Input Impedance, Wave Travel, and Reflections in the Human Pulmonary Arterial Tree: Studies Using an Electrical Analog

An electrical model of the human pulmonary arterial tree has been developed using modern oscillatory flow theory. By comparison with corresponding in vivo measurements of 1) pressure and flow waveshapes, 2) input impedance, and 3) apparent phase velocity, this passive, multisegmental, linear delay line model is shown to bear a close resemblance to reality.     

变结构反应离子刻蚀腔室流场热场的数值仿真

为了提高刻蚀的均匀性, 对400mm反应离子刻蚀(RIE)腔室建立了气体流动的连续流体模型和热传递模型, 研究了反应腔室内压强、流速和温度分布。冷却板恒温285K时, 依次改变入口流量和出口压强, 分别分析了腔室内部基片晶圆附近的流速、压强、温度的分布; 依次改变极板间距离(30mm~60mm)、进气口直径(300mm~620mm)、抽气口直径(50mm~250mm), 分析了反应腔室内气流和温度分布。结果表明, 压强分布呈现出边缘低中心高的特征, 流速呈现边缘高且中心低的特征, 且在小流量时压强的均匀性较好; 压强分布的均匀性随腔室极板间距离增加而有所提高, 且随腔室气体出口面积减小与进口面积增加也有所提高; 基片晶圆上方附近处温度场大面均匀、稳定, 几乎不受入口流量波动变化的影响, 热稳定性良好。该研究对大口径RIE腔室结构设计改进及对大口径反应离子刻蚀工艺控制具有重要意义。     

Effect of the inlet location on the performance of parallel-channel cold-plate

This study numerically examines the influence of inlet locations on the performance of the Multichannel cold-plates. A total of five inlet configurations (namely I-, Z-, ]-, L-, and /spl Gamma/-arrangement) are investigated in this study. The velocity maldistribution and nonuniformity of temperature field caused by the fluid flow are shown in the simulation. For I-arrangement, higher inlet flow rate of the cold-plate shows more considerable maldistribution, and this maldistribution is decreased when the number of channels of the cold-plate is increased. The Z-arrangement and L-arrangements show a pronounced flow-recirculation that eventually leads to a much larger temperature difference along the surface of the cold-plate. Conversely, there is no flow recirculation in the ]-arrangement and a comparatively uniform flow distribution is seen. For the same average inlet velocity, I-arrangement has the highest pressure drop whereas ]-arrangement shows the lowest pressure drop. The I- and /spl Gamma/-arrangement give the best heat transfer performance due to their impingement configurations whereas the Z-arrangement shows the lowest heat transfer performance for its dramatic flow recirculation and maldistribution.     

Vapor levitation epitaxy reactor hydrodynamics

Vapor Levitation Epitaxy (VLE) is a new epitaxial growth technique for III-V compound semiconductor crystals, characterized by upward stagnation flow of a reactant gas stream against a floating, circular semiconductor substrate wafer. In this work, the hydrodynamics of the process have been mathematically modeled by a complete solution of the governing Navier-Stokes equation to obtain radial and axial velocity profiles, pressure distribution under the wafer, and levitation height as a function of operating parameters. In addition, experimental measurements of levitation height as a function of gas flow rate for different wafers and gases have been performed. By the addition of experimental constants to the analytical solution of levitation height to account for system non-idealities, the functional dependences predicted by theory have been verified. In comparison to the complex flow occurring in other vapor phase epitaxy techniques, the hydrodynamics in the VLE reactor are simple, well behaved, and can be fully described by a few algebraic equations.     

Estimation of regurgitant volume and orifice in aorticregurgitation combining CW Doppler and parameter estimation in aWindkessel-like model

A method for noninvasive estimation of regurgitant orifice and volume in aortic regurgitation is proposed and tested in anesthetized open chested pigs. The method can be used with noninvasive measurement of regurgitant jet velocity with continuous wave ultrasound Doppler measurements together with cuff measurements of systolic and diastolic systemic pressure in the arm. These measurements are then used for parameter estimation in a Windkessel-like model which include the regurgitant orifice as a parameter. The aortic volume compliance and the peripheral resistance are also included as parameters measurements in the open chest pigs are used. Electromagnetic flow measurements in the ascending aorta and pulmonary artery are used for control, and a correlation between regurgitant volume obtained from parameter estimation and electromagnetic flow measurements of 0.95 over a range from 2.1 to 17.8 mL is obtained.     

进出口位置对槽道流体分配和换热的影响

针对平行小槽道的流量分配问题,设计了不同的进出口方式,并采用数值方法研究其对槽道散热器内流量分配和换热特性的影响。结果表明,进出口方式对槽道散热器内流量分配特性影响很大;提出流量和换热不均匀系数来评价进出口方式的影响,发现相同进出口方式下,流量不均匀系数随着流量的增大而增大;当槽道散热器流量相同时,顶部中间(UC)进出口形式的散热器内流量不均匀系数最小;当槽道面积一定时,流量不均匀系数随槽道个数增加而减小;流量一定时,槽道的表面温度不平均系数随加热功率的上升而增加;加热功率一定时,热阻随着流量的增加逐渐减小并趋于定值。     

CPU水冷系统散热实验研究

通过对某台式计算机水冷系统CPU吸热盒的换热和阻力特性实验,证明CPU吸热盒内的阻力压降与进口流速成二次方关系,热交换量随流量的增加先增大后减小。然后进行了不同管路布置情况下阻力和换热的性能试验,得出北桥吸热盒与显卡吸热盒并联的管路布置为最优方案,比管路串联布置时的总阻力低2.4%,CPU吸热盒换热量增加了21%。同时推出除CPU吸热盒管路以外的管路总阻力系数和管路阻力损失计算公式。     

芯片微通道换热器的数值模拟与分析

由于水冷散热器体积小,流体在散热器内流动形式复杂,使散热器设计加工和性能测试在常规条件下有一定局限性。通过建立微通道水冷散热器三维模型,运用ANSYS软件对影响散热器性能的因素(进口水温、环境温度、进口流速)进行了模拟分析,得出了不同条件下芯片工作时的温度场分布,为后续微通道水冷散热器的优化设计提供了理论依据。     

两相旋流分离器矿浆内部流场及分离特性研究

利用两相旋流分离器可以实现矿浆的浓缩和液体澄清。为探索两相旋流分离器内部流场及分离特性,文中通过CFD软件Fluent,采用RNG k-ε湍流模型,对两相旋流分离器内部的三维流场进行数值模拟,得出了压力、速度、体积分布、湍流动能和湍流耗散率等参数的分布情况。结果表明,两相分离旋流器内部径向速度由中心沿径向外逐渐增大,离近分离器壁时又逐渐降低,呈现出“M”型驼峰分布。轴向速度呈对称分布,最大值出现在顶部溢流口和底流口。从矿粒和水在旋流器内部的流动轨迹可以看出,矿浆浑浊液从切向进口进入旋流分离器后,矿粒和水在旋流分离器内部作高速旋转运动,形成外旋流和内旋流。密度较重的矿粒从下部底流口流出,密度较轻的水从上部溢流口流出,模拟两相分离效率可达到86.93% 。     

The use of miniature supersonic nozzles for microparticle acceleration: a numerical study

By means of a high-speed gas flow generated by a miniature supersonic nozzle, we proposed a unique biolistic method to accelerate microparticle formulation of drugs to sufficient momentum, to penetrate the outer layer of human skin or mucosal tissue for the treatment of a range of diseases. One of the main concerns for designing and evaluating this system is ensuring microparticles delivery into human skin with a controllable velocity range and spatial distribution. The initial experimental work suggested that the performance of the transdermal delivery strongly depends on aerodynamics of the supersonic nozzles employed. In this paper, computational fluid dynamics (CFD) is utilized to characterize existing prototype biolistic delivery systems, the device with a converging-diverging supersonic nozzle (CDSN) and the device based on the contoured-shock-tube (CST) design, with the aim at investigating the transient gas and particle dynamics in the supersonic nozzles. Whenever possible, predicted pressure and Mach number histories, 2-D flow structures, and particle velocity distributions are made to compare with the corresponding experimental measurements to validate the implemented numerical approach. The gas-particle interaction and performance of two biolistic devices are interrogated and distinguished. Subsequently, the particle impact conditions are presented and discussed. It is demonstrated that the CST can deliver microparticles with a narrow and more controllable velocity range and spatial distribution.     

Moisture assessment in transformers including overloading limits

Summary  A moisture model determines the moisture distribution in cellulose and oil. The model focuses on oil flow, moisture vapour pressure and the saturation properties of oil and cellulose. Measurements of material properties form the basis of each computation model. Direct measurements were performed. Samples of paper and pressboard were aged in oil. The measurements of moisture absorption were performed in air. For given moisture content the moisture vapour pressure reaches lower values than in previous results. Consequently, moisture values in oil reach lower values and the risk of bubbling at rising temperatures reduces. It has, for the first time, been established that bubbling requires a contribution of dissolved gas like air to reach critical vapour pressure levels to obtain bubbling at 150 °C hotspot and with 3% average moisture content and 1.2% in the hotspot respectively. Here oil must absorb on atmosphere air at 70 °C. Without dissolved gas an average moisture content of 4% and a hot spot temperature of about 165 °C would be necessary to come close to a risky condition. The low tendency to bubbling is also favoured by the reduced moisture content in the winding hotspot insulation which is caused by the temperature distribution due to axial oil gradient and winding gradient. The general calculation for individual spots in the transformer insulation like the hotspot is based on the moisture vapour pressure of cellulose and oil as the driving force of moisture migration. The axial temperature distribution, however, generates an axial gradient of moisture vapour pressures in oil. The cellulose insulation reaches the moisture pressure level of its neighbouring oil. The average cellulose moisture content provides basic information about the moisture condition. The calculation model is required to determine the moisture values in a transformer under operation conditions. Aging and bubbling considerations are based on the moisture content of the hotspot. Filling of a transformer with oil often happens at a moisture content of 5 ppm. At low temperatures and slow moisture diffusion into the bulk material the cellulose surface can develop extremely high moisture values. Therefore, a high temperature during filling is recommended. Furthermore, a transformer can, in principle, absorb moisture from the atmosphere or vice verse. The direction of migration is determined by the difference of local moisture vapour pressure between oil and atmosphere which depends on temperature and moisture. The slow migration velocity at low temperatures and tightness of the tank limits the value to below 7% moisture content in cellulose.     

A Method to Determine the Instantaneous Velocity of Pulsatile Blood Flow from Rapid Serial Angiographies

Rapid serial angiography is a common clinical technique for the assessment of important hemodynamic parameters. The accuracy of flow measurements, however, is seriously restricted by the fact that arterial blood exhibits not a constant but a pulsating velocity. In this paper, a method is described which allows the calculation of the instantaneous blood flow velocity by means of indicator concentration measurements.     

Microwave attenuation measurements in satellite-ground links: thepotential of spectral analysis for water vapor profiles retrieval

The authors address the problem of estimating vertical profiles of atmospheric water vapor by means of attenuation measurements simultaneously made at different frequencies along a vertical satellite-ground link. The operating frequencies selected are those around the spectral absorption lines of water vapor at 22.235 GHz. A simulation is presented of multifrequency attenuation measurements, based on an atmospheric propagation model and on radiosonde data providing true profiles of temperature, pressure, and water vapor. The results indicate that such multifrequency measurements are correlated to variations of the vertical profiles of water vapor. It is therefore expected that vertical detail of such profiles depends on number and position of the frequencies utilized     

Optimization study of stacked micro-channel heat sinks for micro-electronic cooling

With smaller inlet flow velocity, a micro-channel stack requires less pumping power to remove a certain rate of heat than a single-layered micro-channel, because it provides a larger heat transfer area. A simple thermal resistance network model was developed to evaluate the overall thermal performance of a stacked micro-channel heat sink. Based on this simple model, in this study, a single objective minimization of overall thermal resistance is carried out using genetic algorithms. The aspect ratio, fin thickness and the ratio of channel width to fin thickness are the variables to be optimized, subject to constraints of maximum pressure drop (4 bar) and maximum volumetric flow rate (1000 ml/min). During the optimization, the overall dimensions, number of layers and pumping power (product of pressure drop and flow rate) are fixed. The study indicates that reduction in thermal resistance can be achieved by optimizing the channel configuration. The effects of number of layers in the stack, pumping power per unit area, and the channel length are also investigated.     

侧面喷流对导通孔内镀液流动影响的数值研究

文章通过数值模拟研究了不同喷流速度、喷嘴孔径和喷嘴板面距离的侧面喷流对通/盲孔内镀液流动的影响。计算了单个圆形喷嘴喷流的轴对称流场,定量给出了喷流在板面的压力分布及其作用区大小,进而对孔内镀液流动特性进行了计算和讨论。计算结果表明:通孔和盲孔孔内镀液交换机制不同。通孔镀液交换主要受孔内外对流控制,孔内镀液流速与孔口压差成正比。盲孔镀液交换主要受孔内外镀液浓差控制。加强喷流可促进通孔内外镀液交换,但对厚径比大于1的盲孔内镀液交换几乎没有影响。     

Computational Patient-Specific Models Based on 3-D Ultrasound Data to Quantify Uterine Arterial Flow During Pregnancy

Information on uterine blood flow rate during pregnancy would widely improve our knowledge on feto-placental patho-physiology. Ultrasonographic flow rate evaluation requires the knowledge of the spatial velocity profiles throughout the investigated vessel; these data may be obtained from hemodynamic simulations with accurate computational models. Recently, computational models of superficial vessels have been created using 3-D ultrasound data; unfortunately, common reconstruction methods are unsuitable for the uterine arteries due to the low quality achievable of imaged deep vessels. In this paper a simplified spline-based technique was applied to create computational models for patient-specific simulations of uterine arterial heamodynamics. Moreover, a novel method to quantify the uterine flow rates was developed based on echo-Doppler measurements and computational data. Preliminary results obtained for four patients indicated a quite narrow range for the blood flow rate through the main uterine artery with large variability in the flow split between corporal and cervical branches. Furthermore, parabolic-like velocity profiles were obtained in the branching region of the different patients, suggesting a clinical use of averaged, not patient-specific, spatial velocity distribution coefficients for the blood flow rate calculation. The developed reconstruction method based on 3-D ultrasound imaging is efficient for creating realistic custom models of the uterine arteries. The results of the fluid dynamic simulations allowed us to quantify the uterine arterial flow and its repartition in normal pregnancies.      

Analysis of pulsed wave Doppler ultrasound spectra obtained from amodel intracoronary catheter

Abnormal arterial blood flow patterns have been implicated in the evolution of various vascular disease processes. Intravascular ultrasound techniques using the pulsed wave Doppler catheter offer the opportunity to characterize these abnormal flow patterns. The authors have developed a mathematical model that predicts the first two moments of the Doppler spectrum obtained using a Doppler catheter based on the distribution of ultrasonic beam power and velocity profile of fluid flow with an arbitrary distribution of flow disturbances. A scaled-up, in vitro experimental arterial system was used to confirm the validity of the model. Comparison of the predicted first two moments of the Doppler spectrum to the experimental values in this system demonstrated that the distribution of beam power significantly affects the magnitude of the first two moments. Additionally, both velocity gradient and velocity fluctuation broadening effects play prominent roles in determining the magnitude of the second moment. These phenomena must therefore be considered when evaluating in vivo Doppler spectra used for the characterization of abnormal flow patterns     

Continuous Pulmonary Capillary Blood Flow Estimation from Measurements of Respiratory Anesthetic Gas Concentration

A noninvasive, on-line estimation scheme has been developed for continuous determination of pulmonary capillary blood flow (PCBF) and related cardiopulmonary parameters from measurements of anesthetic gas concentration based on a gas uptake and distribution model of the body and the lungs. Two moving window algorithms, one based on the well-known off-line maximum likelihood algorithm, and the other based on a frequency response technique, have been investigated for this purpose. Special consideration was given to the sensitivity to various error sources that affect each estimation algorithm. Both computer simulations and in vivo experiments demonstrate that the proposed estimation procedures can be used for on-line PCBF determination provided that the nonestimated system parameters can be measured with sufficient accuracy.     

Pulse oximetry: an improved in vitro model that reduces blood flow-related artifacts

Artifacts may occur in many in vitro models of pulse oximetry due to the optical effects of synchronously oriented and/or deformed erythrocytes. Although these artifacts are most likely negligible in living superficial tissues, they are demonstrated to have considerable influence on the calibration curve obtainable from the in vitro simulation of pulse oximetry in such models, especially at low oxygen saturations. Therefore, we have developed a modified in vitro model which reduces the effect of these artifacts. This is achieved by excluding data obtained during pressure transients and by raising the blood flow velocity. As a result, the model more closely approximates in vivo pulse oximetry, particularly under clinically important conditions of low blood oxygen saturation levels.