长距离供水系统中空气阀的进排气特性参数研究

为研究空气阀进排气特性参数,基于数学模型,通过模拟计算,得出了空气阀的进排气流量系数与流通面积乘积随压差的变化规律;并根据不同压差下的空气阀进排气流量系数与流通面积乘积值,计算了不同进气流量系数下的进气流通面积。结果表明,空气阀的进排气流量系数与流通面积乘积随压差的增大而增大,且排气时乘积的变化幅度小于进气时;进气流通面积与其直径直接对应的面积存在差异。研究结果可为空气阀的设计及选型提供指导作用。     

进口压力对燃气轮机气体燃料阀调节性能的影响及其修正补偿方法研究

燃料调节阀是精确控制燃气轮机燃料流量和机组负荷的基本组件。本文基于调节阀的位移-流量特性及其液压伺服机构组成,建立了燃料阀位置伺服系统的数学模型,分析了燃料阀组及其控制系统的动态响应特性,研究了进口压力对调节阀性能的影响,并提出了一种燃料进口压力修正补偿控制方法。仿真结果表明：经过压力修正后,系统响应频宽提高0.5 Hz,幅值裕量增大20°。     

气道稳流试验的变压差试验方法研究

提出了用于测量发动机气道流动特性的气道变压差试验方法。与目前采用的气道稳流试验方法不同，在试验过程中，采集对应于各气阀升程下的流量和涡流角动量时，不需要保持气缸内恒压差条件，变压差试验只需要确定气阀最大升程时模拟气缸内与环境大气压的初始压差，在变压差条件下进行试验，同样可以得到Ricardo和FEV试验计算方法的平均流量系数和涡流比。变压差试验方法的测量精度与定压差的精度相同，试验操作程序简单可靠，易于实现气道稳流试验的全自动化，对于企业生产线上的批量缸盖检测可以大幅度提高工作效率。     

Numerical investigation for the calculation of TiO2–water nanofluids' pressure drop in plain and enhanced pipes

In this investigation, a numerical model having two-dimensional equations was obtained by a CFD program and authors' experimental data were evaluated for the verification procedure of the numerical outputs. The experimental case study includes the single-phase flow of pure water in plain and micro-fin pipes whereas the numerical one has the simulated results of TiO₂ particles suspended in single phase water flow in equivalent pipes at a constant heat flux. Hydrodynamics and thermal behaviors of the water–TiO₂ flow were calculated by constant heat flux and temperature-dependent settings. Physical specifications of nanofluids were calculated by means of the results of authors' previous ANN analyses. This study illustrates local and average values of temperature, pressure, and velocity distributions in the tested pipes; furthermore, comparisons of pressure drop characteristics are given in terms of nanoparticle concentrations and tube types.     

A mathematical model of variable displacement wobble plate compressor for automotive air conditioning system

Based on the force balance equations, mass and energy conservation equations, a mathematical model of control valve used in the variable displacement wobble plate compressor (VDC) is developed firstly. The dynamic model of the moving components is developed then by analyzing the forces and force moments acting on the piston, piston rod, wobble plate, rotating journal and shaft sleeve. The compression process model is obtained by fitting the data from our experiments. And finally the steady-state mathematical model of VDC is developed by combining the three models above. In order to verify the mathematical model of compressor, a test bench for the control valve and the test system for the VDC have been established, and the simulated results agree well with the experimental data. The simulation results show that there are four operation modes for the VDC, i.e. constant rotary speed and constant piston stroke length (PSL), variable rotary speed and constant PSL, constant rotary speed and variable PSL, variable rotary speed and variable PSL, which have included almost all operation modes of the refrigeration compressor in common use.     

液_液射流雾化的数值模拟与实验研究

建立了液-液雾化机理的数值模拟平台与实验研究平台,对水在非相溶溶液中的喷射雾化机理进行了研究。应用VOF-CSF多相流模型对雾化过程进行了数值模拟,并在相同工况下进行了实验验证和对比。研究表明,所建立的数学模型能成功地模拟连续射流雾化过程,与实验结果取得了非常好的一致性。通过数值模拟和实验相结合的方法,对雾化过程中的射锥高度、射流速度、非相溶介质流速等关键因素的影响进行了探讨,获得了相应的规律:在确定的雾化条件下,雾化液滴粒径呈现出离散性;液滴的运动方式随射流速度的增加由规则逐渐过渡为紊乱;射流速度为3.5 m/s与非相溶介质流速为0.18 m/s时,雾化射锥高度变化趋势发生转变。本文的研究结果对认识液-液射流雾化机理以及相应的工程应用,具有重要的指导意义和实用价值。     

长江砖灶子复杂滩险河段航道治理研究

针对长江砖灶子河段水沙条件多变、滩险特性综合、周边环境复杂的情况,分析了工程河段水文泥沙特性、河床演变规律和滩险碍航成因,结合该河段航道整治目标,提出了疏浚、炸礁、深沱回填和筑坝相结合的整治方案。应用平面二维水沙数学模型分析方案整治效果,经水流条件及河床变形验证,模型精度符合规范要求。在水流条件和典型年泥沙冲淤特性分析的基础上进行方案比选,并探讨了推荐方案的航槽稳定性,结果表明,推荐方案航道尺度满足规划要求且可长期保持,整治效果较好。研究结果可为山区河流复杂综合滩险的有效治理提供借鉴。     

Simulation and performance analysis of control mechanism in variable displacement swash plate compressor

The mathematical model of the control mechanism used in a variable displacement swash plate compressor (VDSC) is developed based on the force balance equation, mass and energy conservation equation. In order to verify the mathematical model, a test bench of control mechanism and test system of VDSC are established, and the simulated results agree well with the experimental data. With the mathematical model, the steady-state performance of control mechanism is simulated. The simulation results show that there is an inflection point (defined as the preset point) to divide the opening process of mass flow compensation control valve into a gradual opening stage and a quick opening stage. In the gradual opening stage, the swash plate case pressure goes down quickly and the mass flow rate rises along with the increase of suction pressure; in the quick opening stage, the swash plate case pressure goes up and the mass flow rate goes down along with the increase of suction pressure. The suction pressure at the preset point is linear inversely proportional to the discharge pressure.     

Three-Dimensional Unstable Non-linear Numerical Analysis of the Underground Coal Gasification with Free Channel

The three-dimensional unstable non-linear coupled mathematical model on the underground coal gasification with free channel is established in this article. The determination methods for the major model parameters are explained. Adopting the SIMPLE method, the numerical solution of the mathematical model is found. Additionally, the patterns of variation and development for the temperature field, concentration field and pressure field in the gasification panel are studied. On the basis of the model test, the calculation results are analyzed. Research shows that calculated values of the temperature field are a little higher than the experimental ones, and the relative error for every measuring point is virtually within 16%. Also, a good conformity takes on between the experimental values for the concentration field of the gas compositions and the calculated ones. The simulated results indicate that the relative calculation error of the pressure field is 10.20%–19.44%. Through the analysis of measured data, the change mechanisms of the gas compositions, heating value and pressure field in the underground gasification with free channel are pointed out.     

汽油机掺醇燃烧进气油膜湿壁温度预测

对进气口喷射汽油机进气门处传热过程进行了分析,建立了进气油膜吸附壁面温度模型.通过冷机状态起动试验和温升过程数据分析,对已有模型结构进行了细化和改进,并基于试验数据及MATLAB参数辨识工具箱对模型参数进行了辨识.根据模型结构及试验数据,分析了油膜吸附壁面温度的关键影响因素和影响规律,以及不同掺混比例乙醇汽油下的差异.油膜吸附壁面温度变化规律类似一阶惯性系统特性,其温升时间常数可视为进气流量的单值函数,但稳态项与多个发动机工况参数有关,而不同乙醇汽油下油膜吸附壁面温度则差异不大.改进与辨识后油膜吸附壁面温度模型在纯汽油及掺醇汽油下均具有较高的预测精度,可直接用于油膜动态补偿器设计.     

塔式炉膛烟气流动特性及非线性现象的数值和实验分析

为研究不同负荷超(超)临界塔式炉膛内燃烧及烟气流动的非线性特性,以某1 000 MW塔式炉膛为原型设计出几何结构和边界条件完全对称的三维简化锅炉模型,运用FLUENT软件模拟了锅炉在3种不同负荷(100%,75%和50%阀门全开工况(VWO))下炉膛内的速度场、温度场及NO_x的分布情况,并分析了非线性特性,最后建立了一个三维冷态切圆射流实验模型并进行验证,提出顺序启动的喷口启动方式。结果表明：不同负荷下,完全对称的炉膛内烟气流动速度、温度和组分分布均存在非线性现象,模拟结果得到关于模型几何竖直中心线不对称的解;喷嘴通过顺序启动方式可使切圆偏斜程度更小,流动形成的切圆能稳定在一个位置,实现流动的精准控制。     

Subcooled water critical pressure and critical flow rate in a safety valve

Subcooled water critical flow phenomena in a safety valve are investigated experimentally at various subcoolings between 10 and 125 K, and about 1 MPa of the inlet pressure with three different disk lifts, 1, 2, and 3 mm. The purpose of this experiment is to find the effects of subcooling and disk lift and to visualize flow patterns in a safety valve when the critical condition is established. All of the experiments show the critical characteristics such as constant throat pressure and constant flow rate when the back pressure is sufficiently decreased. Two correlations, critical pressure ratio and non-equilibrium factor, are developed by using the present experimental data represented in the form of non-dimensional disk lift, subcooling, and pressure. Critical pressure ratios and non-equilibrium factors are considerably affected by different subcoolings while the effect of disk lifts on them is relatively small. A non-equilibrium critical mass flow correlation for the safety valve is also developed based on Fauske's non-equilibrium model and the presented experimental data. The predictions of the correlation are within ±11% of the experimental data.     

A study of solid circulation rate in a circulating fluidized bed

An experimental investigation under cold condition was made to study the effects of some operating/design parameters and non-mechanical L valve configuration on the solid circulation rate in a 4.5 m tall, 0.15 m diameter circulating fluidized bed with riser flow rate varying from 1400 litres/min to 2000 litres/min and bed inventory from 15 kg to 25 kg of sand of average sizes 200 μm, 400 μm and 500 μm. Solid circulation rate was estimated by measuring velocity of sand particle travelling through a vertical Perspex tube section at the bottom of the return leg. It was found to be in the range of 2.8 to 12.3kg/m²s, 0.07 to 9.1kg/m²s and 0.12 to 2.23kg/m²s for sand sizes of 200 μm, 400 μm and 500 μm, respectively for a horizontal L valve. Two mathematical correlations have been developed from the experimental results to predict solid circulation rate as a function of riser flow rate, aeration flow rate, total bed inventory and particle size used.     

湿热地区波纹翅片管式表冷器的运行性能和调节能力研究

表冷器作为空调系统中空气的热湿处理设备在湿热地区应用广泛。然而,随着户式中央空调的发展,它与中小型冷水机的匹配及运行优化仍缺少指南。建立了某9排管空气-水逆流式波纹翅片管式表冷器的传热除湿数学模型。模拟结果分析表明:室外气象参数的影响显著,气温越高且露点温度越高,则其供冷和除湿能力显著提高;在广州和杭州六月份平均气象条件下,调节表冷器的供水温度、供水流速或管外风速,其供冷能力可分别在名义供冷能力的32%~95%以及45%~120%内调节,除湿能力也可相应随之得到调节;入口水温愈低,则变水量或变风量对表冷器供冷及除湿能力的调节作用范围越广;风速愈大且水流速度愈高,则变水温的调节作用范围越广;入口水温越低、风速越大或水流速度越大,则联合调节风量水量、水温水量或水温风量对其供冷和除湿能力的调节作用范围也越广。     

Experimental and numerical analysis of spring stiffness on flow and valve core movement in pilot control globe valve

Valves are widely used for fluid flow control, not only for conventional fluid like water, gas and oil, but also for hydrogen under high pressure and so forth. Under these new conditions, the response time and energy consumption of valves are closely related to the whole performance of the piping system. Pilot-control globe valve (PCGV) is a novel quick response valve, which can utilize the pressure difference before and after the valve core to control the open/close states of the main valve. In this paper, the effects of spring stiffness inside PCGV on the flow and the valve core movement are carried out, respectively. To begin with, the experimental setup is introduces and the 3D numerical model is established. The simulation is carried out in software FLUENT with RNG k-ε turbulence model, User Defined Function method and dynamic mesh regeneration methods under transmit state. Then, a comparison of steady valve core displacements between experiment and simulation is carried out. After that, the effects of spring stiffness on flow characteristics, valve core movement and response times during opening and closing periods are presented. Finally, a spring chosen correction equation is proposed. This work can benefit the further design work of PCGVs or similar valves with springs, and it can be also referred by someone dealing with novel control valves design or flow control issues.     

Performance analysis of a novel hydrogen production system incorporated with hybrid solar collector and phase change material

In this technical article, a novel experimental setup is designed and proposed to produce a hydrogen by using solar energy. This system comprises a hybrid or photovoltaic Thermal (PVT) solar collector, Hoffman's voltameter, heat exchanger unit and Phase Change Material (PCM). The effect of PCM and mass flow rate of water on the hybrid solar collector efficiency and hydrogen yield rate is studied. This experimental results clearly showed that by adding the thermal collector with water, decreases PV module temperature by 20.5% compared with conventional PV module. Based on the measured values, at 12.00 and 0.011 kg/s mass flow rate, about 33.8% of thermal efficiency is obtained for water based hybrid solar collector. Similarly, by adding Paraffin PCM to the water based thermal collector, the maximum electrical efficiency of 9.1% is achieved. From this study, the average value of 17.12% and 18.61% hydrogen yield rate is attained for PVT/water and PVT/water with PCM systems respectively.     

Numerical simulation of horizontal tube bundle falling film flow pattern transformation

It is important to study the falling-film pattern of a horizontal tube bundle in order to set up a heat and mass transfer model accurately. The falling-film pattern of a horizontal tube bundle is simulated in this paper. The technique is based on computational flow dynamics (CFD) for the two-phase flow of gas and water. The experimental results were used to validate the mathematical model. It indicates that the simulation results accord with experimental data well. The simulated results show that the flow pattern varies with different flow rates. Under the different flow rates, it observes the droplet, droplet-columnar, columnar, columnar-sheet and sheet flow patterns. The critical value is 0.0125 kg/s between droplet and columnar, and the critical value is 0.02 kg/s between columnar and sheet.     

含引水和尾水明渠输水的水电站过渡过程分析

鉴于无压明渠的水力特性直接影响含明渠引水式水电站的过渡过程和运行控制,结合有压输水系统的特征线法,采用明渠瞬变流分析的特征隐式格式和相应的边界条件,构建含非自动调节引水明渠、压力前池、尾水池和尾水明渠的引水式水电站的过渡过程分析模型,研究了明渠流水力特性对水电站过渡过程和稳定性的影响。结果表明,在大波动过渡过程中,明渠流水力特性对机组蜗壳进口内水压力和转速极值的影响很小,而尾水渠水力特性及尾水池最低涌波水位决定了尾水管进口的最小内水压力;考虑明渠瞬变流特性的影响,水力干扰下受扰机组的调节品质变化较为明显,而水力-机械系统小波动调节品质变化较小。     

Asymptotic analyses of the start-up stage of Couette flow subjected to different boundary conditions

In this article, the process for reaching “developed” stage was investigated under both imposed shear stress and specified velocity boundary conditions. Four specific situations are investigated. These are (1) constant shear stress, (2) linearly increasing shear stress from zero shear, (3) constant velocity and (4) linearly increasing velocity from stationary. Analytical solutions of velocity distributions under these four situations were obtained. A dimensionless viscosity, defined as the ratio of the measured viscosity calculated based on the measuring principle of Couette-type viscometer to the true viscosity of fluid was proposed to describe the initial transient period. We define the “developed” stage when the dimensionless viscosity is 1% away from its final value or when it reaches 1.01. By analyzing Stokes' first problem, compact models of the dimensionless viscosity were expressed and exact quantitative relations among the initial values of dimensionless viscosity under these four specific situations were found. Time periods for Couette flow to reach the “developed” stage was calculated. The development time is the shortest under the constant velocity boundary and is the longest under the linearly increasing shear stress boundary.