Bubble rise velocity and trajectory in xanthan gum crystal suspension

An experimental set-up was used to visually observe thecharacteristics of bubbles as they moved up a column holdingxanthan gum crystal suspensions. The bubble rise characteristics in xanthan gum solutions with crystal suspension are presented in this paper. The suspensions were made by using different concentrations of xanthan gum solutions with 0.23 mm mean diameter polystyrene crystal particles. The influence of the dimensionless quantities; namelythe Reynolds number, Re, the Weber number, We, and the drag co-efficient, cd, are identified for the determination of the bubble rise velocity. The effect of these dimensionless groups together with the Eötvös number, Eo, the Froude number, Fr, and the bubble deformation parameter, D, on the bubble rise velocity and bubble trajectory are analysed. The experimental results show that the average bubble velocity increases with the increase in bubble volume for xanthan gum crystal suspensions. At high We, Eo and Re, bubbles are spherical-capped and their velocities are found to be very high. At low Weand Eo, the surface tension force is significant compared to the inertia force. The viscous forces were shown to have no substantial effect on the bubble rise velocity for 45 < Re < 299. The results show that the dragco-efficient decreases with the increase in bubble velocity and Re. The trajectory analysis showed that small bubblesfollowed a zigzag motion while larger bubbles followed a spiral motion. The smaller bubbles experienced less horizontalmotion in crystal suspended xanthan gum solutions while larger bubbles exhibited a greater degree of spiralmotion than those seen in the previous studies on the bubble rise in xanthan gum solutions without crystal.