Pressure Drop


by tonyjk
Tags: pressure
tonyjk
tonyjk is offline
#1
Jan9-13, 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
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Travis_King
Travis_King is offline
#2
Jan9-13, 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?
Travis_King
Travis_King is offline
#3
Jan9-13, 05:22 PM
P: 763
If you are asking how this solution to pressure drop is associated with similar ideas such as the Darcy-Weisbach equation, the answer is that the analytical (experimentally derived) Darcy-Weisbach 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 cross-section 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 Hazen-Williams and Darcy-Weisbach are analytical.

tonyjk
tonyjk is offline
#4
Jan9-13, 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
Travis_King
Travis_King is offline
#5
Jan9-13, 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 D-W friction factor for Laminar, fully developed flow in long pipes.
tonyjk
tonyjk is offline
#6
Jan9-13, 06:41 PM
P: 95
Thank you i understand it
Chestermiller
Chestermiller is offline
#7
Jan17-13, 05:21 PM
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Quote Quote by Travis_King View Post
If you are asking how this solution to pressure drop is associated with similar ideas such as the Darcy-Weisbach equation, the answer is that the analytical (experimentally derived) Darcy-Weisbach equation is employable under broader circumstances.
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 Hazen-Williams and Darcy-Weisbach are analytical.
In polymer processing applications, typically involving high viscosity polymer melts (say 1000 Poise), the Poiseuille pressure drop equation is used extensively. This includes the entire man-made fiber industry, polymer granule production industry, and plastics manufacture industry. In addition, it applies to flow of ordinary fluids through capillaries.
Travis_King
Travis_King is offline
#8
Jan17-13, 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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