Thermocapillary Flow with Evaporation and Condensation and Its Effect on Liquid Retention in Low-G Fluid Acquisition Devices


Book Description

The steady motion, thermal and free surface behavior of a volatile, wetting liquid in microgravity are studied using scaling and numerical techniques. The objective is to determine whether the thermocapillary and two-phase convection arising from thermodynamic nonequilibrium along the porous surfaces of spacecraft liquid acquisition devices could cause the retention failures observed with liquid hydrogen and heated vapor pressurant. Why these devices seem immune to retention loss when pressurized with heated helium or heated directly through the porous structure was also examined. Results show that highly wetting fluids exhibit large negative and positive dynamic pressure gradients towards the meniscus interline when superheated and subcooled, respectively. With superheating, the pressure variation and recoil force arising from liquid/vapor phase change exert the same influence on surface morphology and promote retention. With subcooling, however, the pressure distribution produces a suction that degrades mechanical equilibrium of the surface. This result indicates that thermocapillary-induced deformation arising from subcooling and condensation is the likely cause for retention loss. In addition, increasing the level of nonequilibrium by reducing accommodation coefficient suppresses deformation and explains why this failure mode does not occur in instances of direct screen heating or pressurization with a heated inert gas. Schmidt, George R. Marshall Space Flight Center NASA-TP-3463, M-743, NAS 1.60:3463 PROJ. 91-15...




Liquid Acquisition Devices for Advanced In-Space Cryogenic Propulsion Systems


Book Description

Liquid Acquisition Devices for Advanced In-Space Cryogenic Propulsion Systems discusses the importance of reliable cryogenic systems, a pivotal part of everything from engine propulsion to fuel deposits. As some of the most efficient systems involve advanced cryogenic fluid management systems that present challenging issues, the book tackles issues such as the difficulty in obtaining data, the lack of quality data and models, and the complexity in trying to model these systems. The book presents models and experimental data based on rare and hard-to-obtain cryogenic data. Through clear descriptions of practical data and models, readers will explore the development of robust and flexible liquid acquisition devices (LAD) through component-level and full-scale ground experiments, as well as analytical tools. This book presents new and rare experimental data, as well as analytical models, in a fundamental area to the aerospace and space-flight communities. With this data, the reader can consider new and improved ways to design, analyze, and build expensive flight systems. - Presents a definitive reference for design ideas, analysis tools, and performance data on cryogenic liquid acquisition devices - Provides historical perspectives to present fundamental design models and performance data, which are applied to two practical examples throughout the book - Describes a series of models to optimize liquid acquisition device performance, which are confirmed through a variety of parametric component level tests - Includes video clips of experiments on a companion website