Passive and active technologies have been used to control propellant boil-off, but the current state of understanding of cryogenic evaporation and condensation in microgravity is insufficient for designing large cryogenic depots critical to the long-term space exploration missions. One of the key factors limiting the ability to design such systems is the uncertainty in the accommodation coefficients (evaporation and condensation), which are inputs for kinetic modeling of phase change. A novel, combined experimental and computational approach is being used to determine the accommodation coefficients for liquid hydrogen and liquid methane. The experimental effort utilizes the Neutron Imaging Facility located at the National Institute of Standards and Technology (NIST) in Gaithersburg, Maryland to image evaporation and condensation of hydrogenated propellants inside of metallic containers. The computational effort includes numerical solution of a model for phase change in the contact line and thin film regions as well as an CFD effort for determining the appropriate thermal boundary conditions for the numerical solution of the evaporating and condensing liquid. Using all three methods, there is the possibility of extracting the accommodation coefficients from the experimental observations. The experiments are the first known observation of a liquid hydrogen menisci condensing and evaporating inside aluminum and stainless steel cylinders. The experimental technique, complimentary computational thermal model and meniscus shape determination are reported. The computational thermal model has been shown to accurately track the transient thermal response of the test cells. The meniscus shape determination suggests the presence of a finite contact angle, albeit very small, between liquid hydrogen and aluminum oxide.

中文翻译：

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一种研究低温推进剂蒸发和冷凝的新实验

被动和主动技术已被用于控制推进剂蒸发，但目前对微重力中低温蒸发和冷凝的理解不足以设计对长期太空探索任务至关重要的大型低温库。限制此类系统设计能力的关键因素之一是调节系数（蒸发和冷凝）的不确定性，这些系数是相变动力学建模的输入。正在使用一种新颖的、结合实验和计算的方法来确定液态氢和液态甲烷的调节系数。实验工作利用位于盖瑟斯堡的国家标准与技术研究所 (NIST) 的中子成像设施，马里兰州对金属容器内氢化推进剂的蒸发和冷凝进行成像。计算工作包括接触线和薄膜区域相变模型的数值求解，以及用于确定蒸发和冷凝液体数值解的适当热边界条件的 CFD 工作。使用所有三种方法，有可能从实验观察中提取调节系数。这些实验是对液态氢弯月形液在铝制和不锈钢气瓶内冷凝和蒸发的首次已知观察。报告了实验技术、互补计算热模型和弯月面形状确定。计算热模型已被证明可以准确跟踪测试电池的瞬态热响应。弯月面形状测定表明液态氢和氧化铝之间存在有限的接触角，尽管非常小。