Pool Boiling with Non-condensable Gas in Microgravity: Results of a Sounding Rocket Experiment

Pool boiling experiments in microgravity have been performed in the Sounding Rocket Maser 11. A heated plate of 1cm ² was located at the bottom of a small cylindrical tank partly filled with a refrigerant Novec HFE7000 pressurized with Nitrogen. Experiments were performed at different reservoir pressures and wall heat fluxes. The wall heat flux and wall temperature were simultaneously measured during the experiment and the behavior of the bubbles on the heater was filmed with a video camera through the transparent wall of the reservoir. The presence of Nitrogen dissolved inside the liquid led to a strong Marangoni convection around the bubble. The effect of Marangoni convection and evaporation on the wall heat transfer is analyzed in function of the relative values of the wall temperature and saturation temperature.     

低温推进剂贮箱增压过程的传热传质数学模拟

针对火箭发动机地面试验中低温液氧贮箱的预增压和增压过程建立了气相空间的传热、传质数学模型.运用实际气体的状态方程、连续性方程、能量守恒方程以及推进剂与气相空间的传热、传质方程等组成了关于气相空间参数的微分方程组,并运用四阶Runge-Kutta算法对其进行求解.获得了气相空间的压力、温度、增压气体流量、液氧挥发速率以及贮箱壁温等参数的变化规律.结果表明,在发动机启动前的预增压过程中,气相空间的温度和压力急剧增加,液氧的挥发速率也增加很快;发动机启动后的保持增压阶段,由于气相空间的体积不断发生变化,气相空间参数的变化趋于平缓,液氧表面向气相空间的传质速率也趋于稳定.     

Heat Transfer by Thermo-Capillary Convection Sounding Rocket COMPERE Experiment SOURCE

This paper describes the results of a sounding rocket experiment which was partly dedicated to study the heat transfer from a hot wall to a cold liquid with a free surface. Natural or buoyancy-driven convection does not occur in the compensated gravity environment of a ballistic phase. Thermo-capillary convection driven by a temperature gradient along the free surface always occurs if a non-condensable gas is present. This convection increases the heat transfer compared to a pure conductive case. Heat transfer correlations are needed to predict temperature distributions in the tanks of cryogenic upper stages. Future upper stages of the European Ariane V rocket have mission scenarios with multiple ballistic phases. The aims of this paper and of the COMPERE group (French–German research group on propellant behavior in rocket tanks) in general are to provide basic knowledge, correlations and computer models to predict the thermo-fluid behavior of cryogenic propellants for future mission scenarios. Temperature and surface location data from the flight have been compared with numerical calculations to get the heat flux from the wall to the liquid. Since the heat flux measurements along the walls of the transparent test cell were not possible, the analysis of the heat transfer coefficient relies therefore on the numerical modeling which was validated with the flight data. The coincidence between experiment and simulation is fairly good and allows presenting the data in form of a Nusselt number which depends on a characteristic Reynolds number and the Prandtl number. The results are useful for further benchmarking of Computational Fluid Dynamics (CFD) codes such as FLOW-3D and FLUENT, and for the design of future upper stage propellant tanks.     

Numerical modeling of self-pressurization and pressure control by a thermodynamic vent system in a cryogenic tank

This paper presents a numerical model of a system-level test bed—the multipurpose hydrogen test bed (MHTB) using the Generalized Fluid System Simulation Program (GFSSP). MHTB is representative in size and shape of a space transportation vehicle liquid hydrogen propellant tank, and ground-based testing was performed at NASA Marshall Space Flight Center (MSFC) to generate data for cryogenic storage. GFSSP is a finite volume-based network flow analysis software developed at MSFC and used for thermofluid analysis of propulsion systems. GFSSP has been used to model the self-pressurization and ullage pressure control by the Thermodynamic Vent System (TVS). A TVS typically includes a Joule–Thompson (J–T) expansion device, a two-phase heat exchanger (HEX), and a mixing pump and liquid injector to extract thermal energy from the tank without significant loss of liquid propellant. For the MHTB tank, the HEX and liquid injector are combined into a vertical spray bar assembly. Two GFSSP models (Self-Pressurization and TVS) were separately developed and tested and then integrated to simulate the entire system. The Self-Pressurization model consists of multiple ullage nodes, a propellant node, and solid nodes; it computes the heat transfer through multilayer insulation blankets and calculates heat and mass transfer between the ullage and liquid propellant and the ullage and tank wall. A TVS model calculates the flow through a J–T valve, HEX, and spray and vent systems. Two models are integrated by exchanging data through User Subroutines of both models. Results of the integrated models have been compared with MHTB test data at a 50% fill level. Satisfactory comparison was observed between tests and numerical predictions.     

水滴在真空室内结晶过程的模拟

模拟真空室内水滴结晶过程是模拟真空雾化法制备冰浆系统的第一步。模拟了液滴在真空室内从较高的温度降温到零度,之后到一定的过冷度,然后发生相变为液-固两相,到最后为全部固相的整个过程。在该过程中热质传递迅速发生,模拟结果表明蒸发或者升华控制了整个过程。以扩散模型和以对流模型所得到的结果都与实验结果在一定程度上吻合,这是因为通过对流或者导热所传递的热量比相变潜热要小几个数量级。在整个结晶过程中液滴温度的变化表明:液固相变要占据较长的时间,是一个更为重要的过程。考虑重力、浮力和粘滞力的影响给出了液滴在结晶过程中的运动方程。从该模型计算出的液滴结晶过程中下降距离比仅考虑重力作用下给出的要准确。研究结果为更好的设计真空闪蒸室提供了理论依据和参考。     

Investigation of helium injection cooling to liquid oxygen under pressurized condition

Sub-cooling of cryogenic propellant by helium injection is one of the most effective methods for suppressing bulk boiling and keeping sub-cooled liquid oxygen before rocket launch. Compared with the helium injection cooling under atmospheric condition, helium injection cooling under pressurized condition has advantage that it can greatly reduce re-warming time of the sub-cooled liquid oxygen. Helium injection cooling under pressurized condition is characterized by cooling of initially sub-cooled cryogenic liquid, which is significantly different from that of the atmospheric condition where liquid oxygen usually exists at saturated condition. In this paper, we discuss the characteristics of helium injection cooling under pressurized condition, with the associated physical understanding of the process. Experimental results are presented along the simulations of variously combined system parameters based on the finite heat transfer and instantaneous diffusion mass transfer model. A non-dimensional parameter for identifying the cooling regime is conceived. The critical values of the non-dimensional parameters and injected helium temperatures are also estimated.     

制冷系统热回收装置相变材料的分析研究

分析了相变材料特性,并找出了适用子制冷系统热回收装置的相变材料,通过对热物性和工作性能的研究,选取Fecl3·6H2O为本装置的相交蓄能材料,同时建立蓄热体的物理模型及模拟简化模型,在自然对流的影响下,模拟相变材料的蓄、放热特性,找出固——液界面、温度场、速度场、液相比例、传热系数、热流密度、监测点的温度等随时间的变化规律,为制冷系统热回收装置的设计提供了理论依据。     

制冷系统热回收装置相变材料的分析研究

分析了相变材料特性,并找出了适用于制冷系统热回收装置的相变材料,通过对热物性和工作性能的研究,选取Fecl3·6H2O为本装置的相变蓄能材料,同时建立蓄热体的物理模型及模拟简化模型,在自然对流的影响下,模拟相变材料的蓄、放热特性,找出固——液界面、温度场、速度场、液相比例、传热系数、热流密度、监测点的温度等随时间的变化规律,为制冷系统热回收装置的设计提供了理论依据。     

Launch ascent testing of a representative Altair ascent stage methane tank

In order to support long duration cryogenic propellant storage, the NASA is investigating the long duration storage properties of liquid methane. The Methane Lunar Surface Thermal Control (MLSTC) testing is using a tank of the approximate dimensions of the Altair lunar ascent propellant tanks. The tank was insulated with multilayer insulation and placed inside of a vacuum chamber to simulate the various environments that would be encountered during launch and travel from the earth to the lunar surface, including long duration stays on the lunar surface. One of these environments to be studied is the launch and ascent environment; while all the effects of this mission phase cannot be simulated at the same time, an effort was made to simulate as many as possible. Boil-off testing included ambient pressure ground hold testing followed by a rapid depressurization of the vacuum chamber during which the liquid methane tank was allowed to come to steady state condition in the high vacuum environment. The data gathered from the series of tests fit with-in pre-test predictions and yielded much needed test data for rapid depressurization using liquid methane.     

微重力环境低温流体无排气加注过程数值研究

针对加注系统受注贮箱,采用CFD方法就液氮贮箱无排气加注过程开展数值仿真,对比了不同重力水平下的无排气加注性能,分析了加注口结构、壁面初始温度、加注流体温度和加注流量等因素对微重力无排气加注性能的影响规律。所构建的二维轴对称模型将流体区与固壁区一起作为求解区域并划分网格,并通过植入用户自定义程序(UDF)计算加注口液体闪蒸过程及气液之间的热质交换。经过实验数据验证,该模型能够合理展示箱内温度场分布和相分布情况,并获得贮箱压力等参数变化信息。数值计算结果表明:(1)加注条件相同时,微重力工况较常重力工况体现出更好的无排气加注性能。(2)微重力条件下,无排气加注性能几乎不受加注口结构的影响,壁面初始温度和加注流体温度越高,贮箱压力越高,加注流量仅对加注时间有显著影响。     

Experimental investigation on pressurization performance of cryogenic tank during high-temperature helium pressurization process

Sufficient knowledge of thermal performance and pressurization behaviors in cryogenic tanks during rocket launching period is of importance to the design and optimization of a pressurization system. In this paper, ground experiments with liquid oxygen (LO₂) as the cryogenic propellant, high-temperature helium exceeding 600 K as the pressurant gas, and radial diffuser and anti-cone diffuser respectively at the tank inlet were performed. The pressurant gas requirements, axial and radial temperature distributions, and energy distributions inside the propellant tank were obtained and analyzed to evaluate the comprehensive performance of the pressurization system. It was found that the pressurization system with high-temperature helium as the pressurant gas could work well that the tank pressure was controlled within a specified range and a stable discharging liquid rate was achieved. For the radial diffuser case, the injected gas had a direct impact on the tank inner wall. The severe gas-wall heat transfer resulted in about 59% of the total input energy absorbed by the tank wall. For the pressurization case with anti-cone diffuser, the direct impact of high-temperature gas flowing toward the liquid surface resulted in a greater deal of energy transferred to the liquid propellant, and the percentage even reached up to 38%. Moreover, both of the two cases showed that the proportion of energy left in ullage to the total input energy was quite small, and the percentage was only about 22–24%. This may indicate that a more efficient diffuser should be developed to improve the pressurization effect. Generally, the present experimental results are beneficial to the design and optimization of the pressurization system with high-temperature gas supplying the pressurization effect.     

Final test results for the ground operations demonstration unit for liquid hydrogen

Described herein is a comprehensive project—a large-scale test of an integrated refrigeration and storage system called the Ground Operations and Demonstration Unit for Liquid Hydrogen (GODU LH2), sponsored by the Advanced Exploration Systems Program and constructed at Kennedy Space Center. A commercial cryogenic refrigerator interfaced with a 125,000 l liquid hydrogen tank and auxiliary systems in a manner that enabled control of the propellant state by extracting heat via a closed loop Brayton cycle refrigerator coupled to a novel internal heat exchanger. Three primary objectives were demonstrating zero-loss storage and transfer, gaseous liquefaction, and propellant densification. Testing was performed at three different liquid hydrogen fill-levels. Data were collected on tank pressure, internal tank temperature profiles, mass flow in and out of the system, and refrigeration system performance. All test objectives were successfully achieved during approximately two years of testing. A summary of the final results is presented in this paper.     

Performance analysis of no-vent fill process for liquid hydrogen tank in terrestrial and on-orbit environments

Two finite difference computer models, aiming at the process predictions of no-vent fill in normal gravity and microgravity environments respectively, are developed to investigate the filling performance in a liquid hydrogen (LH₂) tank. In the normal gravity case model, the tank/fluid system is divided into five control volume including ullage, bulk liquid, gas–liquid interface, ullage-adjacent wall, and liquid-adjacent wall. In the microgravity case model, vapor–liquid thermal equilibrium state is maintained throughout the process, and only two nodes representing fluid and wall regions are applied. To capture the liquid–wall heat transfer accurately, a series of heat transfer mechanisms are considered and modeled successively, including film boiling, transition boiling, nucleate boiling and liquid natural convection. The two models are validated by comparing their prediction with experimental data, which shows good agreement. Then the two models are used to investigate the performance of no-vent fill in different conditions and several conclusions are obtained. It shows that in the normal gravity environment the no-vent fill experiences a continuous pressure rise during the whole process and the maximum pressure occurs at the end of the operation, while the maximum pressure of the microgravity case occurs at the beginning stage of the process. Moreover, it seems that increasing inlet mass flux has an apparent influence on the pressure evolution of no-vent fill process in normal gravity but a little influence in microgravity. The larger initial wall temperature brings about more significant liquid evaporation during the filling operation, and then causes higher pressure evolution, no matter the filling process occurs under normal gravity or microgravity conditions. Reducing inlet liquid temperature can improve the filling performance in normal gravity, but cannot significantly reduce the maximum pressure in microgravity. The presented work benefits the understanding of the no-vent fill performance and may guide the design of on-orbit no-vent fill system.     

Experimental investigation on no-vent fill process using tetrafluoromethane (CF4)

This paper investigates the transfer of liquid cryogens using a no-vent fill (NVF) process experimentally to identify the dominant NVF parameters. The experimental apparatus has been fabricated with extensive instrumentations to precisely study the effects of each NVF parameter. Liquid tetrafluoromethane (CF₄) is selected as the working fluid due to its similar molecular structures and similar normal boiling point and triple point with liquid methane which has been considered as an attractive future cryogenic propellant. The experimental results show that the initial receiver tank wall temperature and the incoming liquid temperature are the primary factors that characterize the (non-equilibrium) thermodynamic state at the start of a NVF transfer. The supply pressure is also critical as it indicates the ability to condense vapor in the receiver tank. A non-dimensional map based on energy balance is proposed to find acceptable initial conditions of the filling volume at the desired final tank pressure. The non-dimensional map shows good agreement with the NVF data not only in this paper but also in the previous research.     

LNG储罐主容器泄漏时外罐壁的传热特性

以一种LNG储罐为研究对象,利用有限单元法(FEM)分析了在主容器泄漏时的混凝土外罐壁的传热特性,研究了泄漏发生时外罐壁温度随着时间的变化过程,泄漏发展后的外罐壁的温度分布和热流密度,以及热保护边角(TCP)对于外罐壁传热的影响,指出了外罐壁热传导达到稳定后的传热特性.     

Numerical Investigation of Bubble Induced Marangoni Convection: Some Aspects of Bubble Geometry

Thermocapillary or Marangoni convection is a surface tension driven flow that occurs when a gas–liquid or vapor–liquid interface is subjected to a temperature gradient. In the past, the contribution to local heat transfer arising from Marangoni convection has been overlooked as insignificant since under earth gravity it is overshadowed by buoyant convection. This study numerically investigates some aspects of bubble size and shape on local wall heat transfer resulting from Marangoni convection about individual bubbles on a heated wall immersed in a liquid silicone oil layer (Pr = 110) of depth 5 mm. It was found that increasing bubble volume causes an increase in the area over which Marangoni convection has affect. Heat transfer therefore increases with bubble size. Over the effective area, the surface averaged hot wall heat transfer is not affected greatly by bubble shape. The surface averaged heat transfer over the effective area on both the hot and cold walls is affected dramatically by bubble size, but the increase is more profound on the cold wall.     

泄放阀着火时LNG储罐外容器热-结构耦合分析

针对LNG储罐在泄放阀着火的工况,对受到外界高温火焰辐射的LNG外容器的传热和结构进行了耦合分析研究.建立了16万方LNG大型储罐的实体有限元模型,根据规范和相关文献中的推荐方法,获得了泄放阀火焰高温辐射时罐顶外表面的等效辐射温度,根据正常工作时的稳态传热工况进行储罐外容器内表面等效对流传热系数的计算,得到了正常工作时...     

Liquid oxygen liquid acquisition device bubble point tests with high pressure lox at elevated temperatures

When transferring propellant in space, it is most efficient to transfer single phase liquid from a propellant tank to an engine. In earth’s gravity field or under acceleration, propellant transfer is fairly simple. However, in low gravity, withdrawing single-phase fluid becomes a challenge. A variety of propellant management devices (PMDs) are used to ensure single-phase flow. One type of PMD, a liquid acquisition device (LAD) takes advantage of capillary flow and surface tension to acquire liquid. The present work reports on testing with liquid oxygen (LOX) at elevated pressures (and thus temperatures) (maximum pressure 1724 kPa and maximum temperature 122 K) as part of NASA’s continuing cryogenic LAD development program. These tests evaluate LAD performance for LOX stored in higher pressure vessels that may be used in propellant systems using pressure fed engines. Test data shows a significant drop in LAD bubble point values at higher liquid temperatures, consistent with lower liquid surface tension at those temperatures. Test data also indicates that there are no first order effects of helium solubility in LOX on LAD bubble point prediction. Test results here extend the range of data for LOX fluid conditions, and provide insight into factors affecting predicting LAD bubble point pressures.     

啤酒锥型发酵罐温度分布实验研究及分析

利用传热学原理与流体力学原理,并结合啤酒发酵工艺,分析了实验数据,并得出结论：在啤酒发酵过程中,热扩散起主导作用;还分析了发酵各阶段罐壁与罐内发酵液的温差情况,以及环境温度,冷煤温度,酵母对罐壁面温度的影响。     

Thermal Response of a Two-Phase Near-Critical Fluid in Low Gravity: Strong Gas Overheating as Due to a Particular Phase Distribution

An experimental study of the thermal response to a stepwise rise of the wall temperature of two-phase near-critical SF₆ in low gravity for an initial temperature ranging from 0.1 to 10.1 K from the critical temperature is described. The change in the vapor temperature with time considerably exceeds the change in the wall temperature (overheating by up to 23% of the wall temperature rise). This strong vapor overheating phenomenon results from the inhomogeneous adiabatic heating process occurring in the two-phase near-critical fluid while the vapor bubble is thermally isolated from the thermostated walls by the liquid. One-dimensional numerical simulations of heat transfer in near-critical two-phase ³He confirm this explanation. The influence of heat and mass transfer between gas and liquid occurring at short time scales on the thermal behavior is analyzed. A model for adiabatic heat transfer, which neglects phase change but accounts for the difference between the thermophysical properties of the vapor and those of the liquid, is presented. A new characteristic time scale of adiabatic heat transfer is derived, which is found to be larger than that in a one-phase liquid and vapor.