Wink of Knowledge: Viscosity measurement by differential pressure and flow rate
This knowledge wink deals with the viscosity determination of media above the measuring range of the dedicated viscosity sensor VLO-M2. Various media were measured in a wide temperature range, whereby viscosities > 400 mPa∙s were achieved. An FLT-M1_i1 Coriolis sensor was used for the flow measurement. The Coriolis measuring principle is ideally suited for this method thanks to the precisely shaped measuring tube over which the pressure drop is measured.
Why this test?
The viscosity of media has long been an important parameter for lubricants. In the meantime, further direct applications of viscosity have been added in areas such as paints/paints or care products. However, indirect applications such as the quality measurement of oils are also becoming increasingly important. We are presenting a viscosity measurement based on the “old” principle of differential pressure, but rethought using precise Coriolis measurement technology.
What is a Wink of Knowledge?
Do you need to quickly measure, draw or do/build something? The speed with which the result may be achieved counts more than the perfect (scientific) approach. For this reason, we have introduced the Wink of Knowledge. Science in the wink of an eye, so to speak. We don’t want to prove anything scientifically. We simply want to quickly demonstrate something pragmatically. If you are interested, we would be happy to discuss these results in more detail with you and your project.
Results
An FLT-M1_i1 was equipped with a pressure sensor at the inlet and a pressure sensor at the outlet of the device (see Figure 1). The measured variables flow rate, inlet pressure, outlet pressure and temperature were recorded for different media and temperatures.
Figure 1:Test setup consisting of two pressure sensors, the FLT-M1_i1 Coriolis mass flow sensor and a temperature-controlled circulation system
The dynamic viscosity 𝜂 of the medium can be calculated from the measured variables flow rate Q, pressure difference Δp and the geometric variables of the Coriolis measuring tube, length L and radius R, using Hagen-Poiseuille’s law:
An additional correction factor had to be used to correct for the effects of fluid block and pipe curvature. The viscosity calculated with this simple formula was then plotted against the reference values:
Figure 3: Viscosity according to measurements compared to the reference values
The measurements fit the ideal Hagen-Poiseuille law very well over a wide range. Deviations occur primarily at very high or very low medium temperatures. These are probably due to a temperature gradient along the pipe and a temperature difference between the medium and the environment, which makes it impossible to determine an “actual” temperature. This also results in an uncertainty in the reference temperature and thus the reference viscosity. These errors are ±10% in this simple test. However, this can be greatly improved by calibrating and/or restricting the temperature range. A successful and highly developed implementation of the measuring principle for measuring the quality of crude oil has already been carried out by a partner of TrueDyne Sensors AG:
Flow rate and density are included “free of charge” as valuable additional measured variables.
Conclusion
Which sensors were used?
viscosity sensor VLO-M2
- Click here to learn more about our sensor
Flow sensor FLT-M1
- Click here to learn more about our sensor
Sensors that might interest you
Gases
Viscosity
Applications that might interest you
From volume (l)
to mass (kg)
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