Multiphase CFD Analysis and Shape-Optimization of Blood-Contracting Medical Devices.

摘要

This thesis presents a framework for computational fluid dynamics (CFD) analysis and shape-optimization of blood-contacting medical devices. The first aim entailed CFD-driven automatic shape optimization of PediaFlowRTM miniature maglev pediatric heart-assist pump with the goal of improving efficiency and minimizing blood trauma. The blade shape of leeward stator was parameterized by two wrap angles and blade axial length. The result of optimization using a Design of Experiments-Nonlinear Programming by Quadratic Lagrangian (DOE-NLPQL) optimization technique greatly improved efficiency from 19.5% to 27.4%. Numerically predicted blood trauma was in good agreement with experimentally measured values. The second aim focused on optimization of a novel magnetic blood filter for severe malaria, mPharesis(TM). The objective was to maximize capture efficiency of malaria-infected red blood cells (pRBCs) with three independent design variables: channel height, pitch and flow rate. The pRBCs were modeled as paramagnetic particles suspended in a Newtonian fluid. Trajectories of the pRBCs were numerically calculated inside a microchannel exposed to a periodic magnetic field gradient. The resulting length of the optimized design was reduced from 742 mm to 79.7 mm using the DOE-NLPQL optimization technique. The resulting capture efficiency was greatly increased by 57.7%: from 25.5% to 85.2%. The third aim was to develop a two-phase model of blood flow to elucidate the phenomenon of RBCs margination. Using the Theory of Interacting Continua, the plasma was assumed to behave as a Newtonian fluid whereas the RBCs were modeled as rigid spherical particles with viscosity dependent on the shear-rate and hematocrit. The nondimensional simulation of fully-developed steady flow revealed that the drag and lift forces were important interaction forces. Three-dimensional unsteady two-phase simulations predicted RBC depletion in the corner of a sudden expansion channel. The RBC depletion length was found to increase, with decreasing flow rate and hematocrit. The main outcome of this aim showed a qualitatively good agreement between two-phase flow simulation results and experimental data. Therefore, the efforts of multiphase flow and optimization studies have led to identify crucial design factors in the early stage of medical devices, as well as reduce development time and cost. The overall contributions of this dissertation are establishing cutting-edge optimization techniques, constructing a reliable blood trauma model, and implementing a three-dimensional two-phase blood flow code.;Keywords: blood pump; CFD; optimization; blood trauma; malaria; magnetic separation; paramagnetic particle; theory of interacting continua; two-phase flow; plasma; RBC; viscosity; drag force; lift force.