1000MW直接空冷机组散热单元换热特性的数值模拟

以某1 000MW直接空冷机组为例,对机组散热器外部流场进行了数值模拟,分析了不同迎面风速、环境温度、翅片间距以及翅片厚度对散热器外部换热和流动特性的影响.结果表明:随着迎面风速的增大,散热器外部的传热系数和流动阻力均显著增大,环境温度对散热器外部换热和流动特性的影响并不明显,但对总散热量影响较大;较大的翅片间距能增大散热器外部的传热系数、减小流动阻力,但会使单位管长的换热面积减小,总散热量减小;对应于一定的迎面风速,存在较为合理的翅片间距和翅片厚度,迎面风速越大,合理的翅片间距越大,翅片厚度越小.     

百叶窗翅片结构对空气侧流动换热影响的研究进展

百叶窗翅片作为换热器主要翅片形式之一,其结构对空气侧流动换热特性有着重要影响。本文总结了近年来国内外在百叶窗翅片结构对空气侧流动换热影响方面的研究,包括翅片间距、翅片高度、翅片厚度、翅片深度、百叶窗间距及开窗角度对空气侧换热系数、压降、流动效率、传热因子和摩擦因子的影响。研究表明:传热因子随开窗角度和翅片深度的增加而增大,随翅片间距的增加而减小;摩擦因子随开窗角度的增大而增大,随百叶窗间距的增大而减小;其中,开窗角度与翅片深度分别是影响空气侧流动和换热的最主要因素。最后,在百叶窗结构的基础上,提出了对翅片表面进行处理以及使用新型翅片结构等途径来进一步强化空气侧流动换热的建议。     

百叶窗板翅式换热器换热与阻力性能数值模拟研究

为了解决百叶窗板翅式换热器的内部性能优化问题,通过对层流稳态下换热器燃气侧的典型流动换热单元进行建模及流动换热分析,得到了单元体内部速度、流线及温度的分布特性,并通过对换热系数、科尔本传热因子、进出口单位压降、范宁摩擦系数的比较,获得了不同燃气入口速度下翅片间距及翅片角度对换热器换热性能及流动阻力的影响。结果表明:在百叶窗翅片角度及其他尺寸参数不变时,当百叶窗间距为0. 7 mm时其换热性能最优,阻力随间距增大而减小;在翅片间距等参数不变而角度变化时,换热性能与阻力均随角度增大而增大,当百叶窗角度从15°增加至30°时,换热性能的增加幅度较为明显。     

百叶窗翅片管换热器空气侧传热和流动特性数值模拟

采用数值模拟方法对百叶窗翅片管换热器空气侧传热和流动特性进行研究,分析管排数、开窗角度和翅片间距对百叶窗翅片管换热器空气侧性能的影响.结果 表明:空气侧传热系数随管排数增多而降低,最大降幅约12.5％,压降随管排数增多而增大;低雷诺数下百叶窗角度为20°时换热器具有较好的综合性能,较大雷诺数下25°为最佳百叶窗角度;随...     

翅窗间距比对管带式散热器综合性能的影响

为评价散热器的综合性能,对空气流经不同翅窗间距比(F_p/L_p)的百叶窗翅片的流动传热进行数值模拟。首先,得到翅窗间距比与翅片热力性能之间的变化规律:F_p/L_p=0.8~1.1时,传热因子j随F_p/L_p增大而减小;F_p/L_p=1.1~1.2时,j随比值的增大而增大;F_p/L_p1.2时,j随比值增大而减小;阻力因子f则随F_p/L_p增大而减小。同耗材热力性能评价因子j/f1/3先随F_p/L_p增大而增大,在F_p/L_p=1.3处达到最大值,随后略有下降。为反映由散热器紧凑性变化导致的体积变化,引入同体积热力性能评价因子FNTU/f1/3,结果发现:与评价因子j/f1/3不同,FNTU/f1/3随F_p/L_p增大而减小,F_p/L_p1.2时则有小幅回升。最后,为了综合评价散热器性能,提出权衡系数η来体现各个比值的优势,可由此根据实际需求选择翅窗间距比。     

高性能商用车用散热器轻量化设计

为提高商用车冷却模块散热性能,实现冷却模块轻量化,采用计算流体动力学方法分析散热器的散热带高度、波峰距、开窗角度对散热性能的影响,得到最佳冷却模块性能参数;对散热器结构进行优化,并对优化后的散热器进行风洞试验和整车热平衡试验。结果表明：优化后的散热器质量减轻17.9%,散热性能提升1%～8%;通过优化散热带高度、波峰距以及开窗角度,可以提高冷却模块散热性能,实现轻量化,降低生产成本。     

翅片式热管散热器自然对流换热特性分析与多目标结构优化

采用数值计算方法对一种应用于半导体制冷片热端散热的翅片式热管散热器进行模拟,探究自然对流条件下不同翅片参数对散热器换热特性的影响。结合多目标遗传算法(NSGA-Ⅱ),以影响散热器散热的两个主要参数——翅片表面传热系数和肋面效率为优化目标,对散热器整体做出综合优化,并对优化结果进行K均值聚类分析,提出了翅片端优化原则。结果表明,肋面效率对散热器性能的影响有限,提高表面传热系数可显著降低散热器总热阻;与未优化方案相比,所选优化方案可使基板热端面温度下降3.5K,散热器热阻降低18.22%。     

微槽群平板热管散热器传热性能的研究

分别选择不同的翅片间距和高度,对一种新型微槽群平板热管散热器的翅片结构进行优化,得到了热管散热器的最佳整体结构。结果表明:翅片的间距为14mm、高度为60mm时,平板热管散热器的传热性能最好。将热管、管脚以及翅片的温度与实验结果进行对比,结果吻合良好。     

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。     

CO_2微通道气冷器翅片结构对换热性能影响的模拟研究

本文选择适用于微通道换热器的CO_2换热关联式,创建CO_2微通道气冷器的二维模型。采用有限体积法将微通道分成多个微元段,利用Matlab结合Refprop软件计算每个微元段中的流动和换热。用实验结果验证了建立的仿真程序的合理性,模拟翅片结构对换热器性能的影响,依据信噪比的田口方法计算了翅片结构对换热器性能的贡献率,提出了适用于本模型的最佳翅片结构。得出:CO_2微通道换热量和压降随着空气侧的翅片间距和翅片高度的增大而减小,随着翅片宽度的增大而增大,翅片厚度的影响较小;翅片结构对微通道气冷器的性能影响的贡献率分别为:翅片高度42.45%,翅片间距25.73%,翅片宽度24.32%,翅片厚度为7.50%;最佳翅片结构为:翅片高度8 mm,翅片间距1.15mm,翅片宽度17.28 mm,翅片厚度0.08 mm。     

Experimental study on thermal performance of optimum PG brine as a radiator coolant

The present study deals with the experimental impact of an alternative heat transfer fluids for overall performance improvement for radiators. Water and water mixed with anti‐freezing agents such as ethylene glycol (EG) and propylene glycol (PG) are the traditional coolants for an automotive radiator. Comparison of experimental and numerical analysis of optimum brine solution, that is 25% of propylene glycol and water as coolant for the rectangular fin radiator, has been well discussed. A closed loop test rig was designed, and fabricated with a wind tunnel section to achieve uniform velocity at the test section of the rectangular radiator and was tested for performance. Experimental runs were conducted at varying operating temperatures which included the runs for water, and an optimum propylene glycol brine solutions at 70 °C and 80 °C with various flow rates. Results show the energy performance of an optimum brine solution was nearly similar to that of water at high temperatures. The Nusselt number, heat transfer coefficient, and heat transfer rate for an optimum propylene glycol brine is nearly the same as water at 80 °C with a maximum deviation of 15%, 5.7%, and 6.6%, respectively, for theoretical and experimental result comparisons. Air side and coolant side pressure drops had a maximum deviation of 3.66% and 6.6%, respectively. Air and coolant exit temperatures had a deviation of 5% and 3.5%, respectively, with an air frontal velocity of 4.6 m/s in a rectangular fin radiator for an optimum brine solution used as coolant for the automotive radiator. The optimum propylene glycol brine may be environmentally beneficial.     

Multiwalled Carbon Nanotube Nanofluid for Thermal Management of High Heat Generating Computer Processor

Minichannel heat sink geometries with varying fin spacing were tested with de‐ionized water and MWCNT (1 wt %) nanofluid to evaluate their performance with flow components of a liquid cooling kit. Four heat sinks with fin spacing of 0.2 mm, 0.5 mm, 1.0 mm, and 1.5 mm were used in this investigation. Heat sink base temperature was analogous to processor operating temperature which was the prime parameter of interest in this investigation. The base temperature decreased by reducing the fin spacing and using multiwalled carbon nanotube (MWCNT) nanofluid. The lowest value of heat sink base temperature recorded was 49.7 ^°C at a heater power of 255 W by using a heat sink of 0.2 mm fin spacing and MWCNT nanofluid as a coolant. Moreover, as a result of reduced fin spacing and using MWCNT nanofluid as a coolant the value of overall heat transfer coefficient increased from 1200 W/m²K to 1498 W/m²K, translating to about a 15% increase. The value of thermal resistance also dropped by reducing the fin spacing and using MWCNT nanofluid. The most important aspect of the study is that the heat sinks and MWCNT nanofluid proved to be compatible with the pump and radiator of the commercial CPU liquid cooling kit. The pump was capable to handle the pressure drop which resulted by reducing the heat sink fin spacing and by using MWCNT nanofluid. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res, 43(7): 653–666, 2014; Published online 11 November 2013 in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.21107     

R134a在水平内微翅管管内凝结换热的实验研究

对制冷剂R134a在水平强化换热管管内的凝结换热性能进行了实验研究。实验管为两种内微翅管,分别命名为A管和B管。实验件采用套管结构,强化内管外表面和外管内表面之间(管间)走乙二醇水溶液。实验过程中管内冷凝温度为51℃,管间乙二醇水溶液的流速为3.35 m/s,乙二醇水溶液的进口温度根据制冷剂的质量流速做相应调整,以保证试件出口制冷剂有一定的过冷度。实验结果表明:两种水平强化管的管内冷凝换热系数均随着制冷剂质量流速的增加而增大,在制冷剂质量流速从300 kg/(m2.s)增加到700kg/(m2.s)时,A管的管内冷凝换热系数比B管高1.87%到6.28%,而B管的制冷剂流动阻力比A管高9.56%到11.05%,A管的结构优于B管。     

房室间隔缺损介入治疗失败后外科手术治疗的回顾性分析

目的探讨房室间隔缺损介入治疗失败后外科手术的原因及效果,以提高手术成功率。方法选择２０００年１月至２００７年１２月接受经导管介入治疗房间隔缺损（ASD）和室间隔缺损（VSD）失败后,需行外科手术的１３例病例进行回顾性分析。外科手术指征为封堵器脱落７例、Ⅲ°房室传导阻滞（AVB）３例、瓣膜关闭不全２例（其中１例同时合并Ⅲ°AVB）、残余漏１例、封堵失败１例。手术均在体外循环下进行,取出封堵器,修复心内畸形,术后入ICU监护。结果ASD介入治疗患者中,手术探查ASD直径平均３１mm,较术前诊断的平均２６mm增大,两者相比差异有统计学意义（P＜０．０５）。ASD部位为中央型３例,下腔型６例,与术前诊断符合率为４１．７％,不符合率为５８．３％（P＞０．０５）。３例Ⅲ°AVB者术后均恢复窦性心律。心内畸形修复完善,无手术死亡。结论及时采取外科手术治疗介入封堵失败后并发症,效果良好,安全可靠,可避免治疗失败及术后并发症。     

Effect of electric field on heat transfer performance of automobile radiator at low frontal air velocity

The effect of electric field on the performance of automobile radiator is investigated in this work. In this experiment, a louvered fin and flat tube automobile radiator was mounted in a wind tunnel and there was heat exchange between a hot water stream circulating inside the tube and a cold air stream flowing through the external surface. The electric field was supplied on the airside of the heat exchanger and its supply voltage was adjusted from 0 kV to 12 kV.From the experiment, it was found that the unit with electric field pronounced better heat transfer rate, especially at low frontal velocity of air. The correlations for predicting the air-side heat transfer coefficient of the automobile radiator, with and without electric field, at low frontal air velocity were also developed and the predicted results agreed very well with the experimental data.     

Exergy and energy analysis of a wavy fin radiator with variously shaped nanofluids as coolants

The present study deals with the energy and exergy analysis of a wavy fin radiator deploying various shapes of Al₂O ₃‐water as nanocoolant. The effects of radiator effectiveness, pumping power, heat transfer rate, and performance index with variously shaped nanoparticles, mainly spherical, brick, and platelet, on coolant flow rates and air velocities have been investigated. Also, the impacts of entropy, second law efficiency, entropy generation number, and irreversibility on radiator performance analysis have been considered with steady‐state assumptions. Theoretical analysis revealed that the spherical particle–based nanocoolant showed 21.9%, and 18.2% higher effectiveness than platelet and brick nanocoolants. However, minimization in the entropy generation is observed in the platelet shape of the nanoparticle. The second law efficiency is 13% higher for the spherical nanocoolant compared with the brick nanocoolant. An optimum entropy generation number is found at a coolant flow rate of 13 l/min and then gradually decreases with an increase in the coolant flow rate. For all the considered operating parameters, the spherical nanoparticle showed a better performance than brick and platelet nanofluids as a radiator coolant. Due to the enhanced overall performance for the spherical nanofluid, it may be considered as a potential candidate for a radiator coolant.     

Effects of Working Fluid,Tubeside Enhancement and Bundle Depth on the Optimized Fin Geometry of a Horizontal Condenser Tube

A theoretical study has been made to optimize the fin geometry of a horizontal finned tube which is to be usedfor condensers that handle the vapor load of a liquid phase change cooling module.Systematic numerical calcu-lations of the vapor to coolant heat transfer have been performed for parametric values of fin height,fin spacing,vertical bundle depth and tubeside heat transfer coefficient.Three dielectric fluids (R-113,FC-72,and FC-87)at atmospheric pressure were selected as the working fluids.For a single tube with optimized fin geometry,theaverage heat flux increased in the order of FC-87,R-113 and FC-72.Both the optimum fin height and optimumfin spacing increased with increasing vertical bundle depth.     

电子元件散热器翅片自然对流散热性能研究

针对室外电子设备在自然对流条件下的散热问题,设计开发了一种新型散热器翅片结构——翅片开孔式涡流发生器,易于加工且直接与翅片连接,不存在焊接的问题.利用数值模拟的方法探究了涡流发生器的布置方式与攻角对散热器散热的影响.结果 表明:翅片开设三角孔,在翅片间空气流动过程中起到了明显的作用,有效降低了三角形涡流发生器造成的流动...     

Parametric studies on automotive radiators

This paper presents a set of parametric studies performed on automotive radiators by means of a detailed rating and design heat exchanger model developed by the authors. This numerical tool has been previously verified and validated using a wide experimental data bank. A first part of the analysis focuses on the influence of working conditions on both fluids (mass flows, inlet temperatures) and the impact of the selected coolant fluid. Following these studies, the influence of some geometrical parameters is analysed (fin pitch, louver angle) as well as the importance of coolant flow lay-out on the radiator global performance. This work provides an overall behaviour report of automobile radiators working at usual range of operating conditions, while significant knowledge-based design conclusions have also been reported. The results show the utility of this numerical model as a rating and design tool for heat exchangers manufacturers, being a reasonable compromise between classic ε − NTU methods and CFD.     

油浸式自冷变压器用三维肋管散热器换热特性研究

为研究三维肋管散热器的自然对流换热特性,分析不同温升下三维肋管散热器的强化换热性能,搭建了模拟油浸式自冷变压器工作过程的实验平台,在不同功率下分别测试了片间距为45 mm的片式散热器、排间距为45和55 mm的三维肋管散热器的进口温升,拟合得到散热器的温升-功率曲线,计算出3个散热器在相同温升下的散热量.研究表明:相比...