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NUMERICAL SIMULATION OF HYDROGEN-AIR BOUNDARY LAYER FLOWS AUGMENTED BY CATALYTIC SURFACE REACTIONS

机译:催化表面反应增强氢-空气边界层流动的数值模拟

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Catalytic combustion of hydrogen-air boundary layers involves the adsorption of hydrogen and oxygen into a platinum coated surface, chemical reactions of the adsorbed species and the desorption of the resulting products. Re-adsorption of some produced gases is also possible. The catalytic reactions can be beneficial in porous burners and catalytic reactors that use low equivalence ratios. In this case the porous burner flame can be stabilized at low temperatures to prevent any substantial gas emissions, such as nitrogen oxides. The present paper is concerned with the numerical computation of heat transfer and chemical reactions in hydrogen-air mixture boundary layers that flow over platinum coated hot plates. Chemical reactions are included in the gas phase as well as on the solid platinum surface. In the gas phase, eight species are involved in 26 elementary reactions. On the platinum hot surface, additional surface species are included that are involved in 14 additional surface chemical reactions. The platinum surface temperature is fixed, while the properties of the reacting flow are computed. The flow configuration investigated in the present paper is that of a parallel boundary layer. Finite-volume equations are obtained by formal integration over control volumes surrounding each grid node. Hybrid differencing is used to ensure that the finite-difference coefficients are always positive or equal to zero to reflect the real effect of neighboring nodes on a typical central node. The finite-volume equations are solved, iteratively, for the reacting gas flow properties. On the platinum surface, surface species balance equations, under steady-state conditions, are solved numerically. A non-uniform computational grid is used, concentrating most of the nodes in the boundary sub-layer adjoining the catalytic surface. The computed OH concentration is compared with experimental and numerical data of similar geometry. The obtained agreement is fairly good, with differences observed for the location of the peak value of OH. Surface temperature of 1170 K caused fast reactions on the catalytic surface in a very small part at the leading edge of the catalytic flat plate. The computational results for heat and mass transfer and chemical surface reactions at the gas-surface interface are correlated by non-dimensional relations.
机译:氢-空气边界层的催化燃烧涉及氢和氧在铂涂层表面的吸附,被吸附物质的化学反应以及所得产物的解吸。也可以重新吸附一些产生的气体。催化反应在使用低当量比的多孔燃烧器和催化反应器中可能是有益的。在这种情况下,多孔燃烧器的火焰可以在低温下稳定,以防止任何实质性的气体排放,例如氮氧化物。本文涉及流过镀铂热板的氢-空气混合物边界层中的传热和化学反应的数值计算。气相以及固体铂表面都包含化学反应。在气相中,八种物质参与了26个基本反应。在铂热表面上,还包括与14种其他表面化学反应有关的其他表面物质。铂的表面温度是固定的,同时计算反应流的性质。本文研究的流动配置是平行边界层的流动配置。有限体积方程是通过对每个网格节点周围的控制体积进行形式积分获得的。混合差分用于确保有限差分系数始终为正或等于零,以反映典型中心节点上相邻节点的实际效果。迭代求解反应气体流动特性的有限体积方程。在铂表面上,稳态条件下的表面物种平衡方程可以通过数值求解。使用非均匀的计算网格,将邻接催化表面的边界子层中的大多数节点集中。将计算出的OH浓度与类似几何形状的实验和数值数据进行比较。所获得的一致性相当好,在OH峰值的位置上观察到差异。 1170 K的表面温度在催化平板前缘的很小一部分上引起了催化表面上的快速反应。气体-表面界面处的传热和传质以及化学表面反应的计算结果与无量纲关系相关。

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