TABLE OF CONTENTS Viscosity is a measure of a fluid's inherent resistance to flow. Fluid viscosity is very sensitive to changes of temperature; therefore, in this experiment, the viscosities of fluids will be determined at several temperatures and a plot of viscosity versus temperature for oil samples will be made on semi-log paper.
The terms normally used for viscosity are "dynamic" or "absolute" viscosity, which imply that the fluid is in motion. These terms are distinguished from the "kinematic viscosity", which is defined as the dynamic viscosity divided by the density of the fluid.
A poise (g/cm s in CGS units; kg/m s in SI units) is the fluid viscosity that requiresa shearing forceof1dyne tomovea1 cm 2 area plate (parallel to another plate) through the liquid with a velocity of 1 cm/s. A stoke (cm 2/s in CGS units; m 2/s in SI units) is defined as a poise divided by the density.
Several instruments have been developed for measurement of viscosity; they depend on the pressure of the liquid being tested to provide the force to drive the liquid through the instruments providing a measure of the kinematic viscosity, which is expressed in centistokes (cS = cm 2/100 s). The Cannon-Fenske viscometer equipped with a clear, liquid-controlled temperature bath, provides a method for determining viscosity at several temperatures (Figure A5.1). The Saybolt viscometer contains brass viscometer tubes set in a temperature-controlled oil bath with a calibrated orifice placed at the outlet of the viscometer tube.
