42-4 |
A comparative evaluation of oscillating sphere, tube and coaxial cylinder viscometers for in-process measurement of power-law fluids |
J. H. Lee1, T. A. HALEY2, O. H. Campanella3, and Y. R. Kim2. (1) Department of Food Engineering, Taegu University, 15 Naeri-Ri, Jinnryang-Myun, Kyungsan, Kyungpook, 713-714, South Korea, (2) Department of Food Science, Purdue University, 1160 Food Science Bldg, West Lafayette, IN 47907, (3) Department of Agricultural and Biological Engineering, Purdue University, 1146 Agricultural and Biological Engineering Building, West Lafayette, IN 47907 In-line viscosity sensors are of important practical interest to enhance automation in the food industry. From previous studies performed in our laboratory, it was found that in-line viscometry often require additional calibration effort to provide agreement with offline methods. For the proper application of process viscometry, it is necessary to evaluate the performance of in-line viscometers and the calibration methods for various fluid products of different viscosity ranges. The objective is to evaluate the performance and calibration functions of three in-line viscometrs (oscillating sphere, tube , and coaxial cylinder viscometers) in measuring viscosity of CMC solutions at different concentrations. CMC solutions of 1.7 and 2 % (w/w) were used. The experimental apparatus consisted of a closed flow loop that included a feed tank, positive displacement pump, an oscillating sphere, a tube, and a coaxial cylinder viscometer. The flow rate was varied from 33 to 103 L/min by approximately 18 L/min. At each flow rate, in-line viscosity measurements were performed. The power law parameters, n and k, were calculated in an off-line rheometer. The in-line consistency and in-line flow index parameters were calculated for each sample and each viscometer. The in-line and off-line indices were combined to generate calibration functions. The tube and coaxial cylinder viscometers provided flow curves very close to that generated by the off-line rheometer. The oscillating sphere viscometer showed the largest deviation from off-line measurements. After calibration, the output provided by the three process viscometers matched that provided by the off-line rheometer. Calibration functions for both in-line viscometer were not affected by changes in concentration. The output of the in-line coaxial cylinder viscometer was not significantly affected by flow rate. Process viscometry provided accurate flow behavior curves and viscosity determination after proper calibration. The fact that the calibration functions were independent over a given range of concentration indicates that the calibration effort is worthwhile for industrial applications.
Session 42, Food Engineering: Rheology and texture
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