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Viscosity

Viscosity. Brydger Cauch November 27, 2006. Capillary and Cone & Plate Viscometers. Importance. Classifies fluid flow Newtonian or non-Newtonian Motor Oil: 5W30 Higher Number=Thicker. What is viscosity?. Rheology Deformation and flow of matter under the influence of applied stress

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Viscosity

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  1. Viscosity Brydger Cauch November 27, 2006 Capillary and Cone & Plate Viscometers

  2. Importance • Classifies fluid flow • Newtonian or non-Newtonian • Motor Oil: 5W30 • Higher Number=Thicker

  3. What is viscosity? • Rheology • Deformation and flow of matter under the influence of applied stress • Viscosity, elasticity, and plasticity • Viscosity • Measure of the resistance to deformation of a fluid under shear stress

  4. Overview • Theory • Shear Stress • Molecular Origins • Newtonian and non-Newtonian fluids • Operation of capillary and cone & plate viscometers • Calibrations • Parameter for Capillary Viscometer • Calibration Curve for Cone and Plate Viscometer • Viscosity of an unknown fluid • Conclusions • Questions

  5. Theory

  6. Shear Stress Experiment • Internal friction between layers of flow (Wikipedia 2006)

  7. Gases Molecular diffusion between layers of flow Independent of pressure Increases with increasing temperature Newtonian Liquids Additional forces between molecules but exact mechanics unknown Independent of pressure except at very high pressure Decrease with increasing temperature Newtonian and non-Newtonian Molecular Origins

  8. Characterization of Fluids • Newtonian Fluid • Non-Newtonian Fluids are usually complex mixtures (de Nevers 2005)

  9. Operation of Capillary and Cone & Plate Viscometers

  10. Capillary Viscometer • Select appropriate capillary size to give reasonable times • Keep constant temperature • Time fluid falling between two fiducial marks (a) and (b) • Avoid parallax

  11. Brookfield Cone & Plate Viscometer • Shallow angled cone in very close proximity with a flat plate • Important features • Circulating bath to keep constant temperature • Different cone sizes • Level on the instrument • Adjusting ring • Motor speed in RPM • Operation • Adjust cup so pins barely not making contact • Measure torque needed to overcome viscous resistance

  12. Calibrations

  13. Calibration • Capillary Viscometer • Second term neglected for sufficiently long times (>60 sec) • Fluid of known viscosity used to determine parameter B

  14. Calibration Cannon-Fenske Routine Capillary Viscometer: Size 400 with T=25°C (1) Standard deviation (2) Propagated error

  15. Calibration • Brookfield cone and plate viscometer with cone size CP-41 and T=28.5°C

  16. Viscosity of an Unknown Fluid

  17. Unknown Fluid • Capillary Viscometer • Accuracy: 0.7% vs ±0.2% reported • Reproducibility: 0.19% vs ±0.1% (1) Standard deviation (2) Propagated error

  18. Unknown Fluid • Brookfield Cone and Plate Viscometer • Average viscosity=95.5±1.5 cP (st dev) • Accuracy: 1.6% vs ±1%

  19. Results • Unknown fluid determined to be Brookfield Fluid 100 (μ=96.6 cP) • Capillary Viscometer (25°C) • 96.7±0.7 cP • Error of 0.10% • Cone and Plate Viscometer (28.5°C) • 95.5±1.5 cP • Error of 1.1% • Student’s T Test • 84.4% Probability they are the same

  20. Conclusions • Both viscometers straightforward once set up • Capillary viscometer simpler and more accurate • Cone and plate viscometer showed a larger deviation from the known viscosity • Higher temperature creates error • Lower viscosity at a higher temperature follows the expected trend

  21. Review • Theory • Operation of capillary and cone & plate viscometers • Calibrations • Determining the viscosity of an unknown fluid • Results • Conclusions

  22. References • “Viscosity.” Wikipedia. 2006. 24 August 2006. < http://en.wikipedia.org/wiki/Viscosity> • de Nevers, Noel. Fluid Mechanics. McGraw-Hill, New York, 2005. • Shoemaker, D.P., C.W. Garland, and J.W. Nibler. Experiments in Physical Chemistry, 6th ed. Mc-Graw-Hill, New York, 1996. • “Measuring Viscosity with a Digital Viscometer.” 21 June 2005. University of Utah. 24 August 2006. <http://www.che.utah.edu/~ring/Instrumental%20Analysis%20CHE5503/SOP's/DigitalViscosity%20SOP%20Ver%201.22%20%20%206-21-05.PRC.doc>

  23. Questions?

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