1. n. [Enhanced Oil Recovery]

A measure of a fluid's resistance to flow. Viscous forces in a fluid are proportional to the rate at which the fluid velocity is changing in space; the proportionality constant is the viscosity. For Newtonian liquids (liquids that show no variation of viscosity with shear or extension rate), the ratio of extensional viscosity to shear viscosity is 3. This value is Trouton's ratio. For more complex liquids, for example, polymer solutions, Trouton's ratio can be different from 3 and can vary with shear or extension rate.