Читать книгу Agitator Design for Gas-Liquid Fermenters and Bioreactors - Gregory T. Benz - Страница 61

These fluids are called shear thinning because the slope of the shear stress vs. shear rate curve decreases as the shear rate increases. The behavior may be described by a power law model:

(3.21)

The exponent n is called the power law exponent. When it has a value of 1, the equation reverts to Newtonian. When it is less than 1, it is shear thinning. While it can be greater than 1, which would mean a shear thickening behavior, I have never seen a shear thickening fermenter broth. The apparent viscosity can be expressed by dividing by the shear rate on both sides of the equation:

(3.22)

where M is the viscosity coefficient, or the viscosity at a shear rate of 1 (usually in units of 1/s).

Many fermenter broths exhibit this behavior at high cell density loading, or if there is a significant solids content in the broth.