Porous media are extensively employed in gas-liquid separation processes due to their remarkable capillary effects arising from the pores at the micro/nanoscale. However, the coupling between inertial and transverse capillary forces and their respective influences on bubble breakthrough remain insufficiently understood. We designed porous structures with imposed transverse capillary pressures by adding transverse pores to rectangular channels and used an equivalent transverse pressure method to experimentally quantify how transverse capillary forces influence bubble dynamics, the bubble point pressure, and the critical flow rate. The gas-liquid flow patterns were characterized using high-speed imaging and microscopic particle image velocimetry. Compared with pores without imposed transverse pressure, increasing the transverse capillary number to 0.71 for isopropanol and 0.97 for HFE7500, corresponding to an imposed transverse pressure of 600 Pa, leads to notable increases in the normalized bubble point pressure and critical flow rate for a main pore size of 100 mu m, reaching 18.7% and 7.5% for isopropanol and 27.5% and 13.4% for HFE7500, respectively. This enhancement is governed by a synergistic competition mechanism. Transverse pore structures increase the bubble point pressure via contact-line pinning, whereas sufficiently large transverse pressure partially offsets the pinning effect and further strengthens interfacial wetting. These results elucidate the interplay between inertia and transverse capillarity in porous media and provide practical guidance for optimizing the design of capillary-wetted porous structures for efficient gas-liquid separation.

Cryogenic liquid propellants are crucial green solutions for deep-space exploration, but nucleate boiling in on-orbit tanks can threaten long-term storage stability. Establishing gravity scaling laws for bubble growth and wall heat transfer can guide tank insulation design and reduce heat leakage. Nevertheless, the lack of accessible microgravity platforms for cryogenic liquids has constrained cryogenic boiling experiments under microgravity. In this study, a magnetically compensated microgravity testing system for liquid oxygen was established, and an in-house microscopic imaging module with a compensation ring was developed to enable visualization under strong magnetic fields at cryogenic temperatures. Single-bubble pool boiling experiments using liquid oxygen were conducted under different reduced-gravity levels. The growth curves of liquid oxygen bubbles under microgravity revealed a transition from rapid growth to slower growth. The time exponent in the relation D proportional to tn was evaluated, and n = 1/3 was found to best describe the time dependence of bubble diameter under microgravity. The dimensionless bubble diameter D/(alt)1/3 follows a gravity scaling law with a power of-1. Boiling transitions from a buoyancy-dominated regime to a surface-tension-dominated regime as gravity decreases to 0.033 g0, and the heat flux exhibits a jump at this gravity level for all tested wall superheats.

Environment humidity significantly affects the anti-icing performance of a superhydrophobic surface in practical applications. This study experimentally investigates the impingement and freezing of droplets on plane and micro-pillared highly hydrophobic surfaces under different humidity conditions. Results demonstrate that the micro-pillared surface exhibits notable frost suppression and anti-icing benefits at low humidity (when supersaturation degree, SSD, is 1.49), with a frost coverage 26.6% lower than that on the plane surface. Meanwhile, the micro-pillared surface reduces the maximum spreading factor of impacting droplets by up to 39.7%, shortens the stabilization time by 34.3%, and increases the freezing time by 12-27 times prior to frost formation. However, under high humidity (SSD = 6.69), these advantages diminish rapidly. The frost-free state on microstructured surfaces quickly disappears, and then the spreading behavior of droplets becomes similar to that on the plane surface, resulting in no anti-icing benefit. The study further quantifies droplet dynamics on surfaces with different frost conditions, and develops a theoretical model consistent with the experimental data. These findings clarify the time-limited and humidity-dependent anti-icing effectiveness of micro-structured surfaces, providing quantitative insights for practical applications.

Prolonged exposure to space heat fluxes during missions can trigger nucleate boiling and generate detached vapor bubbles in cryogenic propellant tanks, which can disrupt fuel intake and engine ignition under microgravity. Understanding bubble detachment dynamics in cryogenic boiling under microgravity can help improve the reliability of propellant storage. However, such experimental data remain scarce, owing to the lack of long-duration ground-based microgravity platforms for cryogenic liquids. This study created a magnetically compensated microgravity environment to experimentally investigate the detachment behavior of single bubbles during liquid oxygen pool boiling. The variation laws of bubble detachment diameter and frequency were explored under different gravity, wall superheat, liquid subcooling, and pressure. The critical Bond number at bubble detachment remains constant regardless of gravity. The detachment diameter scales with gravity to the power of-1/2. An empirical correlation for bubble detachment frequency incorporating the four control variables was established. The frequency scales with gravity to the power of 0.91.

Computational modeling of multiphase flow systems is crucial across various fields, including chemical engineering, energy, environmental science and aerospace industry, enabling cost-effective design and analysis. However, accurate simulation, prediction, control, and optimization remain difficult due to the high-dimensional, chaotic behavior and dynamic interfaces of multiphase flows. Artificial intelligence (AI), particularly deep learning, physics constrained learning, generative models, and reinforcement learning offer promising tools to overcome these challenges. This review presents the current landscape of AI in multiphase flow research. It highlights AI-enhanced numerical solvers for interface dynamics, including explicit interface tracking and implicit interface capturing, as well as intelligent sparse grid processing. AI-extended simulation implementations are also explored, with an emphasis on generative models such as generative adversarial networks (GANs), variational autoencoders (VAEs) and large language models (LLM)-driven agents that synthesize physically consistent samples and automate complex modeling and simulation workflows. Moreover, AI-oriented control and optimization methods – such as Bayesian optimization (BO), reinforcement learning (RL), and automatic differentiation (AD) – are analyzed for optimizing mixing, stability, and phase distribution, particularly in industrial settings that require real-time, high-performance solutions. Finally, we provide a critical assessment of the challenges and opportunities of learning-based algorithms, emphasizing dataset normalization and model-design regularization to enhance generalization. Overall, this review bridges multiphase-flow mechanics, data science, AI, and computational chemical engineering, and documents an ongoing digital and intelligent progression from fully physics-based equation solving approaches to a physics-coupled, and data-driven integrated computational framework.

Cryogenic quenching is a critical step for the cryogenic systems prior to operation. Despite its importance, there is still significant room for improvement in the efficiency of cryogenic quenching across various applications. This study presents a comprehensive investigation into the mechanism by which heat transfer is enhanced during cooling on aluminum surfaces through the nanoscale boehmite structures. The morphology of the nanolayers formed on aluminum surfaces through boiling water treatment (BWT) is characterized. Following BWT, the boehmite layer is observed to consist of numerous crosslinked nanosheets and dispersed microclusters. Furthermore, the detailed impact of boehmite nanostructure on quenching was investigated by constructing experimental setups utilizing liquid nitrogen as the working fluid. The results show that the Leidenfrost temperature increases by 38 K and the critical heat flux improves by 90 % in quenching when the boehmite nanostructures are present, compared to a plain aluminum alloy surface. Additionally, in pipeline quenching, the time required is reduced to 60 % to 85 % of that needed for a plain aluminum alloy surface across varying Reynolds numbers (Re), with a marked improvement in cooling efficiency at low Re.

Cryogenic propellants, as green fuels, are the first choice for current rockets and spacecraft. Analyzing the forces on growing vapor bubbles in cryogenic liquids under microgravity can help address boiling issues in on-orbit storage tanks and improve their cryogenic insulation abilities. However, due to the lack of long-term ground-based microgravity methods for cryogenic liquids, related research remains limited, and the contradiction between the low surface tension of cryogenic liquids and the dominant role of surface tension in microgravity leaves the bubble force balance poorly understood, with Marangoni effects still overlooked. In this study, a magnetically compensated microgravity apparatus for liquid oxygen was established. The force balance during bubble growth was examined. The concept of the isothermal surface tension force was introduced. It was found that the relative magnitudes of the forces acting during bubble growth remain unchanged across different gravity levels. The Reynolds number reaches its maximum when the bubble diameter becomes 38% of its maximum value across all gravities, and the evolution of vapor bubbles in liquid oxygen is laminar. At lower gravity levels, bubble growth is influenced by the isothermal surface tension for a longer duration, but the buoyancy force ultimately becomes the primary force when the bubble detaches.

Performance degradation of fibrous porous insulation materials in liquefied natural gas (LNG) cargo containment systems (CCS) induced by water vapor intrusion severely endangers the operational safety of LNG carriers. Therefore, research on gas displacement in such materials is a key engineering priority. This study experimentally investigates the forced convection and mass transfer characteristics of fiberglass porous media in LNG CCS, examining how four key parameters - inlet pressure, inlet position, inlet temperature, and porous media bulk density - influence the laws of forced convection and mass transfer as well as the distribution of mass transfer lag zones. A full-scale experimental platform was established to conduct parameter-controlled comparative experiments, with dynamic variation data for temperature, pressure, and dew-point temperatures systematically analyzed. Meanwhile, a quantitative definition method for mass transfer lag zones was proposed to clarify their evolution mechanisms. The results indicate that increasing inlet pressure from 300 Pa to 700 Pa reduces purging time by 42.1%, while increasing porous media bulk density from 32 kg/m3 to 64 kg/m3 effectively eliminates vertical stratification of moisture displacement. A high inlet temperature (95 degrees C) increases purging time by 11.4% compared with the baseline (35 degrees C). Mass transfer lag zones are primarily concentrated in the top region of the porous media, and their formation can be effectively suppressed by optimizing inlet parameters and increasing media bulk density. The findings of this study provide a solid experimental basis and technical support for optimizing the gas-displacement process in LNG containment systems and enhancing operational safety.

Capillary-driven, selective gas-liquid transport based on porous structures is a crucial method for achieving phase separation under microgravity conditions. Previous studies have focused primarily on woven screen-type porous media with fixed geometries that limit the optimization of flow performance. This study proposes a novel, customizable metal porous structure fabricated via laser powder bed fusion. An experimental liquid transport system using liquid nitrogen as the working fluid was established to investigate the effects of micropillar spacing and pressurant gas on bubble-point pressure and liquid acquisition performance. It was found that during the pressurization experiments, as the pressure within the test chamber increased, the total pressure loss across the channel and the rewarmed gas flow rate continuously increased. Upon reaching a critical pressure, the total pressure loss dropped sharply, indicating the failure of phase separation. Both the critical bubble-point pressure of the porous structure and the critical liquid-acquisition flow rate of the channel decreased with increasing micropillar spacing. Specifically, when the spacing increased from 50 mu m to 110 mu m, the critical bubble point pressure decreased by 27.4 %, and the critical flow rate decreased by 29.1 %. Compared to autogenous pressurization, using a non-condensable gas for pressurization increased the bubble point pressure of the porous structure by approximately 9.4 % and raised the critical liquid acquisition flow rate of the channel by about 13

The investigation of the evolution of the cryogenic gas-liquid interface is crucial for the storage and management of cryogenic propellants in on-orbit tanks. Studying the non-isothermal growth of isolated bubbles under normal gravity provides a foundation for understanding the distribution of the cryogenic gas-liquid interface. However, a low boiling point, low surface tension coefficient, and low viscosity lead to bubble behaviors that differ from those of room-temperature liquids, increasing the difficulties in investigating cryogenic behaviors, and the related studies are limited. In this work, a visualization experimental platform for liquid oxygen single bubble pool boiling was established. Liquid oxygen was produced by cooling oxygen with liquid nitrogen, and an optical visualization system was designed to observe bubble behavior. The effects of wall superheat, liquid subcooling, and pressure on bubble growth rate and detachment parameters were investigated. Results indicate that higher wall superheat reduces the waiting time for bubble growth, shortens the bubble growth cycle, and increases the bubble diameter. During the initial growth stage, the bubble diameter follows a D similar to 41/2 trend, transitioning to D similar to 41/3 in the later stage. Bubble growth slows with increasing liquid subcooling, while higher pressure leads to smaller detachment diameters and higher detachment frequencies. The findings compensate for the scarcity of data on the growth of isolated bubbles in cryogenic liquids, and provide important guidance for the development of on-orbit storage and transport technology.

In the study of orbit transfer in deep-space missions， variations in overload conditions induce changes in the interface and thermodynamic behavior of cryogenic propellants inside a cryogenic tank. In this study， a drop-tower experimental platform for liquid oxygen （LOX） reorientation was constructed. The variation in the LOX interface was visualized， and the vapor-phase temperature and pressure were measured. During the drop-tower process， the overload environment transitioned from normal gravity to microgravity. The LOX propagated along the inner wall and formed a liquid layer. The motion of this liquid layer was decoupled from that of the bulk liquid， and the interface center oscillated continuously. Owing to the ascend of the contact line， the gas-liquid interface area increased and LOX evaporated continuously at the contact line. The emergence of the liquid layer resulted in a pressurization rate of 3227 Pa/s at the first oscillation of the contact line， which is approximately 1.8 times higher than the final stabilized pressurization rate. During the entire 2.5 s reorientation process， the pressure in the gas-phase region increased by 4 217 Pa. The temperature variation at 15.2 mm from the interface was affected not only by heat transfer from the solid wall but also by disturbances from the low-temperature gas flow induced by interface oscillations. Additionally， the temperature at this measurement point increased by only 0.351 K during the entire reorientation process. This study provides guidance for the configuration and design of cryogenic-propellant management devices.

Cryogenic propellants often experience reduced-gravity levels during orbital transfer and deep exploration, which leads to uncertainty in their interface structure and equilibrium height. In addition, unexpected thermal leakage can cause evaporation at the three-phase contact line, further complicating the prediction of the interface location. In this research, a cryogenic testing apparatus based on a magnetic compensation platform was developed to investigate the capillary rise equilibrium height on a plate and in the corner of liquid oxygen (LOX) in reduced gravity. A periscope-like visual system is employed to visualize and record the interface evolution in the magnetic compensation region. It is found that wall overheat leads to a decrease in the steady-state contact angle, which differs from the static contact angle. Based on the experimental results of LOX interface at different wall overheat conditions, the relationship between wall superheat and the steady-state contact angle applicable to cryogenic propellants is established. Due to the imperfect internal corner caused by industrial machining, the equilibrium height could only reach a finite value. The operation pressure has little effect on the equilibrium height. As the wall overheat and gravity level increase, the capillary rise equilibrium height decreases. Moreover, dimensionless correlations are developed to predict the capillary rise equilibrium height of LOX on the plate and in a corner. The present study is of significance for predicting the propellant interface height in reduced gravity conditions to design and construct propellant management devices.

Objective:To support complex aerospace missions including manned spaceflight,Mars exploration and space station construction,it is critical to conduct deep-space exploration research for solar-system planets and even extrasolar space.High-specific-impulse cryogenic fluids such as liquid hydrogen-liquid oxygen(LH2-LOX)and liquid oxygen-liquid methane(LOX-LCH4)are primary propellant for deep-space missions.During flight,cryogenic fluids in propellant tanks undergo gravity changes,leading to interface relocation.Owing to low surface tension and viscosity,their interfaces easily deform and break up,resulting in complicated flow behaviors.Meanwhile,increased interfacial and contact areas enhance heat transfer,triggering intense phase change due to low boiling points and latent heats,making thermal states unpredictable.This study aims to reveal the evolution of interface dynamics and thermal behavior during relocation,which is essential for the design of on-orbit propellant management devices. Methods:In this study,a drop-tower experimental platform for LOX reorientation was constructed.The setup,housed in a stainless-steel vacuum chamber with sapphire windows for optical access,uses multilayer insulation and combined LED lighting to enable high-speed visualization.A liquid nitrogen cooling circuit connected via copper braids provides stable precooling and suppresses boiling.The test cell,made of sapphire with high pressure resistance,is instrumented with multiple temperature sensors.LOX is condensed and stabilized at a height of 18.5 mm until thermal drift is below 0.000 1 K/s.The system is then installed in the drop tower tube,adjusted for center-of-mass,and released from 83 m to generate nearly 3.5 s of microgravity at approximately 0.004 4 g₀.High-speed images are recorded and processed using a MATLAB edge-detection algorithm to analyze interface evolution during the relocation process.Meanwhile,the vapor-phase temperature and pressure were measured.During the drop-tower process,the overload environment transitioned from normal gravity to microgravity. Results and Discussions:The LOX propagated along the inner wall and formed a liquid layer.The motion of this liquid layer was decoupled from that of the bulk liquid,and the interface center oscillated continuously.Owing to the ascend of the contact line,the gas-liquid interface area increased,and LOX evaporated continuously at the contact line.The emergence of the liquid layer resulted in a pressurization rate of 3 227 Pa/s at the first oscillation of the contact line,which is approximately 1.8 times higher than the final stabilized pressurization rate.During the entire 2.5 s reorientation process,the pressure in the gas-phase region increased by 4 217 Pa.The temperature variation at 15.2 mm from the interface was affected by not only heat transfer from the solid wall but also disturbances from the low-temperature gas flow induced by interface oscillations.Additionally,the temperature at this measurement point increased by only 0.351 K during the entire reorientation process. Conclusions:This study concludes that the evolution of the LOX interface,temperature and pressure in the ullage in the interface reorientation process.This experiment provides the cryogenic fluid data for simulation validation and guidance for the configuration and design of cryogenic-propellant management devices.

The separation of gas and liquid cryogenic propellants is essential for on-orbit spacecraft refueling, a process that typically involves heat and mass transfer due to the complex thermal conditions in space. This study numerically investigates the gas breakthrough in porous array structures at the pore scale to reveal the mechanism of nonisothermal phase separation in porous media. Liquid oxygen and oxygen vapor were used as working fluids. The gas-liquid interface is captured using the phase-field method. Marangoni flow, which is caused by variations in surface tension, has been taken into account. The flow field, temperature field, bubble growth process, transit time, and critical bubble point pressure are studied with different array pitch, liquid subcooling, and gas superheat. Due to interfacial heat and mass transfer, the bubble size and transit time decrease as the liquid subcooling increases. The bubble increases in size and breaks up into daughter bubbles with the overheated gas. As the gas superheat increases, the critical pressure first increases and then decreases, with 2.5 K as the dividing point. This trend is governed by the interplay of surface tension-temperature dependence, evaporation-driven bubble growth at the gas-liquid interface, and breakup behavior under superheated conditions.

Magnetic compensation can help achieve long-term ground-based microgravity environments for cryogenic fluids. However, existing studies often create compensated-gravity regions too small to replicate fluid behaviors in space conditions. This study developed a magnetically compensated system capable of generating a low-gravity region with a volume of 0.88 L for liquid oxygen. Single-bubble dynamics were used to evaluate gravity levels as low as 0.033 g 0 . The system allows visualization of microscopic fluid behavior with up to 6.13 & times; magnification and an adjustable field of view ranging from 1 to 200 mm.

Enhancing cryogenic quenching efficiency is critical for the thermal management and operational reliability of aerospace propulsion systems. In this study, hierarchical micro/nano composite surfaces were fabricated by depositing boehmite nanostructures onto microgrooved substrates via boiling water treatment. Quenching experiments were conducted under atmospheric pressure using LN2 on surfaces with axial and circumferential grooves of 100 mu m, 300 mu m, and 500 mu m widths. High-speed visualization and transient temperature measurements were employed to characterize the dynamic boiling behavior and heat transfer characteristics throughout the quenching process. The results show that microgrooved surfaces reduced the quenching duration by 33%-47% and increased the average heat flux by 20%-60% compared with untreated aluminum surfaces. The addition of boehmite nanostructures further enhanced the heat transfer performance by 10%-20%. Hierarchical micro/nano surfaces increased the Leidenfrost point by up to 30% and nearly tripled the critical heat flux, with CHF exhibiting clear dependence on groove width and groove orientation. Visualization results reveal that axial grooves facilitate directional vapor escape and liquid replenishment, whereas circumferential grooves restrict vapor transport and reduce rewetting efficiency. Meanwhile, nanoporous boehmite structures enhance capillary-driven liquid spreading and accelerate vapor film destabilization during transition boiling. The coupled effects of groove geometry and nanoscale wettability on transient cryogenic boiling are clarified through combined visualization and heat transfer analysis. These findings provide new insights into the regulation of vapor transport and liquid rewetting on hierarchical surfaces for cryogenic thermal management applications.

In reusable launch vehicles, the sloshing of cryogenic propellants under external excitation poses significant challenges to tank pressure control and thermal management. In this study, a three-dimensional (3-D) numerical model based on the volume of fluid (VOF) method is developed to investigate the non-isothermal sloshing characteristics in a helium-pressurized liquid oxygen (LOX) tank. The model accounts for vapor-liquid phase change, species transfer, and fluid-solid conjugate heat transfer. The effects of sloshing amplitude and frequency on the temperature field, helium distribution, pressure evolution, and interfacial dynamics within the ullage are analyzed. Results indicate that increased sloshing intensity promotes vapor cooling and enhances helium diffusion within the ullage, while increasing helium accumulation near the interface. Intensified sloshing enlarges the interfacial area and strengthens vapor-liquid mixing, thereby accelerating the decay of vapor pressure. Moreover, the relationship between sloshing intensity and frequency is not monotonic. As the sloshing frequency approaches the first natural frequency of the tank (1.15 Hz), fluid motion is significantly amplified, leading to a rapid pressure drop with an average depressurization rate of 933 Pa/s over the initial 15 s, approximately 47 times that observed at 0.6 Hz. Under resonant conditions, the formation of convective vortices disrupts thermal stratification and promotes helium transport toward the interface, resulting in a subsequent recovery of vapor pressure. Notably, under high-intensity sloshing, excitation in the x-direction induces substantial sloshing in the z-direction, giving rise to asymmetric fluid behavior. Therefore, in deep-space applications, resonance should be avoided to ensure the stability of propellant management and spacecraft attitude control.

Preventing microscale ice accretion on critical surfaces is essential for enhancing the reliability of aerospace equipment, power transmission systems, and precision instruments. In this study, aiming to construct an ice-free zone at the submillimeter scale, we focus on the dynamics of the vapor diffusion layer above microstructured surfaces. The effects of key geometrical parameters — including array height, spacing (pitch) ratio, and structural inclination angle — on mass transfer and vapor diffusion are systematically investigated. By decoupling the vapor condensation and icing process into two distinct stages: the nucleation competition preceding icing and the hygroscopic ice transformation following icing, the vapor flux aggregation mechanism at preferential nucleation sites and the mechanism sustaining the steady-state ice-free region are elucidated separately. Dimensionless regional vapor flux ratios are introduced to quantify the driving force of ice hygroscopicity and the ability to maintain the steady-state ice-free region. Numerical simulations reveal that, under fixed environmental conditions, the pitch ratio and height are the dominant influencing factors: reducing the pitch ratio to 2 increases the proportion of vapor flux concentrated at the structure tops to 45%, while increasing the height primarily enhances the sidewalls’ vapor flux trapping capability. Comparison between 2D and 3D models demonstrates that, for identical geometries, the array arrangement form also significantly impacts vapor flux aggregation and concentration field distribution; corresponding correction coefficients for the 3D model relative to the 2D model are provided. Furthermore, a phase diagram of frost coverage is developed, revealing that a 10% increase in ambient humidity leads to a substantial rise in frost coverage and an exponential decay of the critical pitch ratio with increasing humidity. This study elucidates the synergistic regulation of microstructure geometry optimization and environmental parameters, providing a theoretical basis for the design of anti-icing surface engineering.

The interfacial movement and thermodynamic behavior of the cryogenic propellant during the reorientation process is crucial for their on-orbit storage and management systems. However, the low surface tension and viscosity of the cryogenic fluid, together with its low saturation temperature, results in a complex evolution of the interface movement under step changes in gravity. In this work, a cryogenic drop tower apparatus was developed to examine the evolution of interface position, temperature, and pressure. The numerical simulations were also performed to analyze the related phenomenon based on the open-source OpenFoam platform. The results show that the interface center undergoes damped oscillations spanning three complete cycles within 2.5 s. Furthermore, a thin liquid layer forms during the first recession of the contact line, with its motion decoupled from that of the oscillating liquid bulk. The formation of the liquid layer results from significant stress torque at the evaporation-condensation transition, which thins its lower edge. During the secondary rise of the contact line, evaporation dominates the interfacial phase change due to prolonged heat exchange with the wall, preventing liquid-layer formation during the subsequent retreat. Regarding thermodynamic behavior, gas temperature remains unaffected by interface fluctuations at distances exceeding the maximum height of the contact line. The gas temperature continues to rise at a rate of 0.19 K/s beyond 34.8 mm due to heat conduction through the wall. The maximum pressurization rate induced by liquid layer reaches 3227 Pa/s. The present study could provide guidance for the design of on-orbit management for cryogenic propellants.

The transmission of respiratory infectious diseases in transportation cabin has always been a serious challenge. To reduce transmission of aerosol in aircraft cabin, we quantified the aerosol concentration in the passenger breathing area, that measured under different working conditions with air curtain outlet flow rates of 0, 0.08, 0.16 and 0.24 m3/s. The results show that the particle concentrations were reduced up to 53.2