3. Measurement methods

3.1 Capillary flow process

The Ostwald viscometer is used. The laws of liquid flow are given by the following formula (known as Poiseuille's relation):

with E volume V which flows in 1 s under a pressure difference P through a calibrated tube of internal radius r and length L, in which the laminar flow is not modified by the proximity of the tube ends.

The viscosity coefficient η obviously varies with the nature of the liquid and, for the same liquid, with temperature.

In industry, viscosity is generally measured directly by the time required...