This is super COOL! great work. I have seen them in the museums before but never though of putting one in my house until lately. I just bought a 3 disc ultrasonic fogger to humidify my home. and while i was looking for a cool way to use the fogger I came upon your build. BY far the coolest one I've seen. I love the wide pickup area of the bottom disc and the instability of the vortex leading to it wandering around a bit. In short I want to build one just like it!
I saw you used 50mm upright pipes. Any words of wisdom on "sheer hole" spacing and diameter? I remember in one of your videos you mentioned to have at least one hole below the mist source unless you were using a flat base. Think any 50mm computer fan work mounted to the top of the pipe blowing down? I know you mentioned that the velocity is not as important as the direction, But a 50mm fan is a bit smaller than the cage fans you used.
The top fan looks easy enough, Find a "quiet" 8"(200mm) fan and have a good speed control?
The mister section - I'm guessing you are still using a fan to push the mist up out of the reservoir? the acrylic is a great idea with the moisture. I think you said the hexagon was ~ 1 meter in diameter(i'm guessing to the outer points, or across the flat sides?). Would that make the "disc" about 600mm? I like the way the mist lazily drifts out of the holes and gets whipped into the vortex. Any comments about hole diameter or spacing on the disc?
I hate to be compleatly un-creative and attempt to copy your dimensions to a "t" but I've never built one before and if I'm going to put the resources into it, I cant risk it not working. Any help you can provide would be awesome! I want to start cutting ASAP
Thanks!
Dan
Hi Dan, glad you loved the build. Been a bit busy, so apologies for the late reply.
The dimensions for everything in the machine were really just pulled out of my head, there was really no calculation to anything at all. Getting a vortex to form is very easy as long as you follow the basics of vortex physics.
The shear hole size and spacing is not at all crucial, however you want to ensure they're small enough that you actually get a bit of forced airflow out of them. This will vary depending on the size of the pipe and fan you use, but remember you can always add more holes or make them bigger, but not the other way around, so start off small and largely spaced and see how you go.
The blower fans I used are hugely overpowered for the size of machine I built, however because they are located around the outside of the machine, they also act as a barrier to outside wind. I wanted the option to be able to use the machine in a somewhat drafty area without having to worry about enclosing it. In a still environment the vortex at max speed is quite impressive, I did stick a pressure sensor into the eye of it at one point and observed a 20Pa drop in pressure.
A 50mm fan atop the pipes will probably work, but I'm not sure how tall you're planning on making the machine or where you plan to run it. I can say for sure it'll be a lot quieter at max speed than my machine however
Basically as long as you can slightly feel air coming out of the holes in the pipe, it'll work. In a still room, the fans on this machine barely have to be ticking over for a vortex to form. In fact, I much prefer the look of a slower, wispy, more unstable vortex than a high speed one.
The size of the top fan also isn't too critical. I could probably make my machine work with a 120mm computer fan in the top, I just went with larger once again, so I could have a more powerful vortex.
The hexagon is around 900mm "diagonal", yes. It was constructed using a jigsaw so it's not hugely accurate, but close enough. Your guess of 600m dia for the acrylic was spot on
The machine uses 4 misters, which I've wired up in banks of 2 so I can have either 0, 2 or 4 enabled at a time for various fog density. They are just sitting in a small plastic storage container with a small blower fan to force the mist out (way, way overkill, a small axial fan would be more than suitable, I just had the blowers on hand). The container has a PVC fitting mounted in the lid, which a large flower pot base with a small piece of pipe attached just sits into. This allows the water collecting in the pot base to drain back into the fogger tank, and you can easily remove it for cleaning. Here's a photo from testing just to give an idea:
Of course it all increases in complexity once you add the float switches etc:
I was having issues with water siphoning out of the larger reservoir tank by itself, thus the weird combination of pipe fittings on the right. Allows a bit of an air gap to stop the siphon
As for the holes in the fog plate, once again, not really critical, and depends on your fan mostly. I would opt for more smaller holes rather than fewer big holes, as it's not as easy for stuff to fall down into them, and they don't disrupt the airflow on the surface as much.
The vortex will suck fog out through the holes on it's own accord, so it's not really crucial that fog is actually shooting out through the holes. Once I have the machine with me again, I'll probably add more holes so that the fog seeps out a bit slower instead of in jets. But once again, just start off with a few holes, and add more until you're happy.
The extra hole under the fog plate is something you can do as an alternative to having a separate fan just for the fog, but requires the base of the machine to be fairly well sealed. Not needed if you have a separate fan.
There really is no exact science behind building one of these machines (well, I'm sure you could calculate everything out if you really wanted). I've built a heap of them, from tiny 30cm tall desktop versions, to this one standing over 2 metres, all various different designs, no calculations or simulations of any kind, and all of them have worked. Vorticies can be fussy, but just give some spin/shear and some updraft and it'll work. Oh, and let me know how it goes if you decide to go ahead, of course
