Measuring bubble size distribution in a foam fractionation column using a photoelectric capillary probe

A fast and accurate photoelectric capillary probe method was developed in the described research and used to measure the bubble size distribution and void fraction in a continuous foam fractionation column containing ovalbumin. The developed method was able to perform online bubble size measurements through a well-designed data acquisition system associated with a high-speed computer. Bubble size distribution and void fraction information was obtained at two bulk liquid pool positions below the bulk liquid-foam interface, −12cm and −1cm, and one lower foam phase position, +1cm. This information was gathered for different feed solution conditions (ovalbumin concentration and pH) and operating conditions (including superficial gas velocity and feed flow rate). This information was used to calculate the bubble specific area. Thus, the local enrichment of ovalbumin could be estimated and compared with directly obtained experimental results. The bubble size and void fraction information could help understand the dynamic foaming mechanism through a correlation with measured local enrichments.; It was found that the high local enrichment in the lower foam phase is largely attributable to the abrupt increase in bubble size (from 1.7mm to 3.4mm) and the corresponding void fraction (from 0.25 to 0.75), or the specific area increase from the bulk liquid to the foam phase, which followed the enhanced bubble coalescence and gravity drainage (bubble size and void fraction increase).; At intermediate feed flow rates, the bubble size reaches the largest and the corresponding overall enrichment was highest. The void fraction and specific area are both the largest for the largest feed flow rate. The local enrichment in the lower foam phase was maximized the lowest feed flow rate. Therefore, the specific area alone is not sufficient to determine the magnitude of the local enrichment in the foam phase.; With an increase in the superficial gas velocity, the bubble size increased and the specific area decreased, resulting in a decrease in both the local and overall experimentally determined enrichments at high superficial gas velocities.; The bubble diameters for pH 3.5 and 4.5 were the largest of all the four pH's studied. The void fraction was smallest for pH 6.5. In the lower foam phase, the specific area increased as the pH increased from 3.5 to 9.7. Both the local and overall enrichments were highest for pH 9.7 for the continuous ovalbumin foam fractionation process.