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The void fractions of large and small bubbles, αG,L and αG,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 JG 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 JG at constant H0, (3) the void fraction of large bubbles for JG ≤ 0.10 m/s decreases with increasing H0 for H0 ≤ 2400 mm and is almost constant for H0 ≥ 2400 mm while αG,L is independent of H0 for JG ≥ 0.20 m/s, (4) the liquid viscosity does not affects αG,L, (5) the void fraction of small bubbles slightly increases at JG = 0.06 m/s, whereas it is almost constant at JG = 0.10 m/s, and decreases for JG ≥ 0.20 m/s as H0 increases, and (6) the void fraction of small bubbles decreases with increasing the liquid viscosity and dependence of αG,S on H0 is not so different. [ABSTRACT FROM AUTHOR]