
#1
Jan913, 04:24 PM

P: 95

Hello... I can't find the difference between the pressure drop in a pipe due to frictionnal loss and the Pressure difference that cause the flow like in Poiseuille Flow.. Thanks




#2
Jan913, 05:12 PM

P: 763

They are completely different ideas...what specifically don't you understand about either?
Edit: Oh are you talking about like the losses associated with flows like Poiseuille Flow? 



#3
Jan913, 05:22 PM

P: 763

If you are asking how this solution to pressure drop is associated with similar ideas such as the DarcyWeisbach equation, the answer is that the analytical (experimentally derived) DarcyWeisbach equation is employable under broader circumstances.
The assumptions taken for Poiseuille Flow equations are (from wikipedia) "...that the fluid is viscous and incompressible; the flow is laminar through a pipe of constant circular crosssection that is substantially longer than its diameter; and there is no acceleration of fluid in the pipe". In theory this is a nice equation to look at to understand where the mechanical energy is being lost to, but in practical applications of pressure drop analysis it is rarely, if ever, employed. Basically: Poiseuille equation is theoretical, solutions like HazenWilliams and DarcyWeisbach are analytical. 



#4
Jan913, 05:25 PM

P: 95

Pressure Drop
we say that gradient pressure cause flow but in pipe flow the pressure different is due to friction loss




#5
Jan913, 05:39 PM

P: 763

To see how people generally use these equations (Poiseuille is mentioned in there), see here
A solution to Poiseuille's equation is used to approximate the DW friction factor for Laminar, fully developed flow in long pipes. 



#6
Jan913, 06:41 PM

P: 95

Thank you i understand it




#7
Jan1713, 05:21 PM

Sci Advisor
HW Helper
Thanks
PF Gold
P: 4,394





#8
Jan1713, 05:47 PM

P: 763

Thanks for that, I wasn't aware it was so widely used in that industry. I've never personally had any experience with such high viscosity fluids.



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