May 28, 2024

High-precision silicone oil volume flow measurement at 300 °C achieved at the Cologne site

Work on Laser Doppler Velocimetry (LDV)
The optical measuring method is used for the non-invasive determination of velocity vectors in fluid flows such as liquids or gases.
  • PTB and DLR have successfully carried out flow measurements using Laser Doppler Velocimetry in the silicone oil HELISOL XLP at 300 degrees Celsius.
  • High-precision flow measurement is the basis for efficiency measurements in solar thermal power plants and industrial plants.

The mobile pump and heat transfer fluid test stand MOPUW enables the demonstration and research of new types of heat transfer fluids on a pilot plant scale. In the now completed first measurement using Laser Doppler Velocimetry (LDV) at 300 degrees Celsius, DLR, in cooperation with the Physikalisch-Technische Bundesanstalt (PTB), has demonstrated that volume flows of transparent media can be measured optically with high precision at 300 degrees Celsius.

For this purpose, the LDV measuring system of the PTB working group 7.52 was brought to Cologne-Porz and installed at the MOPUW. The system's laser probes can measure the medium flowing through temperature-resistant inspection glass fitting. If the measuring point is then moved to different coordinates in the flow, its velocity can be determined locally in each case. In this way, a flow profile is recorded. The flow profile describes the way in which the heat transfer oil flows through the precision glass tube behind the window. The researchers then use the flow profile to calculate the volume flow of the fluid.

Really accurate

Laser Doppler Velocimetry (LDV) is an optical measurement method for the non-invasive determination of velocity vectors in fluid flows (liquids or gases). It is currently the most accurate, non-invasive method for determining fluid velocities. A laser beam is split into two partial beams using a beam splitter. At the measuring point, these beams intersect and an interference fringe pattern is created in the crossing area. If particles moving with the fluid flow cross the fringe pattern, their scattered light will be modulated. The modulation frequency is proportional to the velocity component perpendicular to the interference fringes and can be measured using a photodetector.

Installation of the LDV system at MOPUW
The LDV measuring system of working group 7.52 of the Physikalisch-Technische-Bundesanstalt was moved to the Cologne-Porz site and installed at the MOPUW.

Validations also for sensor manufacturers

For the validation of different high-temperature flow measurement methods, for example for use in solar power plants and industrial plants, the successful experiment at 300 degrees Celsius will open up future services for the high-precision validation of commercial flow sensors. For this purpose, future flow sensors can be integrated into the system together with the LDV window chamber. The successful test measurement has shown that even higher operating temperatures - for example at 400 degrees Celsius - should be technically feasible. Under certain circumstances, an improved window chamber would have to be used and the impurities originating from the fluid test stand would have to be filtered out even more effectively in the otherwise transparent heat transfer fluid.


Dr. rer. nat. Christian Jung

Head of Department
German Aerospace Center (DLR)
Institute of Future Fuels
Chemical und physical fundamentals
Linder Höhe, 51147 Köln-Porz

Christian Siegel

Communication Officer
German Aerospace Center (DLR)
Institute of Future Fuels
Schneiderstraße 2, 52428 Jülich
Tel: +49 (0) 2461 93730-328