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Investigation of Transient Gas Phase Column Density Due to Droplet EvaporationA NASA robotic refueling mission experiment on board the International Space Station (ISS) was designed to repeatedly transfer simulated cryogenic propellant between two dewars. After each metered transfer, the cryogen was to be vented overboard via sublimation or evaporation. ISS payload providers must conduct analyses to demonstrate that any planned gaseous venting generate no more than a certain level of material that may interfere with optical measurements from other payloads that may be located nearby. This requirement is expressed in terms of a maximum column number density (CND). For the experiment under consideration, fluid droplets likely would accompany any such vapor. Earlier related studies led to development of analytical expressions for column density along general paths for a number of practical cases under steady conditions, including droplet evaporation. These expressions are not appropriate for rapid evaporation of small droplets however, since the droplets cannot sustain mass flow rates consistent with steady conditions. In this work, analytical expressions are developed for estimating column density near a rapidly evaporating droplet along general paths. The influence for instantaneous evaporation is created first as a limiting case, where it is found the peak value occurs at the time it takes a wave of vapor to reach the closest point along the optical path traveling at its most probable thermal speed. Next, the case for finite-period evaporation is evaluated for constant conditions. Compared to the instantaneous case, peak column density occurs shortly after droplet extinction, but at a lower intensity. A new mathematical function is discovered that solves the integrals associated with this case. Finally, ways to account for droplet motion and changes in evaporation rate with size and temperature are discussed in this framework.
Document ID
20190032650
Acquisition Source
Goddard Space Flight Center
Document Type
Abstract
Authors
Woronowicz, M. S.
(KBRwyle Greenbelt, MD, United States)
Date Acquired
November 12, 2019
Publication Date
November 6, 2019
Subject Category
Propellants And Fuels
Report/Patent Number
GSFC-E-DAA-TN74272-1
Meeting Information
Meeting: Contamination, Coatings, Materials, and Planetary (CCMPP) Workshop
Location: Greenbelt, MD
Country: United States
Start Date: November 6, 2019
End Date: November 7, 2019
Sponsors: NASA Goddard Space Flight Center
Distribution Limits
Public
Copyright
Public Use Permitted.
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