Assessments of the Hydrogen–Air Mixture Catalytic Combustion Domain in a Laminar Flow Regime

Abstract

Improving the environmental safety of power facilities is among the top priority problems of the modern science. Conventional energy generation methods on the basis of hydrocarbon fuel are accompanied by significant greenhouse gas emissions. One of promising approaches to reducing the emission is catalytic afterburning, which ensures more complete and controlled fuel oxidation. The article presents a study of heat and mass transfer processes that accompany the streamlining of a flat catalytically active surface by a laminar jet of hydrogen–air mixture directed normally to the surface. The impact jet interaction is studied for the conditions under which Hagen–Poiseuille flow has enough time to settle in the delivery tube at Reynolds numbers Re < 2000. Main attention is paid to evaluating the fuel combustion completeness and determining the chemical activity domain in a laminar regime. The catalyst was based on gamma-alumina (γ-Al₂O₃) that was modified with rare-earth metals and palladium (Pd). As is known, a Stefan flow directed normally to the surface emerges in the course of reactions accompanied by a change in the number of molecules. Comparison with the data reported in the literature shows that chemical reactions running on a palladium catalyst do not have a significant effect on the Sherwood number (Sh) and Nusselt number (Nu). A thermodynamic procedure for evaluating the catalytic reaction domain is proposed, which has been verified by comparison with the hydrogen concentration distribution. By using this procedure, it is possible to calculate the Damkohler number proceeding from the temperature profile on the surface, which can be used for determining the catalytic activity for a surface streamlined by a flow of reagents. The developed approach opens the possibility to estimate the minimal sizes of a heat and mass transfer device required for neutralizing harmful substances.