Homework Help: Flow in branch pipe

foo9008 · May 4, 2016

1. The problem statement, all variables and given/known data
in the notes , the author stated that the water from reservoir 1 could flow to reservoir 2 and 3 ..... i dont understand how could the water flow from 1 to 2 through junction D ? how could the water flow from low to high ?

2. Relevant equations

3. The attempt at a solution

BvU · May 4, 2016

Now my response went into the black hole

Don't see no D !

And water flows under the driving force we call pressure ! As long as p_a > p_b it will flow, up or down or sideways from a to b - as long as there is a path!

foo9008 · May 4, 2016

BvU said: ↑

Now my response went into the black hole

Don't see no D !

And water flows under the driving force we call pressure ! As long as p_a > p_b it will flow, up or down or sideways - as long as there is a path!

do you mean as long as position reservoir A > B , the pressure is large enough for the water to flow upwards?

BvU · May 4, 2016

It's a bit more complicated than that because of the presence of reservoir 3.
It's not the position that 'decides', but the pressure.
From the picture I'd conclude that ##H_J > h_{f2}## is the condition for flow towards the second reservoir. For instance if pipe 3 is very narrow.

foo9008 · May 4, 2016

BvU said: ↑

It's a bit more complicated than that because of the presence of reservoir 3.
It's not the position that 'decides', but the pressure.
From the picture I'd conclude that ##H_J > h_{f2}## is the condition for flow towards the second reservoir. For instance if pipe 3 is very narrow.

##H_J ? what do you mean by it ?

foo9008 · May 4, 2016

BvU said: ↑

It's a bit more complicated than that because of the presence of reservoir 3.
It's not the position that 'decides', but the pressure.
From the picture I'd conclude that ##H_J > h_{f2}## is the condition for flow towards the second reservoir. For instance if pipe 3 is very narrow.

how to know that if P at A > P at B ?

BvU · May 4, 2016

foo9008 said: ↑

how to know that if P at A > P at B ?

That's exactly what they try to teach you with the picture !
##H_J## is the total head at J (what you called D, the branching point). Since that depends on the flows and the flows depend on the head differences, they propose an iterative solution method.

foo9008 · May 4, 2016

BvU said: ↑

That's exactly what they try to teach you with the picture !
##H_J## is the total head at J (what you called D, the branching point). Since that depends on the flows and the flows depend on the head differences, they propose an iterative solution method.

ok , can i also say it as position of A is the highest , so P/( rho g ) + z has the highest value for A ?

foo9008 · May 4, 2016

BvU said: ↑

That's exactly what they try to teach you with the picture !
##H_J## is the total head at J (what you called D, the branching point). Since that depends on the flows and the flows depend on the head differences, they propose an iterative solution method.

i dont understand how could the water flow from q to 3 and Q2 is 0 ?