Experimental analysis of velocity slip at the wall for gas flows of nitrogen, R134a, and R600a through a metallic microtube

• Mass flow rate of nitrogen, R134a, and R600a is measured through a stainless steel microtube.
• Tangential momentum accommodation coefficients derived for rarefied conditions.
• Incomplete accommodation is observed for the three gases.
• The flow was not significantly affected by the gas chemical composition.

This paper reports measurements of mass flow rate of nitrogen, R134a, and R600a through a commercially available stainless steel microtube, which closely reproduces the case of gas leakage through micrometric clearances found in compressor valves. The accuracy of the measurements in the whole rarefaction range considered was verified through comparisons with predictions from the BGK kinetic model and results from the Navier–Stokes equations with modified boundary conditions. Furthermore, values of the tangential momentum accommodation coefficient (TMAC) were obtained by using an analytical approach derived from the solution of the Navier–Stokes equations with modified second-order boundary conditions. An incomplete accommodation is observed for all gases, with α = 0.933 ± 0.004 for nitrogen, 0.956 ± 0.004 for R134a, and 0.974 ± 0.008 for R600a. The results for all gases were very similar, indicating that the gas chemical composition does not significantly affect the flow through microtubes with rough internal surfaces, even when heavy polyatomic molecules are considered.