Hydrodynamics of interfacially driven bioreactors

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Griffin, Shannon, Ruth
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Mechanical engineering
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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 operating principle. 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.
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Rensselaer Polytechnic Institute, Troy, NY
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