29C-1 |
A new method to determine viscosity of liquids |
B. MERT, O. H. Campanella, and H. Sumali. Dept. of Agricultural & Biological Engineering, Purdue Univ., 1146 Agricultural & Biological Engineering Bldg., West Lafayette, IN 47907-1146 Many rheological techniques do not take slip into account. The results are often good for industrial purposes because it can be argued that slip may occur between solid surfaces and processed liquids under processing. However, true rheological behavior of materials under shear deformations can be obtained accurately only by eliminating the effect of slip. It has been recognized that multiphase systems such as emulsions and complex biological liquids may violate the no-slip condition at solid boundaries specifically when high shear stresses are applied. One way to minimize slip at liquid/solid boundaries is by generating a shear deformation in the liquid without using a solid moving surface. The objective of this study was to develop a method to measure the viscosity of liquids by oscillating the testing liquid itself to produce a harmonically varying shear deformation. In the new method, the testing liquid is placed in a tube closed by two pistons and a plastic film. The pistons do not touch the tube but are in contact with the liquid. Two springs are affixed to the pistons to support their motion. A harmonically varying force is applied to one of the pistons and the acceleration of the other piston and the resulting impedance is measured. The damping obtained from the impedance is used to calculate the viscosity. To validate the proposed method carboxyl methyl cellulose solutions were used and their viscosities were measured with the proposed method and a conventional rotational viscometer. An excellent agreement between both results was obtained thus validating the suitability of the proposed method. The new method offers a practical and accurate way to determine viscosity of liquids that can exhibit slippage effects.
Session 29C, Food Engineering: Rheology and texture
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