Numerical Study of Air Chamber for Oscillating Water Column Wave Energy Convertor

Oscillating Water Column （OWC） wave energy converting system is one of the most widely used facilities all over the world. The air chamber is utilized to convert the wave energy into the pneumatic energy. The numerical wave tank based on the two-phase VOF model is established in the present study toinvestigate the operating performance of OWC air chamber. The RANS equations, standard k-ε turbulence model and dynamic mesh technology are employed in the numerical model. The effects of incident wave conditions and shape parameters on the wave energy converting efficiency are studied and the capability of the present numerical wave tank on the corresponding engineering application is validated.

Measurements of Air-kerma in Mammography X-Ray Standard Using Free-air Chamber

Mammography x-rays standard is required to improve the quality of mammary machine and reduce the dose for w omen and staff. The molybdenum target x-rays machine is used as the radiation source and free-air cylindrical chamber is designed for detecting photon. Four standard radiation qualities are established w ith international standard documents as references. The Correction factors including air attenuation,scattered radiation,fluorescence,w all transmission,electron loss are studied in the four radiation quality. The uncertainty in absolute measurement of air-kerma includes air volume measurement of ionization chambers,current measurement,measurement of temperature and pressure,measurement of correction factors,physical constants and orientation of the reference distance. The relative combined standard uncertainty is 0.24%.

Research on characteristics of water motion and influencing factors for the flexible air chamber jig body

The air bag deformation data were obtained by high-speed dynamic videos experiments. Based on gas–liquid flow VOF model, dynamic mesh technique and deformation data, numerical simulations for different structure models were achieved, and the law of water motion and influencing factors were analyzed.The results show that the flow in the length direction of the jig is smooth, and second pulsation appears in the separation time and forms the secondary separation. The installation position of screen and the number of air bags have a great influence on the uniformity of flow and velocity. The screen height cannot be too low to avoid forming the unstable flow. At the same time, the screen height cannot be too high, otherwise water velocity will be too small and was unable to provide enough power. At the height of 1.4m,velocity unevenness is minimum and the best uniform flow can be obtained. Compared with double air bags, there are the following features of single air bag: water flow is not smooth, the time achieving the maximum velocity is too long, maximum velocity is smaller, and overall effect is worse than double air bags.

Water hammer in the pump-rising pipeline system with an air chamber

Water hammer following the tripping of pumps can lead to overpressure and negative pressure. Reduction in overpressure and negative pressure may be necessary to avoid failure, to improve the efficiency of operation and to avoid fatigue of system components. The field tests on the water hammer have been conducted on the pump rising pipeline system with an air chamber. The hydraulic transient was simulated using the method of characteristics. Minimizing the least squares problem representing the difference between the measured and predicted transient response in the system performs the calibration of the simulation program. Among the input variables used in the water hammer analysis, the polytropic exponent, the discharge coefficient and the wave speed were calibrated. The computer program developed in this study will be useful in designing the optimum parameters of an air chamber for the real pump pipeline system. The correct selection of air chamber size and the effect of the inner diameter of the orifice to minimize water hammer have been investigated by both field measurements and numerical modeling.

OWC air chamber performance prediction under impulse turbine damping effects

Oscillating water columns(OWCs)are most widely used in coastal wave energy conversion.The air duct opens into the atmosphere through the air turbine,which is the power take-off device,and this results in a pressure drop across the air chamber.However,because of the complex configure of the impulse turbine and its high rotation speed,it is difficult to install it in the experimental simulator and numerical model.Therefore,the turbine damping effects on the operation of the OWC air chamber are induced to predict its performance more accurately.Orifice plates are used as a substitute for the impulse turbine as it generates a similar pressure drop and power output;the experimental and numerical pressure drops and output powers are compared.A 3D numerical wave tank based on the two-phase VOF model is established using the commercial CFD code Fluent,which can predict air flow and pressure variations in the chamber and duct.Water surface elevations,air flow velocity and pressure variation inside the chamber with the orifice plate are studied numerically,and validated by the corresponding experimental data.The air chamber of the Yongsoo OWC pilot plant is used as the engineering project case.The operating performance of the air chamber installed with a 0.428D orifice plate as the substitute for the designed impulse turbine is computed and analyzed.It is found that the turbine damping effects will cause around 30%reduction in the peak values of the pneumatic energy output of the OWC air chamber in the resonant wave domain.

NUMERICAL AND EXPERIMENTAL STUDY OF THERMAL DISTRIBUTION INSIDE AIR-CONDITIONED AUTOMOBILE CHAMBER

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Generation of a Controlled Polluted Atmosphere for Vehicles’ Cabins Air Quality Characterization

Air pollution induces significant health risks to individuals exposed to high levels of pollutants concentration. For ground vehicles, pollutants infiltrate the car cabin through the ventilation system, leading to potential health issues. To address this problem, a project was undertaken to develop a protocol for characterizing in-cabin air quality. The study involved a closed chamber (the bubble) where its internal multiphase flow has been optimized to create controlled polluted atmospheres. Experiments were conducted to optimize the positioning of the stirring fan and particle generation source, ensuring a homogeneous distribution of fine and ultrafine particles. This study demonstrated the feasibility of implementing a platform dedicated to characterizing the vehicles’ in-cabin air quality under controlled conditions. It allows a better understanding of the dynamics of particle infiltration and the establishment of an optimized protocol for simultaneous measurements of indoor and outdoor concentrations.

气吸双行错置式玉米密植精量排种器设计与试验

针对大豆-玉米复合密植播种模式下传统气吸式排种器单行种盘高转速作业导致充种时间短、气流稳定性差,难以实现高速精量密植播种的问题,设计了一种气吸双行错置式玉米密植精量排种器,阐述了排种器结构与工作原理,对其工作过程及关键部件进行理论分析,构建充种和投种环节的种子力学模型,确定排种盘内外环型孔排布、投种轮、气室等关键结构参数,并开展单、双气道内负压分布、型孔内气流场特性分析,基于DEM-CFD耦合方法对排种器的排种过程进行仿真分析,以作业速度、气室结构和负压为试验因素,充种合格指数、重充指数和漏充指数为评价指标,优选出最优气室结构。通过台架试验开展不同气吸式排种器排种性能对比试验。试验结果表明,在作业速度为5~10 km/h的高速密植工况下,气吸双行错置式密植精量排种器排种合格指数均大于88.7%,且作业速度为10 km/h时,相较于常用单圆环气吸式排种器合格指数提高5.5个百分点,漏播指数降低5.6个百分点;田间试验结果表明,在作业速度为5 km/h下,播种合格指数为95.7%,重播指数为1.6%,漏播指数为2.8%。提出的气吸双行错置式玉米密植精量排种器在高速作业时拥有良好的排种性能,能够满足大豆-玉米高速精量密植播种要求。

Effect of Sealing Air on Oil Droplet and Oil Film Motions in Bearing Chamber

Beating chamber is one of important components that support aero-engine rotors and research on oil droplet and oil film motions is an important part of bearing chamber lubrication and heat transfer design. Consid- ering the pressure of sealing air is an important operating condition that affects the oil droplet and oil film mo- tions, the effect of sealing air pressure on airflow in bearing chamber is investigated in this paper firstly ; and then based on the air velocity and air/wall shear force, the oil droplet moving in core air, deposition of oil droplet im- pact on wall as well as velocity and thickness of oil film are analyzed secondly; the effect of sealing air pressure on oil droplet velocity and trajectory, deposition mass and momentum, as well as oil film velocity and thickness is discussed. The work presented in this paper is conducive to expose the oil/air two phase lubrication mechanism and has certain reference value to guide design of secondary air/oil system.

Design and Characterization of an Aerosol Test Chamber for Emergency Response Patient Contamination Control Simulation and Research

Contaminated or infected patients present a risk of cross-contamination for emergency responders, attending medical personnel and medical facilities as they enter a treatment facility. The controlled conditions of an aerosol test chamber are required to examine factors of contamination, decontamination, and cross-contamination. This study presents the design, construction, and a method for characterizing an aerosol test chamber for a full-sized manikin on a standard North Atlantic Treaty Organization litter. The methodology combined air velocity measurements, aerosol particle counts and size distributions, and computational fluid dynamics modeling to describe the chamber’s performance in three dimensions. This detailed characterization facilitates future experimental design by predicting chamber performance for a variety of patient-focused research.

基于CFD的YJ17卷烟机风室流场分析与优化设计

目的针对ZJ17卷接机YJ17供丝系统中烟丝堵塞、竹节烟和烟支标偏大的现象进行改进。方法采用流体仿真分析软件Solidworks Simulation模拟分析、正交实验及试验验证的方法,设计优化YJ17供丝系统的风室装置,通过模拟仿真不同正压风入口形状、数量、位置对设备运行效率、产品质量的影响,找到三者最优的参数组合。模拟分析发现,在正压风入口形状为圆形,正压风入口数量为3个,正压风入口距离气室边缘的距离为15mm时,风室气流分布更均匀,同时烟丝在离开抛丝辊后受到的下吹风力最大,可使烟丝快速到达吸丝带。结果气室经改进后烟丝堵塞次数降低了39.3%,SD值(20支烟支质量标偏)降低了25%,有效提升了设备的运行效率和卷烟产品的质量。结论基于仿真及正交实验结果,优化了风速出风口位置和直径,气室的流场分析结果可为烟丝吸丝成型及风室结构优化提供一定技术支持。

基于中间气压罐和罐前逆止阀的浮船泵站水锤防护

以云南省元谋县金沙江光伏提水工程的第一级浮船泵站供水系统为例,开展了浮船泵站水锤防护的研究。在参考相关设计规范的基础上,确定了停泵水锤防护标准;通过比较不同水源水位和停泵台数对过渡过程的影响,确定水锤防护的控制工况为水源水位最低、运行机组全部停泵的工况;根据管道沿线地形和浮船泵站的特点,在分析泵出口阀关闭程序、中间气压罐防护效果、罐前逆止阀作用的基础上,提出了“泵出口轴流式逆止阀+中间气压罐+罐前逆止阀”的水锤防护方案。该方案通过泵出口轴流式逆止阀完全防止机组倒转,通过中间气压罐控制管线中的正负水锤压力,通过罐前逆止阀防止倒泄水流对浮船和摇臂联络管的冲击。该防护措施对类似工程有较好的参考意义。

无脉冲微流控片上蠕动微泵研制及其性能研究

为解决微流体连续输送过程中存在的流动脉冲、精度低等问题,研制一种基于微流控技术的片上蠕动微泵。该微泵由微流控芯片和电机驱动系统组成,利用驱动系统中的滚子轴承连续挤压微流控芯片中的微流道,以实现微流体的精确泵送。为研究微泵的流量特性,设计具有气腔稳流功能的微流道,采用光固化3D打印技术与模塑法制作微流控芯片样件;开发电机驱动系统,测试微泵在不同电机转速下的平均流量、总流量和瞬时流量,并将其流量特性与商业蠕动泵的流量特性进行对比。研究结果表明:随着电机转速增加,微泵的平均流量逐渐增大,瞬时流量误差逐渐减小;当电机转速大于60 r/min时,瞬时流量误差可控制在5%以内,其流量精度显著高于商业蠕动泵的流量精度;片上蠕动微泵可有效抑制微流体脉冲,提升微流体控制精度,在精密微流体输送中具有广阔的工程应用前景。

送风参数对老化箱内部温湿度场的影响研究

利用老化箱对机械电子元件进行老化筛选,能有效提高产品的可靠性。老化箱内部温湿度场的均匀性决定了其整体性能,这对老化箱功能有至关重要的影响。为了提高老化箱的性能,基于流体力学原理,利用CFD(computational fluid dynamics,计算流体力学)仿真软件对老化箱简化模型进行仿真模拟,并根据仿真结果确定老化箱内部速度场与温度场的分布情况,以优选不同送风温度、送风速度和送风角度组合下的送风方案。仿真试验采用正交试验法,以送风温度、送风速度和送风角度为试验因素,以能量利用系数、温度不均匀系数和相对湿度不均匀系数为评价指标。通过对仿真试验结果进行极差和方差分析可知,送风角度对能量利用系数的影响最显著,送风温度对温度不均匀系数和相对湿度不均匀系数的影响最显著。针对3个评价指标,得到3种最优方案:送风温度为90℃、送风速度为10 m/s、送风角度为0°,送风温度为90℃、送风速度为12 m/s、送风角度为-10°,以及送风温度为90℃、送风速度为8 m/s、送风角度为0°。最后,开展了老化箱内部温湿度测量实验,并与仿真结果进行了对比。结果表明,仿真结果与实验结果的相对误差较小,均在合理范围内,验证了仿真试验的可靠性和有效性。研究以提高老化箱性能和能量利用率为导向,可为同类老化箱的设计及其送风参数的设置提供参考。

基于冰浆制冷的标准冷源及不确定度分析

房间空调器制冷量的计量结果在不同焓差室间不一致的问题仍困扰着中国空调行业,是国际贸易中容易引发纠纷的计量学问题,亟待研究可对焓差实验室进行标定的标准冷源。在研究国内外房间空调器几种主流的制冷量计量方法以及标准冷源研究现状的基础上,结合对冰浆制冷物理过程的深入理解,提出基于冰浆制冷的标准冷源装置,包括冰浆制备系统和换热系统两大部分。对其进行实验研究及制冷量不确定度分析,验证该标准冷源装置是否具备标定焓差实验室的能力。实验结果表明:在焓差室室外侧为0℃,室内侧为标准制冷工况,m=70 g/s下该标准冷源装置输出制冷量的相对不确定度可以达到1.2%,约为空气焓值法的1/3,可作为标准冷源对焓差室的制冷量测量结果进行标定,有助于提高制冷行业的国际竞争力。

局部内冷空气系统流体网络分析与数字化计算方法

燃气轮机内冷空气系统结构、气路流动与运行工况极为复杂,造成了内冷空气系统流体计算难度很大,传统一维流体网络法的计算精度已经不能满足当代发动机分析与设计的需求,急需开发一种面向燃气轮机内冷空气系统的高精度、快速的系统级别的流体计算方法。本文面向某船用燃气轮机高压转子内冷空气系统的卸荷腔,创新性地利用一维-三维联合仿真计算方法,实现了快速求解流体网络节点信息的同时解析关键区域流动传热细节。研究结果表明,与传统一维流体网络法相比,一维-三维耦合计算可以通过边界数据传递与耦合计算提高整体计算精度,与传统CFD计算方法相比,一维-三维耦合计算可以加快计算收敛速度,以卸荷腔高压涡轮腔室为例,一维-三维联合仿真计算方法可以节约计算收敛时间约83%,同时三维流体计算域可以获得关键区域的流场细节,对系统级别计算下掌握关键区域流动特性具有重要意义。

淬熄高度和空气分配比例对RQL燃烧室燃烧特性的影响

基于富油/淬熄/贫油(RQL)技术原理,设计一种燃气轮机低排放燃烧室.在保持燃烧室进口参数不变的前提下,研究不同淬熄结构高度及空气流量分配比例对燃烧室内流场、温度场及污染物生成特性的影响.结果表明:淬熄结构高度和空气分配比例是影响燃烧室燃烧性能的重要参数,随着淬熄结构高度的降低,燃烧室出口氮氧化物NO_(x)的排放量增加;随着富油区主燃孔与淬熄空气质量流量的空气分配比例降低,燃烧室出口NO_(x)的排放量先降低后增加,存在一个最佳的空气分配比例使NO_(x)排放量最低;热力型NO_(x)的生成量与温度高于1900 K的区域大小和最高燃气温度存在直接关系.基于此设计的燃烧室在所研究的工况下,最低NO_(x)排放量可低于35 mg/m^(3),达到了低污染燃烧室排放标准.

核电厂汽动辅助给水泵转速调节系统鲁棒性提升研究

某核电厂二期工程采用了国产化核级汽动辅助给水泵,调试过程中屡次发生给水泵启动时间超标、启动后转速无法稳定、启动过程中超速跳闸事件。对汽动辅助给水泵调速系统进行了建模及分析,研究了电子调速器、电气转换器、气动定位器、气动增速器等部件的工作特性,分析并通过试验比较了不同流量系数的气动增速器对气动执行机构动态响应特性的影响。采用更换小流量系数气动增速器和调速器参数优化的方法,提升了汽动辅助给水泵调速系统的鲁棒性,解决了给水泵启动失败的问题。该研究的过程和成果可作为国产核级汽动辅助给水泵调速系统的设计参考,对于气动执行机构有关的控制系统参数优化、鲁棒性提升等其他同类问题的处理也有重要的指导意义。

综掘工作面气室降尘技术研究

针对掘进巷道中的粉尘控制问题,传统的长压短抽通风降尘技术存在粉尘扩散区域大、风幕降尘技术存在射流孔易堵塞等弊端。以巴拉素煤矿综掘工作面为工程研究背景,建立了掘进作业过程中的粉尘运动数学模型,得出降低综掘工作面粉尘浓度的关键因素是控制掘进巷道风流场扰动范围及减小粉尘颗粒运动时间。以上述关键因素为依据,在风幕降尘的基础上开发了气室降尘技术,通过在正压风筒末端加装风袖,与风幕共同作用将粉尘封闭在气室区域内,再由负压风机抽出,以提高降尘效率。采用Fluent软件对长压短抽通风降尘、风幕降尘和气室降尘进行模拟对比分析,并优化了气室降尘技术参数。模拟结果表明:采用气室降尘技术时,综掘工作面人体呼吸带位置的粉尘浓度为350 mg/m^(3),较采用长压短抽通风降尘时的600 mg/m^(3)和风幕降尘时的480 mg/m^(3)大幅降低;气室降尘最优技术参数为正压风筒出风口距综掘工作面14 m、负压风筒末端直径0.6 m。在巴拉素煤矿2号煤2号回风大巷综掘工作面进行现场试验,结果表明采用气室降尘时,掘进巷道最低粉尘浓度为118 mg/m^(3),低于采用长压短抽通风降尘时的184 mg/m^(3)和风幕降尘时的156 mg/m^(3),且降尘效率较长压短抽通风降尘平均提高54.8%。

基于CFD数值模拟的汽车中冷器流动均匀性研究

针对汽车中冷器内流道气体流动均匀性差的问题,提出了一种在中冷器气室安装导流板的中冷器结构优化方案。基于CFD数值模拟,对中冷器内部气体质量流量分布、速度场和压力场进行了分析,通过风洞试验验证了仿真模型的有效性。在此基础上,研究了气室导流板对中冷器内流道气体流动均匀性的影响。研究结果表明:合理设置导流板,中冷器各散热管气体平均质量流量偏差由7.66%减小到3.20%,中冷器许用环境温度提高了0.84℃,气室压力损失减少了37.4%,改善了中冷器内流道气体流动均匀性,提高了散热性能,避免了芯体热应力集中,减少了可靠性失效风险。此中冷器结构优化方案可为中冷器流动均匀性研究提供参考。