Size matters.

Microscopic examination of gas-in-fluid dispersions.

Thanks to the FOAM oil aeration test rig flucon customers can test their mechanical components or oil with a quantifiable aeration level. In order to produce a stable, transportable air/oil mixture the gas should be dispersed homogenously, in bubbles of minimum diameters.

Of course the exact gas concentration of the aerated oil is always known due to the integrated CG sensor of the FOAM, but now a digital microscope is added to the setup to find out more about the physical form of the entrained air within the two-phase mixture. Exemplary investigations are then made on aerated transmission fluid.

Aerated oils, or to be more precise: air-in-oil dispersions, are in general volatile mixtures. Due to its low density the gaseous phase is subject to permanent buoyancy force. Thus, especially when stagnant, the aerated oil degasses quite quickly. The longer it is exposed to atmospheric pressure (e.g. in an open reservoir) the less air it will still contain. This tendency will even be enhanced by decreasing viscosities, but also by larger gas bubble volumes. Therefore bubbles need to be as small as possible for the FOAM Flucon Oil Aeration Machine to max out lifetimes of the aerated test media.


A glance at our test setup.

A FOAM XL-x was connected to an open oil reservoir with its main hoses (DN25). In addition a secondary line was added that included both the measurement pump and the CG sensor of the FOAM for inline aeration metering. A digital microscope was added to examine the aerated oil flowing through a special flat sight glass.

When the two-phase mixture escapes the injection hose of the FOAM the previously compressed air bubbles will grow as they become free in an atmospheric surrounding. The measurement pump then sucks in the aerated oil and runs it to the CG sensor for live measurement.


By keeping the flow rate to a minimum the optical analysis, just like the CG measurement, is conducted close to atmospheric pressure, so that the diameters of the compressible bubbles can be determined at the best.


First results are promising.

Looking through the microscope you will find that the entrained air from the FOAM is dispersed in the oil very homogenously. In addition the variation in bubble size is rather small:

Their diameters average at approx. 70 µm, while the variance is limited, so that all diameters found were in between 50 and 85 µm. The average bubble volume was 100 µm³.

The examination was carried out at room temperature and then repeated at 40°C, 80°C and 120°C. Surprisingly the average bubble diameters and variances showed no significant influence of the oil viscosity for the examined section. While the degassing sure increased with the oil temperature, the intelligent CG control of the FOAM was able to compensate for that through its permanent circulation and additional gas introduction.



Click here for a pdf document of the first part of test report.


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