新型自然循环自动清洗式蒸发器及设计原理

以高效蒸发器为目标，旨在以自然循环替代高能耗的强制循环泵、以自动清洗取代加热面盐垢的周期性停车清洗．主要研究沸腾室内的不平衡汽化过程机理，提出动力温度的新概念，采用显热与汽化热转换平衡的研究方法，得到自然循环推动力的工程设计计算式，并且由此引出推动力强化的基本原则，进而获得中试的成功．还提出加热室必须采用能够低流速下自转清洗又高效传热强化的螺旋齿带，才能保障循环总阻力低于推动力．     

内燃机活塞环开口重叠的摩擦机理分析

根据曲轴扭矩传递原理得到了相关数学模型，进而计算了连杆轴颈偏转和活塞往复转动；在考虑燃气压力、往复惯性力和流体摩擦力，以及转动摩擦阻力矩、转动惯性力矩和气体摩擦力矩作用的基础上，提出了活塞环随活塞同步转动的判别条件，建立了活塞环相对转动的分析模型．结果表明：在内燃机工作循环中，连杆轴颈的正、负偏转引起活塞往复转动，在燃气爆发位置附近产生最大偏转和转动幅值；在少量曲轴转角区间内附着力矩小于转动阻力矩，此时活塞环不能与活塞保持同步而是与活塞之间发生相对转动；第二气环转动角度大于第一气环，当2个气环的开口转到相同位置时，活塞环出现开口重叠．     

大型球轴承摩擦力矩试验台的研制及其实用性能的试验研究

为了研究大型轴承的摩擦性能，研制了一种可以测量外径２００～１５００ｍｍ球轴承的启动力矩、运转平均力矩、最大力矩和力矩变化幅值的大型轴承摩擦力矩试验台．这种试验台可以模拟轴承的启动角加速度、转动速度、预负荷和轴向工作负荷等．在此试验台上，对大型角接触球轴承成对预紧时的摩擦力矩与预紧量之间的关系进行了试验研究，并且根据试验结果，提出了一种适用于轴承外径２００～５００ｍｍ，转动速度低于３０ｒ／ｍｉｎ时计算摩擦力矩的经验公式．     

一次性分配的力矩分配法

提出以多跨连续梁为单元参与力矩分配法的设想，导出了任意跨连续梁的杆端转动刚度 和结点处弯矩传递系数的递推计算式，使得设想能够实施．改变了传统力矩分配法的渐近解 法，只需一次性分配就可求得精确解．     

力矩析微

力矩是力学教学中最重要的基础概念之一,但教材中一般会同时给出力对点之矩和力对轴之矩两种定义,这在概念上容易引起学习者的困惑,尤其是空间问题中的力对点之矩,从物理意义的角度讲更是不易理解.本文在利用杠杆原理阐述力矩定义起源的基础上明确指出:力矩本质上即力对轴之矩,是力使刚体绕特定轴转动效应的一种度量,是滑动矢量;而力对点之矩是力对轴之矩的一种抽象的等价表述,是定位矢量,是力矩概念在复杂应用中的进一步发展.这种解释理清了力对点之矩与力对轴之矩两种定义之间的关系,物理意义明确直观,更有利于教学和实践中对力矩概念的清晰理解和准确应用.     

建筑结构基于巴斯金风速谱的系列风振响应的简明封闭解

针对巴斯金风速谱激励下的建筑结构顺风向振动响应表达式复杂的问题,提出了一种简明封闭解法.巴斯金随机谱广泛应用于描述脉动风、随机地震动和路面不平顺等各种随机激励,本文基于留数定理给出巴斯金风速功率谱的二次正交式.综合运用复模态法和虚拟激励法获得了建筑结构系列响应(位移、层间位移及其变化率)功率谱的统一形式的二次正交式,并根据谱矩的定义获得了建筑结构系列响应的方差和谱矩及绝对加速度方差的简明封闭解.运用本文方法对一8层建筑结构进行分析,并与传统虚拟激励法进行对比研究,表明本文所得封闭解正确,并可用于验证虚拟激励法在谱矩和方差分析时的精度和效率.由于本文方法含有复模态法,故可用于各类线性结构基于巴斯金谱的随机响应分析和基于动力可靠度及舒适度的动力优化分析.     

卸载后加载对扭杆刚度下降门槛值的影响

基于损伤力学原理,推导了扭力矩门槛值表达式. 并采用多次卸载后加载的方法 进行定扭角刚度下降实验,得到卸载后加载的剩余扭力矩,进而计算每次加载后的剪 应变门槛值. 实验表明多次卸载后加载的方法可在一定程度上提高剪应变门槛值. 此结论可以用于同类材料在工程应用中需要提高门槛值的构件.     

人体落地冲击力冲量的分析和计算

本根据人体落地受伤是受冲击力的大小、冲击作用时间长短以及冲击力矩(如扭伤)等因素所致的事实出发，将人体着地瞬间看作撞击过程，以冲击力的冲量和冲量矩作为人体和各关节所承受的冲击作用的度量．利用多刚体系统动力学理论及计算方法给出了计算总撞击冲量及关节内冲量、冲量矩的算法；编制了相应的计算程序．以垂直落地为例所作的计算与已有结果一致．     

自转清洗包塑钢丝螺旋的流体动力学优化设计研究

通过传热管内自转清洗钢丝螺旋的动力学理论研究, 得到自转动力矩的理论计算式:动力矩大小与钢丝直径d、螺旋角的sin2α、螺旋外径D²、流速u²、液体密度ρ成正比. 理论计算式与单管流体动力学实验研究结果完全一致. 因此, 该计算式可以作为自转清洗钢丝螺旋结构优化设计和工程应用优化设计的理论基础. 虽然包塑钢丝较粗, 但是流体阻力实验研究结果表明仍然在一般工程的许可范围内.     

交流电动机启动过程的扭振及电震荡

本文建立了电机的扭振方程和电路方程相耦联的统一数学系统,得到了它的解.研究了电源电压、扭转刚度等参数对启动过程的扭振、电磁力矩、电流等的影响,得到了一些有工程实际价值的规律和消除这种大扭振的途径,理论结果和实验结果吻合很好.     

SMA-induced snap-through of unsymmetric fiber-reinforced composite laminates

A theory is developed and experiments designed to study the concept of using shape memory alloy (SMA) wires to effect the snap-through of unsymmetric composite laminates. The concept is presented in the context of structural morphing, that is, a structure changing shape to adjust to changing conditions or to change operating characteristics. While the specific problem studied is a simplification, the overall concept is to potentially take advantage of structures which have multiple equilibrium configurations and expend power only to change the structure from one configuration to another rather than to continuously expend power to hold the structure in the changed configuration. The unsymmetric laminate could be the structure itself, or simply part of a structure. Specifically, a theory is presented which allows for the prediction of the moment levels needed to effect the snap-through event. The moment is generated by a force and support arrangement attached to the laminate. A heated SMA wire attached to the supports provides the force. The necessary SMA constitutive behavior and laminate mechanics are presented. To avoid dealing with the heat transfer aspects of the SMA wire, the theory is used to predict snap-through as a function of SMA wire temperature, which can be measured directly. The geometry and force level considerations of the experiment are discussed, and the results of testing four unsymmetric laminates are compared with predictions. Laminate strain levels vs. temperature and the snap-through temperatures are measured for the these laminates. Repeatability of the experimental results is generally good, and the predictions are in reasonable agreement with the measurements.     

可压缩粘性流中力和力矩的分配律和广义Kutta-Joukowski定理

本文引进了动力学涡量概念,推导出可压缩粘性流中的力和力矩的一般表达式。作用在任意运动物体(系)上的力和力矩可以分别表示成流场中动力学涡量的一阶矩和二阶矩随时间的变化率。 利用 Navier-Stokes 方程求出动力学涡量的变化率,进一步把力和力矩表示成一些显式积分。它们分别对应于产生空气动力的一些特定的物理过程,称之为力和力矩的分配律。同时,流场中任何运动的动力学涡量均产生一个空气动力贡献量。相应的计算公式即为广义Kutta-Joukowski 定理。     

Forced Convective Cooling via Acoustic Streaming in a Narrow Channel Established by a Vibrating Piezoelectric Bimorph

Forced convection in a narrow channel is investigated both numerically and experimentally. The flow field is established through the mechanism of acoustic streaming. This is accomplished by high frequency vibration of one of the channel walls, which is composed of a piezoelectric bimorph. In the numerical computations, the Navier-Stokes equations are decomposed into the acoustic equations and the streaming equations by the perturbation method. The acoustic field is first numerically obtained, which provides the driving force for the streaming field. The streaming field and the associated temperature field are then obtained numerically. Heat losses from a heat source are measured to determine the efficiency of this as a cooling method. The air-flow patterns in the channel between the heat source and the bimorph actuator are visualized using the particle tracking velocimetry. The visualization clearly shows that vortical streaming (acoustic streaming) can be induced by bimorph vibration, which enhances heat transfer between the heat source and the surrounding air. The temperature decreases obtained computationally and experimentally are in good agreement.     

Mixed convective heat transfer characteristics and mechanisms in structured packed beds

The structured packed bed is considered a promising reactor owing to its low pressure drop and good heat transfer performance. In the heat transfer process of thermal storage in packed beds, natural convection plays an important role. To obtain the mixed convective heat transfer characteristics and mechanisms in packed beds, numerical simulations and coupling analyses were carried out in this study on the unsteady process of fluid flow and heat transfer. A three-dimensional model of the flow channel in the packed bed was established, and the Navier–Stokes equations and Laminar model were adopted for the computations. The effects of the driving force on fluid flow around a particle were studied in detail. The differences in velocity and density distributions under different flow directions due to effect of the aiding flow or opposing flow were intuitively demonstrated and quantitatively analyzed. It was found that the driving force strengthens the fluid flow near the particle surface when aiding flow occurs and inhibits the fluid flow when opposing flow occurs. The boundary layer structure was changed by the natural convection, which in turn influences the field synergy angle. For the aiding flow, the coordination between the velocity and density fields is higher than that for the opposing flow. By analysis the effects of physical parameters on mixed convective heat transfer, it is indicated that with an increase in the fluid-solid temperature difference or the particle diameter, or a decrease in the fluid temperature, the strengthening or inhibiting effect of natural convection on the heat transfer became more significant.     

Concepts and realization of microstructure heat exchangers for enhanced heat transfer

Microstructure heat exchangers have unique properties that make them useful for numerous scientific and industrial applications. The power transferred per unit volume is mainly a function of the distance between heat source and heat sink—the smaller this distance, the better the heat transfer. Another parameter governing for the heat transfer is the lateral characteristic dimension of the heat transfer structure; in the case of microchannels, this is the hydraulic diameter. Decreasing this characteristic dimension into the range of several 10s of micrometers leads to very high values for the heat transfer rate.

Another possible way of increasing the heat transfer rate of a heat exchanger is changing the flow regime. Microchannel devices usually operate within the laminar flow regime. By changing from microchannels to three dimensional structures, or to planar geometries with microcolumn arrays, a significant increase of the heat transfer rate can be achieved.

Microheat exchangers in the form of both microchannel devices (with different hydraulic diameters) and microcolumn array devices (with different microcolumn layouts) are presented and compared. Electrically heated microchannel devices are presented, and industrial applications are briefly described.     

Stability and oscillations in a slow-fast flexible joint system with transformation delay

Flexible joints are usually used to transfer velocities in robot systems and may lead to delays in motion transformation due to joint flexibility. In this paper, a linkrotor structure connected by a flexible joint or shaft is firstly modeled to be a slow-fast delayed system when moment of inertia of the lightweight link is far less than that of the heavy rotor. To analyze the stability and oscillations of the slowfast system, the geometric singular perturbation method is extended, with both slow and fast manifolds expressed analytically. The stability of the slow manifold is investigated and critical boundaries are obtained to divide the stable and the unstable regions. To study effects of the transformation delay on the stability and oscillations of the link, two quantitatively different driving forces derived from the negative feedback of the link are considered. The results show that one of these two typical driving forces may drive the link to exhibit a stable state and the other kind of driving force may induce a relaxation oscillation for a very small delay. However, the link loses stability and undergoes regular periodic and bursting oscillation when the transformation delay is large. Basically, a very small delay does not affect the stability of the slow manifold but a large delay affects substantially.     

考虑振动非平衡的可压缩库埃特流动及其传热

新型近空间高超声速飞行器大多具有尖头薄翼的外形,驻点下游机身附近的强剪切流动及气动加热具有显著的非平衡特征.由于加热总量预估和实验测热数据辨识的需要,工程上越来越关注强剪切非平衡流动及气动加热预测问题.本文结合理论建模和直接模拟蒙特卡洛数值模拟,研究了振动非平衡条件下的可压缩库埃特流动的气动力/热问题.首先基于参考温度...     

Heat transfer enhancement in a turbulent natural convection boundary layer along a vertical flat plate

An experimental study on heat transfer enhancement for a turbulent natural convection boundary layer in air along a vertical flat plate has been performed by inserting a long flat plate in the spanwise direction (simple heat transfer promoter) and short flat plates aligned in the spanwise direction (split heat transfer promoter) with clearances into the near-wall region of the boundary layer. For a simple heat transfer promoter, the heat transfer coefficients increase by a peak value of approximately 37% in the downstream region of the promoter compared with those in the usual turbulent natural convection boundary layer. It is found from flow visualization and simultaneous measurements of the flow and thermal fields with hot- and cold-wires that such increase of heat transfer coefficients is mainly caused by the deflection of flows toward the outer region of the boundary layer and the invasion of low-temperature fluids from the outer region to the near-wall region with large-scale vortex motions riding out the promoter. However, heat transfer coefficients for a split heat transfer promoter exhibit an increase in peak value of approximately 60% in the downstream region of the promoter. Flow visualization and PIV measurements show that such remarkable heat transfer enhancement is attributed to longitudinal vortices generated by flows passing through the clearances of the promoter in addition to large-scale vortex motions riding out the promoter. Consequently, it is concluded that heat transfer enhancement of the turbulent natural convection boundary layer can be substantially achieved in a wide area of the turbulent natural convection boundary layer by employing multiple column split heat transfer promoters. It may be expected that the heat transfer enhancement in excess of approximately 40% can be accomplished by inserting such promoters.     

Experimental studies of a hygroscopic condenser-evaporator heat exchanger based on concentration differences of vertically falling films

A concentration-driven power cycle motivated by differences in vapor partial pressures (boiling point rise) and latent heats of brine and water is studied. The condensation of relatively low-pressure, low-temperature vapor occurs on the free interface of a relatively hot falling film of a hygroscopic salt solution due to the reduced vapor pressure of the brine. The heat released is transferred to the evaporating/cooling water film on the other side of a vertical plate separating the brine and water films. The process is maintained because the latent heat of condensation on the brine film is higher than the latent heat of evaporation of pure water. The condensation driving force is the difference between the partial pressure of condensing water vapor and that of water in the brine solution. The simultaneous mass and heat transfer mechanisms associated with this nonisothermal absorption can occur even against an opposing thermal driving force in the condensing vapor phase. Complementing earlier studies by the same authors, a vertical film-type condenser-evaporator heat exchanger is considered. The experimental study deals with the effects of the various parameters involved in this rather unique process and the mechanisms that control them. The experimental results prove the potential of operating this new heat transfer modality and provide the background for the theoretical determination of the optimal performance of this direct-contact power cycle.