29C-2 |
Determination of viscosity of liquids using standing waves in rigid tubes |
B. MERT, H. Sumali, and O. H. Campanella. Dept. of Agricultural & Biological Engineering, Purdue Univ., 1146 Agricultural & Biological Engineering Bldg., West Lafayette, IN 47907-1146 The use of acoustical methods to characterize the rheology of solutions is finding increasing application in the polymer and food area. Most of the current techniques work in the ultrasonic frequency range and measurement of the ultrasound energy attenuation and velocity dispersion is the standard data analysis. The fluid sample is contained in a solid cavity where the ultrasonic waves propagate and standing waves are generated in an unbound medium. For bound mediums, such as cylindrical tubes, the analysis becomes complicated because the complexity of the working equations. Moreover, attenuation and dispersion of the ultrasonic waves can be very high for fluids containing particles which might prevent accurate measurements of the ultrasonic properties. The objective of this study was to develop a method to measure sound attenuation using frequencies lower than those in the ultrasonic range and determine rheological properties of liquids. The equipment designed in our laboratory consists in a wave generator and a thick wall steel tube. It generates one-dimensional standing waves in the tube and attenuation is measured with an impedance head. Analytical equations describing the system were developed. Glycerol-water mixtures with known viscosities were used as testing fluids. The attenuation, obtained by the proposed method, was used to estimate the liquid viscosity. Good agreement between the viscosities obtained with the acoustic method and those given in the literature for these systems validated the applicability of the proposed method. The new methodology can be modified for other applications such as measuring viscosity of fluids in closed cylindrical containers. The method is suitable for in-line applications that require short time measurements. The use of tubes with materials other than steel would make possible the measurement of bulk complex modulus of low viscosity liquids at relatively low frequencies.
Session 29C, Food Engineering: Rheology and texture
|