A generalized Knudsen theory for gas transport with specular and diffuse reflections

Area of Science:

• Physics
• Materials Science
• Chemical Engineering

Background:

• Gas permeation through nanopores is crucial for fundamental science and technology.
• Conventional Knudsen theory assumes diffuse reflection, but recent experiments show ballistic transport due to specular reflections on smooth surfaces.

Purpose of the Study:

• Develop a generalized Knudsen theory to model gas transport under various boundary conditions, including specular reflections.
• Overcome limitations of the Smoluchowski model, which inaccurately predicts infinite flow rates for specular reflection.

Main Methods:

• Developed a generalized Knudsen theory applicable to a spectrum of reflection conditions, from specular to diffuse.
• Validated the proposed model using molecular dynamics simulations across diverse scenarios.

Main Results:

• The generalized Knudsen theory accurately predicts gas flow rates, considering both specular and diffuse reflections.
• Demonstrated that specular reflection can reduce the dissipation flow rate, contrary to previous predictions.
• The model overcomes the divergence issue of the Smoluchowski model for specular reflection.

Conclusions:

• The developed model extends Knudsen theory to free molecular flow with specular reflections.
• Provides crucial insights into gas transport phenomena within confined nanoscale environments.
• Applicable to various boundary conditions, enhancing understanding of gas permeation in nanoporous materials.