This paper studies the shape of an air bubble quasi-statically flowing in the longitudinal direction of narrow channels. Two bottom topographies are treated, i.e., linear and quadratic variations of the gap along the transverse direction. This work analyses the main characteristics of the gas-liquid interface with respect to the wedge aspect ratio. From the convergence of asymptotic, numerical and experimental analyses, we found simple dependences for the finger width and total curvature as a function of channel aspect ratio. These results provide simple and general expressions for the pressure drop needed to overcome capillary forces and push the air finger inside the channel.
We report a study of the capillary pinching of a gas bubble by a wetting liquid inside a pinched channel. The capillary pinching induces very reproducible bubbling, at a very well-defined frequency. There are two regimes associated with drip and jet bubbling. In the latter, we show that highly monodispersed bubbles are formed by our pinched channel. The dynamics of the bubble formation also shows two distinct regimes: a long-duration elongation of the air bubble and a rapid relaxation of the interface after interface breakup. The slow regime depends on the flux imposed and the channel geometry. The rapid deformation dynamic regime depends very weakly on the boundary conditions. Scaling arguments are proposed in the context of the lubrication approximation to describe the two regimes.
In this paper, we present a network method for computing two-phase flows between two rough surfaces with significant contact areas. Low-capillary number drainage is investigated here since one-phase flows have been previously investigated in other contributions. An invasion percolation algorithm is presented for modeling slow displacement of a wetting fluid by a non wetting one between two rough surfaces. Short-correlated Gaussian process is used to model random rough surfaces.The algorithm is based on a network description of the fracture aperture field. The network is constructed from the identification of critical points (saddles and maxima) of the aperture field. The invasion potential is determined from examining drainage process in a flat mini-channel. A direct comparison between numerical prediction and experimental visualizations on an identical geometry has been performed for one realization of an artificial fracture with a moderate fractional contact area of about 0.3. A good agreement is found between predictions and observations.
In microchannel flow, gas-liquid interface behavior is important for many applications, e.g. micro-reactors, micro heat pipes to name only two of them. Microfluidic channels shape are generally rectangular or triangular with associated solid corner. Those corners are interesting for they drastically increase capillary effects of wetting liquids compared to smooth solid boundaries. We study capillarity driven gas–liquid flows in a flat triangular channel. A channel of triangular cross section was micro-machined in a polymeric material and covered by a transparent plexiglas plate. The wetting fluid is injected at a controlled flow rate and the interface motion along the corners is recorded with a CCD video camera. A simple lubrication theory predicts the temporal evolution of the liquid-gas interface. A good agreement is found between those predictions and experimental results. the theory also predicts when the invasion of the channel bulk occurs. The dynamics of the bulk meniscus is discussed. The results suggest that the bulk meniscus dynamics is affected by the growth of the liquid fingers that develop along the edges of the channel.
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