Bubble coalescence in electrolytes: effect of bubble approach velocity-

0525219 - ÚCHP 2022 RIV NL eng J - Journal Article
Orvalho, Sandra - Stanovský, Petr - Růžička, Marek
Bubble coalescence in electrolytes: effect of bubble approach velocity-.
Chemical Engineering Journal. Roč. 460, FEB 2021 (2021), č. článku 125926. ISSN 1385-8947. E-ISSN 1873-3212
R&D Projects: GA ČR(CZ) GA19-09518S
Institutional support: RVO:67985858
Keywords : bubble coalescence * coalescence regime * electrolyte
OECD category: Chemical process engineering
Impact factor: 16.744, year: 2021
Method of publishing: Open access with time embargo

The coalescence of air bubbles in aqueous solutions of electrolytes was studied experimentally. The bubbles were produced from two vertical parallel capillaries in a still liquid and video recorded. Several quantities were evaluated: bubble shape and size, bubble distance, bubble expansion rate, time of the first touch, time of bubble merger, time of bubble detachment. The three state variables were: bubble coalescence efficiency E, transition electrolyte concentration Ct, bubble contact time - coalescence time T. The effect of four control parameters was investigated: electrolyte type (3 inorganic salts: NaCl, Na2SO4, CaCl2), electrolyte concentration C (5 values sparsely covering a broad interval, 0.001 - 2 mol/L), bubble approach velocity V (9 values, from 0.03 to 40 mm/s), bubble diameter D (2 values, 1 and 1.5 mm). The following results were obtained. Coalescence efficiency E decreases with both C and V. Transition concentration Ct is not a material property but depends on the hydrodynamic conditions, Ct decreases with V. Contact time T decreases with V, as T ∼ V-1, and increases with C, roughly as T ∼ C1.9. Bubble approach velocity V plays a dual role: it reduces the coalescence region but accelerates the coalescence process. The transition from coalescence to noncoalescence proceeds via a minimum in the T(V) graphs. Bubble size D reduces the value of Ct, whence the extent of the coalescence region. The three electrolytes behave in a similar way. A scale-estimates model was developed to describe the results. The effect of electrolytes on the coalescence is similar to the effect of liquid viscosity.
Permanent Link: http://hdl.handle.net/11104/0311268