H型翅片椭圆管束传热与阻力特性的实验研究

对H型翅片椭圆管束的管外侧传热与阻力特性进行了模化实验研究,得到了H型翅片椭圆管束的管外侧传热与阻力特性变化规律,分析了横向管间距s_1与纵向管间距s_2对H型翅片椭圆管束传热与阻力特性的影响。研究表明:在研究范围内,随着s_1的增大,管外侧传热性能变差、阻力减小;随着s_2的增大,管外侧传热性能明显变差,阻力明显减小;且纵向管间距s_2对传热与阻力性能的影响比横向管间距s_1更明显。     

圆形基管位置对于H型椭圆管翅片管束传热和流动特性影响

基于FLUENT软件,采用RNG k-ε湍流模型对H型椭圆翅片管束的传热与流动进行数值模拟,分析圆形基管位置对H型椭圆翅片管束的传热和流动的影响。结果表明:圆形基管位置往后移,翅片管束Nu减小,圆形基管处于第一排时,管束传热明显优于后三排位置,其Nu相较于第四排B4型翅片管束的Nu高16%,全椭圆基管A型翅片管束的Nu高15%。圆形基管位置后移,翅片管束f越小,但差别较小。在综合热力性能方面,圆形基管处于第一排时,管束表现最优。     

H形翅片管束传热和阻力特性的试验与数值模拟

根据大型电站锅炉省煤器的运行工况,对单H形和双H形翅片管束气侧的传热与阻力特性进行了模化试验研究,并利用Fluent软件对H形翅片管束的流场和温度场进行了数值模拟,得到单H形和双H形翅片管束的传热与阻力特性变化规律.结果表明:H形翅片管束的传热和阻力特性与气体的Re有关,随着气体Re的增大,气侧Nu不断增大,传热性能提高,而Eu则逐渐减小,并趋于定值;在相同Re下,单H形翅片管束气侧Nu大于双H形翅片管束气侧Nu,而气侧Eu则小于双H形翅片管束气侧Eu;数值计算结果与试验结果误差较小,采用数值计算方法能比较准确地分析H形翅片管束的流动与传热特性.     

螺旋翅片管束传热和阻力特性的试验研究

对13个不同翅片间距、翅片高度、横向管间距、纵向管间距的螺旋翅片管束换热器在不同雷诺数条件下的传热和阻力特性进行了试验研究,得出了翅片间距、翅片高度、横向管间距、纵向管间距及雷诺数与换热特性Nu和阻力特性Eu的准则关系式,并对准则关系式进行了分析.结果表明:随着横向管间距和翅片间距的增大,螺旋翅片管的传热得到强化,但随着纵向管间距和翅片高度的增加,螺旋翅片管的传热有所减弱;随着横向管间距、纵向管间距和翅片间距的增大,螺旋翅片管的阻力减少,但随着翅片高度的增加,螺旋翅片管的阻力增加.     

H型鳍片管性能优化的数值研究

基于Fluent平台,利用Realizable k-ε湍流模型对H型鳍片管的传热特性、阻力特性和综合性能进行了数值研究.结果表明:当烟气流速越高、翅片高度越小、翅片节距越小、管束横向节距越大、管束纵向节距越大时,H型鳍片管的传热系数越大;当烟气流速越高、翅片高度越大、翅片节距越小、管束横向节距越小、管束纵向节距越大时,H型鳍片管的流动阻力越大;当相对翅片高度为h/d=2.105、翅片节距越小、管束横向相对节距为s1/d=2.237、管束纵向节距越小时,H型鳍片管的综合性能最好.     

H型翅片椭圆管低低温省煤器换热与阻力特性研究

为满足燃煤电站节能减排要求,不同型式的翅片管省煤器已广泛应用于新建或在役的电站锅炉中。椭圆管的流线型外形使椭圆管的传热与阻力性能以及防积灰和磨损性能比圆管更佳,为此,对适用于低低温省煤器的不同结构H型翅片椭圆管束的换热与阻力特性进行了模化试验,并与应用于燃煤电站锅炉省煤器的H型翅片圆管束性能进行了比较和分析。结果表明:H型翅片椭圆管束具有明显的优势,值得在低低温省煤器中推广应用。     

新型翅片管束提高自然通风直接空冷系统效率

自然通风直接空冷系统凝汽器单元"Λ"型布局和传统翅片结构使得冷却空气流过翅片管束时发生严重转向,从而显著影响空冷凝汽器的流动传热性能。提出了一种新型翅片管束,其翅片通道与基管椭圆长轴方向呈一定夹角,使翅片通道方向与塔浮升力方向平行。通过CFD数值模拟和实验验证,获得了采用新型倾斜翅片管束的自然通风空冷凝汽器的空气流场和温度场,计算得到了不同环境风速下空冷凝汽器总换热量的变化规律,并与现有翅片管束的空冷凝汽器性能进行了对比。研究结果表明,采用倾斜翅片空冷凝汽器可以显著改善自然通风直接空冷系统热力性能,降低机组背压,提高空冷机组运行的经济性。     

椭圆管H型翅片的翅片效率计算

H型翅片管广泛应用于大型电站锅炉省煤器。根据椭圆管H型翅片的结构和传热特点,推导并提出了分别基于等效圆管环形翅片、等效矩形翅片的3套椭圆管H型翅片的翅片效率计算方法;结合模化试验结果,比较、分析了不同计算方法的差异以及H型翅片结构(翅片开缝宽度与翅片宽度之比s/w)对此差异的影响。结果表明:基于等效圆管环形翅片的计算方法更为合理,且受s/w的影响较小。研究成果可为H型翅片椭圆管束的试验研究和工程实际应用提供参考。     

管间距对开缝翅片管换热器传热与阻力特性的影响

为了获得管间距对开缝翅片管换热器传热与阻力特性的影响规律,对5种不同翅片管换热器进行了数值模拟研究,并进行了模化试验验证。结果表明:开缝翅片管束的传热和阻力特性与翅片侧气体的Re数有关,随着Re数增大,翅片侧Nu数增大,摩擦因子f逐渐减小;纵向间距S2对开缝翅片管换热器的综合流动传热性能的影响较大。数值模拟与试验结果偏差较小,采用数值模拟方法能够比较准确地分析开缝翅片管换热器的传热与阻力特性。     

螺旋翅片管束在余热锅炉中应用分析

在分析余热锅炉受热面传热特点的基础上,指出螺旋翅片管束在余热锅炉中应用的重要性。根据螺旋翅片管束的特点及其在常规电站锅炉中的应用情况,指出了螺旋翅片管束在余热锅炉中应用需解决的问题。     

Heat transfer characteristics in low-temperature latent heat storage systems using salt-hydrates at heat recovery stage

The heat transfer characteristics of a low temperature latent heat storage system have been determined for circular finned and unfinned tubes using sodium acetate trihydrate as a phase change material (PCM). In the heat recovery stage, supercooling of PCM in the finned-tube system is larger than that in the unfinned-tube system. The heat-transfer coefficient between the PCM and the heat-transfer tube surface can be predicted from the steady-state heat conduction equation except the beginning of freezing with some degree of supercooling. The heat transfer is significantly reduced by the void cavities upon shrinkage of PCM in the finned-tube system. The enhancement of heat transfer by thin finned-tube over the unfinned-tube is found to be negligible. The heat-transfer coefficient in the thick finned-tube system is approximately two times higher than that in the unfinned-tube system. The heat transfer coefficients for the unfinned-tube and thick finned-tube systems are found to be 45 150 W/m²-K and 90 250 W/m²-K, respectively. The thermal performance for three different tube systems is found to be strongly affected by the inlet temperature but not by the flow rate of the heat transfer fluid. The amount of heat recovered has been correlated in terms of the Fourier, Stefan, and Reynolds numbers.     

Improvement of heat transfer with perforated circular holes in finned tubes of air-cooled heat exchanger

The present study investigated the effect of perforated circular finned-tube (PCFT) on the convective heat transfer performance of circular finned-tube heat exchangers. The air-side convective heat transfer coefficients increased by 3.55% and 3.31% for 2-hole and 4-hole PCFT cases, respectively. The increase in the convective heat transfer coefficient was related to the reduction of the recirculation region by introducing the perforations at the flow-separation locations on the finned tube. The pressure drop across the finned-tube bundles increased by 0.68% and 2.08% for the 2-hole PCFT and 4-hole PCFT cases, respectively. The greater pressure drop in the case of the 4-hole PCFT might be due to excessive flow disturbances produced by multiple perforations. The fin factor defined as the ratio of the % increase of the convective heat transfer coefficient and that of the pressure drop was 5.19 for the 2-hole PCFT case, whereas that was 1.59 for the 4-hole PCFT case.     

Thermofluid characteristics of frosted finned-tube heat exchangers

The performance of frosted finned-tube heat exchangers of different fin types is investigated by experiments in this paper. The effects of the air flow rate, the air relative humidity, the refrigerant temperature, and the fin type on the thermofluid characteristics of the heat exchangers are discussed. The time variations of the heat transfer rate, the overall heat transfer coefficient, and the pressure drop of the heat exchangers are presented. The heat transfer rate, the overall heat transfer coefficient, and the pressure drop for heat exchangers with re-direction louver fins are higher than those with flat plate fins and one-sided louver fins are. The amount of frost formation is the highest for heat exchangers with re-direction louver fins.     

Peripheral fins for blockage robustness

A peripheral finned-tube, cross-flow heat exchanger (evaporator) is briefly introduced that allows for uninterrupted and effective air flow in the presence of condensate or frost. The peripheral fins are connected to tubes with radial fins and the surface areas of both radial and peripheral fins allow for surface-convection heat transfer. The peripheral fins have a staggered arrangement to allow for alternate air flow paths in the presence of a blockage. Optimized fin structure is sought using one-dimensional fin models. The peripheral fins allow for significant surface-convection by using the stagnation–flow regions as well as the boundary–layer break ups. The CFD results show that the peripheral fins mitigate the pressure drop penalty due to blockages and in this regard present an advantage over the conventional fins. CFD results show that fin pitch can be optimized. The anisotropy of the peripheral fin structure may also allow for easy drainage of the condensate along the tubes when tubes are along gravity.     

Numerical research on heat transfer and flow resistance performance of specially‐shaped rod baffle heat exchangers

In order to overcome the disadvantages of heat transfer performance in the shell side of the common circular cross section rod baffle heat exchanger with a low Reynolds number, a numerical simulation on fluid flow and heat transfer in the shell side with different types of rod baffles is carried out. The rod baffles include the circular cross section, trigonal cross section, and rhombic cross section. The influence of heat transfer enhancement and flow resistance reduction affected by baffles is summarized. It is indicated that the trigonal and rhombic cross section rod baffles present the better performance of heat transfer enhancement and flow resistance reduction. With the rhombic cross section rod baffles in the shell side, the higher heat transfer coefficient and overall property in the shell side are achieved when Re is lower, and the heat transfer coefficient in the shell side is 10% higher than that of a circular cross section rod baffle at the same Reynolds number. The trigonal and rhombic cross section rod baffles in the shell side give more optional structure forms for expanding the application scope of rod baffle heat exchangers. © 2011 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.20388     

三角扰流蛇形翅片管流动换热特性数值研究

蛇形翅片管作为空冷凝汽器基本换热面,其流动与换热性能对空冷电站经济性有着重要影响,基于此,对三角扰流蛇形翅片管的气侧换热及流动特性进行了数值研究,分析了流体温度、压力沿流程方向的变化规律以及迎面风速、扰流三角个数、扰流三角尺寸等因素对蛇形翅片管换热及流动性能的影响,结果表明三角扰流部位局部阻力是沿程阻力的25%～70%,扰流三角对换热有明显的促进作用,换热系数最大提高37%.本研究可为蛇形翅片管的设计及优化提供理论参考.     

不同排列方式下三角翼波纹翅片管换热器的换热性能比较

应用三维数值模拟的方法对加装三角翼涡发生器的波纹翅片管换热器的流动换热特性进行了研究.3排换热圆管按顺排和叉排2种方式排列.结果表明:三角翼产生的纵向涡包括1个主涡和1个角涡.顺排布置时,纵向涡不但改善了尾迹区的换热,同时还大大强化了三角翼下游管排壁面的换热;叉排布置时,纵向涡在遇到后一个波谷时很快被抑制,换热的强化主要作用于尾迹区.ReD=3000时,与无三角翼的波纹翅片相比,三角翼波纹翅片的j、f,因子在顺排和叉排布置中分别增加了15.4%、10.5%和13.1%、7.0%.在不同排列方式下,三角翼产生的纵向涡均提高了波纹翅片管换热器的换热性能.     

两种型号空冷器选用问题的分析

以某炼厂MTBE项目空冷器设计选型为依据,通过计算换热面积,分析风机使用效率、换热能力、运行寿命、维护、投资,比较常用的铝翅片圆管空冷器和钢制矩形翅片椭圆管空冷器的优劣,为石化装置的空冷器选型提供借鉴。     

发电机空冷器传热与阻力特性研究

随着空冷汽轮发电机容量的增大,发电机内各部件的发热量也随之增加,空冷技术的重要性日益突出。但我国的空冷技术与国外相比还有一定差距,因此,利用循环风洞对几个特定结构参数的翅片式空冷器进行了模化试验研究,获得了空气侧传热与阻力特性的准则关系式,就试件结构参数对传热及阻力特性的影响机理做了详细的分析。试验结果不但为国产空冷器的性能与结构优化提供了计算方法,而且为空冷器制造企业实现自主研发提供了可靠的依据。