A7.3 - Ultrasonic Sensor for Viscosity of Mineral Oil for Built-in Pipe Applications

SENSOR+TEST Conferences 2011
2011-06-07 - 2011-06-09
Proceedings SENSOR 2011
A7 - Ultrasonic Sensors II
B. Tittmann, H. Ju - The Pennsylvania State University (USA), E. Gottlieb - Caldon Ultrasonics Technology Center, Pennsylvania (USA)
171 - 176


Ultrasonic methods have been developed to measure the viscosity elastic properties using the shear reflectance, and the mode conversion of the shear waves has been utilized for vegetable oil viscosity measurement by the relation between the shear properties and ultrasonic wave propagation. These methods have been restricted in pipeline applications, because for the protection from harsh fluid conditions such as high temperature and corrosion, ultrasonic transducers can be equipped with steel housings which restrict the mode conversion. The purpose of this research is to extract the shear viscosity of fluids from the volume viscosity in the acoustic absorption. Stokes mathematically derived the volume viscosity in addition to the shear viscosity, but its existence could not be attested until high frequency ultrasonic methods were developed. This paper presents an empirical method for measuring the viscosity of mineral oil. In a built-in pipeline application, conventional ultrasonic methods using shear
reflectance or rheological and acoustical phenomena may fail due to attenuated shear wave propagation and an unpredictable spreading loss by protective housings, and comparable main flows. The empirical method utilizing longitudinal waves eliminates the unknown spreading loss from attenuation measurements on the object fluid by removing the normalized spreading loss per focal length with the measurement of a reference fluid of a known acoustic absorption coefficient. The ultrasonic attenuation of fresh water as the reference fluid and mineral oil as the object fluid were measured along with the sound speed and effective frequency. The empirical equation for the spreading loss in the reference fluid is determined by highorder polynomial fitting. To estimate the shear viscosity of the mineral oil, a linear fit is applied to the total loss difference between the two fluids, whose slope (the absorption coefficient) is combined with an assumed shear-to-volume viscosity relation.
The empirical method predicted the viscosities of two types of the mineral oil with a maximum statistical uncertainty of 8.8% and a maximum systematic error of 12.5% compared to directly measured viscosity using a glass-type viscometer. The validity of this method was examined by comparison with the results from theoretical far-field spreading.