The dissertation work consists of two parts. The first part is an analytical study on forced bubble oscillations in tubes. The second part is a numerical simulation on bubble removal by a submerged needle.; In the first part, damping processes, including thermal dissipation and viscous dissipation, in the oscillations of gas bubbles in tubes are investigated in a linear approximation. The model is simplified as a gas bubble filled in a tube and is bounded by two flat liquid columns. It is found that thermal damping depends on the driving frequency and the geometry in a very complex way. Viscous dissipation is studied separately by considering an oscillatory parallel flow in a round tube. It is found that over a wide range of frequencies, thermal dissipation could exceed viscous damping even in capillaries with a sub-millimeter diameter. Comparison of theory with experiment shows excellent agreement. This work is motivated by the possibility of using pulsating bubbles as actuators in micro-devices.; The second part concentrates on numerical simulation on bubble removal by a submerged needle using Boundary Integral method. Related to this project, two steps—bubble attraction by a submerged needle and bubble entrance to a capillary needle—are taken and these consist of two separate studies. 3D and axisymmetric boundary integral methods are applied to the two problems respectively. The proposed bubble removal method is especially useful in future space operations where gravity is reduced substantially.; A submerged needle is used to remove gas bubbles in a gas-liquid mixture bounded in a tube. A uniform flow is applied in the tube to accelerate the process and provides an extra force simulating buoyancy force in case of micro-gravity. Systematic study is carried out to uncover the effects of suction strength, ambient flow rate, bounding tube wall, gravity, and bubble initial positions. A Laplacian type damping scheme is used to reduce the numerical instability caused by the potential assumption.; The next step—bubble entrance to a capillary needle—focuses on the bubble entrance mechanism. A concurrent flow surrounding the bubble is the primary factor that makes this event happen. In addition to the severe surface deformation, a few interesting phenomena, such as bubble detachment and break-up, could be reproduced. A special correction based on lubrication theory is applied to the numerical scheme to prevent numerical instability. Comparison of numerical simulation with experimental results shows very good agreement.
展开▼
