Past Design Considerations

A significant number of developments have occurred over the past decade to address these important issues of pneumatic conveying (Wypych, 1995a). This chapter summarizes some of the major design considerations that have resulted from this work in relation to long-distance and pipe branching applications. 

Over the past decade, considerable effort has been expended on the design and synthesis of nonpeptidic antagonists for the three receptors (NKl-3) to which SP, NKA, and NKB bind. These antagonists could have therapeutic use in conditions such as migraine, arthritis, inflammatory diseases such as cystitis, psoriasis, asthma, anxiety, depression, and emesis (vomiting). A variety of NKl-3 receptor antagonists have been designed and synthesized. The majority of these compounds are polyheterocyclics. 

The significance of this history is that over a span of many centuries engineers had only about nine basic materials with which to work. Further, they were limited in their design considerations by the properties of these few materials. So, within just the past 60 years we have seen the advent of these fifty or so separate families of plastics and literarily hundreds of modifications of these materials. 

Differences in design practices have in the past handicapped developments that could have reduced costs. For example, some difficulties with past design practices are evident in examining application of the ASME Code and Code Case N-47 to pool type LMFRs, such as Super Phenix. The design of Super Phenix resulted in considerably thinner components. This required different buckling rules. Super Phenix design creep effects were negligible... 

In the past few years, the AEC has required solution excursion analyses for new construction as well as plants already in operation. These hypothetical excursions should be chosen to be representative of the most severe excursion that could be reasonably expected in the particular systems involved since the results of the analysis will, in turn, determine the size and types of the hot exhaust filtering system and shielding thickness, etc. An example of the "most severe excursion may be helpful. Consider a tank 3 ft in diameter by 4 ft high which is shown by a safety review to have solution. For the excursion parameter of maximum total fissions, the most severe condition is a tank that is critical when nearly full hence, the full tank volume is used for the total fission estimate. The specifications of the process systems are usually such that the excursions chosen are limited by practic design considerations to tanks of 2- to 5-ft diam with a height of 1 to 2 diam and a solution transfer rate of 7i gpm or less. 

Definitions Substrate Design Guidelines Thermal Design Considerations Adhesives Solder Paste and Joint Formation... 

Have the appropriate stencil or screen design and materials (e.g., thickness, aperture geometry, wall finish, etc.) for the circuit board product. Design considerations must also address the need to widen fine-pitch aperture openings slightly for printing Pb-free solder paste. 

Process Safety Considerations. Unit optimization studies combined with dynamic simulations of the process may identify operating conditions that are unsafe regarding fire safety, equipment damage potential, and operating sensitivity. Several instances of fires and deflagrations in ethylene oxide production units have been reported in the past (160). These incidents have occurred in both the reaction cycle and ethylene oxide refining areas. Therefore, ethylene oxide units should always be designed to prevent the formation of explosive gas mixtures. 

Fluidised-bed techniques, pioneered with low-density polyethylene, have been applied to PVC powders. These powders can be produced by grinding of conventional granules, either at ambient or sub-zero temperatures or by the use of dry blends (plasticised powders). The fluidised bed process is somewhat competitive with some well-established paste techniques, and has the advantage of a considerable flexibility in compound design. 

As these problems were encountered in the past, it became evident that we did not have at hand the physical or mathematical description of the behavior of materials necessary to produce realistic solutions. Thus, during the past half century, there has been considerable effort expended toward the generation of both experimental data on the static and dynamic mechanical response of materials (steel, plastic, etc.) as well as the formulation of realistic constitutive theories (Appendix A PLASTICS DESIGN TOOLBOX). 

Based on past performances it has been proven that the so-called interchangeable grades of plastics have to be evaluated carefully by the designer as to their affect on the performance of a product. An important consideration to include as far as equivalent... 

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