Session: 7.6 - Experimental methods for multiphase flows

Paper Number: 158577

158577 - Experimental Investigation of Neutrally Buoyant Immiscible Drop Dynamics in Collapsible Vessels 

Abstract: 

Understanding the formation and transport dynamics of neutrally buoyant, immiscible liquid drops in large, thin-walled vessels is crucial for gaining insights into cardiovascular therapeutics, biomedical procedures, and engineering applications. The flexibility of biological vessels makes them prone to structural deformations, such as buckling or collapse, when pressure imbalances occur across the vessel wall. In the human body, vessel deformation and collapse can be caused by various factors, including posture changes, gravity-induced fluid redistribution, muscle contractions, and localized blood vessel bulging due to aneurysm formation. The study of neutrally buoyant drop formation and transport in collapsible tubes is relevant to space physiology, where buoyancy-independent fluid dynamics are essential. Applications include drug delivery systems, small diagnostic devices, spacecraft fluid management, nutrient delivery in bioreactors, and cryogenic fluid handling. Additionally, this research is pertinent to cardiovascular therapies such as endovascular embolization and the general dynamics of thrombus and cell movement in large blood vessels. While microfluidic studies of drop dynamics are extensive, challenges related to larger drops interacting with collapsible veins under buoyant yet constrained or deformed conditions remain underexplored. This gap highlights the need for focused research to better understand these complex fluid-structure interaction systems. In this study, we experimentally investigated the dynamics of neutrally buoyant, immiscible liquid drop formation and transport in a large, thin-walled tube model, focusing on intermediate Reynolds numbers ranging from , which represent typical human venous flow. A tube-in-tube experimental platform was designed to study the drop dynamics. The dispersed phase (ECO-702 Pump Diffusion Oil, Phenylmethyl-dimethyl Cyclosiloxane) and the continuous phase (a 73:27 water-glycerin mixture) were selected to create a neutrally buoyant drop system with a density ratio of nearly 1:1 and a viscosity ratio of 21:1. High-speed cameras were used to record dynamic interactions with the vessel walls and track drop movements. The effects of the internal Weber (Weᵢ) number and external Capillary (Caₒ) number were studied based on image analysis, ultrasound flowmeter, and high-frequency pressure transducers. The results suggest that in undeformed tubes, the Weᵢ controls jet length and total drop volume, whereas Caₒ controls drop size and transport speed. A dripping regime was observed at very low Weᵢ, whereas a jetting regime emerged at higher Weᵢ. In dripping regimes, as Caₒ increased, drops transitioned from a plug flow to small drops traveling with helical trajectories. In jetting regimes, the jet length increased as Weᵢ increased. More drops formed and got chaotic as Caₒ increases. The deformation of cross-sections of the collapsed tubes significantly altered the formation and transport dynamics of the drops. Under varied Weᵢ and Caₒ, dripping drops or jets interact with the collapsed tube walls to exhibit complex results. In highly constricted regions, factors such as drop size, interfacial tension, inertia, viscous force, and local deformation geometry collectively determine whether and how a drop passes through or becomes trapped. This study highlights the critical role of vessel flexibility in controlling drop transport dynamics, a factor often overlooked in previous research. These findings provide valuable insights for biomedical applications, fluid mechanics, and microgravity environments.

Presenting Author: Nafis Resan North Dakota State University

Presenting Author Biography: