laminar flow in an annulus
laminar flow in an annulus
(OP)
I have need to determine laminar flow in an annulus, and I am not sure what to use for the diameter (hydraulic diameter).
My references tell me that hydraulic radius or diameter is not applicable to laminar flow. So my question is what "diameter" should be used to calculate Re as well as flow in Darcy's equation?
(If important, these are going to be conduits less than about 0.2" diameter with an annulus space of about 0.02" and a length of about 0.2". Of course these are all guesses until I can make a reasonable calculation. Calcs will be proven in lab tests.)
Thanks very much.
My references tell me that hydraulic radius or diameter is not applicable to laminar flow. So my question is what "diameter" should be used to calculate Re as well as flow in Darcy's equation?
(If important, these are going to be conduits less than about 0.2" diameter with an annulus space of about 0.02" and a length of about 0.2". Of course these are all guesses until I can make a reasonable calculation. Calcs will be proven in lab tests.)
Thanks very much.
Paul
www.ostand.com





RE: laminar flow in an annulus
It has an equation for determing the hydraulic diameter for flow in an annulus.
There was also a previous thread that discussed what happened when the annulus was very small and the Crane formula no longer appeared to apply.
Patricia Lougheed
******
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RE: laminar flow in an annulus
In case this reference is convenient - the original 1960 Transport Phenomenon by Bird, Stewart and Lightfoot has an analytical solution to laminar flow in an annulus. It doesn't use hydraulic radius.
Good luck,
Latexman
RE: laminar flow in an annulus
RE: laminar flow in an annulus
David
RE: laminar flow in an annulus
Regards,
SNORGY.
RE: laminar flow in an annulus
I *know* you *meant* to type "410"...
Regards,
SNORGY.
RE: laminar flow in an annulus
Patricia Lougheed
******
Please see FAQ731-376: Eng-Tips.com Forum Policies: Eng-Tips.com Forum Policies for tips on how to make the best use of the Eng-Tips Forums.
RE: laminar flow in an annulus
I have missed your FAQ on this topic: really interesting.
RE: laminar flow in an annulus
My annulus is quite small, a fraction of an inch in diameter and using the method described in the faq I get an effective diameter 2.7 times larger than that calculated by the conventional method (4*A)/wetted perimeter.
This along with not having assurance, at this time, that we will be able to maintain concentricity, will lead to some serious lab work to evaluate our device.
Thanks again!
Paul
www.ostand.com
RE: laminar flow in an annulus
David