Shapes of ellipsoidal bubbles in infinite stagnant liquids

•Experimental data of bubble aspect ratios are obtained for various Morton numbers.•An accurate correlation of the aspect ratio is proposed.•The correlation is applicable to ellipsoidal bubbles at various Morton numbers.•Terminal velocities are accurately predicted by making use of the correlation.

Aspect ratios E of ellipsoidal bubbles in infinite stagnant clean liquids are measured for log M = −6.6, −5.5, −4.9 and −3.9, where M is the Morton number. An empirical correlation of E applicable to a wide range of the Morton number is proposed by making use of the present data and Sugihara's data at log M = −11 (2007). The aspect ratio in this correlation is expressed in terms of the combination of the Eötvös number and the bubble Reynolds number to account for the effects of the inertial, viscous, buoyant and surface tension forces on E. Terminal velocities of ellipsoidal bubbles are accurately predicted by using the proposed correlation and a drag correlation proposed by Rastello et al. (2011).