带扰流片的矩形通道的实验研究

以高温透平叶片冷却为应用背景，对带有顺排、错排扰流片的矩形通道进行了实验研究。实验结果表明：在相同的雷诺数下，错排扰流片比顺排扰流片具有更好的强化换热效果，即便保持相同的流动阻力，错排扰流片的冷却效果仍强于顺排扰流片。     

带扰流片的矩形直通道内的流动与换热

建立了矩形直通道内三维可压缩流动与换热模型 ,对来流雷诺数Re在 1× 10 5～ 3× 10 5范围内 ,带顺排和错排扰流片的通道内部对流换热过程进行了模拟计算。计算结果表明 ,矩形扰流片具有明显的强化冷却效果 ,扰流片表面的对流换热系数明显高于光滑表面的值 ,有扰流片区域的壁面温度明显降低 ;错排扰流片与顺排扰流片相比 ,对流换热系数增大 4 %左右。计算结果归纳了传热和流动压降关系式。     

燃气轮机叶片内部扰流肋冷却方式研究进展

随着燃气透平转子进口温度的不断提高,燃气轮机叶片冷却日益重要。带有扰流肋的内部通道冷却是叶片冷却的一个重要部分。综述了内部扰流肋冷却的研究历程与研究现状,详细论述了静止状态下带肋内部通道的换热研究、旋转对带肋通道内换热的影响研究以及扰流肋与其他方式相结合的复合冷却研究。结论指出,在国内外静止状态下带肋通道内的换热研究已经很成熟,旋转对通道内流动与换热的影响是最近几年来的研究热点,而关于旋转状态下复合冷却方式的研究相对较少。优化旋转状态下内部肋结构和将内部扰流肋与其他冷却方式相结合的研究是今后的发展方向。     

带扰流圆柱肋楔形通道的流动与换热数值研究

建立了带扰流圆柱肋楔形通道内的换热与压力损失数值计算模型,采用ANSYS-CFX商用软件数值研究了楔形通道内叉排和顺排柱肋的换热与压损特性,分析了流动与结构参数的影响规律。结果表明:随雷诺数的增大,柱肋表面、柱肋排以及通道底面的平均努赛尔数呈增大趋势;随着x/D的增大,柱肋表面和柱肋排的平均努赛尔数有所降低;随着楔形通道收缩角的增大,柱肋表面和通道底面的平均努赛尔数略有增强;相同条件下的叉排柱肋换热效果要好于顺排柱肋换热效果。范宁摩擦系数随雷诺数增加而略有增大,随x/D增大有较大的降低,随着收缩角的增大而增大。在计算参数内,叉排柱肋且x/D为1.5时的热力性能系数最高。     

新型温差发电装置的结构设计

分析了温差发电装置的内部结构对温差发电效率的影响,并在此基础上设计制作出了一种新型温差发电装置,其内部换热通道的横截面为六边形、通道内部带有错排扰流片。通过错排结构使温度差值变大,提高了传热效率。在发动机转速为3 000 r/min、换热通道入口处尾气温度为130~140℃时,其电压在1.112~1.151 V范围内波动,发电功率为1.325 W。并通过温度-电压的函数模拟,得出温度和电压在相应温度下成正比关系     

涡轮叶片尾缘典型结构的流动与换热特性研究

针对涡轮叶片尾缘"冲击+扰流柱"复合典型冷却结构,通过分析内部流场和换热特性,揭示"冲击+扰流柱"冷却结构中流动发展的过程以及冲击对压力分布和流场分布的影响,揭示涡轮叶片尾缘区内射流冲击扰流柱排通道内换热机理,详细分析了冲击下各个表面的换热情况。结果表明,压比的增大能够有效改善冷却通道端壁的换热性能,但同时增大了压力损失;在两种冲击距离下,n=3d换热效果优于n=6d,但是n=6d的下游换热覆盖效果优于n=3d。顺排时,冲击孔的平均换热系数大约是扰流柱的1.5倍;叉排时,冲击孔的平均换热系数大约是扰流柱的3倍,而其它部位的平均换热系数受排列方式的影响很小。因此,"冲击+扰流柱"冷却结构的匹配,对于优化涡轮叶片尾缘区域的换热及其重要。     

柱肋对缩放层板冷却结构流动和传热的影响

柱肋作为一种冷却通道内的强化换热技术,对提高层板结构的冷却效率有着重要意义。为了研究柱肋对双层板结构冷却性能和流场的影响,数值模拟研究了柱肋高径比分别为1,0.6,0.2,吹风比分别为0.3,0.6,1.0,1.5的原模型和等比例放大5倍模型两种尺度层板冷却结构的冷却效率。结果表明：高径比的变化对原模型冷却效率的影响更加明显,对放大模型的冷却效率影响非常小;吹风比越大,高径比对冷却效率的影响越明显,吹风比从0.3增大到1.5,高径比为0.6的柱肋比高径比为1柱肋的综合冷却效率提高了2%～3%;高径比为0.6的柱肋具有最大的相对压力损失,高径比为0.2和1柱肋的相对应力损失比高径比为0.6时低0.01%～0.07%。     

扰流肋柱在流动方向排列密度对矩形通道表面传热影响的数值研究

运用数值计算的方法将流动方向扰流圆柱排列密度对涡轮叶片尾缘冷却通道中流动传热的影响进行了三维数值研究。研究了流动雷诺数、流动方向圆柱排列密度对肋柱扰流矩形通道表面传热影响的规律。计算结果表明:在研究范围内,肋柱表面的平均Nu均随着Re的增大而增大。在Re相同的情况下,随X/D取值的增大,肋柱表面平均Nu有所减小。Nu在通道进口附近逐渐增加,然后达到充分发展值。传热在迎向流动方向的圆柱侧较强,在流动向背侧表面传热较弱。沿圆柱高度方向在中部传热较强。     

带肋矩形直通道内的冷却空气换热特性研究

采用ANSYS CFX商用软件对带肋矩形直通道内的冷却空气换热特性进行了数值计算,并与文献[4]的实验数据进行了对比,分析了雷诺数Re和肋片角度对努塞尔特数Nu的影响。结果表明:Nu数计算平均值与实验值的变化趋势一致,但计算结果大于实验值;由于肋片的扰流作用,在两个肋片之间的壁面区域产生了两个旋涡,强化了冷却空气与固体壁面的换热;随着Re数的增大,Nu数增大,平均摩擦阻力系数也增大;当肋片角度在45°～60°之间时,冷却通道的强化对流换热效果最好。     

扰流柱对间断交叉肋流动换热特性的影响研究

为了探究扰流柱对间断交叉肋通道流动与换热特性的影响,针对不同扰流柱数量和排布位置建立了不同的交叉肋模型,并通过数值模拟的方法,计算了各模型的阻力系数比、强化换热系数以及综合热效率3个性能指标的变化情况。研究结果表明：随着扰流柱数量的增大,阻力系数比和强化换热系数逐渐增大,而综合热效率不断下降;在进口雷诺数为20 000时,14柱模型与32柱模型相比,阻力系数比升高了15.4%,强化换热系数升高了32%,综合热效率提高了2.6%;将相同数量的扰流柱排布在通道内的不同位置对综合热效率的影响并不明显。     

基于遗传算法的燃气轮机叶片内部柱肋蒸汽冷却通道的优化分析

针对叶片尾缘内部柱肋冷却方式进行数值仿真和优化分析。采用CFX软件进行数值仿真计算,建立圆形柱肋、水滴形柱肋和正方形柱肋3种柱肋形状下,不同柱肋间距的矩形通道模型,验证数值模型的正确性以及网格无关性。分析了顺排和叉排的排列方式下,柱肋形状和柱肋间距对下底面努塞尔数以及整个通道内压力损失的影响,最后通过MATLAB的遗传算法对仿真结果进行优化。研究表明：柱肋模型中,横向和纵向柱肋间距最小时,换热效果最佳,压力损失最大;在顺排和叉排中,正方形柱肋对通道的换热强度的提升效果最明显,圆形柱肋提升效果最小。     

Measurement of endwall heat transfer and pressure drop in a pin-fin wedge duct

This paper discusses the measurements of endwall heat transfer and pressure drop in a wedge-shaped duct inserted with an array of circular pin fins. The endwall surface is coated with a thin layer of thermochromic liquid crystals and a transient test is run to obtain detailed heat transfer distributions. Parametric studies include Reynolds number (10,000?Re?50,000), outlet flow orientation (straight and lateral) and pin configuration (staggered and in-line). The wedge duct has a convergent angle of 12.7°. The pin spacing-to-diameter ratios along the longitude and transverse directions are fixed at s_x/d=s_y/d=2.5. Pin-less wedge duct results are also obtained for comparison. Results indicated that the straight wedge duct with a staggered pin array is most recommended because of its significant endwall heat transfer and moderate pressure-drop penalty; while the turned wedge duct with a staggered pin array is least recommended since it yields the highest pressure drops and raises severe hot spots. A similarity of the pin Reynolds-number dependence of row-averaged Nusselt number is developed in the present wedge duct of accelerating flow.     

Optimization of short micro pin fins in minichannels

Finned minichannels are modeled in order to optimize microstructure geometry and maximize heat transfer dissipation through convection from a heated surface. Six pin fin shapes – circle, square, triangle, ellipse, diamond and hexagon – are used in a staggered array and attached to the bottom heated surface of a rectangular minichannel and analyzed. Also, using square pin fins, different channel clearance over fins are investigated to optimize the fin height of the fins with respect to that of the channel. Fin width and spacing are investigated using a ratio of fin width area to the channel width. Fin material is then varied to investigate the heat dissipation effects. Triangular fins with larger fin height, smaller fin width, and spacing double the fin width maximizes the number of fins in each row and yields better performance. Correlations describing the Nusselt number and the Darcy friction factor are obtained and compared to previous ones from recent studies. These correlations only apply to short fins in the laminar regime. Completely understanding the effects of micro pin fins in a minichannel is essential to maximizing the performance in small scale cooling apparatuses to keep up with future electronic advancements.     

Study and optimization of the thermal performances of the offset rectangular plate fin absorber plates, with various glazing

The low thermophysical characteristics of air used as a heat transfer fluid in the solar collectors with thermal conversion require a fully developed turbulent flow. This increases the thermal heat transfer between the absorber plate and the fluid, which clearly improves the thermal performances of the solar collector with obstacles arranged into the air channel duct. In the present work, we introduce, in solar collector, the offset rectangular plate fins, which are used in heat exchangers. An experimental investigation carried out showed the generated enhancement of thermal performance. The offset rectangular plate fins, mounted in staggered pattern, are oriented parallel to the fluid flow and are soldered to the underside of absorber plate. They are characterized by high heat transfer area per unit volume. High thermal performances are obtained with low pressure losses and in consequence a low electrical power consumption by the fan in comparison to the flat plate collector. The experimental results are all so compared by using two types of transparent cover; double and triple.     

Convective heat transfer and pressure losses across novel heat sinks fabricated by Selective Laser Melting

This study presents the thermal and fluid flow characteristics of five heat sinks that have been fabricated by a rapid manufacturing technique known as Selective Laser Melting. The five heat sinks consist of two conventional designs, the cylindrical pin and rectangular fin array, for comparison purposes, and three novel heat sinks: a staggered elliptical array; a lattice; and a rectangular fin array with rounded corners. The experimental results for the rectangular fin were compared with data from the literature and were found to be consistent. The rectangular fin with rounded corners proved able to transfer the largest amount of heat whilst improving upon the pressure drop performance of the standard rectangular fin array. Although the lattice arrangement made use of the fabrication process’ ability to manufacture heat sinks with high surface area to volume ratios, its performance was limited by the lack of interaction between the cooling air and structure. In terms of both heat transfer performance and pressure drop, the staggered elliptical array, which cannot be manufactured by conventional techniques, outperformed the other heat sinks.     

Single-Phase Cryogenic Flow and Heat Transfer Through Microscale Pin Fin Heat Sinks

Single-phase heat transfer and pressure drop of liquid nitrogen in microscale heat sinks are studied experimentally in this paper. Effects of geometrical variations are characterized on the thermofluidic performance of staggered microscale pin fin heat sinks. Pitch-to-diameter ratio and aspect ratio of the micro pin fins are varied. The pin fins have square shape with 200 or 400 μm width and are oriented at 45 degrees to the flow direction. Thermal performance of the heat sinks is evaluated for Reynolds numbers (based on pin fin hydraulic diameter) from 108 to 570. Results are presented in a nondimensional form in terms of friction factor, Nusselt number, and Reynolds number and are compared with the predictions of existing correlations in the literature for micro pin fin heat sinks. Comparison of flow and heat transfer performance of the micro pin fin heat sinks reveals that at a particular critical Reynolds number of ～250, pin fin heat sinks with the same aspect ratio but larger pitch ratio show a transition in both friction factor and Nusselt number. In order to better characterize this transition, visualization experiments were performed with the Fluorinert PF5060 using an infrared camera. At the critical Reynolds number, for the larger pitch ratio pin fin heat sink, surface thermal intensity profiles suggest periodic flapping of the flow behind the pin fins at a Strouhal number of 0.227.     

Flow structure and heat transfer characteristics of a 90°-turned pin-finned wedge duct with dimples at different locations

In this study, numerical simulations are performed to investigate the effect of dimple location on the flow structure and heat transfer characteristics in a 90°-turned channel with pin fins. Results of the flow structure, heat transfer on the endwall, and friction factor are included in this study. It is found that the dimple location has an impact on the flow structure and heat transfer both for the pin fins arranged with in-line and staggered layout. The horseshoe vortex near the pin fin is influenced by the location of the dimple. The dimple enhances the Nusselt number on the endwall surface significantly. In addition, the dimple location has an effect on the low-speed recirculation, impingement, and vortex which are generated by the dimple. However, the dimple has very limited effects on the friction factor for all cases. It is also found that the area goodness factor and volume goodness factor are improved by the dimple.     

Research on the mechanism of heat transfer enhancement in microchannel heat sinks with micropin fins

In this paper, the pressure drop and heat transfer features of a microchannel applying micropin fins are investigated by numerical simulations and experiments. The microchannel, which is 20-mm long, 2.7-mm wide, and 0.3-mm deep, is fabricated with copper and consisted of staggered diamond micropin fins. The visualization experiments, by means of the advanced technology micro-particle image velocimetry (PIV), are conducted to discuss the mechanism of heat transfer by analysing the flow regimes. Meanwhile, 3D-coupled numerical simulations are applied for the combination with experiments in this research. It is found that the vortex-wake flow is stable at Reynolds number (Re) = 0 to 300, and a steady recirculating zone can be observed in the wake, where a pair of symmetrical vortices is formed. All the time, the vortex-wake flow is unstable at Re = 300 to 650. Under this situation, it is due to the decrease of vorticity that the Nusselt number (Nu) is not significantly increased as it was expected. Thus, when Nu in the pin fin microchannel is predicted, the vorticity should be considered as well as turbulent kinetic energy (TKE). Furthermore, comparative study was carried out based on the mechanism proposed in this study among three kinds of microchannel with different fins, including staggered circular pin fins (CPF), square pin fins (SPF), and diamond pin fins (DPF).     

扰流空心翅片式微流道液冷板流动换热特性研究

液冷板冷却技术是解决高功率芯片热管理问题最有前途的技术之一,带翅片结构的液冷板具有低流阻、低热阻的优势,因而受到广泛关注。目前翅片结构多以实心为主,空心交错翅片对液冷板散热能力和压降等冷却特性的影响尚未得到系统的研究。对此,设计了空心交错翅片液冷板,采用数值模拟的方法研究进口温度和流量对液冷板流动换热特性的影响。模拟结果表明,空心翅片式液冷板具有良好的散热性能,随着进口温度的升高,液冷板温度不均匀性逐渐降低,但降低趋势有所减缓,而流量的增大对降低平均热阻有显著的作用,当进口流量超过1.2 L/min时,液冷板的平均热阻可低于0.04℃/W;然而,流量的增大也提高了流动阻力,当流量增大至1.7 L/min时,流体出口区域形成涡旋,产生回流区,不利于液冷板的散热效果,且流动阻力增大。