Ediguer E. Franco

Viscosity measurement of Newtonian liquids using the complex reflection coefficient

This work presents the implementation of the ultrasonic shear reflectance method for viscosity measurement of Newtonian liquids using wave mode conversion from longitudinal to shear waves and vice versa. The method is based on the measurement of the complex reflection coefficient (magnitude and phase) at a solid-liquid interface. The implemented measurement cell is composed of an ultrasonic transducer, a water buffer, an aluminum prism, a PMMA buffer rod, and a sample chamber. Viscosity measurements were made in the range from 1 to 3.5 MHz for olive oil and for automotive oils (SAE 40, 90, and 250) at 15 and 22.5degC, respectively. Moreover, olive oil and corn oil measurements were conducted in the range from 15 to 30degC at 3.5 and 2.25 MHz, respectively. The ultrasonic measurements, in the case of the less viscous liquids, agree with the results provided by a rotational viscometer, showing Newtonian behavior. In the case of the more viscous liquids, a significant difference was obtained, showing a clear non-Newtonian behavior that cannot be described by the Kelvin-Voigt model.

Ultrasonic viscosity measurement using the shear-wave reflection coefficient with a novel signal processing technique

Real-time viscosity measurement remains a necessity for highly automated industry. To resolve this problem, many studies have been carried out using an ultrasonic shear wave reflectance method. This method is based on the determination of the complex reflection coefficients magnitude and phase at the solid-liquid interface. Although magnitude is a stable quantity and its measurement is relatively simple and precise, phase measurement is a difficult task because of strong temperature dependence. A simplified method that uses only the magnitude of the reflection coefficient and that is valid under the Newtonian regimen has been proposed by some authors, but the obtained viscosity values do not match conventional viscometry measurements. In this work, a mode conversion measurement cell was used to measure glycerin viscosity as a function of temperature (15 to 25°C) and corn syrup-water mixtures as a function of concentration (70 to 100 wt% of corn syrup). Tests were carried out at 1 MHz. A novel signal processing technique that calculates the reflection coefficient magnitude in a frequency band, instead of a single frequency, was studied. The effects of the bandwidth on magnitude and viscosity were analyzed and the results were compared with the values predicted by the Newtonian liquid model. The frequency band technique improved the magnitude results. The obtained viscosity values came close to those measured by the rotational viscometer with percentage errors up to 14%, whereas errors up to 96% were found for the single frequency method.

Viscosity measuring cell using ultrasonic wave mode conversion

This work presents a cell to measure dynamic viscosity of liquids using ultrasonic wave mode conversion from longitudinal to shear wave. The strategy used to obtain the viscosity is based on the measurement of the complex reflection coefficient of shear waves at a solid-liquid interface. Viscosity measurements of automotive oils (SAE90 and SAE140) were obtained in the frequency range from 1 to 10 MHz. These results are compared with the Maxwell model with two relaxation times, showing the dependency of viscosity with frequency. Several parameters affecting viscosity measurements, including the solid material properties, liquid viscosity, and operating frequency are discussed.

P3L-3 Viscosity Measurement of Newtonian Liquids Using The Complex Reflection Coefficient

This work presents the implementation of the ultrasonic shear reflectance method for viscosity measurement of Newtonian liquids using wave mode conversion from longitudinal to shear waves and vice-versa. The method is based on measuring the complex reflection coefficient (magnitude and phase) at a solid-liquid interface. Viscosity measurements were made in the range from 1 to 3.5 MHz at 22.5degC for automotive oil (SAE40) and at 15degC for olive oil. Moreover, measurements of the olive oil were also conducted in the range from 15 to 30degC at 3.5 MHz. The experimental results agree with those provided by a rotational viscometer

Experimental study on the determination of the shear-wave reflection coefficient at the solid-liquid interface

This work implements the ultrasonic shear-wave reflectance method for viscosity measurements. A modeconversion device was used for the dynamic viscosity measurement of mineral oil, SAE 40 automotive oil and glycerin samples at room temperature and 1 MHz. A novel signals processing technique that calculates the reflection coefficient magnitude in a frequency band, instead of a single frequency, was employed, showing an important improvement on the measurement accuracy.

A simple maxwell based model in order to represent the frequency-dependent viscosity measured by ultrasound

A previous work showed that viscosity values measured at high frequency by ultrasound agreed with the values measured at low frequency by the rotational viscometer when special conditions are met, such as relatively low frequency and viscosity. However, these conditions strongly reduce the useful range of the measurement cell. In order to obtain a better measurement range and sensitivity high frequency must be used, but it causes a frequency-dependent decrease on the obtained viscosity values. This work introduces a new simple model in order to represent this frequency-dependent behavior. The model is based on the Maxwell model for viscoelastic materials, but using a variable parameter. This parameter has a physical meaning because it represents the linear behavior of the apparent elasticity measured along with the viscosity by ultrasound. Automotive oils SAE 90 and SAE 250 at 22.5plusmn0.5degC with viscosities at low frequency of 0.6 and 6.7 Pa.s, respectively, were tested in the range of 1-5 MHz. The model was used in order to fit the obtained data using an algorithm of non-linear regression in Matlab. By including the viscosity at low frequency as an unknown fitting parameter, it is possible to extrapolate its value. Relative deviations between the values measured by the viscometer and extrapolated using the model for the SAE 90 and SAE 250 oils were 5.0% and 15.7%, respectively.

Analysis of an ultrasonic viscosity measurement cell with mode conversion

Theoretical and experimental analyses of a cell that measures the viscosity of liquids using longitudinal to shear wave mode conversion are presented. The measurement method is based on the determination of the complex reflection coefficient (magnitude and phase) of shear waves at a solid-liquid interface. The cell is composed of an ultrasonic transducer, a water buffer, an aluminum prism, a PMMA buffer rod and a sample chamber. In order to simulate the cell, a unidimensional model composed by acoustic and electroacoustic transmission lines is implemented using matrix operations. The simulation of viscosity as a function of signal-to-noise ratio, and the temperature dependence, which affects the measurement values if there are gradients inside the cell, are studied. The results show the behavior of the measurement cell to obtain the viscosity error. The cell was tested with olive oil at 3.5 MHz as a function of the temperature. The experimental results agree with those measured by a rotational viscometer for stabilized temperatures.