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Lab Methods

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Viscosity

  • Method ASTM D445
  • Repeatability Variable, see method
  • Reproducibility Variable, see method
  • Blending non-linear
  • Additive Correction No

This test method specifies a procedure for the determination of the kinematic viscosity, n, of liquid petroleum products, both transparent and opaque, by measuring the time for a volume of liquid to flow under gravity through a calibrated glass capillary viscometer. The dynamic viscosity, h, can be obtained by multiplying the kinematic viscosity, n, by the density, r, of the liquid.

Viscosity is defined as a fuel or oils resistance to flow. To put this in simple terms, an example of low viscosity would be water, apple juice, etc which are fast moving and pour quickly out of their container. A higher viscosity fluid example would be tree sap, molasses, or syrup and how it slowly moves out of a container. Temperature is very important to viscosity though. If you heat the same molasses or syrup from room temperature to 150°F it will pour almost as fast as the apple juice or water and the viscosity value will drop.

The petroleum industry applications for viscosity vary. In lubricating oils they are rated basis their viscosity. Engines of different sizes and fuels have varying lubrication qualities that are required to keep them in operation. In residual fuel oils the viscosity is important to ensure the correct amount of fuel is flowing to the engine. An engine and fuel pump system that is designed to handle a viscosity of 300cst will have major issues if a 800cst fuel is introduced to the system. This could result in damage to the fuel pump or the engine (by fuel starvation). The same is true for jet fuel. The viscosity is measured at -20°C (-4°F) to simulate the chill of high altitude conditions which ensure the specs for proper fuel flow are met and the turbine continues to function properly.