WCDMA与CDMA200O多址方式的比较

本文就 WCDMA与 CDMA2 0 0 0采用的多址方式 SC- DS- CDMA和 MC- CDMA进行了比较。介绍了两者的时域扩频及发射原理 ,DS- CDMA的 RAKE接收和 MC- CDMA的 FFT实现。比较了两者的系统容量和频谱效率     

锥序约束下两个指数总体均值的估计

讨论样本容量相等时 ,在锥序约束 a1λ1≤λ2 ≤a2 λ1条件下 ,两个指数总体均值 λi( i=1 ,2 )的估计量 .证明约束极大似然估计 λi 具有比经典极大似然估计 Xi 更小的均方误差 ,并且讨论 λi 对 Xi的功效 e( λi,Xi) ,i=1 ,2 .     

随机正交辛阵的性质和构造方法

分析讨论了正交辛矩阵的性质；研究了现有两种构造随机正交辛矩阵算法的特点；给出了一种构造完全随机的正交辛矩阵的数值实现方法，该完全随机的正交辛矩阵在求解Hamilton矩阵的保结构算法的数值试验中有重要用途。     

稠油注CO_2的方式及其驱油效果的室内实验

针对地层条件下粘度为 10 0mPa·s的稠油 ,采用室内实验方法研究了稠油注CO2 的注入方式 ,包括CO2吞吐、CO2 吞吐转CO2 驱转水驱、CO2 吞吐转水驱、CO2 驱、水驱CO2 段塞、CO2 水交替注入等 ,并对各种注入方式的驱油效率进行了比较。结果表明 ,在实验条件下 ,CO2 水交替注入和CO2 吞吐转水驱的方式驱油效率最高 ,稠油CO2 吞吐然后转为水驱的方式是可行的。该研究可为现场选择合理的注入方式提供技术参数。     

基于遗传算法的油气集输管网运行效率优化

油气集输系统的能量耗散,在油田生产能量消耗中占主导地位.若集输管网各项运行参数没有随着油井开发参数的变化而相应调整,将导致集输系统能耗逐年增加,集输用气和用电单耗不断升高.对于这一问题,以树状双管掺水集输管网为研究对象,在布局一定的情况下,以管网掺水量、掺水温度、掺水压力为参数变量,运用遗传算法编制程序对其优化.以某油区树状双管掺水集输管网为例,通过运算得到优化后的运行参数,管网运行能耗比优化前降低了28%.     

特低渗透油藏水驱油特征实验研究

针对特低渗—超低渗油层渗流特点,选取西峰油田长8油层21块岩心,通过室内水驱油实验研究,分析了低渗透油层驱油效率与储层渗透率的关系,驱油效率与注水倍数的关系,以及驱油效率与驱替压力梯度的关系.研究结果表明,低渗透油层在渗透率较低的范围内,随渗透率的降低,驱油效率则急剧降低;随注水倍数的增加,各含水阶段驱油效率增加的幅度不同,消耗的注水量也不同;随着驱替压力梯度的提高,驱油效率均呈上升趋势.     

洗涤冷却室气液分离空间内液滴重力分离数值研究

在Euler-Lagrange三维坐标系下,建立了液滴重力分离模型.利用该模型模拟了气化炉洗涤冷却室气液分离空间内的气液两相流动.揭示了液滴的运动规律,分析了气液分离空间高度、气流速度以及液滴初始速度对液滴分离效率的影响.研究结果表明:液滴在飞溅进入气液分离空间后作减速运动,越小尺寸液滴的减速越为明显;液滴的分离效率随着气液分离空间高度的增加而提高并趋于稳定;在相同液滴初速度以及相同气液分离空间高度下,随着气流速度的降低,液滴的分离效率反而增大;随着液滴初始速度的提高,获得最大液滴分离效率所需的气液分离空间高度增加.在考虑液滴碰撞效应后,计算得到的液滴分离效率有所提高.     

Influence of wire spacing and plate spacing on electrostatic precipitation of nanoparticles: An approach involving electrostatic shielding and diffusion charging

Electrostatic precipitation is a process widely used as gas cleaning device, to removal particles from gas flows. However, in a conventional and well-sized precipitator, the collection efficiency decreases for ultrafine particles, making it difficult to employ this equipment for controlling nanoparticle pollution. This paper investigates the influence of plate spacing (4 and 6.5 cm) and wire spacing (4, 6, and 12 cm) on the electric current and nanoparticle collection efficiency, considering the effect of diffusion charging and electrostatic shielding. Two laboratory-scale dry wire-plate electrostatic precipitators with different plate spacings were tested for the collection of nanoparticles (6.15–241.4 nm) at three air velocities (1.9, 2.9, and 3.9 cm/s). The results demonstrated the effectiveness of the equipment in removing nanoparticles (99.9%) under the highest electric fields. Higher values of the wire spacing led to increases in the current and the collection efficiency. This was associated with reduced electrostatic shielding, which is more evident in smaller ducts with a higher density of field lines. It is expected that the findings should improve knowledge on electrostatic precipitation of nanoparticles, enabling optimization of collection efficiency by considering the effects of geometric parameters.     

Development and assessment of algorithms for DEM-LES simulations of fluidized bed

The use of high-fidelity Discrete Element Method (DEM) coupled with Computational Fluid Dynamics (CFD) for particle-scale simulations demands extensive simulation times and restricts application to small particulate systems. DEM-CFD simulations require good performance and satisfactory scalability on high-performance computing platforms. A reliable parallel computing strategy must be developed to calculate the collision forces, since collisions can occur between particles that are not on the same processor, or even across processors whose domains are disjoint. The present paper describes a parallelization technique and a numerical verification study based on a number of tests that allow for the assessment of the numerical performance of DEM used in conjunction with Large-Eddy Simulation (LES) to model dense flows in fluidized beds. The fluid phase is computed through solving the volume-averaged four-way coupling Navier-Stokes equations, in which the Smagorinsky sub-grid scale tensor model is used. Furthermore, the performance of Sub-Grid Scale (SGS) turbulence models applied to Fluidized Bed Reactor (FBR) configurations has been assessed and compared. The developed numerical solver represents an interesting combination of techniques that work well for the present purpose of studying particle formation in fluidized beds.     

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.