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# find velocity in pipe Watch

1. water flows from flow tank at A through cat iron pipeline to free surface at B . Given friction factor , f = 0.023, kinematic viscosity = 1.02 x10^-6 (m^2 0 /s , coefficient of losses for entrance , bend , valve = 0.5 , 0.9 and 10 . in this question , i am asked to find the velocity , flow rate , type of flow and pressure at A .for the first part , i'm asked to find the velocity . The flow rate is not given , how could the velocity be found ? Since Q = Av ,

i assume the flow as laminar at first , where reynold number less than 2000 ,so i have f = 64 / Re0.023 = 64(1.02 x10^-6)/ 1000 / ( 1000 x v x 150x10^-3) , v = 2.08x10^-8 , is my answer correct ? my reynold number is rather samll , which is 3.05 only , is it possible ?
2. bump
3. I'll have a look at this later, but I wouldn't assume laminar flow.

In terms of Bernoulli's equation, you know the pressure in the tank, you can assume the velocity is zero, and you know the elevation difference. That might be enough to calculate an entrance velocity for the pipe. You can also workout the pressure at that point, too.
4. (Original post by Smack)
I'll have a look at this later, but I wouldn't assume laminar flow.

In terms of Bernoulli's equation, you know the pressure in the tank, you can assume the velocity is zero, and you know the elevation difference. That might be enough to calculate an entrance velocity for the pipe. You can also workout the pressure at that point, too.
the problem is the pressure at A is unknown , so in the berboulli's equation , we would have 2 unknown , which are velocity and pressure at A , how to solve this ?
5. (Original post by wilson dang)
the problem is the pressure at A is unknown , so in the berboulli's equation , we would have 2 unknown , which are velocity and pressure at A , how to solve this ?
A is open to the air is it not?
6. (Original post by Smack)
A is open to the air is it not?
We can see from figure, it is closed tank, right??

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7. (Original post by wilson dang)
We can see from figure, it is closed tank, right??

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If the tank is not open to the atmosphere and the air in it is pressurised, then ignore any atmospheric effects and just go by the gauge pressure of the water to calculate the velocity, flow rate and type of flow.
8. Well, I havre PA and v2 as unknown in an equation, how to solve this?
9. (Original post by Smack)
If the tank is not open to the atmosphere and the air in it is pressurised, then ignore any atmospheric effects and just go by the gauge pressure of the water to calculate the velocity, flow rate and type of flow.
Since b is open to atmosphere, so atmospheric pressure act on it., so I take atmospheric pressure =0

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10. (Original post by wilson dang)
Since b is open to atmosphere, so atmospheric pressure act on it., so I take atmospheric pressure =0

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If B is open to the atmosphere, surely you can assume that A is also at atmospheric pressure, as taking gauge pressures only works when both sides are at the same atmospheric pressure as the two atmospheric pressures cancel out.
11. (Original post by Smack)
If B is open to the atmosphere, surely you can assume that A is also at atmospheric pressure, as taking gauge pressures only works when both sides are at the same atmospheric pressure as the two atmospheric pressures cancel out.
ya , B is open to atmosphere , so stmospheric pressure act on it .... but b , the pressure act on it is not atmospheric pressure right ? since it's closed....
12. (Original post by wilson dang)
ya , B is open to atmosphere , so stmospheric pressure act on it .... but b , the pressure act on it is not atmospheric pressure right ? since it's closed....
If the air can flow freely from the tank to the atmosphere then the air, and hence tank, could be said to be at atmospheric pressure. If there was no air in the tank and it was not pressurised then there would be no atmospheric pressure acting in it. But it appears you have to calculate the pressure at A as the last part of the question... I would clarify with your lecturer.
13. (Original post by Smack)
If the air can flow freely from the tank to the atmosphere then the air, and hence tank, could be said to be at atmospheric pressure. If there was no air in the tank and it was not pressurised then there would be no atmospheric pressure acting in it. But it appears you have to calculate the pressure at A as the last part of the question... I would clarify with your lecturer.
so , the pressure at A is atmospheric pressure or pressurized pressure ????
14. (Original post by wilson dang)
so , the pressure at A is atmospheric pressure or pressurized pressure ????
As per my post, you need to clarify this with your lecturer.
15. (Original post by Smack)
As per my post, you need to clarify this with your lecturer.
If that is pressurized pressure, then the question can't be done, right???

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16. (Original post by wilson dang)
If that is pressurized pressure, then the question can't be done, right???

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If you can't assume that A and B are at the same pressure then I am not sure how to do the question.

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