New Correlations for the Prediction of Terminal Velocity and Drag Coefficient of a Bubble Rising

The present experimental study was done aimed to investigate dynamic ofa single bubble rising through wall-bounded flow at high Reynoldsnumber. Thus, Rhamnolipid biosurfactant was added to stagnant fluid andbubble diameter was controlled between 2.5 and 3.5mm. The resultedReynolds number was in the range of 400 to 900 depends on biosurfactantconcentration. Rhamnolipid has a low toxicity, a high biodegradabilityand good stability at a wide range of temperatures. The results showedthat terminal velocity linearly depends on Reynolds number. Furthermore,drag coefficient is related to Eötvos number and is autonomous toReynolds number. Finally, to estimate terminal velocity and dragcoefficient, four empirical correlations were developed. Relative errors ofthe proposed correlations were less than of 3.35% and 1.97% for velocityand dimensionless velocity equations, respectively, and average errors oftwo equations proposed for drag coefficient were 4.44% and 3.26%.