Burner heterogeneous

A further consequence of the upstream diffusion to the burner face could be heterogeneous reaction at the burner. Such reaction is likely on metal faces that may have catalytic activity. In this case the mass balance as stated in Eq. 16.99 must be altered by the incorporation of the surface reaction rate. In addition to the burner face in a flame configuration, an analogous situation is encountered in a stagnation-flow chemical-vapor-deposition reactor (as illustrated in Fig. 17.1). Here again, as flow rates are decreased or pressure is lowered, the enhanced diffusion tends to promote species to diffuse upstream toward the inlet manifold. 

Section 16.6.1.1 discusses a mass-flux boundary condition for a burner stabilized flame. Based on a surface mass balance, reformulate this boundary condition, assuming that elementary heterogeneous chamistry may occur at the burner face. 

The surface tension and, to a lesser extent, the viscosity of the sample solution are important factors in nebulization efficiency, since work must be performed in the nebulization step to overcome these properties of the liquid. For this reason, the surface tension and viscosity should be maintained as nearly identical as possible in samples and standards. With reasonably concentrated solutions, this can be done quite simply by diluting the test solution. With less concentrated solutions, it may be necessary to match the matrix composition of samples and standards. Concentrated solutions should also be diluted to avoid encrustation of salts on the nebulizer and burner. The same is true when handling heterogeneous systems such as colloids or solutions high in protein content. 

The management of the marked reactivity loss and the optimization of the relative values of the Doppler and sodium void effects appear to be the two major issues to be dealt with so as to ensure the feasibility of Pu burner cores. In this respect, heterogeneous core designs, in which a part of the inert material replacing the fuel in the dilution process is gathered in specific subassemblies, are of particular interest. 

Homogeneous and heterogeneous burners are usually operated with an excess of air to ensure complete combustion of the fuel. 

In addition to these theoretical questions experimental investigations will be needed. The performance of mixed-oxide fuel with plutonium contents up to 45% under irradiation to high bumup will have to be determined. Reactor physics calculation methods suitable for burner cores will have to be validated by comparison with data from critical assemblies. There may also be a need for experimental work on the thermal hydraulic performance of heterogeneous cores containing both fuel and diluent material. 

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