Understanding diffusion-controlled bubble growth in porous media using experiments and simulations.

Nucleation and subsequent expansion of gas bubbles in porous media is relevant to many applications, including oil recovery, carbon storage, and boiling. We have built an experimental setup using microfluidic chips to study the dynamics of bubble growth in porous media. Visualization experiments of the growth of carbon dioxide bubbles in a supersaturated dodecane solution were conducted. We show that bubbles grow as dissolved gas molecules inside the oversaturated liquid diffuse to the gas-liquid interface. Bubbles expanding inside a porous medium displace the liquid phase until the cluster of the gas-filled pores becomes connected to the outlet at the critical gas saturation, which is used as a measure for the total liquid displacement. Our experiments uniquely focus on the growth of a single bubble and show that larger pressure drops lead to faster bubble growth while resulting in lower critical gas saturations. A nonlinear pore-network model is implemented to simulate bubble growth. We compare model predictions for bubble growth dynamics to our experimental results and present the need for further theoretical development to capture deviations from invasion-percolation when a large pressure drop is applied.

Impulsively Induced Jets from Viscoelastic Films for High-Resolution Printing.

Understanding jet formation from non-Newtonian fluids is important for improving the quality of various printing and dispensing techniques. Here, we use a laser-based nozzleless method to investigate impulsively formed jets of non-Newtonian fluids. Experiments with a time-resolved imaging setup demonstrate multiple regimes during jet formation that can result in zero, single, or multiple drops per laser pulse. These regimes depend on the ink thickness, ink rheology, and laser energy. For optimized printing, it is desirable to select parameters that result in a single-drop breakup; however, the strain-rate dependent rheology of these inks makes it challenging to determine these conditions a priori. Rather, we present a methodology for characterizing these regimes using dimensionless parameters evaluated from the process parameters and measured ink rheology that are obtained prior to printing and, so, offer a criterion for a single-drop breakup.