Investigating bubble dynamics in a bubble column containing shear thinning liquid using a dual-tip probe

Abstract

Bubble dynamics was characterized experimentally in non-Newtonian shear thinning fluids with different viscosities by a dual-tip resistivity probe. The experiments were carried out in a 9 cm diameter column while the superficial gas velocity varied between 0.5 and 7 cm/s. Air, injected through a diffuser, was the dispersed phase and various solutions of carboxy-methyl cellulose were used as the continuous liquid phase. An algorithm was developed to detect each individual contact of bubbles with the probe needles. It was shown that increasing the viscosity produces larger bubbles which make the homogeneous flow regime instable at liquid viscosities greater than 7 cP. It was found that the axial profiles of bubble chord length and velocity are affected by both shear thinning behavior of the solutions and the viscosity of the solution. The shear thinning behavior causes a descending trend of axial distribution of bubble rise velocity. Moreover, gas holdup reaches a maximum in the middle of the column in solutions studied. The probability distribution of bubble chord length was well fitted by a log-normal distribution. However, the bubble rise velocity distribution is Gaussian in the homogeneous regime at low gas flow rates. Correlations are given for evaluating bubble chord length and bubble rise velocity.