Design considerations problems

All compressors have an operating envelope. The size is dependent on the compressor type and the application. If the appropriate design considerations were implemented, then operation within the envelope should be problem-free. The first problem stems from a communication gap. Engi... 

This example points out one of the central problems in stack design for pollution control local, short-term effects may be the most important stack design consideration, but will usually be the aspect of the problem about which the least information is available. 

Typical applications for nylon include small gears, bearings, bushes, sprockets, housings for power tools, terminal blocks and slide rollers. An important design consideration is that nylon absorbs moisture which can affect its properties and dimensional stability. Glass reinforcement reduces this problem and produces an extremely strong, impact resistant material. Another major application of nylon is in fibres which are notoriously strong. The density of nylon is about 1100 kg/m. ... 

Some other problems include clogging of the opening with exhausted material and an opening shape that is not chosen to fit the process which results in use of higher flow rate than necessary, thus increasing the cost of the process. Other problems are described in Design Considerations. 

Concrete exposed to deicer salts, or to a marine environment is subjected to chloride and sodium loading. The ability of concrete to resist the penetration of chlorides and sodium is a primary design consideration in marine or cold environments. The ingress of chlorides into concrete is a major problem due to chloride-induced corrosion of the reinforcing steel and deicer salt scaling [a process by which a thin layer (< 1 mm) of concrete deteriorates from the surface of the concrete]. The penetration of sodium from sea water or deicer salts is generally... 

This section discusses several material and design considerations for FMLs. It highlights some of the problems encountered in designing bathtub systems for hazardous waste landfills and describes the impact of regulations on material and design considerations. 

In spite of the drawbacks enumerated above, fluidized bed reactors have a number of compelling advantages, as we have noted previously. By proper design it is possible to overcome their deficiencies so that their advantages predominate. This book does not discuss in detail the manner in which this problem can be solved, although the design considerations outlined in subsequent sections of this chapter are quite pertinent. For detailed treatments of fluidized bed reactor design, consult the excellent reference works by Kunii and Levenspiel (3) and by Davidson and Harrison (4). 

Matsen (1985) pointed out a number of additional problem areas in scale-up such as consideration of particle size balances which change over time due to reaction, attrition and agglomeration. Erosion of cyclones, slide valves and other components due to abrasive particles are important design considerations for commercial units which may not be resolved in pilot plants. 

To overcome these problems, a number of interesting developments in research and technology have occurred over recent years and these have resulted in the following important design considerations. 

The first example involves flammability issues that are not specifically covered in this Guidelines book. However, the discussion here is highly important for safe process design considerations and represents a good example of the problems of scale-up from test data. Runaway reactions may indeed result in the production of flammable gases so an understanding of the scale-up problems is critical. 

In addition to the active design principles for reducing the risk of sulfide problems, a number of more passive principles exist. The following design considerations are especially relevant for the reduction of corrosion selection of corrosion-resistant materials and design of a well-ventilated sewer system. 

In this paper an overview of the developments in liquid membrane extraction of cephalosporin antibiotics has been presented. The principle of reactive extraction via the so-called liquid-liquid ion exchange extraction mechanism can be exploited to develop liquid membrane processes for extraction of cephalosporin antibiotics. The mathematical models that have been used to simulate experimental data have been discussed. Emulsion liquid membrane and supported liquid membrane could provide high extraction flux for cephalosporins, but stability problems need to be fully resolved for process application. Non-dispersive extraction in hollow fib er membrane is likely to offer an attractive alternative in this respect. The applicability of the liquid membrane process has been discussed from process engineering and design considerations. 

In the acoustic microscope the required signal can be selected not only in the time domain but also in the frequency domain. The ability to select the specimen echo and separate it in time from the unwanted lens echo was the basis of the design considerations of the focal length of the lens, and hence the resolution available ( 3.2 and 4.3). But it is a feet of experience that smaller lens reverberations are always present that cannot be separated in time from the echo from the specimen. These lead to the kind of problem that was illustrated schematically in Fig. 4.5. Moreover, even if such reverberations... 

To counteract the typical misoneism of the world food industry, it is necessary to resort to appropriate scaling-up exercises in pilot- or industrial-plant scale to assess precisely the membrane process performance and reliability, as well as its economical feasibility. There are, however, a number of problems that have undoubtedly limited growth in ED membrane sales, like membrane-fouling problems, design considerations, cleanability, investment and membrane replacement costs, and competing technologies, such as NF and IER. 

The elimination of this rapid energetic surge requires special devices and can not be prevented by crowbars, gas diodes, or overvoltage protectors commonly found in computers and power supplies. Considerable problems exist with filtering devices, unless they are especially made with much higher than expected insulation requirements and are used in conjunction with fast, specifically designed overvoltage protectors. 

If design considerations require it, a much thinner bonded film could be used, or a soft film could be burnished down to much reduced thickness. Under those circumstances it would be possible to use a smoother substrate, but coating performance deteriorates badly if the surface is too smooth, and a miminum acceptable surface roughness would probably be about 0.2 yt/m c.I.a., giving a combined roughness parameter of about 0.3 fjm. It seems probable that in such a case an initial, or a fully-burnished, coating thickness of 1 to 2/>m would give a useful life before any serious problem of asperity penetration arises. 

Continuons emulsion polymerization is one of the few chemical processes in which major design considerations require the use of dynamic or unsteady-state models of the process. This need arises because of important problems associated with sustained oscillations or limit cycles in conversion, particle number and size, and molecular weight. These oscillations can occur in almost all commercial continuous emulsion polymerization processes such as styrene (Brooks et cl., 1978), styrene-butadiene and vinyl acetate (Greene et cl., 1976 Kiparissides et cl., 1980a), methyl methacrylate, and chloropene. In addition to the undesirable variations in the polymer and particle properties that will occur, these oscillations can lead to emulsifier concentrations too low to cover adequately the polymer particles, with the result that excessive agglomeration and fouling can occur. Furthermore, excursions to high conversions in polymer like vinyl acetate... 

Other reactor design considerations may be necessary in special cases. Monomer mass transfer, not normally a problem, can he important if the monomer- aqueous phase interface is small. This is more likely in systems involving gaseous monomers in which the large surface area of the monomer emulsion is not present. In such cases special attention must he paid to gas dispersion and transport. Giher factors that can have a significant effect on reactor design include latex viscosity, heat transfer rates, reaction pressure, and control mechanisms. 

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