In ground-based liquid hydrogen storage and transportation systems, the interlayer pressure within Multilayer Insulation (MLI) exhibits a non-uniform distribution. This is primarily attributed to the combined effects of flow resistance, material outgassing, and cryo-adsorption. Consequently, the interlayer pressure is often significantly higher than the pressure within the vacuum chamber. A clear understanding of the gas transport mechanisms within the interlayers of MLI is critical for enhancing the vacuum lifetime of liquid hydrogen storage tanks and reducing their manufacturing costs. This study developed a gas transport equation for MLI that incorporates both interlayer adsorption effects and variable density factors. By solving a Layer-By-Layer (LBL) model, a dataset of interlayer pressure-temperature samples was established through simulation. Subsequently, interlayer pressure was inversely determined from measured interlayer temperatures, utilizing this sample dataset to address the issue of missing boundary conditions in the governing equations for interlayer gas dynamics. Investigations conducted using a liquid hydrogen calorimeter tested two Variable Density MLI (VD-MLI) configurations. The inversion results revealed that with an increase in the porosity of the reflective shields, the interlayer pressure distribution transitioned from an "L"-shape towards a linear profile. The peak interlayer pressures were found to be 43.43 and 17.71 times the chamber pressure, respectively. The heat flux densities corresponding to the inverse solutions for these two VD-MLI configurations deviated from the experimental results by 13.3 % and 8.7 %, respectively. The interlayer gas transport equation and inversion algorithm proposed in this study enable the efficient and accurate determination of interlayer pressure distribution within VD-MLI. This provides a methodological breakthrough and essential technical tools to support the insulation design, vacuum longevity prediction, and reliability enhancement of liquid hydrogen storage and transportation systems.

Solid air accumulation poses a significant safety risk for liquid hydrogen systems, particularly when oxygenenriched layers form on the solid surfaces. This study experimentally investigated the solidification of the airlike nitrogen-oxygen gas mixtures with different nitrogen-oxygen ratios in liquid hydrogen, documenting morphological characteristics through visual observation and compositional distributions via gas chromatography. The results showed that for the solidification of the gas mixture with a relative oxygen content of 21.96 %, the size of the formed solid particles varied within the range of 0.7 mm to 1.2 mm. Moreover, most of the solid particles were dispersed in the form of powder in liquid hydrogen, and a small portion of solid particles were accumulated to form sheet-shaped or block-shaped aggregates. Compositional analysis revealed significant oxygen enrichment at the solid surface, reaching the maximum relative proportions of 33.64 %. Similarly, gas mixture with 30.42 % relative oxygen content yielded smaller solid particles with a size from 0.5 mm to 1 mm during the solidification, and the morphology of the formed solid particles was basically identical to that formed under air-like condition. The solid air's outer layer consistently exhibited oxygen enrichment with higher oxygen content in the injected gas mixture directly increasing oxygen concentration in the outer surface, which was demonstrated by the maximum relative oxygen proportion attaining 34.33 %. This work significantly expands the existing experimental database of the solidification of air in liquid hydrogen, and also provides valuable experimental reference for the safety design of cryogenic systems.

The thermal protection systems of cryogenic vessels require adaptability under diverse conditions to maintain thermodynamic stability. Given that the transient heat transfer behaviour of Multi-Layer Insulation (MLI) critically determines the thermodynamic performance and operation safety of cryogenic vessels, an experiment study was conducted at liquid nitrogen temperature on the transient heat transfer of a 90-layer MLI material after liquid nitrogen filling. A modified transient-state simulation model incorporating the unsteady heat transfer of spacers was developed and validated to investigate the transient heat transfer characteristics of the material. The variations of the inter-layer temperatures and heat leakage with time were simulated and compared with the experiment. The study shows that the 30th, 60th layer temperatures and heat leakage all decrease first rapidly and then slowly, where the heat leakage decreases from 0.42 W center dot m- 2 to 0.18 W center dot m- 2. The maximum deviations of the 30th, 60th layer temperatures and heat leakage between the simulation and experiment are 5.13 %, 4.78 % and 15.15 %, respectively. The heat leakage prediction accuracy of the revised model reaches +/- 0.0182 W center dot m- 2, which is improved by 23.21 % compared to that of the latest referenced models. The heat leakage is hardly affected by ambient temperature fluctuations, keeping below 0.3 W center dot m- 2 for a long period after liquid nitrogen filling. The study reveals the MLI transient heat transfer characteristics during cryogenic vessel precooling operations, and provides important references for optimizing thermal protection system design and enhancing computational accuracy in cryogenic engineering applications.

As offshore wind farms (OWFs) evolve to larger scale and longer distance, superconducting technology has an opportunity for application.Liquid hydrogen (LH2) is an ideal cooling medium for superconductors used in OWFs and is a high-quality product.Therefore, an offshore power-LH2 co-production and hybrid delivery system based on superconducting technology is designed.The SEC, EXE, and COP of hydrogen liquefaction and subcooling integration process are 8.82 kWh/kgLH2, 40.6%, and 0.15, respectively.LH2 is produced to cool superconducting generators and transported ashore along with electricity using the hybrid energy pipeline.At a LH2 delivery rate of 1 kg/s, the maximum delivery distance of the hybrid energy pipeline can reach 81.7 km.

The burn pond is a relatively efficient and safe way to deal with the hydrogen emitted or leaked in experiments. The aim of this paper is to analyze the performance of the burn pond in bubbling and dispersing hydrogen. The numerical simulation is the primary method utilized in this study, with a small-scale experimental validation. And Taguchi method is proposed to process data and quantify the importance of each factor. The results show that the water depth affects the performance of the burn pond most significantly, accounting for more than 56 %, followed by the outer diameter of caps and the number of slots. In addition to these design factors, the velocity of hydrogen also has a considerable impact on the burn pond. Essentially, the four factors determine the size and kinetic energy of bubbles, which then directly affect the process of bubbling and hydrogen distribution. The conclusions provide an orientation for optimizing the parameters related to bubble caps and the burn pond.

Hydrogen energy has emerged as one of the most promising types of future energy. Accurately predicting the diffusion behavior of liquid hydrogen after an accidental release is one of the most important aspects of promoting the safe use of hydrogen energy. Considering the condensation and freezing of air, a three-dimensional unsteady leakage and diffusion model of liquid hydrogen is developed to predict the distribution of hydrogen vapor cloud and evaporation of liquid hydrogen pool in a large liquid hydrogen release experiment conducted by NASA. During the release of liquid hydrogen, the volume fractions of liquid air and solid air are quite small due to turbulence, and there is almost no liquid air and solid air present in the space directly opposite the leakage source. After the termination of the release, the flow field is more stable and the volume fractions of liquid air and solid air tend to increase, which on the ground can exceed 0.05 and 0.005 respectively at 50 s. This indicates that the ice layer observed in the former experiments may mainly be generated after the release. The evaporation coefficient of hydrogen has a significant effect on the hydrogen flammable volume, as the hydrogen evaporation coefficient increases from 0.006 to 0.06, the flammable volume increases from 1003.3 m3 to 7656.3 m3. As the evaporation coefficient continues to increase from 0.06, the volume growth rate of flammable hydrogen cloud tends to decrease. The flammable volume is not sensitive to the air condensation coefficient in the range of 1-1000, which increases from 6858.8 m3 to 7656.3 m3 as the air condensation coefficient increases from 1 to 1000. This study helps to refine the model for predicting the dispersion characteristics of accidental liquid hydrogen release considering the phase change of the air. (c) 2023 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Storage and transportation of hydrogen in liquid form offers considerable advantages, but the high energy consumption of hydrogen liquefaction processes needs to be addressed. In this study, a novel hydrogen liquefaction process integrated with a dual-pressure organic Rankine cycle (DORC) is proposed. It offers significant energy-saving by efficiently utilizing the cold energy of liquefied natural gas (LNG). The key parameters in the proposed process are investigated, and the results are combined with an improved genetic algorithm for efficient optimization of the process. The optimal exergy efficiency of the proposed process is 48.7%, and the minimal energy consumption is 6.29 kWh/kgLH2. Thanks to the power output (381.3 kW) of the DORC and the energy saved by the cryogenic compression of nitrogen (586.6 kW), energy consumption of the proposed process is reduced by approximately 3.1% compared to that of the process without a DORC. Moreover, an improved helium Brayton refrigeration cycle for hydrogen cryo-cooling is simpler, but less the refrigerant usage and energy consumption compared to the previously proposed cycles. The proposed process demonstrates excellent performance in terms of energy saving and efficiency improvement, providing a low-cost scheme to produce liquid hydrogen. (c) 2023 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

An efficient cyclic cold storage system plays a crucial role in improving the performance of a Liquid Air Energy Storage system. Packed bed cold storage (PBCS) systems, widely researched and employed, demonstrate thermal stability, a broad operational temperature range, and cost-effectiveness. This study developed a two-dimensional transient cyclic solid-PBCS system using a porous media thermal non-equilibrium model, which was implemented in ANSYS Fluent software. During the cold charging and discharging periods, cryogenic nitrogen and nitrogen at ambient temperature were used as working fluids to exchange heat with the solid cold storage medium in the PBCS. Temperature distributions were analyzed during the cold charging, cold discharging, and the consecutive cyclic cold charging-discharging modes. The study systematically examined the impact of mass flow rate and the number of cold storage cycle on key system performance parameters, including heat exchange capacity and cyclic cold exergy efficiency. The results indicated that mass flow rate significantly affects the number of cycles required to reach a steady-state cyclic PBCS system, with higher mass flow rates necessitating more cycles. Optimal cyclic performance of the solid PBCS can be achieved at a moderate superficial mass flow rate. At a superficial mass flow rate of 0.32 kg s(-1) m(-2), the cyclic cold charging exergy efficiency exceeds 99 % and cyclic cold discharging exergy efficiency can over 68 %. The stability of multiple consecutive cold storage cycles in the solid PBCS system is critical to the overall performance of LAES. These findings on the influence of PBCS cold storage cycles and fluid mass flow on system cyclic performance provide valuable theoretical guidance for the practical operation of PBCS cycles.

The Claude cycle is the preferred option for large-scale hydrogen liquefaction. However, the thermophysical properties of hydrogen vary substantially around the critical temperature and are strongly affected by hydrogen pressure. This leads to the fact that the classic Claude cycle is not universal for hydrogen at different pressures. Three innovative Claude cycles have been proposed. The applicability of three hydrogen liquefaction cycles is evaluated from specific energy consumption (SEC) perspective. The classic Claude cycle (Cycle 1) is suitable for the liquefaction of hydrogen with pressure above 3500 kPa, and the SEC for the liquefaction of hydrogen at 3500 kPa is 5.02 kWh/kg LH2 . The Claude cycle (Cycle 2) with two cross-arranged refrigeration cycles is suitable for hydrogen with pressure between 2200 and 3500 kPa, and the SEC is 4.98 kWh/kg LH2 for the liquefaction of hydrogen at 2500 kPa. The Claude cycle (Cycle 3) with a split-flow refrigeration cycle is suitable for hydrogen with pressure less than 2200 kPa, and the SEC for the liquefaction of hydrogen at 1500 kPa is 5.27 kWh/kg LH2 . Furthermore, the reasons for the SEC and applicability of three cycles being affected by hydrogen pressure are investigated by means of parametric analysis, heat exchanger performance analysis, and exergy analysis.

Cryogenic energy storage (CES) is a viable method for grid-scale electrical energy storage. Considering the high energy density and mature application of liquefied natural gas (LNG), we proposed an LNG cryogenic energy storage (LNGES) system. A steady-state process model of the LNGES system was established using Aspen HYSYS. The effects of the natural gas composition and key operating parameters such as the charging pressure, discharging pressure, throttling temperature, and liquid storage pressure on the system performance were investigated. A multi-parameter genetic algorithm model built using the MATLAB software was used to optimize the LNGES system to optimize the round-trip efficiency (RTE). Then, an exergy analysis of the optimal configuration was conducted. The results suggested that the LNGES system could achieve optimal RTE and exergy efficiency values of 60.14% and 71.64%, respectively. Exergy destruction mainly occurred during the compression, throttling, expansion, and heat exchange. The proposed LNGES system could be a promising candidate for the large-scale application of CES technology in power grids and gas networks.

An efficient cyclic cold storage system plays a crucial role in improving the performance of a Liquid Air Energy Storage system. Packed bed cold storage (PBCS) systems, widely researched and employed, demonstrate thermal stability, a broad temperature range, and cost-effectiveness. The present study built a two-dimensional transient porous media-packed bed cold storage model using ANSYS Fluent software. In the cold charging and discharging periods, cryogenic nitrogen and nitrogen at ambient temperature were the working fluids to exchange heat with the solid cold storage medium in the PBCS. Dynamic temperature distributions were explored in fully cold charging, fully cold discharging, and cyclic cold charging-discharging modes. The study systematically examined the influence of operating conditions on critical system performance parameters, including pressure drop, cyclic cold energy capacity, cyclic cold storage efficiency (η_st), and cyclic cold exergy efficiency (η_ex). Results indicated that a high cold end temperature (T_cold) and a low warm end temperature (T_warm) showed a narrow temperature range stored in the PBCS and a prolonged charging-discharging period. A decrease in thermocline thickness and an elevation in the isotherm peak were observed with an increase in the superficial mass flow rate (m ̇_in). Identifying optimal comprehensive operating conditions, including m_in, T_warm, and T_cold, resulted in efficiencies exceeding 98.48% and 89.25% for η_st and η_ex, respectively. It is concluded that heightened efficiencies (η_st and η_ex) are observed under conditions of high T_warm, low T_cold, and large m_in.

Flare stacks, used for emergency venting of redundant hydrogen, can cause jet fires that pose thermal hazards to the surrounding environment. To accurately predict the hazard distance of hydrogen flare, it is necessary to develop a new flare radiation model. Also, the numerical simulations of hydrogen flame are carried out to assess the radiation hazard area of the flares. The results show that the hazard distances predicted by the numerical method and the new model agree well with the HSL data fitted by exponential regression, and the errors are less than ±5%. Furthermore, the new model and simulations were used to analyze the distribution of thermal radiation for hydrogen flare under various release conditions. Increasing the release rates will drive the hazard boundary of flare system to expand. Additionally, as flare height increases, the radiation damage from the flare flame on ground is reduced due to buoyancy of combustion products.

The hydrogen-addition natural gas pipeline is a promising technology for large-scale civilian use, revealing the indoor diffusion behaviors of flammable gas in a leakage acci-dent is of great importance for formulating a safety warning. A three-dimensional un-steady model is established, the distribution characteristics of CH4 and H2 are studied and the dynamic flammable regions are investigated. Case studies are performed to evaluate the effects of hydrogen-addition ratios and floor levels on average concentrations and flammable volumes of CH4 and H2. The results show that the high-concentration region of H2 is always near the leakage hole. The increase rate of flammable gas mixture volume is larger than that of the volume of high-concentration CH4. Under a higher hydrogen -addition ratio, the high-concentration region of CH4 and the flammable region of gas mixture both float up while the high-concentration region of H2 keeps horizontal, the flammable volume of gas mixture increases faster but the final volume is smaller. When the room is ventilated, a bigger wind speed leads to a smaller flammable volume of gas mixture. The flammable volume can be constrained at a quite low value from the begin-ning as the wind speed surpasses 1.5 m/s. When the leakage of hydrogen-addition natural gas occurs, floor 1 takes the most serious ignition risk with the largest flammable volume of 9.87 m3, occupying 44% of the room space. By contrast, the upper floors have quite smaller flammable volumes of gas mixture (under 0.05 m3) and the flammable region is near the leakage hole. The high-concentration region of H2 is affected slightly by the floor height. (c) 2023 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Revealing the interlayer pressure distribution in multilayer insulation (MLI) for cryogen (e.g., liquid hydrogen) containers is very important to improve the insulation-performance-predicting quality. This paper proposed an inversion method to reconstruct the interlayer pressure of multilayer insulations on the basis of experimentally measuring the reflectors’ temperatures. The layer-by-layer (LBL) model was modified by considering the interlayer pressure distribution in MLIs to calculate the reflectors’ temperatures. Groups of pre-given interlayer pressure distributions and the corresponding temperature distributions calculated by the LBL model were used to train an extreme learning machine (ELM) algorithm. Finally, the interlayer pressure distribution of the MLI was reconstructed by the trained ELM algorithm based on the measured reflectors’ temperatures. The method was validated by four additional testing cases. The results showed that the proposed algorithm was accurate in reconstructing the interlayer pressures. Published experimentally measured temperature distributions of a 60-layer MLI were used as input data. The abovementioned inversion method was adopted, and a reasonable interlayer pressure distribution was obtained. Moreover, the thermal insulation performance of the MLI was calculated by the LBL model considering the reconstructed interlayer pressure distribution. We found that the predicted heat flux of the MLI deviated from the experimental results by only 2.77%, while the error of the classical LBL model ignoring the non-ideal vacuum condition was as high as 89%. Meanwhile, the predicted corresponding temperature distribution deviated from the tested value by less than 1.13 K. The proposed method can be applied to assess the interlayer pressure distribution of industrial cryogen containers and precisely predict the thermal insulation performance of a practical multilayer insulation structure.

Improving the efficiency and reducing the cost of hydrogen liquefaction systems have become a subject of importance nowadays. Through the comparison and analysis of existing processes, a hydrogen liquefaction system that can enhance the utilization efficiency of liquefied natural gas (LNG) cold energy is developed. The system includes a dual-pressure organic Rankine cycle (DORC)-assisted LNG regasification process and improved cascade Joule-Brayton refrigeration cycles. To assess the performance of the proposed process, two forms of ORC and three Brayton refrigeration cycles are compared, respectively. The genetic algorithm is applied to optimize the proposed process. The coefficient of performance, exergy efficiency, and specific energy consumption of the proposed process is 0.20, 46.9%, and 6.61 kWh/kgLH2, respectively. Owing to the efficient utilization of LNG cold energy, the power output of the DORC is 16.2% higher than that of a regular ORC. Furthermore, the improved cryo-cooling process exhibits a significant performance enhancement. Compared to two existing processes, the UA value of the heat exchangers in the proposed cryo-cooling process is reduced by 47.6% and 8.3%, respectively, and the required mass flow rate of helium is reduced by 45.3% and 8.6%, respectively. Moreover, the exergy analysis performed on the system indicates that the exergy utilization rate of the hydrogen pre-cooling process is 80.2%, while that of the cryo-cooling process is only 48.7%.

Liquid air energy storage (LAES) technology is helpful for large-scale electrical energy storage (EES), but faces the challenge of insufficient peak power output. To address this issue, this study proposed an efficient and green system integrating LAES, a natural gas power plant (NGPP), and carbon capture. The research explores whether the integration design is theoretically feasible for future adoption in operating the LAES system and NGPP. The effect of the charging pressure, the number of air expansion stages, and electricity prices on the overall thermodynamic and economic characteristics are investigated. The round-trip efficiency and the exergy round-trip efficiency of the proposed system are 47.72% and 69.74%, respectively. The calculations show that the minimum dynamic payback period for such a project is 3.72 years, and the lowest levelized cost of electricity is 0.0802 USD·kWh−1. This work provides a reference for peak-shaving power stations with energy storage and carbon capture.

Hydrogen liquefaction is an essential section for efficient storage and transportation of hydrogen energy. Both the Claude cycle and Brayton refrigeration cycle are available for large-scale hydrogen liquefaction systems. Two large-scale hydrogen liquefiers with the liquefaction capacity of 120 t/d based on the Brayton refrigeration cycle and the Claude cycle, respectively, are analyzed and compared in this study. Sensitivity analysis is used to optimize the parameters of two liquefaction systems in HYSYS. According to the results, the exergy loss and specific energy consumption of the Claude liquefier are 18.98 MW and 5.62 kWh/kgLH, which are 6.6% and 4.4% less than those of the Brayton liquefier, respectively. Exergy analysis reveals the exergy loss of compression and expansion systems in the Claude liquefier is less than that of the Brayton liquefier, while the exergy loss of the throttle valve in the Claude liquefier is more notable. In addition, the molar flow rate of hydrogen used as refrigerant in the Claude liquefier is 10.6% less than that of refrigerant in the Brayton liquefier. Owing to the smaller size requirements of equipment and the lower specific energy consumption, the Claude cycle is more suitable for large-scale hydrogen liquefaction processes.

针对可挥发性有机物(VOCs)的低温脱除,采用波纹通道可破坏不凝气(NCG)层积聚、减小低温相变脱除传质阻力.本文建立了针对锯齿波纹板通道内少量R134a与氮气混合气的低温相变脱除的二维模型,揭示了锯齿齿板底角角度对R134a相变脱除效果的影响特性.结果表明,与平板通道相比,本文采用的对照组等腰三角锯齿波纹板可显著提升单位面积冷壁面上R134a的脱除效率,在本研究条件下R134a时空平均相变速率(α)为0.1268g/(m2·s),提高了144.6%;锯齿波纹板底角(θ)增加时,NCG层在近冷壁面处会依次发生贴壁流动、脱壁掺混,最终形成稳定漩涡的流动阻滞区.当θ为13.30°～35.45°时,NCG层发生显著的脱壁掺混,α在0.082～0.1268g/(m2·s)之间;当θ=17.46°时,α达到最大值0.1268g/(m2·s).当θ过大或过小时,脱壁掺混效果都将衰减,α在较低的水平.本文对用于低浓度VOCs的冷凝-冻结脱除的锯齿波纹板结构设计具有参考意义.

Application of para-ortho hydrogen conversion to a vapor cooled shield (VCS) in a multilayer insulation system can utilize more cooling capacity of cryogenic hydrogen vapor and achieve better thermal protection for liquid hydrogen storage. Based on energy conservation and layer-by-layer model, a thermodynamic model was developed to study a variable density multilayer insulation (VDMLI) structure coupled with one VCS and paraortho hydrogen conversion. The effects of introducing the VCS and different para-ortho hydrogen conversion types were investigated. The maximum heat leakage reduction was 56.44 % after the VCS was installed at the middle of the 43-layer VDMLI with an optimal configuration. The ratio of the distance between the optimal VCS position and the cold boundary to the VDMLI thickness changed from 50 % to 40.41 % in the existence of a continuous para-ortho hydrogen conversion. The heat leakage of the VDMLI with one VCS could be further reduced by 12.99 %, 12.99 % and 10.09 % with a continuous conversion, single-stage isothermal conversion and single-stage adiabatic conversion, respectively. Notably, the adiabatic conversion could be implemented for its relative installation convenience. The heat leakage of the VDMLI could be reduced by 60.44 % after one VCS with an adiabatic conversion is adopted.

Cryogenic energy storage (CES) has garnered attention as a large-scale electric energy storage technology for the storage and regulation of intermittent renewable electric energy in power networks. Nitrogen and argon can be found in the air, whereas methane is the primary component of natural gas, an important clean energy resource. Most research on CES focuses on liquid air energy storage (LAES), with its typical round-trip efficiency (RTE) being approximately 50% (theoretical). This study aims to explore the feasibility of using different gases as working media in CES systems, and consequently, to achieve a high system efficiency by constructing four steady-state process models for the CES systems with air, nitrogen, argon, and methane as working media using Aspen HYSYS. A combined single-parameter analysis and multi-parameter global optimization method was used for system optimization. Further, a group of key independent variables were analysed carefully to determine their reasonable ranges to achieve the ideal system performance, that is, RTE and liquefaction ratio through a single-parameter analysis. Consequently, a multi-parameter genetic algorithm was adopted to globally optimize the CES systems with different working media, and the energy and exergy analyses were conducted for the CES systems under their optimal conditions. The results indicated the high cycle efficiency of methane and a low irreversible loss in the liquefaction cycle. Moreover, the Joule-Thomson valve inlet temperature and charging and discharging pressures considerably affected the system performance. However, exergy loss in the CES system occurred primarily in the compressor, turbine, and liquefaction processes. The maximum optimal RTE of 55.84% was achieved in the liquid methane energy storage (LMES) system. Therefore, the LMES system is expected to exhibit potential for application in the CES technology to realize the integration of natural gas pipelines with renewable power grids on a large scale. Moreover, the results of study have important theoretical significance for the innovation of the CES technology.