冷却塔出塔水温的迭代计算方法

基于麦克尔焓差法原理,对循环水泵运行方式变化前后的进塔风速进行了估算,给出了冷却塔出塔水温的迭代计算方法.用数学方法对冷却塔特性数和冷却数随出塔水温及进塔风速的变化规律进行了分析,并对计算过程中非线性方程的多解选择问题及迭代退出条件进行了研究,最终确定出了符合物理意义的真实解.由此确定的循环水泵各运行方式下的出塔水温可直接用于循环水泵最优运行方式的确定,对现场中冷端系统的优化具有一定的现实意义.     

Optimization of Thermal-Flow Processes in a System of Conjugate Cooling Towers

Abstract

The paper presents the thermal-flow study of a closed cooling system with special emphasis on the working parameters of natural draft wet cooling towers. The authors analyze the possibility of the improvement of the overall cooling efficiency of a closed cooling system consisting of several cooling towers by the proper redistribution of cooling water between individual units. The problem of the optimal redistribution of circulating water between cooling towers is formulated as a mathematical issue involving finding the extrema of the multivariate function with constraints fixing the total mass flow rate of cooling water circulated in the hydraulic installation and the ranges of the hydraulic loads of individual cooling towers. The optimization process requires information about the individual characteristics of each cooling tower, which is achieved by experimental measurements done on real objects. The research done inside the cooling towers enables the identification of the heat and mass transfer processes across its radius. Next, these characteristics are used to calculate the optimal cooling water flow rates to the cooling towers, giving the highest possible mean cooling water temperature drop in the system.     

Prediction of Evaporation Losses in Wet Cooling Towers

The accurate prediction of all aspects of cooling tower behavior is very important. Accurately predicting evaporation losses is significant because water in cooling towers is cooled primarily through the evaporation of a portion of the circulating water, which causes the concentration of dissolved solids and other impurities to increase. An empirical relation is developed on the basis of ASHRAE's rule of thumb that is simple and accurate with a wide range of applicability. The predicted values are in good agreement with experimental data as well as predictions made by an accurate mathematical model.     

A Novel Approach for Energy Efficiency Prediction of Various Natural Draft Wet Cooling Towers Using ANN

Cooling tower is crucial equipment in the cool-end system of power plant and the natural draft counter-flow wet cooling tower(NDWCT) gets wide application. The artificial neural network(ANN) technique is becoming an effective method for the thermal performance investigation of cooling towers. However, the neural network research on the energy efficiency performance of NDWCTs is not sufficient. In this paper, a novel approach was proposed to predict energy efficiency of various NDWCTs by using Back Propagation(BP) neural network: Firstly, based on 638 sets of field test data within 36 diverse NDWCTs in power plant, a three-layer BP neural network model with structure of 8-14-2 was developed. Then the cooling number and evaporation loss of water of different NDWCTs were predicted adopting the BP model. The results show that the established BP neural network has preferable prediction accuracy for the heat and mass transfer performance of NDWCT with various scales. The predicted cooling number and evaporative loss proportion of the testing cooling towers are in good agreement with experimental values with the mean relative error in the range of 2.11%–4.45% and 1.04%–4.52%, respectively. Furthermore, the energy efficiency of different NDWCTs can also be predicted by the proposed BP model with consideration of evaporation loss of water in cooling tower. At last, a novel method for energy efficiency prediction of various NDWCTs using the developed ANN model was proposed. The energy efficiency index(EEI) of different NDWCTs can be achieved readily without measuring the temperature as well as velocity of the outlet air.     

Computational Analysis of Closed Wet Cooling Towers

The thermal and hydraulic performance of plain and oval tubes closed wet cooling tower (CWCT) are investigated numerically. Computational fluid dynamics (CFD), ANSYS Fluent 12.1, is implemented for the numerical solution. Species transport without reactions is adopted to simulate the mass transfer from the air-deluge water interface to the air. Different turbulence models and near-wall treatments are used to assess which model fits the data better. The mass transfer Colburn factor j _m , and friction factor f are presented and compared with experimental data. The proposed CFD model is also applied to predict the mass transfer coefficient of another CWCT and compares well with the experimental data.     

冷却塔和管廊保温技改工程

1概述上海通用汽车有限公司金桥厂区北厂的冷热源站房98年投入使用,提供全厂空调系统用水。共设置15台直燃式双效溴化锂吸收式机组,总计供冷量达52．74MW,燃料为天然气。随着车间产量的增加,生产线扩建,而空调系统设备长期运行,性能衰减,尤其在夏天高温季节,难以满足空调负荷不断增加的需求。公司领导果断决策,启动了最合理改进方案的制定工作,决定投资500万元彻底解决空调系统问题,提高经济能效,同时要考虑环保噪声控制。     

大型电厂冷却塔塔群的数值研究

基于CFD软件和自然通风湿式冷却塔相关理论,建立精确的计算模型,对大型冷却塔的运行工况进行模拟计算。针对塔群中大型冷却塔之间的相互影响,对常见的一字型和正方形排列的四座冷却塔进行模拟计算。对冷却塔附近空气场的压力、速度等进行分析。为以后的工程设计及改进工作提供理论参考。     

Energy and Mass Transfer Phenomena in Natural Draft Cooling Towers

In this paper, the development of natural draft cooling towers diagnostics is presented. Diagnostic method is based on measurements of velocity and temperature fields of the airflow in the entire surface area of cooling tower and the raised phenomenological model of heat and mass transfer in a selected reference vertical segment of cooling tower. Velocity and temperature fields of the airflow were measured with the aid of a remote control mobile robot unit that was developed to enable measurements in an arbitrary measurement point above the spray zones over the entire cooling tower area. Topological structures of the humid air velocity profiles and temperature profiles above the spray zones were obtained at constant integral parameters of a power plant. Measurement results of temperature and mass flow characteristics of the air and water flows in a selected reference vertical segment of cooling tower are presented in the form of phenomenological dependence. Phenomenological dependence links local cooling tower efficiency, geometrical characteristics of spray elements, and air and water flow rates. In the concluding part, both methods are applied together on a selected segment of cooling tower, and local and integral cooling tower efficiency can be determined.     

Reduction in Performance Due to Recirculation in Mechanical Draft Cooling Towers

Abstract

The influence of recirculating warm plume air on the performance of mechanical-draft cooling towers is investigated analytically, numerically, and experimentally. It is shown that the amount of recirculation that occurs is a function of the flow and the thermal and geometric characteristics of the tower. The presence of a wind wall tends to reduce the amount of recirculation. An equation is presented with which the performance effectiveness due to recirculation can be evaluated approximately for a mechanical-draft cooling tower.     

Multi-Objective Optimization Analysis of Structural Design for Large Cooling Towers

ABSTRACT

Equivalent static wind loads (ESWLs) on cooling towers derived even by the refined multiple-mode dynamic algorithm such as the complete quadratic combination theory usually shows quite different types for various design targets. So, it is evitable to bring complex and burdensome calculation for structural design. To this problem, the improved multi-objectives ESWLs method was proposed by combining the wind vibration characteristics of large cooling towers itself. Through several numerical examples, the multi-objective ESWLs distribution characteristics were discussed, and its rationality of application in the cooling towers was also validated.     

椭圆形突片气膜冷却效率的试验研究

为研究突片对气膜冷却效率的影响,设计了3种不同堵塞比的椭圆形突片,采用红外摄像仪对不同形状突片冷却壁面的温度场进行了测试,并分析了气膜冷却效率随吹风比、堵塞比的变化规律.结果表明:突片的存在大大提高了气膜冷却效果;冷却效率随吹风比的增加而增大;且当x/D<7时,存在一个最佳吹风比值;冷却效率随堵塞比的增加而增加;椭圆形突片的气膜冷却效率要高于三角形突片的气膜冷却效率.     

水轮机节能技术在石化行业循环水冷却塔中的应用

水轮机利用循环水泵的富余扬程带动风机运转,以取代风机电机,实现节能的目的。以高效反击混流式水轮机在青岛石化循环水冷却塔中的应用为例,通过监测单开水轮机风机或电动风机时循环水的温降程度,来对比两种风机的运行效果,并在维持系统管网压力、流量不变的条件下,监测水轮机风机正常运行、转速减半、停运至系统稳定,以及重开风机系统、恢复稳定状态下的运行数据,测试水轮机风机运行对循环水系统的影响,从而验证水轮机节能技术的应用效果及经济效益。结果证明,循环水系统存在富余能量,水轮机利用该富裕能量带动风机运转,不增加循环水系统新的能耗;且水轮机风机降温效果与电动风机相当,可替代电机风机运行,满足精细化操作需要。采用水轮机运转风机,可优化循环水系统配置,减少维护保养费用,经济效益较高,具有较好的推广价值。     

快速喷雾结冰技术在循环冷却水塔中的应用

针对我国北方地区发电厂中冷却水塔冬季防冻问题,提出了循环冷却水塔快速喷雾结冰技术．通过与悬挂挡风板冷却塔的对比,论证了快速啧雾结冰技术在优化调节循环水温度及循环冷却水塔防寒防冻方面的明显优势．结果表明：采用快速喷雾结冰技术能够使冷却水塔在严寒季节或天气情况突变时安全运行,可以使机组循环水温度随着环境温度高低和机组负荷大小而自动调整,以达到最佳值,从而提高了机组的经济性．     

The Effect of Windbreak Walls on the Thermal Performance of Natural Draft Dry Cooling Towers

A three-dimensional study using the standard k-? turbulence model to simulate airflow in and around a natural draft dry cooling tower (NDDCT) has been conducted using a general-purpose CFD code. This investigation considered the location and the porosity of windbreak walls' structure on the NDDCT thermal performance. In addition, the effect of the windbreak walls on the thermal performance of two NDDCTs with different capacities has been investigated. Two parameters have been used to show the effect of the windbreak walls on the NDDCT thermal performance. At the reference heat exchanger temperature, the thermal effectiveness parameter has been employed. At the reference rejected heat from the NDDCT, the change in the cooling tower approach parameter has been employed. The results in this paper show an improvement in the NDDCT thermal performance due to the introduction of windbreak walls. Moreover, optimizing the location of the windbreak walls has been shown to have a more significant effect on the NDDCT thermal performance than the porosity of the walls. In addition, the effect of the windbreak walls on the thermal performance is similar for the two NDDCT with different capacities.     

Calcium Phosphate Scale Formation in Power Station Condensers Fed by Cooling Towers: A Case of When Not to Use Scaling Indices

Abstract

Unexpected fouling in condensers on Central Electricity Generating Board power stations operating on the river Trent in the UK in the 1970s prompted an extensive investigation of the phenomenon. Fouling was caused by deposition of calcium phosphate rich scale on the cooling water side. A fouling test rig was specially constructed to study the performance of different chemical treatments. The rig ran two tubes in parallel, one with undosed water, and the latter’s data sets from over 100 “control” tests were analyzed to determine the mechanism and rate of fouling. The trends could not be explained in terms of conventional scaling indices. Insight into the mechanism was provided by separating precipitation (loss from solution) and deposition (adhesion of some of the precipitated mass to the heated surface): scaling was found to be caused by the deposition of particulates in the recirculating cooling water, driven by the change in pH as the water went through the evaporative cooling stage. Quantitative expressions for fouling were generated from tests on 1.83?m long tubes and were found to give a reasonable prediction of the fouling behavior observed on a full sized (18.3?m long) single condenser tube on an operating condenser. The results indicated that recirculating water systems need to be approached very differently to once-through systems, and the use of scaling indices for such systems is not recommended.     

火电厂GEA冷却塔节能优化全程控制策略

对德国GEA公司逆流式自然通风冷却塔控制技术中存在的问题进行了研究,提出了改进措施,首先针对二位制运行闸板阀会造成冷却塔出水温度呈锯齿形变化,导致发电效率下降,煤耗增加,经济性较差的问题,将原二位制运行闸板阀控制方式改为连续型调节方式;其次为了实现冷却塔的全程自动控制将冷却塔出水温度设定值改为自动调整;最后为了解决冷却塔冷却水温度控制中存在的大滞后、大惯性问题,采用带死区的前馈PID策略并结合预测控制思想,通过上述的改进,可以实现冷却塔节能优化全程控制,降低发电煤耗,提高机组运行的可靠性、经济性和安全性。     

湿式冷却塔降雾节水技术的研究与发展

减少湿式冷却塔蒸发损失对火力发电厂节水工作的开展有着重要意义,文中介绍了目前国内外出塔水雾冷凝装置和冷凝剂的研究现状,阐述了降低冷却塔冷却负荷、蒸发预冷、优化运行等降雾节水措施的实施方案,总结分析了湿式冷却塔典型数学模型的研究状况。结果表明:热管与半导体制冷片作为高换热低阻力的新型冷凝装置,应对其加强理论和应用研究;干湿串(并)联冷却塔能够灵活、有效地降低冷却塔冷却负荷,建立干湿运行比例分配的通用性指导原则有助于该措施的广泛应用;为了提高冷却塔模型的精确度,应充分考虑动量、热量、质量3种传递的耦合,并应量化液膜传质阻力和塔内支架阻力对模型精度的影响;此外,节水性能的研究不应局限于典型工况或单种节水措施的应用,应针对冷却塔多个工况或多种节水措施组合应用开展模拟研究,以提高节水方案的适用性与灵活性。     

冷风型空调器蒸发器经济分析

采用优化经济准则来进行蒸发器经济性分析,以每年总偿付费用COST最低作为目标函数,以蒸发温度Te作为自变量,其它参数（如传热系数,进出风温度等）作为给定值,从而把COST视为Te的单值函数,建立一维最优点的蒸发器优化模型,为空调器的计算机优化设计建立了理论基础并提供方法。     

冲角和孔排间距对端壁气膜冷却效率的影响

燃气轮机在变工况运转时透平叶栅和级的特性对燃机总体性能影响极大,而叶栅端壁气膜冷却效率是关键因素。为了提高端壁气膜冷却效率,通过优化气膜孔间距排列的方法,在叶栅端壁20%、50%、90%轴向弦长处和距前缘-10%轴向弦长端壁处布置单排带复合角度的圆柱形气膜冷却孔,运用CFD(计算流体动力学)方法对冲角(10°、0°、-10°)在不同吹风比(1、1.5、2)条件下端壁气膜冷却效率进行对比分析。结果表明:采用气膜孔非等距排列方式能有效缓解因横向压力梯度变化引起的马蹄涡在压力侧的阻隔作用,压力侧冷却效率较高;高吹风比的冷却射流会出现抛射冷却,能有效抑制冷却射流脱离壁面,壁面平均冷却效率提高;主流正冲角有利于提高端壁吸力侧气膜冷却效率,压力侧变化不大。     

硅太阳电池降温保效的方法分析

太阳电池工作时,温度是影响电池转换效率的重要因素之一。硅太阳电池温度特性决定着当温度升高时,电池输出功率降低:电池温度每升高1 K,功率输出减少0.4%~0.5%,效率同比下降0.08%~0.1%。本文以硅太阳电池组件为例,按照导出热量方式的不同,将硅太阳电池冷却分为空气冷却、水冷却、制冷工质冷却、混合冷却等四种方式。着重介绍了几种国内外硅太阳电池的冷却技术、方法的研究成果,说明各种方法、技术的工作原理,并加以对比,得出结论:分频冷却技术从原理上讲冷却效果较好。文末展望了未来几种新型冷却技术。