This letter describes the gas-liquid phase flow patterns and the mechanism of generation of monodisperse microbubbles in a T-junction microfluidic device using the crossflowing shear-rupturing technique. The bubble size is ranged from 100 to 500μm. The air phase states as isolate air slugs, “pearl necklaces,” periodic isolate bubbles, zig-zag bubble patterns, and multiple-bubble layer can be observed in the wider measured channel. The bubble size relates with the continuous phase flow velocity and viscosity as Vb∝1∕(μcuc), while being almost independent of surface tension γ and air phase flow rate Qg, for the conditions used in this work. The bubble formation mechanism by using the crossflowing shear-rupturing technique is different from the hydrodynamic flow focusing and both geometry-dominated breakup techniques. Our system provides independent control of both the size and volume fraction of dispersed bubbles.
Modelling of drying processes without adjustable parameters is still a challenge. As emphasized in several previous works, this might partly be due to the impact of liquid films trapped in corners of the pore space. In this study, we present and analyse a drying experiment with a micromodel, which clearly shows the presence of corner films. In contrast with previous works, however, the corner films do not form a system of interconnected corner films extending over large regions in our micromodel. They rather form isolated capillary rings surrounding the solid blocks of the device, and thus, a quasi-two-dimensional version of liquid bridges often observed in the contact regions between grains in soils and packings of particles. These capillary rings essentially remain confined in the two-phase region. As a result, their impact on drying rate is much smaller than in systems favouring films hydraulically connected over long distances. The capillary liquid ring formation is taken into account in a pore network model of drying leading to satisfactory agreement with the experiment provided that the lateral pinning of liquid phase observed in the experiment is included in the model. Based on this, the model enriches the family of pore network models of drying and can be considered as a step towards the modelling of secondary capillary effects in drying in more complex geometry.tot Total evaporation surface area (m 2 ) A t Cross-sectional area of throats (m 2 ) A r Ring evaporation surface area (m 2 ) h Film height (m) L Lattice spacing (m) L r Ring width (m) L d Network depth (m) M Molar mass (kg kmol −1 ) M Mass flow rate (kg s −1 ) P Total pressure (Pa) P c Capillary pressure (Pa) P l Liquid pressure (Pa) P v Vapour pressure (Pa) P * v Saturation vapour pressure (Pa) P v,∞ Vapour pressure in the bulk air phase (Pa) r t Throat radius (m) r t Mean throat radius (m) r t,d Meniscus radius at ring detachment (m) R Universal gas constant (kJ kmol −1 K −1 ) s BL Boundary layer thickness (m) S Total network saturation (-) t Time (s) T Temperature ( • C) T Mean temperature ( • C) V Volume (m 3 )Greek symbols α Fitting parameter (-) δ Diffusivity (m 2 s −1 ) θContact angle (-) σSurface tension (N m −1 )
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