Influence of Different Vortex Generators on Heat Transfer in Direct Air-Cooled Condensers

通过数值模拟研究了矩形小翼、三角小翼、梯形小翼、柱面梯形翼、柱面三角翼和柱面矩形翼等6种涡流发生器分别安装于直接空冷凝汽器单排蛇形翅片扁管中的压降和换热性能。Re数在600~1800范围内,涡流发生器采用相同高宽比、尾高、攻角以及安装位置。结果表明：矩形小翼的换热及压降增大最多,Re=1729时,相比平直翅片分别增加了14.27%和18.32%。Re=1 729时,柱面梯形翼的压力损失比矩形小翼少4.7%,换热低1.5%。当以（j/j0）/（f/f0）1/3作为综合换热性能评价标准时,柱面梯形翼的综合换热性能最好。另外,考察了柱面梯形翼倾角的影响（0°、6°、12°、20°、24°和26°）,相同工况下,倾角为12°的柱面梯形翼换热最好（较平直翅片增强4.29%~14.1%）、压降最小（增大7.5%~12.8%）且综合换热性能最好。柱面梯形翼因其迎流面积与斜边长度的匹配以及流线型柱面,具有良好的强化传热效果以及较小的压降。

Air interaction around outdoor air-cooled condensers

In order to increase cooling or heating efficiency,a porous computational fluid dynamics（CFD）model is employed to predict the thermo-fluid status and optimize the placement of outdoor units.A full scale model is established to validate the accuracy of CFD simulation in terms of velocity and temperature distributions.The comparison between the measurement and the simulation shows a good agreement.By evaluating the condensers＇ sucked air temperature with CFD for three units installed in a row,it is found that the minimum separation distance among neighboring units is 0.2 m;a vertical wall should be apart from the unit line by at least 0.8 m;and large different operating pressures among units do not impact the flow rate and the heat transfer of the other units meaningfully.

Influence of thermal flow field of cooling tower on recirculation ratio of a direct air-cooled system for a power plant

In order to get thermal flow field of direct air-cooled system,the hot water was supplied to the model of direct air-cooled condenser(ACC). The particle image velocimetery (PIV) experiments were carried out to get thermal flow field of a ACC under different conditions in low velocity wind tunnel,at the same time,the recirculation ratio at cooling tower was measured,so the relationship between flow field characteristics and recirculation ratio of cooling tower can be discussed. From the results we can see that the flow field configuration around cooling tower has great effects on average recirculation ratio under cooling tower. The eddy formed around cooling tower is a key reason that recirculation produces. The eddy intensity relates to velocity magnitude and direction angle,and the configuration of eddy lies on the geometry size of cooling tower. So changing the flow field configuration around cooling tower reasonably can decrease recirculation ratio under cooling tower,and heat dispel effect of ACC can also be improved.

Transient Heat Transfer Study of Direct Contact Condensation of Steam in Spray Cooling Water

We conducted a transient experimental investigation of steam–water direct contact condensation in the absence of noncondensible gas in a laboratory-scale column with the inner diameter of 325 mm and the height of 1045 mm. We applied a new analysis method for the steam state equation to analyze the molar quantity change in steam over the course of the experiment and determined the transient steam variation. We also investigated the influence of flow rates and temperatures ofcooling water on the efficiency ofsteam condensation. Our experimental results show that appropriate increasing of the cooling water flow rate can significantly accelerate the steam condensation. We achieved a rapid increase in the total volumetric heat transfer coefficient by increasing the flow rate of cooling water, which indicated a higher thermal convection between the steam and the cooling water with higher flow rates. We found that the temperature ofcooling water did not play an important role on steam condensation. This method was confirmed to be effective for rapid recovering ofsteam.

Thermodynamic Simulation of CCP in Air-Cooled Heat Pump Unit with HFCs and CO₂Trans-Critical

The exergy analysis and finite time thermodynamic methods had been employed to analyze the compound condensation process (CCP). It was based on the air-cooling heat pump unit. The cooling capacity of the chiller unit is about 1 kW, and the work refrigerant is R22/R407C/R410A/CO2. The MATLAB/SIMULINK software was employed to build the simulation model. The thermodynamic simulation model is significant for the optimization of parameters of the unit, such as condensation and evaporation temperature and mass flow of the sanitary hot water and size of hot water storage tank. The COP of the CCP of R410A system is about 3% - 5% higher than the CCP of the R22 system, while CCP of the R407C system is a little lower than the CCP of R22 system. And the CCP of CO2 trans-critical system has advantage in the hot supply mode. The simulation method provided a theoretical reference for developing the production of CCP with substitute refrigerant R407C/R410A/CO2.

The Experimental Investigation of Recirculation of Air-Cooled System for a Large Power Plant

The paper introduces thermal buoyancy effects to experimental investigation of wind tunnel simulation on direct air-cooled condenser for a large power plant. In order to get thermal flow field of air-cooled tower, PIV experiments are carried out and recirculation ratio of each condition is calculated. Results show that the thermal flow field of the cooling tower has great influence on the recirculation under the cooling tower. Ameliorating the thermal flow field of the cooling tower can reduce the recirculation under the cooling tower and improve the efficiency of air-cooled condenser also.

Research and Demonstration of Direct Air-Cooling System for 600-MW Fossil-Fired Power Plants

Given the distribution feature of resources such as coal and water, the requirements for the development of Chinese power industry, and the fact of monopoly by foreign companies, it is very necessary and significant to independently research and develop air-cooling technologies. Through experimental research, simulative calculation, process and equipment development, field tests and a demonstration project, the design and operation technologies for air-cooling system are grasped and relevant key equipment is developed. The results of the demonstration project show that the technical indicators for the air-cooling system have met or exceeded the design requirements. Part of the research results have been incorporated into the relevant national design standards. The technologies developed have been applied to more than 23 sets of thermal power units of or above 600 MW in China.

基于网络的DIRECT X接口编程实现多媒体图像解压缩传输

本文介绍了图像压缩技术原理及JPEG、MPEG图像压缩格式的解压缩实现,利用微软的DIRECT X接口编程实现网上进行多媒体图像数据的传输,并且本系统可进一步扩展为网上的视频点播(VOD)。

Measures against the adverse impact of natural wind on air-cooled condensers in power plant

The natural wind plays disadvantageous roles in the operation of air-cooled steam condensers in power plant.It is of use to take various measures against the adverse effect of wind for the performance improvement of air-cooled condensers.Based on representative 2×600 MW direct air-cooled power plant,three ways that can arrange and optimize the flow field of cooling air thus enhance the heat transfer of air-cooled condensers were proposed.The physical and mathematical models of air-cooled condensers with various flow leading measures were presented and the flow and temperature fields of cooling air were obtained by CFD simulation.The back pressures of turbine were calculated for different measures on the basis of the heat transfer model of air-cooled condensers.The results show that the performance of air-cooled condensers is improved thus the back pressure of turbine is lowered to some extent by taking measures against the adverse impact of natural wind.

Enhancement of freshwater production of the seawater greenhouse condenser

Seawater greenhouse(SWGH)is a technology established to overcome issues related to open field cultivation in arid areas,such as the high ambient temperature and the shortage of freshwater.It adopts the humidification-dehumidification concept where evaporated moisture from a saline water source is condensed to produce freshwater within the greenhouse body.Various condenser designs are adopted to increase freshwater production in order to meet the irrigation demand.The aim of this study was to experimentally investigate the practicality of using the packed-type direct contact condenser in the SWGH to produce more freshwater at low costs,simple design and high efficiency,and to explore the impact of the manipulating six operational variables(inlet air temperature of the humidifier,air mass flowrate of the humidifier,inlet water temperature of the humidifier,water mass flowrate of the humidifier,inlet water temperature of the dehumidifier and water mass flowrate of the dehumidifier)on freshwater condensation rate.For this purpose,a direct contact condenser was designed and manufactured.Sixty-four full factorial experiments were conducted to study the effect of the six operational variables.Each variable was operated at two levels(high and low flowrate),and each experiment lasted for 10 min and followed by a 30-min waiting time.Results showed that freshwater production varied between 0.257 and 2.590 L for every 10 min.When using Minitab statistical software to investigate the significant variables that contributed to the maximum freshwater production,it was found that the inlet air temperature of the humidifier had the greatest influence,followed by the inlet water temperature of the humidifier;the former had a negative impact while the latter had a positive impact on freshwater production.The response optimizer tool revealed that the optimal combination of variables contributed to maximize freshwater production when all variables were in the high mode and the inlet air temperature of the humidifier was in the low mode.The comparison between the old plastic condenser and the new proposed direct contact condenser showed that the latter can produce 75.9 times more freshwater at the same condenser volume.

Numerical investigation on the cluster effect of an array of axial flow fans for air-cooled condensers in a power plant

The aerodynamic behavior of tens of axial flow fans incorporated with air-cooled condensers in a power plant is different from that of an individual fan.Investigation of the aerodynamic characteristics of axial flow fan array benefits its design optimization and running regulation.Based on a representative 2600 MW direct-dry cooling power plant,the flow rate of each fan and the overall flow rate of the fan array are obtained in the absence of ambient wind and at various wind speeds and directions,using CFD simulation.The cluster factor of each fan and the average cluster factor of the fan array are calculated and analyzed.Results show that the cluster factors are different from each other and that the cluster effect with ambient wind is significantly different from the cluster effect with no wind.The fan at the periphery of the array or upwind of the ambient wind generally has a small cluster factor.The average cluster factor of the array decreases with the increasing wind speeds and also varies widely with wind direction.The cluster effect of the axial flow fan array can be applied to optimize the design and operation of air-cooled condensers in a power plant.

An Influencing Factor - Water-Filter Ratio on Heat Resistance of Condensate Polishing Filter Material in Water

In air-cooled condenser, high temperature condensing water m summer which approaching and exceed 60＊ C, which may result in filter materials degradation and release impurities. This paper discusses an influencing factor, water-filter ratio （soaking solution and filter quality ratio）, on leachable dissolution rate and filter material degradation rate m high temperature water. The UV absorption at 254nm （A254） and the exchange capacity ware measured after heat test as composite indicators. In addition, the Wends of A254 variation with heating time were measured in different water-filter ratio. The stability is probably due to the effect of water-filter ratio. This has been further borne out that, water-filter ratio increases, leachable concentration decreases exponentially and tends to a fLxed value.

Near-zone Direct and Indirect Topographic Effects Based on the Rectangular Prism and Surface Element

Helmert’s second method of condensation is an effective method for terrain reduction in the geoid and quasi-geoid determinations. Condensing the masses outside the geoid to a surface layer on the geoid produces several forms of topographic effects: direct effect on gravity, secondary indirect effect on gravity and indirect effects on the (quasi-) geoid, respectively. To strike a balance between computation accuracy and numerical efficiency, the global integration region of topographic effects is usually divided into near zone and far zone. We focus on the computation of near-zone topographic effects, which are functions of actual topographic masses and condensed masses. Since there have already been mature formulas for gravitational attraction and potential of actual topographic masses using rectangular prism model, we put forward surface element model for condensed masses. Afterwards, the formulas for near-zone direct and indirect effects are obtained easily by combining the rectangular prism model and surface element model. To overcome the planar approximation errors involved with the new formulas for near-zone topographic effects, the Earth’s curvature can be taken into account. It is recommended to apply the formulas based on the rectangular prism and surface element considering the Earth’s curvature to calculate near-zone topographic effects for high-accuracy demand to determine geoid and quasi-geoid.

蒸汽射流直接接触凝结的界面及声压特性

蒸汽射流在液体中的直接接触凝结引发的剧烈界面振荡及声压振荡,可能导致工业管道系统振动甚至失效,采用高速摄像机与高频水听器,捕捉了射流的界面演化行为及其诱导的声压。研究了3种典型凝结流型下射流界面的径向、轴向振荡与声压振荡特性,并阐明声压振荡产生机理。研究发现:声压波动的概率密度函数在间歇流型下呈左偏单峰分布,在界面振荡流型下呈双峰分布,而在稳定流型下呈对称单峰分布;随蒸汽质量流速升高,无量纲径向、轴向界面振荡强度及声压振荡强度整体呈下降趋势,表现出极强的相关性。建立了基于声压参数的射流喷射长度预测模型,预测值与实验值的误差在±1%内。概率密度及相关性分析结果表明,蒸汽射流凝结的声压振荡是由其界面振荡引起的。

厂区布置对钢塔自然通风空冷凝汽器性能的影响

利用计算传热学(NHT)软件FLUENT,在自然通风状态下,对2×350MW机组钢结构外覆铝板冷却塔及直接空冷凝汽器(DACC)的流动和换热性能进行了数值模拟、分析和研究。确定了考核工况,不同环境风向下,周边建筑物对DACC和钢塔性能的影响。结果表明,两机一塔水平矩形布置方式下,平行于A列的来风对钢塔通风和DACC换热有负面影响。不考虑风向频率时,各风向下周边建筑物对DACC总体换热影响约为2.4%。在电厂总平面布置时,应尽量使厂区主导风向避开不利风向,汽机房空冷塔间距还需综合其它因素确定。

励磁绕组与阻尼绕组耦合效应对大型同步调相机转子暂态电流特性的影响

针对大型同步调相机暂态分析时模型精度较低的问题,提出一种考虑励磁绕组与阻尼绕组耦合效应的同步调相机暂态分析精确模型。首先,通过引入特征电抗建立同步调相机考虑励磁绕组与阻尼绕组耦合效应的暂态分析精确模型,并基于励磁电流拟合对特征电抗进行求解。然后,通过三相短路与BC相间短路故障仿真,对比同步调相机传统模型与精确模型的转子暂态电流特性。最后,建立同步调相机机-网暂态仿真模型,分析系统送端交流母线电压波动时同步调相机精确模型的暂态运行特性。研究表明,考虑励磁绕组与阻尼绕组耦合效应时同步调相机转子暂态电流特性的精度更高。三相短路与BC相间短路故障后3个周期内,同步调相机暂态分析精确模型励磁电流峰值平均值的精度分别提高了27.27%和61.53%。

蒸汽直接接触冷凝换热特性实验分析

[目的]为支撑小型模块式反应堆安全壳抑压装置设计与优化,开展蒸汽直接接触冷凝换热特性分析。[方法]利用抑压模拟实验装置对蒸汽直接接触冷凝换热现象进行热工及可视化实验,分析不凝性气体份额、蒸汽质量流速、冷却水过冷度对冷凝换热特性的影响。[结果]结果表明,增加不凝性气体份额会减弱蒸汽冷凝换热;蒸汽质量流速、冷却水过冷度会从多方面影响蒸汽冷凝换热。[结论]所提出的蒸汽直接接触冷凝换热模型预测值与实验值的偏差在±20%以内,能够较为准确地描述蒸汽直接接触冷凝换热的物理过程。

蒸汽射流直接接触凝结诱导振动特性研究

蒸汽射流在管内过冷水流中的直接接触凝结会诱导严重的管道振动。采用高速摄像机与加速度传感器,捕捉了蒸汽射流气羽演化及其诱导的管道振动。通过实验定量描述了考虑气羽形貌的气羽灰度质心振荡与管道振动特性。发现界面振荡流型下气羽灰度质心的振荡幅度最大,间歇振荡流型下次之,稳定凝结流型下最小。随着蒸汽质量流速升高,质心振荡及管道振动强度都向着趋于稳定的方向发展,表现出极强相关性。在此基础上绘制了管道振动强度随蒸汽质量流速及过冷水温度的分布图,振动强度随着过冷水温度的升高而升高。相关性分析表明气羽灰度质心的轴向振荡是沿蒸汽喷射方向的管道振动强度的主导因素。

蒸汽-水膜直接接触冷凝数值模拟研究

蒸汽-水膜直接接触冷凝界面能质传递机理是混合式冷凝器优化设计的基础,以蒸汽-水膜直接接触冷凝为研究对象,基于流体体积(VOF)方法构建了界面相变冷凝能质传递模型,分析了蒸汽质量流量(0.002~0.010 kg/s)、冷却水质量流量(0.30~0.83 kg/s)及流动方向对蒸汽-水膜直接接触冷凝换热的影响。结果表明:冷凝传热系数随蒸汽和冷却水质量流量的增大而增大,相较而言蒸汽质量流量对冷凝换热影响较弱;相比于顺流流动,蒸汽-水膜错流流动时换热效果较好,逆流流动由于相间作用力增加,水膜形状不规则,增大了水膜破碎风险。