TITLE: EXPLORING FAST DRYING AND EVAPORATION FROM NANOFLUIDIC CONDUITS
ABSTRACT: Drying and Evaporation from nanoscale conduits are two ubiquitous phenomena that play critical roles in nature. These two nanoscale liquid-vapor phase change phenomena are known to be significantly “accelerated” compared with the corresponding ones at micro/macroscales, enabling various industrial applications, including oil recovery, electronic cooling, membrane desalination and energy harvesting. Despite the important significance, the fundamental mechanisms for these two accelerated phase-change processes have not been completely understood. In drying process, it is widely accepted that liquid corner flow and film flow could significantly enhance mass transport in micro scale conduits other than the sole contribution by vapor diffusion. However, it is unclear if the same principles will apply to smaller scales and if the vapor diffusivity will change at the nanoscale. For evaporation, the evaporation kinetics at the interface, rather than liquid/vapor transport toward/from the interface, determines the ultimate transport limit and this limit can be significantly higher than the classical prediction derived under quasi-equilibrium evaporation conditions. Still, the contributions to this enhanced kinetically-limited evaporation remains unclear. This prospectus aims to answer these unsolved questions by conducting systematic experimental study on drying and evaporation from single nanochannels and nanopores.
In this prospectus, we demonstrate applying state-of-art fabrication method to examine water drying in individual close-end 2D nanochannels and kinetic-limited evaporation through single nanopores on both silicon nitride and monolayer graphene. We reveal the geometric dependence of drying, decouple individual contributions from vapor and liquid transport to the drying, and extract the water vapor diffusivity in nanochannels with height ranging from 29 nm to 122 nm. The evaporation through silicon nitride nanopores is shown to reach kinetic-limited regime and exhibit a strong diameter dependence with an exponent of -0.66, achieving 66% of the maximum theoretical predication by Hertz-Knudsen relation at a pore diameter of 28 nm. Furthermore, our preliminary results show that evaporation fluxes from nanopores on graphene are faster than that from silicon nitride membrane. We attribute such to the reduced water transport through graphene based nanoconduits and the reduced liquid/vapor transport resistance. Our experimental results suggest that both nanoscale-confinement and material properties play important roles in the kinetics of nanopore evaporation.
We expect this work would help answer the causes behind fast drying and evaporation from different perspectives, advance our understanding of drying/evaporation kinetics, and consequently provide guidance for the efficient design of nanoporous membrane for evaporation purpose.
COMMITTEE: ADVISOR Professor Chuanhua Duan, ME/MSE; Professor Xin Zhang, ME/ECE/BME/MSE; Professor Scott Bunch, ME/MSE, Professor Kamil Ekinci, ME/MSE