湿式冷却塔加装挡风板的数值研究

针对我国北方冬季湿式冷却塔运行时填料下表面、进风口以及基环面等处容易结冰的问题,在冷却塔的进风口处加装挡风板,建立了冷却塔内的传热传质模型,并采用CFD软件模拟和分析了在不同横向风速和不同环境温度下加装不同层数的挡风板时冷却塔的热力特性.结果表明：在风速小于4m/s时,塔内的迎风面空气温度较低,极易结冰;随着风速的增大,低温区逐渐向背风侧转移;当风速为8m/s,环境温度分别为-10℃、-17℃、-23℃时,分别在冷却塔内加装1层、3层和5层挡风板,能大大改善塔内温度场,有效防止塔内结冰.     

自然通风湿式冷却塔防冻数值研究

由于我国北方地区冬季气温较低,冷却塔普遍存在结冰问题,必须采取一定的防冻措施。通过FLUENT软件模拟分析得出进塔水温对塔内不同特征面水温的影响规律,并进一步模拟加装不同层数挡风板后冷却塔内流场的变化。计算结果表明:①当运行工况其它条件不变时,随着进塔水温的升高,塔内不同特征面最低水温升高;②加装一定层数挡风板能使填料下面空气温度场和进风口上沿面空气速度场分布逐渐趋于均匀,有利于防止塔内结冰;③选取进塔水温分别为17.80℃、21.95℃、26.77℃、30.04℃时,分别加装4、3、2、1层挡风板可有效防止塔内结冰。     

1000MW机组自然通风冷却塔降低出塔水温方法研究

以冷却塔相关传热传质理论为基础,应用Fluent数值模拟软件,建立1000MW机组自然通风湿式冷却塔三维数值模拟计算模型。针对冷却塔中心区域换热效率低的问题,提出了在雨区加装导风通道的方案,通过导风通道将塔外冷空气直接导入塔内中心区域进行换热。并对不同导风通道的结构尺寸及个数进行模拟,结果表明:加装最优型导风通道后,冷却塔出塔水温可降低0.66℃。     

湿式冷却塔进风口导流板参数优化及安装实践

冷却塔作为火电厂冷端系统中重要的冷却设备之一,其冷却性能直接影响电厂运行的安全稳定性和经济性,而环境侧风在很大程度上影响冷却塔的冷却性能,可以采取在冷却塔进风口处安装导流板的措施予以改善。针对某600MW机组的自然通风湿式冷却塔,采用CFD软件Fluent,对进风口处安装导流板的冷却塔进行数值模拟。模拟结果表明:导叶板能够增加塔内中心区域的空气上升速度和扰动,加强传热,改善冷却塔冷却性能。导叶板相对最佳的安装角度为20°,导叶板安装数量为80块,出塔水温可以降低1.2K。根据模拟结果对某冷却塔进行改造,通过对比同一塔技改前后出塔水温,发现出塔水温可降低1.6K以上,验证了模拟计算的正确性和该项技术的实用性。     

间接空冷塔内部流场的数值模拟及优化设计

基于RNG k-ε湍流模型和多孔介质模型,对SCAL型自然通风冷却塔的内部流场进行了三维数值模拟,并分析了风速和温度对空冷塔通风量的影响规律。计算结果表明,风速和温度分别为6m/s和42℃时为最不利环境工况。针对不利工况提出了在空冷塔内加装喷嘴组和外接气源的优化措施,并进行了加装装置前后塔内流场特性的数值模拟。结果表明,加装喷气装置后塔内流场明显改善,且通风量增大;综合分析优化结果、运行成本以及可操作性,在进风口截面安装48个喷嘴且流量为0.005kg/s为最理想方案,塔内通风量增加8.259%。该方案对解决电厂间接空冷机组夏季出力不足等问题具有重要的理论意义和工程价值。     

1000MW机组高位收水冷却塔热力性能试验研究

为获得高位收水冷却塔的热力性能,对某1 000MW机组配用的淋水面积为12 075m2的高位收水冷却塔的热力性能进行了试验研究,得到了高位收水冷却塔的热力性能方程式,给出了高位收水冷却塔塔内实测风温分布.以该冷却塔为例,对比分析了相同工艺参数条件下高位收水冷却塔和常规冷却塔出塔水温的差异.结果表明:高位收水冷却塔塔内实测风温在3台循环水泵并联运行工况时比2台循环水泵并联运行工况更均匀;高位收水冷却塔塔内填料处断面风速比常规冷却塔更大;在夏季时同等条件下采用高位收水冷却塔时出塔水温相比常规冷却塔可降低0.8K左右.     

“逆流塔进风口填料切角均风”技术在冷却塔上的应用

通过对某企业供排水车间冷却塔应用进风口填料斜角技术实际项目进行的监测、研究和效益分析,得出冷却塔应用进风口填料斜角技术可达到节能效果的结论。     

基坑式成组冷却塔的选型布置与热流模拟研究

对于基坑式环境，在环境风与冷却塔风机抽力的作用下，冷却塔出风口排出的热空气易被冷却塔进风口再次吸入塔内，形成热风回流，导致冷却塔实际冷效低于设计值。以某会议会展工程为例，通过CFD热流模拟，在基坑式环境下对冷却塔进行合理选型，根据气流组织模拟确定冷却塔的布置位置、方向以及基础高度，保证冷却塔使用能效优良。     

核电机组巨型冷却塔进风口高度优化的三维数值研究

针对目前核电机组采用的巨型冷却塔无实际工程应用的现状,采用Fluent软件建立其三维热力计算模型,研究侧风下巨型冷却塔在不同进风口高度下的冷却效果,分析冷却数等热力性能参数,考察了侧风对塔内流场对称性的影响。以提高供电量为最终目标,综合考虑侧风的影响,确定巨型塔最优的进风口高度值。     

环境侧风对300MW火电机组冷却塔影响的数值模拟

以300MW机组双曲线自然通风冷却塔为研究对象,采用Fluent软件对冷却塔进行了三维数值模拟,分析了变工况下环境侧风对冷却塔冷却性能的影响、环境侧风对冷却塔进风口速度场的影响。研究发现:随着侧风风速的增加,冷却温差先减小后增大,出塔水温先增大后减小;并且,环境侧风的存在会扰乱冷却塔进风口流场,其临界风速值为6m/s。     

An exergy analysis on the performance of a counterflow wet cooling tower

Cooling towers are used to extract waste heat from water to atmospheric air. An energy analysis is usually used to investigate the performance characteristics of cooling tower. However, the energy concept alone is insufficient to describe some important viewpoints on energy utilization. In this study, an exergy analysis is used to indicate exergy and exergy destruction of water and air flowing through the cooling tower. Mathematical model based on heat and mass transfer principle is developed to find the properties of water and air, which will be further used in exergy analysis. The model is validated against experimental data. It is noted from the results that the amount of exergy supplied by water is larger than that absorbed by air, because the system produces entropy. To depict the utilizable exergy between water and air, exergy of each working fluid along the tower are presented. The results show that water exergy decreases continuously from top to bottom. On the other hand, air exergy is expressed in terms of convective and evaporative heat transfer. Exergy of air via convective heat transfer initially loses at inlet and slightly recovers along the flow before leaving the tower. However, exergy of air via evaporative heat transfer is generally high and able to consume exergy supplied by water. Exergy destruction is defined as the difference between water exergy change and air exergy change. It reveals that the cooling processes due to thermodynamics irreversibility perform poorly at bottom and gradually improve along the height of the tower. The results show that the lowest exergy destruction is located at the top of the tower.     

Study on the heat transfer characteristics of an evaporative cooling tower

In the present study, both experimental and theoretical results of the heat transfer characteristics of the cooling tower are investigated. A column packing unit is fabricated from the laminated plastic plates consists of eight layers. Air and water are used as working fluids and the test runs are done at the air and water mass flow rates ranging between 0.01 and 0.07 kg/s, and between 0.04 and 0.08 kg/s, respectively. The inlet air and inlet water temperatures are 23 °C, and between 30 and 40 °C, respectively. A mathematical model based on the conservation equations of mass and energy is developed and solved by an iterative method to determine the heat transfer characteristics of the cooling tower. There is reasonable agreement from the comparison between the measured data and predicted results.     

Extremum seeking control for efficient operation of hybrid ground source heat pump system

The Hybrid Ground Source Heat Pump (GSHP) systems combine the renewable geothermal energy and cooling tower for rejecting the cooling load, which is often adopted for high cooling demand. Model based control can be limited due to variations in ambient conditions, ground-loop heat exchanger (GHE) and equipment characteristics, cost and reliability of sensors. A self-optimizing control scheme is proposed for efficient operation of the hybrid GSHP based on Extremum Seeking Control (ESC), with feedback of the total power consumption and the control inputs of the relative flow rate of cooling tower and the water pump speed. The cooling capacity of the heat pump regulates the evaporator leaving water at 7 °C. A Modelica based dynamic simulation model is developed for a Hybrid GSHP system, with the vertical GHE model adopted from Modelica Buildings Library. The transient heat transfer is implemented with a finite volume method inside and outside the borehole. The proposed ESC scheme is evaluated under the scenarios of fixed cooling load, ramp change in the evaporator inlet water temperature, diurnal sinusoidal cycle of air wet-bulb temperature, and realistic ambient and cooling load condition. Simulation results show the proposed ESC strategy effectively achieves nearly optimal efficiency without the need for plant model.     

超大型湿冷塔进风流场及导流装置数模研究及应用

基于Fluent软件,采用标准k-ε湍流模型进行应力封闭,对某工程塔内传热传质过程进行三维数值计算。计算分析了塔内外空气的速度场、温度场,建立了相关方程及气水两相间传热传质理论模型。结合工程实际情况,对冷却塔进风流场进行深入分析:1)导风板的存在降低了塔侧空气绕流流速,增大了冷却塔进风口流场的对称性,使塔内空气动力场的均匀程度增加;导风板安装高度和长度对冷却塔进风流场产生较大影响,以高11 m、长8 m导风板对# 1、# 2冷却塔性能的改善作用最大;2)导风板安装角度和块数对冷却塔进风流场产生一定影响,在导风板安装角度由0°至20°变化、在导风板安装块数由60块至90块变化时,两塔冷却性能变化影响较小。     

基于焓差理论的带填料逆流闭塔热力性能分析

为了分析不同风量和喷淋水量对填料逆流闭式冷却塔热力性能的影响,建立和验证了带填料逆流闭式冷却塔热质交换的数学模型,基于焓差理论对模型计算的结果进行分析。结果表明：加入填料相当于对盘管区进口的喷淋水进行预冷,降低了喷淋水的平均温度,使带填料闭式冷却塔的冷却性能优于纯盘管闭式冷却塔;风量的增加可以提高带填料逆流闭式冷却塔和纯盘管逆流闭式冷却塔的热力性能,两种塔的冷却性能随风量增加的提升速率相同;喷淋水量的增加对纯盘管逆流闭式冷却塔的热力性能的影响较小,却可以较大幅度提高带填料逆流闭式冷却塔的热力性能。     

A comprehensive approach to cooling tower design

In this paper, a mathematical model for a counterflow wet cooling tower is derived, which is based on one-dimensional heat and mass balance equations using the measured heat transfer coefficient. The balance equations are solved numerically to predict the temperature change of air and water, as well as the humidity as a function of the cooling tower high. Experimental measurements on two pilot-scale cooling towers were carried out in order to analyze the performance of different cooling tower filling materials. Also, the performance of other cooling tower elements, such as droplet separators and water spray nozzles, was investigated in the pilot experiments. The flow distribution, i.e. the velocity field, upstream to the filling material was predicted using the three-dimensional version of the computational fluid dynamics (CFD) code Fluent/uns, version 4.2. The calculated flow fields are presented for different distances between the inlet of the air and the filling material. In addition, the two-dimensional version of the CFD code Fluent/uns, version 4.2, was applied to predict the external airflow around the cooling tower and the backflow in different weather conditions in summer and winter. The research project was carried out in connection to an industrial cooling tower installation.     

Parameter estimation for packed cooling tower operation using a heat input-response technique

A method is proposed for predicting the variations of air and water temperatures and of air humidity in a packed bed counterflow type of cooling tower subjected to a thermal disturbance. Heat input-response measurements are carried out by imposing thermal disturbances on inlet water and inlet air. The air-film and water-film heat transfer coefficients are estimated by fitting in the time domain the measured output temperature/humidity variations to those predicted.     

AP1000核电机组巨型冷却塔型体优化数值计算

根据气水两相间热质传递原理,利用Fluent数值计算软件建立了APl000核电机组用20000m。淋水面积巨型冷却塔的三维计算模型,对双曲线塔筒的母线方程中的特征值及喉部半径的最优取值进行了计算验证,综合分析了特征值及喉部半径对塔内流场、进塔风量、蒸发水量和平均出塔水温的影响,得到了210m高巨型冷却塔的最优型体结构参数．计算结果表明：喉部半径与塔底半径的比值r0／r2=0．6--0．7、塔筒母线方程中的曲率特征值a=0．17～0．18时,冷却塔运行最优．     

Refinement of the Transfer Characteristic Correlation of Wet-Cooling Tower Fills

Transfer characteristic correlations given in the literature for wet-cooling tower fills are generally only a function of the air and water mass flow rates. This is a gross simplification of a very complex heat and mass transfer (evaporative cooling) process. In addition to the effects of the air and water mass flow rates, effects of the inlet water temperature, air drybulb temperature, wetbulb temperature, and fill height on the transfer characteristic, or Merkel number, are investigated in the present study. The accuracy of two different empirical equations is also evaluated. It is found that the transfer characteristic correlations for wet-cooling tower fills are functions of the inlet water temperature and fill height but not of the air drybulb and wetbulb temperatures.