General Properties and Selection Criteria

Proper material selection for chemical and process equipment is one of the first important problems encountered by the designer. Among the many parameters that must be considered are structural strength specifications, heat resistance, corrosion resistance, physical properties, fabrication characteristics, composition and structure of material and cost. 

The properties that materials must have for a particular application depend largely on the environment in which they are to be used in. Material selection begins from determination of equipment, operating conditions, temperature, pressure, and various components in the process. 

No materials have properties that fulfill all requirements. For example, good heat conductivity is a desirable property for the fabrication of heat exchanger surfaces, but not for insulation purposes. Obviously, both positive and negative properties can coexist in a single material. A corrosion resistant material may be insufficient for heat resistance or mechanical strength. Strong materials may be too brittle, e.g., ferrosilicon. Also, materials that have good mechanical and chemical properties may be too expensive. 

Because any material may be characterized by some desirable and nondesirable properties with respect to a specific application, the selection of materials is reduced to a reasonable compromise. In so doing, one strives to select materials so that properties correspond to the basic demands determined by the function and operating conditions of the equipment, tolerating some of the undesirable properties. 

The basic requirement for materials intended for fabricating chemical apparatuses is mostly corrosion resistance because this determines the durability of equipment. Often, corrosion data are reported as a weight loss per unit of surface area per unit of time. It is easy to transfer from such data to the penetration rate using the following relation  

Because any material may be characterized by some desirable and undesirable propterties with resp ect to a sp ecific application, 

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In the selection of an appropriate cell culture system, a number of criteria must be considered (Table 3). These include not only the characteristics of the cell type but also the controllable parameters of the complete transport system such as the permeants, the filter properties, and the assay conditions. In general, most transport experiments employ the experimental design shown schematically in Figure 4 with modifications as discussed below. Typically, the desired cell is seeded onto some sort of semipermeable filter support and allowed to reach confluence. The filter containing the cell monolayer separates the donor and receiver... 

In this chapter, the diverse coupling constants and MEC components identified in the combined electronic-nuclear approach to equilibrium states in molecules and reactants are explored. The reactivity implications of these derivative descriptors of the interaction between the electronic and geometric aspects of the molecular structure will be commented upon within both the EP and EF perspectives. We begin this analysis with a brief survey of the basic concepts and relations of the generalized compliant description of molecular systems, which simultaneously involves the electronic and nuclear degrees-of-freedom. Illustrative numerical data of these derivative properties for selected polyatomic molecules, taken from the recent computational analysis (Nalewajski et al., 2008), will also be discussed from the point of view of their possible applications as reactivity criteria and interpreted as manifestations of the LeChatelier-Braun principle of thermodynamics (Callen, 1962). 

The selection and prioritization of substances for which EQSs are required is generally based on both scientific and political criteria. Scientific criteria include the intensity of use of a substance and its occurrence in the environment (i.e., the likelihood of aquatic exposure) as well as information about its (eco)toxicological properties. Thus, a strong driver might be if a substance belongs to the group of persistent, bio-accumulative, and toxic (PBT) chemicals. Examples can be found in the COMMPS procedure (Fraunhofer IUCT 1999) as well as in the Australian, Canadian, and US approaches, all of which are summarized in Table 4.2. 

Adsorbent selection criteria for any application generally include the following main attributes capacity, selectivity, regenerability, kinetics, durability, and cost. These attributes represent combinations of properties that are strongly affected by the pertinent conditions. For example, the first four govern how much adsorbent is necessary for a particular application, and the last two affect the annual cost. Furthermore, the first three are tied to the equilibrium characteristics, about which much can be said (see Section 14.3). Likewise, kinetics is covered in more detail in Section 14.4. Both will be discussed briefly here, however. Finally, adsorbent cost obviously depends on both its price and lifetime, which can depend on its resistance to attrition, degradation, fouling, and so on. 

Establishing reliable criteria for selecting the most efficient antioxidant, AO, for a particular application is a major unsolved problem in food emulsions and dispersions and one of general importance in nutrition and health. Recent reviews " point to multiple factors that affect activities of antioxidants including the properties and reactions of the antioxidant and the polyunsaturated lipids being oxidized the locations or distributions of the antioxidant within emulsified food the effect of other components on antioxidant activity and the relevance of the model system to real food. Frankel and Meyer s summarized the antioxidant distribution problem highlighthing the crucial role of the antioxidant distributiOTi into emulsifier-rich interfacial layers in hetero-phasic food emulsions[9, 17],... 

A large variety of equipment for drying is available. The selection criteria are beyond the scope of this book. However, in general, agitated dryers and static dryers have to be differentiated, namely, due to their different potential effects on the crop. In the following, drying aspects related to the properties of the crop are discussed. 

In this chapter, the general components of a process simulator and the seven types of input required to simulate a process successfully were reviewed. Each of the seven required inputs was covered in detail selection of chemical components, selection of thermodynamic models, selection of process topology, selection of feed stream properties, selection of equipment parameters, selection of output options, and selection of convergence criteria. 

The performance of stirred vessels is characterized on the basis of the process resnlt for the mixing operation. Detailed mixing mechanisms and design criteria are discnssed in respective chapters for these mixing operations. In this section we cover only the general principles and mixer selection for different ranges of fluid properties. 

The custodial supervisor, in consultation with the laboratory director, should make a selection from those types most readily available that meet the general criteria of effectiveness, residual properties, and low corrosiveness. 

A brief overview of the polymer selection criteria discussed earlier is given in Table 6.6, entitled Polymer Selection Guide. Table 6.6 lists the polymers that are recommended as the preferred alternatives to Vamac G in appUcations where special processing or properties need to be considered. This table should be used as a general guide and it is not intended to be an all-inclusive listing of alternatives. 

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