Pressure in pipe

[chiddler]

In a straight pipe of uniform xsectional area filled with a nonviscous incompressible fluid, pressure at one end is equal to the pressure at the other. Is the following true?

The pipe is not inclined relative to the horizontal since the pressure is constant.

Book says yes, brain says no. Book says that pressure changes via change in height by bernoulli's. Brain says what if you have an inclined pipe with a pump at the lower end?

?

thank you.

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[bajoneswadup]

In a straight pipe of uniform xsectional area filled with a nonviscous incompressible fluid, pressure at one end is equal to the pressure at the other. Is the following true?

The pipe is not inclined relative to the horizontal since the pressure is constant.

Book says yes, brain says no. Book says that pressure changes via change in height by bernoulli's. Brain says what if you have an inclined pipe with a pump at the lower end?

?

thank you.

if you had a pump then yeah but i dont think the question is talking abt a pump. its just sayin b/c density, V, and P are same, there must not be any elevation. i think ur over thinkin dis one yo

 

[dmf2682]

In a straight pipe of uniform xsectional area filled with a nonviscous incompressible fluid, pressure at one end is equal to the pressure at the other. Is the following true?

The pipe is not inclined relative to the horizontal since the pressure is constant.

Book says yes, brain says no. Book says that pressure changes via change in height by bernoulli's. Brain says what if you have an inclined pipe with a pump at the lower end?

?

thank you.

If there's a pump at one end pressure will be greater at that end.

 

[Tatiana3325]

In a straight pipe of uniform xsectional area filled with a nonviscous incompressible fluid, pressure at one end is equal to the pressure at the other. Is the following true?

The pipe is not inclined relative to the horizontal since the pressure is constant.

Book says yes, brain says no. Book says that pressure changes via change in height by bernoulli's. Brain says what if you have an inclined pipe with a pump at the lower end?

?

thank you.

The book is correct.

Your understanding of bernoullis principle is not correct.

 

[chiddler]

If there's a pump at one end pressure will be greater at that end.

No that's not true. The pump is to provide kinetic energy to the water and therefore reduce pressure.

The idea is that the increased pressure at the bottom of the incline is counteracted by the pump.

 

[chiddler]

if you had a pump then yeah but i dont think the question is talking abt a pump. its just sayin b/c density, V, and P are same, there must not be any elevation. i think ur over thinkin dis one yo

maybe :-x

 

[dmf2682]

No that's not true. The pump is to provide kinetic energy to the water and therefore reduce pressure.

The idea is that the increased pressure at the bottom of the incline is counteracted by the pump.

Oh really? Pumps don't increase pressure? So the heart, being a pump, doesn't create blood pressure?

By your reasoning is the kinetic energy at the bottom of the pipe more or less than that at the top?

 

[chiddler]

Oh really? Pumps don't increase pressure? So the heart, being a pump, doesn't create blood pressure?

By your reasoning is the kinetic energy at the bottom of the pipe more or less than that at the top?

Yes I suppose that's correct for a heart like pump. But ok, lets use a different type of pump. The heart works by increasing pressure at one end. Lets use a pump that reduces pressure at one end instead via vacuum.

One that reduces atmospheric pressure at the top of the pipe so that it is nearly 0 while the bottom is attached to a lake. Here, clicky.

By my reasoning, when pressure is constant at each end, kinetic energy is constant throughout the pipe since there is no acceleration. So velocity is the same everywhere.

So now what? Of course what I drew has a pressure differential since water is exiting. But what if pressure is just enough such that the fluid does not move at all.

Now an inclined pipe has the same pressure at both ends.

 

[dmf2682]

Yes I suppose that's correct for a heart like pump. But ok, lets use a different type of pump. The heart works by increasing pressure at one end. Lets use a pump that reduces pressure at one end instead via vacuum.

One that reduces atmospheric pressure at the top of the pipe so that it is nearly 0 while the bottom is attached to a lake. Here, clicky.

By my reasoning, when pressure is constant at each end, kinetic energy is constant throughout the pipe since there is no acceleration. So velocity is the same everywhere.

So now what? Of course what I drew has a pressure differential since water is exiting. But what if pressure is just enough such that the fluid does not move at all.

Now an inclined pipe has the same pressure at both ends.

A couple points to make, and you'll have to excuse me because I'm on my phone.

Kinetic energy has nothing to do with acceleration. It's a function of velocity. If you had a zero flow pipe there's no kinetic energy, and yet if you disconnected the vacuum pump the water would go out the bottom. So the pump does not add kinetic here.

Next, if you had an inclined pipe with a pump on the top and the bottom open to atmosphere as you said, with the water going nowhere, how does that work? Simply put, the pressures are unequal. At the top you have something of less pressure than atmosphere, and at the bottom you have whatever pressure it's exposed to, be it the bottom of a lake, atmosphere, whatever.

Pressures are unequal, so why doesn't it move? They're in equilibrium. On the bottom side you have ambient pressure actually pushing up. On the top you have reduced pressure pushing down. But you also have your gravity term in there also pushing down, what is called a pressure head. That's the product of density, gravity accel and the vertical height diff between the two ends.

 

[chiddler]

A couple points to make, and you'll have to excuse me because I'm on my phone.

Kinetic energy has nothing to do with acceleration. It's a function of velocity. If you had a zero flow pipe there's no kinetic energy, and yet if you disconnected the vacuum pump the water would go out the bottom. So the pump does not add kinetic here.

Next, if you had an inclined pipe with a pump on the top and the bottom open to atmosphere as you said, with the water going nowhere, how does that work? Simply put, the pressures are unequal. At the top you have something of less pressure than atmosphere, and at the bottom you have whatever pressure it's exposed to, be it the bottom of a lake, atmosphere, whatever.

Pressures are unequal, so why doesn't it move? They're in equilibrium. On the bottom side you have ambient pressure actually pushing up. On the top you have reduced pressure pushing down. But you also have your gravity term in there also pushing down, what is called a pressure head. That's the product of density, gravity accel and the vertical height diff between the two ends.

Kinetic energy is relevant to acceleration. If acceleration is 0, then velocity is constant everywhere. Therefore, kinetic energy is constant everywhere since you're not changing mass of a homogeneous fluid.

I see what you're saying about the pressures being unequal. I forgot about pesky gravity...

So if pressure is the same at both ends, we can unequivocally say that the pipe is horizontal with respect to the ground?

 

[dmf2682]

Kinetic energy is relevant to acceleration. If acceleration is 0, then velocity is constant everywhere. Therefore, kinetic energy is constant everywhere since you're not changing mass of a homogeneous fluid.

I see what you're saying about the pressures being unequal. I forgot about pesky gravity...

So if pressure is the same at both ends, we can unequivocally say that the pipe is horizontal with respect to the ground?

Yeah, gotta watch out for gravity. Thermal radiation screwed Prometheus, but gravity screwed him more.

I always hate to say unequivocally so I won't comment on that, especially since I haven't dealt with pipe flow since college.

Edit. We can say no, not in all cases. The two ends just have to be level with respect to the ground. You could have a u shape pipe that has equal pressures at its ends

 

[chiddler]

Yeah, gotta watch out for gravity. Thermal radiation screwed Prometheus, but gravity screwed him more.

I always hate to say unequivocally so I won't comment on that, especially since I haven't dealt with pipe flow since college.

Edit. We can say no, not in all cases. The two ends just have to be level with respect to the ground. You could have a u shape pipe that has equal pressures at its ends

lol

thanks very much that's a good distinction with a U shaped pipe.