Formation and Transport Dynamics of High Speed Gas-Liquid Droplet Microfluidics

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The goal of this project is to understand liquid droplet formation and transport dynamics in gaseous microfluidic systems, including compressibility effects. Understanding liquid droplet formation and transport in gaseous microchannels will have significant impact on the general area of droplet microflows, particularly for gas sampling and dry particle aerosol generation. The knowledge gained will have major implications for next generation microfluidic systems in portable gaseous biochemical diagnostics and sensing applications, as well as in larger scale spray and atomization systems. The rich engineering, physics, and materials challenges tackled here represent a great cross-disciplinary project for the students involved. The results of the project will provide new classroom materials for courses that the PI teach, as well as outreach activities geared towards elementary school audiences. An undergraduate summer internship program aimed at underrepresented Northeastern University freshmen/sophomores will be established to prepare them as multidisciplinary leaders of future engineering challenges.The governing physics behind the liquid droplet formation, detachment, transport, and interaction with the continuous gas phase flow for different geometries and flow conditions will be studied and analyzed. A multi-task research program will be put in place that includes hydraulic and optical diagnostics characterization of droplet formation, detachment and transport interactions, alongside numerical simulations of these processes. The research program includes the following specific thrusts: (1) Experiments and numerical simulation of droplet formation in the dripping and jetting regimes will be conducted for different flow conditions and geometries, including 3D microfluidic flow architectures. The conditions for transition between these two regimes and possible hysteresis effects will also be explored. (2) Characterization and control of the aerodynamics of droplet transport will be conducted after formation and detachment, including electrostatic based control strategies. Droplet evaporation, absorption of vapor species, and internal flow dynamics and mixing characteristics of the droplets will also be addressed. (3) An assessment will be made of the gas phase compressibility effects in terms of flow acceleration and the presence of shock waves. Changes in flow regimes and transitions as well as the droplet transport dynamics due to these effects will be assessed. Similarly, droplet interaction with standing shock waves in the microchannel will be studied.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.