Premix process flux

A novel application of a symmetric porous membrane as a catalyst carrier but not as a permselective barrier is to use the membrane itself as the reaction zone for precise control of the stoichiometric ratio [Sloot et al., 1990]. In this case, the reactants are fed to the different sides of the membrane which is impregnated with a catalyst for a heterogeneous reaction. The products diffuse out of the membrane to its both sides. If the reaction rate is faster than the diffusion rate of the reactant in the membrane, a small reaction zone or theoretically a reaction plane will exist in the membrane. An interesting and important consequence of this type of membrane reactor is that within the reaction zone the molar fluxes of the reactants arc always in stoichiometric ratio and the presence of one reactant in the opposing side of the membrane is avoided. The reaction zone can be maintained inside the membrane as long as the membrane is symmeuic and not ultrathin. Therefore, membrane reactors of this fashion are particularly suited for those processes which require strict stoichiometric feed rates of premixed reactants. A symmetric porous a-alumina membrane of 4.5 mm thick was successfully tested to demonstrate the concept [Sloot et al., 1990]. 

Premix radiant wall burners are mounted horizontally through the wall of a furnace. The burner tip, which penetrates only a few inches inside the hot face of the furnace wall, fires radially along the wall. These burners are almost exclusively used in ethylene cracking furnaces, either alone or in conjunction with floor-mounted, wall-fired burners to provide a uniform heat distribution to the process tubes. In some cases several hundred radiant wall burners are installed in a furnace to fine-tune the radiant heat flux to the process tubes. Figure 18.11 is a rendering of a radiant wall burner. 

Figure 13.14 shows the premix membrane emulsification flux for different process and product parameters. The product flux (Ap = 12bar, dp = 0.8 pm, one pass) decreases from 28m m h to 5m m h with increasing dispersed phase concentration from 30% to 80%. 

Figure 13.14 Flux in premix membrane emulsification for different process and product parameters (Ap=12bar, dp = 0.8pm, one pass).

G.G. Badolato, G. Krug, H.P. Schuch-matm, H. Schubert, Premix Membrane Emulsification Hi ier Flux and Fligher Dispersed Phase Concentration in Membrane Process, Congres Mondial de I Emulsion, Lyon, 2006. 

An extended ILDM method was also developed by Bongers et al. (2002) for specific application in diffusion flames. In their work, the manifold is constructed in composition phase space (PS) instead of composition space, and hence, the chemical ILDM method is extended to the PS-ILDM method. The composition phase space includes not only the species mass fractions and enthalpy but also the diffusive fluxes of species and the diffusive enthalpy flux. The extended equation system therefore is of dimension 2(Ns +1) where Ns is the number of species and hence is twice the dimension of the original system of equations. However, the extension allows the resulting ILDM to take account of diffusion processes that would not be represented by the purely chemical ILDM. Therefore, a low-dimensional slow manifold may be found, even in regions of the flame where there are strong interactions between chemistry and flow. The method is demonstrated for a premixed CO/H2 flame with preferential diffusion. 

Clough et al. [33] compared the effects of three processing methods (referred as processes A, B, and C) on the microstructure of composite solders. In process A, the Cu Sns particles with a size of 50 pm or less were added to a melt of eutectic Sn-Pb solder covered with flux and stirred for about 10 sec. Process B is the same as process A, with the exception that eutectic Sn-Pb solder paste was reflowed first, and the excess flux was removed. The same CugSns particles were then added and stirred in. In process C, composite solder pastes were made by adding flux to premixed powders of eutectic Sn-Pb and about 2-pm Cu particles. This paste was then reflowed and cast. 

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