Multiphase Flow at Small Scales

Abstract

Multiphase flow in confined spaces is prevalent in many natural and scientific phenomena, from subsurface processes to biological processes. In this thesis, we introduce innovative experimental methods to explore the impact of wettability on multiphase flow in porous media using microfluidics, and assess the effectiveness of cloth fabrics as source control devices using high-speed laser visualization. We begin by characterizing the underlying physical and chemical mechanisms of wettability alteration of the thiolene-based polymer NOA81, a promising material for fabricating microfluidic devices. By leveraging this foundation, we design platforms for creating 2D surfaces and 3D monodisperse beads made of NOA81 with controlled wettability. Next, we utilize a micromodel made of NOA81 to investigate viscously-unfavorable spontaneous imbibition dynamics within a strongly water-wet fractured micromodel, a process common in oil recovery from tight reservoirs. Our findings reveal the presence of film flow in both the matrix and the fracture, facilitating the displacement of the defending oil phase through an interconnected oil layer toward the fracture. We also observe an inverse relationship between the viscosity ratio and the thickness of the water film within the matrix-fracture system. Lastly, in response to the COVID-19 pandemic, we extend our investigation into multiphase flow in confined spaces to the context of face masks, specifically examining the effectiveness of cloth masks in reducing respiratory disease transmission. We utilize a novel laser visualization setup, including a mechanical cough simulator and high-speed laser imaging, to evaluate the efficacy of face masks for source control. Our results demonstrate mechanistic differences in mask efficacy between source control and inhalation protection. Moreover, we introduce the active porosity parameter that control the effectiveness of masks as source control for mitigating droplet transmission. This concept represents a novel metric for optimizing mask design and understanding mask efficacy in source control.