| Summary: |
The recent trend in microfluidics has been to work towards the development of integrated devices incorporating multiple fluidic, electronic and mechanical components or chemical processes onto lab-on-a chip devices. This evolution was greatly enhanced by the advances in micromachining technologies.
Multiphase flows occur in many operations in the chemical, petroleum and power generation (such as nuclear power and micro fuel cells). Multiphase flow in micro (diameter < ~ 200 μm) and mini-channels (diameter between 200 μm and 3 mm) has recently gained in importance because of its wide applicability to modern and advanced science and technologies such as micro-electro-mechanical systems (MEMS). Unlike large-scale systems, gas bubbles can present significant problems in microfluidic systems by disturbing and eventually blocking the flow. Interactions on the boundaries between gas, liquid and solid introduce nonlinearity and instabilities. Controlling multiphase flows at the small (mini and micro) scales will allow the development of miniaturized devices (such as microchemical reactors) and will contribute to the understanding of biophysical processes (such as air embolism). The physics of these flows is influenced mainly by surface tension and viscosity and also by wettability and surface roughness which play an important role at these scales. Different two-phase flow patterns can be found when these kind of flows occur in micro and mini-channels Slug flow, also called bubble-train flow, is the flow pattern found in a wide range of applications (such as monoliths catalytic reactors, tubular and hollow fibre membrane ultrafiltration and in the channels of micro direct methanol fuel cells). Until nowadays, only a very limited number of studies present quantitative description (both experimental and numerical) of the hydrodynamics of this two-phase flow at the microscale especially for non-Newtonian fluids.
The aim of this project is the development (d  |
Summary
The recent trend in microfluidics has been to work towards the development of integrated devices incorporating multiple fluidic, electronic and mechanical components or chemical processes onto lab-on-a chip devices. This evolution was greatly enhanced by the advances in micromachining technologies.
Multiphase flows occur in many operations in the chemical, petroleum and power generation (such as nuclear power and micro fuel cells). Multiphase flow in micro (diameter < ~ 200 μm) and mini-channels (diameter between 200 μm and 3 mm) has recently gained in importance because of its wide applicability to modern and advanced science and technologies such as micro-electro-mechanical systems (MEMS). Unlike large-scale systems, gas bubbles can present significant problems in microfluidic systems by disturbing and eventually blocking the flow. Interactions on the boundaries between gas, liquid and solid introduce nonlinearity and instabilities. Controlling multiphase flows at the small (mini and micro) scales will allow the development of miniaturized devices (such as microchemical reactors) and will contribute to the understanding of biophysical processes (such as air embolism). The physics of these flows is influenced mainly by surface tension and viscosity and also by wettability and surface roughness which play an important role at these scales. Different two-phase flow patterns can be found when these kind of flows occur in micro and mini-channels Slug flow, also called bubble-train flow, is the flow pattern found in a wide range of applications (such as monoliths catalytic reactors, tubular and hollow fibre membrane ultrafiltration and in the channels of micro direct methanol fuel cells). Until nowadays, only a very limited number of studies present quantitative description (both experimental and numerical) of the hydrodynamics of this two-phase flow at the microscale especially for non-Newtonian fluids.
The aim of this project is the development (design and construction) of an experimental set-up to study slug flow (or bubble train flow) in mini/ micro channels. The experimental technique will be an adaptation of the microPIV technique (micro Particle Image Velocimetry) to the study of two-phase micro flows. A microPIV system recently acquired (in the scope of the National Re-equipment Programme, funded by FCT) will be available. The hydrodynamic characterization of slug flow with Newtonian (water and aqueous glycerol solutions) and non-Newtonian fluids (CMC and PAA) will be done, for a wide range of operation conditions and shifting from mini to micro channels. Numerical studies involving the adaptation of freeware and in-house developed codes will also be an important milestone of this project. At a final stage of the research activities, a biomedical application of the results obtained will be attempted - the study of gas embolism damage in surgery caused by intravascular air bubbles carried in the bloodstream. The influence of surfactant addition to the evolution of a slow bubble train flow in a microchannel with a liquid resembling blood will be numerically and experimentally investigated.
The enlarged expertise of the team members involved in the project is adequate to the demanding research activities. Some members have a solid numeric background and the others a significant amount of published experimental work on multiphase flows, the most recent of them using a in-house developed technique to study two-phase flows using simultaneously Particle Image Velocimetry and shadowgraphy.
It is hopped that the project contributes to an advance in the microfluidics area with positive impacts in biomedical applications. |