Computer Program for Example

At the first level of detail, it is not necessary to know the internal parameters for all the units, since what is desired is just the overall performance. For example, in a heat exchanger design, it suffices to know the heat duty, the total area, and the temperatures of the output streams the details such as the percentage baffle cut, tube layout, or baffle spacing can be specified later when the details of the proposed plant are better defined. It is important to realize the level of detail modeled by a commercial computer program. For example, a chemical reactor could be modeled as an equilibrium reactor, in which the input stream is brought to a new temperature and pressure and the... 

Many commercial finite element computer programs (for example ABAQUS, ADINA, ANSYS, DYNA, DYNA3D, LS-DYNA, NASTRAN and NONSAP) arc readily available for nonlinear dynamic analysis. Other computer codes, such as CBARCS, COSMOS/M, STABLE, ANSR 1 have been developed specifically for the design of structures to resist blast toads. All these computer programs possess nonlinear analysis capabilities to varying degrees. 

The method involves a simple iteration on only one variable, pH. Simple interval-halving convergence (see Chap. 4) can be used very effectively. The titration curves can be easily converted into simple functions to include in the computer program. For example, straight-line sections can be used to interpolate between data points. 

References to data retrieved from a stand-alone database should cite the source as a computer program (for example, MDL CrossFire Commander, see p 323 f) or as an online reference book (for example, the Kirk-Othmer Encyclopedia of Chemical Technology, see p 305 f), with the data entry number or other identifying information included at the end of the citation. Data retrieved from an Internet-based database should cite the source as a Web site (see pp 316 ff). If the data retrieved are calculated data, also cite the software used for calculation (for example, ACD/Labs). 

Note that the inner surface temperature of the Trombe wall dropped by I C and the outer surface temperature rose by 6.5°C during the first time step vrhile the temperatures at the interior nodes remained the same. This is typical of transient problems in mediums that involve no heat generation. The nodal temperatures at the following time steps are determined similarly with the help of a computer. Note that the dala for ambient temperature and the incident solar radiation change every 3 hours, which corresponds to 12 time steps, and this must be reflected in the computer program. For example, the value o( must be taken to be = 360 for / = 1 12, = 763 for i =... 

For most multiligand systems, the calculations can be carried out easily with the help of computer programs, for example, MINEQL (Westall et al., 1976) or MICROQL (Westall, 1986). The total concentrations of the components (e.g., Pb, C03, etc. of Tableau 6.4a) and the stability constants of the complex species (as illustrated by the log K vector in Tableau 6.4a) are the inputs for such programs. 

The previous procedure is tedious if done by hand calculations. Therefore, it is more convenient to conduct the design with available computer programs. For example, the HE ATX subroutine of the ASPEN PLUS simulator computes heat transfer coefficients, pressure drops, and outlet conditions for a shell-and-tube heat exchanger of known geometry, as illustrated in Example 13.7. It can be used by trial-and-error with the iterative procedure to design an exchanger. 

As discussed in Section 6.4 for ammonia oxidation at a single Pt wire, that is, where the cylindrical wire is heated by an exothermic chemical reaction, the variation of temperature around a cylinder can nowadays be modeled by computer programs, for example, by the finite element method. The geometric structure is approximated by a meshing procedure that is used to define and break the model up into small elements. The differential equations of heat transfer and of the fluid dynamics (Navier-Stokes equations) are then numerically solved. The temperature gradients at the surface of the cylinder (Tcyi = const. = at... 

Calculations that are repeatedly made can be made more accurately, and at lower cost, by using a computer. If, for example, automotive emissions are continually tested over a standardized driving cycle, a computer program to analyze the data is a necessity. Otherwise, days would be spent calculating the data obtained in hours. 

The addition of further components makes the presentation of the phase diagrams increasingly complex. The principles are general, however, and calculation of a vertical section in a quinternary system like Fe-Cr-Mo-W-C [19], for example, is fairly easily done by the use of large computer programs for calculation of phase diagrams based on thermodynamics. 

Some investigations require a preselected temperature program. For example, a substance should be dried at a special temperature, and afterwards one wants to know the complete heating behavior from room temperature to the selected temperature, with an isothermal step and uncontrolled cooling (Fig. 14 D). For such problems some of the commercial instruments are prepared either by computer, or by simple switching clock-programs which allow one to follow a preprogrammed course,... 

A computer program for calculating the scattering coefficients (8.38) and the corresponding cross sections and scattering matrix elements is described in Appendix C all the examples in this section were obtained with this program. 

Example 9.11 employs this method for finding the number of transfer units as a function of liquid to gas ratio, both with finite and infinite values of km/kh. The computer programs for the solution of this example are short but highly desirable. Graphical methods have been widely used and are described for example by Foust et al. (1980). 

---