flow rate/volume/drain rate

ndnd

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How would I figure the time it would take to drain/fill a tank when there is a rate at which it is draining that depends on the volume in the tank which is also changing at a certain rate due to flow into the tank?
 
How would I figure the time it would take to drain/fill a tank when there is a rate at which it is draining that depends on the volume in the tank which is also changing at a certain rate due to flow into the tank?

Using calculus, set up differential equation and solve....
 
If V(t) is the volume at time t, \(\displaystyle \alpha(V)\) is the rate, depending upon the volume, at which the tank drains, and \(\displaystyle beta\) is the rate at which the tank is being filled, then
\(\displaystyle \frac{dV}{dt}= \beta- \alpha(V)\).

Without knowing more about how the rate at which the tank drains "depends on the volume", we cannot say more. If the rate at which the tank drains is proportional to the volume, then \(\displaystyle \alpha(V)= k V\) for constant k and the equation is relatively easy to solve.
 
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Generally, the outflow rate is

proportional to the height of the fluid column, and

Volume is proportional to the height of the fluid column
 
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