Effects of connecting tubing on a two-capillary viscometer

Abstract

Two-capillary viscometry is useful for accurately measuring the temperature dependence of the viscosity of dilute gases. A number of publications show good agreement among measurements by two-capillary and primary viscometry, and ab initio calculation. To the authors' best knowledge, there is no publication describing the effects of connecting tubing on two-capillary viscometry. We present in this paper an investigation by a two-capillary viscometer on the effect of connecting tubing, the available Dean number range and a different method for the stabilization of gas pressures. Our study demonstrates that the incompatibility of connecting tubing causes a systematic error in measurement of dilute gas viscosity. The error diminishes with decreasing Dean number. We discuss the cause of such a systematic error based on analysis of the experimental data. We observe that a Dean number not exceeding 17 is available for our two-capillary viscometer with capillaries made from electro-polished stainless steel. We observed that a piece of coiled connection duct can suppress the instability in the gas pressure by two orders. The results of the above experimental investigations are reported in this paper.