Numerical investigation into the performance of alternative Knudsen pump designs

Abstract

Micro scale pumps that are driven by the thermal transpiration effect are commonly known as Knudsen pumps. The performance of three Knudsen pump designs is numerically determined for a range of rarefaction levels and geometries. A newly developed Knudsen pump, based on a sinusoidal variation in channel width, is compared to previous curved channel designs as well as the canonical Knudsen pump design. A second Knudsen pump design is introduced based on individual pumping elements arranged in a matrix that displays no adverse flow effects. Flow structure, mass flow rate and pressure differential generation ability are investigated for all designs. Mass flow rate and pressure differential characteristics are found to be greatest for the canonical and matrix pump designs respectively. The ability of the matrix pump to vector flow is also demonstrated by a nine-element pump placed at the confluence of four channels and displays the versatility of the design.