Interactions Between Biology and Physics via Viscosity of Fermentation Media

2 Interactions Between Biology and Physics via Viscosity of Fermentation Media 

The rheological classification of liquids is normally given by a general expression, where the shear stress applied t [force length ] and the resulting shear rate y [time ] are correlated as follows (e.g., Metz et al, 1979)  

Non-Newtonian fluids, of which there are several cases a. Power law fluids, where Tq = 0 

The Casson equation is sometimes a very successful alternative approach  

It can be shown that many fermentation media behave like non-Newtonian fluids. Thereby (apparent) viscosity can be a function of either S and/or P and/or X concentration, exhibiting Newtonian and non-Newtonian behavior. The estimation of the rheological properties of biological fluids is summarized in the literature (e.g., Charles, 1978 Metz et al., 1979). Reuss et al. (1980) incorporated rheological considerations into process modeling. When viscosity is taken into account, clearly any correlation that does not contain the variation of viscosity during the fermentation must fail. An approach recently developed by Zlokarnik (1978), originally proposed for water and water-salt solutions, can be successfully used for this purpose (cf. Equ. 3.81)  

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