Fluid mechanics and mass transfer in rotating cylindrical vessels: A numerical and experimental study

This is a study of particulate laden flow in a cylindrical vessel rotating about its horizontal axis. The study has relevance to many areas of science and technology, in particular to space sciences and biotechnology. One form of bioreactor used in biological cell culturing consists of a cylinder rotating about a horizontal axis and filled with a fluid containing microcarriers. The microcarriers may carry biological cells. Under suitable conditions, such a bioreactor may be used to simulate several aspects of microgravity. In this thesis, the fluid mechanics and the mass transfer associated with such flows have been investigated by both numerical and experimental procedures. In regard to the numerical aspects of the investigation, the problem is formulated in terms of the equations governing particulate laden rotating flows and are solved using Direct Numerical Simulation (DNS). The DNS studies are based on the method of Arbitrary Lagrangian-Eulerian scheme in a rotating frame of reference. The advantages of this choice of the reference frame over an inertial frame formulation are demonstrated. Results for particle motion, particle interaction dynamics, and associated dynamic forces/stresses have been presented. New dynamic stable states in the form of a steady circular motion about a fixed point and a bicycle pedaling motion have been identified for a single particle case and a two particle case, respectively. The numerical study has been both extended and complemented by experiments for fundamental biology and tissue engineering applications. In regard to fundamental biology, a mass transfer numerical model to examine the enhanced accumulation of phosphate ion (Pi) on the surface of a microcarrier seeded with osteoblasts (boneforming cells) has been developed and the results presented and discussed in the context of sensitivity to apoptogens. As relevant to tissue engineering, experiments to evaluate the viability and function of Nucleus Pulposus and Mesenchymal Stem Cell pellet cultures in a rotating medium (hydrodynamic focusing bioreactor) with a static Petri Dish culture as a control system have been carried out. Results of histological analysis of pellet cross-sections and Reverse Transcriptase-Polymerase Chain Reaction (RT-PCR) results of genes representative of the cells phenotype have been presented and discussed.