Design of small water nozzles for smooth flow

Hi,

Was wondering if any one else has come across this or can provide any thoughts.

I am trying to make a small desktop version of something like the video below.

Nothing as fancy but i would like to use 32 water streams to create a desktop clock. and the device will be about 30 x 30 cms.

The only difficulty is how to control the water streams

  1. using a jet / pump would not work, first it would need to be able to be switched on and off very quickly and all 32 jets would need to be highly accurate and repeatable.
  2. using standard solonide valves for small stream of water is not accurate due to the time taken to start stop flow and the influence of surface tension and acceleration

so my thought is to create a system were the streams are constantly falling / circulating and then using a system of solenoids to push a surface to divert the water away

Some


thing like this,

that can be interlinked to give this

So as the solenoid pushes forward it divers the stream over the opposite lip where it drains back to the bottom vie the frame.

When the solenoid is pulled back the water drops though the middle slit.

My problem at the moment is getting the nozzles to produce a clean laminar flow.

Working out how to get the solenoids to operate at 160HZ. In theory it will take water about 0.2 seconds to fall 30 cm's and if i want a "display resolution" of 32 X 32 it will need to be able to turn the stream on and of 160 time per second :slight_smile: It may be at this scale only patterns can be produced but i would like to see if i can get get it so i can make this into a digital clock display.

You need to find a fluid dynamics forum.

1 Like

This falling water word display might be more fun. I saw it at MONA in Hobart, Tasmania a few years ago.


@jremington

the nice thing about this is you can use a bitmap image and simply turn on the streams based on the 0,1 cycling though each line in the image every 6ms (which might be hard to reach with a solenoid) and then you could form and image.

So this is pretty much exactly what i want to do and using it to display a digital clock. so each second the time drops down. but you could just as easly make it drop words.

Maybe a clock / calendar

Short video of the MONA display: Falling Water Words at MONA in Tasmania - YouTube

Obviously, such fast solenoids are available, but they are probably rather power hungry.

You want to project a clock on the back of a curtain of water drops?

No. See the thread.

It may be cost prohibitive but you might consider automotive fuel injectors, they switch very fast. Perhaps a junk yard could be a source.

@johnwasser.

No, you sue the water jets to form patterns by turning them on and of in sequence. so you get the appearance of an image falling.

jremington's link to the falling word video shows it well

@jremington,

For the room size displays the solenoid speeds can be quite a bit slower if the dot at the top of an "i" is say 10 cm tall then that an on off time of about 0.03 seconds. but when you get down to a desk top model you would want this to be maybe 5mm so needs to switch at 0.0015 seconds.

A 15ms cycle time might be pushing things with a solenoid, its hard to find specs on a datasheet that say how quickly the can do a complete cycle.

You do know that the images in the water stream in the link you provided are PROJECTED onto a wall of water.
The streams are turned on and off just to control the reflective surface for the image.

Have you calculated how fast you need to turn ON and OFF a valve, or move a shelf back and forth, to just get the 3 cross bars of the number 8 to stay in frame as it falls in 30cm?
Look how big the MONA fall is, try and count how long a part of a character is actually in the air.
In fact a bit of research with a media player will give you accurate answers.

With the diameter of each stream 32 in 30cm or less, will surface tension even allow you to make very thin streams.
You may need to add a surfactant or change fluid viscosity.

Tom... :grinning: :+1: :coffee: :australia:

@TomGeorge.

I was looking at the effect of the water like a 4:29 where rings are dropping. yes the do in that show project images as well. I saw a show like this live in Holland a few years back the the combination of water and light is brilliant.
For a desk to version i am assuming it will be a square display and the horizontal length is ~32cm. based on which means the drop is going to be the same.

and water will take ~0.25seconds to drop this distance (surface tension in a stream means it will be slower as its not in total freefall but this is worst case). Water from a 3mm nozzle will just about keep to a continual stream over the distance if the stream is Laminar at the nozzle. (tested this just using thin sheet rubber with a small hole)

assuming i want resolution of 32 X 32 this would mean i want to be able to interrupt the stream 32 times during this 0.25 s time frame. Or at 120hz, to get 1cm high resolution. Also important it how fast it moves in and out of the stream will determine how clean an image.

I know that electric fuel injection system can run at >100Hz and do so with high accuracy opening / closing with in this time frame. But they also run using high pressure and believe some use the fuel pressure to open or close the valve rather than a return spring.

There are other options than a solenoid moving a shelf, with one possible solution to use an air jet to blow the water away. Again though in manufacturing using air jets to "knock" faulty products off the production line and for sorting is items on conveyer belts traveling in excess of 5ms (twice the speed of what the water will fall at).

So solenoid cycling at <10ms or 100Hz is possible, What i plan to do is get a few solenoids and testing to see how fast they can cycle in a test rig and what is the shortest intervals i can get. then use this to decided the over all size and if it can get some thing "desktop" rather than room scale

:slight_smile:

Thinking back on some earlier work I did with fluid I can suggest some concepts.

  1. Laminar flow typically occurs when the tube/pipe length is at least 5 diameters long.
  2. Interior must be dead smooth with no internal burrs.
  3. Exit must be as close to a perfect cut as possible, again burrs are not your friend. I can't be sure but this requirement suggests your nozzle in post #1 will not work.

Hope this helps.

Hi, thanks that is really helpful as the nozzle on my design is tapered inside. and the exit is ver thin so not perfect. The easy way to fix this is to print a thick lip and directly on to the print bed should give a very clean edge.

Taking what you say i am going to create a number of test nozzles to see if i can get one I can reliable print on resin printer to work.

Thank you

Sounds like a good approach. Be cautions, I'm not sure a 3D printer can print an exit smooth enough.

To get a better understanding of the flow I suggest you go to a hardware store and purchase some small diameter plastic tube of a length 20 times the diameter. Cut the end with a razor knife an see how good it works. If it works the way you want, shorted the tube until you see the flow shape degrading. This will give you a feel for what matters.

If all goes well and you start printing them, you may find you need to purchase a small reamer and clean out the ID.

Wouldn't that be expensive and take several years to go through the courts?

I think you have misunderstood what's happening in the video you linked. The falling words display is completely different from the effect you showed in the video.

In the falling words, the characters are built up as you describe, using solenoids to create the vertical streams of different lengths required to build up the character. These drops are illuminated by a light source which is lit continuously. The important point is that these characters are made from water which must fall at the normal rate of acceleration due to gravity.

In the video you showed us, the patterns can move in any direction: up, down, and sideways, and at any speed. Or they can remain stationary. This can only be achieved by projecting a picture onto a continuous curtain of water.

To summarise: where characters are produced by timed pulses of water, the ONLY effect possible is for them to fall, accelerating due to gravity. Where patterns must do something other than fall downwards, they must be projected onto a continuous curtain of water.

So, these are two completely different approaches. For your clock display, you surely want characters that remain steady, so you can read them. The only way to achieve that is by projecting onto a curtain of water, not by timed solenoid pulses.

@aarg

I have heard that they have very poor defence, they start of putting a lot of pressure on, but it falls of quickly and before you know it is just a wet drip.

2 Likes

@SteveThackery

I have actually been to one of these display in real life. the ones with projection use a mixture of both. the first does not just use projection. It is a mixture of projection and water patterns. In some display they do use strobes to illuminate the water that is dropping like the clock video to give the appearance it is moving up, but having it of set to the rate it is dropping.

In the first video there are two effect going on, the smooth motion is light / video, the curtain effect and other parts are the control of the streams.

Sitting up close to one of these displays it is very clear to see what it projected and what is the water.

And no i don't want a clock that remains steady i for a clock i want exactly what is shown in the dropping word video. if you strobe a light at 4 times a second in a dark room (the time water drops is 0.25 seconds on the size of device i am planning) in time with when the "word" is in the middle of the screen. the same effect you get if you strobe a light on a fan to make it appear the blades are stationary.

But yes I am aware the first video does make heavy use of projection, but that is not the only technique going on. The falling patterns such as at 3:48 are caused by the water not the projection or lights.

I was thinking of this approach and maybe silicone tubing. I use larger for fish tank and you can get some great flow out of this, and you can get it down to a few mm internal diameter.

be interesting to see what resin printer can do, it goes down to 0.05mm resolution and you can get some very crisp edges.

A lot of this is all experimenting and seeing what is possible. So thank you for the input, its been really helpful and giving me lots of ideas to test out.

Cheers