Heat transfer with chemical reaction

MODELLING OF SIMULTANEOUS MASS AND HEAT TRANSFER WITH CHEMICAL REACTION USING THE MAXWELL-STEFAN THEORY—I. MODEL DEVELOPMENT AND ISOTHERMAL STUDY... 

The variation of efficiencies is due to interaction phenomena caused by the simultaneous diffusional transport of several components. From a fundamental point of view one should therefore take these interaction phenomena explicitly into account in the description of the elementary processes (i.e. mass and heat transfer with chemical reaction). In literature this approach has been used within the non-equilibrium stage model (Sivasubramanian and Boston, 1990). Sawistowski (1983) and Sawistowski and Pilavakis (1979) have developed a model describing reactive distillation in a packed column. Their model incorporates a simple representation of the prevailing mass and heat transfer processes supplemented with a rate equation for chemical reaction, allowing chemical enhancement of mass transfer. They assumed elementary reaction kinetics, equal binary diffusion coefficients and equal molar latent heat of evaporation for each component. 

At the end of the filling stage, only heat transfer with chemical reaction occurs, which can be described by the following species and energy balance equations ... 

Frank, M. J. W., Kuipers, J. A. M., Krishna, R., and van Swaaij, W. P. M., Modelling of simultaneous mass and heat transfer with chemical reactions using the Maxwell-Stefan theory— U. Non-isothermal study. Chem. Eng. Sci. 50(10), 1661 (1995b). 

The numerical solution of the energy balance and momentum balance equations can be combined with flow equations to describe heat transfer and chemical reactions in flow situations. The simulation results can be in various forms numerical, graphical, or pictorial. CFD codes are structured around the numerical algorithms and, to provide easy assess to their solving power, CFD commercial packages incorporate user interfaces to input parameters and observe the results. CFD... 

Many industrial processes involve mass transfer processes between a gas/vapour and a liquid. Usually, these transfer processes are described on the basis of Pick s law, but the Maxwell-Stefan theory finds increasing application. Especially for reactive distillation it can be anticipated that the Maxwell-Stefan theory should be used for describing the mass transfer processes. Moreover, with reactive distillation there is a need to take heat transfer and chemical reaction into account. The model developed in this study will be formulated on a generalized basis and as a consequence it can be used for many other gas-liquid and vapour-liquid transfer processes. However, reactive distillation has recently received considerable attention in literature. With reactive distillation reaction and separation are carried out simultaneously in one apparatus, usually a distillation column. This kind of processing can be advantageous for equilibrium reactions. By removing one of the products from the reactive zone by evaporation, the equilibrium is shifted to the product side and consequently higher conversions can be obtained. Commercial applications of reactive distillation are the production of methyl-... 

In this paper only isothermal simulations have been conducted to show the important features of the model to describe mass transfer with chemical reaction. In many industrial processes, distillation, reactive distillation and some absorption processes, heat effects play an important role and therefore cannot be neglected. These effects will be discussed in Part II. 

Astarita, G. Mass Transfer with Chemical Reaction, Elsevier, Amsterdam, 1967. Erank-Kamenetskii, D. A. Diffusion and Heat Transfer in Chemical Kinetics, Plenum Press, New York, 1969. 

In what follows, the preceding evaluation procedure is employed in a somewhat different mode, the main objective now being to obtain expressions for the heat or mass transfer coefficient in complex situations on the basis of information available for some simpler asymptotic cases. The order-of-magnitude procedure replaces the convective diffusion equation by an algebraic equation whose coefficients are determined from exact solutions available in simpler limiting cases [13,14]. Various cases involving free convection, forced convection, mixed convection, diffusion with reaction, convective diffusion with reaction, turbulent mass transfer with chemical reaction, and unsteady heat transfer are examined to demonstrate the usefulness of this simple approach. There are, of course, cases, such as the one treated earlier, in which the constants cannot be obtained because exact solutions are not available even for simpler limiting cases. In such cases, the procedure is still useful to correlate experimental data if the constants are determined on the basis of those data. 

In the last decade we have performed some thousands of experiments in packed adiabatic tubular reactors (CO oxidation), however, we have never observed oscillations. If on certain catalysts (e.g., Pt/Al203) the oscillation are caused by the kinetic mechanism then, apparently, the interactions of heat and mass transfer with chemical reaction suppress the occurence of periodic activity in tubular reactors. 

INSTABILITIES OF FLOWS WITH AND WITHOUT HEAT TRANSFER AND CHEMICAL REACTION... 

This monograph is an outcome of the summer school organized on behalf of CISM in June 2008, for the advanced course titled Instabilities of Flows with and without Heat Transfer and Chemical Reactions . The course was conducted over five days of a working week in the beautiful and peaceful surrounding of Udine with an ashram- hs atmosphere and the course was held quite intensively, with active participation of the lecturers and all the participants, including one of the rectors of the institute. 

Those, among others, were the reasons why the Scientific Council of CISM unanimously accepted Professor Sengupta s proposal for an Advanced Course entitled Instabilities of Flows with and without Heat Transfer and Chemical Reactions . For the favourable decision of the Scientific Council it was also essential that Professor Sengupta himself, an authority in the field, was available for organizing the course, which included the important task of proposing eminent, internationally recognized scientist as lecturers. 

ABSTRACT A novel reactor configuration has been developed in our laboratory which addresses the heat transfer limitations usually encountered in vacuum pyrolysis technology. In order to scale-up this reactor to an industrial scale, a systematic study on the heat transfer, the chemical reactions and the movement of the bed of particles inside the reactor has been carried out over the last ten years. Two different configurations of moving and stirred bed pilot units have been used to scale-up a continuous feed vacuum pyrolysis reactor, in accordance with the principle of similarity. A dynamic model for the reactor scale-up was developed, which includes heat transfer, chemical kinetics and particle flow mechanisms. Based on the results of the experimental and theoretical studies, an industrial vacuum pyrolysis reactor, 14.6 m long and 2.2 m in diameter, has been constructed and operated. The operation of the pyrolysis reactor has been successful, with the reactor capacity reaching the predicted feed rate of 3000 kg/h on a biomass feedstock anhydrous basis. 

COUPLED HEAT AND MASS TRANSFER WITH CHEMICAL REACTION IN BATCH REACTORS... 

Stangle, G.C. and Aksay, LA. (1990) Simultaneous momentum, heat and mass transfer with chemical reaction in a disordered porous medium Application to binder removal from a ceramic green body, Chem. Eng. Sci. 45, 1719. 

Mann.R. "Heat and mass transfer in exothermic gas absorption". (Proceedings of NATO AS on "Mass transfer with chemical reaction in multiphase systems", Turkey, 1981). 

Throughout this process, there will be tradeoffs between the levels of detail included in the different aspects of the model. For example, in a simple batch reactor model, one can include thousands of chemical species and reactions, whereas in a detailed three-dimensional fully coupled model of fluid flow, heat transfer, and chemical reactions, one might be limited to less than 20 chemical species and a similar number of reactions. With continuous advances in both computational hardware and... 

Heat and mass transfer with chemical reaction... 

An industrial chemical reacdor is a complex device in which heat transfer, mass transfer, diffusion, and friction may occur along with chemical reaction, and it must be safe and controllable. In large vessels, questions of mixing of reactants, flow distribution, residence time distribution, and efficient utilization of the surface of porous catalysts also arise. A particular process can be dominated by one of these factors or by several of them for example, a reactor may on occasion be predominantly a heat exchanger or a mass-transfer device. A successful commercial unit is an economic balance of all these factors. 

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