平行平板微型槽间气体的滑移流动

对平行平板微型槽中气体滑移流动的压强分布特性进行了研究。将压强和气体平均分子自由程的关系引入到一阶速度滑移边界条件中,求解Navier-Stokes方程,得到了显式的压强分布表达式。模拟计算结果表明,平行平板间滑移流动的气体压强分布曲线是上凸的下降抛物曲线。在边界滑移条件下,分析了平行平板微型槽在应用中由于微型槽中压力分布变化形成的气体阻尼问题,分析结果表明无滑移边界条件在微尺度流动分析中不再适用。     

三维壁面效应对微喷管性能影响的数值计算

以FLUENT6.1为工具进行并行计算,数值计算求解二维和三维稳态可压缩Navier-Stokes方程,模拟了三维壁面效应对扁平形状硅收缩-扩张微喷管内温度和压力的影响,进而研究了三维壁面效应对微喷管的流量系数和推力效率性能的影响。数值计算结果表明:对于喉部深宽比较小的扁平形微喷管,三维壁面效应较大,三维喷管内流体的速度小于相应的二维喷管内流体的速度,而三维喷管内流体的温度大于相应的二维喷管内流体的温度;二维数值计算的流量和推力均大于对应的三维数值计算结果,其差值随着喉部特征雷诺数的减小而增大。二维数值计算结果不能正确预测喷管出口实际流量和微推力。     

微流体系统中沸腾特性的研究进展

通过分析微流体系统沸腾过程中两相流流型、压降特性和传热特性三个关键问题,总结了微流体系统中沸腾特性的研究进展。分散流、间歇流和环状流是微通道的三类基本流型。流型和传热分析中考虑了壁面润湿性、表面粗糙度及表面缺陷等因素。提出了横跨大尺度到微尺度的综合型流型图和压降预测方法的基本构想。微尺度相变传热领域还需要在流型转化界限、传热分区及预测、临界热流密度等方面进行深入研究,对新型通道结构、新的混合流体和新的应用背景下的特殊流体进行更为广泛的讨论,为微蒸发器的设计、制造及运行提供参考。     

一种微通道换热器的设计与分析(英文)

设计了一种用来测试微通道换热性能的实验装置。该系统由微通道换热器、模拟热源、微型水泵、连通管、测试三通及其它测试元件构成。通过检测温度、压力和流量等参数能够得到微通道的传热和摩阻参数。针对该实验装置,对微通道中流体的压降和传热分别进行分析和研究。实验表明,当微通道水力直径为381μm时,宏观理论公式已不适用于微通道摩阻及其换热的计算。此时,微通道的摩阻比宏观理论计算值小31.6%～41.9%;微通道结构具有良好的换热性能,其Nu可达9.2。     

一种微通道换热器的设计与分析

设计了一种用来测试微通道换热性能的实验装置。该系统由微通道换热器、模拟热源、微型水泵、连通管、测试三通及其它测试元件构成。通过检测温度、压力和流量等参数能够得到微通道的传热和摩阻参数。针对该实验装置，对微通道中流体的压降和传热分别进行分析和研究。实验表明，当微通道水力直径为381μm时，宏观理论公式已不适用于微通道摩阻及其换热的计算。此时，微通道的摩阻比宏观理论计算值小31．6％～41．9％；微通道结构具有良好的换热性能，其Nu可达9．2。     

数字式自动程控气体微流量控制装置

随着科学技术的发展,在许多科研和生产工艺中越来越需要对微流量气体进行比较精确和稳定的控制。例如,在研制梯度光纤工艺中,为了得到折射率梯度分布的光导纤维,就需要对携带化学试剂的气体进行微流量控制,流量变化范围要求从每分钟几毫升到几百毫升。对于微流量气体,特别是流量为每分钟几十毫升以下的控制,目前不少单位还正在研究。我们在微流量的控制方面也作了一些探索和试验,并试制成“数字式自动程控气体微流量控制装置”。本装置没有采用改变阀门开度以控制流量的常规方法,我们自行设计了一种     

微通道尺寸对开通道电渗泵性能的影响

开通道电渗泵的结构简单,性能优越,制作工艺满足标准MEMS微加工工艺,是实现微泵片上集成应用的重要途径之一,可应用于微电子机械系统中作为液压致动元件。开通道电渗泵的压力流量性能与微通道的尺寸参数有直接关系。首先理论分析了微通道的长度、宽度和高度对开通道电渗流性能的影响,得出了各参数对电渗流性能的影响趋势。应用MEMS CAD软件Coventorware对微通道尺寸的影响进行了数值仿真分析,结果表明:数值仿真得出的结论与理论分析相一致,高深宽比微通道的电渗泵,减小宽度W和深度H有助于提高开通道电渗泵的压力,但流量也随之减小,设计时宽度和深度需折衷取值;长度L只对流量有影响,对压力无影响,通过优化设计微通道的几何尺寸可以使开通道电渗泵的压力和流量性能得以提高。     

两种微型热管传热性能对比研究

以波形脉动热管和微槽平板热管为研究对象,基于Mixture模型构建了其三维非稳态数学模型,并对模型可靠性进行了验证。采用该数学模型对比了两种微型热管在相同散热空间和散热热流密度情况下的热阻、平均壁面温度和蒸发段壁面温度均匀性。结果表明:相对于微槽平板热管,波形脉动热管热阻更低,传热性能更好;波形脉动热管蒸发段稳态平均壁面温度更低,且随着热流密度的增加该优势更加明显;波形脉动热管在空间尺度上蒸发段壁面温度均匀性更好,且这种优势在高热流密度情况下更突出,但这种均匀性在时间尺度上变化相对剧烈。     

微通道的流动阻力分析

针对在恶劣温度条件下工作的芯片热控制问题,提出由微泵、微通道、热电模块、智能控制单元、散热片以及液体管道等构成的微通道对流换热设计思想。数值仿真分析了换热微通道结构的速度和压力分布,计算了管道、微通道等部件的阻力损失和换热系统的流动阻力曲线,确定了系统必需的微泵工作性能参数,求解了微泵的最佳工况点。最后,制作了微通道对流换热装置,测得了系统流量和流动阻力,证实了可用经典流体理论来分析该系统的流动阻力。     

一种用于称重的矩形微通道式微悬臂梁

矩形微通道式微悬臂梁传感器可用于检测单个微粒子或细胞的质量,在生物和化学等领域具有非常广泛的应用前景。设计了一种含有矩形微通道的微悬臂梁结构,建立了单个微粒子等效的集中载荷在微悬臂梁中矩形微通道的任意位置时弯曲挠度的理论模型,分析了静态工作模式下的弯曲挠度变化以及研究了单个微粒子的质量及位置对微悬臂梁的弯曲挠度的影响,并用COMSOL Multiphysics仿真软件对矩形微通道式微悬臂梁的弯曲变形进行仿真计算,弯曲挠度的仿真结果与理论计算结果相对误差为1.2%。实验验证了在聚甲基丙烯酸甲酯(PMMA)微粒子的作用下,微悬臂梁的最大弯曲挠度为2.741μm。     

运行参数对SPT器壁腐蚀影响的光谱诊断

影响稳态等离子发动机（简称＂SPT＂）器壁腐蚀的因素很多：鞘层电势、器壁形貌、离子轰击的能量分布等,利用数值模拟的方法研究腐蚀情况比较困难,计算结果和实验结果相差较大。本文基于发射光谱法,利用Avaspace光栅光谱仪对SPT通道器壁特征元素的谱线进行分析。通过测量不同质量流量和放电电压下的陶瓷器壁特征元素谱线强度随时间的变化,结合理论分析得出不同运行参数下发动机器壁腐蚀速率变化的规律。     

Operating characteristics and discharge conditions of a CW 28-µm water vapor laser

The operating characteristics of a CW 28-μm water vapor laser are examined for various parameters which are the discharge current, the water vapor pressure, the wall temperature of the laser tube, the mass flow rate, and the mixing ratio of helium gas or hydrogen gas. Their optimum conditions for getting a maximum output power are found. There is a relation that the maximum output power at various pressures of the water vapor is obtained at the discharge current which dissociates the water-vapor molecule rapidly.     

The influence of wall slip in the measurement of solder pasteviscosity

The wall slip phenomena is known to have a significant effect on the measurement of the viscosity of dense suspensions. In the measurement of the viscosity of solder pastes the effect of wall slip is such that the measured viscosity (also called the apparent viscosity) is much lower than the true viscosity of the paste. Therefore, correction needs to be applied to the measured viscosity in order to obtain the true viscosity of the solder paste. In this paper, we present work on the modeling of the influence of wall slip on viscosity measurement, and a model for predicting the true viscosity based on measurements using parallel plate viscometer. The apparent viscosity values measured at two different plate gaps, but at the same applied shear rate (also called the apparent shear rate), is used for predicting the true viscosity, the wall slip velocity and the thickness of the boundary slip layer. The model was validated using results from solder paste samples measured at three different plate gaps (H=0.5 mm, 1.0 mm and 1.5 mm). Our results show that the predicted values of the true viscosity using the data measured at any two gaps are in reasonably good agreement. The results also show that the influence of the wall slip is significant and that the ratio of the predicted viscosity to the apparent viscosity decreases with increasing apparent shear rate     

Efficient control over heat transfer and hydrodynamics in closed regions due to optimal selection of materials for enclosure walls and external heat load

The effect of the external heat flow density and thermal-physical characteristics of the material of the enclosure walls on the modes of energy, mass, and momentum transfer in a standard component of electronics or electronic equipment with a local heat source is numerically analyzed. The distributions of the streamlines and isotherms in the solution region which reflect the possibility of controlling the thermohydrodynamics in the gas cavity by choosing the corresponding parameters of the external flow and the wall material are obtained. The dependences for the average heat transfer coefficient on the internal surface of one of the vertical walls in the case of variations in the thermal-physical characteristics of the material and the wall thickness are obtained.     

Design, fabrication, and in vitro evaluation of an in vivoultrasonic Doppler wall shear rate measuring device

In vivo wall shear rates have been obtained based on estimates from either volume flow rate or single-point velocity measurements along with the wall no slip assumption and a simple linear regression. Recent results (R.S. Fatemi and S.E. Rittgers, 1994) have shown that, under pulsatile flow conditions, wall shear rates are more accurately predicted by using up to four velocity points and a second- or third-order polynomial curve fit. The authors evaluate the accuracy of a new, in vivo transducer capable of determining wall shear rates nonintrusively from velocities at three points along a line perpendicular to the vessel wall. Three 20-MHz ultrasound crystals were embedded in an elastomer at distances of 1.5 and 2.1 mm with beam angles of 30°, 15°, and 60° to the horizontal plane. Microscopic examination showed that intercrystal spacings were within 1.5% of the design and the crystal angles were placed within 2.0%. In vitro calibration was performed under steady and pulsatile flow conditions with average shear rates being within 4.3±17.3% and 0.2±0.6.0% respectively, of the theoretically predicted values. Furthermore, peak and oscillatory shear rates were within -5.6±2.2% and -2.4±5.7% accuracy, respectively. Results from this study show this device to be capable of providing accurate wall shear rates in vivo     

转动腔体中射流特性的有限元分析

论述了采用有限元法分析转动腔体中射流特性。利用ANSYS-FLOTRAN CFD软件,通过建模、划分网格、加载和求解等途径,计算了在输入不同角速度时二维腔体中由喷嘴喷出气体的流场。结果表明,腔体静止时,射流速度沿腔体中心轴对称分布,腔体中心轴上的速度最大,两侧流速逐渐减小,近壁处为零;腔体转动时,在哥氏力的作用下,射流中心发生偏转,流场相对于腔体中心轴不再对称分布,腔体中各点处的流速分布随角速度而变化,压电射流角速度传感器利用这一特性敏感角速度。     

纳米尺度多晶硅微结构刻蚀研究

以HBr作为刻蚀气体,采用ICP金属刻蚀系统对气体流量、刻蚀压力、离子源功率、偏压功率等工艺参数与刻蚀速率、刻蚀选择比和侧壁垂直度的对应关系进行了大量工艺实验。借助理论分析和工艺条件的优化,开发出一套可满足制备侧壁垂直度的纳米尺度多晶硅密排线结构的优化刻蚀工艺技术。实验结果表明:当采用900 W的离子源功率、11 W的偏压功率、25 cm3/min流量的HBr气体和3 mTorr(1 mTorr=0.133 3 Pa)刻蚀压力的工艺条件时,多晶硅与二氧化硅的刻蚀选择比大于100∶1;在保持离子源功率、偏压功率、气体流量不变的条件下,单纯提高反应腔工艺压力则会大幅提高上述选择比值,同时损失多晶硅和二氧化硅的刻蚀均匀性;HBr气体流量的变化在上述功率及反应腔工艺压力的工艺范围内,对多晶硅与二氧化硅的刻蚀选择比和多晶硅刻蚀的形貌特征均无显著影响。采用上述优化的刻蚀工艺条件,配合纳米电子束光刻技术成功得到多晶硅纳米尺度微结构,其最小线宽为40 nm。     

径向三重流MOCVD反应器输运过程的数值模拟

对径向三重流MOCVD反应器的输运过程进行了二维数值模拟研究．在模拟计算中，分别改变反应腔几何尺寸、导流管位置、流量、压强、温度等条件，得到反应器流场、温场、浓度场的相应变化．根据对模拟结果的分析，发现反应腔内涡旋首先在流动的转折处产生，上下壁面温差的加大使涡旋增大，中管进口流量的增加对涡旋产生抑制作用，内管和外管流量的增加对涡旋产生扩大作用．得出输运过程的优化条件为：反应腔上下壁靠近，导流管水平延长，中管进口流量尽量大于内、外管流量，压强尽量低于10.5Pa，上下壁面温差尽量减小等．     

A mathematical model for slip phenomenon in a cavity-filling process of nanoimprint lithography

Squeeze flow theory has been used as an effective tool to clarify how and which process conditions determine cavity-filling behavior in nanoimprint lithography (NIL). Conventional squeeze flow models used in NIL research fields have assumed no-slip conditions at the solid-to-liquid boundaries, that is, at the stamp-to-polymer or polymer-to-substrate boundaries. The no-slip assumptions are often violated, however, in micrometer- to nanometer-scale fluid flow. It is therefore necessary to adopt slip or partial slip boundary conditions. In this paper, an analytical mathematical model for the cavity-filling process of NIL that takes into account slip or partial slip boundary conditions is derived using squeeze flow theory. Velocity profiles, pressure distributions, imprinting forces, and evolutions of residual thickness can be predicted using this analytical model. This paper also aims to elucidate how far the slip phenomenon is able to promote the process rate.