Exploring Ultimate Water Capillary Evaporation in Nanoscale Conduits

Abstract

Capillary evaporation in nanoscale conduits is an efficient heat/mass transfer strategy that has been widely utilized by both nature and mankind. Despite its broad impact, the ultimate transport limits of capillary evaporation in nanoscale conduits, governed by the evaporation/condensation kinetics at the liquid-vapor interface, have remained poorly understood. Here we report experimental study of the kinetic limits of water capillary evaporation in two dimensional nanochannels using a novel hybrid channel design. Our results show that the kinetic-limited evaporation fluxes break down the limits predicated by the classical Hertz-Knudsen equation by an order of magnitude, reaching values up to 37.5 mm/s with corresponding heat fluxes up to 8500 W/cm. The measured evaporation flux increases with decreasing channel height and relative humidity but decreases as the channel temperature decreases. Our findings have implications for further understanding evaporation at the nanoscale and developing capillary evaporation-based technologies for both energy- and bio-related applications.

Osmotic Pumping and Salt Rejection by Polyelectrolyte Hydrogel for Continuous Solar Desalination

“…While the solar-thermal energy conversion efficiency was intrinsically limited by the performance of the absorber which already reached ~ 94% [6,7] , the overall performance of the solar-thermal desalination system would be compromised without sufficient water supply and the ability to resist salt contamination. To solve this problem, several studies explored the capillary pumping effect a passive liquid supply mechanism where liquid was driven by the capillary pressure in the micro-pores [8,9] , micro-grooves [10] , fibrous meshes [11,12] and carbon foam [13,14] , etc. Although the capillary pumping is able to provide high liquid flux, there are two challenges associated with the capillary-driven desalination.…”

A unified relationship for evaporation kinetics at low Mach numbers

“…While significant theoretical efforts have offered some insights into the gas kinetics in the Knudsen layer, experimental studies have proved difficult due to limitations in vapour removal 10,15 , interface temperature sensing 16,17 , thermal conduction 18,19 , and liquid supply 20,21 . Theoretically, the gas kinetic resistance ( R kinetic ) has been modeled by the Boltzmann transport equation (BTE) which governs the evolution of distribution functions of vapour molecules in the Knudsen layer 12,22 .…”

“…First, sensing the interface temperature can be difficult. Merely placing the sensor remotely does not give enough accuracy 17 and simply inserting a thermocouple into the interface can disturb local evaporation 16 . Further, evaporation is often hindered by thermal conduction 18,19 and viscous loss 20,21 in the liquid, which makes the kinetically limited regime inaccessible.…”

Mechanism and Regulation of Spontaneous Water Transport in Graphene‐Based Nanoslits

“…And the evaporation will be more noticeable in comparison to the flow process. In addition, common enhancement like heating will be more efficient in nanoscale evaporation . All of these make the evaporation a more significant process in nanoscale than macroscale.…”