Gas Evaporation in Space

Abstract

Silver (Ag) was evaporated in argon (Ar) and xenon (Xe) gases at various pressures in the low-gravity environment aboard the space shuttle. Four glass bulbs with filament tips coated with 50 mg of silver were filled with Ar gas of 6.7 Pa (A) or 40 Pa (B) or Xe gas of 0.67 Pa (C) or 1.33 Pa (D) and ignited one by one in the low gravitational field of space. The evaporation temperatures were maintained at 1150°C at which smoke plumes were barely detectable in all cases in the ground experiment. A ball of smoke particles appeared to grow around the evaporation source instead of rising as it would under earth gravity conditions. No smoke was observed in (A), but it was observed in (B) and (C) and bursts of smoke extended in various directions from the smoke ball in the case of (D). The experiment suggested that vapor could be confined locally around the source with high pressure and temperature by the surrounding gas in the low gravity. This suggestion cannot be derived from any conventional model of evaporation in the gas.

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“…13) Since zinc metal has quite a high vapor pressure even at low temperatures, the evaporation rate is expected to be sufficiently high given a short experimental time. In the previous experiments of gas evaporation in an airplane and the Space Shuttle, only particles deposited on the wall of a glass bulb were observed, [10][11][12] but in the present experiment, particles that condensed at various points in the bulb were observed. The shape and size of the deposited particles were observed using a scanning elec-where dT /dh, C p and g are the temperature gradient along the direction of gravity (h is height), the gram specific heat at constant pressure and the acceleration of gravity, respectively.…”

“…Fine silver particles have been produced in a drop capsule, 8,9) an airplane 10,11) and the Space Shuttle. 12) An ideal condition for gas evaporation with no thermal convection was real-…”