Brief Discussion of Viscosity

In later chapters we discuss the evaluation of transport properties for multicomponent mixtures of gases. At this point, however, the intent is to provide only a brief introduction on viscosity, since it is the principal fluid property that appears in the Navier-Stokes equations. The discussion here is limited to single-component fluids. 

There is some limited capability to estimate critical viscosity from other more commonly measured data [35,332], For example, 

The temperature dependence of liquids is very different than for gases, with liquids showing very strong temperature dependencies. For liquids (e.g., temperature below the critical temperature) the viscosity decreases exponentially with increasing temperature, 

Liquid viscosity data is often represented represented empirically in the form 

Notice the very strong temperature dependence and the great variation of viscosities among different types of liquids. The inset shows the viscosity of water on a linear scale, emphasizing the strong temperature dependence. 

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