Читать книгу Fundamentals of Heat Engines - Jamil Ghojel - Страница 30

Generally, the shearing stress τ developed in a moving fluid between a stationary surface and a moving fluid body is proportional to the velocity gradient Δv/Δy, and the constant of proportionality is the dynamic viscosity μ:

Fluids such as water, oil, gasoline, alcohol, kerosene, benzene, and glycerine behave in accordance with this equation and are known as Newtonian fluids. Fluids that behave otherwise (viscosity changes with stress) are known as non‐Newtonian fluids.

The previous equation can be rewritten in terms of the viscosity as

The units of μ can be developed as follows:

The ratio of dynamic viscosity to density of the fluid is the kinematic viscosity ν:

Viscosity of liquids decreases with increasing temperature, and that of gases increases with increasing temperature.