Portland State University. Department of Mechanical and Materials Engineering
Date of Publication
Master of Science (M.S.) in Mechanical Engineering
1 online resource (vi, 66 pages)
Evaporation is important to myriad engineering processes such as cooling, distillation, thin film deposition, and others. In fact, NASA has renewed interest in using cabin air pressure evaporation as a means to recycle waste water in space. As one example, NASA recently conducted experiments aboard the International Space Station (ISS) to measure evaporation rates in microgravity and to determine the impacts of porous structure on the process. It has long been assumed that differences in evaporation rates between 1-g0 and microgravity are small. However, discrepancies by as much as 40% have been observed in practice. The assumption now is that such differences are not only due to a lack of buoyancy in the vapor phase in microgravity (10-6 g0), but also to pore geometries, wetting conditions, and airflow. Numerical models are developed herein to assess the viability of Star CCM+ as a CFD tool to accurately model such phenomena, as well as to identify what mechanisms are responsible for the difference observed in practice between 1-g0 and microgravity. The code is benchmarked via comparisons to Stefan Tube analytical solutions with agreement to within approximately ±1%. Accounting for pore geometry, comparisons to NASA ISS flight data yields results accurate to ±14%. Additionally, the analytical solution to the Stefan Tube is weighted for both the actual free surface area and contact line length yielding results accurate to 4.4% and 6.1% depending on pore geometry.
The CFD models are able to identify the mechanisms responsible for the effects of microgravity on the rate of evaporation and it is shown that these effects can be minimized and even wholly negated by sufficiently high airflow velocity.
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Ringle, Daniel Peter, "A Numerical Investigation of Microgravity Evaporation" (2020). Dissertations and Theses. Paper 5439.