Balanced torsionally oscillating pipe used as a viscosity sensor

S Clara,T Voglhuber-Brunnmaier,B Jakoby,A Tröls,F Feichtinger,A O Niedermayer

doi:10.1088/1361-6501/aae755

S Clara, T Voglhuber-Brunnmaier + Show 4 more

Open Access

https://doi.org/10.1088/1361-6501/aae755

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Abstract

We present a robust viscosity measurement system based on a torsionally oscillating pipe. The sensitive surface of the sensor performs periodic movements in the fluid to be sensed, generating a shear wave that penetrates the fluid. Due to this interaction, the resonance characteristic of the structure is affected, in particular the quality factor decreases with increasing viscosity. The pipe is mounted at its center where it features a nodal point of the preferred resonant mode, reducing temperature issues while simultaneously enabling high quality factors. A mathematical model is presented illustrating how different parameters influence the sensitivity of the sensor. Long-term measurements were performed to demonstrate the time stability of the sensor setup.

Highlights

In chemical or biochemical industrial applications, a huge number of sensors is utilized to monitor production processes [1]
We present a robust viscosity measurement system based on a torsionally oscillating pipe
The pipe is mounted at its center where it features a nodal point of the preferred resonant mode, reducing temperature issues while simultaneously enabling high quality factors

Summary

Introduction

In chemical or biochemical industrial applications, a huge number of sensors is utilized to monitor production processes [1]. The most interesting mode for viscosity measurements is the anti-symmetric (torsional) mode In this mode the outer pipe itself acts as a torsional spring and the two flywheels on the end oscillate against each other, i.e. inversely phased. As the resonator structure is attached to the mounting spring at this point, little energy is transferred to the housing of the sensor This enables very high quality factors and higher sensitivities for low viscous fluids. The most interesting mode of the setup is the anti-symmetric mode This mode has its nodal point in the area where the pipe system is clamped to the mounting spring, reducing mechanical energy transfer to the housing. The value for the quality factor Q and the resonance frequency fr are the mean values of the last 757 values (sampled during approx. 2 h) for each temperature step; the σ value is the associated standard deviation

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