新型底部鼓风式冷却塔的传热性能研究

针对传统机械抽风式冷却塔散热效果差、维修不便、使用寿命短等问题,运用多目标优化方法,设计出一种新型的底部鼓风式冷却塔,并以其为主要研究对象,分析影响冷却塔散热性能的关键因素。基于气-液两相流传热理论,建立冷却塔内部循环水传热计算模型,得到了冷却塔内部流体的温度分布图、迹线图。分析比较了抽风式冷却塔与鼓风式冷却塔的散热效果,结果表明新型鼓风逆流式冷却塔散热效果更好、塔身更低、更符合节能环保要求。同时研究了不同的进风温度对冷却塔冷却效果的影响,得到了满足设计条件的临界进风温度。     

新型鼓风式机械通风冷却塔进风口阻力优化

鼓风式机械通风冷却塔常应用于核电厂重要厂用水系统,为了提高其安全性,提出了一种新型鼓风式冷却塔,但由于结构复杂,其阻力特性不同于常规的鼓风式机械通风冷却塔。针对新型鼓风式机械通风冷却塔的阻力问题,通过三维模型研究了塔内阻力构成,进而确定进风口的优化方案。结果表明,初始方案冷却塔的各部分阻力中,从进风口防飞射物的过滤网至风机外罩入口的阻力最大(约占32.7%)。优化方案在满足防飞射物入侵的前提下,通过调节进风口相关尺寸,使塔入口至网面的阻力系数占比降低了4.8%,网面至风机入口的阻力系数占比降低了1.8%。     

核电大型冷却塔进风口高度的经济性分析

冷却塔进风口高度是循环冷却水系统优化计算和冷却塔塔体优化所共同关注的问题,它关系到塔内空气流场分布和空气阻力计算,影响塔内气水换热效果,对循环冷却水系统及核电机组运行的经济性产生重要影响。通过对填料类型、电价、冷却塔造价、年固定分摊率及厂址气象条件等主要影响因素变化时年费用变化的分析,得出核电大型冷却塔进风口高度设置的最优区间,提出进风口面积与淋水面积比的推荐值应为0.3～0.35,并建议相关的国家规范条文予以修改。     

冷却塔雨区阻力特性研究

冷却塔雨区的阻力特性一直以来都是冷却塔研究的难点问题,本文建立雨区横流模拟试验装置,进行不同雨区高度、雨区深度、淋水密度以及断面风速模拟试验,测试雨区阻力。试验结果分析表明:单位长度雨区阻力系数随雨区高度的增加而增大,随雨区深度的增加而减小,随断面风速的增加而减小,随淋水密度的增加而增大。本文试验成果同时是对现有雨区阻力性能理论的补充和扩展,为超大型冷却塔的设计计算提供技术支持。     

NUMERICAL SIMULATION OF FLOW FIELDS IN A NATURAL DRAFT WET-COOLING TOWER

The flow field in the hyperbolic natural draft wet-cooling tower, which has great effects on the economy and security of power plant, was studied through numerical simulation. The mathematical model was established and analyzed in order to optimize the cooling-tower and to evaluate its efficiency. Various working conditions were considered and compared with each other, such as the circulating water flux, air temperature and tower resistance. It is concluded that when the cooling-tower runs without wind, there is a vacuum region inside the tower and the pressure rises with the increase of the tower height. Meanwhile, the inner flow field is axisymmetrical. The air velocity achieves its climax at the axis. It is also found that the effect of circulating water temperature is equivalent to that of the water flux.     

间接空冷系统塔型优化研究

在间接空冷系统中,散热器和空冷塔是主要的换热部件。散热器的传热性能及空冷塔塔内气流运动的均匀性都会对空冷系统的冷却效率产生严重影响,空冷塔塔型直接影响塔内的气流运动状态。本文通过对不同的空冷塔塔型进行热力、阻力特性的平衡计算,比较各种塔型下空冷塔的冷却效率,给出最优冷却效率下,空冷塔塔型关键比例尺寸。     

超大型自然通风冷却塔进风口区域阻力特性研究

随着淋水面积的逐渐增大,现行的阻力计算公式已不再适用于超大型冷却塔的计算。本文通过对应建立超大型冷却塔冷态气流阻力试验模型,对不同规模冷却塔的支撑结构（包括人字柱及塔内支撑柱）、不同淋水填料阻力、不同进风口高度等进行组合试验,对其相应阻力特性进行了分析,在此基础上提出了适用于超大型常规逆流式自然通风冷却塔进风口区域阻力系数计算公式,并经过了工程验证。     

排烟冷却塔的一维设计计算方法

利用冷却塔排放烟气,须在冷却塔内增加排烟管道,且在填料断面又增加了烟气流量.冷却塔工艺设计如何进行计算,是冷却塔设计遇到的一个新问题.本文在分析了排烟塔气流特性的基础上,参照类似气流阻力的研究结果结合自然塔的热力计算方法,给出了排烟冷却塔的热力阻力一维计算方法,计算与分析结果表明,计算具有一定的精度,可供设计参考.     

核电厂重要厂用水系统鼓风式机械通风冷却塔优化研究

核电厂的重要厂用水系统通常采用鼓风式机械通风冷却塔,而鼓风式机械通风冷却塔的相关研究比较少,对塔内的空气动力特性不太了解.本文通过物理模型试验的方法对其空气动力特性进行研究并对塔型进行优化,研究表明：塔的总阻力系数随塔出口收缩段高度的增大而增大,随收缩段与水平夹角α的减小而减小,随填料安装高度的减小而减小;填料断面风速分布均布系数基本不受收缩段高度的影响,其随α的减小而增大,随填料安装高度的减小而减小.     

PARAMETRIC STUDY ON THE THRUST OF BUBBLY WATER RAMJET WITH A CONVERGING-DIVERGING NOZZLE

To predict the thrust of bubbly water ramjet with a converging-diverging nozzle, the physical processes occurring in the diffuser, mixing chamber and nozzle were analyzed. The mathematical models were constructed separately under the restrictions of certain assumptions. The bubbly nozzle flow was examined using a two-fluid model and accomplished by specifying the water velocity distribution in the nozzle. The numerical analysis of flow field in the nozzle shows that the Mach number at the throat is 1.009, near unity, and supersonic bubble flow appears behind the throat. There is greater thrust produced by bubbly water ramjet, compared with single-phase air ramjets. Subsequently, the influences of vessel velocity, air mass flow rate, inlet area A_m, area ratio (i.e., mixing chamber to inlet area A_m/A_i), and initial bubble radius on the thrust were emphatically investigated. Results indicate that the thrust increases with the increase of air mass flow rate, inlet area and the area ratio, and the decrease of initial bubble radius. However, the thrust weakly depends on the vessel velocity. These analytical and numerical results are useful for further investigation of bubbly water ramjet engine.     

超大型高位集水冷却塔的三维数值模拟研究

高位集水冷却塔具有高效、节能、低噪等优势,在火、核电厂中具有较好的应用业绩。本文采用CFD数值模拟的手段,对某超大型高位集水冷却塔的热力特性以及空气动力特性进行了数值模拟研究。计算结果表明:集水装置的增加对冷却塔形成阻力,但其增加程度要明显小于雨区阻力的减小量;在相同条件下,与常规塔相比,高位集水冷却塔的通风量较大;高位集水冷却塔的冷却性能优于常规塔。     

HEMODYNAMICS FOR ASYMMETRIC INLET AXIAL VELOCITY PROFILE IN CAROTID BIFURCATION MODEL

The asymmetric inlet velocity profile has been observed in phantom model using LDA and in health subjects using Magnet Resonance （MR）. The effects of asymmetric inlet axial velocity profile on the flow field and the Wall Shear Stress （WSS） of carotid bifurcation were numerically studied herein with the TF-AHCB model, The results show that the Wall Shear Stress Gradient （WSSG） in the front part of the sinus for inward-tilting inlet axial velocity profile is nearly 2 times of that for the symmetric one in the beginning of systole, the end of systole, and diastole, respectively. The area of WSS below 5× 10^-3 Pa at the outer wall of the sinus for outward-tilting inlet axial velocity profile is 1.5 times of that for the inward-tilting one during diastole of the cardiac cycle. The asymmetric inlet velocity profiles can reduce the flow velocity near the inner wall of the sinus, which has been normally considered a high velocity region. It is concluded that besides bifurcation geometry and flow waveform, the asymmetry of inlet velocity profile is probably a factor influencing atherosclerosis.     

自然通风湿式冷却塔热力特性数值研究

基于CFD软件和自然通风湿式冷却塔相关理论，对气流运动采用标准 湍流模型，喷淋区和雨区采用离散相模型计算，对填料区建立了基于Poppe理论的数值求解模型，并通过添加自定义源项，实现其在FLUENT中的求解。基于该模型，在不考虑自然风情况下，对某300MW机组自然通风冷却塔的气水流动与热质交换进行数值模拟，分析了淋水密度、进塔水温、喷嘴数和环境条件对冷却塔热力特性的影响。计算结果表明：基于CFD软件的冷却塔数值求解模型有很好的适用性，淋水密度和环境条件对出塔水温影响很大，为进一步完善冷却塔的设计与运行提供了理论依据。     

冷却塔的一个新的热力计算方法－用一维方法作二维计算

本文在对冷却塔雨区热力特性研究的基础上, 进行了逆流式自然通风冷却塔的轴对称二维热力计算, 计算了进风口高度、淋水分布等几个参数变化对冷却水温的影响, 并给出了在均匀布水的条件下, 用简单的一维计算替代复杂的轴对称二维计算的方法, 为设计提供了一个既简单又精确的计算方法. 计算水温和工业塔实测结果非常一致.     

V型掺气坎在龙抬头式泄洪洞中的应用

本文通过试验研究,从掺气坎后空腔区的三维形态考虑,提出了一种新型V型槽式掺气坎(简称V型坎),其主要特点是:坎后射流水舌的流速、挑角和高程沿中心向两侧保持连续变化,其水舌落水点范围即空腔长度成为一连续变化的曲线,且沿曲线水流流速亦呈连续变化,很好地减弱或消除了龙抬头式泄洪洞掺气坎后水流落水处产生的回水.在V型坎出口断面处,水流的三维扩散充分,水舌与空腔的接触面明显增大,对底空腔长度、通气量等掺气特性指标都有明显改善.     

口环间隙泄漏对离心泵空化性能的影响分析

以DG-350型多级离心泵次级叶轮为研究对象,研究了口环间隙对离心泵空化性能产生的影响。通过定常数值模拟,计算出了离心泵的扬程和效率,同时得出了口环与进口段交汇处的速度矢量图、涡量云图和空化区域分布图以及叶轮流道内的空化区域分布图。模拟结果与实验结果的对比分析表明:(1)误差都在实际工程所要求的5%左右,说明计算与模拟结果准确;(2)由于口环与进口段交汇处速度旋涡的存在,使得离心泵的进口段与前口环交汇处区域的压力降低,从而导致了空化现象的发生;(3)随着口环间隙的增大叶轮流道上的空化区域也随之增大,从而减小了流体的过流面积,使流体速度和必须的汽蚀余量增大,NPSHR增大,则叶轮进口处的空化区域也就会增大。     

间接空冷阻力特性试验研究

在间接空冷系统中,关键的换热部件是散热器和空冷塔。散热器的传热性能及其与空冷塔组装后的整塔阻力特性是影响空冷系统冷却效率的主要因素。散热器的传热性能及阻力特性一般由生产厂家提供,但是散热器与空冷塔组装后的整塔阻力特性目前尚无研究成果,并且没有形成统一的总阻力系数的经验计算公式。本文通过建立空冷散热器垂直布置于空冷塔外的物理模型,进行试验研究。通过对试验测取的各个参数的计算分析,最终总结出散热器与空冷塔组装后的整塔阻力系数的经验计算公式,为空冷系统的工艺设计提供参考。     

抗震冷却塔金属淋水填料研究

冷却塔的冷却效果主要由淋水填料的冷却数和冷却塔的有效高度决定,淋水填料的换热性能决定了冷却塔的主要换热效果。为提高抗震冷却塔的抗震效果,淋水填料采用金属填料。通过在某工程中抗震冷却塔金属填料与普通塑料填料应用的对比分析,研究金属填料的特点及适用性,为抗震冷却塔的设计提供依据。     

URANS COMPUTATION OF CAVITATING FLOWS AROUND SKEWED PROPELLERS

Cavitating flows around skewed propellers are investigated numerically by means of the unsteady Reynolds Averaged Navier-Stokes (RANS) Equation method. The standard k-ε turbulence and the modified Z-G-B cavitation models are employed. A measured nominal wake is used for the inlet velocity boundary condition. Predicted cavitating evolution processes and tip cavity patterns are compared with experimental observations. In addition, the influence of the skew angles on the cavitation and unsteadiness performances of propellers operating in a non-uniform wake is also studied. Results show that the modified Z-G-B cavitation model performs better to simulate the cavitating flow cases studied in this paper. Comparisons demonstrate that the skewed propeller with a skew angle of 20 o is the best choice for a given stern wake with a assigned thrust and the minimum force fluctuations.     

A NUMERICAL METHOD FOR CALCULATING THE EFFECTS OF INLET FLOW ON HYDRODYNAMIC CHARACTERISTICS OF A HYDROFOIL-STRUT-POD CONFIGURATION

A numerical method based on the doublet distribution for calculating theeffects of inlet flow on hydrodynamic characteristics of a hydrofoil-strut-pod configurationunder the linearized free water surface condition is presented in this paper.Inlet flow con-dition is represented by a control section S,in the inlet tube on which the axial velocity is u-niform and determined by a given flowrate.The numerical results for some typical casesare compared with corresponding experimental data.It is found that good agreement be-tween computational and experimental results can be achieved.This numerical methodmay be applied to the prediction of foilborne performance characteristics of a waterjet pro-pelled hydrofoil craft and to optimization of integrated hydrofoil waterjet propulsion sys-tem.