Effects of Flow

In this chapter, the general effects of processing conditions (mechanical, thermal, geometrical) on the crystallization phenomena (nucleation, growth, overall kinetics, development of morphologies) will be first discussed. Then, the principles of the modeling of structure 

Finally, four case studies will be presented, which correspond to different influences of the processing conditions on the final microstructures. In cast film extrusion, crystallization occurs after cessation of flow, and the thermal conditions are very important. In fiber spinning and film blowing, it takes place during flow in uniaxial or biaxial conditions, respectively. In injection molding, different situations may be encountered as a function of the location in the part. 

Many papers have been devoted to the relationships between processing conditions, and in particular, flow conditions, microstructure, and properties. In parallel. 

Handbook of Polymer Crystallization, rst Edition. Edited by Ewa Piorkowska and Gregory C. Rutledge. 2013 John Wiley Sons, Inc. Published 2013 by John Wiley Sons, Inc. 

Thermoplastics are composed of flexible macromolecules, which adopt a random-coil conformation at rest, and can be easily deformed by flow. Under flow, they also tend to be oriented along the flow direction. Stretching and orientation of macromolecules in the melt have consequences on crystallization thermodynamics and kinetics, as well as on the subsequent morphologies. 

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Miscellaneous Effects. Depending on individual design characteristics, there are other miscellaneous effects to consider in the determination of the final sizing of a heat exchanger. These include effects of flow maldistribution of both the sheUside and tubeside fluids, stagnant or inactive regions in the tube bundle, and inactive length of the tube in tubesheets. These effects should be individuaUy assessed and appropriate additional areas should be provided. 

The effects of flow nonuniformities, in particular, can be severe in gas systems when the ratio of bed-to-particle diameters is small in liquid systems when viscous fingering occurs as a result of large viscosity gradients in the adsorption bed when very small particles (<50 Im) are used, such as in high performance liqmd chromatography systems and in large-diameter beds. A lower bound of the axial... 

Figure 1. Effect of Flow Program Rate on Elution Time...

Although the Izod and Charpy tests are widely used for plastics, other types of test are also popular. These include tensile impact tests and flexural plate (falling weight) tests. The latter is particularly useful in situations where the effects of flow anisotropy are being assessed. In addition, arbitrary end-product tests are widely used to provide reassurance that unforseen factors have not emerged to reduce the impact performance of the product. 

Elow rate determines the separation time and can significantly affect resolution and efficiency. The effect of flow rate on HETP for TSK-GEL SW and TSK-GEL SWxi analytical columns is shown in Fig. 4.6. Resolution is typically higher at slower flow rates, although results shown in Fig. 5B indicate that, with increasing sample load, the faster flow rates can give higher resolution. 

The effect of flow rate on resolution by Toyopearl HW-55F and Toyopearl HW-55S columns has been studied using a bovine serum albumin sample. Eor both columns, resolution decreased with increasing flow rate (46). Resolution is increased, however, with decreasing particle size (47). Resolution is proportional to the square root of the column length, as theoretically expected, and indicates that longer columns can be packed as well as shorter columns. Therefore, for samples difficult to resolve, the solution may be to increase the column length. 

Effect of Flow Rate and Temperature on Enantiomeric Separations... 

Fig. 2-10. The effect of flow rate on the resolution of methylphenidate enantiomers on vancomycin CSP (250 x 4.6 mm). The mobile phase was methanol 1.0 % triethyl-ammonium acetate (95/5 v/v) pH 4.1 at ambient temperature (23 °C).

The effect of flowing temperatures on gas flow can be disregarded for temperatures between 30°F and 150°F. Corrections should apply to other temperatures above or below [11]. 

Figure 9-79D. COg absorption from atmosphere effect of flow rates on Koa at elevated pressure. Reproduced by permission of the American Institute of Chemical Engineers, Spector, N. A., and Dodge, B. F., Trans. A.I.Ch.E., V. 42 (1946) p. 827 all rights resenred.

Impingement attack (sometimes termed erosion corrosion) is a result of the combined effect of flow and corrosion on a metal surface and it occurs when metal is removed from the surface under conditions where passivation is insufficiently rapid. It is a function of flow, corrosion and passivation. 

The corrosive and mechanical effects of flow are observed in pipes, especially at bends and downstream of flow disturbances, tube and shell heat exchangers, valves and pumps. More corrosion and/or harder materials are used in such areas. Austenitic stainless steels work harden and hence are superior in flowing conditions to ferritic stainless steels of otherwise similar corrosion resistance. Hard... 

Zembura has made specific use of the rotating disc for investigation of the effect of flow on corrosion reactions. This work has shown that it is possible to determine the type of control (activation or concentration polarisation) of zinc dissolving in 0.1 N Na2S04 (de-aerated), which followed closely the predicted increase in hydrogen ion reduction as the flow rate increased, and proved that in this example... 

The rotating disc and rotating cylinder have been successfully applied in the laboratory to study the effect of flow on corrosion rates and are much easier to use than actual pipelines and other real geometries. The results of these tests can now be correlated to geometries likely to be found in pipes, pumps, bends, etc. in plant by use of dimensionless group analysis. There-... 

Effect of Flow During Conditions that Lead to Film Formation... 

Tinker, T. Proceedings of the General Discussion onHeat Transfer, September, 1951, p. 89. Analysis of the fluid flow pattern in shell and tube exchangers and the effect of flow distribution on the heat exchanger performance, (Inst, of Mech. Eng. and Am, Soc. Mech. Eng.). 

In Spite of the existence of numerous experimental and theoretical investigations, a number of principal problems related to micro-fluid hydrodynamics are not well-studied. There are contradictory data on the drag in micro-channels, transition from laminar to turbulent flow, etc. That leads to difficulties in understanding the essence of this phenomenon and is a basis for questionable discoveries of special microeffects (Duncan and Peterson 1994 Ho and Tai 1998 Plam 2000 Herwig 2000 Herwig and Hausner 2003 Gad-el-Hak 2003). The latter were revealed by comparison of experimental data with predictions of a conventional theory based on the Navier-Stokes equations. The discrepancy between these data was interpreted as a display of new effects of flow in micro-channels. It should be noted that actual conditions of several experiments were often not identical to conditions that were used in the theoretical models. For this reason, the analysis of sources of disparity between the theory and experiment is of significance. 

The Effect of Flow Regime on the Continuous Emulsion Polymerisation of Styrene in a Tubular Reactor , Can. J. of Chem. 25, 565 (1977)... 

Biggs BJ, Close ME (1989) Periphyton biomass dynamics in gravel bed rivers the relative effects of flows and nutrients. Freshw Biol 22 209-231... 

Mas-Marti E, Garcia-Berthou E, Sabater S, Tomanova S, Munoz I (2009) Effects of flow temporality on fish assemblage and trophic ecology, Hydrobiologia (in press)... 

Considerable work has been done in the past in formulating mechanistic models of the physical processes that are perceived to be responsible for the deleterious effects of flow. In practically all of these a primary flow stress is identified as the cause of the observed effects. The most relevant flow stresses are thought to originate from ... 

Fig. 16. Effects of flow regime on cell viability measured by trypan blue. Exposure time 1 h [1]...

Figure 2 shows the effect of flow rate on column efficiency using the SW-2000 column with cytochrome C. The column efficiency expressed as the number of theoretical plates (N) was dependent on flow rate, a result typical of size exclusion chromatography. 

Figure 2. Effect of flow rate on the efficiency (N) of the Spherogel TSK-SW 2000 column. The conditions were as indicated in Figure 1 using cytochrome C as test solute.

Effect of Flow Improver Additives on Paraffin Deposition... 

P. Eaton and G. Sutton. The effect of flow on inhibitor film life. In Proceedings Volume. 49th Annu NACE Int Corrosion Conf (Corrosion 94) (Baltimore, MD, 2/27-3/4), 1994. 

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