NOVEL CAPILLARY PULSE VISCOMETER FOR NON-NEWTONIAN FLUIDS

This article describes the design and principle of operation of an uns teady-state capillary pulse viscometer for measuring the rheology of n on-Newtonian fluids at elevated pressures and elevated temperatures. T he relevant equations for the flow of a power-law fluid in a capillary tube under a transient pressure gradient that decays at a rate propor tional to the fluid flux in the tube are derived. The viscometer does not require a pump to generate a steady flow and is relatively simple and cheap to manufacture. Only a small amount of the test fluid is req uired and it is comparatively faster than other steady-state atmospher ic pressure viscometers. Furthermore, the viscosity of the test fluid is measured over a range of shear rates with each run. The pressure de cay across the capillary tube is recorded, and the apparent viscosity is calculated as a function of shea, rate from the relevant flow equat ions. The viscometer has been used to measure the viscosity of polymer solutions over a wide range of concentrations [250-2500 parts per mil lion by weight (wppm)] and the results compared with data using a stea dy-state commercial viscometer. The accuracy of the instrument is comp arable to or better than that of other types of viscometers. (C) 1996 American Institute of Physics.