MEASUREMENTS OF CONDENSATION AND EVAPORATION OF CARBON DIOXIDE, NITROGEN, AND ARGON AT CRYOGENIC TEMPERATURES USING A MOLECULAR BEAM
Abstract
A high intensity, aerodynamic molecular beam generator combined with a sensitive modulated beam detector was used in the study of the condensation and evaporation processes of carbon dioxide, nitrogen, and argon (CO2, N2, and Ar) on cryogenically cooled surfaces. Molecular beams were impinged on a polished copper target at surface temperatures between 20 and 300K. The results of these experiments have shown that: (1) Room temperature molecular beams of CO2, N2, and Ar scattered from a copper surface at temperatures below 300K follow a cosine law scattering pattern. The scattering pattern remains unchanged after the initiation of condensation and also during the evaporation process. The scattering pattern was insensitive to angle of incidence for angles between 0 and 80 deg relative to the surface normal. (2) The initiation of condensation of CO2, N2, and Ar gases on cryogenically cooled surfaces follows a definite gas pressure and surface temperature relation which is predicted by the theoretical relations derived by Frenkel. (3) The measured CO2 evaporation rate between 75 and 95K is in agreement with the extrapolation from published values at higher temperatures. (4) After initiation of condensation, the value of the capture coefficient is observed to approach a unity value. The high detector sensitivity allows measurements of capture coefficient up to 0. 995.
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 01, 1968
- Accession Number
- AD0674596
Entities
People
- J. H. Heald Jr.
- R. F. Brown
Organizations
- Arnold Engineering Development Complex