Need help on best slot

[rygh]

So now that I have a long scrubber (22 inches), I am having real trouble building a good slot that evenly distributes the water on the screen.
I have a lot of tools and can make straight slots/holes/cuts/whatever.
This is a basic vertical design. Pipe on top. Singe layer plastic mesh for the screen.
viewtopic.php?f=3&t=645&start=10 (http://www.algaescrubber.net/forums/viewtopic.php?f=3&t=645&start=10)

I tried a thin slot, but not enough water comes out.
I tried a wider slot, but water poured out very randomly, based a lot on how the screen bent back and forth a bit.
I tried short horizontal cuts every inch, which is better, but seems too far apart, and it was a hack on the one with the large slot.
For my old first semi-horizontal, I used holes, but that was a pain.

To be honest, what I have is probably "good enough", but I really want to do it right.

Any thoughts on the best method?

[Bridgeport]

Also been wanting to experiment on a way to get the water to flow more evenly.Most of the time for me ,the water seems to gush towards the end of the pipe. I'm working on gluing something inside the pipe that will direct the flow and get the water to spread more evenly across the slot. Will post my results.

[SantaMonica]

All slots "fill in" as the algae grows. It grows the most where the flow is highest, thus reducing the flow there.

A single layer of plastic canvas should start with a 1/8 slot, then widen slightly to 3/16 if it's too tight. Lift the screen/pipe out of the water while it's running, and see if the flow is constant across the bottom. My slots have a slightly rough fit with the screen, and there are no cross slots.

[rygh]

Good to hear it is self adjusting.
I guess I now have a reason to not bother shading the slot that carefully. ;)

I will probably experiment with the cross-cuts a bit more though.
It is really bad with just a slot. The screen is really wavy in the slot. Maybe I will flatten that as well.

Finally got my new tubing yesterday as well. Made a HUGE difference in flow. So I can cut a lot more holes.
(I was using 0.75" before, went to 1.25". Pump at that head is about 900 GPH)

[sklywag]

A scientist I am not. But using smaller diameter pipe I would think create pressure and force it to come out more at the end of the slot. As larger diameter would give the water space to hit the end of the pipe and backflow a little back to the entrance area. Nor am I a master of my own language.

[Gigaah]

I've had problem in my early scrubber design not shading the slot. It tended to clog up the slot then start spraying out of any open area due to high pressure. It also created havoc on my overflow because of the changing back pressure. I'm no expert scrubber builder tho. I ended up shading the slot and drilling a hole in the end cap of my slot pip for a small relief hose.

[rygh]

Well, after various experimentation, I did manage to get something that worked quite well.
First, I started with a fairly large 1.25" pipe.
Then I made a standard 1/8" slot.
I have fairly high flow, so that was not wide enough, and while good, did not cover that evenly.

I then drilled 3/16" holes in the slot every 1/2".
Basically, making the slot "bumpy", and slightly larger every half inch.
That worked great.
I may make the holes even slightly larger, since I am still getting a tiny bit of overflow out my relief hole.

The "bumpy" aspect of the slot reduces the horizontal velocity component, especially near where the water enters the pipe.

[Gigaah]

Is there any way I can see flow pictures? I've been trying to work this out too and deal with the fluid velocity problem myself.

I might try adding holes to my dual slot design i've been working on. Two 1/16" slots 90 degrees off from where the normal slot is. The screen hangs from shower curtain rings and touches the pipe(no slot in the bottom of the pipe. The biggest problem is it takes about 2" before the water wraps around from the slots in the side of the pipe to the bottom where the screen grabs it. If I can solve this problem with a few holes then I'm starting to like this design more. It won't really fill with algae since the slots are on the side of the pipe and there is not a screen in the way to change the flow. Right now the flow is a bit heavier towards the end of the pipe. I'll have to give the holes a shot next cleaning.
[attachment=0:1ls6f4ub]IMG_3175.JPG[/attachment:1ls6f4ub]

[rygh]

I will try to find some food coloring and take some pics soon.
I have a small bucket of water test setup.
Hmm. Fresh water test. Hope there is no big difference.

[craig1]

Looking forward to the pics on this one. Finally got all my parts today (except the acrylic, that'll come after the bench tests). But I'm having the same issue as you, flow seems to be uneven.

Admittedly part of the fun of having a reef tank is experimenting... Cautiously of course! :)

[rygh]

Took the pics, but then the wife needed the camera. Stay tuned.

Looking closely, the first inch or two is not as good as I would like.
I might drill a hole from the top, just before the start of the screen, and insert a small pipe.
That would act as a baffle, and slow down the flow in the beginning.
And if it does not work, it is just another overflow hole.

I am also considered bringing water into the slot pipe from both ends, but the extra pipes become a big hassle.

[rygh]

Ok, here is the slot, with the slightly larger holes drilled every half inch.
Easy with a drill press, but probably a royal pain without.

[rygh]

Here is the bottom of half of the screen. Pretty good.
I lifted it up. It is really in the water when running.

There are two separate screens in each ATS box. Mostly because that was the size they sold.

[rygh]

Here is the main flow on the screen, looking good.
I tried to add blue food coloring for the pics, but still hard to see.

[rygh]

This part is still a bit of a problem. It is the side where the water enters.
About 3/4" of the right side of the mesh gets little water.
And you can see the horizontal component of the flow if you look carefully.
Probably not helped by where I put the clip.
I am probably not going to worry about it though.

[Gigaah]

I posed the question in a..albiet sorta dead Computational fluid dynamics forum. The only answer from the one person that must go there was to. Taper the pipe, or taper the slit. something to keep in mind.
Go straight to the experts..thats how I do it.

This idea didn't pan out for me exactly. It sort of works but I think the baffels are too large and the flow ends up too much on the infeed end. i started knocking out some of the baffels thru the slit(its egg crate by the way). That helped a great deal but I still think the baffels that it makes are too large. I'm trying to slow the flow down and attempt to even out the flow. It was kinda a hassle so I scrapped the idea..however the concept might prove usefull to someone else. I super glued each end onto the pipe. the baffles break of pretty easy..its the very edge of a sheet of egg crate.

[attachment=1:7rzwe6zs]IMG_3183.JPG[/attachment:7rzwe6zs]

[attachment=1:7rzwe6zs]IMG_3183.JPG[/attachment:7rzwe6zs]

[rygh]

Tapering the pipe and/or slit will theoretically compensate for the pressure difference, and make the flow
even across the length of the pipe. So that helps.
But that is probably easier to do by changing the spacing of the extra wider holes. Say from 3/4 on the pressure end, to 3/8 on the other.

But the taper will do nothing to fix the horizontal velocity component of the water.
Baffles should help that.

Another crazy thought is a smaller pipe. with lots of random holes, inside a larger pipe that has a slot. But a pain.

For now, my plan is to just ignore it. I have so many other things to build.