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Thread: vortex size

  1. #21
    Oyagoi bekko's Avatar
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    I understand the small vs. large particle differences, and drag coefficient of the wall. But, I am not positive I understand the force that pushes particles towards the center of a gyre.

    Increasing the drag coefficient of the wall surface may not be advantageous. Yes, it will result in more debris being pulled out of suspension. However, the goal is to remove the debris from the system entirely before it decomposes further and releases nitrogenous compounds and DOM to the water. Barring micro-screen filtration, the most efficient way to remove debris from the system is to "spin" it to the center of a swirl separator where it can be entrained and dumped when the waste valve is opened. By roughening the wall texture, you impede migration of settled debris along the tank surface towards the waste port. This is no better than adding matala mat, brushes or other substrate to the separation tank. Yes, you catch debris, but it is not removed from the system until the substrate is taken out and hosed off. Its a nasty job and it is not practicle to remove and clean the substrate, or to wash down the walls of the tank, on a frequent basis, so the stuff just sits there and decomposes. It is practical to open the waste valve on a frequent basis and dump debris which has collected near the bottom of the cone. But to make it work, the separator tank capacity and bottom slope must be properly sized to the flow.



    I am on the northwest corner of Kaneohe Bay, three miles past Hygienic Store.



    steve

  2. #22
    Sansai Bancherd's Avatar
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    Hi Steve:

    I am sorry, I graduated from Castle High School in Kaneohe in 1971(oops, my age is showing). My parents' house was on top of a hill on Lilipuna road, overlooking the valley and perhaps part of Kaneohe Bay. I left the area for "mainland" right after my graduation and can not remember much.

    I plan to use microscreen in my next pond, but have been thinking about "vortex settlement for a while".

    I have to think about how to explain in terms of forces pushing the particles towards the center, but it is fairly straight forward if you looked at it from the energy point of view.

    I did not mean to suggest that we should roughen the wall's surface to the point of trapping particles. I think the data presented by "Peter Menear" was very convincing. He could improve the effectiveness of the "vortex chamber" by placing sheets of inert materials with vertical ridges in the "vortex". I will have to dig around my notes, "Peter Menear" posted the data on NI-board a few years back.

    I have an idea that might work. How about putting in a vertical sheet of plastic screen material, spiralling towards the center of the vortex. Water enters the vortex at the outer edge of the spiral, then exits the vortex at the center of the spiral. This should improve the effectiveness of settlement without trapping particles on the walls.

    By the way, thank you for the discussion. This is very refreshing.

  3. #23
    Oyagoi bekko's Avatar
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    How about a really large vortex which is followed by microscreen. Could be designed so that the vortex could be taken off-line and used as a Q-tank as needed. When the vortex is off-line, the microscreen cleaning requirements would go up (daily?), but water quality would not suffer.

    Castle HS is at the other end of the Bay - drive past it every day.

    steve

  4. #24
    Daihonmei
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    first filtration. It has already been discussed and accepted by many that the best of both worlds is to HAVE both worlds.....a microscreen in a suitable vortex chamber....the vortex chamber removes the dense particles so the micro strainer only has to deal with the floaters.

    now as to where the heavies settle on the bottom......

    the movement of the "heavies" to the bottom is as I have already stated. HOWEVER once the particles are on the bottom they are dealing with another dynamic...their interaction with the surface of the bottom. This interaction is different than the interaction of the heavies with the wall because GRAVITY forces the heavies to have a greater friction with the bottom.
    And consider this. The heavies will still move if the water movement is fast enough. Yet as the heavies randomly bounce around in a circle if the current is fast enough to move them, and tey will stack up in an area where the movement is slower...just as trash and snow stacks up when the wind moves it.
    Now I will stop talking about poop in a never-ending swirling toilet.

  5. #25
    Oyagoi bekko's Avatar
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    Gee, before you stopped talking, I was hoping you would try to explain why debris is moved to the center.

    steve

  6. #26
    Daihonmei
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    The problem is that I don't mind talking physics I just hate typing....but, the reason the stuff collects in the middle is the same reason snow drifts form. The water's speed near the center is slower than the movement of the water towards the outside. The water must be a certain speed in order to break the hold the particles have on the bottom due to gravity, The speed in the center is not fast enough to break this bond.
    While the particles that are on the outside move in a circle they also bounce away from and toward the center. When they move randomly closer to the center they may move into an area where the current is not strong enough to keep them moving. And there they stay. While those that move to the outside contact the wall and stay in a high energy area and continue to move util they "find" the dead zone.....just like snowflakes and trash.

  7. #27
    Jumbo
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    This is all being made more complicated than it needs to be--

    a settlement chamber is just that- it settles out heavy material ( heavier than the weight of water) by slowing the water or by creating counter eddies to drop the solids out of solution. So you can have a very large chamber to slow water rapidly entering from the drain OR physical barriers like baffles to slow the water physically ( like an oar in the water) so that counter currents cause solids to fall out of circulation.

    a screen or brushes , on the other hand , act as barriers to block solids being carried in water currents. This strictly a physical barrier idea.These things strain or trap waste from contining on into the next chamber/section.

    a vortex, a true vortex, is supposed to be a circular chamber that sets up a gentle swirling and allows solids to be pulled down the OUTSIDE walls of the vortex. This is a classic setting up of a boundry layer along the wall where water near the walls does not move at the same speed as the the rest of the water due the friction of the walls. The solids slow at that wall area and 'fall' out of solution. The trouble is, most vortexes are not size correctly for the water flow and therefore spin too quickly. This instead, results in a movement of the solids into the center of the current where the material tends to settle out. This is the least efficient because the exit pipe is either in the center or at the opposite side of the entry port and will once again pull waste back into solution. The exit pipe needs to be set when you actually know which method you wise to incorporate.
    The ideal is to have a properly sized vortex operating on true vortex principles and the pick up in the center.
    JR

  8. #28
    Oyagoi bekko's Avatar
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    I must be doing it all wrong because I have always put the the tangential inlet low on the vertical wall, put the waste drain at the bottom-center of the cone, and out the pump suction at the top center near the surface. While the water is swirling, there is a net movement of particles down toward a central deposition zone and a net movement of water up toward the pump suction. I am embarassed to say that I have never owned a Vortex-brand filter, but I have built a few swirl separators. I did not know that the flow was that low in a Vortex. However, since size (footprint) is an issue, I would think you would want to use the approach which processes water the fastest (high unit volume per unit area per unit time). That would make a swirl separator more desirable in many applications.

    steve hopkins

  9. #29
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    Steve, I guess that depends on how efficient you want or need to be? The introduction of the answer unit proved one thing to all who used it in their existing vortex/sump- that is, 40- 80% of the fine materials were being carried through to the next chamber/vortex with the rapid current! So most of these concepts of incorporating centrifugal force and centripetal force in a cylinder are not near as efficient as we once thought. The main flaws being speed of water/ size of vortex and location of exit port.

    centrifugal force- the force that tends to impel objects outward.
    centripetal force- the force that is necessary to keep objects moving in a circular path and migrating inward towards the center.

    In truth, the vortex works on yet a third principle - boundary layer dynamics.

    JR

  10. #30
    Sansai shiromujigirl's Avatar
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    Is the space available to this pond builder a constraint? Because I think he needs an 8 foot diameter settling tank and 1/4 horse power pump for each bottom drain, and a 1/4 horse power pump can pull 5000 gph if you use a 2.5 inch suction line and pond return pipe after the biofilter, mine can anyway.

    When I built my sixth pond and made mistakes with each, by then I was friends with those kings of practicality and droppings, the Sewage Treatment Guys. "Its all about dwell time", they told me as a visited their installation with a kerchief around my face like a bandit, "You need a 15 minute dwell time in a wide diameter tank to give the settlable solids time to settle out".

    Now, I had peered into those 4 foot diameter purpose made vortex tanks that were around at the time, each costing as much as a pedigreed cow, and saw the particles whizzing around at dizzying speed. No wonder we now had to, the dealers told us, buy yet another terribly expensive "peice of kit" to remove the, why, 40 to 80 percent of the particles that went whizzing through the vortex tanks, boundry layer or no!

    So I figured my pump could put out, with the special 2.5 " piping, 5000 gph.The 1500 gallon 8' diameter settling tank I made out of a poly tank from a farm store costing $400 and filled up to 1250 gallon level, gives a 15 minute dwell time. The 4 inch drain pipe from the pond enters the tank 1/3 the way up and makes an L turn. The two 4" pipes to the biofilters are near the top of the water level and draw from the side, (sorry JR).

    Perhaps the pond builder could have one 4" pipe off a properly sized settling tank go to a submerged biofilter and another going to a tank from which the bakki shower drew.

    While I have lain awake nights thinking the same things about forces affecting the particles of droppings as you gentlemen, I have always fallen asleep before reaching any conclussions. However, I do know that this arrangement works. SMG

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