The thermal conductivity of graphene materials rapidly decreases with the increase of thickness, seriously hindering its application potential in high heat flow scenarios. Here, a novel strategy for synthesizing expandable-thickness graphene block (GPB) with high thermal conductivity is proposed via multiscale blending and multistage pressure induction (MBP). The reduction of the in-plane thermal conductivity with the increase of thickness of the proposed GPB-MBP is lowered by more than 94% compared to existing graphene materials, and the maximum thickness of GPB-MBP reaches 12.1 mm, which is more than 10 times that of the existing graphene materials. Compared with the thickest existing graphene material of 1.05 mm, the in-plane thermal conductivity and cross-plane thermal conductivity of GPB-MBP are 4.7-7.4 times and 6.2-6.6 times higher, respectively. The maximum thermal diffusion ability of GPB-MBP reaches 6.3 W/K, which is 8-53 times higher than that of existing graphene materials. Furthermore, the proportional relationship between in-plane thermal conductivity and the logarithm of length was discovered on macroscopic graphene materials for the first time. The new strategy for synthesizing expandable-thickness GPB offers a new approach for high-heat-flux thermal management.

High efficiency compact reactors for carbon dioxide (CO2) hydrogenation to methanol have the advantages of high heat and mass transfer efficiency, good temperature control and safety in industrial applications, but the mechanism of influence of various factors on the reaction performance of direct CO2 hydrogenation to methanol in microchannel reactor is unclear. In this study, the reaction kinetic model, flow and heat transfer numerical model of syngas and cooling medium were established for the direct methanol synthesis process of CO2 hydrogenation in microchannel reactors. Model validation indicates a strong correlation with 94 experimental data, with an error of less than 15 %. Both temperature and pressure significantly enhance CO2 conversion, while methanol selectivity decreases with rising temperature but increases with higher pressure. The interlaced reinforcement structure arrangement in the microchannel can reduce the temperature rise to 2.43 K. Increasing the size of the reinforcement structure will enhance the heat dissipation effect, but it will cause a relatively large pressure drop. Compared with the traditional reactors, the simulated microchannel reactor can increase the annual methanol output per unit volume by no less than 180 %, reaching 11.3 kT/(year & sdot;m3). The novelty lies in the numerical model development and structure optimization of microchannel reactor for offshore carbon dioxide (CO2) hydrogenation system. The research results provide an efficient and feasible technical solution for converting carbon dioxide to methanol at sea.

Offshore green methanol synthesis by CO2 hydrogenation is a new alternative for offshore wind power transport, but the influence of locations on offshore green methanol system viability remains unclear. Moreover, wind variations, system configurations and operation strategy can all influence the performance of green methanol production at different locations. In this study, an economic model for the full offshore green methanol value chain, covering wind power generation, hydrogen production, methanol synthesis and purification is established, and the influence of wind variability, system configurations and operational strategies across different locations on economic viability is quantitatively investigated. Compared to existing literature, the production cost of offshore green methanol production is 10 %-20 % lower respectively in shallow-water and deep-water regions in South China sea due to lower equipment investment costs driven by ongoing development, more optimized wind utilization strategies, and better wind resources in the South China sea. The future economic viability of offshore green methanol synthesis process is projected based on equipment investment trends in the future, and green methanol will be economically viable in 2030 in both shallow and deep waters.

The dual-pack air-cycle refrigeration system (ACS) is responsible for providing cooling to the personnel environment in most civil aircraft. During flight tests of a newly developed civil aircraft, the dual-pack air-cycle refrigeration system (ACS) exhibits significant divergence in the operating states of the two refrigeration packs. To address this issue, a dynamic system model of the dual-pack ACS was established based on a proposed system framework with improved dynamic pressure nodes, where dynamic outlet temperatures and pressures of every component can be explicitly solved. Besides for compressor outlet temperature, the steady-state deviations of temperatures, pressures, and mass flow rates are within 4.4 K, 2.1%, and 5.1%, respectively. A temperature control method that directly utilizes the readings from the two mixer temperature sensors was introduced and optimized based on the established model. Comparisons show that the convergence of the mixer outlet temperatures was accelerated, the maximum deviation was reduced, and the penalty metrics were decreased by 29.23% ∼ 50.16%. The control method can handle operating conditions with different initial TCV openings and imbalanced ram air pressures. Under the presence of TCV stepper motor step loss, the sensitivity and convergence speed are severely affected, but the temperature control deviation can still be maintained below 4 °C for most of the time during the flight.

Efficient thermal management of airborne electronics is critical for aerospace missions involving high maneuverability and power density. While cascaded phase change materials (PCMs) show theoretical promise, existing research is largely confined to static ground conditions, leaving their physical mechanisms under dynamic flight environments unexplored. A custom-coded three-dimensional (3D) distributed parameter numerical model was developed to systematically investigate the heat transfer and dynamic adaptability of cascaded PCM sinks across all flight inclinations (0-180 degrees) and accelerations (0.1g-9g). A multi-level synchronous melting mechanism was identified in the cascaded structure under conduction-dominated regimes, fundamentally different from the topdown unidirectional melting in single-stage PCMs, which extended the thermal management time by 39.9 %. The cascaded heat sink was found to exhibit remarkable dynamic stability under varying flight conditions, with a temperature response shift below 5 % and a performance variation of only 1.84 % across all tested conditions, demonstrating that the cascaded structure effectively mitigates performance fluctuations induced by acceleration and inclination. A performance reversal was observed as the inclination decreased from 135 degrees to 0 degrees and the acceleration increased from 0.1g to 9g. Under these strong convection regimes, the single-stage configuration outperformed the cascaded design due to the latter's lower total enthalpy and the structural damping of largescale Rayleigh-Benard circulation. The novelty lies in the revelation of the multi-level synchronous melting mechanism and dynamic adaptability of cascaded PCM heat sinks under flight conditions, along with the elucidation of the performance reversal triggered by the trade-off between the cascaded design and the material's energy storage capacity. The findings provide theoretical criteria for mission-oriented design: cascaded structures are optimal for dynamic adaptability in maneuvering flights, while single-stage sinks are favored for strongconvection environments.

Offshore green methanol synthesis by CO2 hydrogenation is a new alternative for offshore wind power storage, but there is no reported system design of the offshore green methanol synthesis process, and the system performance remains unclear. The offshore environment requires several new requirements, making it different from the onshore methanol synthesis process. In this study, a novel offshore green methanol synthesis process by CO2 hydrogenation is proposed, and the specific components and new process for offshore environment are designed, including pervaporation unit, gas-cooled reactor, heat exchange system, offshore wind electricity supply and additional CO2 recycle; the models of the units, the kinetic property and the system process are developed and modelled based on offshore environment. In the system process, a pervaporation unit and an additional CO2 recycle are introduced to adapt the swing condition on offshore platform and further increase the methanol yield, and the units are designed with compact and anti-sloshing structure. The models of the units, the kinetic property and the system process are developed and verified by comparing with existing study demonstrating prediction deviations below 10 %. Based on the verified model, the equilibrium and single-pass CO2 conversion characteristics are analyzed, and the optimal operation temperature and pressure (70 bar and 220 degrees C) are obtained for the reactor to optimize its methanol yield. The system process is optimized to obtain the best methanol yield up to 93.38 %, and the optimal system operation conditions are obtained at the separation temperature of 40 degrees C and the feed ratio of 3 based on the optimal reaction temperature and pressure; the additional CO2 recycle is demonstrated to provide 2.5 % higher methanol yield and methanol production. The research results provide a basis for the system optimization design of offshore green methanol synthesis process by CO2 hydrogenation.

Phase change materials are crucial to advanced thermal management systems for aerospace applications. However, the confinement of research to high-Pr fluids leads to the governing physics for low-Pr fluids unknown and a general predictive model for melting dynamics lacking. In current research, the gap was addressed through a comparative investigation of melting heat transfer in high-Pr eicosane and low-Pr gallium across all inclination angles (0-180(degrees)) and accelerations (0.1-9 g). The hydrodynamic instability was found to govern low-Pr fluid melting under inclined hypergravity conditions, which is fundamentally distinct from the Rayleigh-Benard thermal instability of high-Pr fluids. Crucially, the chaotic vortices generated by hydrodynamic instability were found to deteriorate melting heat transfer by impeding heat transport to the solid-liquid interface, whereas Rayleigh-Benard instability enhances it. A general predictive model was developed for different fluids with wide Pr range (0.02-75), all inclinations and accelerations, demonstrating high predicting accuracy for melting characteristics (>90 %) and heat transfer (>75 %). The novelty of current research lies in revealing the hydrodynamic instability mechanisms governing low-Pr fluids and developing a general melting dynamics predicting model for wide Pr (0.02-75), all inclinations and accelerations. The findings provide fundamental physical insights and a general melting predictive model for dynamic aerospace applications.

In the present study, an innovative cascaded phase change material (PCM) heat sink using organic PCMs was proposed for electronic thermal management. The design arranges multiple PCMs with progressively lower melting points along the heat transfer path, allowing active control of the melt front. A numerical model with 5 % accuracy was developed to evaluate thermal performance. Based on the validated model, the effects of PCM stage numbers, PCM volume fractions, fin types, and fin volume fractions were analyzed. The fin volume fractions were further optimized using a support vector machine (SVM) and genetic algorithm (GA) methods. Results showed that a three-stage PCM heat sink with pin fins and increasing configurations outperformed single-stage PCM heat sinks, enhancing heat transfer by up to 36.7 %. Additionally, the innovative cascaded PCM heat sink with a uniform 20 % fin volume fraction across the three stages achieved a 38.8 % improvement compared to singlestage configurations. When the fin volume fractions were set to 24.1 %, 17.6 %, and 13.0 % for the three stages, thermal performance of the innovative cascaded PCM heat sink was enhanced by up to 39.8 % compared to single-stage configurations. The findings provide valuable insights for the design and application of PCMbased thermal management systems, potentially leading to more efficient solutions for various engineering fields.

Organic phase change materials (OPCMs) and liquid metals (LMs) are widely used in thermal energy storage (TES) and thermal management systems in aerospace applications, yet the effects of flight acceleration on their performance and clear selection criteria remain unclear. In this study, validated enthalpy-porosity numerical models were developed to compare the melting behavior of eicosane and gallium and to develop selection guidelines. The investigation revealed that gallium melts predominantly via heat conduction, while eicosane melts primarily through natural convection, attributable to gallium's thermal conductivity being 225 times greater than that of eicosane. Complete melting occurred in 14.68 s for gallium and 810.66 s for eicosane, with gallium exhibiting a volumetric latent heat of 489 MJ/m3 (2.5 times that of eicosane) and a heat storage rate of 3.33 kW compared to 0.024 kW for eicosane. Heat flux during eicosane melting remained around 10-1 W/cm2, whereas gallium reached up to 101 W/cm2. In applications with strict limitations on weight, insulation requirements, and susceptibility to corrosion, OPCMs are recommended, whereas in applications with low constraints, LMs are advised. Under flight acceleration, eicosane's melting time increased from 811 s under normal gravity to 1200 s in microgravity (a 48 % increase) and decreased by 56 % under hypergravity (ares = 19g). In contrast, gallium's melting time increased from 13.09 s in microgravity to 14.68 s under normal gravity (12 % increase) and to 20.69 s at 19g (58 % increase), as enhanced natural convection raised the temperature of the melted region. Dimensionless correlations for the melting fraction and Nusselt number were derived. These findings offer valuable insights for designing PCM-based TES and thermal management systems in aerospace applications, thereby enhancing reliability and efficiency under dynamic flight conditions.

Existing enhancement methods for PCMs functions by replacing PCMs with enhanced structures, which reduces the heat storage capacity of PCM heat sinks. In the present study, a novel cascaded PCM heat sink using organic PCMs was proposed for thermal management of electronics. The design arranges multiple PCMs with progressively lower melting points along the heat transfer path, allowing active control of the melt front. Enthalpyporosity numerical models with 5 % accuracy were developed to evaluate heat transfer characteristics. The proposed cascaded and conventional single PCM heat sinks were fabricated and experimentally compared. Based on the validated model, the influences of the configuration of multiple PCMs, heat flux, and internal convection were investigated. The results found that compared to conventional single PCM heat sink, the proposed cascaded configuration significantly improved thermal management performance, achieving up to a of 25.48 % enhancement in heat transfer at heat fluxes ranging from 0.1 to 0.75 W center dot cm- 2. The performance of the increasing configuration was optimal, which surpassed that of uniform configuration by 2.11 %. In configurations at angles of 0 degrees, 90 degrees, and 180 degrees between the heat transfer path and gravity direction, the proposed cascaded PCM heat sink consistently outperformed single PCM heat sinks by more than 20 %. The novelty lies in exploring the influences of the configuration of multiple PCMs, heat flux, and internal convection on the performance of cascaded PCM heat sinks. The findings provide valuable insights for the design and application of PCM-based thermal management systems, potentially leading to more efficient solutions for various engineering fields.

Firefighting aircraft are highly effective against forest fires, but hazardous low-altitude operations often lead to accidents. Increasing the flight altitude is an effective way to enhance flight safety; however, a higher dropping altitude can result in greater atomization of the liquid retardant, thereby reducing the thickness of the ground coverage. The use of firefighting bags can effectively prevent atomization, providing a viable solution to improve firefighting efficiency at higher drop altitudes. To analyze the effectiveness of firefighting bags, this paper establishes a mathematical model capable of calculating the bag falling trajectory and drop pattern characteristics. A kinetic model is built to solve the transient position and rotational attitude, and a ground pattern model is presented to obtain the coverage levels. The model is validated by a real-scale dropping experiment. The prediction deviations for the pattern lengths are 20 %, 16.1 %, and 18.75 %, respectively, while the prediction deviations for the 95 % pattern widths are -0.2 m, 0.1 m, and -0.8 m, respectively. The firefighting efficiency of the bags is further investigated under various conditions, and the results show that the effectiveness of the bags is not significantly affected by drop height and can achieve acceptable drop patterns in high-altitude dropping systems.

Offshore green methanol synthesis by CO2 hydrogenation is a new alternative for offshore wind power transport, but the system's dynamic performance and control strategy remain unclear. In this study, a dynamic model for offshore methanol synthesis by CO2 hydrogenation is established, and a novel control strategy is proposed based on the offshore methanol synthesis process, including different control methods of H2/CO2 feed ratio(molar ratio between hydrogen and carbon dioxide), two separate controllers that control the temperature of gas-cooled reactor, and an override controller that control the recycle flow rate and its composition. The fixed H2/CO2 feed ratio control method and the average H2/CO2 feed ratio control method are proposed and their performance under step and periodic feed reductions are compared. The fixed H2/CO2 feed ratio control method is recommended as it can achieve up to 92.67 % CO2 conversion rate under different feed reductions, which is promising comparing with the CO2 conversion rate of 36.85 % without feed ratio control. The average H2/CO2 feed ratio control method can reach 87.70 %-92.69 % CO2 conversion rate, but it requires additional heat duty to maintain the reactor temperature and needs to work with short periods. The results prove the necessity of H2/CO2 feed ratio control under feed fluctuations, and provide a basis for the system control strategy design of offshore green methanol synthesis process by CO2 hydrogenation.

The performance of ocean thermal energy conversion (OTEC) systems in the South China Sea differs significantly due to its relatively low surface seawater temperature, and the influence mechanisms remain unclear. In the present study, numerical models for OTEC systems were developed for Rankine, Kalina, and Uehara OTEC cycles, and a distributed parameter model and a mass flow rate distribution model for parallel PHEs were utilized to accurately evaluate the effects of heat transfer and pressure drop characteristics on overall cycle performance. The influences of operation conditions on performance of various OTEC systems in the South China Sea were analyzed. Results indicate that, under equivalent operating conditions, the low surface temperature in the South China Sea reduces thermal efficiency by 13.29 % compared to other regions. To achieve comparable efficiency levels, the condensation temperature must decrease by at least 3 degrees C. The Rankine cycle achieves maximally 64 % higher thermal efficiency than the Kalina and Uehara cycles, while the Uehara cycle exhibits 8.38 % and 22.02 % higher net power generation efficiency compared to the Kalina and Rankine cycles, respectively. Decreasing the temperature differences between the seawater inlet and outlet for both the evaporator and condenser improves thermal efficiency, but overly small temperature differences cause significant pressure drops of the heat exchangers. The minimum pressure drop is observed when the temperature difference is between 3 and 5 degrees C. To maximize net power generation efficiency, a balance between heat transfer efficiency and pressure drop must be maintained. The optimal temperature changes for power generation are 4.5 degrees C for the Rankine cycle and 5.5 degrees C for the Kalina and Uehara cycles. To ensure positive annual power generation efficiency under seasonal variations in the South China Sea, the Uehara cycle combined with cold seawater temperature of 3-4 degrees C is recommended. The findings provide valuable insights into the design and operation of OTEC systems, leading to potential energy and environmental advantages.

Metal foam has great potential for improving jet impingement boiling heat transfer, and the effect mechanism of metal foam structures is unclear. In this study, the boiling heat transfer characteristics of confined jet impingement on metal foam covered surfaces with different structures were experimentally investigated, and the effects of pore density, porosity, and thickness were analyzed. The results show that, as the pore density varies from 20 PPI to 40 PPI, the heat transfer coefficient increases and then decreases, while the critical heat flux continues to decrease; compared with the metal foam cover with a pore density of 40 PPI, the 20 PPI one has a 17.1 % higher critical heat flux, and the 25 PPI one has a 27.5 % greater maximum heat transfer coefficient; as the porosity decreases from 97 % to 92 %, both the critical heat flux and maximum heat transfer coefficient rise by approximately 10 %; as the thickness increases from 3.0 mm to 5.0 mm, the critical heat flux for 20 PPI rises by 12.0 %, but it declines by 21.2 % for 40 PPI. New correlations for the heat transfer coefficient and critical heat flux of the jet impingement boiling were developed with average deviations of 6.8 - 8.9 %.

The printed circuit heat exchanger (PCHE) has a great potential for the application in various compact energy systems. However, the there is no existing heat transfer and pressure drop correlations on condensation in PCHE zigzag semicircular channel. In this study, the flow and heat transfer characteristics of condensation in the PCHE zigzag semicircular channel were analyzed numerically. The flow patterns of annular flow, annular wavy flow and plug flow were observed in the channel, and the flow pattern transition line correlations were developed. As the mass flux increases, the transition vapor quality from annular flow to intermittent flow decreases gradually. Both the condensation pressure drop and the heat transfer coefficient reach their peaks as the vapor quality is around 0.78, and the pressure drop decreases with the increase of saturation temperature. The heat transfer coefficient decreases as the saturation temperature increases when the vapor quality is less than 0.6, while it increases slightly as the saturation temperature increases when the vapor quality is greater than 0.6. New correlations for condensation pressure drop and heat transfer in PCHE zigzag semicircular channel are developed. The average errors of the developed condensation pressure drop and heat transfer correlations are 11.0 % and 7.9 %, respectively.

In this study, a new series of eutectic phase change materials (EPCMs) was specifically designed for the thermal management of electronic devices. These EPCMs, formulated by combining fatty acids and paraffin, exhibit adjustable melting points and enhanced latent heat capacities. A eutectic point prediction model was proposed and validated, enabling precise property prediction of EPCMs. Characterization of these synthesized EPCMs was conducted through various methods. This research fills a significant gap in current phase change material (PCM) technology by providing solutions with specific phase transition temperatures, spanning ranges of 48.8 to 49.8 degrees C, 54.0 to 54.7 degrees C, and 62.5 to 66.3 degrees C. These novel materials not only expand the phase transition temperature range of existing PCMs but also elevate their latent heat capacity. The practical application of these EPCMs in thermal management of the electronic devices was further experimentally investigated. Under constant heat fluxes of 2, 4, and 6 kW/m2, the EPCMs effectively extended the time taken for electronic devices to reach the critical temperature of 55 degrees C by 8.6, 7.8, and 6.6 times, respectively, compared to devices without EPCMs. Furthermore, in tests with pulsed heat flux conditions (6 kW/m2, 10 min on/80 min off), incorporating EPCMs successfully restricted the maximum temperature to 50.2 degrees C, well below the critical threshold. Overall, the results of this study demonstrate the synthesized EPCMs' substantial effectiveness in enhancing the thermal management of electronic devices.

The vapor injection linear compressor exhibits a distinctive mass flowrate distribution characteristic compared to other vapor injection compressors, making it promising for application in dual-temperature zones refrigerating systems. In this study, a novel system of dual-temperature zone refrigerators featuring two parallel evaporators is proposed, and numerical models of the vapor injection linear compressor and its system are established, and then validated by experimental results. Theoretical analysis is conducted to explore the cooling performance and capacity-modulating characteristics of the system. Compared to traditional refrigeration systems, the vapor injection of medium-pressure refrigerant enhances the cooling capacity and performance at a large piston stroke while deteriorating the freezing capacity at a small piston stroke. This system offers the flexibility of adjusting the cooling ratio by modulating supply voltage and driving frequency to meet the cooling requirements. Correspondingly, special control strategies for this kind of system for the best performance are proposed in this study. Additionally, the structural parameters significantly influence the cooling performance: a larger injection area and a smaller distance to the top death center prove to be more advantageous for overall cooling performance. This research provides valuable insights for optimizing the structural parameters and control strategies, serving as a beneficial reference for future innovative refrigeration technologies.

Newly developed airliners have adopted supplemental cooling systems (SCS) to provide for non-cabin cooling requirements. In the present study, dynamic component models for compressor and phase change heat exchangers were developed with dynamic decoupling and explicit solution methods, and pressure zone separation and solution methods are developed based to obtain dynamic pressures as key values. A dynamic VCRU subsystem model is established, and the result under single-unit startup condition shows pressure deviations less than 0.16 %, with a simulation time ratio of 5.65 %, exhibiting good overall performance at both precision and speed. A dynamic SCS system model is developed, and the simulation of a 9000 s flight took 1973.3 s to complete. Result in the cruise phase shows the condensation and evaporation temperatures are in the ranges of 28.39-31.33 degrees C and -17.93 to -10.71 degrees C, respectively, meeting their respective designed ranges of 30 f 5 degrees C and -15 f 5 degrees C. These results reflects good consistency of the model with actual system characteristics. Control optimization is conducted based on the developed model to eliminate temperature fluctuation. The optimization reduced the maximum temperature deviation from 0.4004 K to 0.0019 K after system starting process, proving the feasibility of control method optimization based on the developed dynamic simulation model.

In order to optimize the design of high-altitude sprinkling system of fire-fighting aircraft, it is necessary to establish a model reflecting the high-altitude spraying and distribution mechanism of mass fire extinguishing bags during the flight. Based on the discrete element method and the computational fluid dynamics method, a high-altitude spraying and distributing model of aircraft mass fire extinguishing bags is established, and the spraying characteristics and landing area distribution at different flight speeds and altitudes are obtained. The model is verified by experiments. The deviations between simulated landing distribution and experimental data are less than 20.0%. The research results provide a theoretical model for the development of aircraft high altitude fire extinguishing system, so as to significantly improve the fire extinguishing performance of aircraft spraying system.

Metal foam has great potential for promoting boiling heat transfer due to its complex porous structure and extraordinarily large specific surface area. The boiling heat transfer characteristics of confined single jet impingement on a metal foam covered surface were experimentally investigated for the first time, and the new data were compared with those on the smooth surface. The experimental results show that, the heat transfer performance of metal foam is affected by jet velocity and subcooled degree in the nucleate boiling region due to the significant contribution of single-phase convection heat transfer; critical heat flux of the metal foam covered surface is 10 %-36 % higher than that of the smooth surface, representing a maximal of 206.7 W center dot cm(-2); the highest heat transfer coefficient is up to 39.9 kW center dot m(-2)center dot K-1, 31 % greater than that of the smooth surface; at the same surface superheated degree, the heat flux of the metal foam covered surface is 9 %-166 % greater than that of the smooth surface; at the same heat flux, the heat transfer coefficient on the metal foam covered surface is 14 %-90 % higher than that of the smooth surface; the metal foam cover reduces surface superheated degree by up to 16.8 K at the onset of nucleate boiling.