Meniscus Curvature Effect on the Asymmetric Mass Transport through Nanochannels in Capillary Condensation Regime

• Published in: Journal of physical chemistry. C 2018-12, Vol.122 (51), p.29537-29548
• Main Authors: Petukhov, D. I, Berekchiian, M. V, Eliseev, A. A
• Format: Article
• Language: English
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/acs.jpcc.8b08289

This study reports on experimental evidence for large mass flux difference in opposite flow directions through asymmetric membranes in capillary condensation regime. Anodic alumina membranes with pore diameters of 10–80 nm in the selective layer and 40–80 nm in the supporting layer were inspected for permeance variation depending on the feed and permeate pressure conditions. Starting pressure of capillary condensation was found to follow the Thompson–Kelvin equation for pore diameters at the upstream side of a membrane. The experimental ratio between the permeances in the upstream and downstream membrane orientations attained ∼2 at the feed pressure close to condensation pressure for membranes containing pores of small diameters. The experimental data were treated assuming Knudsen and viscous vapor transport in the gaseous state and Poiseuille flow in liquid condensate. It is shown that condensate transport through the nanochannels in the capillary condensation regime is mostly governed by the condensing/evaporating menisci curvatures deviating from the thermodynamic equilibrium value and gradually changing with pressure conditions. Coincidently, the curvature of meniscus is controlled by the liquid influx velocity and velocity distribution in nanochannels, giving rise to a self-regulating regime of flow. At high liquid intake velocities, the curvature radius of meniscus significantly increases, being accompanied by a serious drop of liquid evaporation efficiency. The effect is ascribed to a sequential evaporation of liquid in the pore center and vapor condensation close to the pore walls, generating gas–liquid rotating flow.