Study Of Gas-liquid Two Phase Flow And Generating Compound Micro-bubbles

Bubble is composed of shell and internal gas. It has an excellent shading capacity and deformability because of it’s special structure. It is widely used in coating, cosmetics, food, medical field, etc. Microfluidics is an important method to study gas-liquid and liquid-liquid two phase flow, and it could be used to generate monodispersed and multilayer microbubbles.In this thesis, microchannels were designed and fabricated using polydimethylsiloxane (PDMS) with the focus on the process of generating microbubbles in the cross channel flow-focusing device at the junction angle of75°. The gas phase was air, and the liquid phase was liquid paraffin/silicone oil. The factors that influenced the bubble size and flow pattern were discussed. The result shows that the size of microbubble decreases with the liquid phase flow rate increases. The flow pattern changed from slug flow to bubble flow, and the mechanism of forming these two flow patterns was analyzed. Also, the size of microbubble decrease with the viscosity of liquid phase increased.It is difficult to generate compound microbubbles when gas phase is injected into the microfluidic chip directly. In the thesis, the mechanical oscillation and microfludics were combined to generate compound microbubbles. First, we generates suspension of microbubbles as a gas phase source, and then the compound mircrobubbles were generated in the microfluidic device. The compound microbubbles contain numerous smaller sized mirobubbles, which have the potentials as theraputical microbubble ultrasound contrast agents. Using this method to get the multilayer microbubbles is simpler and more easy than microfluidic chip alone.