Three-dimensional (3D) evaluation of liquid distribution in shake flask using an optical fluorescence technique

Biotechnological development in shake flask necessitates vital engineering parameters e.g. volumetric power input, mixing time, gas liquid mass transfer coefficient, hydromechanical stress and effective shear rate. Determination and optimization of these parameters through experiments are labor-intensive and time-consuming. Computational Fluid Dynamics (CFD) provides the ability to predict and validate these parameters in bioprocess engineering. This work provides ample experimental data which are easily accessible for future validations to represent the hydrodynamics of the fluid flow in the shake flask.

A non-invasive measuring technique using an optical fluorescence method was developed for shake flasks containing a fluorescent solution with a waterlike viscosity at varying filling volume (V_L = 15 to 40 mL) and shaking frequency (n = 150 to 450 rpm) at a constant shaking diameter (d_o = 25 mm). The method detected the leading edge (LB) and tail of the rotating bulk liquid (TB) relative to the direction of the centrifugal acceleration at varying circumferential heights from the base of the shake flask. The determined LB and TB points were translated into three-dimensional (3D) circumferential liquid distribution plots. The maximum liquid height (H_max) of the bulk liquid increased with increasing filling volume and shaking frequency of the shaking flask, as expected. The toroidal shapes of LB and TB are clearly asymmetrical and the measured TB differed by the elongation of the liquid particularly towards the torus part of the shake flask.

The 3D liquid distribution data collected at varying filling volume and shaking frequency, comprising of LB and TB values relative to the direction of the centrifugal acceleration are essential for validating future numerical solutions using CFD to predict vital engineering parameters in shake flask.