# Basic fluid dynamics

1. Jan 28, 2013

### bootsnbraces

Hi guys and girls,

I hope you can help an electronics engineer out of his place in the mechanical world:uhh:

My very basic question is for a vessel holding a liquid at a given pressure and a given opening in the vessel how can i calculate exit velocity and mass flow rate? Like if i blow a balloon up to say 1 bar (good balloon huh and then put a 1mm hole inside it how fast will the air be travelling as it leaves the balloon?

I dont need anything to detailed ( not worried about internal friction losses etc) and for now i can assume the vessel is fed by constant pressure mechanism i.e it wont drop pressure as it empties!

Any help gratefully recieved

2. Jan 28, 2013

### jbriggs444

Ignoring friction, the exit velocity should be just enough to squirt a stream back up to the height of the surface of the fluid.

That's about 30 feet for water at one atmosphere. 30 feet at one g is about 45 feet per second. Double the pressure and you multiply the stream velocity by sqrt(2).