Rheonics inline density and viscosity sensors were used in the EMPIR EURAMET Safest project [1] and gave accurate viscosity and density measurements on test fluids mimicking fuels in laboratory settings [2]. The need for improved flow metrology in fuel lines is critical for sustainability in the road and maritime transport sector. The Safest project sought to compare commercial sensors for inline density and viscosity measuring. Rheonics sensors were found to give reliably accurate viscosity and density measurements [3].

Analysis of sensor results

Three universities contributed findings, each from a singular brand, for in-line density and viscosity measurement devices. Their experimental setups and methods vary greatly and can be found in full in the EMPIR EURAMET Safest project deliverables (D7) [3].

Conclusions from commercial sensor outcomes are compared in the report on a superficial level due to the varied protocols, however all three brands tested were individually deemed to give acceptable density measurements. The brands tested cover the main types of density meters on the market:

1. Balanced Torsional Resonator (BTR)
2. Vibrating tube (VT)
3. Tuning fork (TF)
4. Coriolis meter (CM)

Imperial College experiments testing Rheonics sensors

Balanced torsional resonator based process density and viscosity sensors, SRD, from Rheonics are tested with a thermostatic bath containing the inline sensor chamber while flow rate of test fluid is controlled with an ISCO syringe pump. Experiments were performed at 15, 35, 55, and 75 °C, 1 – 100 bar, and 0 – 45 ml/min. Continuous flow is maintained and the system is equilibrated for 15 minutes prior to measurements. Despite this, the chamber never reaches the bath set-point temperature. Output viscosities from the SRD are considered reliable and accurate. Correction fits are applied and then the data matches reference data produced from Tait-Andrade equations (appendix of [3]). These correction fits become necessary due to observed temperature inhomogeneity in the system despite reaching an equilibrium. Deviation in temperature along the sensor length means viscosity in the chamber is not equal throughout. The same deviation exists for density however the SRD density measurements are deemed accurate and reliable without corrections herein. There can, however, be polynomial corrections applied here to match reference data more perfectly. Temperature inhomogeneity in the system can also cause deviations in density measurements when opposing ends of the sensor are not in thermal equilibrium, a longer probe could be used to ensure the internal resonator is fully immersed in a uniform temperature environment.

Rheonics process viscometer SRV is also evaluated and found to give acceptable measurements for viscosity and temperature inline.

Testing of vibrating tube density meters was performed with Anton Paar L-Dens 3300 and 7400 at Chemnitz University of Technology at 15, 25, and 35 °C, 1 – 10 bar, and 0 – 15 ml/min. These were also completed at small lab scale. At pressures below 2 bar, the measurement became impossible as the oscillation of the vibrating tube became unstable at low flow rates. Low flow rates, and static measurements, were used despite device specifications due to limited sample volumes. Device specifications stated these low flowrates would lead to sample heating within the tubes and this effect was observed (+3 °C). Nevertheless, both sensors were deemed to provide accurate density measurements with L-Dens 7400 slightly outperforming L-Dens 3300 but the experimentalists note the need to actually maintain dynamic process conditions for optimal accuracy.