Total pressure

About: Total pressure is a research topic. Over the lifetime, 5199 publications have been published within this topic receiving 66658 citations.

Surface retexturing of Pt wires during the catalytic oxidation of CO

Abstract: The catalytic properties of Pt, which have been studied in a variety of forms of the metal (single crystals, wires or dispersed on a support), may be influenced by the method of preparing the metal surface. Pt surfaces undergo retexturing1 during catalytic reactions at high temperatures (>1,000 K) and a relatively facile sintering process has also been described2. Engel and Ertl3 have reviewed the heterogeneous oxidation of carbon monoxide on Pt (CO + 1/2 O2 → CO2), emphasizing studies concerned with the behaviour of the reaction at very low pressures and on clean surfaces (for example, on single crystal faces). Under these conditions the kinetic behaviour is determined by the ratio of the partial pressures of the reactants and is relatively insensitive to the total pressure. Here, we describe microscopic and kinetic observations of the oxidation on Pt wire surfaces below 600 K and at atmospheric pressure. The surface reactions are apparently more complicated here than at low pressure; extrapolations from the low to the high pressure regimes may not be applicable because of changes in the rate-controlling parameters. We present evidence of the mobility of Pt atoms (often considered immobile) on the surface and suggest that the catalyst functions through formation of oxy- and/or carboxyl-Pt complexes in a two-dimensional chemisorbed layer, envisaged as a monolayer possessing fluid properties and enhanced reactivity, containing both adsorbed reactant gases and mobile catalyst atoms.

A comparison of disturbance levels measured in hypersonic tunnels using a hot-wire anemometer and a pitot pressure probe.

Abstract: Disturbance levels were measured in the test section of a Mach 5 blowdown jet using a constant-current, hot-wire anemometer and a pressure transducer. The disturbance levels, measured by the two instruments and normalized by local mean values, agreed within about 30%, with the pitot data higher than the hot-wire data. The rms disturbance levels measured with the hot-wire anemometer and converted to pitot pressures using a quasi-steady flow analysis, were about two-thirds the levels measured with the pitot probe. The variation of the normalized rms disturbance levels with stagnation pressure indicated that transition occurred in the boundary layer on the nozzle wall and influenced the outputs of the instruments located at the exit of the nozzle when the total pressure was about 35 N/sq cm. Below this pressure the disturbance levels decreased markedly. At higher pressures the disturbances were predominantly aerodynamic noise generated by the turbulent boundary layer on the nozzle wall.