微尺度悬臂管颤振的有限维研究

基于修正的偶应力理论并考虑Lagrange应变张量所给出的几何非线性,运用Hamilton原理建立了微尺度悬臂管平面振动的积分-微分方程通过Galerkin方法将原积分-微分方程离散成常微分方程组,研究了临界流速-质量比曲线的不同阶Galerkin近似解与精确解的符合程度以及它们对材料长度尺寸参数的依赖性对不同的模态截断数,运用基于中心流形-范式理论的投影法计算了临界流速处系统的第一Lyapunov(李雅谱诺夫)系数和临界特征值关于流速的变化率,以此为基础分析了系统的分岔模式,探讨了模态截断数对系统动力学性质的影响临界流速-质量比曲线的滞后部分及交点处的动力学性质表明,系统存在不同的分岔方向,用6个模态的Galerkin离散化方程作分岔图对此进行了验证,并通过理论分析及数值方法分别计算了颤振的固有频率.     

空间分数阶非Newton流体本构及圆管流动规律研究

对非Newton流体的本构及流动规律进行研究是分析、预测和控制非Newton流体在管道中流动的关键.实验表明非Newton流体在流动过程中具有历史记忆性,基于空间分数阶微积分方法,建立了分数阶非Newton流体本构模型;并推导了该模型在圆管中的流速分布、流量、平均流速、压降、平均Reynolds数等管道流动参数;提出了分数阶非Newton流体圆管流态判别准则.研究表明非Newton流体的圆管流层间的切应力可以通过流速的轴向分布大小来描述.对于不含屈服切应力的分数阶非Newton流体,分数阶的阶数越大,断面流速分布越均匀,记忆能力越强.分数阶的阶数大小反映了流体对全域空间的记忆性强弱;而对于含有屈服切应力的分数阶非Newton流体,分数阶的阶数越大,速梯区流速分布越均匀,流核区速度越小.分数阶的阶数大小反映了局部空间记忆性强弱.该研究为非Newton流体的记忆特征提供了一种新的建模方法.     

Vortex dynamics of a trapezoidal bluff body placed inside a circular pipe

The influence of Reynolds number and blockage ratio on the vortex dynamics of a trapezoidal bluff body placed inside a circular pipe is studied experimentally and numerically. Low aspect ratio, high blockage ratio, curved end conditions (junction of pipe and bluff body), axisymmetric upstream flow with shear and turbulence are some of the intrinsic features of this class of bluff body flows which have been scarcely addressed in the literature. A large range (200:200,000) of Reynolds number (Re_D) is covered in this study, encompassing all the three pipe flow regimes (laminar, transition and turbulent). Four different flow regimes are defined based on the distinct features of Strouhal number (St)–Re_D relation: steady, laminar irregular, transition and turbulent. The wake in the steady regime is stationary with no oscillations in the shear layer. The laminar regime is termed as irregular owing to irregular vortex shedding. The vortex shedding in this regime is observed to be symmetric. The emergence of separation bubble downstream of the bluff body on either side is another interesting feature of this regime, which is further observed to be symmetric. Two pairs of mean streamwise vortices are noticed in the near-wake regime, which are termed as reverse dipole-type wake topology. Beyond the irregular laminar regime, the Strouhal number falls gradually and vortex shedding becomes more periodic. This regime is named transition and occurs close to the Reynolds number at which transition to turbulence takes place in a fully developed pipe. The turbulent regime is characterised by a nearly constant Strouhal number. Typical Karman-type vortex shedding is noticed in this regime. The convection velocity, wake width formation length and irrecoverable pressure loss are quantified to highlight the influence of blockage ratio. These results will be useful to develop basic understanding of vortex dynamics of confined bluff body flow for several practical applications.     

铁磁性加载复合管壳电子注聚焦性能的研究

大功率行波管通常利用复合管壳提升高频系统的集成度和散热特性。宽带行波管采用复合管壳高频制造工艺时,由于加载翼片含有铁磁性材料（纯铁）使得聚焦系统的横向磁场分量变大,径向和角向磁场分量呈非均匀性,电子注聚焦困难。本文研究了周期永磁聚焦系统横向磁场产生的原因并建立理论模型,并对磁场分量和其对电子注形态的影响进行了仿真,仿真结果与理论计算结果一致。根据横向磁场分布模型对加载翼片的形状和数量进行优化仿真,结果表明9片齿形加载翼片方案可在保持慢波电路参数的同时,降低聚焦系统的横向磁场分量,改善电子注聚焦效果。     

小长径比垂直管气液两相流动特性分析

实验观察了小长径比垂直上流管内流型及特点,并对管入口处的压力波动特性和系统的压差波动特性进行了试验研究.结果表明:小长径比(L/D)垂直管内流型表现为泡状流、塞状流、乳沫状流、环状流和液束环状流;分别增加管线中的气量、液量,或者同时增加气液流量,均会造成垂直管入口处压力波动的均值和最大压力的增加;压力信号的概率密度(PDF)大部分呈双峰分布,也存在单峰和多峰分布;差压信号的概率密度符合正态分布,其功率谱密度同压力信号相比具有频率波动范围宽、幅值小的特点.     

Empirical Study of an Air-to-Air Heat Pipe Heat Exchanger in Tropical Climates

Abstract

This article presents the empirical study of a heat pipe heat exchanger that was directly experiencing the ambient tropical air in its evaporator section. The performance of the heat pipe heat exchanger was monitored during two weeks of operation to determine the performance curves. The temperature of return air was controlled at about 22°C as the representative temperature of inside air, and a face velocity of 2 m/s on the heat pipe heat exchanger coil was established for this purpose. It was found that for the present investigation, the heat pipe heat exchanger can pay for itself in 1.5 years.     

高炉冲渣水余热回收的可行性研究

根据高炉冲渣水的余热特点,提出了一个采用分离式热管换热器的余热回收的方案。文中对余热回收方案中换热设备的结构特点进行了描述。     

CPL技术在空间飞行器上的应用

本文对ＣＰＬ技术进行了简要概述,介绍了其工作原理与工作特性,并讨论了ＣＰＬ技术在空间飞行器上的可能应用方式。其中,对ＣＰＬ技术应用于空间设备的散热进行了全面阐述,并给予理论分析;此外,对ＣＰＬ技术应用于空间设备的主动热控制,也作了简要介绍;对ＣＰＬ技术未来有发展前景的应用方式进行了展望。     

表面作用对分离式热管小螺旋管蒸发段两相流动与换热特性的影响

本文应用界面化学理论研究表面作用对分离式热管小螺旋管蒸发段管内流动和换热特性的影响。通过实验及分析,提出通过在一定范围内提高热管工作温度和添加润湿剂以降低水的表面张九提高管内壁的粗糙度以增强液膜的铺展性能。利用这两种方法可以有效地增强小螺旋管内壁面的润湿性能,从而提高管内换热性能．