Photographic Study of Bubble Size and Void Fraction Distributions in a Gas-Liquid Stirred Tank with Hollow Blade Turbine

The distributions of local Sauter mean bubble size, gas void fraction, and interfacial area in a standard stirred tank equipped with a half elliptical blade disk turbine (HEDT) have been investigated at different gas flow rates using photography techniques. In the identification of bubble size, the liquid phase is dyed with fluorescent rhodamine to make the gas-liquid interfaces clearly visible under a laser sheet. An image processing algorithm is used to analyze the bubbles interface, and the algorithm's reliability has been validated by comparing with manual counting method. The image accuracy is about 0.05 mm, and the minimum identifiable bubble is 0.45 mm. The investigation of the distributions of void fraction is based on a "depth field" method through a calibration experiment. Results show that the local void fraction and interfacial area distributions are similar, and the maximum values are located below the impeller. The tank-averaged Sauter bubble size increases slightly with increasing ventilation, and the increase in void fraction with increasing ventilation is nearly in the same proportions.