Effect of channel size on liquid‐liquid plug flow in small channels

Abstract

The hydrodynamic properties of plug flow were investigated in small channels with 0.5-, 1-, and 2-mm internal diameter, for an ionic liquid/aqueous two-phase system with the aqueous phase forming the dispersed plugs. Bright field Particle Image Velocimetry combined with high-speed imaging were used to obtain plug length, velocity, and film thickness, and to acquire velocity profiles within the plugs. Plug length decreased with mixture velocity, while for constant mixture velocity it increased with channel size. Plug velocity increased with increasing mixture velocity and channel size. The film thickness was predicted reasonably well for Ca > 0.08 by Taylor's (Taylor, J Fluid Mech. 1961;10(2):161-165) model. A fully developed laminar profile was established in the central region of the plugs. Circulation times in the plugs decreased with increasing channel size. Pressure drop was predicted reasonably well by a modified literature model, using a new correlation for the film thickness derived from experimental values.

Residual film thickness following immiscible fluid displacement in noncircular microchannels at large capillary number

“…A similar trend was observed by Aussillous and Quere, who used channels with diameters from 0.4 to 1.4 mm for Ca < 0.05 and by Han and Shikazono who used channels of 0.3–1.3 mm diameter for Ca < 0.08. However the results reported by Tsaoulidis and Angeli, who studied the film thickness in 0.5–2 mm channels, suggest an insignificant effect of channel size on the film thickness up to values of Ca < 0.2.…”

Experimental investigations of non‐Newtonian/Newtonian liquid‐liquid flows in microchannels

“…As reported in the literature, in Newtonian systems, the film thickness is increased either by increasing the velocity or the viscosity of the continuous phase, which leads to increased Ca number. 22,42 However, for these Newtonian cases, the maximum increase of the film thickness is by a factor of 2 (even at higher Ca number, i.e., 0.003 < Ca < 0.180) while for the shear-thinning fluids used in the experiments, the increase is by a factor of 4 (0.007 < Ca < 0.027).…”

“…2. From the different velocities that have been used in the literature for the calculation of the Capillary number (e.g., plug, slug, or continuous phase velocities 4,22,43 ), the plug velocity was chosen because it is related to the film thickness (see Bretherton 41 ; Eain et al 42 ). The dimensionless film thickness was found to increase with increasing Capillary number.…”

“…Tsaoulidis and Angeli 22 used an image acquisition system based on bright field PIV to visualize film thickness and recirculation patterns in liquid plugs at small channels of varying size. Chinaud et al 23 obtained velocity profiles within both liquid phases during plug breakage at the T-junction inlet of a microchannel using a two-color mPIV technique.…”

The Impact of Pore‐Scale Flow Regimes on Upscaling of Immiscible Two‐Phase Flow in Porous Media

“…The plug flow regime consists in a sequence of taps of a continuous phase and elongated bubbles (or elongated drops in liquid-liquid systems), which are surrounded by a film of the continuous phase (plug region; see Figure 1c). This flow regime has been extensively studied both in large pipes (see Fabre & Line, 1992;Picchi, Manerba, et al, 2015b) and in capillary tubes (see, e.g., Abu-Al-Saud et al, 2017;Jovanovic et al, 2011;Kawahara et al, 2002;Tsaoulidis & Angeli, 2016;Ullmann & Brauner, 2007;Wegmann & von Rohr, 2006;Yagodnitsyna et al, 2016). Plug flow is also intrinsically an intermittent flow regime: since the bubble (or drop) length is not constant (see Hout et al, 1992), we refer to the average length of the elongated bubble; see, for example, the experimental works by Kashid and Agar (2007) and Tsaoulidis and Angeli (2016).…”