Generation, transport, and deposition of tungsten-oxide aerosols at 1000 °C in flowing air/steam mixtures

Abstract Experiments were conducted to measure the rates of oxidation and vaporization of tungsten in flowing air, steam, and air/steam mixtures in laminar flow. Also measured were the downstream transport of tungsten-oxide condensation aerosols and their region of deposition, including plateout in the superheated flow tube, rainout in the condenser, and ambient discharge that was collected on an array of sub-micron aerosol filters. The nominal conditions of the tests, with the exception of the first two tests, were tungsten temperatures of 1000 °C, gas mixture temperatures of 200 °C, and boundary temperatures of 150–200 °C. It was observed that the tungsten oxidation rates were greatest in all air and least in all steam, and generally decreased non-linearly as the steam mole fraction increased. The tungsten oxidation rates in all air were more than five times greater than the tungsten oxidation rates in all steam. The tungsten vaporization rate was zero in all air, and increased with increasing steam mole fraction. The vaporization rate became maximum at a steam mole fraction of 0.85 and decreased thereafter as the steam mole fraction was increased to unity. The tungsten-oxide was transported downstream as condensation aerosols, initially flowing upwards from the tungsten rod through an 18-in. long, 1-in. OD quartz tube, around a 90° bend with a 3.5-in. radius, and laterally through a 24-in. horizontal run. The entire length of the quartz glass flow path was heated by electrical resistance clamshell heaters whose temperatures were individually controlled and monitored. The tungsten-oxide plateout in the quartz tube was collected, nearly all of which was deposited at the end of the heated zone near the entrance to the steam condenser that was cold. The tungsten-oxide that rained out in the condenser as the steam condensed was collected with the condensate and weighed after being dried. The aerosol smoke that escaped the condenser was collected on the sub-micron filter assemblies. There was no aerosol generation for the case of all air, so the plateout, condensate, and smoke were all zero. For the case of all steam, there was very little plateout in the superheated regions; almost all of the aerosol was collected in the condensate from the condenser and there was no smoke discharge into the filters. For the experiments with intermediate air/steam fractions, there was some aerosol plateout, considerable aerosol in the condensate, and aerosol smoke discharged from the condenser with the escaping air.