Energy dissipation by the stirrer

In fact the viscosity influences both the heat balance and the mass balance. It has been shown how the heat transfer coefficient is affected by the viscosity. But the energy dissipation by the stirrer is also strongly dependent on viscosity (see Section 11.4.4). Furthermore, viscosity affects the molecular diffusion, the mass transport, the mixing time, or the residence time distribution, and therefore the reaction rate. Since the reaction rates influence the chain length and particle sizes, they have a direct effect on the polymer properties. In turn they affect the viscosity and the shear forces - there is a feedback effect. Such complex interactions cannot be described by analytical equations, so empirical models must be used. Often... 

The energy dissipated by the stirrer is often small compared with the other terms in the case of emulsion polymerization, because of the low viscosity and reduced agitation speeds, and can therefore often be neglected. Even if this is not entirely accurate, it is possible to include this quantity in the term for heat loss, generally used as a correction term for calorimetric calculations. 

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