Small tank fluid dynamics

Discussion in 'General Discussions and Advice' started by FransSny, 30 Jun 2010.

  1. FransSny

    FransSny

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    Wonder if anyone can help. I am sitting with a tank 250 mm x 500 mm x 300 h. Corner overflow box ( almost 20 mm space from rim of tank to water level). Here is my problem, as soon as I add flow to the tank (using small via aqua powerhead just over 100 l / hr...cant really as the sticker is worn off :p) it creates a "whirlpool" type effect thus having drips over the sides.

    The only time it doesnt do this is when I put the pump on one of the "long" sides (which is cool now while testing but not practical for where it needs to fit), could this be because of the long narrow design ?

    Really stumped as I cant keep on lowering the overflow
     
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  3. jacquesb

    jacquesb Retired Moderator

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    Frans - might it work if you would use a small SEIO powerhead perhaps, ie a M620? I think that the whirlpool effect might be because of the uni-directional/jet-like water flow coming out of the Via Aqua pump?
     
  4. leslie hempel

    leslie hempel Moderator MASA Contributor

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    mmm interesting pictures are worth a thousand words :whistling:
     
  5. lIghty

    lIghty

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    does it do this when the water is flowing parallel to the long side or the sort side?

    Yeah, like Les says a pic is worth a 1000 words.
     
  6. RiaanP

    RiaanP Moderator

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    Use conduit fittings and have powerhead in the back pointing forward then put a 90 bend on end so water runs the long length of tank instead of the short length.
     
  7. FransSny

    FransSny Thread Starter

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    I added some food colourant to see what happens and it seems like as soon as flow comes from the back (overflow side) and runs along the length of the tank it happens.

    I will try and take a vid with the cell & post, my reason of deduction says that the narrowness & length is an issue..almost like wind blowing down a narrow corridor comapred to wind over a wide area (ok lets not go into the scale of my analogy again)

    This is just freaking me out as it doesnt make sense, the only solution I see is an overflow along the breadth of the back ?
     
  8. mandarinman

    mandarinman

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    use a rainbar unit with the holes in the rainbar just below the surface. if flow is still too great drill additional holes in rainbar unit.. if this fails borrow one of my seios.
     
  9. Reef Maniac

    Reef Maniac MASA Contributor

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    Hi Frans,

    Are you testing this tank with just water, and no rock? If so, I suspect that as soon as you add rock, the flow pattern will change, and you won't have that whirlpool any more... You could also try to place the pump deeper in the tank (if that's possible...) and angle it to move the water more towards the surface - the added "head" could perhaps help.

    Hennie
     
  10. FransSny

    FransSny Thread Starter

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    Hi hennie , just using water at the mo. Unfortunately the purpose for what these tanks are going to be used does not allow for LR , substrate etc.. the catch with these tanks being so small is keeping max water level without spilling...actually just curious at the moment, always good to know things like this for future use
     
  11. SIMS

    SIMS

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    are these frag tanks or fish holding tanks?
     
  12. jacquesb

    jacquesb Retired Moderator

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    Great ideas guys. Frans - try these out. Perhaps it would work for you?
     
  13. FransSny

    FransSny Thread Starter

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    Yes JB I actually think the rainbar is a excellent idea. I have however taken off the overflow box and that seems to have fixed the problem, maybe because of the small & narrow shape the box does something with how the flow "builds up speed"

    Holding tanks sims, not mine though but little things like this turn an easy build into a nightmare
     
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