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Moisture Absorption, Mass Loss and Evaporative Resistance of Clothing in transient condition

Journal of Donghua University(English Edition) 2006年第5期23卷 54-58页

作者： Chuansi Gao Ingvar Holmr The Thermal Environment Laboratory Division of Ergonomics Department of Design Sciences Faculty of Engineering Lund University Box 118 22100 Lund Sweden

The water vapour resistance of clothing ensembles is not as commonly determined as dry thermal insulation. The measurement techniques are more complicated and the measurement values differ among laboratories. Due to complicated moisture transfer process through clothing ensemble, the moisture absorbed and evaporated varies in transient and steady state phases depending on properties, thickness of clothing, and environmental conditions. The purpose of this study was to measure moisture gain inside hygroscopic underwear, and hydrophobic and permeable outer wear as a function of time, to investigate mass loss from ＂skin＂ as well as from the manikin, to quantify evaporative heat loss and total heat loss from the manikin, and to determine water vaponr resistance of clothing. Manikin Tore was used by wearing wet ＂skin＂ to simulate sweating condition. Moisture content in the inner garment gain shows an exponential relation against time. Moisture in the outer permeable layer shows little gain. On the contrary, mass loss directly from the wet skin decreases exponentially. The mass loss from the manikin is relatively stable throughout three test phases. The evaporative heat loss is about 2/3 of the total heat loss from the sweating manikin. While measuring the evaporative resistance of clothing ensembles with hygroscopic inner garment and permeable outer garment, unlike to measure ensembles with impermeable outer layer, one hour measurement time is enough to get relatively stable results. The variation between the 1^rt hour and the 3^nd hour is less than 5%. The length of transient period and measurement time is dependent on the permeability, thickness of clothing ensembles and environmental conditions.

关键词： moisture absorption mass loss evaporative resistance transient condition clothing ensemble.

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Impact of Typical Steady-state conditions and transient conditions on Flow Ripple and Its Test Accuracy for Axial Piston Pump

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Chinese Journal of Mechanical Engineering 2015年第5期28卷 1012-1022页

作者： XU Bing HU Min ZHANG Junhui State Key Laboratory of Fluid Power Transmission and Control Zhejiang University

The current research about the flow ripple of axial piston pump mainly focuses on the effect of the structure of parts on the flow ripple. Therein, the structure of parts are usually designed and optimized at rated working conditions. However, the pump usually has to work in large-scale and time-variant working conditions. Therefore, the flow ripple characteristics of pump and analysis for its test accuracy with respect to variant steady-state conditions and transient conditions in a wide range of operating parameters are focused in this paper. First, a simulation model has been constructed, which takes the kinematics of oil film within friction pairs into account for higher accuracy. Afterwards, a test bed which adopts Secondary Source Method is built to verify the model. The simulation and tests results show that the angular position of the piston, corresponding to the position where the peak flow ripple is produced, varies with the different pressure. The pulsating amplitude and pulsation rate of flow ripple increase with the rise of pressure and the variation rate of pressure. For the pump working at a constant speed, the flow pulsation rate decreases dramatically with the increasing speed when the speed is less than 27.78% of the maximum speed, subsequently presents a small decrease tendency with the speed further increasing. With the rise of the variation rate of speed, the pulsating amplitude and pulsation rate of flow ripple increase. As the swash plate angle augments, the pulsating amplitude of flow ripple increases, nevertheless the flow pulsation rate decreases. In contrast with the effect of the variation of pressure, the test accuracy of flow ripple is more sensitive to the variation of speed. It makes the test accuracy above 96.20% available for the pulsating amplitude of pressure deviating within a range of ~6% from the mean pressure. However, with a variation of speed deviating within a range of ±2% from the mean speed, the attainable test accuracy o

关键词： axial piston pump flow ripple test accuracy steady-state condition transient condition wide operating ranges

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A novel approach for predicting inlet pressure of aircraft hydraulic pumps under transient conditions

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Chinese Journal of Aeronautics 2019年第11期32卷 2566-2576页

作者： Yan WANG Hongkang DONG Yongling HE School of Transportation Science and Engineering Beihang University

Cavitation caused by insufficient suction is a major factor that influences the life of aircraft pumps. Currently, pressurizing the tank can solve the cavitation problem under steady largeflow conditions. However, this method is not always effective under transient conditions(from zero flow to full flow in a very short time). Moreover, to apply and design other measures, such as a boost impeller, the suction dynamics during the transient period must be investigated. In this paper,a novel approach based on the pressure wave propagation theory is proposed for predicting the inlet pressure of an aircraft pump under transient conditions. First, a dynamic model of a typical aircraft pump is established in the form of differential equations. Then, the transient flow model of the inlet line is described using momentum and continuity equations, and the governing equations are discretized by the method of characteristics and the finite difference method. The simulated results are in good agreement with the results from verification tests. Further simulation analysis indicates that the wave velocity and transient time may influence the inlet and reservoir pressure as well as the size of the inlet line. Finally, solutions for upgrading the inlet pressure are discussed. These solutions provide guidelines for designing inlet installations.

关键词： Aircraft hydraulic pump Boost impeller Inlet pressure Method of characteristics transient condition Wave propagation

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External Characteristics and Internal Flow Features of a Centrifugal Pump during Rapid Startup

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Chinese Journal of Mechanical Engineering 2011年第5期24卷 798-804页

作者： ZHU Zuchao GUO Xiaomei CUI Baoling LI Yi Laboratory of Fluid Power Transmission Zhejiang Sci-Tech University Hangzhou 310018 China Mechanical and Electronic Engineering Department Zhejiang Water Conservancy and Hydropower College Hangzhou 310018 China

Centrifugal pumps always work under steady conditions,and many researches focus on the steady *** transient conditions,such as sudden startup and shutdown,are *** researches on the inner flow of centrifugal pumps under transient conditions have been done,and they show that the transient operation is different from the steady *** order to research the evolution of unsteady flow in a centrifugal pump under transient conditions,and to investigate the mechanism of transient effects by analyzing the unsteady flow in a centrifugal pump,the external characteristic experiment and the internal flow numerical calculation of the centrifugal pump with an open impeller during startup is *** relationships of the rotation speed,capacity and head between start-time are obtained by the external characteristics *** numerical calculations under startup process are carried out by using the k-e model and N-S *** distribution of velocity and pressure in the inner channel of the tested pump was obtained by choosing fourteen start-time points and twelve geometrical points in the impeller channel during *** calculation results show that the velocity and the pressure increase linearly with the start-time before rotation＇s speed gets steady,then changes almost horizontally after rotation speed becomes steady,then fluctuates until being *** internal flow characteristics are in good agreement with the external characteristic experimental results and numerical *** simulation methods and results make the basis for the diagnosis and optimization of under flow in the centrifugal pump during transient operation.

关键词： centrifugal pump numerical calculation transient condition startup

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MULTI-STEP PREDICTIVE MODEL OF AIR FUEL RATIO FOR GASOLINE ENGINE BASED ON NEURAL NETWORK

MULTI-STEP PREDICTIVE MODEL OF AIR FUEL RATIO FOR GASOLINE E...

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2006年中国机械工程学会年会暨中国工程院机械与运载工程学部首届年会

作者： HOU Zhixiang, WU Yihu College of Automobile and Mechanical Engineering, Changsha University of Science and Technology, Changsha 410076, China

Air fuel ratio is a key index affecting the emission of gasoline engine. A multi-step predictive model of air fuel ratio based on neural network was provided in this paper to overcome air fuel ratio t

关键词： gasoline engine transient condition air fuel ratio neural networks multi-step prediction.

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AIR FUEL RATIO ACCURATE CONTROL BASED ON RBF NEURAL NETWORKS

AIR FUEL RATIO ACCURATE CONTROL BASED ON RBF NEURAL NETWORKS

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第七届海内外青年设计与制造科学会议

作者： Hou Zhixiang, Wu Yihu and Yu Dan College of Automobile and Mechanical Engineering, Changsha University of Science and Technology, China College of information science and engineering, Central South University, China College of Traffic and Transportation, Changsha University of Science and Technology, China

＜正＞Air fuel ratio accurate control is a key index decreasing emission and fuel consumption of gasoline engine, and its accurate control is very difficulty, especial under transient conditions. The composite air fuel ratio control strategy based on neural networks is advocated in this paper, where feedback control is achieved by means of regular PI controller to ensure the system stability and anti-disturbance, and feedforward control is achieved by virtue of neural networks controller to enhance response ability of control system under transient conditions. Radius basis function neural network whose inputs are the engine rotation speed and the throttle degree which are the two chief factors affecting engine admission volume is adopted. Overall control output of the system is generated by neural networks through on line study the output of PI controller. The system can effectively avoid the present defects elicited by enormous calibration to accurate control air fuel ration under transient condition with fair self-adaptability. The simulation was finished using experiment data of HL495 gasoline engine, and the results show the effectiveness of this control method.

关键词： Gasoline engine Mean value model transient condition Air fuel ratio control Neural networks

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汽轮机通流及汽水系统可视化建模的研究

汽轮机通流及汽水系统可视化建模的研究

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作者：梁亚丛华北电力大学（北京）

学位级别：硕士

汽轮机及其热力系统在变工况条件下，通流部分各级的性能参数及汽轮机热力系统的各参数都要发生相应的变化，要确定变工况下汽轮机及其热力系统的各经济性参数及进行强度和安全性方面的分析，需对其进行详细地、客观地热力核算。本论文... 详细信息

汽轮机及其热力系统在变工况条件下，通流部分各级的性能参数及汽轮机热力系统的各参数都要发生相应的变化，要确定变工况下汽轮机及其热力系统的各经济性参数及进行强度和安全性方面的分析，需对其进行详细地、客观地热力核算。本论文采用最新算法对汽轮机通流及汽轮机热力系统的各经济性参数进行了较准确的计算，并采用面向对象的编程语言java编制出了灵活性和准确性较高的热力计算程序。本论文完善了水蒸汽性质计算的函数，通过任意两个独立的水蒸汽状态参数量便可求得其它状态参数变量。然后，在分析汽轮机变工况热力核算的逆序法和顺序法的基础上，引出了混合算法，该算法经验算具有较高的准确性和收敛性。并采用矩阵方法对汽轮机热力系统进行了模拟计算。

关键词： thermal calculation of steam turbines calculation of steam property transient condition thermal balance

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