Reaction unsteady

The simulation example DRY is based directly on the above treatment, whereas ENZDYN models the case of unsteady-state diffusion, when combined with chemical reaction. Unsteady-state heat conduction can be treated in an exactly analogous manner, though for cases of complex geometry, with multiple heat sources and sinks, the reader is referred to specialist texts, such as Carslaw and Jaeger (1959). 

P4.04.07. FIRST ORDER REVERSIBLE REACTION. UNSTEADY AND STEADY. 

ALCOHOL METRONIDAZOLE Disulfiram-like reaction. Unsteadiness, and incoordination caused by metronidazole may be aggravated by alcohol Metronidazole inhibits aldehyde dehydrogenase. Additive side-effects Avoid co-ingestion... 

In a double shock wave with chemical reactions, unsteady behavior can lead to a p-v space path that is not necessarily well described by Rayleigh lines. However, we assume here that for a given period of time the p-v space path can be transiently approximated by a set of Rayleigh lines. This description is valid when the timescale of the pressure change at point B in Figure 2 is less than the time required for a material element to progress from the initial state to the final shocked state. A more quantitative version of this statement is formulated in the remainder of this section. 

Mass transfer processes are complicated, usually involving turbulent flow, heat transfer, multiple phases, chemical reactions, unsteady operation, as well as the influences from internal construction of the equipment and many other factors. To study such complicated system, we propose a novel scientific computing framework in which all the relevant equations on mass transfer, fluid-dynamics, heat transfer, chemical reactions, and all other influencing factors are involved and solved numerically. This is the main task and research methodology of computational mass transfer (CMT). 

In principle, Chen, given the flux relations there is no difficulty in constructing differencial equations to describe the behavior of a catalyst pellet in steady or unsteady states. In practice, however, this simple procedure is obstructed by the implicit nature of the flux relations, since an explicit solution of usefully compact form is obtainable only for binary mixtures- In steady states this impasse is avoided by using certain, relations between Che flux vectors which are associated with the stoichiometry of Che chemical reaction or reactions taking place in the pellet, and the major part of Chapter 11 is concerned with the derivation, application and limitations of these stoichiometric relations. Fortunately they permit practicable solution procedures to be constructed regardless of the number of substances in the reaction mixture, provided there are only one or two stoichiomeCrically independent chemical reactions. 

The unsteady state equations for a CESTR involving a second order reaction with constant heat input are ... 

Clearly the accurate measurement of the final (infinity time) instrument reading is necessary for the application of the preceding methods, as exemplified by Eq. (2-52) for the spectrophotometric determination of a first-order rate constant. It sometimes happens, however, that this final value cannot be accurately measured. Among the reasons for this inability to determine are the occurrence of a slow secondary reaction, the precipitation of a product, an unsteady instrumental baseline, or simply a reaction so slow that it is inconvenient to wait for its completion. Methods have been devised to allow the rate constant to be evaluated without a known value of in the process, of course, an estimate of A is also obtainable. 

Uses. Its principal use is for the prepn of di-fluoramine-contg org compds. Mixts with H2 have been proposed as rocket propints, but all attempts to use these mixts as such have been plagued by erratic, unsteady reactions, accompanied by low order explns. The addn of 02 seems to reduce this problem somewhat (Ref 10) Refs 1) C.B. Colburn A. Kennedy, JACS 80, 5004 (1958) 2) G.T. Armstrong et al,... 

Hicks (H6) and Frazer and Hicks (F3) considered the ignition model in which exothermic, exponentially temperature-dependent reactions occur within the solid phase. Assuming a uniformly mixed solid phase, the one-dimensional unsteady heat-flow equation relates the propellant temperature, depth from the surface, and time by the nonlinear equation ... 

In the theoretical treatment, the heat- and mass-transfer processes shown in Fig. 6 were considered. Simultaneous solution of the equations describing the behavior of the unsteady-state reaction system permits the temperature history of the propellant surface to be calculated from the instant of oxidizer propellant contact to the runaway reaction stage. 

The simplified equation (for the general equations, see Section IV, L) in the case of unsteady-state diffusion with a simultaneous chemical reaction in isothermal, incompressible dilute binary solutions with constant p and D and with coupled phenomena neglected is... 

In the film-penetration model (H19), it is assumed that the reactant A penetrates through the surface element by one-dimensional unsteady-state molecular diffusion. Convective transport is assumed to be insignificant. The diffusing stream of the reactant A is depleted along the path of diffusion by its reversible reaction with the reactant B, which is an existing component of the liquid surface element. If such a reaction can be represented as... 

Gal-Or and Hoelscher (G5) have recently proposed a mathematical model that takes into account interaction between bubbles (or drops) in a swarm as well as the effect of bubble-size distribution. The analysis is presented for unsteady-state mass transfer with and without chemical reaction, and for steady-state diffusion to a family of moving bubbles. 

For an unsteady-state process, equation 10.170 may be solved analyticaly only in the case of a first-order reaction n = 1). In this case ... 

The heat transfer problem which must be solved in order to calculate the temperature profiles has been posed by Lee and Macosko(lO) as a coupled unsteady state heat conduction problem in the adjoining domains of the reaction mixture and of the nonadiabatic, nonisothermal mold wall. Figure 5 shows the geometry of interest. The following assumptions were made 1) no flow in the reaction mixture (typical molds fill in <2 sec.) ... 

The inlet monomer concentration was varied sinusoidally to determine the effect of these changes on Dp, the time-averaged polydispersity, when compared with the steady-state case. For the unsteady state CSTR, the pseudo steady-state assumption for active centres was used to simplify computations. In both of the mechanisms considered, D increases with respect to the steady-state value (for constant conversion and number average chain length y ) as the frequency of the oscillation in the monomer feed concentration is decreased. The maximum deviation in D thus occurs as lo 0. However, it was predicted that the value of D could only be increased by 10-325S with respect to the steady state depending on reaction mechanism and the amplitude of the oscillating feed. Laurence and Vasudevan (12) considered a reaction with combination termination and no chain transfer. 

The calculations for the experimental reaction rates are based on an unsteady state heat transfer analysis. We computed the overall heat transfer coefficient of the system and estimated the experimental rates as follows dT... 

Equations (14.1)-(14.3) are a set of simultaneous ODEs that govern the performance of an unsteady CSTR. The minimum set is just Equation (14.2), which governs the reaction of a single component with time-varying inlet concentration. The maximum set has separate ODEs for each of the variables... 

Unsteady behavior in an isothermal perfect mixer is governed by a maximum of -I- 1 ordinary differential equations. Except for highly complicated reactions such as polymerizations (where N is theoretically infinite), solutions are usually straightforward. Numerical methods for unsteady CSTRs are similar to those used for steady-state PFRs, and analytical solutions are usually possible when the reaction is first order. 

Unsteady reaction data are often an excellent means for estimating physical parameters that would be difficult or impossible to elucidate from steady-state measurements. However, the associated problems in nonlinear optimization can be formidable. A recent review and comparison of methods is given by... 

A 5% CoOj/Ti02 catalyst is quite active for the wet TCE oxidation at very low reaction temperatures, such as 310 K, and our proposed model of different forms of CoO species existing with the fresh catalyst can reasonably explain the unsteady-state catalytic behavior at the initial period during the wet catalysis. 

Chemical Kinetics, Tank and Tubular Reactor Fundamentals, Residence Time Distributions, Multiphase Reaction Systems, Basic Reactor Types, Batch Reactor Dynamics, Semi-batch Reactors, Control and Stability of Nonisotheimal Reactors. Complex Reactions with Feeding Strategies, Liquid Phase Tubular Reactors, Gas Phase Tubular Reactors, Axial Dispersion, Unsteady State Tubular Reactor Models... 

The reactivity of vanadyl pyrophosphate (VO)2P207, catalyst for n-butane oxidation to maleic anhydride, was investigated under steady and unsteady conditions, in order to obtain iirformation on the status of the active surface in reaction conditions. Specific treatments of hydrolysis and oxidation were applied in order to modify the characteristics of the surface layer of the catalyst, and then the unsteady catalytic performance was followed along with the reaction time, until the steady original behavior was restored. It was found that the transformations occurring on the vanadyl pyrophosphate surface depend on the catalyst characteristics (i.e., on the PfV atomic ratio) and on the reaction conditions. 

Figure 55.4 compares the Raman spectra of the two samples spectra were recorded at 380°C in a 15% O2/N2 stream, on equilibrated catalysts downloaded after reaction. Catalyst VN 1.06 was not oxidized in the air stream, whereas in the case of catalyst PA 1.00 bands typical of a phosphate, ai-VOP04, appeared in the spectrum. These bands were not present in the spectmm of the equilibrated catalyst recorded at room temperature. Indeed, the spectra of the two equilibrated catalysts were quite similar when recorded at room temperature. This result confirms that the surface of catalyst VN 1.06 is less oxidizable than that of catalyst PA 1.00. Therefore, the latter is likely more oxidized than the former one under reaction conditions. A treatment in a more oxidant atmosphere than the reactive n-butane/air feed modifies the surface of catalyst VN 1.06, and leads to the unsteady behavior shown in Figure 55.1. The same treatment did not alter the surface of the equihbrated catalyst P/V 1.00 that was already in an oxidized state under reaction conditions.

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