Date of Award

2016

Document Type

Open Access Master's Report

Degree Name

Master of Science in Mechanical Engineering (MS)

Administrative Home Department

Department of Mechanical Engineering-Engineering Mechanics

Advisor 1

Jeffrey Allen

Advisor 2

Chang Kyoung Choi

Committee Member 1

Gregory Odegard

Committee Member 2

Gowtham

Abstract

Evaporation is ubiquitous in nature and occurs even in a microgravity space envi- ronment. Long term space missions require storage of cryogenic propellents and an accurate prediction of phase change rates. Kinetic theory has been used to model and predict evaporation rates for over a century but the reported values of accommodation coefficients are highly inconsistent and no accurate data is available for cryogens. The proposed study involves a combined experimental and computational approach to ex- tract the accommodation coefficients. Neutron imaging is used as the visualization technique due to the difference in attenuation between the cryogen and the metallic container. Phase change tests are conducted using liquid hydrogen and methane at a range of saturation points between 15 psia and 30 psia. In order to account for the thermal gradient in the wall at the interface, a CFD thermal model is employed. Results from neutron imaging and the thermal model serve as boundary conditions to a transition film kinetic model. Using a combination of neutron imaging, CFD thermal model and kinetic model, there is a possibility to extract the accommodation coefficient while accounting for the curvature, disjoining pressure, nanoscale interac- tions and a variable wall temperature at the interface. An accommodation coefficient of 0.5705 ± 0.0001 is obtained for liquid hydrogen evaporating from a 10mm Al6061 cylinder at 21K using a constant wall temperature of 21.00005.

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