Influence on the Flow Properties

The behaviour of powders is often quite different from the behaviour of liquids and gases. Engineers and scientists are used to dealing with liquids and gases whose properties can be readily measured, tabulated and even calculated. With particle systems the picture is quite different. The flow properties of certain powders may depend not only on the particle size, size distribution and shape, but also on surface properties, on the humidity of the atmosphere and the state of compaction of the powder. These variables are not easy to characterise and so their influence on the flow properties is difficult to predict. In the case of particle systems it is almost always necessary to perform appropriate measurements on the actual powder in question rather than to rely on tabulated data. The measurements made are generally measurements of bulk properties, such as bulk density and shear stress. 

One could ask whether the presence of an adsorbed surfactant is really necessary. The answer is yes. The soap layer, although only a monolayer thick, has a profound influence on the flow properties of the film liquid be-... 

The main classes of plasticizers for polymeric ISEs are defined by now and comprise lipophilic esters and ethers [90], The regular plasticizer content in polymeric membranes is up to 66% and its influence on the membrane properties cannot be neglected. Compatibility with the membrane polymer is an obvious prerequisite, but other plasticizer parameters must be taken into account, with polarity and lipophilicity as the most important ones. The nature of the plasticizer influences sensor selectivity and detection limits, but often the reasons are not straightforward. The specific solvation of ions by the plasticizer may influence the apparent ion-ionophore complex formation constants, as these may vary in different matrices. Ion-pair formation constants also depend on the solvent polarity, but in polymeric membranes such correlations are rather qualitative. Insufficient plasticizer lipophilicity may cause its leaching, which is especially undesired for in-vivo measurements, for microelectrodes and sensors working under flow conditions. Extension of plasticizer alkyl chains in order to enhance lipophilicity is only a partial problem solution, as it may lead to membrane component incompatibility. The concept of plasticizer-free membranes with active compounds, covalently attached to the polymer, has been intensively studied in recent years [91]. 

The bubbles exert a very strong influence on the flow pattern in the bed and provide the mechanisim for the high degree of mixing of solids which occurs. The properties and behaviour of the bubbles are describe later in this Section. 

Machado, A. L. C., and Lucas, E. F. 2002. Influence of Ethyl co-Vinyl Acetate Copolymers on the Flow Properties of Wax Synthetic Systems. I. Appl. Polym. Sci., 85, 1337-1348. 

Weld lines (also known as knit lines) are a potential source of weakness in molded and extruded plastic products. These occur when separate polymer melt flows meet and weld more or less into each other. Knit lines arise from flows around barriers, as in double or multigating and use of inserts in injection molding. The primary source of weld lines in extrusion is flow around spiders (multiarmed devices that hold the extrusion die). The melt temperature and melt elasticity (which is mentioned in the next section of this chapter) have major influences on the mechanical properties of weld lines. The tensile and impact strength of plastics that fail without appreciable yielding may be reduced considerably by in doublegated moldings, compared to that of samples without weld lines. Polystryrene and SAN copolymers are typical of such materials. The effects of weld lines is relatively minor with ductile amorphous plastics like ABS and polycarbonate and with semicrystalline polymers such as polyoxymethylene. Tliis is because these materials can reduce stress concentrations by yielding [22]. 

Van Ooteghem, M. De Winter, B. Ludwig, A. Influence of the mixing conditions on the flow properties of powders to be filled into hard gelatin capsules. Acta Pharm. Jugosl. 1998, 38, 287-295. 

The degree to which the above blending mechanisms influence a process depends on the flow properties (such as cohesion) of the materials being blended and the specific equipment selected, as discussed in subsequent sections of this chapter. 

The influence of phase volume on the flow properties of an emulsion is shown in Fig. 7.26. In this diagram the relative viscosity of the system increases with increasing 4>, and at any given phase volume increases with decreasing mean particle size, D. These and other factors which affect emulsion viscosity are listed in Table 7.6. 

A large proportion of the structural features which can impact on the flow properties of a reservoir are below the resolution of seismic data. Therefore, understanding the spatial distribution and internal structure of fault zones can be fundamental to the flow behaviour of hydrocarbon reservoirs. This section reviews the important geometrical characteristics of fault zones and sub-seismic deformation features which can influence fault seal analysis. 

Many industrial processes are affected by the influence of particulate materials on the flow properties of material. Flow properties of materials can be adjusted by fillers to meet the requirements. Flow properties can also be adversely affected by numerous phenomena related to the presence of filler in formulations.One common example is related to the flow of industrial slurries which contain concentrated suspensions of small particles. Such suspensions are usually non-Newtonian fluids with a yield stress which is formed through strong interactions between particles. During flow, these interactions are continuously broken and rebuilt. A solid deposit formed on the slopes and walls is an adverse effect of this property. 

Electroviscous Effect Any influence of electric double layer(s) on the flow properties of a fluid. The primary electroviscous effect refers to an increase in apparent viscosity when a dispersion of charged colloidal species is sheared. The secondary electroviscous effect refers to the increase in viscosity of a dispersion of charged colloidal species that is caused by their mutual electrostatic repulsion (overlapping of electric double layers). An example of the tertiary electroviscous effect would be for polyelectrolytes in solution where changes in polyelectrolyte molecule conformations and their associated effect on solution apparent viscosity occur. 

Parnell-Clunies, E. M., Kakuda, Y. and de Man, J, M. (1986a). Influence of heat treatment of milk on the flow properties of yogurt. J. Food Scl 51, 1459-1462. 

When coupled to gas adsorption data, calorimetric data can be very useful for the textural characterization of carbons. The use of chemical probes with different molecular sizes allow determining the pore size distribution [288-295]. On the other hand, relevant information concerning chemical properties of the carbon surfaces and their influence on the sorption properties of carbons can be obtained when using the appropriate calorimetric technique. Immersion, flow adsorption and gas-adsorption calorimetry have been employed for the study of surface chemistry of carbons. For instance, immersion calorimetry provides a direct measurement of the energy involved in the interaction of vapor molecules of the immersion liquid with the surface of the solid. This energy depends on the chemical nature of the solid surfajoe and the probe molecules, i.e. the specific interaction between the solid and the liquid. Comparison between enthalpies of immersion into liquids with different polarities provides a picture of the surface chemistry of the solid. Although calorimetric techniques are not able to completely characterize the complex surface chemistry of carbons, they represent a valuable complement to other techniques. 

Donskoi and co-workers [54] showed that each of the components of a chlorosulfonated polyethylene (CSPE) mix has its own influence on the fireproofing properties and chemical processes that occur. In this case, the thermal properties of the vulcanisates of CSPE were studied, and also the heat flows from the flame on the surface of the specimen. It was established that the thermooxidative breakdown of CSPE and vulcanisates based on it during heating under dynamic conditions, is a multi-stage process. The results of tests involving various fillers and plasticisers made it possible to create rubber-like, high-impact resistant materials. 

Natov, M Djagarova, E. Influence of Small Amormts of Powdered Substances on the Flow Properties of the Polymer Melts. Angew. Makromolek. Chemie, 1968, Vol.2,180 - 189 (in German)... 

In many instances it is difficult to process polyethylenes, especially where it comes to recycling. Studies were performed on the blending of different types of polyethylene in order to improve processing [28-32]. Typically, one would expect a processing agent (wax) to improve the melt flow of the polymer to be processed, without having a detrimental influence on the mechanical properties and thermal stability of that polymer. 

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