# Water drainage from a tank

1. Aug 17, 2011

### robhowe

Hi there, ive been looking at some of the drainage equations i have found aroundthese forums and im struggling a lot to understand. im 13 and good at maths, where i struggle is reading the advanced equations and figuring out what some of the posters mean.

Basicly i have a tank 50 cm across x 50 cm deep. The length is 300 cm. There is a 13mm drainage hole, im trying to figure out how quickly the tank will drain.

I only need an approx answer so is there a simple equation to work this out, So i can adjust the drainage hole size??

thankyou

2. Aug 17, 2011

### gsal

Last edited by a moderator: Apr 26, 2017
3. Aug 17, 2011

### robhowe

as i explained i dont understand the advanced formula, im looking for a simple equation. Or just a more detailed description.

4. Aug 18, 2011

### gsal

It does not get any simpler than that, though...this is the simple formula that results out of the general differential formula after integrating for a tank with constant cross-section....here is again, with better subscripts:

$time = \frac{2*A_{tank}\left(\sqrt{h_{1}}-\sqrt{h_{2}}\right)}{C_{d}*A_{orifice}*\sqrt{2g}}$

Atank is the surface (cross sectional) area of the tank and Aorifice is the cross sectional area of the orifice the water is going to come out through.

h1 is the height (from the ground) of the water level at the beginning (when you open the orifice) and h2 is the height at which the orifice is.

As suggested in the other post, Cd can be set to some value like 0.6 or 0.7; g is just gravity.