行波型超声粉体输送装置输送机理的研究

研究了行波型超声粉体输送装置,其输送机理是利用压晟陶瓷的超声振动激起输送管中的衰减行波,由衰减行波引起输送管管壁质点的椭圆运动从而输送粉体,并从波动理论的角度证明了行波型超声粉体输送装置中衰减行波和椭圆运动的存在,分析了管壁质点椭圆运动输送粉体的原理,为该装置的进一步研究提供了理论依据。该装置具有结构简单,控制精度高和噪声小等特点,有着广阔的应用前景。     

基于轴向振动配粉技术的药物微量配粉

针对轴向振动配粉技术在植入式可降解缓释给药系统微量配粉中的应用,搭建了轴向振动配粉实验台。采用毛细玻璃漏斗和圆锥状塑料吸头作为配粉管,研究两者稳定流动的振动幅值区间,讨论了振动频率对稳定出粉起始幅值、振动幅值对出粉流量及出粉流量稳定性的影响。结果表明：采用圆锥状塑料吸头作为配粉管的配粉过程更稳定,并且具有良好的抗堵性能;振动频率越大,实现配粉需要的起始激振幅度越小;在固定激振频率下,出粉流量随振幅先增大后减小,且管体中粉体处于充分流动状态;在激振频率为50 Hz,150 Hz,振幅为200~300 μm和35~50 μm时,可以得到最大且不随振幅改变的稳定出粉流量。实验论证了轴向振动配粉技术可以实现微量粉体的稳定、精确配给。     

单盘转子的瞬态不平衡动力相应分析

建立了Jeffcot转子的瞬态运动方程,采用S imu link程序进行数值仿真,得到转子系统在不同加速度下的瞬态动力响应。就不同加速度下转子系统振动的振幅、相位、进动角速度随时间和转速的变化规律分别作了较详细的讨论,得出了相应的结论。发现转子变速越过临界转速时,振幅、相位和进动角速度均与转子偏心相对于转子挠曲面的位置有关。进动角速度波动的极小值和极大值都对应着响应曲线过临界后波动的极小值。振幅、相位、进动角速度在过临界后的波动频率随转速增加而增加。该仿真结果与试验结论相吻合[4]。     

振幅对颤振球磨机粉磨效率的影响研究

针对颤振球磨机通过运动耦合增强粉磨能力的问题,基于EDEM仿真分析了不同振幅下筒体内介质运动形态,获得了不同振幅下磨机内介质碰撞能量分布,据此得出了各振幅下磨机粉磨能力的对比,然后通过调整振动电机内偏心块夹角改变了颤振球磨机的振幅,进行了不同振幅下的粉磨实验,验证了仿真分析得到的结果。仿真与粉磨实验研究结果表明:通过调整振幅可以改变磨机筒体内研磨介质的碰撞能量分布,采用大振幅有利于粉碎较粗物料,采用小振幅有利于粉碎较细物料,在粉磨过程中调整振幅以适应物料粒度的不断变化是提高磨机粉磨效率的有效途径。     

一维振动式滚磨光整加工颗粒流场的离散元模拟分析

为研究一维振动式滚磨光整加工中不同振幅、频率、筒宽下的颗粒流场分布及运动特征,基于离散元法对滚磨光整加工过程进行数值模拟与分析.研究发现:加工过程中,颗粒群可根据颗粒位置分为上中下三层,上层颗粒速度波动较大,且在一段时间后,颗粒速度会处于动态平衡状态;中层和底层颗粒速度始终在一定范围内波动,且具有周期性;不同层域的颗粒开始运动后都会有爬升,一段时间后处于动态平衡,上层颗粒的爬升值最大,底层颗粒的爬升值最小;随着频率和振幅增加,颗粒的爬升高度增加;筒宽越宽,爬升高度越小.     

基于消除线性滑动的杆状超声电机研究

研究了外圆面质点线性滑动及振幅分布对提高杆状弯曲振动超声电机驱动效率的影响。系统分析了质点的有效椭圆运动及线性滑动的特点,得出杆状弯曲振动超声电机定子的外圆面中点无线性滑动的结论;采用有限元分析方法分析定子表面质点有效椭圆运动振幅分布与其几何参数之间的关系,并据此对定子进行了参数优化,使定子振幅相对集中在中点位置,以提高电机效率。研究结果为采用中点驱动模式电机的设计提供了理论依据。     

三质点三自由度非线性的气动激振系统振动的初步研究

引言由活塞—气缸组成的气动激振器中,活塞若在图(3)图(4)两力的作用下运动,可以证明它是一个稳定的周期运动,在相平面中可画出一个稳定的极限环。当把这激振器按装在一个振动系统上时,将引起振动系统的振动,而完成一定的工作。本文研究的是一个三质点三自由度的气动激振系统的运动规律,主要关心的是求其振动基本频率和振幅。     

组合振动筛筛面颗粒松散与分层仿真研究

为了分析组合振动筛合理参数,采用颗粒粘结和Hertz-Mindlin模型,应用三维离散元法模拟分析筛面上物料的松散和分层,以颗粒间键粘结的平均数和物料沿筛面方向的平均切向力的大小作为衡量物料的松散效果,得到颗粒间键粘结的平均数随振幅、振动强度和筛面倾角的增加均减小,物料对筛面的平均切向力随振幅、振动强度和筛面倾角的增加均增大。当振幅大于7mm、振动强度大于5.5和筛面倾角大于25°时,松散效果趋于稳定,对松散后的物料在筛面上分层效果的研究,得到组合振动筛参数为上筛在高频小振幅下的松散分层效果好,下筛在低频大振幅下物料运动时间延长,透筛效果增加。     

立式振动磨磨介运动分析及振动强度设计

以提高立式振动磨的粉碎效果与效率为目的,深入分析其工作机理及磨钵内磨介运动情况,得出了磨钵内磨介的受力方程;在此基础上,以粉体力学中单颗粒破碎试验和研究为依据,建立了磨钵内粉体颗粒的二维粉碎受力模型,得出了物料粉碎粒径与振动强度的关系式,为立式振动磨及磨钵的设计提供理论指导。     

电子束选区熔化技术中可控振动落粉铺粉系统的研究

分析了快速成形技术中常用供粉系统与铺粉系统的优缺点。结合电子束选区熔化成形技术在真空环境下人工无法干预、成形区域温度高、成形件刚度大等特点和接触式铺粉机构遇到凸起后经常无法越过而导致成形中断的实验情况,提出了一种可控振动落粉铺粉方案。设计了具有粉末结拱与振动破拱功能且不与成形件相接触的上置式铺粉筛及具有称重传感器反馈的铺粉系统,通过改变铺粉筛的运行速度和加速度实现粉末铺送功能。实验结果表明,该系统运行可靠,在铺粉筛中粉末量一定的情况下可实现均匀铺粉,铺粉厚度通过改变铺粉筛运行速度和加速度来获取,最小粉末层厚度可达0.1mm。     

The effect of vibration on the hemorheological characteristics of non-aggregated blood

The present study investigates the hemorheological characteristics of blood flow with applying vibration to a non-aggregating red blood cell suspension. In order to obtain the non-aggregating RBC suspension, blood samples were treated with vibration at a specified condition, which viscosities were taken before and after the treatment, respectively. The viscosity of the blood samples after treatment was higher than before treatment. These treated blood samples were forced to flow through a capillary tube that was vibrated perpendicularly to the direction of the flow. The experimental results showed that vibration caused a reduction of the flow resistance of the non-aggregated blood. The reduction of the flow resistance was strongly dependent on both frequency and amplitude of vibration. These results show potential in treating various diseases in the microcirculation associated with blood cell aggregation.     

Numerical simulation of the effects of a suction line heat exchanger on vapor compression refrigeration cycle performance

Most modern refrigerators incorporate heat transfer between the refrigerant in a capillary tube and the refrigerant in a suction line. This heat transfer is achieved by a non-adiabatic capillary tube called a capillary tube-suction line heat exchanger and is supposed to improve the performance of the small vapor compression refrigeration cycle by removing some enthalpy of the refrigerant at the evaporator entrance. To investigate the effects of this heat transfer on the refrigeration cycle, a computer program was developed based on conservation equations of mass, momentum, and energy. The non-adiabatic capillary tube model is based on a homogeneous two-phase flow model. The simulation results show that both the location and length of the heat exchange section influence the coefficient of performance (COP) as well as the cooling capacity. It is noteworthy that the influence was not monotonic; that is, the performance may be deteriorated under certain conditions.     

Propagation characteristics of compression waves reflected from the open end of a duct

The present study addresses the distortion of the compression wave reflected from an open end of a shock tube. An experiment is carried out using the simple shock tube with an open end. Computational work is also performed to represent the experimented flows. The second-order Total Variation Diminishing scheme is employed to numerically solve the unsteady, axisy-mmetric, inviscid, compressible governing equations. Both the experimented and predicted results are in good agreement. The generation and development mechanisms of the compression wave, which is reflected from the open end of the shock tube, are obtained in detail from the present computations. The effect of size of the baffle plate at the open-end that causes the reflection of the incident expansion wave is found negligible. A good correlation is obtained for transition of the reflected compression wave to a shock wave inside the tube. The present data show that for a given wave length of the incident expansion wave the transition of the reflected compression wave to a shock wave can be predicted with good accuracy.     

用数值方法分析绝热毛细管的流量特性

根据均相流假设，用两相流基本方程建立了毛细管的数学模型，采用一种快速、有效的计算方法对绝热毛细管的流量特性进行数值模拟，并把计算结果与实验数据进行了对比分析。     

Study of moist air flow through the ludwieg tube

The time-dependent behavior of unsteady condensation of moist air through the Ludwieg tube is investigated by using a computational fluid dynamics (CFD) work. The twodimensional, compressible, Navier-Stokes equations, fully coupled with the condensate droplet growth equations, are numerically solved by a third-order MUSCL type TVD finite-difference scheme, with a second-order fractional time step. Baldwin-Lomax turbulence model is employed to close the governing equations. The predicted results are compared with the previous experiments using the Ludwieg tube with a diaphragm downstream. The present computations represent the experimental flows well. The time-dependent unsteady condensation charac-teristics are discussed based upon the present predicted results. The results obtained clearly show that for an initial relative humidity below 30% there is no periodic oscillation of the condensation shock wave, but for an initial relative humidity over 40% the periodic excursions of the condensation shock occurs in the Ludwieg tube, and the frequency increases with the initial relative humidity. It is also found that total pressure loss due to unsteady condensation in the Ludwieg tube should not be ignored even for a very low initial relative humidity and it results from the periodic excursions of the condensation shock wave.     

节流短管内制冷剂流动的两流体模型

制冷剂在短管内的两相节流过程存在显著的动力学和热力学非平衡特性。建立了描述节流短管内制冷剂两相流的六方程两流体模型,模型中考虑了相间速度滑移和温度滑移。计算表明,制冷剂在短管内比在毛细管(长管)内的闪蒸过程具有更大的相间速度滑移和温度滑移。对R134a在短管内的流量特性进行了预测,与试验数据偏差小于±20％。     

毛细管地板辐射采暖特性试验研究

描述了毛细管地板辐射采暖试验系统、毛细管辐射板铺设形式、地板构造以及具体试验方法;通过试验分析了毛细管辐射板供热能力、辐射板加热层温度、地板表面温度以及室内温度的变化特性.研究得出了毛细管辐射板供热能力较强,毛细管辐射采暖时室内温度响应较快,室内温度场分布均匀性较好.     

The influence of tube and membrane structure on dynamic instability in furnace wall tubes of a fossil fired once-through boiler in a simulated furnace environment

A numerical model was developed to investigate dynamic instability in fossil fired once through boilers and the influence of the dynamics of tube and membrane structure furnace wall tubes on the stability boundary was examined. In order to predict density wave oscillation (DWO), the most common type of dynamic instability, a time domain nonlinear analysis approach was used to give a transient flow field in the tubes. The tubes were divided into one-dimensional finite volumes along their lengths and equations of conservation of mass, momentum and energy were discretized to give algebraic equations. The SIMPLE algorithm was adopted to solve these equations. Analysis of two-dimensional transient conduction across a tube-membrane section of each volume was performed concurrently and the resulting heat transfer between tube inner wall and fluid was included in the source term of the energy equation. After verification with results in available literature, the model was applied to a wall tube section of a 700 MW boiler furnace in subcritical once-through condition. The stability boundaries for three types of tube configuration were predicted, and it was found that the dynamics of tube configuration can have a significant effect on the flow instability in the boiler furnace wall tubes.     

CO_2跨临界循环中绝热毛细管性能试验研究

搭建了CO2跨临界循环毛细管性能试验台,通过控制变量法,分析了毛细管尺寸(管径、长度)和系统运行工况(入口压力、入口温度)等参数对毛细管质量流量的影响趋势和程度,而且发现:即使在非临界流的情况下,蒸发压力对质量流量的影响也很小。运用量纲分析法计算出了毛细管质量流量无量纲试验关联式:根据毛细管出口压力、入口温度、管径和长度可计算出毛细管CO2质量流量,并对该方程的可靠性进行了分析。结果表明:95%的预测值和试验值偏差维持在了±10%以内。     

毛细管长度对热泵热水器系统动态性能的影响

对使用4种不同长度毛细管的空气源热泵热水器系统的动态性能进行了试验研究,分析了毛细管长度对压缩机排气温度、系统耗功率、蒸发压力、冷凝压力、制热量及系统性能系数(COP)等的影响.试验结果表明,在加热初始阶段,采用短毛细管的热泵热水器系统性能优于使用长毛细管的系统性能,而在加热后期则恰好相反.为了提高加热周期内热泵系统的平均性能系数,在加热过程中分别切换使用长度为150mm、250mm和350mm的3种毛细管,其动态性能试验表明,可大大提高热泵热水器系统的性能,其平均COP约为4.6.在整个加热阶段,压缩机的排气温度未超过90℃,保证了压缩机在一个安全稳定的条件下运行.