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  1. #1
    Extreme Koi Member Rank = Nanasai NickK-UK's Avatar
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    Post filter fines/polish sieve?

    I was thinking how, in a gravity fed system, you could produce a post-filtration sieve.

    Requriements
    * low maintenance with automatic waste removal and cleaning - so this should be able to run for a 2 week stint without maintainance (enough for a holiday)
    * 30,000 lph capacity
    * 10 microns would be awesome but you're looking at £333 for a mesh to give an idea of cost. However going slightly larger is cheaper so 20-25 micron is a good starting point.
    * positioned post drum and bio to polish

    Flow rate is a product of mesh open area per unit, dimensions in units and the pressure applied.

    So our pressure is very low - it's gravity fed and there's a low pressure applied to the mesh. Without enough area, to allow the flow rate through the mesh open area we get back pressure.

    4" => PI*R^2 = 3.142 * 2*2 = 12.568 square inches of water area (ideal flow)

    So - first flow rate:
    Micron #sieve standard % of open space wet surface area needed
    25 #500 25% (twill) 4" pipe = 12.568 / 0.25 = 50.272 sq inches for clean flow. or a 7.1" x 7.1" screen = 15,000lph clean

    30,000lph = 2x4" = 25.136 / 0.25 = 100.544 sq in clean flow or 10.1" x 10.1" screen for 30,000lph clean

    With a 50% waste load max surface area reduction we need 202 square inches of wet filter area or a 14.3"x14.3" screen wet area.

    With a 75% waste max load surface area reduction we need 402 square inches of wet filter area or 20.1"x20.1".

    For example 25 micron mesh: https://www.themeshcompany.com/produ...33.html#SID=61

    The flow rate would also be constructed by the mesh itself - turbulence, back pressure, event the supporting frame that is required to support the mesh - Personally I'd probably go over kill and simply go for a 20"x20" wet screen area. Now if that's a drum, that's 20" of the drum diameter in the water of a 20" long drum. For a mesh gravity sieve that's a 20" wide sieve with a longer screen because the water isn't presented straight at the mesh and there is a slope required (you could widen the sieve but remember the flow rate has to flow over the entire sieve width.

    So I got thinking about vortices. They're used to separate fines under high pressure, but what if they're used to break up the flow across the mesh - kind of like sweeping a curved mesh.

    IMG_7895.jpg

    Then the idea is to concentrate waste at the tip of the cone, then allow an automated valve to open and close, using the water pressure to flush the waste to drainage. This idea doesn't use gravity and the water to push the waste to the waste collection area but uses vortices to first push the water against the mesh, then lift the waste off the mesh (vortices travel through the mesh in both directions) and then that slowly moves the waste down to the farthest end like a conveyor.

    The length of the vortex chain would depend on the flow rate and pressure (power for the chain). Although the chain wouldn't be stable - there should be enough vortices per minute hitting the screen to provide a good action.

    An extension of this idea is to have the mesh like a drum - a pure cone rather than straight sides. This would will the drum cone to be spray cleaned once in a while but not relying on the spray clean to remove the waste.


    1700 litres on 50 watts
    Planned 11,777 litres on 58 watts. 1300l anoxic, 4" airlifts, Solum 16, bio.

  2. #2
    Like a drum after a drum?


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  3. #3
    Extreme Koi Member Rank = Nanasai NickK-UK's Avatar
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    Quote Originally Posted by bigcarpchaser View Post
    Like a drum after a drum?
    Yes.

    Although you'll get larger pieces (filter snail poop) and dead bio bacteria clumps etc but in the main it would be small particles that could be moved with minimal effort by vortices/turbluence. It wouldn't have to cope with the matted clumps of algae for example that have already been filtered.

    I did think about a vortex with a separator plate - like workshop dust filters, but the particle mass vs the water mass is too low, so I suspect they'd simply just flow back out of the filter. Works well on sand as a prefilter for a pond vaccum I made once.
    1700 litres on 50 watts
    Planned 11,777 litres on 58 watts. 1300l anoxic, 4" airlifts, Solum 16, bio.

  4. #4
    Extreme Koi Member Rank = Nanasai NickK-UK's Avatar
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    Just reading up.. it's pithing down outside..


    If you have vortices in a chain they look like this:
    Unknown.jpg
    Source: Going with the Flow | The Dish on Sciencethedishonscience.stanford.edu

    So you can can see what I mean by having a filter and having the vortices push the waste along the mesh. The key is getting the size of the object creating the vortex, the speed of flow and the power. Possibly this may help: Vortex Street - an overview | ScienceDirect Topics

    Now.. covering a couple of ideas at once.

    First is - reducing the damage caused by water falls and water flowing down hill. There was a photo of a drop where instead of using water hitting like a waterfall, the control using a number of vortices reduced the energy hitting the bottom of the watercourse to reduce erosion. There are also on way valves and restrictive created that resist high pressure by using a chain of vortices, causing a vortex created by a side chamber to block some of the flow.. I can't find the image - a hill side and a concrete weir with alternating chambers at the side all the way down the hill side to control the water and prevent damage without moving parts.

    This is a neat paper - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3765293/ - this is using a vortex to manage the water being drive through a pipe with a junction. The pressure of the pipe outside from the junction etc can be tuned and it separates particles according to size. Including an example of separating all the larger particles. It needs a laminar flow by the looks of it using the 'sorter' at the start. Now a flow rate of 2x4" is too large to realistically catch all at once. However a chain of these could easily remove all of the fines in a flow of water but the danger is that it will slow/restrict the flow - acting like the like the restrictive valve.

    So back to having leaky walls - I've tried to show my thinking here - the mesh walls (blue) and the push of the waste to the walls (green) and lift of waste from the walls (red) as the vortex returns. Input from the left, outlet from the right - waste concentration point in the middle right.
    Unknown - with arrows.jpg

    This was inspired by watching a couple of flows of particles on the Draco drum, move both through the mesh but also return back through the mesh caused by turbulence.

    Using a stainless steel coffee fliter cone would give a good approximation, scale down the input and use an obstruction to create the vortex chains.
    1700 litres on 50 watts
    Planned 11,777 litres on 58 watts. 1300l anoxic, 4" airlifts, Solum 16, bio.

  5. #5
    I think I see where youíre at, instead of a parabolic sieve itís conical?
    How about an adaption of this method?

    https://qc-teichfilter.de/english-site/


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  6. #6
    Extreme Koi Member Rank = Nanasai NickK-UK's Avatar
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    Quote Originally Posted by bigcarpchaser View Post
    I think I see where you’re at, instead of a parabolic sieve it’s conical?
    How about an adaption of this method?

    https://qc-teichfilter.de/english-site/
    I've seen that before - basically an inverse drum. Only issue I have with that is the pump is running all the time although that could the driven by air jets through the mesh instead either by a back rinse water 'burp' of air, a constant lift or simply using air jets to dislodge the waste. Air may cause the fines to float with their own little bubble but the resulting foaming may also help remove some dissolved organics like a fractionator.
    An alternative - rather than have a spray bar is simply have a propeller that forces the liquid back out - unsettling the waste. That way it only needs triggering once every so often
    The plus point is that the entire mesh is used as a wet area.

    On the vortex idea - I was thinking of a more aggressive version that could be done using Taylor-Couette flows - having a spinning cylinder inside with a mesh being between the wall and the internal cylinder. Depending on the setup - you could get either stable or unstable configurations of vortices you don't simply get stuff stuck to the mesh but builds up.

    Only issue with agitating the water too much is it breaks soft fines up further. So you want a strong enough vortex to interact with the fine but not strong enough to obliterate it.

    I was thinking horizontal rather than vertical for the 'drum' but horizontal would work - even two (one for each outlet). However adding gravity provides additional force for faster coalesce. Thinking of rotating upwards and reversing - so the water enters the opposite way around as a ring and the obstruction then creates a ring vortex that travels down the mesh, unsettling the waste towards the outside edge of the pipe - perhaps a but then comes - a ring of holes which could get blocked so not perhaps the best way unless the holes are large and a air-lift-esque outer chamber then takes the waste and a valve operates - the water still forces the waste out through the output pipes to waste.
    1700 litres on 50 watts
    Planned 11,777 litres on 58 watts. 1300l anoxic, 4" airlifts, Solum 16, bio.

  7. #7
    Extreme Koi Member Rank = Nanasai NickK-UK's Avatar
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    Interesting paper in making a concentrator using a TC with cylinders and a membrane: N

    This is seems to be very close to my idea about using TC and a 25 micron screen between. The concentrate is the waste.

    Also seen an interesting idea of putting air into the bottom - essentially being like a fractionator. The bubbles then are torn apart by the vortices.

 

 

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