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Measuring Liquid Viscosity Using Acoustic Absorption.

This presentation details innovative methods for measuring liquid viscosity via acoustic absorption, particularly addressing limitations encountered by traditional rheometers in food industry applications. The proposed techniques utilize acoustic waves to analyze liquid behavior, determining viscosity through complex acoustic speed measurements. The study emphasizes the importance of absorption coefficients and relaxation times in correlating viscosity with vibration responses of fluid-filled structures. This research sets the foundation for developing a practical and efficient on-line viscosity measurement system.

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Measuring Liquid Viscosity Using Acoustic Absorption.

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  1. Measuring Liquid Viscosity Using Acoustic Absorption. Presentation to NRL by ASEE Summer Faculty Fellow candidate Hartono Sumali Purdue University March 26, 2001 http://pasture.ecn.purdue.edu/~sumali/research/tube1.pdf

  2. Motivation • Food industry rheometers rely on boundary layers. • Fail to work with solid-liquid slip (mayonnaise etc). • Fail to obtain zero-shear viscosity. • Cannot be used on-line. • Acoustic waves attenuate with liquid absorption.

  3. Possible Approaches • Attenuation over distance • Simple fundamental phenomenon • Requires long aparatus. • Reflection coefficient • Ultrasonics have shown success. Empirical/ calibration. • Three-dimensional nature complicates fundamental analysis

  4. Approaches pursued so far • Longitudinal waves in tubes • Low-frequency in narrow tube allows simple 1-D analysis. • Fluid loading of plate vibration. • Simple device.

  5. Measuring complex acoustic speed with a tube. • Measure impedances of driving piston (Zm0) and end piston (ZmL). • Measure “total tube impedance” Slender tube Piston speed Exciting force uL(w) F(w) Zm0 ZmL Longitudinal waves Piston impedance Piston impedance

  6. Total tube impedance F/uL Piston speed Exciting force uL(w) • Pressure amplitude at position x and wavenumber k is F(w) Zm0 ZmL L = tube length, m AandBare constants from boundary conditions • Boundary conditions: • F = pressure at (x=0) times piston area + speed at (x=0) times Zm0 • Pressure at (x=L) times piston area = speed at (x=L) times ZmL.

  7. Obtaining complex acoustic speed • Total tube impedance F/uL = total tube impedance, N/(m/s2) Zm0, ZmL = piston impedance in-vacuo, N/(m/s2) S = piston area, m2 r = liquid density, kg/m3 L = tube length, m w = frequency, rad/s Measured Known • Solve for complex acoustic speed c.

  8. Obtaining viscosity from complex c • From complex acoustic speed c, obtain relaxation time t using • From relaxation time t , obtain absorption coefficient a using c = real speed, m/s • Viscosity h can be related to absorption coefficient a. r = density, kg/m3 a = tube radius, m (Exact relationship to be determined)

  9. Experimental Aparatus Force from shaker or hammer. Mesured with force transducer • F/uL is obtained using FFT analyzer. Piston with spring beam Accelerometer

  10. Results so far: Accelerances 60 0 dB = 1 m/s2/N • Piston in-vacuo • Tube with water, theoretical. -20 500 0 Hz • Tube with water, experimental. 25 -5 0 Hz 100

  11. Measuring viscosity using plates • Box is filled with liquid. • Accelerance obtained with force transducer and accelerometer.

  12. Analytical model of plate • Plate deflection w at point (x,y) is summation of modal responses • p is modal coordinate from From modal analysis • f is mode shape, w is natural frequency. z is damping.

  13. 20 -30 Hz 60 Results with plate: Accelerance with difference liquid viscosities • Liquid viscosity or concentration of Carboxy-Methyl Cellulose (CMC) : High, medium, low • Theoretical 20 Hz -10 60 • Experimental

  14. Relationship between damping and viscosity From first mode data

  15. Conclusions so far • Higher viscosity results in higher damping. • Absorption coefficient appears to have an important role in relating viscosity to vibration responses of liquid-filled structures. • Much work is yet to be done to develop a method to masure viscosity using acoustic waves.

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