The Student Room Group
Uni students - Complete our survey >>
Uni students - Complete our survey >>
Uni students - Complete our survey >>

find velocity in pipe

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 ?
Reply 1
Avatar for wilson dang
wilson dang
OP
7
bump
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.
Reply 3
Avatar for wilson dang
wilson dang
OP
7
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 ?
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?
Reply 5
Avatar for wilson dang
wilson dang
OP
7
Original post by Smack
A is open to the air is it not?

We can see from figure, it is closed tank, right??

Sent from my C6502 using Tapatalk
Original post by wilson dang
We can see from figure, it is closed tank, right??

Sent from my C6502 using Tapatalk


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.
Reply 7
Avatar for wilson dang
wilson dang
OP
7
Well, I havre PA and v2 as unknown in an equation, how to solve this?uploadfromtaptalk1463651157880.jpg
Reply 8
Avatar for wilson dang
wilson dang
OP
7
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

Sent from my C6502 using Tapatalk
Original post by wilson dang
Since b is open to atmosphere, so atmospheric pressure act on it., so I take atmospheric pressure =0

Sent from my C6502 using Tapatalk


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.
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....
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.
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 ????
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.
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???

Sent from my C6502 using Tapatalk
Original post by wilson dang
If that is pressurized pressure, then the question can't be done, right???

Sent from my C6502 using Tapatalk


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

Quick Reply

Related discussions

Latest

Trending

Trending

Articles for you