Rheoceptor™ - How It Works

 Dielectric
    Analyzers

 Viscometers

 Rheometers

 Company
    Information
 

How It Works
The viscometer employs a rotating cam in a fluid filled cylindrical cavity that has a flush-mounted pressure transducer. There is a wedge shaped clearance between the rotating cam and the inner wall of the cylindrical cavity. The can generates excess hydrodynamic pressure in the wedge-shaped region between its outer edge and the cavity wall. As the cam passes the transducer, the measured pressure increases, reaches a maximum, and then decreases.

Pressure vs. Time profile from a cam with two lobes

The amplitudes Dp_max of the pressure fluctuations are proportional to viscosity h

where

h₁ and h₂ are the inlet and outlet gaps, L and V are the cam length and velocity. c_f is a calibration factor that for Newtonian fluids is ideally one, and for power law fluids with shear thinning exponent n is 1/n. Calibration factors are useful over limited but broad ranges of materials and conditions. The shear rate of the viscoity measurement is equal to the cam speed divided by the mean gap distance.

where

A cam with two lobes of different clearance is used for dual shear rate measurements. The amplitudes of the two pressure pulses are analyzed to determine the low and high shear rate viscosity.

How It's Used
CEP can design cams and build them into extruders, gear pumps or reactors. We can supply the instrumentation to continuously capture pressure versus time profiles, determine pulse amplitudes and timing, and issue reports to process control systems. The basic outputs are viscosities 1 and 2, shear rates 1 and 2 and temperature. Any quantity calculable from these, including temperature compensated viscosity, can also be reported.