The causes for temperature fluctuations on catalytic wires



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Random temperature fluctuations can be observed on the surface of catalytic wires when an exothermic mass transfer limited chemical reaction takes place on them. In industrial reactors, these large magnitude temperature fluctuations (flickering) have a deleterious influence on the rate of metal loss from the gauzes. An experimental investigation was undertaken to determine the main causes of flickering. The surface temperature fluctuations on single platinum wires were measured with an infrared detector during the oxidation of hydrogen or ammonia in excess air. Independent measurements of turbulence intensity and concentration fluctuations in the gaseous mixture were made. The rms amplitude of the latter was measured by means of an aspirating probe. The characteristic time for wire temperature changes was much greater than the characteristic time for changes in surface concentration for these reaction experiments. The results indicate that concentration fluctuations due to incomplete mixing of the reactants are the main cause of the temperature fluctuations.