A high-flow Knudsen pump using a polymer membrane: Performance at and below atmospheric pressures

This paper describes a miniature gas (Knudsen) pump that utilizes thermomolecular flow through a nanoporous membrane. A temperature gradient along the length of a pore that supports free molecular gas flow at atmospheric pressure pumps gas molecules from the cold end to the hot end. In contrast with past work, the membrane material is mixed cellulose which provides superior uniformity in pore diameter and porosity. The final packaged volume of the Knudsen pump is 14×14×4.4 mm
³
. For an input power of 1.4 W, a single stage Knudsen pump based on these nanoporous polymer membrane has a temperature bias of 30 K across the thickness of the membrane, which provides 0.4 sccm flow against a 330 Pa pressure head. The load characteristics of the pump suggest that the pump can provide as much as 0.93 sccm gas flow in the absence of a load. Knudsen pump operation at sub-atmospheric pressures is also reported.