Physical sensors for water-in-oil emulsions

For many applications, the detection of water content in an oily base liquid is of crucial importance. Typical examples are automotive oils, e.g. engine and transmission oils, where water content in the order of a few percent needs to be detected. In this contribution, we analyze the suitability of permittivity and viscosity sensors for this application. It turns out, that permittivity sensors yield a clear indication of the water content in the oil being moreover to first order independent of the exact permittivity of the contaminating water. On the other hand, the output of microacoustic viscosity sensors, in contrast to conventional rotational rheometers, is hardly influenced by the water content as long as the droplet size is larger than the penetration depth of the evanescent microacoustic wave. Thus, they can be used for continued monitoring of the base oil’s viscosity even in case of an apparent water contamination.