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High-Viscosity Fluids PDF Print

   Method employed  


  • A novel Vibrating-Wire Viscometer has been developed for the measurement of the viscosity of high-viscosity liquids, 5-100 mPa s. According to this technique, a vertical wire, constrained not to move at its two ends, is placed in the fluid. If an oscillation is initiated by the displacement of the wire from its equilibrium position then, following a short-lived initial transient, the motion will conform to a damped, simple harmonic motion, characteristic of the viscosity of the fluid. The motion resembles the movement of a quitar string.

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The actual instrument employs a 300μm-diameter 50mm-length tungsten wire fixed at both ends. Two permanent samarium-cobalt magnets, placed around the wire, are employed for the electromagnetic initiation of the oscillations as well as for their detection.

Following initiation of the motion, the signal induced in the vibrating wire is observed with a bridge in which the wire forms one arm. The out-of-balance signal, amplified by 30,000 times, is then observed with an A/D converter coupled to a microcomputer at a rate of 50 kHz with a resolution of 12 bits.

The logarithmic decrement and the frequency of oscillation, are then obtained from the recorded data with the aid of a non-linear least squares fitting procedure, and from them the viscosity is obtained by a full theoretical analysis.

   Ranges & uncertainties  

 

  • Liquids - Present instruments cover the following ranges:
    - Pressure: 0.1 to 400 bars
    - Temperature: -70 to +100 'C
    - Uncertainty: 0.5%

   Systems sudied so far  


  • Selected papers:
    Assael M.J., and Mylona S.K, “A Novel Vibrating-Wire Instrument for the Measurement of the Viscosity of High-Viscosity Fluids”, J. Chem. Engin. Data (2013) DOI: dx.doi.org/10.1021/je301306e
 
 
 

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