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

Abstract

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.

Tuning the Optical Properties of Hyperbolic Metamaterials by Controlling the Volume Fraction of Metallic Nanorods

“…The decrease in the rate of pore branching with the AAO film thickness agrees with the decrease in the rate of the porous structure self-ordering observed earlier [30]. It is worth noting that the analysis of the number of the filled channels from the side of the current collector is the direct method of the measurement of the fractions of straight, blocked, and branched channels, which is greatly important for the refinement of the theoretical models describing the processes of the templated electrodeposition [24,31] and different pressure-driven membrane processes where AAO films are implemented as membranes [20,32,33].…”

Influence of heat transfer and wetting angle on condensable fluid flow through nanoporous anodic alumina membranes

“…This measurement technique was previously described in detail in ref. 10 , 23 and 33 . The typical experiment was started from 1 bar at the feed and the permeate side of the membrane.…”

Composite membranes based on geometrically constrained PIM-1 for dehumidification of gas mixtures

“…A significant increase in sorption capacity of the AAO-40 substrate is observed at the humidity of 75 % which can be attributed to the capillary condensation of water vapor in nanometer-sized channels of the AAO [7,19,20]. According to the Kelvin equation, the capillary radius can be estimated as:…”

“…Among membrane separation technologies, capillary transport of water vapor appears favorable as providing both high permeance and selectivity due to the blockage of membrane channels by the condensate. Membrane operation in the capillary transport regime has been previously reported for inorganic membranes, including Vycor glass [5], porous anodic alumina [6,7], graphene oxide [8,9], as well as microporous polymer membranes with thermodynamic (reverse) selectivity, including polysulfone, sulfonated polyether-etherketon (sPEEK) and poly-trimethylsylilpropyne (PTMSP) [10,11]. Due to high solubility of water vapors in hydrophilic microporous polymers, it becomes possible to achieve outstanding membrane performance.…”