Wall-less reactor

This reaction has been studied using batch reactors, perfectly stirred continuous reactors, tubular continuous reactors, BENSON type reactors, wall-less reactors and shock tubes. The reaction has been carried out at temperatures between 700 and 1300 K, at pressures of 0.1 Pa to 10 Pa and at reaction times of 10 s to 10 s. The effects of the nature and of the area of the reactor walls as well as those of various additives have also been studied. The diversity of the studies carried out by a dozen teams throughout the world, the particularly widespread range of operating conditions (600 K for the temperature, which represents 11 orders of magnitude for the rate of initiation, 8 orders of magnitude for the pressure and reaction duration) make the pyrolysis of neopentane into a model radical reaction. 

Since this initial work, analysis of these batch systems has been further expanded to include reactant consumption, beginning with the work of Rice, Allen, and Campbell. Furthermore, an excellent study of stability with a generalized nth order reaction rate and the effect of the heat capacity of the reactor walls (when Le 1) was presented by Balakotaiah, Kodra, and Nguyen. They verified previous work which showed the boundary to runaway behavior occurs when two inflection points appear in the reaction trajectory between the initial and final states. In the limit of 7 oo and 6c = 0, the safe criteria under adiabatic conditions (a = 0) is given as B < Le + /n) and for highly exothermic reactions (B 1) with large cooling (a > 1) the safe criteria approaches Semenov s classical result x/B > e. 

Here x is the extent of the reaction (or scaled concentration of the reagent B), X2 is the normalized temperature of the complex liquid-solid medium, Pei and Pc2 are the Peclet numbers for mass and heat transport, Le is the Lewis number, is the longitudinal spatial coordinate. Da is the Damkohler number, 7 is the normalized activation energy of the reaction, /) is the transverse residence time of fluid in the reactor determined by the rate of cross-flow, b is the adiabatic temperature rise for the empty reactor (without packing), / iv is the surface heat transfer coefficient, and X2w the temperature of the reactor walls [22],... 

Figures le and If illustrate two typical LPCVD reactor configurations. These reactors operate at —50 Pa, and wall temperatures are approximately...

The model is based on the schematic representation of the commercial reactor shown in Figure le. The wafers are supported concentrically and perpendicular to the flow direction within the tube. The heats of reaction associated with the deposition reactions are small because of the low growth rates obtained with LPCVD ( 2 A/s). Furthermore, at high temperatures (1000 K) and low pressures (100 Pa), radiation is the dominant heat-transfer mechanism. Therefore, temperature differences between wafers and the furnace wall will be small. This small temperature difference eliminates the need for an energy balance. Moreover, buoyancy-driven secondary flows are unlikely. In fact, because of the rapid diffusion, the details of the flow field... 

T. Giornelli, A. Lofberg, L. Guillou, S. Paul, V. Le Courtois, E. Bordes-Richard, Catalytic wall reactor. Catalytic coatings of stainless steel by VOx/TiCL and Co/Si02 catalysts, Catal. Today 128 (2007) 201. 

Likewise, SiC has been considered a suitable material for the coolant channels of the blankets of fusion reactors created from a SiC composite (Ward and Dudaev, 2008), and also as a low-activation structural material to protect against the excessive heat loads of the metal first wall of a potential fusion reactor (Hopkins, 1974). The key figure of merit for the latter application is a high thermal shock resistance, R", which is necessary to withstand the stresses introduced by startups and plasma disruptions, together with the thermal cycling associated with normal pulsed mode operation. In this case, Rf = Ob k (l - t lE-a, where CTj, is the flexural strength, k the thermal conductivity, v the Poisson ratio, E the modulus of elasticity, and a the coefficient of thermal expansion. 

GiomeUi, T., Lofberg, A., GuUlou, L, Paul, S., Le Courtois, V., and Bordes-Ridiard, E. (2007) Catalytic wall reactor catalytic coatings of stainless steel by VO,/Tr02 and Co/Si02 catalysts. Catal. Today, 128 (3-4), 201-207. 

Here the solids flow can be expected to be more close to plugflow (no downflow along the walls). Much information on this type of reactors is availed>le within oil and chemical companies. Little data appeared in the open literature on mass transfer, conversion and mixing. 

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