Abstract ：

Bubble condensation is a fundamental issue in the direct contact condensation (DCC) process, which is extremely hard to predict due to the intense mass transfer and flow instability. Aiming at the cryogenic oxygen bubble evolution and pressure oscillation, a modified energy balance mass transfer model is adopted based on the height function method. The height function method is used to calculate the real-time interfacial curvature, modifying the mass transfer rate that emerged in CFD simulation. The modified model is validated to be convincing and accurate by a steam bubble condensation simulation. The results indicate that the cryogenic bubbles condense faster with a more intense mass transfer process, compared with the near-room-temperature mediums. The corresponding amplitude of pressure oscillation for the cryogenic mediums is approximately 3 ∼ 4 times as larger as that for near-room-temperature mediums. It is found that both the condensation rate and the frequency of pressure oscillation are repressed with the increase of bubble volume. That means that a big bubble condensation might produce a low-frequency pressure oscillation. In addition, both the condensation rate and the intensity of the pressure oscillation increase with the increase of subcooling. The average amplitude of pressure oscillation has a power function law with subcooling. These conclusions provide a theoretical basis for a deep understanding of the cryogenic DCC process. © 2023 Elsevier Ltd

Keyword ：

Curvature estimation; Heat and mass transfer; Height function; Oxygen bubble condensation; Pressure oscillation

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Abstract ：

Combination of the hydrogen pre-cooling and liquefied natural gas gasification processes is forward-looking in the hydrogen liquefaction industry. To enhance the cold energy utilization, a hydrogen liquefaction process integrated in conjunction with a liquefied natural gas gasification process assisted by an organic Rankine cycle is designed. Furthermore, a simplified refrigeration system incorporating a dual-pressure Joule-Brayton cycle is developed to provide efficient cryo-cooling for the hydrogen. A binary mixture consisting of ethylene and propane is preferred as the working fluid for the organic Rankine cycle when liquefied natural gas gasification pressure is 30 bar, which results in 2.2% and 15.5% improvement in the liquefied natural gas cold energy utilization compared to the organic Rankine cycle with the pure refrigeration as the working fluid and the hydrogen pre-cooling process without the organic Rankine cycle, respectively. In the proposed cryo-cooling process using two Joule-Brayton cascade cycles, the utilization rate of the input exergy reaches 48.84%. The exergy loss generated in the compressors and coolers accounts for approximately 66.2% of the total exergy loss. Therefore, they are regarded as the priority targets for improving the hydrogen liquefaction system. After the optimization of the proposed process using the genetic algorithm, optimal results are obtained with a specific energy consumption of 6.59 kWh/kgH2 and an exergy efficiency of 47.0%. © 2022 Elsevier Ltd

Keyword ：

Binary mixtures Brayton cycle Energy utilization Ethylene Exergy Gases Gasification Genetic algorithms Liquefied natural gas Rankine cycle

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Abstract ：

A numerical model considering phase change and heat transfer was established by the Euler-Euler two-fluid method to investigate the storage characteristics and two-phase flow field of slush hydrogen. Numerous numerical simulations were performed to discuss the effect of particle diameter (dp = 0.02–0.5 mm), content of solid hydrogen (αs = 10%–50%), and heat leakage (q = 50–200W·m−2) on the flow field. It was found that particle deposition could occur during the storage process, and there exist moving vortices with contrary directions under specific conditions. The sedimentation characteristics and vortex size are influenced by many factors including particle size, solid hydrogen content, and heat leakage. An increase in particle size could lead to the strengthening of precipitation and the expansion of the counterclockwise vortex region on the right side of the tank. And the increase in solid hydrogen content could result in more deposition and more collisions and friction between particles. Moreover, the increase in heat leakage could increase the area of the counterclockwise vortex. Numerical results of the deposition and flow field characteristics in the storage tank could clearly show the physical law of the slush hydrogen so that the uniform distribution of slush hydrogen could be promoted for efficient storage and application. © 2023 Hydrogen Energy Publications LLC

Keyword ：

Cryogenic tank; Euler-euler two-fluid method; Flow field characteristic; Moving vortices; Slush hydrogen

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Abstract ：

For direct contact condensation (DCC) simulation, it is a challenge to capture the numerical characteristic of pressure oscillation precisely, especially the frequency and amplitude. It is the most crucial key issue to calculate the mass transfer across the vapor-liquid interface. Up to now, the pressure characteristic is generally obtained by experiment and the existing mass transfer models always lead to unacceptable deviation from the experiment result. In order to estimate the accurate pressure characteristic, a modified mass transfer model is originally proposed based on the height function method in this paper. An estimation method for the interfacial area density in this model is derived from the algebraic spherical model with the mean bubble diameter. This method correlates the interfacial area concentration with the measurable interfacial curvature and the interfacial curvature is calculated by the height function method. The proposed model is then employed based on the VOF method for the verification of Stefan's analytical problem and steam bubble condensation problem. The corresponding numerical results are both in great agreement with the analytical and experimental results. In addition, the proposed model achieves its advantage for the steam flow condensation to obtain more accurate results of pressure oscillation than other mass transfer models. The numerical result of pressure oscillation frequency is 8.9 Hz, close to the experimental data of 10 Hz with a deviation of 11%. However, the energy balance model and Lee model predict that the frequencies are 31.5 Hz and 19 Hz relatively with the corresponding deviation of 215% and 90%. It is validated to be convincing with excellent accuracy and shows promise for extensive numerical simulation for direct contact condensation applications. © 2022 Elsevier Ltd

Keyword ：

Curvature estimation; Direct contact condensation; Heat and mass transfer; Height function; Mass transfer model; Pressure oscillation

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Abstract ：

In a novel high temperature superconducting (HTS) hybrid energy pipe, the liquefied natural gas (LNG) and electricity are transported together along the energy pipeline to attain high energy transmission efficiency. When the pipe is exposed to thermal disturbance, the protective medium, liquid nitro...

Keyword ：

Boiling heat transfer Current sharing HTS cable Hybrid energy pipe Liquefied natural gas Multi-field coupled

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Abstract ：

Slush hydrogen can be used as a promising propulsion fuel for deep space exploration vehicles because of its more excellent thermodynamic properties compared with liquid hydrogen. To study stratification and settlement characteristics of slush hydrogen in cryogenic tanks, a transient model based on ...

Keyword ：

critical diameter numerical simulation settlement characteristics slush hydrogen

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Abstract ：

为了研究筛网LAD通道结构在低温推进剂中的气液分离及输送性能,设计、加工了覆盖筛网的圆管通道并通过可视化实验获得了液氮中LAD通道有效工作时的极限排放高度,并分析了流动损失的组成。结果表明,325×2 300 Dutch Twill型编织筛网在自增压过程中发生泡破时的液氮极限排放高度为280 mm,所产生的水力静压损失为2 222.64 Pa。分析认为,筛网在液氮中自增压的泡破裕度比氦气增压低是静压损失低于理论值的主要原因,筛网的焊接变形及玻璃杜瓦漏热不足是可能的次要原因。

Keyword ：

LAD 表面张力 低温流体 泡破点

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Abstract ：

设计研制了一套基于G-M制冷机的常压常温氢气直接液化的小型装置,包括液氢杜瓦、正仲转换装置、供气系统、液氢输送系统和测量系统等,提出了微正压氢液化工艺方法,制定了氢操作流程工艺及安全防护措施,并开展了实验测试。实验结果表明,该氢液化方案是可行且有效的,该装置是安全可靠的。在压力为162 kPa时,该小型氢液化装置的氢气液化速率可达到0.585 L/h。同时,该装置具备一边液化,一边加注供液的功能,满足科学实验连续使用的要求。

Keyword ：

G-M制冷机 氢能 氢液化方案 小型氢液化装置 液氢实验测试

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Abstract ：

Future cryogenic vehicle requires a fast propellant fueling as well as a rapid pipeline quenching operation. In the present study, a novel interior micro-fin tube concept, with a series of cyclic fins arranged along the flow direction and has the size of 1 mm in both of fin height and fin width, is ...

Keyword ：

Cryogenic quenching Film boiling Flow boiling Heat transfer Micro-fin

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Abstract ：

Future aerospace vehicle requires a fast propellant fueling and a rapid launching. In the present study, a high-pressure chilldown test platform is established, and two different tube structures, including a straight tube and an interior micro-fin tube, are tested under different inlet Reynolds numb...

Keyword ：

Cryogenic chilldown Fast fueling Film boiling Micro-fin tube Two-phase flow

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