The persistent formation and accumulation of gas bubbles during water electrolysis hinder charge transfer and mass transport, thereby creating an additional overpotential that limits efficiency at large scale. In this study, radial porous nickel electrodes (T4-RF, T6-RF) with expanded pores of different thicknesses are fabricated by radial freeze-casting to enhance the transport of bubbles. The electrochemical test results show that compared with the common aligned porous electrode and the improved dual-aligned porous electrode, the radial porous nickel electrode also has a lower Tafel slope and a greater the current density normalized by the ECSA (jECSA). And they exhibit superior hydrogen evolution performance at high current density. Further, the phase-field method is used to numerical simulate bubble transport in pores with different structures, with particular emphasis on the influence of the dilation angle of radial porous electrode on bubble transport. The results show that expanded pores significantly improve bubble transport, and even a small dilation angle can substantially improve electrode performance. And unlike the aligned and dual-aligned porous electrodes, the expanded pores of the radial porous structure reduce the transport resistance related to the electrode thickness, enabling its performance to be further enhanced as the thickness increases.

Thermal interface materials are critical components for ensuring efficient heat dissipation in thermal management systems. The current research focus is to fabricate thermal interface materials (TIMs) that demonstrate high thermal conductivity while at low filler loadings. In this study, an aligned, thermally conductive skeleton was fabricated via the freeze casting method, utilizing carbon nanofibers (CNFs) and nickel (Ni) particles. This skeleton was subsequently infiltrated with silicone rubber (SR) to obtain the polymer composite. Within the aligned skeleton, CNFs and Ni particles are densely packed, with the Ni particles acting as conductive bridges between adjacent CNFs. This bridging effect facilitates a substantial enhancement in the overall thermal conductivity with only a minimal addition of Ni. By combining the skeleton’s microstructure with thermal performance, the effects of key parameters on thermal conductivity were systematically investigated. A maximum thermal conductivity improvement of 64.8% was achieved by hybridizing CNFs with a small amount of Ni (1.09 vol%) compared to the CNF-only counterpart. Furthermore, at a low total loading (8.02 vol% CNFs and 1.09 vol% Ni), the composite achieved a thermal conductivity of 3.30 W/(m·K). This value was 47.2% higher than that of a CNF-only TIM and 36.2% higher than that of a composite prepared by common freezing under the same filler composition. Additionally, the incorporation of Ni enhanced the composite’s thermal stability. Moreover, the composite exhibited a favorable combination of enhanced mechanical strength and excellent elasticity.

Porosity is a fundamental barrier to defect-free laser processing, originating from bubble formation. In light of the current lack of sufficient research in bubble formation, this study employs a 3D multi-phase thermo-fluidic model to investigate keyhole closure and bubble formation mechanisms. Simulations reveal that shutting off the laser during keyhole mode readily induces bubble formation, whereas conduction mode produces no bubbles owing to greater keyhole stability. By increasing the surface tension, the transition to keyhole mode can be delayed, thereby postponing or reducing the risk of bubble formation. Accordingly, the study quantified the transition time distribution within the parameter space of surface tension and recoil pressure, confirming that increasing surface tension or reducing recoil pressure delays the mode transition, thereby suppressing bubble formation. Furthermore, by independently modulating laser process parameters, this study systematically investigates the influence of melt pool geometric parameters on bubble formation mechanisms. The results demonstrate that bubbles tend to form under a smaller laser beam diameter, which is attributed to vortex collisions within the melt pool resulting from a relatively high aspect ratio. As laser heating time increases, the keyhole starts to experience intense fluctuations. During this keyhole mode, the aspect ratio gradually stabilizes, losing its correlation with bubble formation. The influencing parameter shifts to a newly proposed dimensionless parameter, the depth ratio, defined as the ratio of keyhole depth to melt pool depth. This study employs a parameter-morphology-defect correlation analysis to investigate the mechanism of bubble formation induced by keyhole collapse. Furthermore, it proposes a potential approach for effectively suppressing pore defects by introducing qualitative guidance based on real-time monitoring of melt pool dynamics (aspect ratio, depth ratio) to optimize process parameters.

The meniscus-guided 3D-printed microtube formation process is a micro-scale 3D self-assembly manufacturing process. However, the non-uniform dynamic evolution of nanoparticle concentration in the microscale spatially and temporally, coupled with the complex deposition behavior of nanoparticles, leads to the challenge of microtube formation and its internal structure adjustment. In this paper, meniscus-guided 3D printing of microtubes is performed using an aqueous molybdenum trioxide nanoink under different conditions to show how microtube formation and the final internal structure are affected by the nanoparticles’ deposition dynamics. It is found that, under different micropipette pulling speeds or during the printing of microtubes of different final heights, increased collision duration among nanoparticles leads to increased nanoparticle deposition, which changes the microtube wall inclination and decreases the microtube hollowness. Increased nanoink concentration leads to weaker wetting of the nanoink on the substrate and increased nanoparticle deposition, resulting in a straighter outer wall, a more inclined inner wall, and decreased hollowness. Increased substrate temperature leads to increased nanoparticle deposition at the gas-liquid-solid three-phase contact line and enhanced thermophoretic movement along the vertical thermal gradient, which results in a straighter inner wall of the microtubes and increased hollowness. Based on nanoparticle deposition dynamics, a theoretical model describing the internal profile of 3D-printed microtubes is developed, which agrees well with the experimental measurement results. The increment of the suspended nanoparticle collision durations from the microtube top toward its bottom during the microtube formation process contributes to the microtube wall thickness variation and the final microtube structure.

Selective laser melting (SLM) is one of the most widely used additive manufacturing technologies for producing complex metallic components. It has gained significant attention in the field of industrial manufacturing. Balling is a distinct defect phenomenon in SLM that disrupts the formation of uniform melt lines, resulting in rough, discontinuous surface morphologies. However, the factors that affect the formation of balling are unclear. This study presents a three-dimensional multiphase multicomponent lattice Boltzmann method coupled with a liquid-solid phase change model to simulate the spreading and solidification behavior of molten droplets on cold substrates, following particle melting in the selective laser melting process to study the balling phenomenon. The effects of key process parameters, including substrate temperature, surface wettability, and heating duration, are systematically investigated to reveal their impacts in controlling the molten droplet behavior and mitigating the balling phenomenon commonly observed in SLM. Graphics processing unit based parallel computation is employed to enhance simulation efficiency. The results indicate that a higher substrate temperature and increased surface hydrophilicity, combined with appropriate control of the heating duration, can effectively suppress the occurrence of the balling phenomenon. This study provides new insight into controlling droplet dynamics to improve the quality and reliability of the SLM process.

Under high current density conditions, the hydrogen evolution reaction (HER) performance in alkaline electrolysis is significantly affected by gas bubbles. To mitigate the negative impact of bubbles on electrode performance and improve bubble transport efficiency, radial porous nickel electrodes (RPNEs) are fabricated using a bidirectional freeze-casting method. Compared to aligned porous nickel electrodes (APNEs), the electrodes in this study feature a radially expanded pore structure, which facilitates the removal of gas bubbles, resulting in superior HER performance. Furthermore, by adjusting the freezing temperature and slurry concentration, a series of RPNEs with varying pore dilation angles and thicknesses are prepared, and their HER performance is evaluated. The results indicate that for thicker electrodes, increasing the pore dilation angle significantly improves HER performance. Notably, when the freezing temperature is -10 degrees C and the electrode thickness is 1100 mu m, the RPNE exhibits optimal performance, with an overpotential of only 212 mV at 300 mA/cm2 and a Tafel slope of 83.92mV/dec, while also demonstrating excellent stability.

A novel boiling heat transfer enhancement method using the laser-induced cavitation bubble has been proposed. The enhancement of boiling heat transfer by the laser-induced cavitation bubble has been studied through two experiments. One is the single boiling bubble experiment, which is investigated using high-speed photography. It was found that the nucleation wall superheat (Delta T-wall) reduced to 1.65 K, representing a 10.65 K decrease compared to normal nucleation due to the influence of the cavitation bubble. Three typical boiling modes have been identified and proposed: the single bubble mode, the continuous mode, and the film mode. The first boiling bubble induced by the cavitation bubble exhibits unique dynamic characteristics, with a periodic change in its aspect ratio observed, corresponding to the cavitation bubble oscillation under the influence of the Bjerknes force. In addition, its inertia-controlled growth mode becomes more significant, and its duration is also extended. The departure diameter is also larger than the following bubbles. Another experiment focused on pool boiling to evaluate the effectiveness of laser-induced cavitation bubbles in enhancing heat transfer. The results demonstrate that the heat transfer coefficient was significantly improved at both low and high wall superheats, whereas only limited enhancement was observed at intermediate superheats. Although the heat transfer performance is improved, the critical heat flux occurs at a lower wall superheat.

The construction of the lunar base requires the additive manufacturing of lunar regolith bricks using in-situ resources (e.g., lunar regolith and solar energy). Laser or solar powder bed fusion with a large laser spot has the potential to utilize in-situ resources. However, there are difficulties in forming melting tracks with no substrate on the regolith powder bed. This study focused on millimeter-sized spots and processes with no substrate. The continuous deposition of the tracks through wrapping was analyzed through in-situ observation with a highspeed camera. The track discontinuity will occur if the newly formed melting droplet fails to make contact and fuse with the leading edge of the track. The track maintained continuity until the scan velocity increased above a critical value. The critical scan velocity equation of the track discontinuous transition was derived. Finally, a lunar regolith brick measuring 50x50x50 mm was fabricated with track continuity process parameters.

Bubble management in electrocatalysis is very important for reducing overpotential of hydrogen evolution reaction. In this paper, a pore structure model of an aligned porous electrode is established, and the effect of pore size and pore length on bubble transport is studied using the phase field method. The entire transport process of the bubble can be divided into two stages: the motion of bubbles inside pores and the detachment from the pores. The results show that increasing pore size can significantly increase the velocity of the bubble within the pore. Regarding the detachment process of bubble from pores, the movement velocity of the bubble is accelerated due to the different Laplace pressure of the bubble in the inner and outer parts of the pore. However, the pressure gradient decreases with an increase in pore size, resulting in weakened acceleration effect. These two effects are contradictory, and the final effect of the pore size on the bubble transport is related to the pore length. The shorter pore length and smaller pore size strengthen the promotion of the detachment process to bubble transport. In addition, the simulation results provide explanations for electrochemical measurements and bubble visualizations.

To delve deeper into the shapes and positions of the solidification front, as well as the detailed temperature distributions under various solidification conditions, this study employed the commercial software ANSYS FLUENT to conduct a meticulous numerical simulation of the two-dimensional solidification process in freeze casting. As part of the research, the enthalpy-porous media solidification/melting model was chosen as the core theoretical framework, and the accuracy of the numerical calculations was verified by comparing them with locally measured temperature changes from experiments. Subsequently, we further examined the influence mechanisms of factors such as cold source temperature, solid content, mold depth, and mold thermal conductivity on the speed of the solidification front. This is crucial because, in the freeze casting process, the speed of the solidification front directly determines the formation and evolution of macropore structures. The results of the simulation analysis indicate that an increase in mold thermal conductivity, a decrease in cold source temperature, a shallower mold depth, and a higher solid content all lead to a corresponding increase in the movement speed of the solidification front. These simulation outcomes not only provide strong theoretical support for optimizing the process parameters of freeze casting but also aid in achieving more precise control over the microstructure of materials, thus enabling a more efficient and accurate material preparation process.

In the current investigation, the pool boiling heat transfer process of patterned porous surfaces, as well as a smooth surface, in ethanol was examined from an academic perspective. The freeze casting (also known as icetemplating) processes was used to fabricate the structured surfaces. It was discovered that freeze-casted coatings significantly improved the performance of boiling heat transfer in comparison to the smooth surface (SMS). The most remarkable increase in Critical Heat Flux (CHF) was achieved by checkerboard porous surface(CHECKERBOARD), with an improvement of 81.6% relative to that of SMS. The maximum Heat Transfer Coefficient (HTC) enhancement was obtained by full porous surface (FULLY-COVERED), with an HTC value 215.8% higher than that of the SMS. For the semicircular porous surface (SEMICIRCULAR), striped porous surface (STRIPED), annular porous surface (ANNULAR) and checkerboard porous surface(CHECKERBOARD) with 50% coating coverage, CHECKERBOARD demonstrated the best heat transfer performance, with CHF and HTC increased by 32.3% and 48.9%, respectively, compared to the SEMICIRCULAR surface. The mechanism of liquid supply at the CHF of the patterned porous surfaces was investigated through phenomenological observations of the boiling phenomena. A modified model, accounting for the coalesced bubble departure frequency and capillary wicking effects, was proposed for CHF prediction. It is noteworthy that the fluid replenishment considers both vertical and lateral replenishment of porous coatings. The CHF data from this study, along with existing literature, were utilized to validate the model, and the predicted results exhibited good agreement with the experimental data, with errors within & PLUSMN;8%.

The interaction of laser-induced cavitation bubbles with air bubbles attached to the upper surface of a horizontal plate was studied with high-speed photography. On the cavitation bubble side, the dimensionless distance parameter, γ=4.5 for vertical jets from cavitation bubbles as proposed in previous research and the dimensionless parameter, γ=5.8 for oblique upward jets have been established. On the attached air bubble side, the relationship between the dimensionless distance parameter, γa and the four types of morphology (Omega, hemisphere, hemisphere to hat with split, and hemisphere to hat without split) of attached air bubbles, as well as the three modes of jets (initial, multiple, and delay), has been demonstrated. The split of the small bubble from the attached bubble is primarily due to the vertical velocity differences brought about by the multiple collapses of cavitation bubbles and the pulsation of attached bubbles. Subsequent studies on the detachment behavior of attached bubbles determined the ideal dimensionless distance, γa=3.4 for detachment. The surface ripples play a dominant role in promoting the detachment of attached bubbles at greater distances.

In situ Resource Utilization (ISRU) is currently the focus of strong interest for human's deep-space exploration. Water recovery from extraterrestrial planets is an important task for ISRU, because water is the most important resource in the life cycle of astronauts. However, due to the harsh environment in deep-space, the water extraction technology is not mature and still undergoing a slow development. In this work, we develop a novel drilling-based thermal method for water extraction from icy lunar regolith. A full loop of water recovery, including regolith drilling, thermal heating, water evaporation, condensation and collection is investigated in a pilot-scale unit. A CUG-type lunar regolith simulant (LRS) is hydrated with water, and the mixture is frozen at a temperature of -80 degrees C. The icy LRS is drilled at the cryogenic condition, and then the hollow drill rod is thermally heated to drive water to evaporate. The water vapor is transported in a closed loop to a tapered condenser where the vapor condenses to liquid. Both the regolith drilling and the water extraction processes are investigated under varying working conditions. The results show that the power consumption of the LRS drilling is dependent on both the cryogenic condition and the initial water content in the LRS. The average power consumption increases from 15 W to 40 W when the water content increases from 2% to 6%. The drilling-based thermal method is effective for water recovery from icy LRS. Over 80% of water in the LRS sample excavated into the drill's chamber is recovered. The overall water collection rate reaches 0.75 ml/min with the initial water content of 6%. The energy efficiency is about 8.6 W h/g. However, as the water content is reduced to about 2%, the water collection rate decreases to only 0.1-0.3 ml/min.

为了研究3D喷墨打印中液滴在壁面的铺展、凝固现象与机理,基于格子玻尔兹曼方法(Lattice Boltzmann method,LBM),建立了三维多组分相变模型,模拟计算了单液滴在低We数条件下与低温基板碰撞后的演变过程.在模拟过程中考虑了壁温、壁面润湿性等因素对于液滴的铺展、凝固的影响.模拟结果表明,在非润湿性壁面,液滴铺展产生震荡阻尼现象,通过改变壁温控制液滴凝固速度可以达到阻碍或者促进液滴铺展;而在润湿性壁面,凝固会阻碍液滴铺展,液滴最终铺展因子随接触角减小而降低,并且与壁温成正比关系.此外,壁温在低于一定范围后才会对液滴形貌(铺展因子、接触角)造成明显影响.

To improve the thermal conductivity of thermal interface materials (TIM), we constructed a dual-aligned scaffold, i.e., both aligned carbon nanofiber (CNFs) in the microscopic structures and directional microporous channels, serving as the heat conduction paths of TIMs. The dual-aligned scaffold was firstly fabricated by combining magnetic alignment and conventional freeze-casting, and the composites of the dual-aligned scaffold and silicone rubber (D-AS/SR) were then obtained by immersing the dual-aligned scaffold into the silicone rubber with vacuum assistance. Through this method, not only the high axial thermal conductivity of CNFs can be fully utilized, but also a long-range continuous and parallel structure can be fabricated as the heat conduction paths of TIMs. The results show that the thermal conductivity of the D-AS/SR composites reached 4.66 W/(m center dot K) at 7.73 vol% CNFs, which is 1.5 times higher than that of the composites constructed by conventional freezing casting and 25 times higher than that of pure silicone rubber. Additionally, the compressive strength of the D-AS/SR composites was greatly improved, whereas the electrical insulation of the composites was significantly reduced, which limited the use of D-AS/SR composites in conditions requiring good electrical insulation.

The efficiency of water electrolysis is significantly affected by the bubbles on the surface and inside the electrode. To enhance the gas–liquid transfer within the porous electrodes, we developed an innovative design termed dual-aligned porous electrode (D-APE), achieved by integrating magnetic alignment with freeze casting techniques. This paper investigates the hydrogen evolution performance of porous electrodes prepared using four different methods: evaporation, magnetic-aligned evaporation, freeze casting, and dual-aligned methods. The findings demonstrate that the magnetic-aligned process effectively alters the electrode structure, resulting in improved hydrogen evolution performance. Notably, among all the examined electrodes, the D-APE exhibits the highest hydrogen evolution performance, with further enhancements observed with prolonged the time of magnetic alignment. Furthermore, a comparison is made between electrodes prepared using the freeze casting method and the dual-aligned method at various thickness. The results show that the thinner D-APE exhibits excellent hydrogen evolution performance at high current density. Moreover, the D-APE demonstrates significantly improved material utilization rates compared to the conventional freeze casting method, offering promising prospects for enhancing the efficiency of water electrolysis.

The formation of continuous melt tracks through a low-power beam for powder bed fusion is hindered by the inadequate thermal conductivity exhibited by a loose powder bed.To increase the depth of energy penetration during the solar convergent molten lunar soil printing process,an in-situ observation study of the melt pool formation process was conducted when a large-sized spot melted a simulated lunar soil powder bed.To simulate the concentrating spot of sunlight,the laser spot was expanded to millimeter scale and impacted directly on the surface of a thick powder bed lacking a substrate.Using a technique of high-speed imaging,the development of melting droplets was observed.The partially melted surface powder was discovered to exhibit a large-scale interparticle cooperation referred to as the"wrapping"process.In this process,the powder bed's surface layer was rolled up,separated from the powder bed,and joined to the molten droplet,resulting in a growth that is discontinuous.The growth law of melting droplet size was investigated and compared with experimental results based on the energy conservation relationship between the spot and the heating of the powder bed.The results indicate that melt droplets generated by a low-power,large-spot laser cannot extend beyond the range of the spot.The higher the power density,the less complete the powder melting while a wrapping process occurs,which increases the energy efficiency of this operation.The utilization of the wrapping mechanism effectively overcomes the constraint posed by the low thermal conductivity,particularly in the context of lunar soil powder bed fusion technology.This mechanism enables the direct printing of melting tracks on substantial powder beds.

Aligned porous electrodes with different pore sizes and thicknesses are prepared by freezing casting method, and the effect of the electrode thickness and pore size on hydrogen evolution reaction (HER) performance and bubble removal capability are experimentally studied. The results show that the pore size and thickness of the aligned porous electrodes have a significant impact on the HER performance by affecting the electrochemical active surface area (ECSA) and bubble transport process. The influence of pore sizes and electrode thicknesses on HER performance are different with current density. In the region of low current density, the effect of electrode thickness on electrochemical performance is more significant than that of pore size. While at high current density pore size becomes a limiting factor for electrochemical performance. Additionally, the Δζγ is proposed to evaluate the bubble removal capability, and a small Δζγ indicates the good bubble removal efficiency.

Establishing an energy supply on the Moon is one tremendous challenge in research on the lunar environment due to limitations regarding the carrying capacity and cost of traditional means of rocket. In this paper, a lunar energy storage and conversion system based on in-situ resource utilization (LES-ISRU) is demonstrated, and its operating performance is investigated. The proposed system consists of three subsystems: a high-magnification solar energy concentrating device, an energy storage system based on the in-situ utilization of lunar regolith, and a thermoelectric conversion device. The experimental results show that the in-situ energy storage system can store about 394 kJ of thermal energy for power supply purposes, and the heat supply can be sustained for about 14 h without solar energy input. The thermoelectric conversion device takes full advantage of a Stirling generator to generate power up to about 8.3 W during the Moon daytime. The thermal energy stored by the in-situ energy storage system can realize a continuous power supply for 51 min at night on the Moon. The new system developed in this study can efficiently collect and transform solar energy using extraterrestrial in-situ resources, providing a sustainable power and heat replenishment solution for future deep-space missions.

Future lunar base additive manufacturing is accelerated by ground-based technology. Naturally, loosely packed lunar regolith must be directly treated into a solid surface on the first layer of lunar base construction. Solar powder bed fusion (Solar PBF), with huge spot sizes and low energy densities, is the most efficient energy and material usage method on the moon. However, the powder bed's low heat conductivity hinders energy penetration. This investigation used a millimeter-scale laser beam to recreate the solar PBF spot. The beam was directed at the powder bed without substrate. In-situ observation revealed a wrapping mechanism works for multiple parameters. The wrapping process was primarily observed with lunar regolith simulant CUG-1A, and SS316L was used for comparison under a similar spot and no substrate. The periodic wrapping helps to form deeper melt tracks. The wrapping process has the potential to produce a substrate on a loose powder bed directly.