Influence of wall conditions on friction factor for flow of gases under slip condition

In this paper, the measurement of friction factor in gas with slip at the wall is presented; these are made to encompass the following aspects: change in pipe material, pipe wall roughness, and channel geometry, for various gases. Two different wall materials (stainless steel and copper), three different grades of roughness, and two wall geometries (circular and square) are considered in this study. The gases employed in this investigation are nitrogen, oxygen and argon. The ranges of Knudsen number and Reynolds numbers covered in this study are 0.0022–0.024 and 0.54–13.2, respectively. The experimental setup is validated by comparing the friction factor close to the continuum and slip flow regimes for nitrogen against available results in the literature. The experimental results suggest that the friction factor is affected by the wall roughness and geometry of cross-section, in addition to the amount of rarefaction. However, the effect of changing the gas or pipe material is minimal. A correlation for slip flow in square duct is also proposed. This is one of the first such detailed studies and has implications for both gas flow in microchannels and rarefied gas in large pipes.