Numerical investigation of the performance and gas flow characteristics of a novel low-temperature-driven multistage Knudsen pump

The Knudsen pump, which operates based on the thermal transpiration effect and contains no moving parts, offers a promising solution for microfluidic transport. Its ability to function at low temperatures is particularly advantageous for applications such as hydrogen transportation, which help mitigate leakage risks, and space cryogenic systems, which require high reliability and compact design. This paper develops a numerical model of the low-temperature-driven Knudsen pump (LT-KP) based on the Navier-Stokes equations, incorporating velocity slip and temperature jump boundary conditions. The model simulates and evaluates the pressurization performance and the internal gas flow characteristics of the Knudsen pump over a temperature range extending from liquid nitrogen to room temperature. The simulation results indicate that a single-stage LT-KP can achieve a compression ratio of 1.02 under a temperature gradient of 223 K and an initial pressure of 1 atm. The study further investigates the impact of structural and operational parameters, including the number of stages, temperature gradients, gas rarefaction degree, microchannel dimensions, and gas types. More importantly, a design scheme for a closed-cycle dilution refrigerator incorporating LT-KP is proposed. The simulation results demonstrate that the 10-stage LT-KP, driven by the cascaded temperature gradients of 4 K-40 K and 40 K-300 K, can achieve pressurization from 5 mbar to 200 mbar. This research addresses the knowledge gap regarding Knudsen pump operation in cryogenic environments and provides valuable guidance for its application in refrigeration systems.