Liquid crystal technique application for heat transfer investigation in a fin-tube heat exchanger element

The use of thermochromic liquid crystal technique (LCT) and true-colour image processing system in heat transfer modelling is described. Experimental procedure, led on rig at Technical University of Gdansk, cover full-field flow patterns in heat exchanger element (flat plate with fine-tubes in-line, staggered and with vortex generators) describing local heat transfer coefficient and Nusselt number on the surfaces. Also the dependence of average heat transfer and pressure drop on Reynolds number and geometrical parameters is investigated.     

侧置三角小翼的管翅式换热器特性研究

通过三维数值模拟,对侧置三角小翼纵向涡发生器的顺排和叉排管翅式换热器的流动和传热特性进行了研究。结果表明:在研究的Re数范围内,采用侧置三角小翼措施后,无论对顺排还是叉排管翅式换热器,其换热增强的比例均大于阻力增大的比例;在低Re数时,采用该强化措施的结构比高Re数时具有更优的换热和阻力综合性能。侧置三角小翼强化换热的内在机理可以归结为改善了温度场和速度场的协同性,即减小了速度和温度梯度间的夹角。     

叶片尾缘内冷通道中最佳强化传热的针肋排列结构研究

本文应用湍流模型对涡轮叶片尾缘针肋通道的换热与流动进行了二维数值模拟研究。为了研究通道内针肋排列 方式对换热与流动的影响,对三种不同的针肋排列方式的通道进行了数值模拟计算。比较了顺排和叉排的区别,并提出了 一种沿流向叉排的针肋排列方式,且对各种排列的传热和阻力特性进行了综合分析和比较。     

EXPERIMENTAL STUDY OF HEAT TRANSFER FROM A DISCRETE SOURCE TO A CIRCULAR LIQUID JET WITH ANNULAR COLLECTION OF THE SPENT FLUID

This study reports an experimental investigation of evaporative heat transfer and pressure drop of R-134a flowing downward inside vertical corrugated tubes with different corrugation pitches. The double tube test section is 0.5 m long with refrigerant flowing in the inner tube and hot water flowing in the annulus. The inner tubes are comprised of one smooth tube and three corrugated tubes with different corrugation pitches of 6.35, 8.46, and 12.7 mm. The test runs are performed at evaporating temperatures of 10°C, 15°C, and 20°C; heat fluxes of 20, 25, and 30 kW/m²; and mass fluxes of 200, 300, and 400 kg/m²s. The experimental data obtained from the smooth tube are plotted with flow pattern map for vertical flow. Comparisons between smooth and corrugated tubes on the heat transfer and pressure drop are also discussed. It is observed that the heat transfer coefficient and frictional pressure drop obtained from the corrugated tubes are higher than those from the smooth tube. Furthermore, the heat transfer coefficient and frictional pressure drop increase as the corrugation pitch decreases. The maximum heat transfer enhancement factor and penalty factor are up to 1.22 and 4.0, respectively.     

高效低阻强化换热技术的三场协同性探讨

在流场和温度场协同的基础上,分析了流场和压力场的协同配合关系.分析表明:在换热强化基本相同的情况下,增大速度和压力梯度间的夹角,可以改善速度场和压力场的协同性,从而减小压降的增大,实现较小压降下获得较高的换热性能.说明了高效低阻强化换热的技术在于温度场、速度场和压力场的较好协同.     

Numerical and Experimental Comparative Study on Nanofluids Flow and Heat Transfer in a Ribbed Triangular Duct

Numerical and experimental investigation is carried out to study the effect of combined vortex generator and nanofluids on turbulent heat transfer and fluid flow characteristics in an equilateral triangular duct. A triangular duct provides a lower heat transfer rate and lower pressure drop compared to other duct configurations. The improvement of heat transfer of these ducts increases their importance for providing higher heat transfer and lower pressure drop. Two different types of nanoparticles, namely Al₂O₃ and SiO₂, suspended in distilled water with two particle concentrations are successfully prepared and experimentally tested. The numerical and experimental results show dramatic heat transfer enhancement by using a vortex generator and nanofluids, simultaneously accomplished with a moderate increase in the friction factor. A low deviation has been seen between the present numerical and experimental results.     

几何参数对低波纹通道流动与换热特性的影响

本文对几种不同几何模型的低波纹通道进行了传热及阻力性能数值研究,在一定的流速范围内得出了传热和阻力的特性曲线.分析了通道高度、波纹波峰高度、通道宽度对流动与换热的影响.结果表明,通道高度越小,换热越强,同时压降也增加;波纹波峰高度越大,换热加强,压降也相应增加;通道宽度越大,换热几乎不变,但压降随之降低.     

Effects of fin pitch and tube diameter on the air-side performance of tube bank fin heat exchanger with the fins punched plane and curved rectangular vortex generators

Tube bank fin heat exchangers with vortex generators are widely used in the field of industrial applications. The effects of the fin pitch and the tube diameter on the air-side performance of the tube bank fin heat exchanger with plane rectangular vortex generators (PRVG) and curved rectangular vortex generators (CRVG) are experimentally studied in this paper. Performance comparison is carried out between the fins with PRVG and CRVG. The experimental results show that both PRVG and CRVG can effectively enhance heat transfer performance compared with the plain fin. Both the fin pitch and the tube diameter have obvious effect on f compared with the effect on Nu, especially for the fin with PRVG. The characteristics of Nu, f, and Nu/f^1/3 are different for the fins with PRVG and CRVG. The fin with CRVG has a better heat transfer performance than the fin with PRVG for all the cases studied in this paper.     

肋片双面带涡产生器的扁管管片式散热器数值研究

采用数值模拟的方法,研究了流道内上下两肋片均布置有涡产生器的扁管管片式散热板芯的传热与阻力特性,并与流道单面布置涡产生器的换热板芯进行了对比.结果表明,采用双面带涡产生器的肋片表面能在提高Nu的同时,降低流动阻力,换热性能得到了明显的提高,在Re=1500时,平均Nu数提高了8.6%,横向平均Nu最大提高了30%,阻力下降了6.5%.     

原表面回热器换热阻力特性试验研究

本文对研制加工的适用于 100 kW 微型燃气轮机的 CW(Cross Wavy) 原表面回热器进行了试验研究,通过对两侧流体进、出口温度、压力等的测量,重点分析了燃气流量、入口温度及空气进口压力变化对换热阻力的影响,得出了在变工况下回热器的流动与换热性能规律,结果表明:所研制的 CW 原表面回热器空、燃气两侧换热均匀,提高了换热效率,两侧压降都有不同程度降低,并得出了有工程应用价值的 Nu-Re 及 f-RE 准则关系式,可为原表面回热器的设计制造提供参考.     

高温空气在蜂窝陶瓷体内蓄热特性研究

采用数值模拟方法对不同孔隙率和孔壁厚的蜂窝陶瓷体的蓄热特性进行研究。对高温空气在不同结构的蜂窝陶瓷体内流动过程中的压降、温度及蜂窝陶瓷体的蓄热特性进行了分析。研究结果表明：流体在蜂窝陶瓷内流动时,处于层流阶段的压降仅为湍流情况下的1／10。蜂窝陶瓷蓄热体的蓄热时间与蓄热体的孔壁厚成正比。蓄热体孔壁厚h=2mm时,出口空...     

汽车空调用冷凝器总成的分析与研究

1引言在汽车空调冷凝器性能评价中，流动与传热特性无疑占有重要位置，但它并非唯一评价指标。象其它热交换器一样，评价其是否具有应用价值，影响因素较多，例如：（1）以流动与传热为代表的热工性能；（2）可靠性与寿命评价；（3）材料与工艺性能；（4）制造成本；（5）体积、重量与噪音等指标。目前，汽车空调冷凝器分为三种：管片式、管带式和平行流式。许多文献认为，平行流式的热工性能最优，而管片式最欢，但这并不意味着平行流式肯定将成为我国汽车空调冷凝器的发展趋势。本文认为：（1）平行流式工艺复杂，所需材料近期内难以国产…     

高粘度流体横掠花瓣管管束的参数优化

运用数值模拟和正交试验的方法,设计并开展了高粘度流体横掠花瓣形翅片管管束的试验。试验选取了实际中一个有代表性的结构进行建模,依据流速、翅片高度、节距和偏转角度的不同取值进行分组,对每一组数值计算,从而确定了流体在花瓣形翅片管管外流动的对流换热系数α和压降Δp的影响因素及其影响情况。用传热综合因子η来评估传热效果的好坏,结果表明u=0.5m/s,a=2.5mm,b=0.9mm,β=6°为最优的参数组合,综合传热因子达到1.9。     

EXPERIMENTAL INVESTIGATION OF HEAT TRANSFER AND PRESSURE DROP CHARACTERISTICS OF W-TYPE SPIRALLY FLUTED TUBES

A new w-type spirally fluted tube with enhanced heat transfer characteristics was developed and manufactured. The heat transfer and pressure drop characteristics of tubes with various geometric parameters were measured over a range of Reynolds numbers from 8,000 to 30,000 for water flowing horizontally through the tube with steam condensing on the outside surface. Experimental correlations for the pressure drop and the heat transfer coefficient were developed from a large amount of data using multivariable linear regression analysis. Factors influencing the heat transfer and flow were analyzed. The experiments showed that heat transfer coefficient can be increased by 3–8% with the pressure drop reduced by 5–10% compared with an ordinary spirally fluted tube.     

载气汽油在水平螺旋扁管管束中的沸腾换热

以汽油-空气为介质,在不凝性气体质量含量不超过5%时,对导程为200mm的螺旋扁管管束中的沸腾换热进行了实验研究,分析了沸腾换热系数随两相质量流量的变化规律以及流动压降随空气流量的变化规律。得到了相应条件下,载气汽油在该导程的螺旋扁管管束中的沸腾换热实验关联式。     

内嵌微流道低温共烧陶瓷基板传热性能（英）

随着系统级封装（SIP）所容纳的电子元器件和集成密度迅速增加,传统的散热方法（热通孔、风冷散热等）越来越难以满足系统级封装的热管理需求。低温共烧陶瓷（LTCC）作为常见的封装基板材料之一,设计并研制了三种内嵌于LTCC基板的微流道,其中包括直排型、蛇型和螺旋型微流道（高度为0.3 mm,宽度分别为0.4, 0.5和0.8 mm）。通过数值仿真和红外热像仪测试相结合的方式分析了微流道网络结构、流体质量流量、雷诺数、材料热导率对内嵌微流道LTCC基板换热性能的影响,实验结果表明:当去离子水的流量为10 mL/min,热源等效功率为2 W/cm2时,直排型微流道的LTCC基板最高温度在3.1 kPa输入泵压差下能降低75.4 ℃,蛇型微流道的LTCC基板最高温度在85.8 kPa输入泵压差下能降低80.2 ℃,螺旋型微流道的LTCC基板最高温度在103.1 kPa输入泵压差下能降低86.7 ℃。在三种微流道中,直排型微流道具有最小的雷诺数,在相同的输入泵压差下有最好的散热性能。窄的直排型微流道（0.4 mm）在相同的流道排布密度和流体流量时比宽的微流道（0.8 mm）能多降低基板温度10 ℃。此外,提高封装材料的热导率有助于提高微流道的换热性能。     

不同布置形式百页窗翅片通道热力性能的试验研究

本文以空气为介质,对四组百页窗式翅片通道的传热特性和流动阻力进行了试验研究。四组试验件的几何尺寸相同,只是翅片上百页窗的开窗段不同,分别是３ｍｍ、 ６．５ ｍｍ、前３ｍｍ后 ６．５ ｍｍ及各组开窗段间距交替为 ３ ｍｍ与 ６．５ ｍｍ。传热试验得出的四种试验通道 Ｎｕ～ Ｒｅ关系相同,而阻力则以开窗段间距 ３ ｍｍ的为最低。     

车用温差发电装置换热性能的数值模拟研究

建立了用于汽车尾气温差发电器的尾气通道和冷却水通道热交换的三维模型,在运行工况下,对光滑尾气通道和带有平直翅片的尾气通道的换热性能进行了数值模拟,其中翅片通道结构包括了不同的翅片高度以及翅片间距.根据模拟结果并结合通道的压降,得到了翅片高度为9mm、间距为2mm的翅片通道结构为较优的通道结构.结合翅片尾气换热通道的换热...     

带扰流微细槽道冷却系统的实验研究

 针对高热流密度器件的散热问题,设计了有扰流微细槽道散热器。采用去离子水为工作介质,对其内流动和换热特性进行实验研究,结果表明：流体流过槽道时单位长度压降与雷诺数成正比,扰流对槽道内压降特性影响较小;存在最佳的雷诺数使有无扰流情况下槽道内换热努谢尔特数差别最大,并拟合了不同情况下努谢尔特数和雷诺数的关系式;采用进口段无量纲加热长度分析发现,扰流导致流体的热进口段长度增加;分析压降和进口热阻特性可以发现,在槽道长度一定时存在最佳流速使带扰流的微槽道的性能最佳。     

一种内螺纹强化管的冷凝实验研究

实验研究了环保替代制冷工质R410A、R22在水平强化管内冷凝换热特性,探索了热流密度、水流速度对换热特性、压降的影响。实验测试管为内螺纹强化管,长度为5.2 m,外径为9.52 mm。实验结果表明:制冷剂R410A、R22的传热系数和压降随热流密度的增大而增大,同时内螺纹管的换热系数还随管外冷却水流量的增加而升高,压降随冷凝温度的升高而降低,而R410A比R22有更好的换热效率和较小的压降。