Session: 01-02: Micro/Nanofluidics and Lab-On-A-Chip

Paper Number: 132556

132556 - Unlocking Nanoscale Capillary Condensation-Driven Transport 

Abstract: 

Nanomembrane materials hold significant promise in diverse applications, including energy development, energy conversion, biomedicine, and water purification. The efficient transport of fluids within nanomembrane pores forms the foundation for the high-performance operation of devices based on these materials. Due to the intricate nanoscale confinement effects, previous studies have identified anomalous gas and liquid transport phenomena in nanoscale pores, such as the specular reflection transport of gases and ultra-low-resistance flow of liquids. Moreover, fluids in nanoscale pores may exhibit unique phase-change characteristics. This complexity in fluid transport within nanoscale pores warrants further in-depth investigation. This study systematically explores the transport of ideal Lennard-Jones fluids, simple gases like helium, polar water vapor, and complex organic gases through nanochannels. Surprisingly, under specific pressures, we discover a capillary condensation-driven high-speed flow mechanism, distinct from conventional gas and liquid flow mechanisms. This multiphase flow mechanism holds the potential to further enhance the performance of nanomembranes and pave the way for new applications.

 

Utilizing molecular dynamics simulations on the LAMMPS platform, we initially investigate the transport characteristics of helium and long-chain alkanes in various nanochannels. The simulation system comprises a top reservoir filled with gases, a nanochannel mimicking membranes, and a bottom reservoir without gases. The nanochannel length ranges from 1 to hundreds of nanometers, with height varying from subnanometers to several nanometers. Atomic interactions are described using the 12-6 Lennard-Jones potential combined with electrostatic potential, applying a cutoff radius of 1 nm and periodic boundary conditions in all directions. The temperature is maintained at 300K using the NVT ensemble. Our findings reveal that the transport of helium, a simple gas, qualitatively aligns with Knudsen's theory. However, for long-chain alkanes, the flow deviates significantly from traditional gas transport theories. Thermal property analysis of alkanes indicates a phase transition within nanochannels, transitioning from gas state outside the channels to liquid state within. We investigate the effects of different pressures, temperatures, and fluid-solid interactions on the flow of Lennard-Jones fluids in nanochannels to elucidate the impact of phase change on flow, and subsequently establish a theoretical model to describe the capillary condensation-driven flow. Based on this unique flow behavior, we propose several application forms utilizing the most common fluid water, as the working fluid, demonstrating significant potential in water purification and efficient heat management. This work holds theoretical significance in advancing our understanding of fluid transport mechanisms at the nanoscale and establishes a theoretical foundation for the development of efficient membrane materials and energy systems.

Presenting Author: Runfeng Zhou Xi'an Jiaotong University

Presenting Author Biography: Runfeng Zhou is currently a PhD student at Xi'an Jiaotong University, China, advised by Prof. Chengzhen Sun. He has earned his bachelor's degree in new energy science & engineering at Xi'an Jiaotong University, China. He passionates about the transport phenomena at the nano- and interfical scales, and combines theory and simulations to explore the underlying mechanisms of nanoconfined fluids at the molecular level. He has published 17 peer-reviewed papers.

Authors:

Runfeng Zhou Xi'an Jiaotong University
Chengzhen Sun Xi'an Jiaotong University