5' Skimmer Build in Progress

from reading the specs in the AES catalog, it appears that the bubble size of the fine pore stones is about half that of the medium pore stones. I would imagine that this will greatly affect the rise rate of the bubbles.

I have not read what is here... but there is some discussion of bubble rise rates and how to derive them. I have also not read the UCLA paper (are their equations in it?)

http://ams.allenpress.com/amsonline...0.1175/1520-04852000)030<2163:TCBBSS>2.0.CO;2

and look here (this is a terminal velocity discussion... but seems to be in the ball park of what is being hypothisized here)

http://www.ncbi.nlm.nih.gov/entrez/...ve&db=PubMed&list_uids=10397862&dopt=Abstract

Bean
 
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Yes the UCLA paper does some calcs to predict bubble behavior. I tried to model those calcs on lines 48 & 49. I do not believe my calcs on those lines are right. I am fairly confident in the base Re calc on line 51 though.

Dale
 
Back to the dwell/bombardment thing....

It appears as the velocity rises, the dwell time does also. This is counter intuative. (yeah I know... I am stuck on that one silly calc). However it appears that my 4" PVC 4' skimmer plans will only require .4 cfm using the fine pore stones. I will add ports for recirc, but am not sure I am going to hook them up (I do have an extra eheim laying around).
 
Any of you guys ever seen how a Prizm works? Why can't you employ some plastic insert that actually uses the rise against itself? That is what I am going to do. Anyone get that? You create a barrier within the chamber that bounces the bubbles back down into the water flowing downward.
 
as I mentioned Im not sure you can effectively slow the bubbles. my setup doesnt have the capabilities, but if someone can manipulate their flow of water and see if the bubbles change velocity. it seems a majority are uneffected, seems to take less force to accelerate the water around the bubble column rather than trying to hold the bubbles down. there is just nothing to stop it from happening.
 
Maybe a plate similar to a phoban reactor. If you used sponges it may be another thing to clean regularly. But I would think the sponges would just grab the junk off and clog quickly. The plates may make the bubbles combine into larger one too.
 
This gets into reynolds calcs again.

Bubble pull water with them...in turn the counter current trys to push the water back down. The net results is turbulance and the squishing of the lead edge of the bubble. As to how all of this relates to the skimmer and it's mathematical operation... I will leave that to somebody else.

The bottom line is that we want the smalles bubbles possible. Small bubbles rise slower, are easier to "hold down" and do not deform easily. The net result is a very calm skimmer (low reynolds number) and efficient skimming.

Using a recirc pump seems to be a way to get the extra small bubbles, but the turbulance is greatly increased due to velocity. The extra fine stones seem to be out of the question due to their 25 PSI requirement and the need for one mother of an air compressor.

At this point I have 2 choices. Spend ~300 on an ASM or ~300 on a 4" PVC CC skimmer (most of the cost is the air pump). I am curious as to which will be better spent money.

Bean
 
that is why the recirculating skimmers do so well. they pull the bubbles down in the chamber with out causing excessive turbulance inside the skimmer. there will alwayse be some form of turbulance in side the body. you cant do anything to stop that. the bubbles rising will cause that no matter what. but limiting the amount of turbulance will increase skimming ability. thats why bubble king has a defuser in there skimmers.
 
Well I have a bit of promising testing.

I measured my bubble dwell time at 7 seconds for a 55" rise. That equates to 7.86 in/s.

I measured the bubble dwell time at 8 seconds for a 55" rise when I had 7.8 gpm flow. My calculator predicted 8.2 seconds. So my basic math is tracking atleast at this point of the flow. We will see how it progresses.

My margin for error is pretty large. My stop watch is not that accurate, and I am trying to cordinate seeing the bubbles at the same time stopping the pump.

Dale
 
are you mesuring your dwell time by shutting off the pump(s) and then counting the time it takes for the bubbles to finish rising to the top of the body?
 
either way the numbers may be wrong. in my observations it took a few seconds to get the flow going. the first bubbles had to start the current, but once the water gets moving the bubbles moved faster.

I know Im not making this easy to do, but for an accurate measurement, you would need to count a bubble's start and stop within a continuing stream of bubbles. not the first or last bubble's time.

Im aware how impossible that would be :)
 
I have a lot of 4" DWV around.... just stopped at Lowes. 10' Sections of 6" are $35. I may have to stick with the 4" stuff to keep costs down.
 
I counted the teh time from air start till bubbles. I did this repeatedly. I the did air stop till end of bubbles. They were consistent.
 
I just built a skimmer with a 10.5 inch acrylic reaction chamber. The body is 52 inches. There is a 4-5 inch cone riser and a 8 inch
riser tube made of 4 inch acrylic. I am wondering if a Hailea V-60
air pump will do the job on this thing. I built a manifold with 6 three inch fine pore airstones from aquaticeco mounted vertically.
The pump is supposed to be 60 lpm. I am just not sure about the pressure calculations.

Mike
 
Something to consider: if the ultra fine air stones need 25 psi, what about using a regular air compressor? I went to Lowes, and they have a Porter-Cable air compressor - not too big - and it only costs $159. This is certainly in the price range of the other air pumps we have been looking at. Obviously you would need a proper fish room for such a device, but it has the power. I doubt it would as efficeint electrically, but then it would only run a bit to fill the tank and then stop for a while. My only concern: air compressors are not usually run 24/7, so I wonder how long it would last.
 
A big part of the problem with the air compressors is the water condensation/oils used with them entering the water. I guess you could have some kind of filter but I think you would still get some in the skimmer.
 
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