| Most viscosity measurement methods ignore liquid's elasticity,which can cause some errors in viscosity measurements for viscoelastic liquids,e.g.polyacrylamide and/or hydroxyethyl cellulose solutions widely used in industry.This thesis presents a new approach to measure viscosity for viscoelastic liquid utilizing longitudinal guided wave,by investigating the relationship between guided wave propagation characteristics in cylindrical viscoelastic filled tubes and liquid properties,and whether the characteristics are elasticity insensitive or can distinguish the effects of liquid viscosity and elasticity.Our research not only provides a novel method for viscosity measurement,but also promotes the development of the guided wave theory of liquid-filled tubes.This thesis studies the viscosity measurement of viscoelastic fluid using longitudinal guided waves in liquid filled tubes in four aspects below:(1)A liquid property test system based on 3D-printed flexible hinges and a fiber optic displacement sensor is proposed for liquid viscoelasticity observations and analyses.The effects of fluid density,elasticity and viscosity on the sensing structure are equivalent to additional induced mass,stiffness and damping,respectively.As the oscillation component has no assembly and no lubrication,this device can eliminate interferences from any uncertainty damping/stiffness,i.e.there are only liquid stiffness/damping to be measured and constant stiffness/damping of hinges in the system,which can ensure accurate measurements.Accurately observing and confirming liquid viscoelasticity can provide basic liquid properties and references for the research on guided wave characteristics in liquid-filled tubes.Experimental results also indicate the additional stiffness is mainly caused by the liquid elasticity/storage modulus.(2)Algorithms and softwares for longitudinal guided waves of single and multiple layers of tubes are developed based on global matrix method(GMM),which can calculate phase velocity dispersion curves,group velocity dispersion curves,attenuation dispersion curves and displacement field distributions.The calculation results agree well with both experimental results and COMSOL simulation results.Verified Algorithms and softwares are the foundation for further studying the effect of fluid properties on longitudinal guided waves in fluid filled tubes.(3)In view of the facts that precision of traditional viscometers is susceptible to liquid elasticity,and conventional L guided wave dispersions are insensitive to viscosity,via calculations and analyses,a viscosity measurement method for viscoelastic liquids using longitudinal guided waves in capillary tubes is proposed.The mathematical relationship between the cut-off frequency of the nth mode and the pipe's inner radius,the liquid viscosity,and density is established.When the fluid viscosity is very high or the pipe's inner radius is very small,both shear and compression forces play an important role in the fluid acoustic field,which leads to new longitudinal modes.Velocity dispersion curves of the new modes caused by the small radius stretch noticeably toward the right as the liquid viscosity increases,which can be characterized by cut-off frequencies.(4)A viscosity measurement system based on capillary guided wave method is built,and in order to overcome frequency-selective attenuations and low coupling efficiencies of the PZT to measure capillary guided waves,a working-point trackable fiber-optic hydrophone with high acoustic resolution is proposed at the same time.Experiment results verifies: the linear relationship between the cut-off frequency and the liquid viscosity,the precision increases as the pipe's inner radius decreases,and the guided wave is only sensitive to the liquid viscosity but not elasticity.This thesis finally achieves viscosity measurements for viscoelastic liquids using longitudinal guided waves in capillary. |
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