Study on Void Fractions of Large and Small Bubbles in a Bubble Column.

The void fractions of large and small bubbles, α_G,L and α_G,S, in a bubble column were measured by means of the DGD (Dynamic Gas Disengagement) method. The column diameter was 200 mm and the initial liquid heights H₀ were 800, 1600, 2400, and 3000 mm. We dealt with heterogeneous bubbly flows with the superficial gas velocity J_G from 0.06 to 0.30 m/s. Three kinds of liquids were used as the liquid phase to understand effects of the liquid viscosity on the void fractions. The following conclusions were obtained: (1) an experimental database of the void fractions of large and small bubbles was obtained at various initial liquid heights and liquid viscosities, (2) the void fractions of large and small bubbles increase with increasing J_G at constant H₀, (3) the void fraction of large bubbles for J_G ≤ 0.10 m/s decreases with increasing H₀ for H₀ ≤ 2400 mm and is almost constant for H₀ ≥ 2400 mm while α_G,L is independent of H₀ for J_G ≥ 0.20 m/s, (4) the liquid viscosity does not affects α_G,L, (5) the void fraction of small bubbles slightly increases at J_G = 0.06 m/s, whereas it is almost constant at J_G = 0.10 m/s, and decreases for J_G ≥ 0.20 m/s as H₀ increases, and (6) the void fraction of small bubbles decreases with increasing the liquid viscosity and dependence of α_G,S on H₀ is not so different. [ABSTRACT FROM AUTHOR]