An investigation of transient three-dimensional buoyancy-driven flow and heat transfer in a closed horizontal annulus
Abstract Buoyancy-driven flow and heat transfer in a horizontal annulus bounded by two impermeable boundaries in the axial direction are numerically investigated in this work. A transient three-dimensional analysis of the end effects on heat transfer and the corresponding flow field is presented. The effects of the axial impermeable boundaries are shown to be characterized by retardation of the flow field through the viscous shearing force in regions near the end walls. The results show that the temperature distribution remains unchanged in the core region provided that the annulus length to outer radius ratio is larger than a critical value. Flow and temperature fields are found to be symmetrical with respect to the mid-axial plane of the annulus. A number of interesting features resulting from the sudden heating of the inner cylinder are presented. Finally, a thorough presentation of formation of flow and temperature fields as a result of the sudden heating of the inner cylinder is given.
Effects of a geometric perturbation on buoyancy induced flow and heat transfer in a cylindrical annulus
Abstract A numerical investigation has been carried out to study the effect of a geometric perturbation on the three-dimensional buoyancy-driven flow and heat transfer in an annular cavity with impermeable end walls. The numerical scheme used in the present study is based on a Galerkin method of finite element formulation. The nature of the three-dimensional flow-field has been analyzed in detail. The local and average Nusselt numbers were obtained for a wide range of Rayleigh numbers, and the heat transfer performance was compared with that for the closed horizontal annulus without a perturbation. The effect of variation of a number of key geometric parameters of the perturbation on the overall heat transfer behavior has been studied. Some of the key features due to the introduction of the perturbation, and qualitative and quantitative effects of the perturbation within the annulus are discussed. It is shown that the introduction of the geometric perturbation can lead to a large increase in the overall heat transfer within the annulus.
Computational fluid dynamics as a development tool for rotary blood pumps.
Computational fluid dynamics (CFD) is beginning to significantly impact the development of biomedical devices, in particular rotary cardiac assist devices. The University of Pittsburgh's McGowan Center for Artificial Organ Development has extensively used CFD as the primary tool to analyze and design a novel axial flow blood pump having a magnetically suspended rotor. The blood-contacting surfaces of the pump were developed using a design strategy based on CFD that involved closely coupling a Navier-Stokes solver to a parameterized geometry modeler and advanced mesh movement techniques. CFD-based blood damage models for shear-induced hemolysis as well as surrogate functions describing thrombosis potential were employed to help guide design improvements. This CFD-based design approach resulted in the timely development of a pump subjected to multiple geometric refinements without building expensive physical prototypes for each design iteration. A physical prototype of the final improved pump was fabricated and experimentally analyzed using particle imaging flow visualization. The CFD predicted results correlated well with the experimental data including pressure-flow (H-Q) performance and specific flow field features. It is estimated that the present CFD-based design approach shortened the overall design time frame from an order of years to months.