Experimental study of oxygen catalytic recombination in a shock tube

Abstract

The effect of oxygen catalytic recombination on metal-, metal-oxide-, silicon- carbide-, and carbon-coated surfaces has been experimentally investigated. The experiments were conducted in a shock tube located in the Hypersonic Laboratory at the Korea Advanced Institute of Science and Technology. The test gas considered was a mixture of 21% oxygen and 79% argon by volume. Surface heat-transfer rates at shock tube end-wall were measured using a thin-film gauge. During the testing, the surface of the gauges was polished to a high degree of smoothness and maintained at or near the room temperature. Eight different surfaces, coated with aluminum, iron, titanium, aluminum oxide, iron oxide, titanium dioxide, silicon carbide, and carbon were considered during experiments. Prior to testing, the surface quality was examined using tools for microscopic and macroscopic analyses, thereby characterizing the initial condition. Three different levels of surface roughness of the test samples were also considered to investigate the effect of surface roughness on catalytic phenomena. Efficiency of the oxygen catalytic recombination was determined by evaluating the measured heat-transfer rates whilst referring to existing theories based on binary and tertiary gas mixtures. As observed, catalytic efficiencies corresponding to the aluminium-, iron-, and titanium-coated smooth surfaces measured 0.0034, 0.0036, and 0.0039, respectively, whereas those corresponding to aluminum-oxide-, iron-oxide-, and titanium-oxide-coated surfaces measured 0.0015, 0.0011, and 0.0022, respectively. For the silicon-carbide- and carbon-coated wall, the efficiency were determined to be about 0.0031 and 0.0027, respectively. In the case of the roughened wall, it was found that with an increase in the level of surface roughness, the catalytic activity at the surface is increased. Additionally, an electrical preheating technique applied to a silicon-dioxide-, titanium-, silicon-carbide-, and carbon-coated test model in a shock tube has demonstrated surface temperature around 500 K. The measurement of surface heat-transfer rate at such elevated surface temperatures was also achieved. With the $SiO_2$ data at such preheated surface temperatures, it was found that the present efficiency is comparable to the existing data.