Flow curve measurement
A sample flow curve is a rheologically measurable curve that relates its viscosity to the shear rate applied to it.
Why measure flow curves?
Flow curves are particularly used for dimensioning industrial processes or pilots. The choice of pumps, tubes, exchangers, etc. indeed depends on the ability of fluids to deform under their flow stresses.
Why is a simple viscosity measurement not enough?
For the majority of fluids, the viscosity does not depend solely on the temperature. It also depends on the mechanical stress applied to it. For example, a yogurt that does not flow when tilted will flow when shaken, a water/cornstarch mixture may behave like a wall if hit hard, etc.
Newtonian fluids are the only and rare fluids whose viscosity does not depend on the applied mechanical stress. The best known of this type is water, but this property is also shared by oils, hydrocarbons, etc.
For other fluids, the viscosity does not only depend on the temperature. A shear-thickening fluid sees its viscosity increase when the applied shear stress increases. Conversely, a shear-thinning fluid has a viscosity which decreases with mechanical stress.
How are flow curves measured?
Flow curves are measured using a rheometer. The choice of measurement geometry is made according to your samples (appearance, composition, etc.). The measurement temperature is regulated over a wide temperature range. Measurements can be made under an increasing or decreasing shear gradient.