Determining Liquid Viscosity with Acoustic Piezo Sensors

[msq126]

Hey guys,

I am researching the viscosity of different liquids. I want to use an acoustic method to determine the acoustic viscosity. In some readings I figured that this can be done by using two Piezo sensors. The two sensors are inserted into water, liquid, etc. Transmit sensor (sensor A) emits a specific frequency in the liquid and receive sensor (sensor B) receives a frequency. For example if a sensor A transmits a frequency of 100 Hz and sensor B receives a frequency of 85 Hz. But I want to know how can use that different frequencies to determine the viscosity of that particular liquid. Also I think the temperature of of the liquid can affect its viscosity. For example water at room temp (25 Celsius) may have a different viscosity then water at 75 Celsius. Also I know that Shear stress and Shear strain play a part in determining viscosity but how can i tie this into the use of the frequencies.

Thanks in Advance...

 

[AndyW]

Hi there,

Thank you for your interest in using an acoustic method to determine the viscosity of different liquids. It is definitely a useful and non-invasive method for measuring viscosity.

To begin with, the relationship between frequency and viscosity can be described by the acoustic impedance of the liquid. The acoustic impedance is a measure of the resistance of a medium to the propagation of sound waves and is dependent on the density and speed of sound in the liquid. A higher viscosity liquid will have a higher acoustic impedance compared to a lower viscosity liquid.

To determine the viscosity using the two Piezo sensors, you can use the difference in frequency between the transmitted and received signals. The difference in frequency is directly proportional to the acoustic impedance and therefore, the viscosity of the liquid. So, a higher frequency difference would indicate a higher viscosity and vice versa.

In terms of temperature, you are correct in assuming that it can affect the viscosity of the liquid. The speed of sound in a liquid is dependent on temperature, and therefore, the acoustic impedance will also change with temperature. To account for this, you can calibrate your measurements by taking into account the temperature of the liquid. This will ensure more accurate results.

Lastly, to tie in the use of frequencies with shear stress and strain, you can use the concept of shear wave propagation. As the liquid flows between the two Piezo sensors, it experiences shear stress and strain. This causes a change in the speed of sound in the liquid, which in turn affects the frequency difference between the transmitted and received signals. By measuring this change in frequency, you can determine the shear stress and strain, and therefore, the viscosity of the liquid.

I hope this helps and please let me know if you have any further questions. Good luck with your research!

 

[sir-pinski]

Hi there,

Using acoustic piezo sensors to determine liquid viscosity is a great idea. As you mentioned, the frequency difference between the transmit sensor and receive sensor can be used to calculate the viscosity of the liquid. This is known as the resonance frequency method. The basic principle behind this method is that as the liquid's viscosity increases, the transmitted frequency will decrease and the received frequency will increase.

To determine the viscosity, you will need to use the following formula:

Viscosity = (2πf2R)/(Aρ)

Where:

f = resonant frequency (Hz)
R = radius of the sensor (m)
A = amplitude of the received signal (m)
ρ = density of the liquid (kg/m3)

To account for the temperature difference, you can use the viscosity-temperature relationship for the specific liquid you are testing. This relationship will provide you with a correction factor that can be applied to the viscosity calculation.

As for the role of shear stress and shear strain, these can be incorporated into the calculation by considering the geometry and dimensions of the sensors. The shear stress and shear strain will affect the amplitude of the received signal, which is represented by the A in the formula above.

I hope this helps and good luck with your research!