FLuent换热器的相变模拟计算.ppt

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1、Company Confidential Copyright 2001 Fluent Inc.All rights reserved.,1,New Initiatives at Fluent Inc.,Phase Change in Heat Exchangers,Brian Bell,Fluent Inc.,UGM 2001,敢桶系俯擂暴羔一拣脱润栋匪窑奉朔昏沂无资忻据患苟恒匠尼土咀掷奖幼FLuent换热器的相变模拟计算FLuent换热器的相变模拟计算,Company Confidential Copyright 2001 Fluent Inc.All rights reserved.,2,

2、Motivation,Demonstrate the use of Fluent to model phase change in heat exchangersProcesses of interestCondensationEvaporationBoiling Illustrate how to model one such process through use of a detailed exampleShell-and-tube condenserProvide motivation for users to begin developing models of their own

3、devices,铃衍盎咋还酞盗爱烂桑缔颧藤床障讲咱雪拘个怒诣砧张识雹痴嘘撮涨风措FLuent换热器的相变模拟计算FLuent换热器的相变模拟计算,Company Confidential Copyright 2001 Fluent Inc.All rights reserved.,3,Outline,Problem DescriptionShell-and-tube condenserPure vapor condensationNon-condensable gasesModeling ApproachPorous mediumHeat and mass transfer modelingM

4、odel ImplementationUser-Defined Functions and User-Defined MemoryResultsSteam condenser with non-condensable gasesCommercial chiller condenser,咳敞黎衍话烛斟悠造惺锰扒懒冰卓稼评村付疯颤厢绢犀亦统恨慎类师王渗FLuent换热器的相变模拟计算FLuent换热器的相变模拟计算,Company Confidential Copyright 2001 Fluent Inc.All rights reserved.,4,Description of Problem

5、,Shell-and-tube condenser,毗忍种送瓤滦霄苗寻利谴辰放封繁偏专有堕颖娶叭纺胞桃邱寞卫跃褐傀妓FLuent换热器的相变模拟计算FLuent换热器的相变模拟计算,Company Confidential Copyright 2001 Fluent Inc.All rights reserved.,5,Goals of CFD Modeling,Condenser performance characterized by heat and mass transfer rateCFD allows evaluation of factors affecting heat and

6、 mass transfer in condenserTube bundle configurationTube arrangementNumber of passesLocation of inlet portsBafflesPressure dropVelocity fieldNon-condensablesLocation and configuration of purge systemResults allow identification of potential design improvements,瘟你褒迁欢秸愤挫径综倾蕊秸瑞每羡陶曙揖斟障呛谐捣诽樊拜姚袜咎跨曲FLuent换

7、热器的相变模拟计算FLuent换热器的相变模拟计算,Company Confidential Copyright 2001 Fluent Inc.All rights reserved.,6,Film Condensation Process,Driving potential for condensation is the temperature difference between vapor and cooling waterDriving potential variation caused by Pressure dropRise of cooling water temperatu

8、reNon-condensables,杂沸镍霄靛谩橡碟输配量陈笑重琼烷唉哑迫渝镰颐岔坠三退钙截溜怂殖嚼FLuent换热器的相变模拟计算FLuent换热器的相变模拟计算,Company Confidential Copyright 2001 Fluent Inc.All rights reserved.,7,CFD Modeling Theory,Porous medium approachTube bundle treated as porous mediumEnables computationally efficient modeling of entire condenserCompar

9、ison with detailed modeling approachIn 2-D,O(100)-O(1000)control volumes per tube versus more than one tube per control volumeHeat and mass transfer modelsCondensation rate calculationCondensation rate determined from local flow field and cooling water temperatureLiquid film flow rate tracked in bun

10、dle from top to bottomCooling water temperature tracked from inlet to outlet,揍租扮扛鸯痪落箕翅仲不期谈宙蜕畏杏纠蟹后俏热搐靛赔净规恒赌拌陷湃FLuent换热器的相变模拟计算FLuent换热器的相变模拟计算,Company Confidential Copyright 2001 Fluent Inc.All rights reserved.,8,Porous Medium Approach,Representation of tube bundle as porous mediumPorosity is only re

11、quired parameterPorosity defined as ratio of fluid volume to total volume,Example:staggered tube bundle with equilateral triangular layout,Porosity,b,expressed as:,堡啮晋佛扩渍水冕炊罚餐哀贿妒秆锄植鲸亩控乓耶袜保永手滦局笔舌湘撒FLuent换热器的相变模拟计算FLuent换热器的相变模拟计算,Company Confidential Copyright 2001 Fluent Inc.All rights reserved.,9,T

12、ransport Equations,Generic transport equation for porous medium approach,Distributed resistance takes form of source terms that model details of the flow that are not resolved by the gridPorosity in convection and diffusion terms not modeled in FluentDistributed resistance terms most significant in

13、tube bundle region,哎上吻扼奄靡闰劫僧鹏倚奶徐报氢须扎碘庇何蛾宛帮职矗陛锋毖虐庶京寒FLuent换热器的相变模拟计算FLuent换热器的相变模拟计算,Company Confidential Copyright 2001 Fluent Inc.All rights reserved.,10,Evaluation of Modeling Approach,AdvantagesComputationally efficientDoes an alternate,tractable approach exist?Approach demonstrated to give meani

14、ngful data by several authorsDisadvantagesLoss of some flow details due to averagingCan be overcome by detailed modeling of small regions of condenser,秀绒蛙篇缨台限慢阳种石潜在扼一穿淖奔讣廖蛮维包腕提低碘幂此维冕官FLuent换热器的相变模拟计算FLuent换热器的相变模拟计算,Company Confidential Copyright 2001 Fluent Inc.All rights reserved.,11,Heat Transfer

15、 Process,Film condensation on horizontal tube,Cooling Water,Tube Wall,Condensate Film,Liquid-vapor Interface,RefrigerantVapor,Latent heat released at liquid-vapor interface transferred to cooling water,折瞥券显峦翠客爹雍恫遁朱称疯沤瓣贪菲坑赫载稗氰管柬勾磨两书车症桩FLuent换热器的相变模拟计算FLuent换热器的相变模拟计算,Company Confidential Copyright 20

16、01 Fluent Inc.All rights reserved.,12,Heat Transfer Model,Heat transfer is modeled by coupling of thermal resistance network with CFD code,Tcw,Tt,i,Tt,o,Ti,Rcw,Rtube,Rcond,Cooling Water,CFD code provides interface temperature,Ti Cooling water and tube thermal resistances are generally well-knownFilm

17、 heat transfer coefficient is required for Rcond,驴胺荤帕百恢冉咐翟洛察恨舔哇隶囚球泛微秸乎扶象寺畦采坪尺猜纳镑喳FLuent换热器的相变模拟计算FLuent换热器的相变模拟计算,Company Confidential Copyright 2001 Fluent Inc.All rights reserved.,13,Film Heat Transfer Coefficient,Critical component of heat transfer modelObtain from experiment,Or obtain from liter

18、atureSteam condensation on smooth tubes,Figure courtesy of Kansas State University,Professor Steve Eckles,and Duane L.Randall,衣悔劝粪去恳士必砌尘全决滩加片卑今选疟拟忙谴猾憨权妙锌界茁陨肄葱FLuent换热器的相变模拟计算FLuent换热器的相变模拟计算,Company Confidential Copyright 2001 Fluent Inc.All rights reserved.,14,Modeling Assumptions,Effect of liquid

19、on flow field is neglectedApproach can also be implemented in Eulerian-Eulerian multiphase frameworkSatisfactory model for liquid phase representation not currently availablePublished results of this type of model do not appear to show significant advantageVapor is assumed to be saturatedNo superhea

20、tingVapor temperature determined from pressure field calculated by CFD code,捌足带黔隔掳嚷语纺侧织季弦钙闽坡椎幽峪管幅膏绪层绵观叶最尺重滩山FLuent换热器的相变模拟计算FLuent换热器的相变模拟计算,Company Confidential Copyright 2001 Fluent Inc.All rights reserved.,15,Implementation of Model with UDFs,UDFs are required for:Source terms required by porous

21、medium approachCondensation ratePressure drop in porous regionRepresentation of tube bundlePorosityCondensate film flow rate accountingCooling water temperature calculation with multiple tube passes,姜纺孪崭瞪茫哲尿醚灶束描梗挤洲浴槛戒袜过威蒙望帐订床喉善惹瞪枫幌FLuent换热器的相变模拟计算FLuent换热器的相变模拟计算,Company Confidential Copyright 2001

22、Fluent Inc.All rights reserved.,16,Cooling water temperature calculation for each segmentEvery iteration,condensation rate is summed over each segmentInlet cooling water temperature=outlet temperature from previous segmentSegment outlet cooling water temperature calculated by energy balance.Log-mean

23、 temperature for each segment calculated based on vapor temperature and cooling water inlet and outlet temperatures,Tube Bundle Representation,Bundle consists of N passes and M segmentsEach segment defined as unique cell zone,Example:2 Pass bundleN=2,M=4,奈廷魂奠圾赤娄盎绸丑佩臀基纯澎希听崭棍赌纸岳望钟筐嚼善珠畏土熟和FLuent换热器的相变模

24、拟计算FLuent换热器的相变模拟计算,Company Confidential Copyright 2001 Fluent Inc.All rights reserved.,17,Tube Bundle Grid Structure,Structured,cartesian grid used in tube bundleEach control volume has unique i,j,k index,Grid structure created with UDFsGrid generator,solver do NOT utilize structureUsed to track co

25、ndensate film flow rate,昆访弯质纶禹禾倘踪棋孔劣冒浸地朽湘尽捞霞逞揖够摧图垮末革溶又窥或FLuent换热器的相变模拟计算FLuent换热器的相变模拟计算,Company Confidential Copyright 2001 Fluent Inc.All rights reserved.,18,Source Terms,Algorithm for source term in continuity equationObtain pressure,velocity and species mass fraction(if necessary)from current so

26、lution valuesObtain film Reynolds number and cooling water temperature from User-Defined MemoryCalculate heat flux based on current value of solution variables Translate heat flux into volumetric mass source termUnder-relax source termSi+1=Si+a(So Si)Required for solution stability.Alpha typically 0

27、.01 0.10Value of source term from previous iteration,So,stored in User-Defined MemorySource term in momentum equations Calculated using empirical correlations with tube bundle porosity and current velocity,郸痔甸脖蹄苑星慰自这率烤悲宁缝贪彼粪跋累习渗娩至闷惊抑般受例害遵FLuent换热器的相变模拟计算FLuent换热器的相变模拟计算,Company Confidential Copyrigh

28、t 2001 Fluent Inc.All rights reserved.,19,Define_On_Demand Functions,Define_On_Demand functions executed once per iterationUpdate condensate film mass flow rateUpdate cooling water temperatureAssume uniform temperature for each bundle segmentNew values stored in User-defined memoryAutomatic Define_O

29、n_Demand execution possibleExample:,扮访俯枷毒蛹型芽矾年临晃廖澳踩炬锋真呢磁瞅照抒映歇汐糯缕裸真躇羚FLuent换热器的相变模拟计算FLuent换热器的相变模拟计算,Company Confidential Copyright 2001 Fluent Inc.All rights reserved.,20,Solution Algorithm,Initialize Solution:Assign porosity,tube bundle orientation,Update cooling water temperature and liquid conde

30、nsate mass flow rate,Calculate source terms,Solve flow equations,Yes,No,Solution Converged?,Stop,织揣农匈爆酥隋绣琼汽煞更灰喉誓籍帘茄穷抒疾城聂体猿豆咎村债息旋辙FLuent换热器的相变模拟计算FLuent换热器的相变模拟计算,Company Confidential Copyright 2001 Fluent Inc.All rights reserved.,21,Examples,Steam condensation with non-condensable gases,McAllister C

31、ondenserfrom:Bush et al.,1990,Proc.Int.Symp.On Condensers and Condensation,姓敌导佃厄仕峨缕杏酝弗吸豺扑避泳股曲偷融才葱羞漂似富餐灵媳凉提鸵FLuent换热器的相变模拟计算FLuent换热器的相变模拟计算,Company Confidential Copyright 2001 Fluent Inc.All rights reserved.,22,McAllister Condenser Geometry,Boundary conditions and model inputsShell Dimensions 1.02 m

32、 X 1.22 m X 0.78 m,Cooling water flow directionInlet temperature:17.8 CInlet velocity:1.19 m/s,Tube BundleSingle pass,4 segmentsOuter Diameter:.0254 mInner Diameter:.0242 mPitch:.0349 mPorosity:0.52,PurgeMass flow rate:.011 kg/s,InletPressure:27670 PaAir mass fraction:0.00122,猪纤讶霓液谈囊阴篙瓮孟挖把巢溯窜麻送年礼丰挤治

33、蓄苔淬廊惩潮两嚼侄FLuent换热器的相变模拟计算FLuent换热器的相变模拟计算,Company Confidential Copyright 2001 Fluent Inc.All rights reserved.,23,Condenser Grid,15,000 Control VolumesSimple geometry allows structured grid throughout domain,Grid profile in x-z plane,定乡哑渴滚混断梢坦密湃工舜坷姜篷酮臭帅准蔬孪祷回捧颧铱隋溢草唉抄FLuent换热器的相变模拟计算FLuent换热器的相变模拟计算,Co

34、mpany Confidential Copyright 2001 Fluent Inc.All rights reserved.,24,Results,Condensation Rate,Inlet mass flow rateCFD:2.124 kg/sExp.:2.032 kg/sError:4.5%,Cooling water temperature contours,Volumetric condensation rate contours,桌镐费韶战里展镀磺污邻硅邦吨瘟用首潘榴织乌介藏岩哎纸垣趁此堂鲸匈FLuent换热器的相变模拟计算FLuent换热器的相变模拟计算,Company

35、 Confidential Copyright 2001 Fluent Inc.All rights reserved.,25,McAllister Condenser Flow Field,Velocity MagnitudeMax:34.4 m/sMin:0.02 m/s,PressureMax:27,663 PaMin:27,530 Pa,Air Mass FractionMax:.534Min:.00122,Condensation Rate*Max:6.1 kg/smMin:0.0 kg/sm,*Minimum condensation rate in tube bundle is

36、0.18 kg/sm,暗胳盲才琅言暖少盏晕却浸脓隘酣扬乍阀运秦矮朗年葛途密蛙屿掖蝗蚌蠢FLuent换热器的相变模拟计算FLuent换热器的相变模拟计算,Company Confidential Copyright 2001 Fluent Inc.All rights reserved.,26,Effect of Air on Condensation Rate,Volumetric condensation rate contours without air,Volumetric condensation rate contours with air,Comparison of modelin

37、g results with and without non-condensable gases,写耙粹耙鸦沈铜即测厚辅躲囊狸嵌原庚茫鹤钮获拥侣惩洁尼淌叔本白欢遮FLuent换热器的相变模拟计算FLuent换热器的相变模拟计算,Company Confidential Copyright 2001 Fluent Inc.All rights reserved.,27,Effect of Inundationon Condensation Rate,Tracking condensate film flow rate from upper tubes to lower tubes allows

38、use of inundation correction factor,Contours of condensate film mass flow rate,Contours of volumetric condensation rate,拘涉珊瘴洞坡幅拱流瘤投陵借佐弃艇曰寅搪靴廷男壹农诧赌危赢柴莉弧源FLuent换热器的相变模拟计算FLuent换热器的相变模拟计算,Company Confidential Copyright 2001 Fluent Inc.All rights reserved.,28,Conclusions,Modeling phase change processes

39、in heat exchangers is possible in Fluent 5 through the use of UDFs This approach is well-suited for falling film condensation or evaporation processesHeat and mass transfer models must be provided by the userCFD modeling of McAllister condenserDescription of model development process intended to serve as a reference for users who wish to develop similar modelsAccurate results demonstrate the potential of this approach,孪瘤辰搂称蜂跳预个渔夏霍楞玉拯襄尘蹦衍族卡荒野廉帜擅当括刚呐蕾但FLuent换热器的相变模拟计算FLuent换热器的相变模拟计算,