Chemical programs, total number

STANJAN The Element Potential Method for Chemical Equilibrium Analysis Implementation in the Interactive Program STANJAN, W.C. Reynolds, Thermosciences Division, Department of Mechanical Engineering, Stanford University, Stanford, CA, 1986. A computer program for IBM PC and compatibles for making chemical equilibrium calculations in an interactive environment. The equilibrium calculations use a version of the method of element potentials in which exact equations for the gas-phase mole fractions are derived in terms of Lagrange multipliers associated with the atomic constraints. The Lagrange multipliers (the element potentials ) and the total number of moles are adjusted to meet the constraints and to render the sum of mole fractions unity. If condensed phases are present, their populations also are adjusted to achieve phase equilibrium. However, the condensed-phase species need not be present in the gas-phase, and this enables the method to deal with problems in which the gas-phase mole fraction of a condensed-phase species is extremely low, as with the formation of carbon particulates. 

Table II gives a general description of the program features such as total number of elements, aqueous species, gases, organic species, redox species, solid species, pressure and temperature ranges over which calculations can be made, an indication of the types of equations used for computing activity coefficients, numerical method used for calculating distribution of species and the total number of iterations required by these models for each of the two test cases. The chemical analyses for the two test cases are summarized in Table III. The seawater compilation was prepared in several units to assure consistency between concentrations for proper entry into the aqueous models.

Once programmed, the dynamic simulation will be used to understand the various processes going on inside a complex plant and to make usable predictions of the behaviour that will result from any changes or disturbances that may occur on the real plant, represented on the simulation by forcing functions or alterations to the chosen starting conditions. A basic first step is to characterize the condition of the plant at any given instant in time, and it is the state vector that, taken in conjunction with its associated mathematical model, allows us to do this. The state vector is an ordered collection of all the state variables. For a typical chemical plant, the state vector will consist of a number of temperatures, pressures, levels and valve positions, and the total number of state variables will be the dimension or order of the plant. For those... 

Figure 8, Total number of full-time graduate students enrolled in chemical engineering programs...

Fig. 4.1 (a) Total number of catalytically produced CO2 molecules as a function of cluster size, (b) Total number of produced CO2 molecules per atom as a function of cluster size. The CO molecules produced by oxidation of CO are studied by means of temperature-programmed desorption mass spectrometry (Reprinted with permission from Heiz et al. 1999, Copyright 1999 American Chemical Society)... 

If one has the programs to solve the Schrodinger equation in atoms, one can think about a quantum mechanical description of simple chemical systems. In NaCl e.g., one already has to deal with 28 electrons, and only 8 out of them determine the chemical bond. In more complex systems, the total number of electrons becomes fairly large, and the number of valence electrons is substantially lower. This is a rather frustrating situation, if one realizes that the core electrons are essentially chemically inactif, and remain intimately bound to their nucleus. 

Figure 1 Is a flow sheet showing some significant aspects of the Iterative analysis. The first step In the program Is to Input data for about 50 physical, chemical and kinetic properties of the reactants. Each loop of this analysis Is conducted at a specified solution temperature T K. Some of the variables computed In each loop are the monomer conversion, polymer concentration, monomer and polymer volume fractions, effective polymer molecular weight, cumulative number average molecular weight, cumulative weight average molecular weight, solution viscosity, polymerization rate, ratio of polymerization rates between the current and previous steps, the total pressure and the partial pressures of the monomer, the solvent, and the nitrogen.

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