Newsgroup sci.mech.fluids 2913

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Graduate Research/Teaching Assistantships are available for students    
interested in pursuing a PhD in the area of computational fluid
dynamics.
Focus of the research is on direct numerical simulation (DNS) of complex
three-dimensional wake flows, heat transfer and fluid-structure
interaction problems.
Preference will be given to students with some previous experience in
CFD.
Foreign students need to have a demonstrated spoken English
capability     
(TSE or TA experience is acceptable).
Interested students should send their resume to:
Dr. R. Mittal
237 MEB
Dept. of Mechanical Engineering
University of Florida
Gainesville, FL 32611-6300

This is the subject of a friendly debate between a good friend of
mine,  who happens to be
a plumber and myself.(not a plumber)
I'm not sure if I posted this in the best newsgroup but it is the
educated mind of a engineer
that can settle this question in hydraulics.
Lets assume, that you have a perfectly functional and working lawn
sprinkler system,
powered by a electric moter. If you could snap your fingers and all
horizontal  conduits
were now eight inches in diameter, how would the increse in conduit
size effect the
performance of the system?
I say, that since water is uncompresable, the pump will be supplying
the same volume of
water to the spray heads, and that the larger pipe size actually means
less hydraulic
resistence and the system might even be improved. It is the pump that
determines the
pressure in the system with a given amount of flow determined by the
spray heads
Plumber says, that the pump will have a harder time pumping the extra
amount of heavy
water, and that the back pressure created by the greater resistence in
the smaller conduits
is needed to keep the pressure at the spray heads  
Is there a engineer out there that can put an end to this
debate???????
Sasha.

sasha wrote:
> 
> This is the subject of a friendly debate between a good friend of
> mine,  who happens to be
> a plumber and myself.(not a plumber)
> 
> 
> I'm not sure if I posted this in the best newsgroup but it is the
> educated mind of a engineer
> that can settle this question in hydraulics.
> 
THis is the right newsgroup...
> Lets assume, that you have a perfectly functional and working lawn
> sprinkler system,
> powered by a electric moter. If you could snap your fingers and all
> horizontal  conduits
> were now eight inches in diameter, how would the increse in conduit
> size effect the
> performance of the system?
> 
> I say, that since water is uncompresable, the pump will be supplying
> the same volume of
> water to the spray heads, and that the larger pipe size actually means
> less hydraulic
> resistence and the system might even be improved. It is the pump that
> determines the
> pressure in the system with a given amount of flow determined by the
> spray heads
> 
> Plumber says, that the pump will have a harder time pumping the extra
> amount of heavy
> water, and that the back pressure created by the greater resistence in
> the smaller conduits
> is needed to keep the pressure at the spray heads
> 
> Is there a engineer out there that can put an end to this
> debate???????
> 
> Sasha.
Plumber's right... I'd be able to prove it since I had a project back in 
college that dealt with the design on a sprinkler tube, and it is the 
pressure that pushes the water out of the little holes. 
Plus, if you're keeping the same pump with the increased pipe ID, the 
pump won't work as efficiently, and there would be less pressure inside 
the piping. It all has to do with pump curves and system curves.
As I said, I did a project similar to this back in Fluids 1... I'd 
explain it better, but I have a bugger of a headache right now... and I 
can't find my project work... *shrug*
If someone can corroborate (sp?) this, most appreciated...
Minstrel
-- 
Adam Johnson			BlackWing
tengu@concentric.net		Minstrel
http://www.concentric.net/~tengu/
"Well did you ever get the feeling that the story's too damned real
      and in the present tense?
 Or that everybody's on the stage and it seems like you're the only
      person sitting in the audience?"
                         --- Jethro Tull, "Skating Away on the Thin Ice 
to a New Day"

Hello, I'm looking for information about fluid flow sensors.  Any pointers
to web pages or elsewhere will be appreciated.  
Thanks.
-- 
Waleed Meleis                                           meleis@ece.neu.edu

I would be grateful if I could get references for the following
problem:
We have a cylinder/sphere near a wall moving along it.
What is the lift force acting on the ple if we assume that
it cannot rotate? This should be perhaps a basic textbook
problem, but we haven't found it solved.
Picture:
                   ^ F (lift force)
                   !
                   !
                   !
                 * * *
                *     *  ---------->  v (velocity)
                *  R  *
                 * * *
                   !
                   x
                   !
____________________________________________no slip wall___________
Thank you in advance,
Antti Koponen
       Address:
       Department of Physics, University of Jyvaskyla
       P.O. Box 35 (Survontie 9) FIN-40351 University of Jyvaskyla,
Finland
       Tel: +358-41-602378 Fax: +358-41-602351
       Email: ako@kroisos.jyfl.jyu.fi

sasha wrote:
> 
> Lets assume, that you have a perfectly functional and working lawn
> sprinkler system,
> powered by a electric moter. If you could snap your fingers and all
> horizontal  conduits
> were now eight inches in diameter, how would the increse in conduit
> size effect the
> performance of the system?
> 
> I say, that since water is uncompresable, the pump will be supplying
> the same volume of
> water to the spray heads, .....
> 
> Plumber says, that the pump will have a harder time pumping the extra
> amount of heavy
> water, ....
On balance I'd say that you were more correct than the plumber.
The increase in diameter - provided the fluid flow in the pipes remains
turbulent - will reduce the pressure drop in the system and more flow rate will
be able to be passed by the pump.
Provided there is no increase in the vertical height of the pipes, the effective
"weight" of the water at the pump outlet will remain the same.
The statement that "the back pressure in the pipes is needed .." is not true.
The pressure at the pump is maintained by the header pressure which, presumably
will remain unchanged in the system.  The flow rate thru the sprinkler is
governed by the outlet pressure from the pump minus the line loss  and divided
by the sprinkler's loss coefficient (a function of hole size, X-sectional area
etc..).  Clearly any reduction in line loss will mean more flow thru the
sprinkler - on top of the gain in flow rate from improved pump performance.

In article <327EB136.182D@concentric.net>,
   Minstrel  wrote:
>sasha wrote:
>> 
>> This is the subject of a friendly debate between a good 
friend of
>> mine,  who happens to be
>> a plumber and myself.(not a plumber)
>> 
>> 
>> I'm not sure if I posted this in the best newsgroup but 
it is the
>> educated mind of a engineer
>> that can settle this question in hydraulics.
>> 
>
>THis is the right newsgroup...
>
>
>> Lets assume, that you have a perfectly functional and 
working lawn
>> sprinkler system,
>> powered by a electric moter. If you could snap your 
fingers and all
>> horizontal  conduits
>> were now eight inches in diameter, how would the increse 
in conduit
>> size effect the
>> performance of the system?
>> 
>> I say, that since water is uncompresable, the pump will 
be supplying
>> the same volume of
>> water to the spray heads, and that the larger pipe size 
actually means
>> less hydraulic
>> resistence and the system might even be improved. It is 
the pump that
>> determines the
>> pressure in the system with a given amount of flow 
determined by the
>> spray heads
>> 
>> Plumber says, that the pump will have a harder time 
pumping the extra
>> amount of heavy
>> water, and that the back pressure created by the greater 
resistence in
>> the smaller conduits
>> is needed to keep the pressure at the spray heads
>> 
>> Is there a engineer out there that can put an end to this
>> debate???????
>> 
>> Sasha.
>
>Plumber's right... I'd be able to prove it since I had a 
project back in 
>college that dealt with the design on a sprinkler tube, and 
it is the 
>pressure that pushes the water out of the little holes. 
>Plus, if you're keeping the same pump with the increased 
pipe ID, the 
>pump won't work as efficiently, and there would be less 
pressure inside 
>the piping. It all has to do with pump curves and system 
curves.
>
>As I said, I did a project similar to this back in Fluids 
1... I'd 
>explain it better, but I have a bugger of a headache right 
now... and I 
>can't find my project work... *shrug*
>If someone can corroborate (sp?) this, most appreciated...
>
>Minstrel
>
>
I'd say that you better do the college project again.
Almost all of the pressure drop will be taken at the 
sprinkler nozzles (where the water comes out), as these 
nozzles are very small orifices compared to the diameter of 
the piping that supplies them.  Increasing the piping 
diameter of the pipe going to the sprinkler will 
theoretically decrease the pressure drop in the system 
upstream of the sprinkler, leading to a higher pressure at 
the sprinkler (not lower).  However, it is likely that the 
sprinkler takes 90-95% of the pressure drop in this system. 
Thus, while it is theoretically correct to increase piping 
diameter for the sake of efficiency, you will see little or 
no practical increase as a result.
Regarding the effect on the pump, it will continue to see 
approximately the same flow rate.  Since the pump discharge 
pressure will remain more or less the same, assuming a 
centrifugal pump (see curve of discharge pressure vs. flow 
rate, if it exists), the pump's driver should use about the 
same amount of energy as before.  In other words, there will 
be a slight improvement in the sprinkler system efficiency 
(slightly more water flow), but if you try to measure it, 
you will not be able to detect a significant difference 
unless the original piping diameter upstream of the 
sprinkler is very small.  
On purely theoretical grounds, Sasha wins the bet.
===================================================================
For some *very* interesting alternate viewpoints, look at
http://www.hamblin.com/mf.main/welcome.html

Best reference I know is Happel, J. and H. Brenner (1965) Low Reynolds 
Number Hydrodynamics.  (A more recent edition may exist.) 

Steven Vogel wrote:
> 
> Best reference I know is Happel, J. and H. Brenner (1965) Low Reynolds
> Number Hydrodynamics.  (A more recent edition may exist.)
I think I heard that there was a new edition of this book in last
year or two.  I am not sure on this, but if correct it would 
contain updated references.
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                       Thermal/Fluid System Design and Analysis          >

Try Rheol. Acta. 33,185 (1994) or Int. J. Multiphase flow, 16 899.
David Auerbach