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Selected food applications of squeezing flow viscometry
Abstract
The theoretical behavior of a double layered array of two Newtonian liquids is described in terms of dimensionless force-time or thickness-time relationships. In lubricated flow at a constant displacement rate, when the viscosity ratio was higher than ten, a distinct transient region, reminiscent of viscoelastic deformation was clearly evident in the force-time curves. Under constant load, in contrast, the array's behavior was always similar to that of a single layer with an intermediate viscosity. In nonlubricated flow the force levels were about tenfold or more higher than in lubricated flows under the same conditions. The relative position of the force-time curves in flows at a constant displacement rate or thickness-time curves under constant load, is not only determined by the layer's thickness and viscosity ratios, as is the case in lubricated flow, but also by the relation between frictional and viscous effects. Force-time relationships of a double layered array of two power law liquids in squeezing flow at a constant displacement rate were generated with a computer. As in the case of a single layer, lubrication or lack of it has the strongest influence on the magnitude of the forces and the flow pattern. Transient flow regimes that were prominent in the behavior of Newtonian liquid arrays in lubricated squeezing flow were also found in the behavior of the power law liquids. The preparation of a sample for viscosity measurement or its mere insertion into the viscometer can cause, in a variety of materials, a significant change in the sample's rheological behavior. To bypass this problem it was proposed to collect or set a thin specimen in a wide container and subject it to squeezing flow using a wide plate. The method was demonstrated with experimental results of silicone oils with known viscosity. Rotational viscometry accompanied by high test range of shear rates is quite suspected to be able to keep the flow at walls of the bob and the cup from slipping. Viscosities by using different size of bobs did not agree. On the other hand, squeezing viscometry is used at very low shear rates. It was proved that the slippage in rotational viscometry is greater than in squeezing viscometry. (Abstract shortened with permission of author.)
Subject Area
Chemical engineering
Recommended Citation
Lee, Seung Ju, "Selected food applications of squeezing flow viscometry" (1990). Doctoral Dissertations Available from Proquest. AAI9110174.
https://scholarworks.umass.edu/dissertations/AAI9110174