1.1 Viscosity Definitions

There are several different “types” of viscosities that one may encounter in fluid dynamics. First, we differentiate between the kinematic and dynamic viscosities, referred to by symbols ν and μ or η. They are related via the density of the medium, with ν = η∕ρ. The units of dynamic viscosity are Poise or Pa.s and the dimensions are [ML^-1T^-1]. Kinematic viscosity has dimensions of [L²T^-1] and is thus sometimes referred to as a momentum diffusivity. For a complex fluid in which a solvent viscosity η_s is modified to the a concentration c of a second phase species resulting in an overall viscosity η, the following viscosities are defined in Table 1.

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Table 1: Definition of Viscosities Name Expression Relative Viscosity ηr = η∕ηs Specific Viscosity ηsp = ηr - 1 Reduced Viscosity ηred = ηsp∕c Inherent Viscosity limc→0(ηr∕c) Intrinsic Viscosity = limc→0(ηsp∕c)

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