Roughness and rarefaction effects on flow characteristics in microchannels

Experiments are conducted for nitrogen and helium gaseous flow through rough and smooth micro channels. The experimental results show that the surface roughness increases the flow resistance significantly even though the relative height is rather small. This is one of the major factors which causes the disagreements on the friction factor of microchannel flow in the literature; for the gaseous flow in the slip regime, an evident lower flow resistance is observed due to the gas rarefaction effect which causes the mass flow rate increase compared with the continuum flow.