Thermal Science 2013 Volume 17, Issue 4, Pages: 1245-1250
doi:10.2298/TSCI1304245A
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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