Bubble Rise Velocity and Drag Co-efficient at High Reynolds Number in Power-Law Fluids

Air bubbles are used in chemical, biochemical, environmental, and food process for improving the heat and mass transfer. Due to the dominance of non-Newtonian liquids used in various process industries, an understanding of bubble rise in rheologically complex liquids has grown to be important. An experimental study of the bubble rise velocity and drag co-efficient at high Reynolds number in non-Newtonian (Power-Law) fluids are presented in this paper. The main characteristics, namely, the bubble velocity and the drag relationship are investigated at high Reynolds numbers (Re<4000). The experiments were conducted in 125 mm and 400 mm cylindrical column at liquid heights of 1 m, 1.2 m, 1.4 m and 1.6 m by introducing different bubble volumes (from 0.1mL to 20.0mL) corresponding to each height. The bubble rise velocity and bubble size were measured using a combination of non-intrusive (high speed photographic) method and digital image processing. The parameters that significantly affect the rise of air bubble are identified. The effect of different liquid heights and bubble volumes on the bubble rise velocity is analysed and the influence of two different sizes of tubes on the bubble velocity for various bubble volume is discussed. A correlation of the drag coefficient at high Reynolds number is explained and compared with the results of other analytical and experimental studies available in the literature. Key-words: Bubble rise velocity, bubble volume, drags co-efficient, Reynolds number, power-law fluid, non-intrusive method