# What laws of physics apply when a flow of air is divided?

The question is rather simple, but I'm not sure if there is a simple answer to it. Let`s say I've got a flow of air (5 bar, 25 l/min) running through a 6mm hose. Then this flow hits a branch dividing the stream into 4. Is the physics of it so straight forward that one only divides the flow by the number of outlets (provided that all 4 branches have the same conditions in resistance, temperature etc)?

All suggestions are very appreciated :)

• All of them :-) Oct 1, 2015 at 13:08

In general, if you have a system in steady state, if you have 25 l/min coming in, you must have 25 l/min going out. If you have more or less than 25 l/min going out, then the pressure will fall or rise respectively. Since you specify that the pressure remains fixed at 5 bar, this implies that the outflow is also 25 l/min. For 4 output branches, the sum of air flowing through them will be 25 l/min, and since they are all equal, the air flow will be divided equally among them. What the pressure is inside of the output branches will depend on the size of the branches however, which has not been specified.

As for a specific principle in physics, you should look up more information on the continuity equation, which describes transport of fluid well.

https://en.wikipedia.org/wiki/Continuity_equation