INFLUENCE OF MIMIC CARDIAC RATE ON HYDRODYNAMICS OF DIFFERENT MECHANICAL PROSTHETIC CARDIAC VALVES IN VITRO

Objective To assess the influence of mimic cardiac rate on hydrodynamics of different mechanical prosthetic cardiac valves. Methods US-made CarboMedics bileaflet valve, China-made Jiuling bileaflet valve and C-L tilting disc valve were tested via a pulsatile flow simulator in the aortic position. Testing conditions were set at mimic cardiac rates of 55 bpm, 75 bpm, 100 bpm with a constant mimic cardiac output of 4 L/min. The mean pressure differences (ΔP), leakage volumes (LEV) and closing volumes (CLV) across each valve, and effective orifice areas (EOA) were analyzed. Results Within physiological range, ΔP, LEV, and CLV decreased as mimic cardiac rate increased, with a large extent of variance. EOA increased along with an increase in mimic cardiac rate. It was a different response in terms of cardiac rate alteration for different types of mechanical prosthetic cardiac valves. Conclusion Mimic cardiac rate change affects hydrodynamics of mechanical prosthetic cardiac valves. Within physiological range, the hydrodynamic of prosthetic bileaflet valve is better than that of tilting disc valve.

Modeling of fluid-induced vibrations and identification of hydrodynamic forces on flow control valves

Dynamics and vibration of control valves under flow-induced vibration are analyzed. Hydrodynamic load characteristics and structural response under flow-induced vibration are mainly influenced by inertia, damping, elastic, geometric characteristics and hydraulic parameters. The purpose of this work is to investigate the dynamic behavior of control valves in the response to self-excited fluid flow. An analytical and numerical method is developed to simulate the dynamic and vibrational behavior of sliding dam valves, in response to flow excitation. In order to demonstrate the effectiveness of proposed model, the simulation results are validated with experimental ones. Finally, to achieve the optimal valve geometry, numerical results for various shapes of valves are compared. Rounded valve with the least amount of flow turbulence obtains lower fluctuations and vibration amplitude compared with the flat and steep valves. Simulation results demonstrate that with the optimal design requirements of valves, vibration amplitude can be reduced by an average to 30%.

In Vitro Study of Hydrodynam ics at DifferentSimulated Cardiac Output for a Newly JiulingBileaflet Heart Valve Prostheses

Objective:To assess the hydrodynamic function of a newly China-made Jiuling bileaflet heart valve prosthesis at different simulated cardiac output.Methods:Jiuling valve,CarboMedics valve and C-L tilting disc valve have been tested in the aortic position of the pulsatile flow simulator.The testing condition is set at the simulated cardiac output of 2.0,3.0,4.0,and 5.0 L/min and a constant pulsatile frequency of 75 beats/min.The mean pressure difference(ΔP),leakage volume(LEV)and closing volume(CLV)across each valve,and the effective orifice area(EOA)have been analyzed.Results:The mean ΔP of all the Jiuling valves is in the range of below 10 mmHg and decreases with increasing the tissue annulus diameter.The ΔP of 25 mm CarboMedics is about 1.5 times of the same sized Jiuling valve and 27mm C-L tilting disc valve is about 71.8% higher than the same sized Jiuling valve.The EOA of the Jiuling mechanical valves increases with increasing the given cardiac output or the tissue annulus diameter,but 25 mm CarboMedics and 27 mm C-L tilting disc valve is similar to 21 mm and 23 mm Jiuling heart valve.The CLV of the Jiuling prosthetic cardiac valve is in the range of below 11%(normalized by stroke volume),25 mm Jiuling valve is about 56.4% lower than 25 mm CarboMedics and 27 mm Jiuling valve is about 11.4% higher than 27 mm C-L tilting disc valve.The LEV of the Jiuling prosthetic cardiac valves is in the range of below 28.9% (normalized by stroke volume),25 mm Jiuling prosthetic valve is about lower 27.3% than 25 mm CarboMedics and 27 mm Jiuling valve is about lower 11.2% than 27 mm C-L tilting disc valve.Conclusion:For a given tissue diameter,the newly Jiuling heart valve prostheses show more satisfactory hemodynamic characteristics at different cardiac output.

INVESTIGATION ON THE DYNAMIC RESPONSE PERFORMANCE OF A NOVEL THREE-WAY SOLENOID VALVE

Objective A novel high-speed three-way solenoid valve is developed, which is used for the common-rail injection system equipped on DME powered engine. In order to improve the dynamic response performance of the three-way solenoid. Methods Experimental studies have been conducted to investigate the effects of spool stroke, drive voltage, negative demagnetizing pulse and two drive schemes on the dynamic response performance of the three-way solenoid valve. Results The results show that the dynamic response performance of the three-way solenoid valve can be remarkably improved by shortening the spool stroke and increasing the drive voltage. Simultaneously, the difference between the response time of closing valve and that of opening valve decreases. At each different drive voltage, there exists an optimal negative demagnetizing pulse corresponding to the same positive exciting pulse. At this optimal pulse, the dynamic response performance of the three-way solenoid valve is the best. In addition, the high drive voltage can lead to the smaller optimal negative demagnetizing pulse. It is also indicated from the experiments that the dynamic response performance of the three-way solenoid valve is better when the NO.1 drive scheme is adopted. The lower drive voltage results in the larger difference between the dynamic response performances for the two drive schemes. Conclusion The dynamic response performance of a novel three-way solenoid valve is good.

A Novel SiC Foam Valve Tray for Distillation Columns

The novel SiC foam valve tray was made of thin slices of SiC foam material with a high specific surfacearea. Hydrodynamic performances of the novel SiC foam valve tray were studied with air-water system at atmos-pheric pressure. These performance parameters included pressure drop, entrainment, weeping and clear liquidheight. The mass transfer efficiency of the SiC foam valve tray was measured in laboratory plate column. Comparedwith the F1 float valve tray, the dry pressure drop was decreased about 25%, the entrainment rate was about 70%lower at high gas load, the weeping was much better, and the mass transfer efficiency was far higher. Thus, theoverall performance of the novel SiC foam valve tray was better than that of F1 float valve tray.

COMPARISON OF ALLOGRAFT AORTIC VALVE ORIFICE AREA ESTIMATED BY GORLIN FORMULA AND THE CONTINUITY EQUATION IN A PULSATILE DUPLICATOR

During the hydrodynamic characteristic testing of aortic valve allograft (AVA),the testing condition was adjusted to obtain the best hydraulic performance of AVA.The testing condition,the character of the circulation duplicator,is regarded as to beconsistent with the human circulation in vivo.Then the comparison among the re-sults of AVA orifice area (AVA) estimated by Gorlin formula,the continuity equa-tion and their modified types,respectively,was performed.

COMPARISON OF THE DUPLICATOR'S CARDIAC CYCLE WITH THAT OF HUMAN LEFT HEART CIRCULATION WHEN AORTIC VALVE ALLOGRAFT TESTED

By adjusting the testing condition,we obtained the best pulse hydrodynamic per-formance of aortic valve allograft tested in the duplicator made by Chengdu Universi-ty of Science and Technology.Meanwhile,we regarded the condition of the duplicatoras the consilience of human left circulation.By comparing the results(comparison)ofthe different periods of the cardiac cycle including beat to beat interval(RR),systolictime(ST),left ventricular eject time(LVET)and the relationship between them,which got from the observation on volunteers with normal or prostheses aortic valveby using two dimensional Doppler echocardiography,with that of the testing condi-

球型调节阀液动力矩特性仿真及优化设计

为了获得液体火箭发动机调节阀的液动力矩特性,采用kubota空化模型和标准k-ε湍流模型针对某型调节阀在发动机运行工况下的空化流动开展了数值仿真研究,通过与液流实验数据的对比验证模型准确性,并定量分析了阀芯液动力矩的影响因素、分布特性和演化规律。研究结果表明:阀芯液动力矩大小取决于开度、压差和阀芯流道直径。相同压差下,开度由10°增加至80°,液动力矩单调增加,方向均为使阀芯关闭。相同开度下,压差分别增至3倍和5倍,液动力矩分别变化为原来的3倍和5倍左右。液动力矩分布主要由密封面力矩和主流道力矩两部分组成。随着开度的增加,密封面力矩先减小后增加,主流道力矩先增加后减小。阀芯流道直径由70 mm减小为60 mm,液动力矩最大值增加了24.5 N·m。这是因为相同发动机工况下,减小流道直径使得阀芯开度增加,主流道力矩增加数值大于密封面力矩减小数值,所以总液动力矩呈增加特征。提出了削去原始模型主流道下壁面区域的优化方案,优化模型在100%工况时液动力矩仅为13.2 N·m,且优化模型的流通面积保持不变。与降低流道直径的优化方案相比,所提出的针对主流道下壁面优化方案液动力矩最大值减小了94.4 N·m,大大减轻了控制电机的负荷,已成功经过多次发动机试车考核,提高了液体火箭发动机的可靠性,并为实现发动机轻量化提供了重要参考。

非全周开口滑阀液动力分析及补偿

为研究某型比例阀在换向过程中,最大开口处驱动电流过大的问题,利用CFD对U形槽非全周开口滑阀的流场进行数值模拟,研究了不同阀开口处的液动力及流量,同时对原阀芯结构进行优化,在出口侧台阶上加两个对称分布的节流槽,并对不同节流槽半径和阀口开度时的液动力进行了比较。结果表明:原结构瞬态液动力在2.94 mm处到达峰值,随后迅速减小。节流槽半径为2.5 mm时,液动力补偿效果较好,相较于原结构最大液动力降低了21%,且大开口处液动力变化较为平缓。该研究为滑阀结构的优化设计提供指导。

DN80二通插装式伺服阀动态特性优化研究

针对国产DN80二通插装式伺服阀阶跃响应时间长的问题,提出先导控制腔优化方法以提高动态特性。首先建立先导控制腔三维数模,利用Fluent软件详细分析了主阀芯不同开口度的液动力分布情况,将先导控制腔的直径优化为90 mm;然后结合仿真软件AMESim对DN80二通插装式伺服阀进行动态特性研究。仿真结果表明:先导腔结构参数优化后减小了液动力,提高了动态响应特性。最后对优化后的DN80二通插装式伺服阀进行实验测试,其阶跃响应时间由40 ms缩短至23 ms,显著提高的了动态特性,验证仿真与优化的准确性。

Y型固定阀塔板流体力学性能的研究

采用直径1.2 m、高6 m、内置4层塔板的有机玻璃冷模塔,以空气-水为介质,对三种开孔率(5.30%,8.07%,9.40%)的Y型固定阀塔板进行了流体力学性能研究。考察了Y型固定阀塔板结构参数和操作参数对塔板压降、雾沫夹带率和漏液率的影响。实验结果表明,在相同操作条件下,相比开孔率为8.07%,9.40%的Y型固定阀塔板,开孔率为5.30%的Y型固定阀塔板的综合性能更优。

高性能蒸汽安全阀高阶流场仿真及试验验证

电站锅炉高性能蒸汽安全阀具有开启压力准确、启闭压差小、密封性好、调整方便等特点,其设计选型关系到锅炉机组的安全性,但在高温高压工况下,会因泄漏、振动和汽蚀等问题无法正常实现超压保护。为提高高性能蒸汽安全阀的性能,应用流固耦合仿真计算软件,选用五阶精度格式的结构化网格,开展不同介质、压力、温度的高阶流场仿真研究,同时结合试验验证得到精确的阀门内部流动机理,对优化高性能蒸汽安全阀结构参数及工程应用具有重要指导意义。

基于CFD方法的大口径三偏心蝶阀动水力矩计算

为解决大口径三偏心蝶阀在工程应用中遇到的阀板停滞、无法继续打开的问题,使用CFD方法,对三偏心蝶阀各个开度进行了数值仿真,得到了完整的可视化流场信息。通过截取流体区域中截面上的速度与压力分布云图,直观地展现了不同开度下流场的变化趋势。通过分析阀板承受的流体冲击力和压力的变化特征,归纳了动水力矩的发展趋势和成因。通过后处理读取流场数据,得到了动水力矩大小随三偏心蝶阀开度的变化关系。通过对比蝶阀阻力矩与执行机构输出力矩曲线,分析了问题发生的原因,并给出了合理的建议。研究结果表明,CFD方法对于三偏心蝶阀动水力矩的准确求解行之有效,也为执行机构的选型搭配提供了参考依据。

二尖瓣反流对主动脉瓣流体动力学性能影响的试验研究

目的有关心脏瓣膜之间相互影响的研究在临床上开展相对受限,体外测试的数据也尚显不足。该文利用可精细控制反流量的二尖瓣反流模型对一种主动脉瓣膜进行体外流体动力学性能研究。方法在固定心率、每搏输出量以及平均主动脉压的条件下,逐步增加二尖瓣反流模型的反流量,对待测主动脉瓣膜进行流体动力学性能测试。结果借助二尖瓣反流模型对机械式主动脉瓣膜(25AJ-501)的流体动力学性能进行研究发现,主动脉瓣膜的有效瓣口面积及跨瓣压差均与二尖瓣反流程度的大小存在负相关关系。结论建立的借助可精细调节反流量的二尖瓣反流模型的测试方法,可以用于二尖瓣反流对主动脉瓣膜流体动力学性能的研究。

旋启式轴流止回阀的结构特性分析

论述了轴流式止回阀的优缺点,重点介绍了旋启式轴流止回阀这一全新的止回阀产品。分析了旋启式轴流止回阀和常规止回阀结构上的不同,及其在不同工况下的性能区别。描述了旋启式轴流止回阀的技术特点和优势,使用有限元的方法对旋启式轴流止回阀的优势进行了多方面的分析,对旋启式轴流止回阀的应用前景进行了展望。

外展盘式控制角阀动水扭矩和动水力的应用研究

外展盘式控制角阀在高压差工况下运行时,常规的阀杆与连接块螺纹连接结构很容易出现相对转动,进而可能导致阀杆脱落,严重时甚至会引发装置安全事故。此外,高压差流体产生的动水力容易导致阀芯导向叶片磨损阀座密封面及阀座内孔,致使阀门产生动作卡涩现象,影响了阀门的控制精度。基于数值计算,分析阀芯导向叶片结构、安装角度对阀芯所受动水扭矩及动水力的影响,对工程应用中阀杆与连接块连接形式及阀芯导向叶片安装角度的选择有重要指导意义。

ADV微分浮阀塔板的研究和应用

应用空气－水物系，在直径为６００ ｍ ｍ 的塔内，对ＡＤＶ微分浮阀塔板的流体力学进行了试验研究，测定了临界孔速、塔板压降、雾沫夹带率和液体泄漏率。应用空气－水－氧气物系，测定了ＡＤＶ 微分浮阀塔板的传质效率，并与Ｆ１ 型浮阀塔板进行了对比试验研究。试验结果表明，ＡＤＶ微分浮阀塔板比Ｆ１型浮阀塔板具有更好的流体力学和传质性能。通过对试验数据进行回归，获得了计算临界孔速、塔板压降、雾沫夹带率和泄漏点孔速的关联式，用于ＡＤＶ 微分浮阀塔板的水力学计算。并介绍了ＡＤＶ 微分浮阀塔板的工业应用情况。

新型浮阀塔板研究进展

介绍了在传统圆盘形浮阀、条形浮阀及固定阀塔板基础上研究开发的新型浮阀塔板。分析了各种新型浮阀塔板的结构特点、流体力学性能和传质性能,并比较了各种新型浮阀塔板的优缺点,概述了在不同生产工况下浮阀塔板的选择。

3种微灌砂过滤器水动三向阀性能比较试验研究

为了研究不同水动三向阀对砂石过滤器进行过滤和反冲洗过程切换的影响,通过对市场上常用的2种进口水动三向阀和国内自主生产的水动三向阀进行试验对比,测试了3种阀门过滤和反冲洗条件的水头损失、启闭时间、最小切换压力等参数.测试结果表明:不同阀门过滤和反冲洗条件下的水头损失差异具有统计学意义,建立了3种阀门正向过滤和反向反冲洗过程的水头损失和流量的回归模型,符合幂函数关系;国产阀门在水损控制上与进口阀门差异不大;在60~350 k Pa条件下进行3种阀门启闭时间和最小切换压力试验,测得3种阀门正向切换时间均长于反向切换时间,且单腔结构三向阀的启闭时间要长于双腔结构阀门,而国产三向阀在材料和精度上的不足导致阀门在启闭时间和最小切换压力两方面均落后于进口阀门.试验数据对实际应用中阀门选型及灌溉规划设计能够提供一定的数据参考.

三用阀阀芯微造型的动压润滑性能

以煤矿三用阀中的安全阀阀芯的密封面为研究对象,通过在阀芯表面开设微造型以改善其润滑及抗磨损性能。建立阀芯微造型的数学模型,采用基于N-S方程的计算流体力学方法对微造型区域进行流场分析。通过得到不同结构参数及速度参数下的阀芯表面压力分布曲线及阀芯承载力曲线,探究在阀芯表面开设微造型对改善其动压润滑性能的影响效果。分析结果表明:在水压三用阀阀芯表面开设的微造型能产生良好的动压润滑效果;动压润滑性能随壁面间隙的增大,先略有下降然后再逐渐增强;随微造型深度的加深,先提高而后再逐渐下降;而不断增大微造型半径及壁面移动速度均能使动压润滑性能不断提升。