STEADY SHEAR RHEOLOGY AND FLUID MECHANICS OF SEMI-SOLID FOODS AND FACILITATION OF THEIR TRANSPORT.

摘要

The steady shear rheology of four semi-solid food materials; ketchup, mustard, apple sauce and tomato paste was studied by generating and comparing flow data using cone and plate, parallel plate and capillary measurements over the shear rate range of 0.05 s('-1) to 1600 s('-1). Superposition of flow data was demonstrated and correlations obtained using the power law, Bingham Plastic, Herschel-Bulkley and Casson models were compared. In the low shear rate range ((gamma) = 0.05 s('-1) to 1.0 s('-1)) the Bingham Plastic model, in the high shear rate range ((gamma) = 1.0 s('-1) to 1600 s('-1)) the Herschel-Bulkley model were shown to be most successful.;The effect of different tube wall characteristics on the steady shear tube flow of the four semi-solid foods was also examined generating shear stress vs. shear rate data using tubes made of galvanized steel, PVC, teflon and glass. A significant dependence of the wall shear stress on the wall material selected was observed and lowest stress measurements were obtained using glass with reductions in the range of 6% to 21%.;Fluid mechanics predictions of average velocities in pipe flow of the semi-solid foods studied using power law, Herschel-Bulkley and Casson models were compared to the experimentally obtained data and it was shown that the equation using the Herschel-Bulkley model is best suited for use in the design of flow processes for the foods studied.;A new method for facilitating the transport of thick semi-solid foods through lubrication was studied in inclined plane and pipe flow geometries using tomato paste as a model thick material and carboxymethyl cellulose dispersons as model lubricants. It was shown that facilitation of flow of thick materials was possible through lubrication. 17-53 fold increase in flow rates in pipe flow were obtained. Flow times in inclined plane and flow rates in pipe flow were predicted by mathematical models.;The wall effect in the tube flow of the semi-solid foods studied was investigated using three different I.D.-tubes (0.884 cm, 0.647 cm, 0.430 cm) with L/D ratios of 65. The strong dependence of flow data on the tube diameter used was well explained with the apparent slip phenomenon. True flow curves for each food material were obtained applying appropriate corrections for slip.