Hi. I want to make measurements in a straight microchannel having an aspect ratio of (width/depth = 2.5) at very low Reynolds numbers (Re is in between 0.001 to 0.01). What should be the criteria for the hydraulic or the entrance length of the channel to obtain a fully developed flow?
I could not any articles at such low Re; any comments or suggestion or references to published research are highly appreciated.
Dear Subhani,
Please find here a pdf of Yovanovich, M.M., and Y.S. Muzychka, Modeling Friction Factors in Non-Circular Ducts for Developing Laminar Flow, 2nd AIAA Theoretical Fluid Mechanics Meeting, Paper No. 98-2492, 1998. In this paper the entrance length of all kind of different cross sections is discussed, including rectangles with different aspect ratio. Typically the rule of thumb for a circular channel holds, i.e. Le = 0.06Re*Dh, assuming a uniform inlet velocity in the channel. Note that the entrance length can be longer when this is not the case. Hence with small Reynolds numbers your flow will be fully developed easily within one hydraulic diameter channel length.
Hope this helps.
Regards,
Paul
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