Observation of liquid hydrogen jet on flashing and evaporation characteristics

The evaporation speed of liquid hydrogen jet has been measured using high speed CCD camera. In the evaporation process the diameter of injected liquid hydrogen droplet plays important role. The experimental parameters for injection condition had been selected such as injection temperature and size of injection hole diameter which influences injected diameter of liquid droplet. Liquid hydrogen had been injected into the spray chamber that was filled with gaseous helium at room temperature. The liquid hydrogen jet moves in the horizontal direction and the images of the evaporation processes had been acquired from the observation window using high speed CCD camera. With this method it has been shown that evaporation speed of liquid hydrogen is influenced by injection temperature and size of injection hole diameter.     

EDU liquid acquisition device outflow tests in liquid hydrogen: Experiments and analytical modeling

This paper presents experiments and modeling of the most recent set of liquid acquisition device (LAD) vertical outflow tests conducted in liquid hydrogen. The Engineering Development Unit (EDU) was a relatively large tank (4.25 m³) used to mimic a storage tank for a cryogenic storage and transfer flight demonstration test. Six 1-g propellant tank outflow tests were conducted with a standard 325 × 2300 rectangular cross-section curved LAD channel conformal to the tank walls over a range of tank pressure (158–221 kPa), ullage temperature (22–39 K), and mass flow rate (0.0103–0.0187 kg/s) per arm. An analytical LAD channel solver, an exact solution to the Navier-Stokes equations, is used to model propellant outflow for the LAD channel. Results shows that the breakdown height of the LAD is dominated by liquid and ullage gas temperatures, with a secondary effect of flow rate. The best performance is always obtained by exposing the channel to cold pressurant gas and low flow rates, consistent with the cryogenic bubble point model. The model tracks the trends in the data and shows that the contribution of flow-through-screen pressure drop is minimized for bottom outflow in 1-g, versus the standard inverted outflow.     

Screen channel liquid acquisition device outflow tests in liquid hydrogen

This paper presents experimental design and test results of the recently concluded 1-g inverted vertical outflow testing of two 325 × 2300 full scale liquid acquisition device (LAD) channels in liquid hydrogen (LH₂). One of the channels had a perforated plate and internal cooling from a thermodynamic vent system (TVS) to enhance performance. The LADs were mounted in a tank to simulate 1-g outflow over a wide range of LH₂ temperatures (20.3–24.2 K), pressures (100–350 kPa), and flow rates (0.010–0.055 kg/s). Results indicate that the breakdown point is dominated by liquid temperature, with a second order dependence on mass flow rate through the LAD. The best performance is always achieved in the coldest liquid states for both channels, consistent with bubble point theory. Higher flow rates cause the standard channel to break down relatively earlier than the TVS cooled channel. Both the internal TVS heat exchanger and subcooling the liquid in the propellant tank are shown to significantly improve LAD performance.     

Frequency characteristics of liquid hydrogen cavitating flow over a NACA0015 hydrofoil

Large eddy simulation on unsteady cavitating flow of liquid hydrogen over a three-dimensional NACA0015 hydrofoil with the attack angle (α) of 6° are carried out to investigate the dynamic features of cavity with the existence of thermal effects. The numerical model considers the compressibility of both liquid and vapor phase, and is validated by comparing the results with the available experimental data. Special emphasis is put on analyzing the frequency characteristics of cavitation cloud. Strouhal number (St) is plotted against σ/2α (σ is cavitation number), and the water cavitation data reported by Andrt et al. are also used as a reference. It is found that the St number for LH₂ cavitation is much smaller than the water, in which the thermal effects are generally not considered, at the same σ/2α value when it is greater than about 2.0, while it returns to the same level as water when σ/2α decreases to below 2.0. The reason is primarily ascribed to the thermal effects, and the detailed explanations are given based on the recognitions that the shedding mechanism of cavitation clouds is predominated by the combined action of the vortex flow and thermal effects. While, when σ/2α decreases to a critical value, the relative effect of the thermal effects on the cavitation dynamics is greatly weakened compared with the mechanism due to the vortex flow, like those in isothermal cavitation flow in traditional fluids. The results provide a deeper understanding of the cryogenic fluid cavitation flow.     

Cryogenic design and test results of 30-m flexible hybrid energy transfer line with liquid hydrogen and superconducting MgB2 cable

In this paper we present the development of a new hybrid energy transfer line with 30 m length. The line is essentially a flexible 30 m hydrogen cryostat that has three sections with different types of thermal insulation in each section: simple vacuum superinsulation, vacuum superinsulation with liquid nitrogen precooling and active evaporating cryostatting (AEC) system. We performed thermo-hydraulic tests of the cryostat to compare three thermo-insulating methods. The tests were made at temperatures from 20 to 26 K, hydrogen flow from 70 to 450 g/s and pressure from 0.25 to 0.5 MPa. It was found that AEC thermal insulation was the most effective in reducing heat transfer from room temperature to liquid hydrogen in ∼10 m section of the cryostat, indicating that it can be used for long superconducting power cables. High voltage current leads were developed as well. The current leads and superconducting MgB₂ cable passed high voltage DC test up to 50 kV DC. Critical current of the cable at ∼21 K was 3500 A. It means that the 30 m hybrid energy system developed is able to deliver ∼50–60 MW of chemical power and ∼50–75 MW of electrical power, i.e. up to ∼135 MW in total.     

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.     

Dielectric coefficient and density of subcooled liquid hydrogen

Here we present precision dielectric coefficient measurements of subcooled equilibrium liquid hydrogen in the temperature range from 15 to 23 K and under pressures up to 1 MPa. The measurements were performed using a three-terminal flat plate capacitor and a single-frequency, ultra-precision capacitance bridge. These results are combined with the previously published data to express the dielectric coefficient in the form of the Clausius-Mossotti relation with a new correlation. The results reported in this paper are expected to be especially useful for capacitance-based measurements involving fluid hydrogen such as liquid level, mass gauging and void fraction measurements in two phase flow. Also, a new equation of state gives the density as a function of pressure and temperature for the subcooled liquid phase.     

液氧回灌阀燃爆事故分析及预防

介绍一起因液氧回灌阀反向使用造成阀门爆裂、导致空分设备停车的事故，分析了造成事故的原因及采取的防范措施。     

Development of density and mass flow rate measurement technologies for slush hydrogen

Slush hydrogen is a two-phase solid-liquid cryogenic fluid consisting of solid hydrogen particles in liquid hydrogen. Compared to liquid hydrogen, the density is about 16% greater at a solid mass ratio (solid fraction) of 50%, and the cryogenic heat capacity (enthalpy) is about 18% higher. Various applications are anticipated, including fuel for reusable space shuttles, coolant for cold neutron generation, as well as the transport and storage of hydrogen as a clean energy source. At a solid fraction of within 50%, piped transport can be conducted in the same way as for normal fluids. This paper reports on the slush hydrogen technology in terms of the measurement of the density and the mass flow rate.     

液氧回灌阀燃爆事故分析及预防

介绍一起因液氧回灌阀反向使用造成阀门爆裂、导致空分设备停车的事故,分析了造成事故的原因及采取的防范措施。     

A new experiment for investigating evaporation and condensation of cryogenic propellants

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.     

液氢加注系统氢气置换计算

为准确掌握火箭液氢加注系统氢气置换的具体参数,以火箭贮箱为研究对象,对液氢加注系统氢气置换过程进行数学建模,采用一元气体动力学方法计算得到氢气置换的次数、消耗量和充放气时间.通过分析计算不同放气终止压力对总时间的影响,建议将放气终止压力由0.11 MPa提高为0.14 MPa.     

液氧泵回流阀爆裂事故原因分析

介绍一起液氧内压缩流程中液氧泵回流阀爆裂事故的经过和破坏情况,初步认为事故的原因可能是阀门制造缺陷导致升压过程中上阀体破裂后高压液氧泄漏,进而引发化学性爆炸。最后提出了防止液氧泵回流阀燃爆的预防措施。     

液氢管路绝热设计与效果分析

通过总结液氢管路绝热设计和使用的经验,着重分析了夹层气体压强与漏热和表观导热系数以及气体压强回升与时间的定量关系,提出了工程设计中绝热性能及真空寿命的确定方法.     

火箭推进剂液氢中氦的分析方法

使用气相色谱法分析氢中氦时,在常用色谱柱上氦出峰在氢后面,并且位置很近,较大的氢峰会掩盖氦峰。针对上述问题,研制了一种新的色谱柱固定相,用于色谱法分析氢中氦组分。给出了这种固定相对氢、氦组分的分离原理、制作方法和实验过程。实验结果表明,采用气相色谱热导检测器,配用金属钯做色谱柱固定相,可成功地完成对氢、氦组分的分离和检测。     

Capillary cooling of superconducting coils with two-phase hydrogen or nitrogen

Superconducting coils in AC application, such as in the stator of superconducting motors, have losses which warm up the coil and so limit the performance. Good thermal contact between the coil and the cooling agent is important. In this research we investigate the possibility of cooling the coils by a cryoliquid, such as liquid hydrogen or liquid nitrogen, flowing through capillaries in thermal contact with the coils.     

胶氢制备技术研究

根据胶氢动力学稳定条件,推导出胶凝剂颗粒尺寸与密度的函数关系,并给出不同浓度下,液氢能够成胶的颗粒临界尺寸。从聚集稳定性出发,以颗粒与氢分子相互作用关系解释了胶氢成胶能够实现及其稳定相对较弱的原因。进行了胶氮、胶氢制备实验,但结果不是很理想。通过分析,原因在于低温密封条件下的高速搅拌目前难以实现,凝胶剂颗粒过大,超过能够形成胶体的直径要求。     

液氢泄漏扩散数值模拟研究

通过ALOHA软件进行了不同风速、环境温度、泄漏量扩散模拟,分析了不同风速、温度、泄漏量条件下的扩散规律。结果表明,泄漏扩散距离随着风速的增大而变小,风速越大,泄漏扩散范围越小;泄漏扩散距离随着环境温度的升高而变大,温度越高,泄漏扩散范围越大;泄漏扩散距离随着泄漏量的增加而变大,泄漏量越大,泄漏扩散范围越大。将液氢蒸发和氢气扩散试验的体积分数数据与ALOHA软件模拟数据进行对比,结果表明:ALOHA软件对氢的体积分数值模拟结果具有良好的精度,在液氢泄漏事故应急中具实用性。     

Determination of the parahydrogen fraction in a liquid hydrogen target using energy-dependent slow neutron transmission

The NPDGamma collaboration is performing a measurement of the very small parity-violating asymmetry in the angular distribution of the 2.2 MeV γ-rays from the capture of polarized cold neutrons on protons (A_γ). The estimated size of A_γ is 5×10⁻⁸, and the measured asymmetry is proportional to the neutron polarization upon capture. Since the interaction of polarized neutrons with one of the two hydrogen molecular states (orthohydrogen) can lead to neutron spin-flip scattering, it is essential that the hydrogen in the target is mostly in the molecular state that will not depolarize the neutrons (≥99.8% parahydrogen). For that purpose, in the first stage of the NPDGamma experiment at the Los Alamos Neutron Science Center (LANSCE), we operated a 16-l liquid hydrogen target, which was filled in two different occasions. The parahydrogen fraction in the target was accurately determined in situ by relative neutron transmission measurements. The result of these measurements indicate that the fraction of parahydrogen in equilibrium was 0.9998±0.0002 in the first data taking run and 0.9956±0.0002 in the second. We describe the parahydrogen monitor system, relevant aspects of the hydrogen target, and the procedure to determine the fraction of parahydrogen in the target. Also assuming thermal equilibrium of the target, we extract the scattering cross-section for neutrons on parahydrogen.