管束横向节距对气体冷却器换热及阻力特性影响试验研究

改善汽轮发电机冷却技术是提高汽轮发电机单机容量的最有效、最现实途径。气体冷却器是汽轮发电机的重要设备之一。其传热与阻力性能将直接影响汽轮发电机的运行经济性和可靠性。为实现汽轮发电机气体冷却器的优化设计,对管束不同横向节距的波纹翅片型穿片式冷却器的换热和阻力性能进行了试验研究,分析了管束横向节距对气体冷却器换热和阻力性能的影响规律。研究成果对汽轮发电机气体冷却器的结构与性能优化具有重要的指导作用。     

汽轮发电机气体冷却器性能试验研究

气体冷却器是汽轮发电机的重要设备之一。其传热与阻力性能将直接影响汽轮发电机的运行经济性和可靠性。为实现汽轮发电机气体冷却器的优化设计,对不同翅片间距的翅片管冷却器的传热和阻力性能进行了试验研究,得到了Re在3 000~190 000之间换热器翅片侧的传热和阻力特性,并分析了风速和翅片间距对气体冷却器传热和阻力性能的影响规律。研究成果对汽轮发电机气体冷却器的结构与性能优化具有重要的指导作用。     

穿片式气体冷却器研究进展

气体冷却器是汽轮发电机通风冷却系统的重要设备。其性能直接影响汽轮发电机的通风冷却效果及设备的运行可靠性。介绍了几种不同翅片形式（平直片、波纹片、条缝片、百叶窗片、穿孔片）的穿片式气体冷却器的换热和阻力特性的研究进展。通过对前人研究成果的归纳和总结,指出了以往研究的一些不足。     

发动机废气再循环冷却器性能计算仿真

发动机废气再循环是有效降低Nox的重要方法,废气再循环冷却器的设计开发显得尤其重要。本文,结合现有EGR冷却器结构参数,利用DOE的设计方法,通过对三种不同结构形式的EGR冷却器进行传热和阻力性能测试。同时通过多元回归分析,建立EGR冷却器热侧传热和流动实验关联式,并进一步利用Visual Baisc开发工具,建立EGR冷却器性能计算仿真平台。该仿真平台的开发,有效的提高了EGR冷却器设计计算精度和产品开发速度。     

空压机内置冷却器的热力性能优化

为了提升空压机内置冷却器的热力性能,选取冷却器的最小结构单元,基于k-ε湍流模型建立百叶窗翅片流动传热的数值模型,分析百叶窗翅片结构参数对冷却器内部流动传热特性的影响。结果表明：增大百叶窗倾角、翅片厚度,气流与翅片之间的对流传热能力增强,流动阻力增加;增加百叶窗间距,冷却器传热效果增强,流动阻力减小。百叶窗倾角为29°、间距为1.6 mm、翅片厚度为0.08 mm时,翅片的综合热力性能最佳。     

轧片式铝翅椭圆钢管空冷器的传热性能及流动阻力

轧片式铝翅椭圆钢管空气冷却器具有传热性能高 ,阻力系数低等优点 ,可应用于干旱缺水地区的空冷发电厂和大中型变压器等。给出了这种强化传热管束的试验测量结果。     

顺排与叉排套片式换热器的热力性能对比研究

套片式换热器的管束排列形式一般都是叉排,顺排非常少见。由于顺排形式的套片式换热器通常比叉排的流动阻力更小,因而对一些流动阻力有限制的场合,可以考虑使用顺排形式的套片式换热器。为论证这一点,对某种结构形式的顺排套片式换热器和叉排套片式换热器的热力性能进行了对比研究。为便于对比、分析,两个换热器试件的纵向管间距及管排数设计成相等。结果显示:两个试件的热力性能非常接近。分析表明,在某些应用场合,套片式换热器排列成顺排是更合适的选择。图7参6     

车辆发动机冷却模块试验与仿真研究

为了提高车辆发动机冷却模块传热与阻力性能的仿真精度,以某液压挖掘机包括增压中冷器、液压油冷却器和水箱散热器在内的冷却模块为研究对象,采用3D和1D联合仿真技术,对冷却模块各散热元件进行传热和阻力性能的仿真.进一步对冷却模块进行风洞试验,并将试验结果与仿真结果进行对比.仿真结果表明:该模型对增压中冷器、液压油冷却器及水箱散热器传热性能的偏差分别为-4.02 0A、-5.8%和4.37%,冷却模块系统阻力偏差为-7.38%.采用联合仿真技术相对于1D仿真,可明显提高仿真精度.     

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。     

圆弧型开缝翅片管空气冷却器传热与阻力特性试验研究

对3种不同翅片间距的圆弧型开缝翅片管空气冷却器进行试验研究,得到迎面风速在1.0~3.0 m/s空气侧传热与阻力特性变化规律,分析了迎面风速、翅片间距对换热器传热与阻力特性的影响;雷诺数Re在1200~3800,综合性能指标随着Re的增大而增大;当Re1800时,Pf=1.7 mm的综合流动传热性能最好,当Re1800时,Pf=2.5 mm的综合流动传热性能最好;圆弧型开缝翅片管的综合流动传热性能比平直翅片管高。     

含尘气流中换热器管壁磨损特性的实验研究

对光滑圆管(0—T管)、高频焊螺旋翅片管(HF—T管)及镍基渗层钎焊螺旋翅片管(HF—T—NL管)的磨损特性进行了实验研究，确定了各种管子的磨损量及磨损部位，并对其抗磨损性能进行了比较。结果表明：由于镍基渗层极大地提高了管材的表面硬度，同时有效地增强了管子的抗氧化腐蚀能力，从而使镍基渗层钎焊螺旋翅片管的耐磨损性能远远优于其它两种换热管。使用镍基渗层钎焊螺旋翅片管可大大地提高换热设备在高温含尘气流中的工作寿命。图6表4参9     

连续型与锯齿型螺旋翅片管翅片效率计算与分析

介绍了烟气换热领域常用的两类高频焊钢质螺旋翅片管.指出目前存在多种连续型与锯齿型高频焊螺旋翅片管翅片效率计算方法,不便于同类换热实验结果的相互比较.通过深入分析与计算比较,对连续型与锯齿型高频焊螺旋翅片管分别给出了建议的翅片效率计算方法,供相关的工程设计及实验研究选用.两种管型的翅片效率比较表明,锯齿翅片的翅片效率较高,提高的幅度随翅片高度增大而增大.     

新型钢制散热器翅片管的传热分析及优化

通过试验测得了翅片管的温度分布 ,得出这种新型散热器翅片管的自然对流换热规律。通过对试验数据的分析整理得到了肋壁平均换热系数的经验公式。分析了翅高比、翅片夹角对平均换热系数、平均辐射换热系数的影响。以金属热强度最大为目标函数 ,采用解多变量最优化问题的坐标轮换法得出了该形式翅片管的最佳结构尺寸。     

椭圆翅片管空冷器流动传热特性的研究

用稳态的恒壁温法对3个椭圆翅片管空冷器和1个圆翅片管空冷器的传热和阻力特性进行了研究,得到空冷器空气侧的传热与阻力性能,在相同的迎风面流速下,椭圆翅片管比圆翅片管空气侧换热系数约大3－7倍;在相同的换热系数下,椭圆翅片管比圆翅片管的压降低。     

径向错列翅片管内凝结对流换热数值模拟分析

采用数值模拟方法,对径向错列翅片管内含不凝结气体水蒸气的凝结对流换热及阻力特性进行了综合分析。将编写的自定义函数(UDF)导入ANSYS FLUENT软件,对新型强化管传热性能和阻力性能进行了数值模拟,并根据管长方向壁面上蒸汽质量分数的变化情况,讨论分析了凝结过程中翅片管传热性能的变化规律。分析结果表明:与光管相比,内翅片管的强化传热效果随翅数增多、翅片换热接触面积增大而更加显著;另一方面,翅片管的流动阻力相应增大,对管路换热产生不良影响。在所研究翅型范围内16翅y=2x~2型翅片管综合强化换热效果更优;此外随着换热过程的持续,蒸汽凝结逐渐放缓;入口速度增大导致水蒸气凝结不充分,对换热效果的提升有一定制约。     

The effect of the number of tube rows on heat,mass and momentum transfer in flat-plate finned tube heat exchangers

The effect of the number of tube rows on heat, mass and momentum transfer is experimentally investigated for flat-plate, finned-tube heat exchangers which consist of aluminum fins and copper tubes. Four flat-plate finned-tube heat exchangers are identical except for changes in the number of tube rows (1 to 4). Heat-transfer coefficients for wet and dry surface conditions are obtained for both heating and cooling of moist air flowing over finned tubes. The air velocity was varied from 0.9 to 4 m/s. Heat transfer, Colburn and friction factors are determinated for different tube rows numbers while the Reynolds number were being warried. It is found that the values of Colburn and friction factors for wet surfaces are higher than for dry surfaces and for both conditions the Colburn and friction factors decrease with an increase in the tube row numbers.     

滴状翅片管传热及阻力特性的试验研究

对滴状翅片管的传热及阻力性能进行了试验,给出了不同风速、温度下的试验结果。探讨了对流换热系数的分离方法。依据实测的数据,将管外空气横掠管簇的对流换热系数从传热系数中分离了出来。对管外的对流换热特性、阻力特性进行了分析研究,并整理成了无量纲准则式。试验表明滴状翅片管的阻力较小,试件性能达到国际先进水平。     

Numerical investigation of heat transfer and pressure drop in enhanced tubes

This study investigates passive heat transfer enhancement techniques to determine the distribution of temperature and static pressure in test tubes, the friction factor, the heat flux, the temperature difference between the inlet and outlet fluid temperatures, the pressure drop penalty and the numerical convective heat transfer coefficient, and then compares the results to the experimental data of Zdaniuk et al. It predicts the single-phase friction factors for the smooth and enhanced tubes by means of the empirical correlations of Blasius and Zdaniuk et al. This study performed calculations on a smooth tube and two helically finned tubes with different geometric parameters also used in the analyses of Zdaniuk et al. It also performed calculations on two corrugated tubes in the simulation study. In Zdaniuk et al.'s experimental setup, the horizontal test section was a 2.74 m long countercurrent flow double tube heat exchanger with the fluid of water flowing in the inner copper tube (15.57–15.64 mm i.d.) and cooling water flowing in the annulus (31.75 mm i.d.). Their test runs were performed at a temperature around 20 °C for cold water flowing in the annulus while Reynolds numbers ranged from 12,000 to 57,000 for the water flowing in the inner tube. A single-phase numerical model having three-dimensional equations is employed with either constant or temperature dependent properties to study the hydrodynamics and thermal behaviors of the flow. The temperature contours are presented for inlet, outlet and fully developed regions of the tube. The variations of the fluid temperature and static pressure along tube length are shown in the paper. The results obtained from a numerical analysis for the helically tubes were validated by various friction factor correlations, such as those found by Blasius and Zdaniuk et al. Then, numerical results were obtained for the two corrugated tubes as a simulation study. The present study found that the average deviation is less than 5% for the friction factors obtained by the Fluent CFD program while Blasius's correlation has the average deviation of less than 10%. The corrugated tubes have a higher heat transfer coefficient than smooth tubes but a lower coefficient than helically finned tubes. The paper also investigates the pressure drop penalty for the heat transfer enhancement.     

Heat transfer augmentation in 3D internally finned and microfinned helical tube

Experiments are performed to investigate the single-phase flow and flow-boiling heat transfer augmentation in 3D internally finned and micro-finned helical tubes. The tests for single-phase flow heat transfer augmentation are carried out in helical tubes with a curvature of 0.0663 and a length of 1.15 m, and the examined range of the Reynolds number varies from 1000 to 8500. Within the applied range of Reynolds number, compared with the smooth helical tube, the average heat transfer augmentation ratio for the two finned tubes is 71% and 103%, but associated with a flow resistance increase of 90% and 140%, respectively. A higher fin height gives a higher heat transfer rate and a larger friction flow resistance. The tests for flow-boiling heat transfer are carried out in 3D internally micro-finned helical tube with a curvature of 0.0605 and a length of 0.668 m. Compared with that in the smooth helical tube, the boiling heat transfer coefficient in the 3D internally micro-finned helical tube is increased by 40-120% under varied mass flow rate and wall heat flux conditions, meanwhile, the flow resistance is increased by 18-119%, respectively.