MECHANICS OF MOTION AND DEFORMATION OF A SINGLE BUBBLE RISING THROUGH QUIESCENT HIGHLY VISCOUS NEWTONIAN AND NON-NEWTONIAN MEDIA

The present paper, which is predominantly experimental, provides information on bubble shape, drag coefficient and bubble rocking in highly viscous Newtonian and non-Newtonian media, which was hitherto lacking. Results covering a wide range of bubble size (about 0.2-3 cm equivalent spherical diameter) are reported. The observed changes in bubble shape as the ratio of the major axis of the bubble to equivalent spherical diameter and the aspect ratio are shown, and empirical correlations are obtained. The drag coefficient calculated from the terminal velocity data for gas bubbles provides reasonable agreement with the Hadamard-Rybczynski equation in both highly viscous Newtonian and non-Newtonian media in the low Reynolds number region. Furthermore, bubble rocking caused by wake shedding was observed in the higher Reynolds number region in non-Newtonian media. The Strouhal number including bubble rocking frequency is correlated with the Reynolds number and the Morton number.