Storage tank emptying time

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how can be determine
the emptying time of Water storage tank sizing 18m x 18m x 2.4m with 
inflow rate of 4lps when inflow and outflow ends at the same time. The 
outlet is 6 inch gate valve

thank you!

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6 Answers

  1. Hi,

    I think the comparison between inflow and outflow is quite large, hence with Qout >> Qin with Qout is estimated using this formula:

    Qout=mu*A*sqrt(2*g*h)

    you can neglect the inflow (Qin) and use the following formula:

    t=[(2*A0)/(mu*A*sqrt(2*g))] * (sqrt(h1) - sqrt(h2))

    where A0 is your tank cross section (which is constant with respect to tank height I assume), mu is orifice outlet coefficient or gate valve coefficient in this case, g is gravitational acceleration, h1 and h2 is the water level before and after (in this case h2 is 0 since it will be emptied).

     

    In case you want to include the Qin, you need to use another approach since it involves tank/reservoir storage equation. Also another treatment is needed if the areal cross section of the tank is not constant e.g. cone shaped.

  3. The tank will attain a level around 5 hours of commencement of draining at which the cover over an assumed bottom 6 inch outlet will be inadequate to make the outlet run full. At this point if the inflow rate is regulated to reduce to zero, tank runs out very soon thereafter.

  5. Where At is the area of the tank (18 m X 18 m)

    Ao is the cross area of the open valve

    g is gravity and

    Cd is the coefficient for the tipe and size of valve, I believe is 3076, see https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&ved=2ahUKEwjs0p2jq7DuAhUlnq0KHaK9D4cQFjAAegQIBRAC&url=https%3A%2F%2Fglobalsupplyline.com.au%2Fwp-content%2Fuploads%2F2014%2F10%2FGate-Globe-Check-Valves-Flow.pdf&usg=AOvVaw1sSUMuyRoM9SuVUF7yN93K