it will not travel perfectly down...

[absolom7691]

I know this thread is older, but it doesn't look like anyone got around to building any of these. Anyone got a working one? Water or fog? I, too, am interested in making a fog screen. Looks very nice! As others have said, that video and on that page, there is no really detailed build steps (like stuff on MakeBlog).

For the fog screen, It looks like he is using a clod flow (home made) fog machine, not necessarily "cold steam" (atomized), like in the description. I found a website that sells big "cold steam" ultrasonic foggers: http://www.mainlandmart.com/foggers.html. I wonder how these would stack up since the fog will evaporate rather than hang around like conventional Glycol.

[The_Doctor]

Got some ideas about that...
There are things that make air curtains for industrial cooling, paint drying, etc, they rely on a very high pressure from a very fine jet to train airflow from ambient air around them. They move a greater volume of air than is first propelled from the jet. They are also fairly directional, and can withstand some lateral air pressure.

If you had a few of these jets parallel but moderately widely spaced, you might be able to train a fog stream into a curtain with them, even against the pressure of a local light breeze. Similarly a fine water spray might form a curtain. You'd need a LOT of pressure, and it might result in audible background hiss, but it might form a tight curtain where gravity alone can't do it.

[liteglow]

I have a 9 head mist-maker !
And I did once try to make a fog-curtain.

I did use many straws in a line with a fan to make the wind so the mist blow.
The straws make the jet laminar so there is no turbulence.

I did never work any more with this, it did take to much time and you need a water tank +++..

here is a tiny tiny tiny test of a 10min DIY mist fog screen :P haha:

http://www.youtube.com/watch?v=5-Tgh_33Skg

This was done from a tiny tiny 1-head mist maker!

[The_Doctor]

I thought of those but assumed (wrongly perhaps) that they wouldn't make enough mist. It's very wet stuff but in some places that could help with the atmosphere. Try it with tiny very strong jets if you can. RS Components sell the things I was describing. Expensive, but once you know what to find, there might be cheap ways. Actually gas jets for gas fires and pilot lights out to do it. A small workshop air compressor ought to be strong enough to drive them. A very thin mist curtain might be great too, it might look truly invisible, but show a strong beam making an image apparently suspended by nothing.

[absolom7691]

Very nice, I didn't see that video. I think I missed that post! You should finish it, if you have the gumption. Looks awesome.

I was thinking that a regular household AC/Furnace squirrel cage blower would do the trick. Those move a ton of air and are not that loud. I would like to try and build a 5 ft wide cutrain. I think I will give the laminar flow (sandwich) design a try. I will most likely use a glycol/glycerin fogger.

Anyone make juice before? I am wondering if I make some and go light on the glycerin, if it will dissapate faster. That way, I could keep a constant flow without filling up a room completely with fog. Has anyone tried this with home-brew juice?

[liteglow]

The biggest mist maker, make allot of mist
And actually it`s not so wet as you should think..

after some time I would not recommend having it indoor in a small area.
But if it was at high pressure (if that is what you talk about) maybe it can make a nice curtain.
Again, if you have to high pressure on the mist, it would maybe just be one big sky of smoke...

[absolom7691]

I am seriously looking at that 12 head mister maker. I am just wondering if it will generate enough for a 5 foot wide curtain.

[absolom7691]

That would look neat if it were barely visible. That way, you could show your graphics and then beams without a noseeum net. I was probably going to try this... now, I am definitely! I will post pics. I just need to get a few days off to break ground.

[Things]

To make a 5 foot long curtain, it may be better to buy a few separate misters than just 1 big bank of them. Like you see in liteglow's video, the fog doesn't come out evenly, and could ruin the effect. That or some clever piping system to get the fog even.

My thoughts are that maybe a continuous fog machine with volume control may work better than water based mist? It would hang around much longer for large curtains.

[absolom7691]

That is what I am going to try at this point, a regular fogger. The thing I want to try and avoid though, is the fog lingering. I am wondering if I mix up some fluid of my own and tone the glycerin way back. I don't know what the ratio is for regular fluid, but maybe cut back the glycerin by half. Hopfully it will dissapate faster so that a continuous flow would not cloud up the room.

[liteglow]

there was a link here some more post up...
That is the place where I did buy my mist maker.
they have both 110 and 220 volt.

i would recomend you to have 2 mist makers, and use 10-15x with 120mm computer fan to blow it maybe ?
I have seen other fog screens, and they use many many many computer fans.

in my video the mist is going UP !
But it will be allot better when the mist is falling down....

if you want, i can take some more videos of my mist maker

[The_Doctor]

Some of you keep missing the point. You want HIGH pressure in very fine jets. Think about it. The high speed of the laminar flow is very important, a fast flow causes low pressure to train the higher pressure of surrounding air (plus any fog or mist) into the low pressure field so it will stay there for a greater distance. (It's the same reason aeroplanes fly.) You'll have to experiment with best even-ness for diffusing the light beam but no amount of AC fans or computer fans is going to do anything but piss you off. All that would do is give you a second-rate hazer. What you're after is a little local jetstream.

[liteglow]

Doctor: I dont want to make discussion about high power air, and low power air.
As I have not yet tested out high power jet air with mist

Maybe you are correct....?

But the fact that I know the laminar water jets DONT like high pressure water.
My guess is that a mist "floating free" in the air will not stay laminar when it jets down in high speed.

The light weight particles that fall down will not stay on course when they are pumped out in extremely high speed.


I base this on the PROfessional fig screens that only use small amount of wind to push the mist out\down from the machine.


But again, I have not tried anything with "jet" speed, so maybe it can work...

[The_Doctor]

I mentioned air jets, not water jets. Water jets are different, you don't want too great a change in pressure or you end up with an aerosol spray.

Back to air jets.... by 'jet' I don't mean screaming supersonics. I just mean jet, literally, a very narrow fast flow. To start with the jet has to be fast enough to propel mass firmly in one direction, and to create a low pressure region in the flow once the initial expansion is done. The speed will drop as air from outside is 'trained' alongside the main flow, as kinetic energy is exchanged between the two regions. Don't take my word for it, people use this a lot in industry, it was news to me once but easy to see as true just by thinking about it. There is no 'maybe' about this. Mist or fog wouldn't be propelled at high speed, you just have to produce it close to the start of the flow, and it will be drawn alongside it before it merges into it. It might drift fairly slowly if it isn't directed right into the flowing region, that's another aspect open to experiment, the effects on angle of intercept and speed of fog production. What matters is that the fast flow of one fluid in another of similar density will create a region that is clearly defined because the faster flow has lower pressure, so its content is maintained in a narrow stream by the higher pressure alongside it.


Regarding 'professional', that doesn't always mean best method. You only have to see the way PRO is slapped on seriously dodgy cheap audio stage amps to know how tawdry and hidebound some PRO practises really are. PRO very often means 'as cheap and basic as possible so no-one cares if the club punters smash it up'. Hardly a guide to innovation. Until the late 80's a 'professional' microphone meant a moving coil type barely fit for broadband speech. Anything else was considered a 'studio' mic, and too fancy for 'real pros'.

Another obvious merit to the jet flow idea is the source can be a very lightweight narrow pipe fitted with jet nozzles. In a large installation it would be a very discreet system, finer than a curtain rail. After the start, the mass of fog and gas will be moving downward in a stream that gravity will help with. If you can chill the fog before it meets the laminar flow that will help too. it might even be possible to get the chilling done by mixing something with the air fed to the jets, but I don't know a cheap or environmentally kosher way to do that. Best to chill the fog as that's where most of the mass is anyway. Cold fog alone tends to drop like a slow ghost of a stone.

Edit: Actually the bulky pipe needed to duct fog to the top of the curtain would make the thin pressure rail pointless. I mean why hide one if you can't hide the other? But then again, in showbusiness, part of the magic is in illusion, and things that CAN be hidden always offer more scope for good illusions.

[absolom7691]

I think a large 1/2 hp squirrel cage blower would provide enough pressure to feed into the laminar tube system that I need to build. Should be fairly high pressure. Those fans have enough guts to push a/c through a two story home. Should work here. I am thinking of trying drinking straws for the jets. Maybe making the bank about 20 layers thick of straws. That is going to take a LOT of straws. I am also wondering... would it be best to use a thin felt or window screen to stablize the flowing air? I want to elimiate the buffeting that you would feel from a conventional fan. That way, it is just smooth and constant pressure. I think it would also equalize the flow over all the jets so that they are at the same pressure. Or, now that I think about it, incorporating your idea of a pipe with many holes in it. That would spread the air flow out so there is no 1 inlet but rather several all the way across.

The_Doctor, I apologize for not knowing your name, but what do you think? Very high pressure, across several outlet holes that feed into the chamber before exiting out of the laminar tubes?

The fog, be it atmoized mist or glycol, i think that will be the last thing I worry about. The laminar flow, high pressure creating a low pressure zone is my first obstacle.

[The_Doctor]

No need to apologise, I rarely tell people it because it probably doesn't sound any more believable than this one. It's a sort of open secret, it's Crow. Alias Lostgallifreyan in several bits of net including eBay. I think a few people here knew all that but not many. I like using this netname though so I'll stay with it. Old habit.

Anyway.... I saw a YouTube page:
http://www.youtube.com/watch?v=OV-IazRk0sU
Didn't see the vid, I rarely install flash in any session, but I read the comments, people doing the same thing as in this thread. I also looked into 'air knives' and the Coanda effect.

Apparently compressed air isn't as efficient, nor are separate nozzles. Ideally a 'plenum' space formed by a pipe having a teardrop (or apple pip) shaped cross section, with the slit at the sharp end, is most efficient, and is best fed by an industrial blower, perhaps the kind used for inline pumping of air in 100 mm ducting might be enough. High pressure CAN also be efficient but only if the coanda effect's main business is confined to a ring nozzle a bit like that inside a 'vortex tube' as used for heating and cooling stuff. In this case it would circulate to form a small ring surrounding a region of low pressure (not by accident are vortex tubes sometimes called tornado tubes). This low pressure draws in high volumes of ambient air and a bias to exit the ring plane in one direction pushes all that air in high volume and high speed in the same direction. Not saying that this is any good for fog curtains, but it's interesting and might have some use in laser shows, for bulk diffusion of fog perhaps, as the fog won't get reduced by impacts with fan blades.

Basically it seems you can use an AC blower, if it's an inline duct thing, but it still has to feed the flow generating slot thing, a kind of big gentle air knife. Someone mentioned a 95% efficiency for the method but I don't understand the context for the claim so I won't do any more than mention it too. Separate jets drop the efficiency to 60% as claimed in that same forgotten reference, but it is easier to build that way. I think a lot of trial and error might be needed to get the slot or jet aperture size (and separation) right, and the flow rates, etc, as well incident angle and speed at which fog is passed to the main flow.

[absolom7691]

Thank you very much for all the info. I will check all this out. I just bought 1000 drinking straws ($3). Cheap enough to try out. I am going to try and knock together a small one and see how it goes. It looks like a have a bit of trial and error in front of me, but that is the best way I learn. i will try this out and see the results. I am going to also look into your suggestions as well. I have several months before halloween so, I have some time!

Well, seeing as how this thread was titled Water Screens.... I think, once I begin construction of my test design, I will get another thread going.

Thanks again for the info, Crow. My name is Brian, BTW.