Gas flow in a short micro-tube

• Sliding of wall adsorbed molecules contributes significantly to gas transport.
• Gas flow due to sliding adsorbed molecules rises linearly with gas molecular weight.
• Viscous flow rate follows a power law with exponent independent of nature of gas.

The flow of gases into high vacuum through a short micro-tube of 20.5 μm diameter and 15 μm length has been measured for inlet pressures up to 1 atm. At low pressures molecular flow is found to be augmented by an additional mode of gas transport, whose contribution increases linearly with both inlet pressure and the molecular weight of the gas. This additional mode of transport is ascribed to the sliding movement of gas adsorbed on the tube wall. At higher pressures the flow rate can be accurately represented by a power law, the exponent of which is independent of the nature of the gas, whilst the coefficient increases with the molecular weight.