MANUAL Published: 08 November 2019

Chapter 43 | Flow Properties and Shear Stability


The viscosity of fuels and lubricants determines whether a fluid is suitable for its intended use. For example, a fuel's viscosity affects how well it vaporizes or atomizes, which in turn affects combustion and energy output. A lubricant's viscosity affects how well it will maintain a film between two moving surfaces. This chapter begins with a review of the evolution of viscosity measurement techniques for fuels and lubricants. The easiest way to measure viscosity is with the use of gravity as the driving force, and this was how many of the initial viscosity measurements were made. This resulted in the viscosity units being unique to the device used. A need for increased measurement range and precision led to the development of the capillary viscometer, which yields kinematic viscosity. Included is a review of the various capillary viscometer designs and the constraints on their use. Another approach to measuring viscosity is by applying a force to move one surface past another parallel surface. Rotational viscometers do this with several different configurations to achieve parallel surfaces to varying degrees. The various configurations are reviewed as are the factors needed to calculate the measured viscosity. This chapter includes a review of several other unique viscosity measurement techniques. Shear stability measurements apply primarily to lubricants. It is an assessment of whether a lubricant will experience a decrease in viscosity as a result of applying very high shear stresses. The various bench test methods are reviewed.

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Henderson, Kenneth
McEinri Associates LLC, Port Matilda, PA, US
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Developed by Committee: D02
Pages: 1485–1517
DOI: 10.1520/MNL3720150019
ISBN-EB: 978-0-8031-7090-2
ISBN-13: 978-0-8031-7089-6