微尺度平面射流冲击的强化传热实验研究

本文以煤油为工质进行了窄缝射流冲击传热实验研究。对射流冲击平板时的局部传热分布做了测定，并发现了局部换热强化现象，这是由于存在壁面射流区边界层流动由层流向湍流的过渡。实验采用宽度为１２５μｍ的窄缝喷嘴，射流出口速度为６～１４ｍ／ｓ，雷诺数Ｒｅ范围６００～１２００。     

液柱冲击式湿法脱硫装置的试验研究

本文提出了一种液柱冲击式湿法脱硫装置,对该装置的吸收段阻力特性和脱硫特性进行了试验研究,对试验结果进行了分析．分析发现了在塔内风速为２ｍ／ｓ～２．９ｍ／ｓ范围内,脱硫效率随塔内风速的增大而增加这一不同于其它装置的特点,得到了在塔内风速 ２．６ ｍ／ｓ,喷液量３０ｍ３／ｈ时脱硫效率高、阻力低这个比较经济的工况点．     

窄缝通道中液氮的沸腾传热研究第一部分:窄缝通道尺寸对传热特性的影响

窄缝通道中的液氮沸腾传热特性有别于开放空间中的情况.文中对常压下液氮在矩形窄缝通道内的沸腾传热进行了实验研究,系统地研究了窄缝几何结构参数和倾角对液氮的沸腾传热特性的影响.     

射流冲击泡沫金属流动液膜传热的实验研究

薄液膜蒸发由于其优良的传热特性而被广泛应用于工业领域。在流动液膜上表面覆盖铜质泡沫金属,并耦合空气射流冲击,能够进一步强化传热。多孔泡沫金属提供的毛细驱动力能够有效控制流动液膜的厚度以避免干涸,同时多孔材料特殊的固体骨架构造可以扩大固液、气液传热面积。为了研究射流冲击条件下多孔介质覆盖流动液膜的传热特性,本文通过实验方法,对包括液膜流速Vf、空气射流速度Va、液膜厚度δf和多孔介质孔隙率ε在内的影响因素进行分析,研究并对比这些因素对加热壁面温度Tw、表面传热系数hw以及传热系数提升率的影响。     

加热面上液滴的冲击行为及Leidenfrost现象

以银及覆有绝热薄层的银为传热面，利用高速摄影技术，考察了传热面特性及初始温度对液滴冲击行为的影响，讨论了Ｌｅｉｄｅｎｆｒｏｓｔ点的发生机理，并对冲击液滴在传热面上的最大扩展直径及滞留时间进行了理论分析。初始传热面温度为Ｌｅｉｄｅｎｆｒｏｓｔ温度时，无论有无覆层，液滴冲击时均发生固液接触，液滴在传热面上的滞留时间大于液滴的自由振动周期。     

常压下液氮窄缝池沸腾实验研究

采用玻璃钢 (FRP)制成的矩形窄缝 ,对三种不同的间隙尺寸 ,分加热面与水平面呈 0°,4 5°,90°,135°,180°五种角度 ,以液氮为工质进行了 15组池沸腾实验。得出结论 :液氮在窄缝中的沸腾传热有明显的强化换热效果 ;加热面所处角度不同 ,在相同热负荷下壁面过热度亦不同 ,滑移汽泡和微液膜蒸发机理在通道中发挥的作用也相应不同。该研究对于有限空间传热强化的机理和实际应用都有一定的参考价值和指导意义。     

N─甲基吡咯烷酮两相闭式热虹吸管传热特性的实验研究

本文报道了用Ｎ—甲基吡咯烷酮（Ｃ５Ｈ９ＮＯ３）为工质以光滑管与三维内翅片管为管壳制成的两相闭式逆流热虹吸管的传热特性。实验结果表明在工作温度为２２０～３５０℃，热负荷为８．２～１７．３ｋＷ／ｍ２范围内光滑热虹吸管蒸发段与凝结段换热系数的积分平均值分别约为１７００Ｗ／ｍ２·℃和１６００Ｗ／ｍ２·℃。由于三维翅片的强化传热作用，使三维内翅片热虹吸管蒸发段与凝结段换热系数分别比光滑管增大了２０％～４０％和７０％～１６０％。实验表明Ｎ—甲基吡咯烷酮综合传热性能优于萘，可望作为中温热管工质使用。     

射流冲击泡沫金属强化电子器件冷却的实验研究

实验研究射流冲击泡沫金属的强化传热在电子器件冷却中的作用,分析热流密度、传热面与喷射气流温度差、喷射速度和喷嘴距泡沫金属上表面的高度等因素对传热特性的影响。在泡沫金属材质为铜,孔隙率为0.96,喷嘴宽度为0.5cm的情况下,喷嘴距泡沫金属上表面高度越低和喷射速度越大,泡沫金属的传热效果越明显,冷却效果越显著,并对实验数据,进行最小二乘法拟合,得到相应的拟合方程式。该文的分析结果,可为射流冲击泡沫金属强化传热技术的应用提供一定指导和借鉴。     

1.06μm激光辐照金盘靶的软X光转换

在１．０６μｍ激光辐照金盘靶实验中，利用坪响应Ｘ光二级管探测器测量了软Ｘ光能量（０．１－１．５ｋｅＶ）角分布，得到了软Ｘ光转换效率。实验条件：激光波长λＬ＝１．０６μｍ，ＥＬ＝６０－５００Ｊ，τｐｍ≈８００ｐｓ，ｆ／１．７，ＩＬ＝１０＾１＾３－１０＾１＾４Ｗ／ｃｍ＾２。实验结果表明：软Ｘ光能量角分粗略呈α＋ｂｃｏｓθ分布，软Ｘ光转换效率随激光强度的增加而降低。当靶面激光焦斑直径２３５μｍ，激光强度     

对心碰撞的约束关系

题一，在光滑平面上，质量ｍ１＝１ｋｇ的小球，以ｖ１０＝５ｍ／ｓ的速度向前运动，与质量ｍ２＝２ｋｇ以ｖ２０＝２ｍ／ｓ的速度向前运动的小球发生正碰撞，设碰后ｍ２的速度ｖ２＝５ｍ／ｓ，求碰后ｍ１的速度ｖ１的大小和方向．图示．题二，同上题，设碰后ｍ２的速度ｖ...     

Experimental investigation for enhanced ferrofluid heat transfer under magnetic field effect

This paper reports an experimental work on the convective heat transfer of ferrofluid flowing through a heated copper tube in the laminar regime in the presence of magnetic field. Significant enhancement on the heat transfer of ferrofluid by applying various orders of magnetic field is observed in this experiment. Also in this experiment, the effect of magnetic nanoparticles concentrations and magnet position have been investigated. The main reason for the enhancement of heat transfer coefficient could be caused due to remarkable changes in thermophysical properties of ferrofluid under the influence of applied magnetic field.     

方柱微结构表面射流-流动沸腾强化换热

采用长×宽×厚为10 mm×10 mm×0.5 mm的硅片来模拟实际芯片散热,通过干腐蚀技术在其表面加工出宽×高分别为50μm×60μm,50μm×120μm的方柱微结构,实验研究了方柱微结构在射流冲击下的流动沸腾换热性能。过冷度为25℃和35℃,横流速度V_c为0.5,1.0,1.5 m/s,喷射速度V_j为0～2 m/s,冷却工质为FC-72。实验结果和同工况下的光滑表面作了对比。结果表明,方柱微结构由于换热面积的增加从而表现出优于光滑表面的强化换热性能,增加过冷度和提高V_c以及V_j都提高了芯片在高热流密度下的换热性能,但随着V_c的增加,射流冲击的强化作用减弱,低流动高喷射的强化效果最为明显。方柱肋片效率随着热流密度的增加而减小,随着V_c(V_j)增加,方柱肋片效率也逐渐下降,但降幅随着V_c的增加而减小。     

磁流体流动与传热的格子Boltzmann模拟

考虑外加磁场下磁流体中纳米磁性粒子所受的各种作用力,建立了用于模拟磁流体流动与传热特性的两相格子Boltzmann模型,模拟了外加不同方向梯度磁场下平板间磁流体的流动与传热过程,计算了磁流体与平板间对流换热的Nusselt数,分析了磁场梯度方向、大小对Nusselt数的影响．     

均匀高压电场强化R123池沸腾传热实验研究

利用EHD技术进行了工质R123的池内平板沸腾强化传热实验研究.在该实验中,换热面为一平板并接地作为0电极,高压电极为平行于换热面的网状电极.实验结果表明,正电压的强化效果较好,电压越高,强化效果越好.低热流密度下,EHD对沸腾换热的强化效果比高热流密度的强化效果好.起沸点随着电压的增加而增加,同不加电压时相比,在20 kV时,起沸点提高了4倍.     

MEASUREMENTS OF LOCAL HEAT TRANSFER COEFFICIENTS FROM A FLAT PLATE TO A PAIR OF CIRCULAR AIR IMPINGING JETS

Local heat transfer coefficients from a flat plate to a pair of circular air impinging jets are investigated experimentally, A pair of well-controlled, fully developed circular air impinging jets at room temperature are used in the experiments. The experimental method in this investigation is the transient liquid-crystal technique. During the experiments, the surface liquid-crystal color distribution of the test plate is recorded using a video imaging acquisition system, and the color information is translated into a surface temperature distribution through a digital color image processing unit. Local heat transfer coefficients art obtained using a surface transient heat conduction analysis. The flow Reynolds number of the jet is kept at 23,000. The jet-to-plate distance and the jet-to-jet spacing are varied in the experiment. Detailed radial heat transfer distributions at different radial directions are obtained and analyzed for L/D = 2, 4, 6, 8, and 10. The effect of jet spacing distance (S/D =1.75, 3.5,5.25, 7.0) is analyzed by comparing to data obtained from a single jet with similar flow configurations.     

Stress waves propagation in solids under high-speed liquid impact

The high-speed liquid/solid impact phenomenon is often seen in many technicalfields such as, water jet cutting technology[1], rain erosion of aviation vehicles[2] and ro-tor blades erosion in large steam turbines[3]. Recently, China Aerodynamics ResearchCenter reported experimental results of rain erosion of hypervelocity projectile[4]; Xi’anJiaotong University reported numerical simulation of high-speed liquid drop impact on asolid surface[5]. In analyzing the mechanism of material’s dama…     

BOILING CHARACTERISTICS OF R-11 IN COMPACT TUBE BUNDLES WITH SMOOTH AND ENHANCED TUBES

This study presents new data on nucleate boiling heat transfer obtained in compact horizontal tube bundles with small tube gaps. The experiment investigates the heat transfer enhancement effects by the restricted spaces comprising the compact tube bundles and the enhanced heat transfer tubes for nucleate boiling heat transfer of R-11 at atmospheric pressure. A roll-worked tube was used as a new type of enhanced heat transfer tube. The experimental results show that the small tube gaps can greatly enhance boiling heat transfer in a smooth tube bundle, while enhancement effects of small gaps were not quite significant for the enhanced tube bundle. There is a compound effect from the enhanced surface and the restricted space only for the enhanced tube bundle with the tube gap of 0.5 mm. The effects of the tube positions within both compact tube bundles on the boiling heat transfer were minor.     

Flow and Heat Transfer Characteristics of in-Line Impinging Jets With Cross-Flow At Short Jet-To-Plate Distance

The aim of this research is to numerically and experimentally study the flow and heat transfer characteristics of in-line impinging jets in cross-flow. The jets from a row of round orifices are perpendicularly impinged on the inner surface of a rectangular wind tunnel at a short distance between the orifice plate and impinged surface (H) of 2D, where D is a diameter of the orifice. The jet velocity was fixed corresponding to Re = 13,400 for all experiments, and the cross-flow velocity was varied at three different velocity ratios (velocity ratio, jet velocity/cross-flow velocity) of 3, 5, and 7. The heat transfer characteristic was visualized using a thermochromic liquid crystal sheet, and the Nusselt number distribution was evaluated by an image processing technique. The flow pattern on the impinged surface was also visualized by an oil film technique. The numerical simulation was used to explore a flow interaction between the impinging jets and cross-flow. The results indicated that Nusselt number peak increased by the increasing cross-flow velocity for short jet-to-plate distance. For the range determined, the maximum local Nusselt number peak was obtained at VR = 3 as the consequence of high velocity and high turbulence kinetic energy of jet impingement.     

Experimental Investigation of the Effect of Multiple Synthetic Jets on Heat Transfer and Pressure Loss in Minichannels

Synthetic jets can enhance thermal performance by creating wall impingement, disrupting boundary layers, and enhancing mixing within a minichannel. This study investigates using multiple synthetic jets along the length of minichannels with an aqueous–glycol mixture. Using synthetic jets, an average heat transfer coefficient increase up to 81% was demonstrated. It was also shown that pressure loss can be reduced by 78% while maintaining equivalent heat transfer performance. The effects of momentum ratio, frequency, and bulk Graetz number on heat transfer and pressure loss is presented along with an empirical correlation that predicts the heat transfer enhancement.     

Effect of electric field on the enhanced heat transfer characteristic of an evaporator with multilayered sintered copper mesh

In this paper, it was investigated experimentally that the effect of different kinds of working fluid on the thermal performance of evaporator with capillary wick consisted by multilayered sintered copper mesh under different electric field strengths at the operating pressure of 1.01 × 10⁵ Pa R141b and R123 were used as the working fluids. The electric field strength in this study was in the range of 0kV/m–1600 kV/m, respectively. The experimental results showed that the applied electric field strength has significant effect on heat transfer characteristic. The heat transfer enhancement effects increased with the increase of the electric field. Under the applied electric field strength, the maximum heat transfer enhancement factors could reach as high as 1.5 and 1.32 for the two kinds of working fluids in the experiment.