# Junction affects the flow of water?

• foo9008
In summary: D' ?)In summary, the author is discussing a problem with a diagram that includes points A, B, C, and D. The author states that if point D is below point B, then the heights and flows at points 2 and Q2 will be equal to zero. The author then asks for clarification on what this means, specifically if it means that water cannot flow in or out of point B. The conversation also includes discussions on potential typos and inconsistencies in the author's statements.
foo9008

## Homework Statement

based on this picture in the notes , the author gave that if D is below B , then h2 and Q2 = 0 , what dos it mean ? what does it mean ? water cannot flow out and in from B ?

## The Attempt at a Solution

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Hey, there is D ! Doesn't this look a lot like the other thread ?
But this time there is no ##h_2## (or no ##h_{f2}## ?
Could you merge the threads and try to get completeness ?
Or should I ask a mentor ?

What exactly are the litteral words the author uses ? Because D is definitely below B as anyone can see. At least if the top of the picture represents 'up'.

@foo9008, in past threads on this, or very similar problems, the solution technique was iterative. You could start with arbitrary assumptions about flows and iteratively adjust them until the correct solution emerged. Are you sure that is not what the author is doing here, assuming Q2 to be zero as a first guess?
If you don't think that is the explanation, please post the exact text.

foo9008
@BvU and @haruspex , here's the full text , can you explain about the author gave that if D is below B , then h2 and Q2 = 0 , what dos it mean ? what does it mean ? water cannot flow out and in from B ?
no , this is just notes , while in the another thread is just the sample problem which shares the same diagram with the notes

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foo9008 said:
@BvU and @haruspex , here's the full text , can you explain about the author gave that if D is below B , then h2 and Q2 = 0 , what dos it mean ? what does it mean ? water cannot flow out and in from B ?
no , this is just notes , while in the another thread is just the sample problem which shares the same diagram with the notes
The text is clearly inconsistent, so there must be a typo. I suggest that the first one should read "if P is at the same height as B". (And I assume the author is using P and D interchangeably.)

foo9008
haruspex said:
The text is clearly inconsistent, so there must be a typo. I suggest that the first one should read "if P is at the same height as B". (And I assume the author is using P and D interchangeably.)
ok , do you mean it should be when D is same height as B , no water will flow out , so Q2 and h2 = 0 ?

@haruspex , the last statement is also wrong , am i right ? it stated that when P is below B , the water is definitely out of B , so Q1 + Q2 = Q3 ?
but , it also can be water from A flow into B and C which means (Q1 = Q2 + Q3) ?
depending on the situations , am i right ?

foo9008 said:
@haruspex , the last statement is also wrong , am i right ? it stated that when P is below B , the water is definitely out of B , so Q1 + Q2 = Q3 ?
but , it also can be water from A flow into B and C which means (Q1 = Q2 + Q3) ?
depending on the situations , am i right ?
I agree that intuitively it could flow down from C, but if viscosity is being ignored then intuition may mislead. I need to think about it some more.
Have you tried analysing it using Bernoulli?

foo9008
haruspex said:
I agree that intuitively it could flow down from C, but if viscosity is being ignored then intuition may mislead. I need to think about it some more.
Have you tried analysing it using Bernoulli?
i think you mean B ? do you mean if the viscocsty is ignore , then the intuition of water from a can flow up to C is correct ?

foo9008 said:
i think you mean B ? do you mean if the viscocsty is ignore , then the intuition of water from a can flow up to C is correct ?
Yes, B. I mean if there is viscosity then I expect it can flow up to B, but without viscosity I'm not sure.

foo9008
haruspex said:
Yes, B. I mean if there is viscosity then I expect it can flow up to B, but without viscosity I'm not sure.
so , by saying that when P is below B , the water is definitely out of B , so Q1 + Q2 = Q3 , the author assuming water has no viscosity , so the water can't flow from A up to C ?

foo9008 said:
so , by saying that when P is below B , the water is definitely out of B , so Q1 + Q2 = Q3 , the author assuming water has no viscosity , so the water can't flow from A up to C ?
That's what the author is saying, but I don't know how that is shown.

Messy threads, this one and the -- 98% identical to this one -- other thread which I find a lot more sensible.
The note in post #4 here clarifies a few things -- and messes up others.
• Haru fixed the first 'If P is below' which should have been 'at'.
• The term 'elevation of P' confused me no end
I'm not used to working in terms of 'head', only with pressure, but I think 'elevation of P' is the same as ##H_J## and then ##P_D## is understandably the pressure at D .
What P is I find declared nowhere (whatever happened to 'all variables and given/known data' in the template -- my addition: including the dimensions ) ?
That would make for ##\ \ H_J = P = Z_D + P_D/(\rho g)\ \ ## (so not ##\ \ Z_D + P_D/\rho \; g \ \ ##, nitpicking, I know) and now I'm still a bit dazzled but back in the race.​
• 'the pipes are sufficiently long that we can neglect minor losses and velocity head' also is cryptic to me. long ? or wide ? The idea is to ignore friction loss (viscosity = 0) ? But why ignore 'velocity head' - when ##V^2/g## is featuring clearly in the other thread ? Or is velocity head something else than this term from the Bernoulli equation ?
@haruspex, could you look at the other thread, see if it is identical and if so, see if the combination makes sense ?

BvU said:
Messy threads, this one and the -- 98% identical to this one -- other thread which I find a lot more sensible.
The note in post #4 here clarifies a few things -- and messes up others.
• Haru fixed the first 'If P is below' which should have been 'at'.
• The term 'elevation of P' confused me no end
I'm not used to working in terms of 'head', only with pressure, but I think 'elevation of P' is the same as ##H_J## and then ##P_D## is understandably the pressure at D .
What P is I find declared nowhere (whatever happened to 'all variables and given/known data' in the template -- my addition: including the dimensions ) ?
That would make for ##\ \ H_J = P = Z_D + P_D/(\rho g)\ \ ## (so not ##\ \ Z_D + P_D/\rho \; g \ \ ##, nitpicking, I know) and now I'm still a bit dazzled but back in the race.​
• 'the pipes are sufficiently long that we can neglect minor losses and velocity head' also is cryptic to me. long ? or wide ? The idea is to ignore friction loss (viscosity = 0) ? But why ignore 'velocity head' - when ##V^2/g## is featuring clearly in the other thread ? Or is velocity head something else than this term from the Bernoulli equation ?
@haruspex, could you look at the other thread, see if it is identical and if so, see if the combination makes sense ?
I might be starting to get what is going on here. As you say, we have no definition of P. I was taking it to be interchangeable with D, but I now think it is an energy level associated with D.
The diagram in the other thread shows the physical arrangement of pipes, plus a schematic "energy line". Note that the slopes are not the same between the two. In the schematic there is an energy level HJ associated with the junction.
There is a similar energy diagram in the current thread, this time using dashed lines. I suggest "P" in the text refers to the energy level at D. If this is equal to that at B then there is no flow to or from B, etc. That makes sense.

Now, none of these diagrams can be handled with simple Bernoulli. Either there is viscosity or the flows will accelerate. I'm not sure which of those the author assumes, maybe it doesn't matter.

## 1. How does a junction affect the flow of water?

A junction can either increase or decrease the flow of water, depending on its design and location. If the junction is smooth and gradual, it can help to reduce turbulence and increase the velocity of the water, resulting in a faster flow. However, if the junction is sudden and sharp, it can cause eddies and turbulence, slowing down the flow of water.

## 2. What factors determine the impact of a junction on water flow?

The shape, size, and angle of the junction are important factors that determine its impact on water flow. The roughness of the surface, the speed of the water, and the properties of the fluid also play a role in determining the effect of a junction on flow.

## 3. How do junctions affect the distribution of water in a system?

Junctions can significantly impact the distribution of water in a system. If the junction is designed to split the flow of water, it can help to evenly distribute the water to multiple outlets. On the other hand, a poorly designed junction can cause uneven distribution, with some outlets receiving more water than others.

## 4. Can junctions cause blockages in water systems?

Yes, if a junction is not properly designed or maintained, it can cause blockages in water systems. Sharp or abrupt junctions can create eddies and turbulence, which can lead to the accumulation of sediments and debris, causing blockages and reducing the flow of water.

## 5. How can the impact of a junction on water flow be mitigated?

The impact of a junction on water flow can be mitigated by designing and constructing the junction with smooth and gradual transitions. This can help to reduce turbulence and increase the velocity of the water. Regular maintenance and cleaning of the junction can also prevent blockages and ensure optimal flow of water in the system.

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