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boundary conditions, pressure losses due to friction
Posted 2011年1月14日 GMT-5 12:01 Fluid & Heat, Computational Fluid Dynamics (CFD) Version 3.5a 1 Reply
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Hi! i need help one more time =(
my question is - i have flow of fluid in the pipe, i know mass flow rate, and i know inlet pressure.
How can i calculate pressure losses due to friction?
Thanks =)
my question is - i have flow of fluid in the pipe, i know mass flow rate, and i know inlet pressure.
How can i calculate pressure losses due to friction?
Thanks =)
1 Reply Last Post 2011年1月14日 GMT-5 15:14
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Posted:
1 decade ago
Hi
if I remember right (CFD is not my main occupation) head losses in a pipe system comes from known pipe parameters: length, section ..., liquide properties: density, viscuosity ... environmental values: temperature, pressure ..., but also surface roughness of the piping, all for laminar flow, and with turbulences everything is even more fun ;)
Formulas relating these are Poiseille, for pressure drop of the flow, mass & momentum conservation in general ...
So if you can express all this in a reasonnable way , including enough BC, as you are suggesting, except for one unknown (i.e pipe surface roughness), then you can get Comsol to find by least square (via a global equation) the best fit for this unknown (sure I suppose there is only 1 unique solution)
It's not a precooked answer, but at least it's the methodology I would use ;)
PS: in engineering fluidics, I find there are very many "engineering" formulas, obtained in empiric ways, I have learned to be rather suspicious about them and always analyse carefully the units in there, as many of the "constants" are very physics dependet, based on often forgotten assumptions.
--
Good luck
Ivar
if I remember right (CFD is not my main occupation) head losses in a pipe system comes from known pipe parameters: length, section ..., liquide properties: density, viscuosity ... environmental values: temperature, pressure ..., but also surface roughness of the piping, all for laminar flow, and with turbulences everything is even more fun ;)
Formulas relating these are Poiseille, for pressure drop of the flow, mass & momentum conservation in general ...
So if you can express all this in a reasonnable way , including enough BC, as you are suggesting, except for one unknown (i.e pipe surface roughness), then you can get Comsol to find by least square (via a global equation) the best fit for this unknown (sure I suppose there is only 1 unique solution)
It's not a precooked answer, but at least it's the methodology I would use ;)
PS: in engineering fluidics, I find there are very many "engineering" formulas, obtained in empiric ways, I have learned to be rather suspicious about them and always analyse carefully the units in there, as many of the "constants" are very physics dependet, based on often forgotten assumptions.
--
Good luck
Ivar