NUMERICAL RESEARCH ON IMPACT OF AIR SYSTEM BLEEDING ON COMPRESSOR PERFORMANCE

Bled air from the high pressure compressor takes up 3%—5% in the air system.However,there are not many studies on the compressor performance after bleeding.By analyzing the low-speed single-stage compressors,six bleeding structures are presented according to their influence mechanism on the compressor performance,and five kinds of bleeding rate are applied to one of the structures.A numerical simulation is performed to study the influence of bleeding rates and structures on the compressor performance.The results show that for the stators with the large flow separation in the corner,bleeding a small amount of air from the end-wall region can improve the total pressure increase and the stability margin.Moreover there is an optimum value of the bleeding rate in the stator casing.

Thermodynamic Modeling and Simulation of Air System Control Device

This paper aims to obtain the thermodynamic characteristics of the air system control device sealing part in different compressor bleed air and ambient temperature.On the basis of considering the main factors affecting the heat exchange process and simplifying the physical model of the air system control device,the thermodynamic model of air system control device is established based on the basic theory of laminar flow heat transfer and heat conduction theory.Then the piston motion characteristics and the thermodynamic characteristics of the air system control device seal are simulated.The simulation results show that the valve actuation dynamic time of piston is about 0.13 s in the actual working conditions,and the temperature effect on the dynamic response of the piston rod is only 5 ms when the inlet air temperature at 300 ℃ and 370 ℃.The maximum temperature of the air system control device sealing part is not more than 290 ℃ under long time working condition of compressor air entraining.The highest temperature of the sealing part can reach up to 340 ℃ when the air flow temperature reaches the limit temperature of 370 ℃,and the longest duration working temperature limit is not more than 14 s.Therefore,the selection of control device sealing material should consider the work characteristic of instantaneous temperature limit.

A New Unsteady Fluid Network Approach to Simulate the Characteristics of the Air System of a Gas Turbine System

In this paper, a novel unsteady fluid network simulation method to compute the air system of jet engine was coded to predict the characteristics of pressure, temperature and mass flow rate of the flow and the temperature of the solid in the gas turbine engine. The fluid and solid areas are divided into the network comprised of branches and nodes, and the method solves transient mass, energy conservation equations at each node and momentum conservation equation at each branch by a newly deduced numerical method. With this method, to simulate complicated fluid and solid system in short time becomes possible. To verify the code developed, it has been applied to simulate a gas turbine model against the widely used commercial software Flowmaster. And the comparisons show that the two are in good agreement. Then the verified program is applied to the prediction of the characteristics of a designed turbine disk and air-cooling system associated to it, and useful information is obtained.

Aircraft Clean Air Requirements Using Bleed Air Systems

There are certification and airworthiness requirements relevant to the provision of clean breathing air in the crew and passenger compartments. There have been continuing reports and studies over the years regarding oil fumes in aircraft, including impaired crew performance. Oil fumes are viewed in varying ways ranging from rare seal bearing failures, to low level leakage in normal flight. A Masters of Science (MSc) research degree was undertaken to assess whether there is any gap between the certification requirements for the provision of clean air in crew and passenger compartments, and the theoretical and practical implementation of the requirements using the bleed air system. A comprehensive literature search reviewed applicable certification standards, documented and theoretical understanding of oil leakage. Two types of interviews were conducted to address the research questions. Key aviation regulators were questioned about the process by which they certify and ensure compliance with the clean air requirements. Aerospace engineers and sealing professionals were interviewed about their understanding of how oil may leak past compressor oil bearing seals, and into the air supply under various flight conditions. The outcome of the research showed that there is a gap between the clean air certification requirements, and the theoretical and practical implementation of the requirements using the bleed air system. Low level oil leakage into the aircraft cabin in normal flight operations is a function of the design of the engine lubricating system and bleed air systems, both utilising pressurised air. The use of the bleed air system to supply the regulatory required air quality standards is not being met or being enforced as required.

Analysis of the Behavior of a Turbomachine Driven by a Compressed Air System

Different experiments in high speed turbomachines require expensive and sophisticated infrastructure to implement their impulsion and reach high regimes. In developed countries, this can be achieved by using aeroderivative gas turbines or DC motors of about 400 HP. This paper presents an experimental system designed and built with the intention of performing behavior studies in test turbomachinery. The proposed installation uses compressed air as driving fluid, which allows the turbomachinery to reach high rotational speeds where very important phenomena occur. An analysis is carried out considering the rotational speed behavior of an internal combustion engine turbocharger of the Perkins series when it is driven by pressures ranging from 4.2 kg/cm2 to zero. Additionally, another experiment couples an automotive electrical generator with the turbine to observe the system operation when a load is applied. The behavior of the pressure is analyzed when it is in function of the time of air discharge that goes from a compressed air storage tank to the turbocharger for its impulsion. This is an experimental system that can be designed and constructed economically within the bounds of any public university.

Air purifier or fresh air system?A comparison of energy consumption and cost in urban China residential buildings

Chinese urban residential buildings face serious indoor air quality problems.Air purification systems(e.g.,air purifiers,fresh air systems)that supply fresh air or purify indoor air are widely used in residential buildings to improve indoor air quality.Considering the challenges of energy conservation and emission reduction,it is urgent to guide residents on choosing appropriate air purification systems.The key problem is how to identify the best air purification system with the lowest energy consumption or operating cost.Comparisons of air purification systems have rarely been conducted on the premise that they should deliver air such that the main indoor pollutant concentrations all meet air quality standards.Also ignored in comparisons are the increased filtration resistance caused by dust accumulation on the filter and the cost of filter replacement.In this study,we propose a method to compare residential air purification systems based on energy consumption and total cost,and we provide methods to select air purification systems in China's different climatic regions.We used a standard two-person bedroom as the example,and determined the most suitable(minimum cost or energy consumption)air purification systems for the capital cities of the provinces in Chinese mainland.

Systemic air embolism associated with endoscopic retrograde cholangiopancreatography: A case report

BACKGROUND Endoscopic retrograde cholangiopancreatography(ERCP)is a key procedure for diagnosing and treating biliary and pancreatic disorders.Although effective,it carries risks,including rare but severe complications such as air embolism.CASE SUMMARY We report a case of a 58-year-old man who developed extensive air embolism during ERCP.He previously underwent a Whipple procedure and experienced a sudden drop in vital signs and loss of consciousness.Immediate intervention with hyperbaric oxygen therapy and supportive care led to gradual recovery.Imaging confirmed widespread air embolism,which resolved with continued treatment.CONCLUSION Air embolism is a rare,critical complication of ERCP,especially in patients with prior surgery such as pancreaticoduodenectomy.Early detection and prompt treatment,including hyperbaric oxygen therapy,are crucial for favorable out-comes.

Enhancing Patients Outcomes and Infection Control through Smart Indoor Air Quality Monitoring Systems

Air pollution poses a critical threat to public health and environmental sustainability globally, and Nigeria is no exception. Despite significant economic growth and urban development, Nigeria faces substantial air quality challenges, particularly in urban centers. While outdoor air pollution has received considerable attention, the issue of indoor air quality remains underexplored yet equally critical. This study aims to develop a reliable, cost-effective, and user-friendly solution for continuous monitoring and reporting of indoor air quality, accessible from anywhere via a web interface. Addressing the urgent need for effective indoor air quality monitoring in urban hospitals, the research focuses on designing and implementing a smart indoor air quality monitoring system using Arduino technology. Employing an Arduino Uno, ESP8266 Wi-Fi module, and MQ135 gas sensor, the system collects real-time air quality data, transmits it to the ThingSpeak cloud platform, and visualizes it through a user-friendly web interface. This project offers a cost-effective, portable, and reliable solution for monitoring indoor air quality, aiming to mitigate health risks and promote a healthier living environment.

Simulation of the secondary air system of turbofan engines:Insights from 1D-3D modeling

Focusing on the internal flow and heat transfer analysis,a platform for the performance evaluation of the Secondary Air System(SAS)is developed.A multi-fidelity modeling technique has been developed in a turbofan engine model under different flight conditions.A turbine blade cool-ing model which integrates external heat transfer calculations and coolant side modeling with com-mon components is proposed.In addition,the Computational Fluid Dynamics(CFD)method is selected to capture the complex flow field structure in the preswirl system.The validity of the SAS models is compared with publicly available data.An elaborately designed cooling system for the AGTF30 engine is analyzed through three main branches.It is found that the 1D-3D mod-eling technique can provide more accurate predictions of the SAS for the AGTF30 engine.The results demonstrate the versatility and flexibility of the SAS models,thereby indicating the capacity of meeting most of the demands of flow and thermal analysis of the SAS.

Multi-scale simulation model of air system based on cross-dimensional data transmission method

The Secondary Air System(SAS)plays an important role in the safe operation and performance of aeroengines.The traditional 1D-3D coupling method loses information when used for secondary air systems,which affects the calculation accuracy.In this paper,a Cross-dimensional Data Transmission method(CDT)from 3D to 1D is proposed by introducing flow field uniformity into the data transmission.First,a uniformity index was established to quantify the flow field parameter distribution characteristics,and a uniformity index prediction model based on the locally weighted regression method(Lowess)was established to quickly obtain the flow field information.Then,an information selection criterion in 3D to 1D data transmission was established based on the Spearman rank correlation coefficient between the uniformity index and the accuracy of coupling calculation,and the calculation method was automatically determined according to the established criterion.Finally,a modified function was obtained by fitting the ratio of the 3D mass-average parameters to the analytical solution,which are then used to modify the selected parameters at the 1D-3D interface.Taking a typical disk cavity air system as an example,the results show that the calculation accuracy of the CDT method is greatly improved by a relative 53.88%compared with the traditional 1D-3D coupling method.Furthermore,the CDT method achieves a speedup of 2 to 3 orders of magnitude compared to the 3D calculation.

A review on system and materials for aqueous flexible metal-air batteries

The exploration of aqueous flexible metal-air batteries with high energy density and durability has attracted many research efforts with the demand for portable and wearable electronic devices.Aqueous flexible metal-air batteries feature Earth-abundant materials,environmental friendliness,and operational safety.Each part of one metal-air battery can significantly affect the overall performance.This review starts with the fundamental working principles and the basic battery configurations and then highlights on the common issues and the recent advances in designing high-performance metal electrodes,solid-state electrolytes,and air electrodes.Bifunctional oxygen electrocatalysts with high activity and long-term stability for constructing efficient air electrodes in flexible metal-air batteries are summarized including metal-free carbon-based materials and nonprecious Co/Fe-based materials(alloys,metal oxides,metal sulfites,metal phosphates,metal nitrates,single-site metal-nitrogen-carbon materials,and composites).Finally,a perspective is provided on the existing challenges and possible future research directions in optimizing the performance and lifetime of the flexible aqueous solid-state metal-air batteries.

An approach for simulating the air brake system of long freight trains based on fluid dynamics

Air brake systems are critical equipment for railway trains, which affects the running safety of the trains significantly. To study air braking characteristics of long freight trains, an approach for simulating air brake systems based on fuid dynamics theory was proposed. The structures and working mechanisms of locomotive and wagon air brakes are introduced, and mathematical models of the pipes, brake valves, reservoirs or chambers, cylinders, etc., are presented.Besides, the dynamic motions of parts in the main valve are considered. The simulation model of the whole air brake system is then formulated, and the solving method based on the finite-difference method is used. New efficient pipe boundary conditions without iterations are developed for brake pipes and branch pipes, which can achieve higher computational efficiency. The proposed approach for simulating the air brake system is validated by comparing with published measured data. Simulation results of different train formations indicate that models that consider the dynamic behavior of brake pipes are recommended for predicting the characteristics of long trains under service braking conditions.

具有时滞效应的air2stream河流水温模型及应用研究

高精度河流水温模型对于深入了解水温的时空变化特征和河流生态修复具有重要意义。基于数据驱动的air2stream模型在保证预测精度的同时,避免了计算的复杂性,已成为河流水温模拟常用的模型。由于水的热惯性及水文条件等的影响,河流水温变化往往显著滞后于气温变化,而air2stream原模型并未考虑滞后效应,导致该模型在流量未知情况下实际精度偏低。为解决该问题,采用气温-水温皮尔逊相关系数计算时滞天数,构建具有时滞的air2stream新模型,进一步根据长江中下游地区两个监测站的多年实测数据验证新模型的有效性和稳定性。结果表明:新模型在不引进额外观测数据的条件下具有更高精度且性能更稳定。相比原模型,在两个监测站新模型的均方根误差分别降低约4.29%和5.85%。新模型具有精度高、水文要素需求少的特点,可为长江中下游的水环境影响评价和生态保护提供依据。

Mastering air combat game with deep reinforcement learning

Reinforcement learning has been applied to air combat problems in recent years,and the idea of curriculum learning is often used for reinforcement learning,but traditional curriculum learning suffers from the problem of plasticity loss in neural networks.Plasticity loss is the difficulty of learning new knowledge after the network has converged.To this end,we propose a motivational curriculum learning distributed proximal policy optimization(MCLDPPO)algorithm,through which trained agents can significantly outperform the predictive game tree and mainstream reinforcement learning methods.The motivational curriculum learning is designed to help the agent gradually improve its combat ability by observing the agent's unsatisfactory performance and providing appropriate rewards as a guide.Furthermore,a complete tactical maneuver is encapsulated based on the existing air combat knowledge,and through the flexible use of these maneuvers,some tactics beyond human knowledge can be realized.In addition,we designed an interruption mechanism for the agent to increase the frequency of decisionmaking when the agent faces an emergency.When the number of threats received by the agent changes,the current action is interrupted in order to reacquire observations and make decisions again.Using the interruption mechanism can significantly improve the performance of the agent.To simulate actual air combat better,we use digital twin technology to simulate real air battles and propose a parallel battlefield mechanism that can run multiple simulation environments simultaneously,effectively improving data throughput.The experimental results demonstrate that the agent can fully utilize the situational information to make reasonable decisions and provide tactical adaptation in the air combat,verifying the effectiveness of the algorithmic framework proposed in this paper.

基于Aqua卫星AIRS数据的南大洋大气逆温和逆湿特性研究

南大洋大气普遍存在着逆温和逆湿现象,其分布和变化对海-冰-气之间的物质和通量交换具有重要影响。利用Aqua卫星上搭载的大气红外探测器(AIRS)观测数据,提取了南大洋大气的逆温和逆湿特性,并研究了其时空分布与变化特征。此外,以全球无线电探空数据集的探测结果为参考值,分析了AIRS在进行大气逆温和逆湿探测过程中受到云量影响的特征。结果表明,AIRS估计的逆温特性受云量的影响较小,在多云条件下AIRS也可精确地估计逆温特性。利用AIRS最新的第7版(V7)数据产品对2004-2020年南大洋大气逆温和逆湿的频率(强度)进行研究,发现秋冬季比春夏季高(强),在龙尼冰架、罗斯冰架和南极半岛附近的海域的大气出现逆温和逆湿现象较其他区域更频繁,且强度更强。

Recent progress of self-supported air electrodes for flexible Zn-air batteries

Smart wearable devices are regarded to be the next prevailing technology product after smartphones and smart homes,and thus there has recently been rapid development in flexible electronic energy storage devices.Among them,flexible solid-state zinc-air batteries have received widespread attention because of their high energy density,good safety,and stability.Efficient bifunctional oxygen electrocatalysts are the primary consideration in the development of flexible solid-state zinc-air batteries,and self-supported air cathodes are strong candidates because of their advantages including simplified fabrication process,reduced interfacial resistance,accelerated electron transfer,and good flexibility.This review outlines the research progress in the design and construction of nanoarray bifunctional oxygen electrocatalysts.Starting from the configuration and basic principles of zinc-air batteries and the strategies for the design of bifunctional oxygen electrocatalysts,a detailed discussion of self-supported air cathodes on carbon and metal substrates and their uses in flexible zinc-air batteries will follow.Finally,the challenges and opportunities in the development of flexible zinc-air batteries will be discussed.

Exploring the relationship between ambient sulfur dioxide and semen quality parameters:A systematic review and meta-analysis

Objective:To investigate the relationship between ambient sulfur dioxide(SO2)exposure and semen quality parameters.Methods:A systematic literature search was conducted to identify relevant studies investigating the association between SO2 exposure and semen quality parameters.This search encompassed the timeframe from January 2000 to May 2023 and included electronic databases such as Web of Science,Google Scholar,PubMed,Cochrane,and Scopus.Pooled effect estimates with 95%confidence intervals(CI)were calculated using percent changes(PC).The meta-analysis included seven studies with 6711 participants and 15087 semen samples.Results:The results revealed a significant negative association between ambient SO2 exposure and certain semen quality parameters.In particular,SO2 exposure was associated with a significant decrease in progressive motility(PC=0.032;95%CI:-0.063 to-0.001;P=0.044)and sperm concentration(PC=-0.020;95%CI:-0.036 to-0.005;P=0.012).However,no statistically significant associations were observed for total sperm count(PC=-0.038;95%CI:-0.079 to 0.003;P=0.070),seminal fluid volume(PC=-0.009;95%CI:-0.048 to-0.030;P=0.662)and sperm motility(PC=-0.17;95%CI:-0.363 to 0.022;P=0.830).In addition,the results of the subgroup analysis revealed specific variables that were associated with the decrease in relevant sperm parameters.Conclusions:This systematic review and meta-analysis provides compelling evidence supporting a consistent negative association between exposure to ambient SO2 and semen quality parameters.

Inhibition mechanism of air nanobubbles on brass corrosion in circulating cooling water systems

Air nanobubbles(A-NBs)were used to inhibit the brass corrosion in circulating cooling water for the first time in the study.The results of mass loss method and electrochemical method showed that A-NBs had the obvious corrosion inhibition effect.The inhibition rate reached 52%at 35℃.The impedance and surface characterization results of corrosion samples indicated that the corrosion inhibition mechanisms of A-NBs mainly included adsorption of corrosion ions,promoting the formation of the passivation film on metal surface and the formation of the bubble layer and scale film on metal surface.A-NBs are potential excellent corrosion inhibitors.

Co/CoO heterojunction rich in oxygen vacancies introduced by O_(2) plasma embedded in mesoporous walls of carbon nanoboxes covered with carbon nanotubes for rechargeable zinc-air battery

Herein,Co/CoO heterojunction nanoparticles(NPs)rich in oxygen vacancies embedded in mesoporous walls of nitrogen-doped hollow carbon nanoboxes coupled with nitrogen-doped carbon nanotubes(P-Co/CoOV@NHCNB@NCNT)are well designed through zeolite-imidazole framework(ZIF-67)carbonization,chemical vapor deposition,and O_(2) plasma treatment.As a result,the threedimensional NHCNBs coupled with NCNTs and unique heterojunction with rich oxygen vacancies reduce the charge transport resistance and accelerate the catalytic reaction rate of the P-Co/CoOV@NHCNB@NCNT,and they display exceedingly good electrocatalytic performance for oxygen reduction reaction(ORR,halfwave potential[EORR,1/2=0.855 V vs.reversible hydrogen electrode])and oxygen evolution reaction(OER,overpotential(η_(OER,10)=377mV@10mA cm^(−2)),which exceeds that of the commercial Pt/C+RuO_(2) and most of the formerly reported electrocatalysts.Impressively,both the aqueous and flexible foldable all-solid-state rechargeable zinc-air batteries(ZABs)assembled with the P-Co/CoOV@NHCNB@NCNT catalyst reveal a large maximum power density and outstanding long-term cycling stability.First-principles density functional theory calculations show that the formation of heterojunctions and oxygen vacancies enhances conductivity,reduces reaction energy barriers,and accelerates reaction kinetics rates.This work opens up a new avenue for the facile construction of highly active,structurally stable,and cost-effective bifunctional catalysts for ZABs.

Research on Operation Optimization of Heating System Based on Electric Storage Coupled Solar Energy and Air Source Heat Pump

For heating systems based on electricity storage coupled with solar energy and an air source heat pump(ECSA),choosing the appropriate combination of heat sources according to local conditions is the key to improving economic efficiency.In this paper,four cities in three climatic regions in China were selected,namely Nanjing in the hot summer and cold winter region,Tianjin in the cold region,Shenyang and Harbin in the severe cold winter region.The levelized cost of heat(LCOH)was used as the economic evaluation index,and the energy consumption and emissions of different pollutants were analyzed.TRNSYS software was used to simulate and analyze the system performance.The Hooke-Jeeves optimization algorithm and GenOpt software were used to optimize the system parameters.The results showed that ECSA systemhad an excellent operation effect in cold region and hot summer and cold winter region.Compared with ECS system,the systemenergy consumption,and the emission of different pollutants of ECSA system can be reduced by a maximum of 1.37 times.In cold region,the initial investment in an air source heat pump is higher due to the lower ambient temperature,resulting in an increase in the LOCH value of ECSA system.After the LOCH value of ECSA system in each region was optimized,the heating cost of the system was reduced,but also resulted in an increase in energy consumption and the emission of different pollutant gases.