Need help in figuring out flow dynamics

Discussion in 'General Discussions and Advice' started by dendrosa, 25 Jul 2008.

  1. dendrosa

    dendrosa Member

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    Hi Hennie, I'm busy setting up a new tank. The size is 1.8m x 0.9m x 0.7m which will be a room divider, so visable on 3 sides. As can be seen from the sketch below, I want to install a partition approx 25mm in front of the overflow. This partition will have screened cutouts for overflow, pump return flow and outlets for 6 pumps. ( I presently have 4* Tunze 6100's, extra outlets for possible future expansion.) These pumps will be in two banks of 3 ea. located in two chambers of approx 200mm by 200mm on either side of the overflow chamber.

    Now my problem. With all 3 pumps operating at once in either one of the chambers, means that the pumps are pushing out some 36 000 lph. This volume of water needs to be replenished by being drawn through the screen in the centre of the partition and then through the 25 mm gap between the partition and the front plate of the overflow.

    I need to try and figure out what the drop in the water level is going to be in the pump chamber to prevent the pumps from cavitating.

    [​IMG]
     
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  3. Warr7207

    Warr7207

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    Wow, that is one wicked system dude.
     
  4. Reef Maniac

    Reef Maniac MASA Contributor

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    I agree, that is quite a good idea.

    I will have to give this some thought, but gut feeling is that the drop in the water level in the two pump chambers will not be more than 5mm - 10mm at most. You can use the "flow in a rectangular channel" function of the water flow calculator to get a rough idea (although the "channel" will now be vertical...). If you use the "channel slope" as the drop in the water level you could approximate the flow in the "channel" between the 25mm gap and the pump chambers... this is of course not what I designed the calculator for, as in a real channel the water flow is controlled by gravity and not by the suction of three pumps, but it could still be useful as a "what if..."

    In cases like this I believe that proving the design in practice is much easier than trying to calculate it accurately, as there are always some unknowns to muddle the formulas. Why don't you just keep the divider loose and test it with the pumps before you do the final gluing. Worst case would then be that you might have to increase the 25mm to (say) 50mm if it does not work the first time...

    Hennie
     
    Last edited: 26 Jul 2008
  5. dendrosa

    dendrosa Thread Starter Member

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    Thanks for the encouraging reply! My concern was that it would drop the level by as much as 50 mm!
    You are right though, it s best to test by trial and error. I should have the partition built by the end of the weekend, after which I'll fill the tank with fresh water and play around.
     
  6. Reef Maniac

    Reef Maniac MASA Contributor

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    Great

    Please give feedback on how it actually worked (water level drop, etc.) as it would help to sharpen the old "gut feeling" - and of course, we can then all steal your idea :thumbup:

    Hennie
     
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