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Implementation of a concentric cylinder rheometer for high pressures


T. Regueira1, M. Comunas1, L. Lugo2, X. Paredes1 and J. Fernandez1

1University of Santiago de Compostela, Spain
2University of Vigo, Spain

Keywords: pressure
property: viscosity
material: polymer, lubricant

One of the goals of our research projects is to study, from an experimental and theoretical point of view, the flow properties of lubricants such as vegetable, synthetic oils and ionic liquids over wide pressure intervals. With this aim, we have installed a rheometric technique based on a Reologica StressTech HTHP concentric cylinder. This instrument consists in a DIN53019 concentric cylinder measurement and relies on Couette flow, involving confinement of the sample between a stationary cup and a rotating bob. The inner cylinder is suspended by a magnetic coupling and rotates on low friction bearings. The measuring range for torque is from 0.1 to 40 mNm and for shear rate from 20 to 1000 s-1. The rheometer is equipped with a high pressure cell that can be used for liquids at pressures up to 1000 bar. We have found that this equipment is appropriate for liquids with viscosities higher than 50 mPa·s The equipment has been calibrated for each liquid by using precise viscosity values at atmospheric pressure measured with a rotational Stabinger viscometer. At present, our rheometric technique can operate from 298.15 to 353.15 K and up to 75 MPa. The apparatus is connected to a data acquisition unit and a computer through the Rheoexplorer software. To verify the right operation of the equipment under Newtonian regime, we have performed flow curves and the viscosities were compared with previous literature data for polyalphaolefin PAO40 and a polybutene. Average absolute deviations around 6% have been obtained, over the entire temperature and pressure intervals, with the viscosity values reported by Bair [1]. In the near future this apparatus will be used to analyze the rheological behavior of viscous ionic liquids and other lubricants.

Acknowledgements. We express our gratitude to Dr. Scott Bair (Georgia Institute of Technology, Atlanta) for providing viscosity values of a PAO40 and to Prof. Martínez-Boza (University of Huelva, Spain) for his useful advice. This work is being supported by Spanish Ministry of Science and Innovation and the UE FEDER Program under CTQ2008-06498-C02-01/PPQ project. We are very grateful to INEOS Oligomers for providing a polybutene sample. L. L. acknowledges the financial support from the Ramon y Cajal Program. T.R. acknowledges financial support provided by the FPU program.

References
  1. S. Bair, Tribol. Trans. 43, 91 (2000)

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