CAPILLARY VISCOMETRY BY PERTURBATION OF FLOW AND COMPOSITION

A new technique for making viscosity measurements on gas mixtures is i ntroduced. The composition and flowrate of a mixture flouring through a capillary tube are perturbed by adding a small stream of perturbatio n gas. This is usually a pure, individual component of the mixture. Th e pressure at the inlet of the capillary tube rises when the perturbat ion gas is added and this pressure increase is proportional to the flo wrate change. Because there is empty volume between the point where th e perturbation gas is added and the capillary tube, it is some time la ter that the pressure changes again when the composition of the gas fl owing through the tube changes. This second pressure change is proport ional to the change in viscosity. The ratio of these two steps of pres sure is proportional to d ln mu/dX(i) where mu is the viscosity and Xi is the mole fraction of component i. An apparatus has been developed which is capable of making measurements with suitable precision and so me preliminary data for the nitrogen-argon system at 1.2 bar and 24 de grees C are given. (C) 1998 Elsevier Science Ltd. All rights reserved.