A two-phase approach for on-line optimization of chemical processes was proposed by Jang et al. This approach addresses some crucial difficulties encountered with chemical processes such as imperfect models, nonlinearity, presence of operating constraints, and the multivariable nature of most processes. The approach was adapted for application to an industrial scale problem, namely, the optimal operation of a packed tubular reactor for the production of ethylene oxide. This application exhibits many characteristics cited above which makes on-line optimization a challenging problem. Results using a simulation study show that the two-phase approach holds considerable promise. The paper concludes with suggestions regarding the application of the proposed approach to industrial processes.Considerable progress has been made in the field of chemical process control in the last decade. The availability of low-cost microcomputers is revolutionizing the field of instrumentation and control hardware. Process engineers now have access to vast amounts of operational information and computing power. Networking allows access to larger computers from the plant operating site. Plant managers are increasingly looking into ways of reducing energy consumption, raw materials, waste, and production costs using these newly acquired capabilities. This is evidenced by the recent publications from industry extolling virtues of computer control and plant optimiza-
The nonlinear stress relaxation of a nearly monodisperse, moderately entangled polystyrene solution (i.e., roughly seven entanglements per chain at equilibrium) in single step-strain flow is investigated quantitatively by a detailed comparison of an existing set of experimental data with a simulation based on the tube model. The proposed simulation enables the effects of primary nonlinear relaxation mechanisms other than chain retraction to be identified more clearly and investigated individually. Two peculiar nonlinear relaxation behaviors are observed in this experiment. One is concerned with an apparent enhancement in the stress relaxation at short times, and the other is responsible for a seeming slowdown of the stress relaxation at long times. These findings are discussed within the tube model, in view of the effects of convective constraint release, partial strand extension, and nonaffine deformation.
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