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Influence of bubbles characteristics on the skin friction and velocity gradient on solid sphere
Author(s) -
Essadki A. H.,
Nikov I.,
Delmas H.
Publication year - 2011
Publication title -
the canadian journal of chemical engineering
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.404
H-Index - 67
eISSN - 1939-019X
pISSN - 0008-4034
DOI - 10.1002/cjce.20647
Subject(s) - bubble , mechanics , coalescence (physics) , spheres , volume (thermodynamics) , distributor , dead zone , velocity gradient , two dimensional gas , materials science , physics , thermodynamics , geology , mass spectrometry , oceanography , astronomy , astrobiology , quantum mechanics
A detailed study of the effects of individual bubbles at high gas flow‐rate has shown, that the dominant influence on skin friction over a solid sphere is the bubble volume in compared to bubble frequency. Nevertheless the bubble frequency is very important in case of low gas flow‐rate. Referring to bubbles produced by a gas distributor, statistical and spectral analyses were performed to study the influence of bubbling on exposure time and magnitude of fluctuations. Referring to a calibrated bubble train, the existence of critical frequency is demonstrated. A bubble with larger volume and a mobile, oscillatory surface generates larger velocity gradient. In the case of gas distribution, histograms of the velocity gradient for a 2 mm glass sphere creating bubble coalescence reveal the maximum exceeds 48 000 s −1 in the front zone and 2000 s −1 in the rear zone ( θ = 180°). For 5 mm plastic spheres creating bubble break‐up, the maximum of the velocity gradient is only 8100 s −1 for the front part of the sphere and 2000 s −1 in the rear zone.