Viscosity contributions

Neglecting the vapour pressure and viscosity contributions and replacing P by P sinWjt gives Eq. 2.29. 

Shear enhancement effects in foam formation can be understood through the modified cavity model. Shear force behaves as catalyst to reduce energy barrier to allow a quik path from stable gas cavity to unstable bubble phase. It can be concluded that both shear rate and viscosity contribute to foam nucleation in the continuous foam extrusion process. Therefore, proper die opening and process conditions will help to optimise the foam product. 11 refs. 

Note that for all the times considered in this problem, except t = 10 s, the viscosity contribution to the compliance is negligible, so that in the present case one has / = for t < 10" s. 

The cavities thus formed will expand. This would suggest that the increase in total surface energy due to the creation of new surface would be a contributor to the tack force. However, in an analysis of cavity expansion within a polyisobutene oil, Hoffman and Myers— found that surface tension contributed only 7 percent and the viscosity contributed 93 percent to the work of separation of the oil film. 

Stability can be reached if the density of the dispersed phase exactly matches that of the continuous phase. This is difficult to achieve in practice as the volumic expansion coefficients are different for oil and water. Density matching accordingly holds only at one temperature. Decreasing the particle size reduces the separation rate but does not stop it. Moreover, particle size reduction commonly leads to a viscosity increase, and even to gelling. Increasing the viscosity contributes to separation reduction but it is not very easy to achieve in practice. 

A decrease of the viscosity contribution of the free polyelectrolyte due to the release of the counterions and the increase of the ionic strength A dilution of the starting solutions according to the added amount of the cationic ones... 

Pulp-Serum Separation. As for freeze concentration, high viscosity contributes to limiting the degree of concentration which can be achieved by membrane concentration. Since the insoluble solids present in citrus juices contribute significantly to viscosity, one consideration for process development is to separate the pulp from the clear serum, prior to concentration. Because consumers recognize that citrus juices are cloudy and contain pulpy material, it becomes a requirement to blend the separated pulp back with the product concentrate (31). 

For evaluation of DUEVs, with less shear viscosity contribution to the total response, the modified stagnation technique is the procedure of preference. For practical applications the vacuum-suction filament-draw technique is probably the more valuable because the deformation rates in many applications are not solely extensional in nature. The comments regarding the velocity gradients in the tubeless siphon (41) are appropriate to the fiber-suction approach flow in a tubeless siphon approximates extensional flow in a sense that the largest components of the velocity gradient tensors are diagonal ones. ... 

Confinanent along the z-axis of the trap is assured by a static voltage applied to the end sections, near the axis of the trap. The shape of the ion cloud results from a balance between the viscosity contributions (laser cooUng, buffer gas collisions), the coulombic interactions, and the confin ent potential [20]. The shape of the ion cloud can be controlled by the shape and positions of the end-section electrodes, as well as by the magnitudes of the DC voltages applied to them. 

Asphaltene constituents in coal liquids are important for several reasons (1) they contribute to many problems in the processing of crude oil (2) they contribute to instabilities in processing (3) they lead to excessive viscosity, contributing to pumping expense, clogging, and slow processing (4) the presence of asphaltene constituents can lead to incompatibility with some solvents used in petroleum processing and (5) asphaltene constituents lead to coke formation under some circumstances. 

Intermolecular adhesion between the polyether chains of a typical silicone surfactant and the underlying polyurethane liquid matrix could increase the surface viscosity contribution in PU films and foams. 

In recent papers Kuhn has considered the influence of the presence of potential barriers on the time which a long chain molecule needs to change its shape to a considerable extent. These considerations lead to the concept inner viscosity of the molecular chain, which determines the velocity with which changes in shape will take place under the influence of external forces. A brief account is given on p. 114 in connection with the treatment of the viscosity contribution of chain molecules in solution. 

The formula (28) is essentially the same as that obtained by Huggins on the basis of rigid instead of flexible coiled structures. This is due to the fact that at low values of shear-rate, the deformation of the molecule is small and its viscosity contribution consequently negligibly different from that of the undeformed molecule. At higher rates of shear, however, Huggins introduced a correction for flexibility, whereas, according to our treatment, the result (28) is independent of the velocity gradient (see also p. 113). 

Finally, a few words may be added with regard to the viscosity at high rates of shear. From the hydrodynamic theory of rod-shaped particles it can be inferred that the viscosity contribution of the rods is decreased as the rate of shear increases This is due to the fact that the particles are more and more oriented in the direction of flow. With flexible long-chain molecules this effect does not exist. It is true that here also the orientation is more pronounced at high rates of shear. This would result in a lower viscosity. At the same time, however, the elastic forces generated by the deformation of the molecules are increased. As the result of these two effects the viscosity is independent of the rate of shear. 

The formula for is similar in nature to that for the viscosity contribution ... 

If the two ends of a molecule are connected to form a ring, the viscosity contribution is reduced by a factor 2. 

The study shows that the amount of particle release is highn for smaller size particles compared to larger particle rizes. With increase in additional load and alnarion time there is a gradual increase in number of particles released for all the particle sizes. The presence of wood pulp and viscose contributes to higher particle release. From the comparison of seven samples, it was observed that the samples SI (PP), S2 (PLA) and S3 (Lyocell/PET) have lower particle release ability compared to other wipes samples. Therefore these wipes can be preferred > eie lower particle release fiom wipes is desired. 

Since the viscosity contributes to the phase morphology, the molecular weights of the blend components will also play an important role in blend preparation. Similarly in SBR and EVA, the relative monomer composition will affect the blend properties and compatibility. 

Interrelationships among the Viscoelastic Material Functions. There is a continuing disagreement within the molecular viscoelasticity commimity about which of the above methods should be used to characterize a material (20). In fact, if one can obtain the zero shear rate viscosity and any of the other functions, these methods are all equivalent. The issue, however, revolves aroimd the fact that some features that appear in the dynamic modulus disappear if the compliance is used as the function to represent the data and vice versa. Also, some measurements are more or less dominated by the viscosity contribution. As a result, some problems of misinterpretation of data could be averted if workers who prefer modulus representations would calculate the compliances. In addition, those who measure the compliance should calculate the moduli in order to provide the data in the format that is more common in the field because of the large number of commercial instruments that obtain dynamic moduli. The advent of modern software packages that make the interrelationships easily calculated makes this dispute seem to go away. The pathways to determine the different material functions, one from the other, are shown in Figure 6. 

The amplitude of the established oscillation depends on the applied frequency with a maximum at the resonance frequency. The surface elasticity increases the effective elasticity of the system, and therefore, the presence of a surfactant at the surface increases the resonance frequency. The surface viscosity contributes to the total energy dissipation and increases the damping in the system. This leads to a decrease of the resonance maximum of the amplitude and to an increase of the phase shift V. On the other hand, increase in the elasticity decreases the phase shift. Thus, the presence of a surfactant in the solution can lead to an increased as well as a decreased phase shift depending on the applied frequency. The phase shift T varies from zero at small frequencies to -7t at large frequencies and passes through - Tdl at... 

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