Crane 410 Changed - Hydraulic Radius (Diameter) for extreme aspect ratios

[SharpBarb]

I'm reviewing a calculation that used one half the width of a narrow channel as the hydraulic radius. Their reference is Crane TP 410 (2001) which states "In such cases [narrow shapes], the hydraulic radius is approximately equal to one-half the width of the passage."


I checked this using my 2009 versions of Crane TP 410 and the text has been replaced with "For extremely narrow shapes such as annular or elongated openings, where width is small relative to length, hydraulic radius may not provide accurate results."

So, why the change? Was the prior approximation inaccurate or was this just an oversight?

 

[MikeHalloran]

For narrow passages, the approximate models we use for prediction of the behavior of roundish and squarish channels just fall apart. They always have.


Mike Halloran
Pembroke Pines, FL, USA

 

[ione]

Great stuff here

http://www.eng-tips.com/viewthread.cfm?qid=236832