High-humidity environments challenge aircraft environmental control systems (ECS) by inducing outlet free water droplet and pipe icing/clogging, endangering flight safety. To address ECS dehumidification limitations under high-humidity conditions, this study employs the enthalpy method and endoreversible thermodynamic analysis to investigate three typical configurations (three-wheel, split four-wheel, enhanced split four-wheel bootstrap systems) and derive their thermal characteristic expressions, thereby revealing the mechanism of heat-moisture-work conversion. Comparative analysis yields wet condition design strategies: staged expansion can mitigate the extremely low temperature caused by single-stage expansion, while an additional water separator is required to remove condensed water in the turbines. Furthermore, the effects of environmental parameters and key components on the dehumidification performance of ECS are systematically investigated. Sensitivity analysis identifies critical components, revealing the secondary heat exchanger effectiveness and compressor pressure ratio as most influential on dehumidification. Slight parameter optimization of these components improves the enhanced split four-wheel bootstrap system's ambient dew point adaptability from 20 degrees C to 27 degrees C. This study innovatively provides a comprehensive assessment of ECS thermal performance, improvement directions, and potential under high-humidity conditions, filling gaps in systematic thermodynamic analysis of ECS dehumidification limits and laying a solid theoretical foundation for enhancing ECS high-humidity adaptability.

Compact heat exchangers play a significant role in the heat transfer process of aircraft cabin air cycle systems (ACSs), and their heat transfer performance significantly influences system refrigeration efficiency. During flight, the inlet conditions of heat exchangers exhibit significant transient characteristics, such as changes in air temperature and mass flow rate. Accurately characterizing the thermal response of heat exchangers is therefore essential for predicting outlet temperatures, as well as for optimizing ACS control strategies. This study proposes a scaling-lumped transient method (SLTM) for plate-fin heat exchangers by improving the scaling law model and time constant lumped model, enabling direct prediction of the transient outlet thermal response of heat exchangers under step or ramp transient input and variable heat exchanger structures. A transient performance testbed for heat exchangers was developed. Three types of transient input condition tests, including inlet flow rate step changes, inlet temperature ramp changes, and simultaneous changes, were conducted for three plate-fin heat exchangers with straight, corrugated, and serrated fins. The results showed that the average error between the experimental data and SLTM did not exceed 1 %, with a maximum error of 3.4 %. The scaling regression of all transient data further revealed the heat-transfer mechanism of the transient thermal response. This study provides an efficient and accurate transient performance prediction method, advancing the design and application of plate-fin heat exchangers.

A parafoil is a crucial aerodynamic deceleration device used in the field of airdrop. The overall objective of this paper is to study the aerodynamic characteristics of the curving process of the canopy using the lattice Boltzmann method, to verify it with the experimental results, and to analyze the stalling phenomenon using the finite volume method(FVM). Simulations were conducted to analyze the aerodynamic curves of four−stage models of canopies, examining the flow field characteristics. Additionally, the influence of air chamber structures is also analyzed. The reasons for differences in the aerodynamic characteristics are discussed based on the results obtained. The reliability of utilizing the lattice Boltzmann method for aerodynamic simulations is demonstrated. Overall, the lift coefficient of models II/III/IV was increased by 30.97% compared with model I, which proved the effectiveness of the air chamber structure and curving process. Notably, different curved canopies showed significantly improved lift and drag aerodynamic characteristics to varying extents, highlighting their robustness. Also, it was observed that air chamber partitions exerted a greater influence compared to perforation. Through validation and analysis, it was determined the accuracy of the LBM improved up to 10.9% with respect to the FVM. These findings provide a valuable reference for parafoil experiments and simulation research.

The converter valve of ultra-high-voltage direct current grid requires a large amount of cooling water for heat dissipation. Considering the generated waste heat, this study proposes a heat pump-driven mechanical vapor compression (HP-MVC) desalination system based on traditional power-driven mechanical vapor compression (MVC). Using the scaling-endoreversible thermodynamic model, the analytical solutions of the structural equation and operating boundary of the proposed HP-MVC system were derived, which is the innovation of this study. The effects of different component parameters on the thermodynamic characteristics and operation boundaries of the HP-MVC were determined. The results revealed that the HP-MVC system alternately exhibited heat-drive dominant and power-drive dominant modes, in which the specific power consumption was lower in the former. When the recovery ratio was 0.3, with an increase in the pressure ratio from 1.15 to 1.50, the heat supplemented by the heat pump decreased by 31.9 %, and the specific power consumption increased by 63.1 %. The analytical solutions of the structural equation provide a theoretical basis for the efficient operation of the system, and the operation boundaries demonstrate the difference between HP-MVC and traditional MVC. The HP-MVC reduces heat dissipation requirements and results in a more energy-efficient desalination system, which is a typical mutually beneficial design and worth promoting.

As fighter aircraft become more advanced, traditional air cycle systems have fallen short of meeting the complex environmental control requirements. Advanced fighters such as the F-22 Raptor have responded to these challenges by adopting integrated thermal management systems. These systems feature complex thermodynamic processes and intricate information transmission pathways among various components, creating a sophisticated network structure. To unravel the complexity of such systems, this paper employs a blend of thermodynamics and information theory. We conduct multi-level analysis using structure entropy method and centrality algorithms to explore the information transmission characteristics within these thermodynamic systems. At the system level, we find that variation in environmental parameters have only a 1 % impact on order degree, whereas the influence from the system's own structure is more pronounced. At the component level, within the whole system, the varies components in AFT PAO and fuel loops emerge as critical hubs for information transmission. Among these components, the PAO/Fuel stands out as the most important, with closeness and betweenness centrality exceeding that of all other components by at least 11.5 % and 29.1 %. This study offers a theoretical foundation for the optimization of thermodynamic system structure and layout, viewed through the lens of information theory.

Humidification and dehumidification are among the most important desalination technologies, in which humidifiers and dehumidifiers are the key components. Previous research has mainly focused on overall system improvement, but few studies have focused on the thermodynamic limitations of the humidification and dehumidification processes. By introducing temperature and enthalpy effectiveness, the thermodynamic limits have been explored. It was successfully established that there are three operating states for the humidifier and dehumidifier. The analytical expressions of enthalpy and temperature effectiveness boundary values in each state were obtained. The results of visualizing the influence of mass flow ratio, inlet temperature, inlet and outlet relative humidity, and pressure on the feasible range of enthalpy and temperature effectiveness were presented. This study explores the thermodynamic limits of heat and mass transfer equipment that can be applied to other types of humidification and dehumidification equipment.

A Reverse-Brayton cycle represented by the B787 electrical driven environmental control system is used as the analysis object, including the thermodynamic process of two-stage compression, intercooling, and regeneration. An analytical expression for the thermodynamic performance of the cycle is derived based on the endoreversible thermodynamic analysis model (ETM). Combined with a genetic algorithm, an ETM-based optimization approach (ETM-OA) is proposed. Using this method, it is found that the coefficient of performance is increased by 34.1 % and 48.4 % under two typical flight conditions, respectively, and the corresponding system entropy generation number is reduced by 30.2 % and 51.1 %, respectively. Both ETM-OA and entropy generation analysis show that the electric supercharging module, secondary heat exchanger, and air cycle machine are key components of the system. This study provides a convenient method for obtaining the thermal power conversion mechanism of complex thermal cycles and conducting optimization analysis.

The application of the Kane equation in analyzing airdrop dynamics problems is rare. The main objective of this paper is to apply the Kane equation dynamics model to the analysis of the status continuity problem during the out-of-cabin process and the line sail phenomenon during the extra-vehicular process. In the out-of-cabin process, an analysis of off-aircraft security and traction ratio impact was conducted. Furthermore, the BP neural network model was trained to predict the status transition of the payload for a multiple airdrop mission. In the extra-vehicular process, the spring network method was used together with the Kane equation to analyze the form and overload of the parachute line. The modeling avoids complex equations and derivations. The results suggest significant potential applications of the Kane equation in precision airdrop missions during out-of-cabin and extra-vehicular processes without heavy reliance on experimental data.

Air cycle systems (ACSs) are primarily used in aircraft environmental control systems (ECSs) to provide a suitable cabin temperature and pressure environment for passengers and avionics. It comprises heat exchangers, compressors, turbines, water separators, and various other components that are interconnected to form an information-transmission network. Traditional research on ACSs has focused primarily on their thermal performance. This study abstracted ACSs into network graphs based on their information-transmission characteristics, determined the weight of each information-transmission route using the fuel weight penalty method, calculated and compared the order degree of different ACSs using the structure entropy method, and measured the importance of each component using centrality for the first time. The results showed that the order degree of the ACSs gradually increased with an increase in the number of wheels in the air cycle machine (ACM), and ACSs with high-pressure water separation had a higher order degree under wet conditions than under dry conditions. Moreover, based on the centrality of each vertex in the graphs, the ACM and secondary heat exchanger in the ACS were fundamentally important and should be focused on during the system design. The methodology proposed in this study provides a theoretical basis for the evaluation of the ACS organizational structure and the design performance of components.

Accurate collection and analysis of ground reaction force (GRF) data are crucial for optimizing the technical movements of speed skaters; however, it has been a challenge for the limitations of experimental equipment and application scenarios. Therefore, we proposed a novel approach for estimating GRF based on kinematics obtained from markerless video tracking systems and achieved low errors compared with the experimental data. Our method allows for further biomechanical analysis, including muscle force and power, during speed skating competitions.

The high power of blade servers inside small data centers (DCs) can cause heat accumulation, which can degrade the performance of DCs. To address the problem of heat dissipation, we performed periodic experiments on a thermal management system based on a phase change material. The effects of time ratio, heating power, and cooling water temperature on the performance of thermal control and periodic stability were investigated. Information entropy reflects uncertainty by transforming a variable changes over time into a single parameter representing inhomogeneity of time. Herein, it was introduced as an evaluation index of thermal control performance. The results verified that the peak temperature of the heating surface can be maintained below 80 degrees C for several periods under specific conditions. Additionally, the information entropy results of the experimental data reflected the thermal control performance of the system and validated the experimental conditions. Based on the experimental results and the corresponding information entropy analysis, we proposed a design strategy for the system parameters and a method for reducing the number of measuring points. The obtained results formed the basis for the thermal management design of the server level of DCs, other electronic equipment, and electric vehicles.

The landing phase of an airdrop process is prone to accidents, and thus, it is important to assess the landing reliability for an airdrop system. However, full field tests to assess the reliability are unacceptable due to their cost and the time required. As such, it is necessary to estimate the reliability in the design stage. To address this problem, a method based on vine-Bayesian Network (vine-BN) is proposed to assess the landing reliability by fusing multisource information. First, the network structure is determined by the relationship between data of simulation or ground tests and failure modes. Then, nodes are defined as random variables on [0, 1] based on the definition of the performance metric. Finally, the dependence between nodes is quantified by expert opinions. To illustrate the effectiveness of the method, a particular ground test or simulation is chosen to establish a network for a typical heavy cargo airdrop system (HCADS). Forward and backward propagation is carried out on the network. The forward analysis predicts the landing reliability in the design stage through multisource information fusion. Beta distribution is applied to fit the fusion result, so Bayesian inference is made to perform field test times decision-making. The backward analysis works to identify the key performance metrics related to landing reliability. The results and analysis manifest that vine-BN is feasible for fusing multisource information. Through the network, the reliability of the current design can be predicted effectively, and the field test times can be remarkably reduced. This method plays a crucial role in airdrop system design and reducing test time and labor.

For more than a century, it has been widely believed that there is a clear gap between molecular motions at the microscopic level and turbulent fluctuations at the macroscopic level. However, recent studies have demonstrated that the thermal fluctuations resulted from molecular motions have nonnegligible effects on the dissipation range of turbulence. To further clarify the reviving debate on this topic, we employ the molecular-level direct simulation Monte Carlo (DSMC) method to simulate homogeneous turbulence with different turbulent Mach numbers, extending the previous studies by considering the effect of compressibility. Our results show that, for both one-dimensional (1D) stationary turbulence and two-dimensional (2D) decaying isotropic turbulence, the turbulent energy spectra are significantly changed due to thermal fluctuations below the spatial scale comparable to the turbulent dissipation length scale. The energy spectra caused by thermal fluctuations for different spatial dimen-sions d present different scaling laws of the wavenumber kas k((d-1)). For 2D cases, we show that the effect of thermal fluctuations on the spectrum of compressible velocity component is greatly affected by the change of compressibility. The 2D spectra of density, temperature and pressure are also obtained, showing the same scaling law at large wavenumbers as found for the energy spectra. Moreover, it is found that the effects of thermal fluctuations on the thermodynamic spectra are the same as those on the spectra of compressible velocity component.

Plateaus, one of the most important terrain types in China, contain high-quality agricultural and livestock re-sources. However, due to their natural conditions, they host major deficiencies in cold chain logistics. Existing studies have focused on improving the temperature regulation capabilities of cold chain vehicle refrigeration or air conditioning systems, but have neglected the unique low-pressure environment faced by the Plateau cold chain transport vehicles. Using zoning design, air and vapor cycle refrigeration technologies, this study proposed a bootstrap-type integrated environmental control system (BIECS) and simple-type integrated environmental control system (SIECS) to realize vehicle "micro-environmental control." The analytical solution of the thermal characteristics of the system was obtained based on the scaling-endoreversible thermodynamic analysis model. Moreover, the influence of ambient humidity on the thermal performance of the system was evaluated based on the enthalpy method. According to the typical working conditions, the system performances using different refrigerants, R404A, R448A, and R452A, were analyzed at different trailer temperatures, cooling capacities, and altitudes. Our results showed that, under the same design requirements, the coefficient of performance (COP) of the BIECS was slightly higher than that of the SIECS. Higher the trailer temperature and cooling capacity, higher is the COP of the system. Comparing the three refrigerants under the same working conditions, compared with R404A, the COP of the BIECS and SIECS increased by 13.4 % and 10.9 %, respectively, using R484A, and increased by 6.1 % and 5.0 %, respectively, using R452A. The performance of the systems that used R448A was the best. The system could ensure a 2.4-km cab pressure altitude at an ambient altitude of 5 km, but the COP could decrease by 31.8-35.6 %, compared to that on the plains. This study provides and comprehensively evaluates a new technical solution for the environmental control of Plateau cold chain transportation vehicles. It also provides comprehensive health protection measures for drivers and technical support for the promotion and development of Plateau cold chains.

实验室是高校教学科研的重要组成部分,随着现代科技的迅猛发展,提高本科教学的实验效率是目前十分重要的一项工作.尤其是在实验室的测控领域,现代数字化的测控平台已经成为测量仪器的基础.针对我校航空学院教学实验任务重,原有实验设备效率低,测试精度与自动化程度不高等问题,需要对不同的教学内容设计通用、简便、易学的虚拟仿真教学实验方案、研究响应的教学方法是文章探讨的关键问题.文章依据目前教学实验中常用的代表性的虚拟仿真软硬件,采用基于虚拟仿真平台的飞行器环境控制课程实验教学方法,从飞行器环控课程实验课程的建设过程中可以看出虚拟仿真手段具有较强的优势,文章采用的教学方法使学生具有抽象思维、模型凝练、自主学习、应用实践和探索创新能力,以及定性与定量分析和动手能力,解决综合性实际工程问题的能力.

Spacecraft may encounter emergency pressure relief situations during manned space exploration missions, such as when micrometeoroids break through the bulkheads. The pressure emergency is one of the main threats to the missions in low earth orbit or deep space explorations to the Moon and Mars. It is critical to develop a pressure protection scheme for emergency contingencies. In this study, in order to improve the safety and reliability of spacecraft protection, a periodic recompression recovery scheme (PRRS) is proposed for cabin pressure protection. The PRRS adopts a combined mode of cabin emergency recompression, cabin pressure maintenance, gas recovery, and spacesuit protection, which can provide astronauts with a variety of safety protection methods. A mathematical model of cabin pressure control is established by using the lumped parameter method, and the gas consumption of three types of pressure protection systems are compared. The PRRS adopts the mature technologies and could provide the reliable pressure emergency protection. Compared with the traditional continuous gas supply scheme, the PRRS can reduce gas consumption by more than 85%. In the case of limited spacecraft gas resources, the PRRS promises a longer survival time for returning astronauts. This study can provide a design idea for the overall design of manned spacecraft in the future. (c) 2022 COSPAR. Published by Elsevier B.V. All rights reserved.

The ram-air parafoil, which can be controlled to achieve stable and precise landing, plays an important role in the field of precision airdrop. The overall goal of the paper is to discuss the effectiveness of three methods in trajectory planning and apply them to simulations and predictions under certain random conditions, thereby improving the landing precision and avoid complicated derivations in traditional dynamics. A trajectory planning model based on a back propagation neural network (BPNN) is proposed. Considering the influence of the apparent mass and random wind field, genetic algorithm (GA) is the landing points accuracy optimization algorithm supplying a database verified by Kane equation (KE) model on which the BPNN is trained, verified, and tested. BPNN is the model to predict a large number of airdrop landing points data after training. Simultaneously, the effects of the different control methods and random wind speeds on the dynamic characteristics of the parafoil are analyzed. In KE, GA, and BPNN, the BPNN model features the highest landing point precision among the three methods. The radius that 95% landing points are lied in of BPNN can reach 6.30 m, which is only 77.0% of the GA and 54.6% of the traditional KE model. In addition, the influence of cutting-in angle and transition radius on the landing point error is analyzed. Our results indicate significant potential application of GA and BPNN in the field of precision airdrop.

A water sublimator is a thermal control device that uses the phase change latent heat of water for heat rejection in space. It can allow effective heat dissipation in a microgravity environment. Existing models of water sub-limators mainly focus on numerical simulations and do not calculate the temperature distribution and phase change interface position accurately. Furthermore, very few theoretical studies have been conducted. This study investigates a porous plate water sublimator, establishes the governing equations of each stage of a sublimator working in the periodic mode, and performs discrete calculations using the finite volume method. Additionally, a dimensionless analysis of the governing equations is conducted, and the flow in the evaporation process occurring in the porous plate is solved analytically. The results show that the sublimator enters a stable state after several periods. The effects of the thickness and pore diameter of the porous plate, feedwater pressure, and the type of working fluid on the evaporation process are discussed. It was observed that a large pore diameter and high feedwater pressure resulted in a rapid rise in the liquid level in the porous plate. An adaptive mesh method is used to induce a change in the length and number of meshes in accordance with the interface movement, thereby solving the problem caused by changes in the calculation domain. Moreover, an analytical solution of the evaporation process in the porous plate is provided, and it has universal significance for describing similar phenomena.

针对水升华器在实际航天工程应用中的工作特性,以升华模式下的水升华器为研究对象,应用一维稳态导热、自由分子流动等理论模型,对水升华器内部热质平衡进行分析,得到了升华模式下的冰层厚度、升华温度等理论计算结果,并推导得到升华模式最大热载荷的无量纲特性曲线.利用商用软件ANSYS Fluent进行数值仿真,基于焓-多孔模型描述了水在水升华器给水腔内的结冰过程,求解了不同孔度、孔径等设计参数下水升华器的工作特性,将仿真结果与理论计算对比,发现两者具有较好的一致性.建立的无量纲特性曲线和数值算法对预测不同设计工况下水升华器升华模式的工作特性具有指导意义.