Viscosity effects, during temperature

If the viscosity varies during flow for some reason (decreases with rising temperature or increases as a result of a chemical reaction such as polymerization), the linear Poiseuille P-vs-Q relation is violated and the pressure drop - flow rate curve may become nonmonotonic. This effect in polymerizing reactors can be explained by the fact that the most viscous products of a reaction are swept out of the reactor with increasing flow rate and are replaced. Instead, a reactor is refilled with a fresh reactive mixture of low viscosity. This leads to a decrease of the volume-averaged integral viscosity and therefore the pressure drop decreases. This can be illustrated by the following relationship ... 

Although we analyze most polymer processes as isothermal problems, many are non-isothermal even at steady state conditions. The non-isothermal effects during flow are often difficult to analyze, and make analytical solutions cumbersome or, in many cases impossible. The non-isothermal behavior is complicated further when the energy equation and the momentum balance are fully coupled. This occurs when viscous dissipation is sufficiently high to raise the temperature enough to affect the viscosity of the melt. 

Warren JW and Price JC. 1977. Drug migration during drying of tablet granulations. II. Effect of binder solution viscosity and drying temperature. J. Pharm. Sci. 66 1409-1412. 

A wide range of temperatures are encountered during processing and storage of fluid foods, so that the effect of temperature on rheological properties needs to be documented. The effect of temperature on either apparent viscosity at a specified shear rate (Equation 2.42) or the consistency index, K, of the power law model (Equation 2.43) of a fluid can be described often by the Arrhenius relationship. The effect of temperature on apparent viscosity can be described by the Arrhenius relationship ... 

Steady-state shear stress-shear rate measurements are by far the most commonly used method in many industrial laboratories. Basically, the dispersion is stored at various temperatures and the yield value and plastic viscosity r are measured at various intervals of time. Any flocculation in the formulation should be accompanied by an increase in tr and r. One rapid technique for studying the effect of temperature changes on the flocculation of a formulation is to perform temperature sweep experiments, running the samples from perhaps 5 to 50 °C. Any trend in the variation of tr and r with temperature can quickly provide an indication of the temperature range at which a dispersion will remain stable, since during that temperature range cr and r will remain constant. 

Because many liquid foods are subjected to a wide range of temperatures during processing, storage,and transportation the effect of temperature on the viscosity function is of interest. The Arrhenius model (Equation 7)... 

Increasing the temperature due to radioactive heating decreases the viscosity of fluid. Within the zone of maximum temperature viscosity decreases up to four times in comparison with its reference value. This temperature effect on viscosity exists during all 300 years of simulation. 

It can be proved that the refractive index of the mixtures depends linearly on the percentage of ethylene glycol. In the S-1 photoreaction both the photoisomerisation steps strongly depend on the absolute viscosity, whereas 3 is very small and stays nearly constant during the photoreaction. Since the determined values of quantum yield fit even for different mixtures of water/ethylene glycol with viscosity adjusted to the same value by variation of temperature (see Fig. 5.53), polarity effects of the solvent will influence the photoreaction less than viscosity effects [178]. 

---