Numerical study of solar-wind tower systems for ventilation of dwellings

Numerical study is carried out of a simplified system of solar-wind tower for ventilation of dwellings. The conservation equations for mass, momentum and energy for mixed convection in two-dimensional coordinates are solved by the control volume method and Simpler algorithm. The governing parameters of the problem are Rayleigh number Ra, Reynolds number, Re (or Richardson number, Ri), the dimensionless conductivity of the solid medium, k_r and the geometrical parameters. Nusselt number Nu and dimensionless volume flow rate are calculated as a function of the governing parameters, and streamlines and isotherms are produced. The results show that the important parameters affecting the ventilation performance are Ra, Re (or Ri), and the geometrical parameters, the aspect ratio A, the exit port size h₁/L and to a lesser degree, the wall thickness ℓ₁/L.     

Thermodynamic study of wet cooling tower performance

An analytical model was developed to describe thermodynamically the water evaporation process inside a counter‐flow wet cooling tower, where the air stream is in direct contact with the falling water, based on the implementation of the energy and mass balance between air and water stream describing thus, the rate of change of air temperature, humidity ratio, water temperature and evaporated water mass along tower height. The reliability of model predictions was ensured by comparisons made with pertinent experimental data, which were obtained from the literature. The paper elaborated the effect of atmospheric conditions, water mass flow rate and water inlet temperature on the variation of the thermodynamic properties of moist air inside the cooling tower and on its thermal performance characteristics. The analysis of the theoretical results revealed that the thermal performance of the cooling tower is sensitive to the degree of saturation of inlet air. Hence, the cooling capacity of the cooling tower increases with decreasing inlet air wet bulb temperature whereas the overall water temperature fall is curtailed with increasing water to air mass ratio. The change of inlet water temperature does not affect seriously the thermal behaviour of the cooling tower. Copyright © 2005 John Wiley & Sons, Ltd.     

电站空冷系统比较及存在问题分析

空冷系统代表了未来电站冷却技术的发展方向,是"富煤少水"地区或干燥地区建设火力发电厂的最佳选择,现简要介绍了电站三种空冷系统、并对三种空冷系统进行了比较,分析了三种空冷系统运行中存在的主要问题,如机组运行防冻及渡夏等,并对此提出相应防治对策,从而有效克服空冷系统运行中出现的问题,提高机组安全经济运行水平;最后对空冷系统相关问题提出建议。     

Full-scale simulation of flow field in ammonia-based wet flue gas desulfurization double tower

With the increasingly strict environmental requirements, sintering flue gas desulfurization in double tower had been applied to improve desulfurization efficiency and reduce the “ammonia escape” and “aerosol” phenomena. In this work, the operating conditions of a sintering plant were simulated by ANSYS CFX and the flow fields without and with fluid spray of a full-scale ammonia-based wet flue gas desulfurization (WFGD) double tower were investigated. According to the results, the evaporating tower had a profound cooling effect on flue gas with spray. The gas flow distribution was non-uniform in evaporating tower, which needed further optimizations. The flow with spray was more uniform in both towers. The pressure drop mainly took place in absorption areas of desulfurization tower. The velocity of inlet region with spray was lower than that without spray in desulfurization tower. The temperature decreased along with the forward direction of gas flow due to the heat transfer with spray in desulfurization tower. The study provided useful data for further optimization in order to achieve high desulfurization efficiency.     

空冷发电有利于西部大开发

空冷发电是解决富能源而缺水的西部地区大开发的好办法。本文简要介绍各种类型的空冷发电厂,着重讨论设计造型问题,以及某些注意事项。     

发电厂直接空冷系统的可行性探讨

根据我国目前水资源的基本情况 ,阐明了建造空冷发电厂的必要性 ,多方面比较了直接空冷系统与湿冷系统的特点 ,以及由此带来的相应主设备选型上的差异。从技术经济学角度出发分析了水源对于冷却系统的重要性 ,结合具体实例分析了建设直接空冷机组的可行性 ,最后提出了一些探讨性的见解     

大型电厂空冷技术及其特点分析

我国华北、西北、东北广大地区是煤炭的主要产地,但水资源短缺已成为这些地区电力工业发展、经济建设及人民生活水平提高的制约因素之一。空冷机组是解决富煤贫水地区的电力工业发展问题的有效措施。介绍了国内外电厂空冷技术的发展状况,分析了国内外电厂广泛应用的三种空冷系统的主要特点。     

冷却塔外复杂流场的数值模拟与实验研究

对某能源中心楼顶的冷却塔组、烟囱、通风孔等散热设备及整个楼顶空间的流场与温度场进行了整体数值模拟,探讨了高温烟囱帽引起的排烟方向改变对冷却塔组进风处空气温度场及流场的影响,并进行了实验测试。结果表明,烟囱帽使排烟向下折转,导致冷却塔进风处下部位置空气温度显著升高;较低的烟囱烟气直排时,高温烟气会先抬升一段距离,然后受冷却塔进风处负压区吸引进入冷却塔内。     

喷嘴处气穴现象的数值模拟分析

Fluent软件是用于模拟和分析在复杂几何区域内的流体流动与热交换问题的专用CFD软件。将k-e模型与多相流技术Mixture模型相结合,借助Fluent软件进行多相流分析,对喷嘴处的气穴流场进行了数值模拟,并计算了模型内二维轴对称气穴流场的液态水的体积分数分布及压力分布。     

直接空冷机组冷端传热特性研究

以直接空冷机组冷端系统传热特性为研究对象,充分考虑排汽管道压损、水蒸气压差对排汽压力的影响,建立直接空冷机组冷端换热数学模型,并对影响空冷凝汽器传热的因素进行研究分析。研究结果对直接空冷机组冷端系统保持最佳运行状态,保障凝汽器的安全和经济运行具有重要的指导作用。     

计算流体力学在喷淋塔内流场模拟方面的研究进展及展望

介绍了采用计算流体力学方法对湿法脱硫喷淋塔内流场模拟的理论研究情况,对研究结果进行了分析,并对以后的研究工作进行了展望.     

Optimization of heat sink geometries for impingement air-cooling of LSI packages

This paper describes the use of our previous study's prediction procedures for calculating thermal resistance and pressure drop. The procedures are used in the optimization of heat sink geometries for impingement air-cooling of LSI packages. Two types of heat sinks are considered: ones with longitudinal fins and ones with pin fins. We optimized the heat sink geometries by evaluating 16 parameters simultaneously. The parameters included fin thickness, spacing, and height. For the longitudinal fins, the optimal fin thicknesses were found to be between 0.12 and 0.15 mm, depending on which of the four types of fans were used. For pin fins, the optimal pin diameters were between 0.39 and 0.40 mm. Under constant pumping power, the optimal thermal resistance of the longitudinal fins was about 60% that of the pin fins. For both types of heat sinks, the optimal thermal resistance for four off-the-shelf fans was only slightly (maximum about 1%) higher than the theoretical optimum for the same pumping power. When manufacturing cost performance is considered, the most economical fin thickness and diameter are about 5 to 10 times higher than the optimal values calculated without respect for manufacturing costs. These values almost correspond to the actual limits of extrusion and press heat-sink manufacturing processes. © 1999 Scripta Technica, Heat Trans Asian Res, 28(2): 138–151, 1999     

Efficiency control in a commercial counter flow wet cooling tower

This paper presents open and closed-loop analyses of a counter flow wet cooling tower. The closed-loop system analysis was based on a comparative evaluation of three control strategies. The first and second comprised a split-range control of the cooling water temperature and an index of thermal performance (efficiency), respectively, and the third strategy comprised a combination of override and split-range control in order to control two performance indexes (efficiency and effectiveness). In this case, a SISO (Single-Input Single-Output) loop for each controlled variable is considered. In each case the water loss through evaporation and the energy consumption in the cooling tower (pump and fans) were estimated in order to analyze its eco-efficiency. All the simulation tests were carried out considering the same regulatory problem and the results show a notable improvement in the tower’s performance when compared to open-loop operation, thus attesting the potential benefits of the use of an efficient control strategy for such equipment.     

空冷单元内加装导流装置后内部流场的数值模拟

针对某厂600 MW直接空冷机组空冷单元翅片管近壁面处上部空气流速低的情况,根据该厂空冷单元的实际尺寸建立了空冷单元及内部导流装置模型。利用计算流体力学软件,对加装导流装置前后空冷单元内流场进行了模拟分析,并对导流板的安装位置和尺寸进行了优化调整。数值模拟和计算分析的结果表明,加装导流装置后,空冷单元内空气流动低速区范围缩小,并且在靠近翅片管处空气速度也有一定的提高,为该厂空冷单元的设计优化提供了理论参考。     

采用辐射管加热的辊底式热处理炉数值仿真及其分析

以某公司拟建的采用辐射管加热的辊底式热处理炉为研究对象,在详细分析其传热机理的基础上,建立了炉内钢坯加热过程的二维传热数学模型.采用交替隐式格式的TDMA数值计算方法,开发出了采用辐射管加热的辊底式热处理炉钢坯加热过程二维传热模型计算机数值仿真系统,并进行了大量的数值仿真计算.所得结论为该公司即将开展的辊底式热处理炉模型优化控制奠定了坚实的理论基础.     

进气道稳流试验装置内三维流动特性的数值模拟

使用FLUENT商业软件，采用RNG κ-ε湍流模型，对稳定流动实验条件下，不同进气道角度时切向进气道一气门一气缸内的流场，在两种气门升程下进行了三维数值模拟；分析了气道一气门一气缸内气体的稳态流动特性；总结了不同气道角度、不同气门升程时气道和缸内气体流动的变化规律。随着气门升程的增加，气道角度对缸内涡流的影响增大，并且涡流和滚流相互抑制。     

Numerical model of evaporative cooling processes in a new type of cooling tower

A numerical model for studying the evaporative cooling processes that take place in a new type of cooling tower has been developed. In contrast to conventional cooling towers, this new device called Hydrosolar Roof presents lower droplet fall and uses renewable energy instead of fans to generate the air mass flow within the tower. The numerical model developed to analyse its performance is based on computational flow dynamics for the two-phase flow of humid air and water droplets. The Eulerian approach is used for the gas flow phase and the Lagrangian approach for the water droplet flow phase, with two-way coupling between both phases. Experimental results from a full-scale prototype in real conditions have been used for validation. The main results of this study show the strong influence of the average water drop size on efficiency of the system and reveal the effect of other variables like wet bulb temperature, water mass flow to air mass flow ratio and temperature gap between water inlet temperature and wet bulb temperature. Nondimensional numerical correlation of efficiency as a function of these significant parameters has been calculated.     

生物质燃气中焦油净化的试验研究

对生物质燃气中焦油的净化进行试验研究,通过在喷淋塔前设置空冷塔的焦油净化系统,并以稻秸秆为原料考察热解温度对生物质燃气中焦油在空冷塔和喷淋塔中的分配情况及化学组成的影响。结果表明,生物质燃气中80%的焦油可在空冷塔中富集,当热解温度由500℃升至750℃时,空冷塔中焦油的占比由84.26%降至80.55%,喷淋塔中焦油占比由15.74%升至19.45%;生物质焦油中超过99%、81%、84%和93%的酚类化合物、烷烯烃、含氮化合物和含氧化合物(除酚类化合物外)在空冷塔中富集,而超过76%的芳烃及其衍生物在喷淋塔中富集。     

风力发电机组塔架仿真和分析

简单介绍了风力发电机组塔架的类型和风力发电机组塔架设计的重要性。分别在某种参考风速及其风向改变90°和180°条件下,运用风力发电机组设计软件Bladed for Windows对风力发电机组塔架风载荷进行了仿真分析。最后,结合仿真结果和实际情况分析了叶片安装角、风轮锥角、风轮仰角、悬距、塔架气动阻力系数和塔架线密度等对塔架风载荷的影响。为风力发电机组的塔架设计提供了参考。     

Numerical simulation of a closed wet cooling tower with novel design

A closed wet cooling tower with novel design was proposed and numerically investigated. The studied cooling tower consists of two main parts: one heat and mass transfer unit (HMTU) and one heat transfer unit (HTU). In the HMTU, copper tubes are arranged as heat transfer tubes while plastic tubes are collocated to enlarge the mass transfer area between the spray water and the airflow. In the HTU, only copper tubes are adopted as heat transfer tubes. Heat and mass transfer process takes place among the process water, airflow and spray water in the HMTU, while in the HTU only heat transfer between the process water and the spray water is observed. A transient one dimensional distributed-parameter model was adopted to evaluate the cooling tower performance under different operating conditions. Determination of heat and mass transfer coefficients, as well as the influence of Lewis number on the cooling tower performance, was presented.