A hydrodynamic description of the flow behavior in shaken flasks

• We examine the hydrodynamic performance in shaken flasks.
• The flask geometry and oscillating frequency determine the flow pattern and turbulent intensity in the flasks.
• 150 rpm was the orbital velocity providing the highest turbulent intensity.
• The one-baffle configuration showed the best mixing performance.

Shaking flasks bioreactors have been employed extensively in biotechnology research for a long time. Despite of their wide application and importance, there is still insufficient knowledge about the hydrodynamic factors that determine the correct performance of growing cultures. The objective of this work is to provide a hydrodynamic description of the parameters which control the effective performance of such bioprocesses. The flow behavior of shaken flasks was examined using the particle image velocimetry technique (PIV) to capture the mixing dynamics for a range of operating conditions. The velocity fields and turbulent intensities were obtained. For all cases, the chaotic-like fluid motion increased with the orbital speed of the shaker. The behavior of conventional, coiled and baffled flasks was analyzed for shaking speeds ranging from 25 to 250 rpm; at high shaking rates the turbulent distribution increased for each flask configuration but the average value differed significantly. The highest turbulent intensity was found for the one-baffle arrangement, which is about 25% larger than the other configurations. We found that the highest turbulent production for all the different geometric conditions occurred at a shaking speed of about 150 rpm, which is in good agreement with the findings reported for the production of bacterial cultures at such shaking rate.