Optimizations and Interpretations of Signal from Liquid Distribution Setup in Shake Flask

摘要

Shake flasks have been used for screening process in fermentations for a long time. The oxygen transfer rates of the fermentation media change with viscosity. The liquid distribution in hydrophilic shake flask becomes asymmetrical as the viscosity of the liquid increases. Therefore, a non-invasive optical technique has been developed to collect angular information on the shape of the liquid at different operating conditions like shaking frequency, shaking diameter, and filling volume. This technique uses light emitting diodes, a photomultiplier tube and fluorescent solution. 16 sets of optical fibers with each set comprises of 2 optical fibers arranged in certain angle of incident light between the fibers are attached at different heights of the outside wall of a shake flask. Blue lights from the light emitting diodes are switched alternately at different heights and excite the fluorescent molecules in the flask. The emission lights are then sent through the optical fibers back to the head-on photomultiplier tube. With LabVIEW program, automatic and manual mode of signal data collections from the photomultiplier tubes are available. The digital signals received and saved indicating the liquid distribution are then analyzed in MATHLAB for the shape. However, prior to the identification of the shape of the liquid distribution in shake flask, the optimizations of the signal parameters are investigated. The influences of the intensity of the light emitting diodes and the photomultiplier tube's sensitivity level to the liquid distribution's signal at a certain shaking frequency and at each height at a fixed filling volume are observed. Varying these parameters change the output voltages from the photomultiplier tube. However, the shapes of the liquid distributions remain the same. The varying numbers of rotations collected in reference to the mean show acceptable percentage deviations but slight sharp increases of the percentage are shown especially at the start of the bulk liquid. With the information, signals obtained and interpreted from this setup depict invaluable information on the hydrodynamic of the liquid distribution in shake flask.