螺旋翅片热管数值模拟及场协同分析张艳霞.docx

1、螺旋翅片热管数值模拟及场协同分析张艳霞分类号 密级 U D C 编号 螺旋翅片热管数值模拟及场协同分析南京工业大学学 位 论 文 螺旋翅片热管数值模拟 及场协同分析张艳霞指导教师姓名 张 红 教授申请学位级别工学硕士学科、专业热能工程论文提交日期2011年3月二一一 年 三 月Numerical study on spiral finned heat pipe and field synergy principle analysis Dissertation Submitted toNanjing University of Technologyin partial fulfillment o

2、f requirementfor the degree ofMaster of EngineeringByYanxia Zhang Supervisor:Prof. Hong ZhangMarch 2011摘 要数值模拟方法已成为换热器研究的重要手段，然而至今为止，对热管换热器数值模拟研究却鲜见报道。这其中的原因主要是由于在热管换热器中，冷热流体间的热量主要是靠热管内工作介质蒸发和冷凝的相变进行传递的，因而导致热管换热器的总体性能一方面取决于热管元件本身的性能，另一方面又取决于管壳间流体流动和传热的特性，这两方面综合影响决定了热管换热器数值模拟研究与管壳式换热器相比具有很大的难度。本文旨以热管

3、单管模拟为基础，探索热管换热器模拟中一些参数的选择，进一步模拟螺旋翅片热管及螺旋翅片管束，得到速度场和温度场分布，在此基础上形成速度场和温度场的协同性的评测方法，并建立热管外对流换热的场协同理论。通过场协同理论对热管对流换热性能进行分析研究，通过改变热管外部结构参数调整流场的速度和温度分布，从而改善速度场与温度场的协同性，提高热管对流换热的性能，为进一步模拟研究热管换热器提供了依据。主要研究的内容和结果可概括如下：（1）本文首先建立了单根热管流固耦合传热模型，应用计算流体力学软件FLUENT的标准k-模型对其传热与流动进行数值计算，在200104范围内探索热管当量导热系数的取值对模拟结果的影响

4、。结果表明，热管当量导热系数取值处于102数量级时，随着的增加，换热量增加比较明显，整个热管的温度分布还有不均匀现象；但是达到103数量级后，随着热管导热系数取值的变化，换热量变化并不大，说明给流固耦合模型设置适当的导热系数即可合理地模拟热管换热器。（2）对热管单管模型热侧为高温气体的情况，利用FLUENT软件提供的DO辐射模型，计算了常用的不同成分的烟气在不同工况下的辐射换热量，模拟结果表明：烟气的吸收系数从0.2m-1增大到5m-1，平均辐射换热量只减小了1.1 %。烟气吸收系数对辐射换热量的影响不大，烟气温度才是辐射换热量的决定因素。烟气温度超过600时，辐射所占百分比大于5%，应予以考

5、虑。在模拟常用的不同成分高温烟气时，吸收系数可近似取为1。（3）在探索得到热管换热器模拟中几个重要参数的选择基础上，建立了湍流状态下螺旋翅片热管单管的三维换热模型。对影响螺旋翅片管管外传热的翅片几何参数（翅片高度、间距、厚度）进行了详细计算分析，得到了单管螺旋翅片热管的Nu以及压降与Re的关系曲线，并拟合得到了两种不同表达形式的传热准则数Nu方程式。（4）建立了湍流状态下螺旋翅片热管管束的三维换热模型，研究了排列方式以及水平间距对热管管束的传热与流动的影响。顺排、叉排两种排列方式对比发现，叉排时流体在管间交替收缩和扩张的弯曲通道中流动，比顺排时在管间直通道的流动扰动剧烈。计算结果表明叉排时平均

6、Nu比顺排时大14.3%，平均压降比顺排时大10.2%。这个结论表明，相同管间距下顺排管束的换热强度比叉排低，但管外流动阻力的降低幅度要小。在布管时要综合考虑这两方面的因素。水平间距对于热管换热器的传热能力存在最佳位置，且不同排列方式下，最佳位置不一样。本模型中选用直径16mm，翅片高度6mm的热管，其顺排时，最佳水平间距为42mm；叉排时，最佳水平间距为40mm。两种排列方式下水平间距增大或减少，都能使传热性能有所减弱。（5）对本文中建立的各种传热模型建立了热管外对流换热的场协同理论。计算结果表明对于在相同管间距的条件下，顺排时的整场平均协同角比叉排时大1.7%；顺排时最佳水平间距42mm,

7、 其对应的平均协同角最小，为64.87，叉排时最佳水平间距为40mm，对应的平均协同角最小，为63.97。本文利用FLUENT软件对热管换热器单管及管束进行了数值模拟研究，并用场协同理论对结果进行了分析，为进一步模拟计算热管换热器提供了新的依据。关键词： 热管换热器； 螺旋翅片热管；数值模拟； 场协同ABSTRACTNumerical simulation has become an important means for heat exchangers research. But so far, numerical simulation about heat pipe heat exchan

8、ger (HPHE) is rarely reported. The reason is that the energy transfer between hot and cold fluid depends on phase transition of work fluid. So the overall performance of HPHE not only depends on the performance of single heat pipe itself, but also on the flow and heat transfer characteristics of flu

9、id between tube and shell. The two factors determine that numerical simulation for HPHE is more difficult compared to shell-and-tube heat exchanger. A single heat pipe heat transfer model was established firstly and the impact of effective thermal conductivity in a certain range on simulation result

10、s was explored. Then numerical simulation for spiral finned heat pipe and spiral finned bundle was researched. Velocity and temperature distributions were obtained. Furthermore, field synergy principle for the convective heat transfer analysis of the outside heat pipe was established. The factors th

11、at affect convective heat transfer were also analyzed from the view point of field synergy principle. The velocity and temperature distribution can be optimized by changing the external structure parameter of heat pipe. And the synergy between the velocity and temperature can be improved. The heat t

12、ransfer outside the heat pipe can be enhanced. Main research contents and conclusions could be summarized as follows:(1)Based on the Computational Fluid Dynamics, the standard k- model of Fluent，a fluid-solid interaction(FSI) heat transfer model for a single heat pipe was established and the impact

13、of effective thermal conductivity in a certain range on simulation results was explored. The simulation results showed that when set heat pipe thermal conductivity on the order of 102, the total heat transfer increased rapidly with the increase of thermal conductivity. Once set the thermal conductiv

14、ity over the order of 103, the heat transfer rate varied little with the change of thermal conductivity. This demonstrated that when set the appropriate heat pipe thermal conductivity for the heat pipe, FSI model can be used for the simulation of heat pipe heat exchanger.(2)Based on the FSI model, r

15、adiation heat transfer rate of distinct components gas in different conditions was calculated with DO radiation model provided by Fluent. The result showed when gas absorption coefficient increased from 0.2m-1 to 5m-1, the average radiation heat transfer reduced only 1.1%. It demonstrated that the g

16、as absorption coefficient has little effect on radiation heat transfer rate. The gas temperature is the determining factor of radiation heat transfer. When the gas temperature is over 600 , the percentage of radiation heat transfer is greater than 5%. So the radiation should be considered now. In th

17、e simulation for different components high temperature gas, the absorption coefficient can be approximately taken as 1. (3)Three-dimensional numerical simulations were performed for turbulent heat transfer and fluid flow characteristics of spiral finned heat pipe after getting some important paramet

18、ers. Three factors that affected the heat transfer of spiral finned heat pipe were examined: fin height, fin pitch and fin thickness. The curve of Nu and pressure drop with Re were obtained for single spiral finned heat pipe. Two different forms of Nu formulae were fitted.(4)Three-dimensional numeri

19、cal investigation was performed for heat transfer characteristics and flow structure of spiral finned heat pipe bundle with two different arrangements. Compared with in-line arrangement, fluid flowed alternately changed channel in staggered arrangement. The calculation results showed in staggered ar

20、rangement the average Nu number is 14.3% greater than that of in-line arrangement. And the pressure drop increased 10.2%.This result showed when under the same tube space, heat transfer rate was great in staggered arrangement, however the resistance outside the tube was larger than in in-line arrang

21、ement. So when design a HPHE, the two factors should been taken into account. There was a optimal horizontal spacing for HPHE. The optimal horizontal spacing value was not the same for two different arrangements. In this paper, heat pipe bundles with 16 diameters, 6 fin height were investigated in t

22、wo different arrangement. It found for in-line arrangement, the optimal horizontal spacing was 42mm, however in staggered arrangement, the optimal horizontal spacing was 40mm. The total heat transfer performance would deteriorate when the horizontal spacing was larger or smaller than the optimal val

23、ue.(5)Field synergy principle for the convective heat transfer analysis of the outside heat pipe was established. The result showed the average intersection angle in-inline arrangement is 1.7% larger than that of in staggered arrangement when at the same tube spacing. The optimal horizontal spacing

24、was 42mm, and the corresponding minimum average intersection angle is 64.87 in-inline arrangement. When in staggered arrangement, the optimal horizontal spacing was 40mm correspond to its minimum average intersection angle 63.97.In this paper, three-dimensional numerical simulations were performed f

25、or both single heat pipe and pipe bundles. The result was analyzed from the view point of field synergy principle. This study provided the basis for the further simulation of heat pipe heat exchanger.KYYWORDS: Heat pipe heat exchanger; Spiral finned heat pipe; Numerical simulation; Field synergy pri

26、nciple第一章 绪论1.1课题背景能源是发展国民经济的重要物质基础，是人类赖以生存的必要条件，能源的开发和利用程度直接影响着国民经济的发展和人民物质文化生活水平的提高，余热回收是合理利用能源、节约能源、提高能源利用率等方面不可忽视的问题。热管及由此而构成的热管换热器作为一种新型的高效换热器在余热回收领域发挥着重大作用。热管换热器属于热流体与冷流体互不接触的表面式换热器。热管换热器与其他形式的换热器比较起来有许多的优点，但其最独特的有以下几点：1）传热性能好：热管换热器优良传热性能的获得，首先是在两流体侧都方便地实现了翅化，增大了冷热流体的热交换面积，大大减小了两侧的对流热阻，因而强化了整个

27、传热过程；其次，把传统的换热器的交叉流型改为纯逆流流动，在不改变冷热流体入口温度的条件下增大了该传热过程中冷热流体换热的平均温压；再次，把一侧气体的管内流动改为垂直外掠流动。这三方面的原因可使热管换热器较其他形式的换热器的传热性能好得多。2）冷、热流体两侧的传热面可以自由布置：热管换热器的传热元件是热管，其蒸发段、冷凝段长度及翅化比按给定的传热量、流体温度、流量以及各流体的性质及清洁程度等两侧独立决定，互不牵连。这就从结构上确保热管换热器能适用于温度、流量及清洁程度相差悬殊的两种流体间的传热。这一特点，其他形式的换热器均不具有。3）传热面局部破坏时，能确保两流体彼此不掺混，热管换热器杜绝流体间

28、掺混现象。在这种换热器中，当某个热管元件某一端壳壁损坏时，造成的影响仅仅是该元件失效而停止传热。两种流体仍被元件另一端的壳壁隔开。通过元件壳壁的泄漏不会发生，因而能确保流体的品质不致变坏。再加上单根热管元件损坏后更换方便，并不影响换热器整体，因而在流体品质要求严格，冷热流体不能相互污染的情况下进行热交换时，热管换热器自然是理想的换热设备。4）热管换热器有较高的防积灰堵灰能力：热管是烟气在管外壁流动横掠换热，烟气的扰动性加强。再加上热管壁温高，管外始终呈干燥状态，因此，也就不会结膜不易黏附烟灰，因而它就能有效地防止堵塞。5）热管换热器有较高的抗低温腐蚀的能力：在设计中可根据工况特点调整热管加热段

29、和冷凝段的长度，以及通过调整低温处热管冷、热两段翅片的间距、数量等办法来调整烟气侧与空气侧的换热面积，从而达到控制热管壁温的目的，使烟气侧壁温高于运行工况露点温度，从而避免露点腐蚀。按照热流体和冷流体的状态，热管换热器可分为气气式、气液式、液液式。从热管换热器结构型式来看，热管换热器可分为整体式、分离式、回转式和组合式1。热管换热器的应用已从20世纪60年代末用于宇航的热控制，扩展到目前的电子工业、余热回收、新能源及化学工程等众多方面，且收到了显著的效果。热管热流密度的可调节性使它可以用于高热流密度的电子元器件，提高了电子元件的稳定性和使用寿命。我国青藏铁路地基工程中也用到了热管，其作用是将路

30、基的热量导出来，从而使这个由冻土构成的路基不会融化。目前，青藏铁路的线路和设备设施都保持了正常的运行状态2-3。化学反应往往有热效应相伴随的，对于放热反应，需要及时移走热量，而对于吸热反应，则需及时供给热量才能维持化学反应的正常进行。利用热管换热器移走化学反应热或供给化学反应热4，可以把化学反应控制在理想的温度范围内进行，从而可以得到高质量的产品，提高产量。在余热回收方面的，工业排气的温度往往高达上XX，将热管换热器用于工业排气的余热回收中，可回收余热，使之加热空气作为助燃空气使用或作为烘房的热源；可以加热水，用作锅炉给水，或使水产生蒸汽供其他方面使用；也可以加热排气本身，避免腐蚀排烟设备。1

31、.2 气气热管换热器应用介绍图1-1是一台典型的气气式热管换热器。通过这种换热器的两种换热流体都是气体。由于在热管上增加了翅片，这就克服了气体换热系数小的缺点，使得所需的换热热管数目大大减少。在所有的气-气式换热设备中，可以与热管换热器竞争的只有板翅式换热器。但换热流体通过板翅式换热器的压力降却要比热管换热器大得多。由于气-气式热管换热器的体积紧凑，压力降小，所以其被用在众多热量回收场合。图1-1 气气式热管换热器Fig.1-1 Gas -gas heat pipe heat exchanger热管式空气预热器是常见的气气型热管式换热器，它是利用排烟余热，预热进入炉子的助燃空气，不仅可以节约燃

32、料，提高燃料的利用率，还可以减轻对环境的污染。因此，热管空气预热器在余热回收利用中得到非常广泛的应用。福建省永安发电厂2130 t/h 型燃用无烟煤锅炉，1987年加装前置式热管空气预热器，低温段空气预热器入口风温由3040升高到8590，排烟温度由151降低到133，锅炉效率提高了2.68。四川成都热电厂5煤粉炉，1987 年利用热管式空气预热器代替卧式玻璃管空气预热器，排烟温度降低了21.5。滦河发电厂2煤粉炉，1991 年利用热管式空气预热器代替回转式空气预热器，年经济效益250万元5。由于热管式换热器具有小温差下传递大热量的特点，在一般电站锅炉中作为前置式的空气预热器，将会回收利用大量能源6。上海第八钢铁厂在四车间轧钢加热炉上采用气气型热管式换热器，将助燃空气从20预热到8090，废气从280下降到190，每小时回收废气余热为419 MJ7。气气热管换热器还可由管内充有不同工质的热管组成，称为组合式热管换