Water Resources Study Module

[MMS]

Can you please email me study material to [email protected]

THANKS

 

[owillis28]

Solutions to water resources study module

jfus

do you have the solution for the problem on page 18? I went to check my work and found I didn't have the solution. If anyone else has it, please post.

thanks

owillis

 

[owillis28]

Nevermind - I found my mistake.

owillis

 

[jartgo]

I got a question on Fluid Dynamics question on Page 15. why can't I use the mass balance equation here? I mean shouldn't the product of velocity and area be the same no matter what.

I believe that the question in this problem is misleading. I did it correctly only because I saw that they gave pressures and it would have been easy enough to use the energy equation. However, in this situation, you've lost flow somewhere and the picture doesn't show there to be an oppurtunity to lose any flow. At any rate, that's why you can't use the continuity or mass balance...there is flow that is unaccounted for in this solution.

 

[IlPadrino]

I believe that the question in this problem is misleading. I did it correctly only because I saw that they gave pressures and it would have been easy enough to use the energy equation. However, in this situation, you've lost flow somewhere and the picture doesn't show there to be an oppurtunity to lose any flow. At any rate, that's why you can't use the continuity or mass balance...there is flow that is unaccounted for in this solution.

Jartgo,

I don't think the question is misleading. Maybe strange in that pressure decreases as a result of a constriction which seems counter-intuitive. Is there any real-world case where this can happen?

When talking about "lost" flow, I think most people visual fluid going somewhere different and there being a loss in mass. That's what you seem to imply above because you talk about there not being any opportunity to lose flow.

In this case, the flow *velocity* decreases. We know this has to happen because the pressure decreases and, in this problem, a decrease in pressure MUST be accompanied by an increase in velocity to keep the total energy equal. This also seems intuitive to me because I think of molecules getting further apart when pressure decreases and this implies there's less "stuff" passing by a point at any given time interval. Is this the principle behind the continuity equation which includes a term for mass density?

The problem says to ignore friction head loss, which if accounted for would further decrease the velocity in pipe B. And still, in the problem, the discharge through pipe B is less than in pipe A. This can ONLY happen at steady state if the density of the fluid increases. And we usually assume that density of water is constant even over significant changes in pressure. So I'm left to conclude the values given in the problem can only occur if it's not at steady state.

I would feel bad for the person that applied the continuity equation for liquids which says discharge at steady-state through any pipes in series is equal at all points - and decided the velocity at B was 63 fps. Luckily that's not a choice given!

Am I missing something important?

 

[jartgo]

Jartgo,
I don't think the question is misleading. Maybe strange in that pressure decreases as a result of a constriction which seems counter-intuitive. Is there any real-world case where this can happen?

When talking about "lost" flow, I think most people visual fluid going somewhere different and there being a loss in mass. That's what you seem to imply above because you talk about there not being any opportunity to lose flow.

In this case, the flow *velocity* decreases. We know this has to happen because the pressure decreases and, in this problem, a decrease in pressure MUST be accompanied by an increase in velocity to keep the total energy equal. This also seems intuitive to me because I think of molecules getting further apart when pressure decreases and this implies there's less "stuff" passing by a point at any given time interval. Is this the principle behind the continuity equation which includes a term for mass density?

The problem says to ignore friction head loss, which if accounted for would further decrease the velocity in pipe B. And still, in the problem, the discharge through pipe B is less than in pipe A. This can ONLY happen at steady state if the density of the fluid increases. And we usually assume that density of water is constant even over significant changes in pressure. So I'm left to conclude the values given in the problem can only occur if it's not at steady state.

I would feel bad for the person that applied the continuity equation for liquids which says discharge at steady-state through any pipes in series is equal at all points - and decided the velocity at B was 63 fps. Luckily that's not a choice given!

Am I missing something important?

I think so. All else constant, pressure will always decreases with a constriction. Why? Because velocity must increase through the constriction to adhere to the continuity equation. Subsequently, pressure must decrease through the constriction thanks to Mr. Bernoulli, keeping total energy in check. A real world example would be a venturi meter, which uses this exact situation to measure flow through a pipe.

In hydraulcs, the continuity equation is essentially conservation of mass. So, when I said there was a loss of flow...I did mean there was a loss of mass. That is, velocity in pipe A (2.5" dia) is 0.76/0.03325 = 22.86 fps. So, contrary to your statement above, velocity increases in this case (I think you may have meant to say "increases"), as it should. But the area of pipe B is (1.5" dia) 0.01414 s.f. so the flow in pipe B is 0.01414s.f. * 45fps = 0.636 cfs...obviously less than the original 0.76 cfs.

Essentially, there's a leak in this pipe that isn't shown. If not, the pressure in B would be 84 psi, and the resulting velocity in B would be 53.7 fps.

 

[ACLakey]

Please send me a copy if it is still available.

[email protected]

 

[IlPadrino]

I think so. All else constant, pressure will always decreases with a constriction. Why? Because velocity must increase through the constriction to adhere to the continuity equation. Subsequently, pressure must decrease through the constriction thanks to Mr. Bernoulli, keeping total energy in check. A real world example would be a venturi meter, which uses this exact situation to measure flow through a pipe.
In hydraulcs, the continuity equation is essentially conservation of mass. So, when I said there was a loss of flow...I did mean there was a loss of mass. That is, velocity in pipe A (2.5" dia) is 0.76/0.03325 = 22.86 fps. So, contrary to your statement above, velocity increases in this case (I think you may have meant to say "increases"), as it should. But the area of pipe B is (1.5" dia) 0.01414 s.f. so the flow in pipe B is 0.01414s.f. * 45fps = 0.636 cfs...obviously less than the original 0.76 cfs.

Essentially, there's a leak in this pipe that isn't shown. If not, the pressure in B would be 84 psi, and the resulting velocity in B would be 53.7 fps.

Sorry I missed your response...

Yes, I meant increase. OK - I get it... with an incompressible fluid, mass flow rate must ALWAYS be constant. I'm not sure steady state has anything to do with it.

I have no idea why I wrote a pressure decrease resulting from a constriction was strange our counter-intuitive... it's what happens in every house!

So the author of the problem probably just got lazy. Thanks for pointing it out!

 

[rarara]

As promised (especially for you Undertaker), I have began scanning in class notes for the PE.
The water resources section is complete and available for use.

Shoot me a PM with an e-mail address and I will e-mail it to you. I broke it down into two files and they are PDFs.

Just let me know if you want it, because I think the files are a little too big to post here.

I will also be putting review questions up for each section as well.

Can you please email me at [email protected]

 

[Hopeful]

Can someone send me the Water Resources Study Module please. My e mail address is [email protected]

Thanks in advance

 

[karnati]

Can someone send me the Water Resources Study Module please. My e mail address is [email protected]
Thanks in advance

could someone please email me water resourse study modle at [email protected]

thanks,

Karnati

 

[xoxojenjen]

Can someone forward the water resources study module to me? [email protected] ... thanks!!!! :thankyou:

 

[DIZZEE]

Can someone please send me the WR study module as well.

Thanks!

[email protected]

 

[Shree]

Can you please send me a copy if it is still available to [email protected].

Thank you.

 

[Hans]

As promised (especially for you Undertaker), I have began scanning in class notes for the PE.
The water resources section is complete and available for use.

Shoot me a PM with an e-mail address and I will e-mail it to you. I broke it down into two files and they are PDFs.

Just let me know if you want it, because I think the files are a little too big to post here.

I will also be putting review questions up for each section as well.

Here is my e-mail [email protected]

 

[bside]

If these are still available I would love a copy [email protected]

 

[charmless.k]

As promised (especially for you Undertaker), I have began scanning in class notes for the PE.
The water resources section is complete and available for use.

Shoot me a PM with an e-mail address and I will e-mail it to you. I broke it down into two files and they are PDFs.

Just let me know if you want it, because I think the files are a little too big to post here.

I will also be putting review questions up for each section as well.

Email [email protected]

 

[FINK_RB_PE]

Please send to [email protected]

Thanks!

 

[sridwan]

Hi,

Can anybody help me out with the CONSTRUCTION ENGINEERING NOTES (AM part) for the April, 08 test? I have CERM 10th and don't want to buy the new version only for the construction section.

Thanks.

 

[IlPadrino]

Hi,Can anybody help me out with the CONSTRUCTION ENGINEERING NOTES (AM part) for the April, 08 test? I have CERM 10th and don't want to buy the new version only for the construction section.

Thanks.

I've heard the next edition of the CERM will include ConE, but for now the only "stuff" I know of is the NCEES sample exam. Have you purchased that?