The Value

The value x can be assigned to any variable in an assignment statement. In such a case, x is treated as a don t-care for synthesis purposes. A synthesis system may intelligently select either a logic-0 or a logic-1 for the value x that leads to optimal logic. 

II Synthesis system will automatically select // logic-0 or logic-1. 

When value x is used in a case item of a case statement (not casex, casez), the branch corresponding to that case item is considered never to execute for synthesis purposes. 

2 bx Out = In // This branch will never occur for // synthesis, default Out = In  

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In Equation (24), a is the estimated standard deviation for each of the measured variables, i.e. pressure, temperature, and liquid-phase and vapor-phase compositions. The values assigned to a determine the relative weighting between the tieline data and the vapor-liquid equilibrium data this weighting determines how well the ternary system is represented. This weighting depends first, on the estimated accuracy of the ternary data, relative to that of the binary vapor-liquid data and second, on how remote the temperature of the binary data is from that of the ternary data and finally, on how important in a design the liquid-liquid equilibria are relative to the vapor-liquid equilibria. Typical values which we use in data reduction are Op = 1 mm Hg, = 0.05°C, = 0.001, and = 0.003... 

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. 

Two generally accepted models for the vapor phase were discussed in Chapter 3 and one particular model for the liquid phase (UNIQUAC) was discussed in Chapter 4. Unfortunately, these, and all other presently available models, are only approximate when used to calculate equilibrium properties of dense fluid mixtures. Therefore, any such model must contain a number of adjustable parameters, which can only be obtained from experimental measurements. The predictions of the model may be sensitive to the values selected for model parameters, and the data available may contain significant measurement errors. Thus, it is of major importance that serious consideration be given to the proper treatment of experimental measurements for mixtures to obtain the most appropriate values for parameters in models such as UNIQUAC. 

PARAMETER USED TO CALCULATE PART OF CHEMICAL CONTRIBUTION TO THE SECOND VIRIAL COEFFICIENT. CALCULATED ONE OF TWO WAYS DEPENDING ON THE VALUE OF ETA(IJ). 

What is the minimum selectivity of decane which must be achieved for profitable operation The values of the materials involved together with their molecular weights are given in Table 4.1. 

More than 7.5 MW could be added from a hot utility to the first interval, but the objective is to find the minimum hot and cold utility. Thus from Fig. 6.186, QHmin = 7.5MW and Qcmm = 10MW. This corresponds with the values obtained from the composite curves in Fig. 6.5a. One further important piece of information can be deduced from the cascade in Fig. 6.186. The point where the heat flow goes to zero at T = 145°C corresponds to the pinch. Thus the actual hot and cold stream pinch temperatures are 150 and 140°C. Again, this agrees with the result from the composite curves in Fig. 6.5a. 

Now recalculate the network area target substituting for in Fig. 7.5. Table 7.2 is revised to the values shown in Table 7.3 ... 

Example 7.5 For the process in Fig. 6.2, determine the value of and the total cost of the heat exchsinger network at the optimal setting of the... 

The value of PRODUCT formation and the raw materials cost of FEED that reacts to PRODUCT are constant. Alternatively, if the byproduct has no value, the cost of disposal should be included as... 

In most processes, the largest individual cost is raw materials. Raw materials costs and product prices tend to have the largest influence on the economic performance of the process. The value of raw materials and products depends on whether the materials in question are being bought and sold under a contractual arrangement (either within or outside the company) or on the open market (the spot price). Open-market prices can fluctuate considerably with time. Products are normally sold at below open-market price when under a contractual arrangement. 

The values of raw materials and products can be found in trade journals such as Chemical Marketing Reporter (Schnell Publishing Company) and European Chemical News (Reed Business Publishing... 

The problem with this approach is that if the steam generated in the boilers is at a very high pressure and/or the ratio of power to fuel costs is high, then the value of low-pressure steam can be extremely low or even negative. This is not sensible and discourages efficient use of low-pressure steam, since it leads to low-pressure steam with a value considerably less than its fuel value. 

These marginal costing approaches to costing steam are unsatisfactory. Within operating companies, few subjects generate more controversy than the value placed on different steam levels. 

Cooling water costs tend to be low relative to the value of both fuel and electricity. The cost of cooling duty provided by cooling water is on the order of 1 percent that of the cost of power. For example, if power costs 0.07 kW h, then cooling water will typically cost 0.07 X 0.01/3600 = 0.19 x 10 kJ or 0.19 GJ L... 

The value of NPV is, of course, directly dependent on the choice of the fractional interest rate i. 

The value of i given by this equation is known as the discounted cash-flow rate of return (DCFRR). It may be found graphically or by trial and error. 

The higher the value of the DCFRR for a project, the more attractive it is. The minimum acceptable value of the DCFRR is the market interest rate. If the DCFRR is lower than market interest rate, it would be better to put money in the bank. For a DCFRR value greater than this, the project will show a profit for a lesser value, it will show a loss. 

The value of Pi 2 required in each 1-2 shell to satisfy a chosen value of Xp is defined by... 

These expressions define Pn-2n for number of 1-2 shells in series in terms of R and Xp in each shell. The expressions can be used to define the number of 1-2 shells in series required to satisfy a specified value of Xp in each shell for a given R and Pjv 2n- Hence the relationship can be inverted to find the value of N which satisfies Xp exactly in each 1-2 shell in the series ... 

The strength of an acid is measured by the value of its dissociation constant, strong acids, e.g. HCl, HNO3. being substantially fully ionized in solution and weak acids predominately unionized. 

The wave function T i oo ( = 11 / = 0, w = 0) corresponds to a spherical electronic distribution around the nucleus and is an example of an s orbital. Solutions of other wave functions may be described in terms of p and d orbitals, atomic radii Half the closest distance of approach of atoms in the structure of the elements. This is easily defined for regular structures, e.g. close-packed metals, but is less easy to define in elements with irregular structures, e.g. As. The values may differ between allo-tropes (e.g. C-C 1 -54 A in diamond and 1 -42 A in planes of graphite). Atomic radii are very different from ionic and covalent radii. 

The term p is a reaction constant and is mathematically evaluated for a particular reaction by plotting log kjkQ against a. The slope of the straight lines is p, and reflects the sensitivity of the reaction under study to effects of substituents. The value of p is obviously affected by temperature, solvent changes, etc. 

As in the case of density or specific gravity, the refractive index, n, for hydrocarbons varies in relation to their chemical structures. The value of n follows the order n paraffins < n naphthenes < n aromatics and it increases with molecular weight. 

For a substance, A, whose partial pressure is p, the values (intensities) of ions 57 and 43, for example are given as(Ji)... 

The values for hydrocarbons of different chemical families (see Chapter 3) are as follows ... 

The values obtained for the acentric factor differ significantly from one another. As shown in Figure 4.3, this factor depends on the temperature, the physical property being considered, and the method used. 

Hexane is an easy example. The variations in acentric factors are much more pronounced for heavy polar or polarizable components. It comes as no surprise that the values reported from different sources are not identical. 

For petroleum fractions, the values should be calculated starting with the standard specific gravity accor( ing to the relation ... 

It is difficult to judge the accuracy of these methods because data are scarce. Table 4.9 compares the values obtained by different weighting methods with experimental values for a mixture of n-hexane-n-hexadecane at 25°C. The ASTM method shows results very close to those obtained experimentally. 

The value of coefficient depends on the composition. As the mole fraction of component A approaches 0, approaches ZJ g the diffusion coefficient of component A in the solvent B at infinite dilution. The coefficient Z g can be estimated by the Wilke and Chang (1955) method ... 

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