Search Results (301)

The traction behavior in cryogenic solid-lubricated ball bearings (CSLBBs) used in liquid rocket engines (LREs) affects not only the dynamic response of the bearing but also the lubricity and wear characteristics of the solid lubrication coating. The traction coefficient between the ball and raceway depends on factors such as contact material, relative sliding velocity, and contact pressure. However, existing traction curve models for CSLBBs typically consider only one or two of these factors, limiting the accuracy and applicability of theoretical predictions. In this study, a novel traction model for CSLBBs is proposed, which incorporates the combined effects of contact material, relative sliding velocity, and contact pressure. Based on this model, a tribo-dynamic framework is developed to investigate the tribological and dynamic behavior of CSLBBs. The model is validated through both theoretical analysis and experimental data. Results show that the inclusion of solid lubricant effects significantly alters the relative sliding and frictional forces between the rolling elements and the raceway. These changes in turn influence the impact dynamics between the rolling elements and the cage, leading to notable variations in the bearing’s vibrational response. The findings may offer valuable insights for the wear resistance and vibration reduction design of CSLBBs. Full article

Variable-thrust liquid rocket engines are essential for precision landing in deep-space exploration, reusable launch vehicle recovery, high-accuracy orbital maneuvers, and emergency obstacle evasions of space drones. However, with the increasingly complex space missions, challenges remain with the development of different technical schemes. In view of these issues, this paper systematically reviews the technology’s evolution through mechanical throttling, electromechanical precision regulation, and commercial space-driven deep throttling. Then, the development of key variable thrust technologies for liquid rocket engines is summarized from the perspective of thrust regulation and control strategy. For instance, thrust regulation requires synergistic flow control devices and adjustable pintle injectors to dynamically match flow rates with injection pressure drops, ensuring combustion stability across wide thrust ranges—particularly under extreme conditions during space drones’ high-maneuver orbital adjustments—though pintle injector optimization for such scenarios remains challenging. System control must address strong multivariable coupling, response delays, and high-disturbance environments, as well as bottlenecks in sensor reliability and nonlinear modeling. Furthermore, prospects are made in response to the research progress, and breakthroughs are required in cryogenic wide-range flow regulation for liquid oxygen-methane propellants, combustion stability during deep throttling, and AI-based intelligent control to support space drones’ autonomous orbital transfer, rapid reusability, and on-demand trajectory correction in complex deep-space missions. Full article

Cryosurgery employs extremely low temperatures to destroy abnormal or cancerous tissue. Conventional systems use cryogenic fluids like liquid nitrogen or argon, which pose challenges in handling, cost, and precise temperature control. This study explores thermoelectric (TE) cooling using the Peltier effect as an efficient alternative. A numerical optimization of multi-stage TE coolers using bismuth telluride (Bi₂Te₃) is performed through finite element analysis in COMSOL Multiphysics. Results show that the optimized multi-stage TE system achieves a minimum temperature of −70 °C, a 90 K temperature difference, and 4.0 W cooling power—outperforming single-stage (SS) systems with a maximum ΔT of 73.27 K. The study also investigates the effects of material properties, current density, and geometry on performance. An optimized multi-stage (MS) configuration improves cooling efficiency by 22.8%, demonstrating the potential of TE devices as compact, energy-efficient, and precise solutions for cryosurgical applications. Future work will explore advanced nanomaterials and hybrid systems to further improve performance in biomedical cooling. Full article

Liquid hydrogen (LH₂) storage using carbon-fiber-reinforced composite pressure vessels is facing increasing demands in aerospace engineering. However, hydrogen permeation in epoxy resin matrixes seriously jeopardizes the function and safety of the cryogenic vessels, and the micro-behavior of hydrogen permeation in epoxy resins remains mysterious. This study performed molecular dynamics (MD) simulations to investigate the hydrogen molecule permeation behaviors in two types of epoxy resin systems, with similar epoxy reins of bisphenol A diglycidyl ether (DGEBA) and different curing agents, i.e., 4,4′-diaminodiphenylmethane (DDM) and polypropylene glycol bis(2-aminopropyl ether) (PEA). The influencing factors, including the cross-linking degrees and temperatures, on hydrogen permeation were analyzed. It was revealed that increased cross-linking degrees enhance the tortuosity of hydrogen diffusion pathways, thereby inhibiting permeation. The adsorption characteristics demonstrated high sensitivity to temperature variations, leading to intensified hydrogen permeation at low temperatures. By triggering defects in the epoxy resin systems by uniaxial tensile simulation, high consistency between the simulation results and the results from helium permeability experiments can be achieved due to the micro-defects in the simulation model that are more realistic in practical materials. The findings provide theoretical insights into micro-scale permeation behavior and facilitate the development of high-performance epoxy resins in liquid hydrogen storage. Full article

This study explores how production technology influences spray-applied rigid polyurethane (PUR) foam insulation’s cryogenic performance. In cryogenic applications such as liquid gas storage, insulation must minimise heat transfer and resist moisture ingress under severe thermal gradients. Experimental aluminium vessels were insulated with PUR foam of varying thicknesses and surface conditions—rough, machined smooth, and with a urea-based protective coating—and then tested using dynamic boil-off of liquid nitrogen (LN₂). Foam properties, including adhesion, mechanical strength, thermal expansion, thermal conductivity, and closed-cell content, were evaluated. The results revealed that thicker insulation reduced both effective thermal conductivity and moisture uptake. Although the urea-coated vessel showed minimal water absorption, the coating increased overall thermal conductivity due to its heat conduction and condensation behaviour. Moisture was primarily absorbed near the foam surface, and no cumulative effects were observed during repeated tests. The effective thermal conductivity was determined by interpolating boil-off data, confirming that insulation performance strongly depends on thickness, surface condition, and environmental humidity. These findings provide valuable guidance for the design and application of PUR foam insulation in cryogenic environments. Full article

This investigation presents the comprehensive thermo-structural analysis of the propellant tanks utilized in the CROME propulsion system, focused on examining the structural effects caused by the storage of liquid nitrogen, liquid oxygen, and liquid methane. These fluids operate at extremely low temperatures and generate large thermal stress gradients in the tanks, significantly influencing their structural properties. For this reason, it is of vital importance to inspect the generation of mechanical and thermal stresses in the tanks to assess the risk of structural failure. To accomplish this effort, this analysis evaluates the tanks containing liquid nitrogen, liquid oxygen, and liquid methane at pressures of 200.0 psi and 400.0 psi. A coupled finite element analysis was performed in Star-CCM+ to compute the resulting Von Mises stresses under steady-state conditions. These stress results were used to determine the factor of safety in each case, enabling a quantitative assessment of structural integrity in the tanks while operating with cryogenic fluids under different pressure loadings. Full article

Heterogeneity of pore and fracture structures has become an important factor affecting the migration of methane and water in coal reservoirs. However, controlling factors of pore and fracture structure collected from coal seam 10 in Taliqike Formation, Kubai Coalfield, Xinjiang need to be studied. In this paper, carbon dioxide adsorption, cryogenic liquid nitrogen, and high-pressure mercury intrusion, as well as coal microscopic components, were used to study pore volumes and characterize pore diameter distribution heterogeneity. By the theory of single weight and multiple fractal formations, the heterogeneity of the pore fracture structure of coal reservoir is expressed, and the influencing factors of the heterogeneity of the pore fracture structure and the pore volume are also discussed. The results are as follows. (1) Micro-pore distribution presents a distinct bidirectional state, with the main peak at approximately 0.6 nm and 0.85 nm. R_o,max has an obvious influence on micro-pore volume. The single-fractal dimension of micro-pore is not affected by a micro-pore volume but is influenced by other factors such as R_o,max and microscopic composition. The heterogeneity of the low-value area controls the heterogeneity of micro-pore diameter distribution. (2) For lower R_o,max samples, mesopores of these samples are ink bottle-shaped pores, and the pore connectivity is poor. In contrast, meso-pore of higher thermal evolution coal samples are mostly simple pores, such as parallel plates. The main mesopores are 10–100 nm pores, accounting for 75% of the total meso-pore volume. For the single fractal dimension, D₁ is greater than D₂, which also shows that the heterogeneity of a pore structure greater than 4 nm is much stronger than that of a pore structure less than 4 nm in these samples. (3) For lower R_o,max samples, double S-shaped curves with distinct hysteresis loop are obtained, while samples of higher R_o,max samples show parallel curves, suggesting that macro-pore of this type of sample develops parallel plate-like pore. There is a positive relationship between D₋₁₀–D₀ and D₋₁₀–D₁₀, while D₀–D₁₀ and D₋₁₀–D₀ have a weak correlation. With the increase of 2–10 nm pore volume, pore distribution heterogeneity of lower value area (D₋₁₀–D₀) weakens. This indicates that pore volume is an important factor affecting the multifractal variation. Full article

As interest in liquid hydrogen (LH₂) continues to grow within the energy and mobility sectors, so does the demand for testing capabilities at deep cryogenics temperatures. However, cost-, complexity-, and safety-related challenges associated with handling LH₂ effectively limit the landscape of possible options. As an alternative, LH₂ temperatures can be accessed via a helium-based cryogenic refrigerator, or “cryocooler”. Recently, NASA and its partners CB&I and Shell began the development of a cryocooler-based calorimeter to characterize the thermal performance of insulations and other materials down to 20 K. Deemed the Guarded Hot Cylinder (GHC), the apparatus utilizes a small vacuum chamber in conjunction with a GM cryocooler and trim heater to control the cold boundary temperature. A sealed, cylindrical copper cup bolts to the cryocooler and houses the material specimen, with an internal, cylindrical test heater assembly to maintain the warm boundary. The steady-state heat load, traveling radially through the specimen, is measured via the electrical input power to the test heater and then used to evaluate the material’s absolute thermal performance. Initial checkout and validation of the GHC using a common bulk-fill insulation material showed close agreement with published data from standardized LN₂ boiloff calorimetry testing. The instrument is now considered a lab standard, with the goal of incorporating it into the ASTM C1774 standard in the future, and it is in continuous use, examining insulation materials for next-generation LH₂ applications. Full article

Using hydrogen as a working fluid in cryocoolers can potentially benefit cryocooling technologies and hydrogen liquefaction. Moreover, in flow-through thermoacoustic systems, hydrogen can be efficiently cooled and undergo ortho-parahydrogen isomeric conversion, which is important for the efficient storage of cryogenic hydrogen. A traveling-wave regenerator is analyzed in this study, using the thermoacoustic theory with a superimposed mean flow and an empirical correlation for hydrogen isomer conversion. A regenerator with hydrogen fluid is shown to achieve higher performance in comparison with helium as the working fluid. However, the hydrogen system performance degrades at supercritical pressures and subcritical temperatures in compressed liquid states. In regenerators with mean flow, using hydrogen as the working fluid leads to higher cooling powers and efficiencies, but helium systems are able to achieve colder temperatures. Full article

Liquid hydrogen is regarded as a key energy source and propellant for lunar bases due to its high energy density and abundance of polar water ice resources. However, its low boiling point and high latent heat of vaporization pose severe challenges for storage and management under the extreme lunar environment characterized by wide temperature variations, low pressure, and low gravity. This paper reviews the strategies for siting and deployment of liquid hydrogen storage systems on the Moon and the technical challenges posed by the lunar environment, with particular attention for thermal management technologies. Passive technologies include advanced insulation materials, thermal shielding, gas-cooled shielding layers, ortho-para hydrogen conversion, and passive venting, which optimize insulation performance and structural design to effectively reduce evaporation losses and maintain storage stability. Active technologies, such as cryogenic fluid mixing, thermodynamic venting, and refrigeration systems, dynamically regulate heat transfer and pressure variations within storage tanks, further enhancing storage efficiency and system reliability. In addition, this paper explores boil-off hydrogen recovery and reutilization strategies for liquid hydrogen, including hydrogen reliquefaction, mechanical, and non-mechanical compression. By recycling vaporized hydrogen, these strategies reduce resource waste and support the sustainable development of energy systems for lunar bases. In conclusion, this paper systematically evaluates passive and active thermal management technologies as well as vapor recovery strategies along with their technical adaptability, and then proposes feasible storage designs for the lunar environment. These efforts provide critical theoretical foundations and technical references for achieving safe and efficient storage of liquid hydrogen and energy self-sufficiency in lunar bases. Full article

This review article investigates the rising global energy demand, which is primarily driven by population growth and industrialization, raising significant environmental concerns due to the extensive reliance on fossil fuels. In response, hydrogen is being explored as a potential eco-friendly energy solution to meet the urgent need for sustainable energy. This review covers various hydrogen storage methods, including compressed gas, cryogenic liquids, solid materials, and electrochemical techniques. Among these, electrochemical technology is highly regarded as a leading experimental approach for hydrogen storage, and it is noted for its outstanding performance under normal conditions. The characteristics of a material’s surface play a crucial role in determining its electrochemical hydrogen storage capacity. Innovative materials, such as graphene oxide and 3D graphene oxide, are particularly significant in this regard, as they can significantly enhance hydrogen storage capacity; electrochemical hydrogen storage functions by incorporating atomic hydrogen into carbon materials following the reduction of water. This article underscores the significance of green energy and the need to ensure safety and precision at room temperature and ambient pressure using electrochemical hydrogen storage techniques and mechanisms. Furthermore, it offers a comprehensive review of developments in electrochemical hydrogen storage and its mechanisms, focusing on carbon, graphene oxide, and the contributions of 3D graphene foam. Full article

With the increasing severity of climate change, Carbon Capture, Utilization, and Storage (CCUS) technology has become essential for reducing atmospheric CO₂. Marine carbon sequestration, which stores CO₂ in seabed geological structures, offers advantages such as large storage capacity and high stability. Cryogenic hoses are critical for the ship-to-ship transfer of liquid CO₂ from transportation vessels to offshore carbon sequestration platforms, but their design methods and mechanical analysis remain inadequately understood. This study reviews existing cryogenic hose designs, including reinforced corrugated hoses, vacuum-insulated hoses, and composite hoses, to assess their suitability for liquid CO₂ transfer. Based on CO₂’s physicochemical properties, a conceptual composite hose structure is proposed, featuring a double-spring-supported internal composite hose, thermal insulation layer, and outer sheath. Practical recommendations for material selection, corrosion prevention, and monitoring strategies are provided to improve flexibility, pressure resistance, and thermal insulation, enabling reliable long-distance tandem transfer. A mechanical analysis framework is developed to evaluate structural performance under conditions including mechanical loads, thermal stress, and dynamic responses. This manuscript includes an introduction to the background, the methodology for data collection, a review of existing designs, an analysis of CO₂ characteristics, the proposed design methods, the mechanical analysis framework, a discussion of challenges, and the conclusions. Full article

To achieve the sustainability goals set for the European aviation sector, hydrogen-powered solutions are currently being investigated. Storage solutions are of particular interest, with liquid hydrogen tanks posing numerous challenges with regard to the structural integrity of materials at cryogenic temperatures, as well as safety issues because of the high flammability of hydrogen. In this context and in the scope of the Horizon 2020 Clean Aviation Joint Undertaking (CAJU) project H2ELIOS, the gas permeability behavior of prepreg tape carbon fibre reinforced polymer (CFRP) material was studied. Investigations were performed after thermal shock to 20 K (liquid hydrogen immersion) as well as after a uniaxial stress application at 77 K to identify the shift from Fickian behavior after diverse aging conditions. Helium gas permeation was tested at room temperature (RT), and its representativeness to hydrogen permeation in a range of temperatures was considered in the study. The material’s permeation behavior was compared to ideal Fickian diffusion as a means of identifying related permeation barrier function degradation. Finally, it was possible to identify Fickian, near-Fickian, and non-Fickian behaviors and correlate them with the material’s preconditioning. Full article

The decarbonization of the economy is impacting all activities and sectors worldwide. Transport, particularly aircraft transport, is involved in this endeavor; shifting to H2-powered aircraft is one of the identified options for decarbonization, which implies the need for the effective implementation of complex cryogenic LH₂ storage. Modeling tank storage via a Digital Twin (DTwin) is of paramount relevance to facilitate the design process (gains, operating scenarios) and for the extrapolation of experimental measurements on a particular set-up to future tanks with other materials or dimensions. The present paper contributes to this issue, presenting the model under development as part of the H2ELIOS project and the preliminary model results. Full article

The Cryo-PoF project is an R&D project funded by the Italian Insitute for Nuclear Research (INFN) in Milano-Bicocca (Italy). The technology at the basis of the project is Power over Fiber (PoF). By sending laser light through an optical fiber, this technology delivers electrical power to a photovoltaic power converter, in order to power sensors or electrical devices. Among the several advantages this solution can provide, we can underline the spark-free operation when electric fields are present, the removal of noise induced by power lines, the absence of interference with electromagnetic fields, and robustness in hostile environments. R&D for the application of PoF in cryogenic environments started at Fermilab in 2020; for the DUNE Vertical Drift detector, it was needed to operate the Photon Detector System on a high-voltage cathode surface. Cryo-PoF, starting from this project, developed a single-laser input line system to power, at cryogenic temperatures, both an electronic amplifier and Photon Detection devices, tuning their bias by means of the input laser power, without adding ancillary fibers. The results obtained in Milano-Bicocca will be discussed, presenting the tests performed using power photosensors at liquid nitrogen temperature. Full article