Bubble Dislodgment in a Capillary Network with Microscopic Multichannels and Multibifurcation Features

Abstract

Bubble lodgment in complex capillary network is a common issue in many industrial and biological processes. Research work reported in literature only investigated bubble dislodgement in single channels, and did not consider the effect of network complexity on the dislodgement. This paper focuses on the pressure required to dislodge single bubble from a microscopic capillary network, and investigates what factors affecting the dislodging pressure, to facilitate the precise control of bubble flows in porous media. A capillary network with multi-bifurcation and smoothly-changed diameter is designed to closely mimic the structure of the physiological vascular networks. Over 600 bubble dislodgement experiments have been conducted to understand the effect of network structure, channel dimensions, and bubble length on the dislodging pressure. The results indicate that network structure is a dominant factor affecting the dislodging pressure, and dislodging pressure increases with the increase in network complexity. The effect of bubble length on the dislodging pressure depends on bubble length. When the bubble length is less than a certain value, which is around 2 mm in this study, the dislodging pressure increases significantly with the decrease of bubble length. Once the bubble length is larger than 2 mm, the dislodging pressure is independent of bubble length. A model has been proposed to explain the bubble dislodgement in complex capillary networks. The impact of network structure on the bubble dislodging pressure is characterized by a parameter cj. The model indicates that the dislodging pressure is the function of bubble length, channel dimension and network structure. The analysis of model parameters and shows that parameter cj, rather than the channel size dominates the dislodging pressure for bubbles with length greater than 2 mm, and the increase rate of the dislodging pressure is significantly affected by both channel size and parameter cj.

Evolution of Thin-Liquid Films Surrounding Bubbles in Microfluidics and Their Impact on the Pressure Drop and Fluid Movement

“…For the bubble with the same length, the pressure drop varies with the degree of lubrication, which is very difficult to evaluate. The correlation between the pressure drop and bubble length for the removal of dry bubbles in microfluidics with DI water as the working liquid has been derived previously, and the details can be found in refs and . Our experimental results (Figure ) agree well with eq , suggesting that eq describes well the dry bubble removal from different microfluidic networks filled with different working liquids. where K is the absolute permeability of the microchannel, L j is the bubble moving distance, ρ l is the density of the working liquid, and f f is the frictional factor, which is closely related to fluid velocity and viscosity.…”

“…The capillary pressure drop for the rectangular microchannel is given by the derived Young–Laplace equation as where r is the equivalent radius of the microchannel. The dynamic (advancing or receding) contact angle (θ d ) is the function of the static contact angle (θ s ) and interface velocity (θ b ), and it can be expressed as , …”

“…The dynamics of lodged and dry bubbles require further investigation in terms of the evolution of liquid film deposition between the bubble and channel wall, as the evolution of the liquid film significantly determines the resistance applied on the bubble during the removal of lodged bubble. Our group has investigated the pressure required for removing dry bubbles (1 < L/D < 5) from microfluidic networks with multiple bifurcations and highly interconnected microbranches. , This study focuses on the evolution of liquid film deposition between the dry and lodged bubble and nonideal surface and its relationship with the bubble dynamics during the bubble removal process. A theoretical correlation of the maximum bubble velocity within the bubble removal process has been derived as a function of bubble length, fluid viscosity, surface tension, geometry of the cross-sectional area, and dimensions of the microchannel.…”

Design and Fabrication of a Fully-Integrated, Miniaturised Fluidic System for the Analysis of Enzyme Kinetics

“…Laser cutting is a further option [ 30 , 31 ]. For example, a capillary network with consistent channel depths was engraved on 2 mm thick acrylic, in order to study bubble lodgement in industrial and biological processes [ 32 ]. This complex capillary system mimicked physiological vascular networks with rectangular channels between 0.26 and 0.52 mm.…”

Design and Fabrication of a Fully-Integrated, Miniaturised Fluidic System for the Analysis of Enzyme Kinetics

“…Laser cutting is a further option [25][26]. For example, a capillary network with 3 of 13 consistent channel depths was engraved on 2 mm thick acrylic, in order to study bubble lodgment in industrial and biological processes [27]. This complex capillary system mimicked physiological vascular networks with rectangular channels between 0.26-0.52 mm.…”