This thesis provides a comprehensive exploration of the hydrodynamics of interfacially drivenbioreactors, specifically focusing on the Ring-Sheared Drop (RSD), a device onboard the International
Space Station (ISS), and its Earth-Analog, the Knife-Edge (surface) Viscometer
(KEV). The RSD offers several advantages as a space-based bioreactor, including scalability,
superior gas transport due to increased surface area, and minimal solid surfaces to avoid
fouling, thereby providing an optimal environment for microorganism growth. The RSD, a
device operating in microgravity, and its terrestrial counterpart, the KEV, share a fundamental
The RSD is a liquid drop held by two knife-edge rings, one of which rotates, inducing
mixing primarily through surface shear viscosity. Similarly, the KEV, a fluid-filled cylindrical
dish, uses a rotating knife edge in contact with the interface, also driving mixing via surface
shear viscosity. This similarity allows the KEV to serve as a valuable experimental model
for studying interfacially driven flow and validating computational models on Earth.
The thesis delves into the physics of gas transport as well as some engineering aspects
in these devices. The analysis covers gas transport into the KEV, providing a baseline for
understanding species transport. Gas transport into the KEV was analyzed with using the
Carreu-Yasuda model to represent an E. coli suspension, and a power-law model to represent
a yeast suspension. The KEV was modeled with a density gradient corresponding to CO2
absorption. Consequently, the effect of the density gradient induced by CO2 was modeled,
revealing its impact on flow and mixing in the KEV.
Through these investigations, a detailed analysis of gas transport into the KEV is
presented. Notable aspects include the use of the Carreau-Yasuda and power-law models to
represent E. coli and yeast suspensions, respectively. The incorporation of a density gradient
associated with CO2 absorption, revealed its influence on flow and mixing within the KEV.
Experiments were also conducted, providing a visual comparison to numerical simulations.
An oil-water simulated RSD was developed to study RSD hydrodynamics in the laboratory.
The design process required contact angle experiments to ensure correspondence with
the geometry of the RSD onboard the ISS. This process is also detailed in this thesis. The
final chapter explores gas transport in the RSD, modeling the non-Newtonian bulk viscosity of E. coli and yeast. Additionally, this study investigates gas transport and mixing using an
oscillating knife edge.
Collectively, these studies illuminate the crucial aspects of RSD and KEV hydrodynamics
when used as bioreactors. Consequently, this research contributes to the ongoing
development of the next generation of interfacially driven bioreactors for space applications.;
August2023; School of Engineering
Dept. of Mechanical, Aerospace, and Nuclear Engineering;
Rensselaer Polytechnic Institute, Troy, NY
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