Without knowing a fluid's density, can its density be correctly determined by measuring both kinematic and dynamic viscosity directly, and then dividing these values?

Can one determine cStokes and cPoise directly, then divide the cPoise by the cStoke and get density?


1 Answer 1


Sure, if you can somehow measure the kinematic viscosity directly. But the value may not be very accurate, since kinematic viscosity and dynamic viscosity are much more sensitive to temperature than density (at least for a liquid). Also, if you are trying to back out the kinematic viscosity indirectly from measurements of pressure drop in turbulent flow, for example, the value you estimate for the kinematic viscosity may not be very accurate because the friction factor/Reynolds number correlation is only accurate to about 10%. So, if you want to know the density, you should measure it directly, and, if you want to know the viscosity, you should measure the dynamic viscosity directly.

  • $\begingroup$ So, only absolute viscosity can be measured directly (without knowing density), and, devices that output kinematic viscosity measure absolute viscosity and density simultaneously to determine kinematic viscosity? i.e. there are no devices that can measure kinematic viscosity directly without knowing density? $\endgroup$
    – Armadillo
    Jan 12, 2016 at 15:46
  • $\begingroup$ It's possible to measure kinematic viscosity indirectly using a dynamic test (time dependent variation), but, why bother, since dynamic viscosity can so easily be measured in a steady state test. $\endgroup$ Jan 12, 2016 at 16:05
  • $\begingroup$ So a device like the Cannon-Fenske tube measures the kinematic viscosity, but does so indirectly, and it must be "Calibration against a standard liquid of known viscosity or against a second viscometer with a known constant must be made before use." - source: kimble-chase.com/… $\endgroup$
    – Armadillo
    Jan 12, 2016 at 16:11
  • $\begingroup$ I guess I misspoke. The Cannon-Fenske uses Hagen-Poiseulle, but it uses gravity to drive the flow. So it automatically delivers the kinematic viscosity. But, if you are really serious about making viscosity measurements, I recommend against this device. My understanding is that it is typically used to make spot measurements on process fluids to determine whether, at a particular point in the process, they are up to specs. For serious viscosity measurements, more sophisticated and accurate devices are desirable. This is particularly so for non-Newtonian fluids. $\endgroup$ Jan 12, 2016 at 17:19
  • $\begingroup$ If is uses the Hagen-Poiseulle, wouldn't it need the dynamic viscosity value? Plus fluid density to convert the dynamic viscosity to kinematic? I am basing this question off of the equation presented here: en.wikipedia.org/wiki/… $\endgroup$
    – Armadillo
    Jan 12, 2016 at 18:41

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