Jet aeration study by flow visualization method with rheoscopic fluid

The paper is devoted to investigating the jet aeration peculiarities in bioreactors based on the optical flow visualization method with rheoscopic fluid. The air distribution problem in fermentation medium in loop bioreactors aerated by jet devices is very actual for microbial cultivation but still insufficiently studied. The motion and mixing of air and fluid flows were studied in the jet aerator model of the jet loop bioreactor FT-0.325p for microbial pesticide manufacturing. The model represented the axial section of the jet aerator designed at a scale of 1:1 and made from an acrylic glass plate of 1.5 mm thickness. The jet aerator model was inserted between two thick acrylic glass plates (10 and 16 mm) containing flow channels for fluid and air supply and air-fluid mixture drain. The rheoscopic fluid was the water suspension of stearic acid (1:20 by mass). The fluid and pressured air were supplied to the model by a pump and air compressor respectively during the experiments. The fluid flow rate was changed from 2 to 6 dm3·min-1 with step of 1 dm3·min-1. The motion of the rheoscopic fluid and air-fluid mixing was caught on video on each value of fluid flow rate with simultaneous detection of flow static pressures and flow rates. Flow pattern analysis combined with estimated hydrodynamic parameters allowed us to evaluate the effect of initial flow conditions on mixing efficiency. At mixing of flows, air was distributed in the mixture as small air jets, packed into conglomerates, which were well seen on the frame-by-frame analysis of video records. The efficient aeration modes based on the well-aerated regions’ size and location inside the aerator were identified with reference to the mixture flow regime. New data about air-fluid mixing can be the ground of the mathematical model development of jet aeration of fermentation medium in bioreactors.