Magnitude Of Yield Stress Research Articles

Rheological Properties of Tomato Concentrates as Affected by Particle Size and Methods of Concentration

ABSTRACTShear rate‐shear stress data were obtained on tomato concentrates made from juices that were produced using finisher screen openings (FSO): 0.020, 0.027, 0.033, and 0.045 in. In general, the apparent viscosity of the concentrates at a shear rate of 100 set‐1 increased with increase in FSO. However, concentrates made from juice using a 0.027 in FSO had the highest apparent viscosity. Magnitudes of yield stress of concentrates increased in direct proportion to FSO. Apparent viscosities of concentrates made by evaporating tomato juice were lower than those obtained either by evaporating the serum or by reverse osmosis concentration of the serum.

Flow Properties of Low‐Pulp Concentrated Orange Juice: Effect of Temperature and Concentration

ABSTRACTThree 65° Brix low‐pulp concentrated orange juice (COJ) samples, between −19 and 30°C were shear‐thinning (pseudoplastic) fluids with negligible magnitudes of yield stress. The simple power law model fit welt the shear rate‐shear stress data. For one sample, the Powell‐Eyring model also described the data well. The Arrhenius model described the effect of temperature on the apparent viscosity and the consistency index of the power law model. The activation energy of flow (Ea) was 10.7 ± 0.2 kcal/g mole. The models of Harper and El Sahrigi and Christiansen and Craig were suitable for describing the combined effect of temperature and shear rate. The magnitude of Ea decreased with decrease in concentration. Apparent viscosity and K increased exponeitially with concentration.

The slip process during yield-point deformation

When Frank-Read dislocation sources are pinned by solute atoms, the mode of dynamic operation of the source is altered. In particular the source may be activated even though the yield-point stress is as much as 15 per cent lower than the critical operating stress of the source, and, further, the number of dislocation loops per burst is strongly dependent on the relative magnitudes of yield stress and critical stress. A qualitative application of these results to the yield-point phenomenon is made.