Choosing

We choose this form because we want to express the fugacity f ... 

Finally, values of n must be obtained when specific ("chemical") interactions can occur. These are difficult to estimate a priori but reasonable approximations can often be made by choosing a value (Appendix C) for a chemically similar system. 

Using the ternary tie-line data and the binary VLE data for the miscible binary pairs, the optimum binary parameters are obtained for each ternary of the type 1-2-i for i = 3. .. m. This results in multiple sets of the parameters for the 1-2 binary, since this binary occurs in each of the ternaries containing two liquid phases. To determine a single set of parameters to represent the 1-2 binary system, the values obtained from initial data reduction of each of the ternary systems are plotted with their approximate confidence ellipses. We choose a single optimum set from the intersection of the confidence ellipses. Finally, with the parameters for the 1-2 binary set at their optimum value, the parameters are adjusted for the remaining miscible binary in each ternary, i.e. the parameters for the 2-i binary system in each ternary of the type 1-2-i for i = 3. .. m. This adjustment is made, again, using the ternary tie-line data and binary VLE data. 

The subsequent representations are probably reliable within the range of data used (always less broad than 200° to 600°K), but they are only approximations outside that range. The functions are, however, always monotonic in temperature, to provide appropriate corrections when iterative programs choose temperature excursions outside the range of data. 

The correlations were generated by first choosing from the literature the best sets of vapor-pressure data for each fluid. 

The user may also choose to use the vapor-pressure equation instead of the fugacity at zero pressure. 

Most processes are catalyzed where catalysts for the reaction are known. The strategy will be to choose the catalyst, if one is to be used, and the ideal characteristics and operating conditions needed for the reaction system. Decisions must be made in terms of reactor... 

The lack of suitable catalysts is the most common reason preventing the exploitation of novel reaction paths. At the first stage of design, it is impossible to look ahead and see all the consequences of choosing one reaction path or another, but some things are clear even at this stage. Consider the following example. 

Having made a choice of the reaction path, we need to choose a reactor type and make some assessment of the conditions in the reactor. This allows assessment of reactor performance for the chosen reaction path in order for the design to proceed. 

Figure 2.2 summarizes these arguments to choose a reactor for systems of multiple reactions in parallel. 

In the preceding section, the choice of reactor type was made on the basis of which gave the most appropriate concentration profile as the reaction progressed in order to minimize volume for single reactions or maximize selectivity for multiple reactions for a given conversion. However, after making the decision to choose one type of reactor or another, there are still important concentration effects to be considered. 

The choice of reactor temperature, pressure, arid hence phase must, in the first instance, take account of the desired equilibrium and selectivity effects. If there is still freedom to choose between gas and liquid phase, operation in the liquid phase is preferred. 

Raw materials efficiency. In choosing the reactor, the overriding consideration is usually raw materials efficiency (bearing in mind materials of construction, safety, etc.). Raw material costs are usually the most important costs in the whole process. Also, any inefficiency in raw materials use is likely to create waste streams that become an environmental problem. The reactor creates inefficiency in the use of raw materials in the following ways ... 

Figure 2.10 Choosing the reactor to maximize selectivity for multiple reactions producing byproducts.

Given the choice of a batch rather than continuous process, does this need a different approach to the synthesis of the reaction and separation and recycle system In fact, a different approach is not needed. We start by assuming the process to be continuous and then, if choosing to use batch operation, replace continuous steps by batch steps. It is simpler to start with continuous process operation... 

Figure 5.11 Choosing nonadjacent keys leads to the prefractionator arrangement.

In choosing to transfer heat, say XP, from the system above the pinch to the system below the pinch, as shown in Fig. 6.8a, then above the pinch there is a heat deficit of XP. The only way this can... 

Choose a reference cost law for the heat exchangers. Greatest accuracy results if the category of streams which makes the largest contribution to capital cost is chosen as reference. ... 

Distillation. There is a large inventory of boiling liquid, sometimes under pressure, in a distillation column, both in the base and held up in the column. If a sequence of columns is involved, then, as discussed in Chap. 5, the sequence can be chosen to minimize the inventory of hazardous material. If all materials are equally hazardous, then choosing the sequence that tends to minimize the flow rate of nonkey components also will tend to minimize the inventory. Use of the dividing-wall column shown in Fig. 5.17c will reduce considerably the inventory relative to two simple columns. Dividing-wall columns are inherently safer than conventional arrangements because they lower not only the inventory but also the number of items of equipment and hence lower the potential for leaks. 

Choose the distillation sequence to minimize the inventory of hazardous material. 

Feed purification. Impurities that enter with the feed inevitably cause waste. If feed impurities undergo reaction, then this causes waste from the reactor, as already discussed. If the feed impurity does not undergo reaction, then it can be separated out from the process in a number of ways, as discussed in Sec. 4.1. The greatest source of waste occurs when we choose to use a purge. Impurity builds up in the recycle, and we would like it to build up to a high concentration to minimize waste of feed materials and product in the purge. However, two factors limit the extent to which the feed impurity can be allowed to build up ... 

The reactor is highly exothermic, and the data have been extracted as the molten salt being a hot stream. The basis of this is that it is assumed that the molten salt circuit is an essential feature of the reactor design. Thereafter, there is freedom within reason to choose how the molten salt is cooled. 

Predicting future cash flows for a project is extremely difficult with many uncertainties, including the project life. However, providing that consistent assumptions are made, projections of cash flows can be used to choose between competing projects. 

Choosing the number of 1-2 shells in series to be the next largest integer above N ensures a practical exchanger design satisfying Xp. 

In order to draw the property-yield curves for gasolines , it suffices to choose the initial point, which coilild be or 20°C, the end point being variable and situated between the end point of the heaviest gasoline cut which can be produced (200-220°C) and about 350°C. 

Many companies choose to represent a continuous distribution with discrete values using the p90, p50, plO values. The discrete probabilities which are then attached to these values are then 25%, 50%, 25%, for a normal distribution. 

With unlimited resources, the investor would take on all projects which meet the screening criteria. Project ranking is necessary to optimise the business when the investor s resources are limited and there are two or more projects to choose between. 

If a company has a number of projects at various stages of development, it has the option to pay for decommissioning with cash generated from younger fields. A company with only one project will not have this option and may choose to build up a... 

The case of thin-skin regime appears in various industrial sectors such as aerospace (with aluminium parts) and also nuclear in tubes (with ferromagnetic parts or mild steel components). The detection of deeper defects depends of course on the choice of the frequency and the dimension of the probe. Modelling can evaluate different solutions for a type of testing in order to help to choose the best NDT system. 

It is very important to make classification of dynamic models and choose an appropriate one to provide similarity between model behavior and real characteristics of the material. The following general classification of the models is proposed for consideration deterministic, stochastic or their combination, linear, nonlinear, stationary or non-stationary, ergodic or non-ergodic. 

Some discontinuities may be identified by a conventional two-dimensional ultrasonic technique, from which the well-known C-scan image is the most popular. The C-scan technique is relatively easy to implement and the results from several NDE studies have been very encouraging [1]. In the case of cylindrical specimens, a circular C-scan image is convenient to show discontinuity information. The circular C-scan image shows the peak amplitude of a back-scattered pulse received in the circular array. The axial scan direction is shown as a function of transducer position in the circular array. The circular C-scan image serves also as an initial step for choosing circular B-scan profiles. The latter provides a mapping between distance to the discontinuity and transducer position in the circular array. 

By choosing the proper correlation algorithm, it is possible to realise sensitive filters for other types of defects (e.g. corrosion). Fig. 5.2 shows an example for the suppression of signals which do not exhibit the expected defect stmcture (Two parallel white lines near upper central rim portion of Fig. 5.2). The largest improvement in SNR is obtained here by using the expression (ai ai+x /ai+yj), since for a gradiometric excitation, one expects the crack response to show two maxima (a, aj+x) with a minimum (a m) in the centre (see Fig. 5.3). 

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