fluid+flow+behavior_tee

Fluids exhibit several types of flow behaviors.

[[image:fluid_tly.png width="823" height="393"]]
- Flow curve shows shear stress directly proportional to shear rate, and the plot begins at origin. - contains compounds of low MW (e.g., salts and sugars), do not contain dissolved polymer (e.g., pectins, proteins, starches, gums) and dissolved solids.
 * NEWTONIAN FLUID ** - Viscosity do not depend on shear rate.
 * NON-NEWTONIAN FLUID **
 * Time Dependent behavior - viscosity changes with time under constant shear rate. Apparent viscosity at given shear rate may have significant different.
 * Time Independent behavior - viscosity changes with shear rate, but independent of previous shear history. Apparent viscosity or single point viscosity can be used.

__**SHEAR- THINNING**__ (high structured food, e.g., emulsion and suspension) Shear-thinning often a result of: - orientation of non-spherical particles in the direction of flow. (e.g.,pumping of chocolate mass) - deformation of spherical droplets to elliptical droplets in emulsion.(e.g., production of low fat margarine) - breaking of particle aggregates in suspension.(e.g., stirring yoghurt)

**PSEUDOPLASTIC** - shear rate increase, viscosity decrease. For example, peanut butter is very viscous mass at rtp. The faster u stir, the thinner the peanut butter becomes.

**BINGHAM PLASTIC** - also a pseudoplastic material, behaves like Newtonian fluid but it posses a YIELD STRESS which it has to be overcome.

__** SHE **____** AR **____** - THICKENING **__ (uncommon) **DILATANT** - shear rate increase, viscosity increase. For example, corn starch and cold water form a mixture that is called dilatant or shear-thickening.