Thermal Science 2013 Volume 17, Issue 4, Pages: 1245-1250
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Hagen number versus Bejan number
Awad Mohamed M.
This study presents Hagen number vs. Bejan number. Although their physical
meaning is not the same because the former represents the dimensionless
pressure gradient while the latter represents the dimensionless pressure
drop, it will be shown that Hagen number coincides with Bejan number in cases
where the characteristic length (l) is equal to the flow length (L). Also, a
new expression of Bejan number in the Hagen-Poiseuille flow will be
introduced. At the end, extending the Hagen number to a general form will be
presented. For the case of Reynolds analogy (Pr = Sc = 1), all these three
definitions of Hagen number will be the same.
Keywords: Hagen number, Bejan number, momentum diffusivity, thermal diffusivity, mass diffusivity