Micro-Slit Viscometers
Viscosity measurement using flow through a slit dates back to 1838 when Mr. Jean Louis Marie Poiseuille conducted experiments to characterize the liquid flow through a pipe. He found that a viscous flow through a circular pipe requires pressure to overcome the wall shear stress. That was the birth of Hagen-Poiseuille flow equation. The slit viscometer geometry has flows analogous to the cylindrical pipe but has the additional advantage that no entrance or exit pressure drop corrections are needed. Detailed information regarding the implementation of this principal with modern MEMS and microfluidic science is further explained in a paper by RheoSense, Inc.
Generally, the slit viscosity technology offers the following advantages:
- Measures true (absolute) viscosity for both Newtonian and non-Newtonian fluids
- Enclosed system eliminates air interface and sample evaporation effects
- Measurements can be made using very small sample volumes
- Laminar flow even at high shear rates due to low Reynolds number
- Slit flow simulates real application flow conditions like drug injection or inkjetting.
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