Volume flow rate

Angello90

Ok another stupid/smart question,

I got a bath with x m^3 volume. And a water flow rate of a tap is y m/s. I also know pressure and velocity. How can I calculate time to fill up bathtub? I know it's simple but I can not figure it out!

LostConjugate

You need to know the volume of water coming in per second, then it is easy. If you know the velocity you don't need to know the pressure. However that is not enough, you can have any volume of water at the same velocity/pressure.

Angello90

Ok, so let's say the radius of pipe is r. This would give the area of outlet. Multiplying Q by A would give me (m/s) by (m^2), thus giving me volume of water coming out.

Does it make any sense?

LostConjugate

Exactly, so you have m^3/s. If the bathtub fills up at x cubic meters then it takes x/Av seconds.

Now if it is hot or cold water then you have to account for the room temperature difference and it becomes a differential equation with an exponential coefficient in the solution.