Fluidan’s Unique Technology

This is How RheoStream® Works

By following the numbers on the picture (right), you can follow the progress of a measurement:

① A sample is drawn from process equipment
② The syringe pump controls flow rates in pulses ③
④ A preheater/cooler ensures a steady temperature of the measurement
⑤ The liquid flows through a thin tube (capillary)
⑥ A pressure difference (ΔP) is measured for each pulse
⑦ The instrument computer converts pressure signals into viscosity values
⑧  Displays results on the user interface
⑨ Spent sample is collected as waste

Liquids are categorized as Newtonian or non-Newtonian.

Newtonian liquids have constant viscosity across shear rates, non-Newtonian do not.

What does that mean?
Shear rate is the rate of deformation of the liquid.  Imagine that you drag a boat through the liquid – in a thin liquid the force required is less than in a thick liquid.  And the faster you drag the boat (= the higher the shear rate) the more force is required.  In rheology the force is expressed as shear stress (unit is pressure, Pascal) and the speed is expressed as shear rate (unit is reciprocal seconds, /s).

“flow curve”. Measuring shear stress and viscosity across a range of shear rates is called “viscometry”.

In a Newtonian liquid the force required is proportional to the speed – the ratio between shear stress and shear rate is the viscosity (unit is Pa·s).

Examples of Newtonian liquids are water, oil and honey, going from thin to thick, or from low to high viscosity.

Shear Thinning Liquids

Non-Newtonian liquids do not behave in the same way.  It does get harder to drag the boat when you go faster, but not proportionally.  Most thick liquids are shear thinning, meaning that it gets relatively easier as shear rate is increased – the viscosity drops as shear rate is increased. Some, more rare cases exist, when viscosity is increasing with shear rate.