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.     

Theoretical Investigation on Thermal Performance of New Structure Closed Wet Cooling Tower

Thermal performance of closed wet cooling tower (CWCT) with packing is analyzed using experiments and numerical simulations. The effect of cooling water flow direction on the performance is discussed. The results show that the packing plays an important role in improving the cooling effect of the CWCT. Under the same operating conditions, the cooling water outlet temperature of CWCT with packing is lower than that of CWCT without packing between 0.6°C and 1.5°C the cooling efficiency of CWCT with packing is higher than that of CWCT without packing between 6.0% and 14.8%. The concurrent cooling water flow direction results in more uniform temperature differences between cooling water and the spray water, which can benefit the cooling water outlet temperature 0.3–0.7°C and the cooling efficiency 3.0–9.5%.     

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。     

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。     

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.     

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.     

A Novel Approach for Energy and Water Conservation by Using Silver-Carbon Quantum Dots Hybrid Nanofluids in Wet Cooling Towers Systems

This study presents the use of Silver-Carbon Quantum Dots (Ag-CQD) hybrid nanofluids,prepared by a facile wet chemical method,for heat transfer enhancement of w...     

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。     

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.     

减缓闭冷水系统的腐蚀分析及运行方案

介绍了吴泾热电厂300MW机组闭冷水系统的结构和功能。针对闭冷水系统出现的腐蚀隐患问题,按照GB/T 12145-2008对闭冷水的要求,进行了技术分析和深度排摸。通过实验室挂片、调整运行和试验运行,制定了提高pH值及投加缓蚀剂的运行方案。实施减缓闭冷水系统腐蚀方案后,有效地减缓了闭冷水系统对金属设备的腐蚀。2010年12月份闭冷水水质检测结果:25℃时,铜含量为6.49μg/L,铁含量为8.16μg/L,pH值为8.2,电导率为6.7μS/cm,溶氧为5.67mg/L,表明减缓闭冷水系统腐蚀效果明显,在取得较好经济效益的同时,提高了机组的运行安全性。     

The Use of a Thermo-Fluid Dynamic Efficiency in Cooling Towers

A thermo-fluid dynamic efficiency is defined for a mechanical draft water-cooling tower. It allows evaluating the heat transfer related to the pressure drop. It could also be used in isolated fills in different types of water-cooling towers. Thermo-fluid dynamic efficiency values obtained with available experimental results acquired from commercial fills are shown, and it can be concluded that this efficiency is not a function of the height of the fill.     

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.     

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.     

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。     

“烟塔合一”技术采用烟气余热换热器的节能效果分析

"烟塔合一"技术,即取消火电厂中的烟囱,将锅炉经除尘脱硫后排出的烟气,经自然通风冷却塔排放到大气中。用等效热降的方法分析了"烟塔合一"技术增设烟气余热换热器的节能效果,并以660 MW机组为例,进行了几种方案比较。定量计算结果得出的结论对指导发电厂采用"烟塔合一"技术烟气余热换热器的设计具有重要的意义。     

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．     

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.     

立式降膜闭式冷却塔设计程序研究

提出一种立式降膜闭式冷却塔的设计计算方法,按照此方法使用Visual Basic 6.0开发工具设计计算程序,并对程序流程进行详细说明。结果显示,该计算程序适用于立式扭曲管中不同工艺流体（冷却水、喷淋水和空气）进行换热的各种工况。通过对比程序计算和手工计算结果,发现二者吻合程度较好,因此通过计算程序能够提高开发人员的设计效率和准确性,减少迭代计算工作量,方便对不同设计方案结果进行比较。后续可以衍生出针对各种发生相变过程（制冷剂、水蒸气冷凝等）的热力计算。     

柴油机水套的计算流体动力学(CFD)分析

应用AVL公司SWIFI软件，对生产中的6缸柴油机水套进行了CFD分析。机冷器的CFl)分析表明：冷却水流平均速度在0．8～1．0ms之间，保持有较好的流动情况，基本满足机油冷却要求；缸体CFD分析表明：缸体各截面的水流速度达到0．5m/s，已能够满足设计要求，但环绕水流量比短路水流量少约三分之一，因此进出水孔的相对位置还需要调整；缸盖CFD分析认为：1-4缸受到二次冷却的效果较好，对于第5缸、第6缸因受到二次冷却的效果减弱(甚至没有)而导致的缸盖水流动情况不好，可以通过改变进、排气道和鼻梁区的几何尺寸来改善其在关键区域的水流动情况。     

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。