Margules viscometer

Experimental techniques such as those used to measure specific values of viscosity (e.g. softening point) are still in common use, but are not as powerful as those in which a range of viscosities can be measured. Hence, only the Margules (1 to 106 Pa-s), parallel plate (103 to 108), and beam bending viscometers (107 to 1014 Pa-s) will be discussed here. These devices are manufactured and marketed by Theta Industries. 

This device is calibrated using NIST standard fluids (oils), where spindles are inserted to a known depth and either the crucible or the spindle is rotated at a known speed. The actual 

5Such a device is manufactured by Haake Buchler Instruments. 

The following expression, derived in section 10.3 may be used for absolute measurements of viscosity  

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While all of the viscosity measurements can be calibrated using well-characterized viscosity standards, the viscosity using these instruments may in fact be calculated from first principles. As an example, a derivation in full is provided for the Margules viscometer ... 

For elastic bodies, the shear stress is related to the shear strain by the shear modulus. For viscous fluids, the shear stress is related to the shear strain rate by the viscosity. We note that for laminar viscous flow in a Margules viscometer (Figure 10.7), radial fluid displacement is zero (gr = 0). Thus, differentiating with respect to time ... 

Figure 10.7 Two concentric cylinders with a viscous fluid between Margules viscometer.

The relationship between viscosity, angular velocity, and torque for a Newtonian fluid in a concentric cylinder viscometer is given by the Margules equation (eq. 26) (21,146), where M is the torque on the inner cylinder, h the length of the inner cylinder, Q the relative angular velocity of the cylinder in radians per second, T the radius of the inner cylinder wall, the radius of the outer cylinder wall, and an instmment constant. 

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