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。     

Experimental Study on Flow and Heat Transfer in a 19.6-μm Microtube

The flow and the heat transfer characteristics in a quartz microtube with an inner diameter of 0.0196 mm are investigated experimentally. Measuring the pressure drop between the inlet and outlet of the microtube and the average temperature of the microtube wall heated by steam when the working fluid is distilled water, the corresponding friction factors and Nusselt number are obtained. The experimental results show the friction factors in the microtube exceed those of the Hagen–Poiseuille prediction due to the predominance of the effects of the electrical double layer and the entrance. Also, the experimental Nusselt number is less than the classical laminar at Reynolds number < 500 due to the effect of the variation of the thermophysical properties with the temperature.     

FLOW BOILING THROUGH V-SHAPE MICROCHANNELS

An experimental facility was set up to study the flow and boiling heat transfer characteristics of water and methanol flowing through V-shape microchannels. The microchannels have hydraulic diameters ranging from 0.2 to 0.6 mm and V-shape groove angles 0 of 30 to 60°. Both the heat transfer and the pressure drop were affected by the thermofluid and geometric parameters such as liquid flow velocity, subcooling, and the hydraulic diameter and groove angle of the microchannels. The experiments indicted that there exists both an optimum hydraulic diameter and an optimum groove angle. The visualization experiments showed that, if there was a good seal between the glass cover and the microchanneled test plate, no bubbles were observed in the microchannels for flow boiling with heat fluxes as high as of the order of 10⁶ W/m², at which fully nucleate boiling with a large number of bubbles would be expected in conventional situations. Fluctuating liquid flow was induced in the microchannels when many bubbles formed in the inlet plenum.     

微柱群阻力特性实验研究

以去离子水为工质,流经直径为0.5 aim,高度分别为1.0 mm、0.75 mm、0.5 mm和0.25 mm的圆柱组成的柱群板,其宽度与长宽分别为3.5 mm和40 mm,测量通道进出口压差及流量,研究微柱群内部分别在叉排和顺排时液体流动的阻力特性.研究表明,微柱群内流动阻力系数f,随Re数的增大而逐渐减小,当Re数大于500时,f基本不变;微柱高度和直径之间存在一个有利于流动的最佳比例,该值介于1到1.5之间;顺排微柱群的f明显小于叉排微柱群,其,值为叉排微柱群的0.5倍.     

具有隔板的平行通道内空气混合对流换热数值模拟

本文以锅炉干排渣装置为背景,对抽象的理论模型具有隔板的平行通道内空气混合对流换热进行了数值模拟.数值计算表明,在Re＞1000时应采用非稳态数学模型进行数值模拟;在Re＞500时,自然对流机制对流动和换热的影响基本可以忽略.数值计算给出了不同Re时的进出口无量纲压差、局部的Nux和平均Nu以及流线图.这些结果可为深入研究干排渣装置中流动和换热特性提供参考.     

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.     

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。     

Experimental investigation of flow boiling heat transfer enhancement under ultrasound fields in a minichannel heat sink

Ultrasound is considered to be an effective active heat transfer enhancement method, which is widely used in various fields. But there is no clear understanding of flow boiling heat transfer characteristics in micro/mini-channels under ultrasonic field since the studies related are limited up to now. In this paper, a novel minichannel heat exchanger with two ultrasonic transducers inside the inlet and outlet plenum respectively is designed to experimentally investigate the impacts of ultrasound on flow boiling heat transfer enhancement in a minichannel heat sink. Flow visualization analyses reveal that ultrasound can promote rapid bubble motion, bubble detachment from heating wall surface and thereby new bubble generation, and decrease the length of confined bubble. Furthermore, the flow boiling experiments are initiated employing working fluid R141b at different ultrasonic parameters (e.g., frequency, power, angle of radiation) and heat flux under three types of ultrasound excitations: no ultrasound (NU), single inlet ultrasound (IU), inlet and outlet ultrasound (IOU). The results indicate that ultrasound has obvious augmentation effects on flow boiling heat transfer even though the intensification effects will be limited with the heat flux increases. The higher ultrasonic power, the lower ultrasonic frequency and the higher ultrasonic radiation angle, the better intensification efficiency. The maximum enhancement ratio of h_ave in the saturated boiling section reaches 1.88 at 50 W, 23 kHz and 45° under the experimental conditions. This study will be beneficial for future applications of ultrasound on flow boiling heat transfer in micro/mini-channels.     

翅片管束式管壳式换热器三维数值模拟研究

本文提出了运用多孔介质模型、分布阻力模型和k-ε湍流模型对壳侧为翅片管束的壳管式换热器壳侧速度场与温度场进行三维数值模拟的方法,并对一相应类型换热器壳侧的流动与换热进行了数值模拟,得出了壳侧流场参数的图示以及壳侧进出口压降,温差,换热量随壳侧Re变化的特性曲线。     

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。     

Thermo-Hydraulic Behavior of Microchannel Heat Exchanger System

This article presents an experimental study of thermo-hydrodynamic phenomena in a microchannel heat exchanger system. The aim of this investigation is to develop correlations between flow/thermal characteristics in the manifolds and the heat transfer performance of the microchannel. A rectangular microchannel fabricated by a laser-machining technique with channel width and hydraulic diameter of 87 μm and 0.17 mm, respectively, and a trapezoidal-shaped manifold are used in this study. The heat sink is subjected to iso-flux heating condition with liquid convective cooling through the channels. The temporal and spatial evolutions of temperature as well as total pressure drop across the system are monitored using appropriate sensors. Data obtained from this study were used to establish relationships between parameters such as longitudinal wall conduction factor, residence and switching time, and thermal spreading resistance with Reynolds number. Result shows that there exist an optimum Reynolds number and conditions for the microchannel heat exchanger system to result in maximum heat transfer performance. The condition in which the inlet manifold temperature surpasses the exit fluid temperature results in lower junction temperature. It further shows that for a high Reynolds number, the longitudinal wall conduction parameter is greater than unity and that the fluid has sufficient dwelling time to absorb heat from the wall of the manifold, leading to high thermal performance.     

波纹板式空冷器阻力与传热特性实验研究

在可改变风量和热水流量的实验条件下,对波纹板式空冷器的阻力与传热特性进行实验研究。得到了空气侧的阻力降关联式以及两侧的对流换热系数关联式,其适用于热水雷诺数在2000-8000之间、空气雷诺数在2000-10000之间。在相同工况下,比较了波纹板式、光管式和翅片管式空冷器的性能指标,结果表明:迎面风速在2.45-4.1 m/s之间,波纹板式空冷器传热系数达到100-160 W/m2/℃;约比光管式提高70%,但只有以管束外表面为基准的翅片管式传热系数的六分之一;板式空冷器单位体积换热量约是翅片管式空冷器的1.5倍,是光管式的15倍;板式空冷器单位功耗换热量约是光管式空冷器的5.5倍,而翅片管式空冷器与光管式空冷器则相差不大。     

Experimental Investigation of Transient Forced Convection of Liquid Methane in a Channel at High Heat Flux Conditions

Transient heat transfer of liquid methane under forced convection in a 1.8 mm × 1.8 mm asymmetrically heated square channel was investigated. This study is aimed at understanding the heat transfer behavior of cryogenic propellant in cooling channels of a regeneratively cooled rocket engine at the start-up condition. To simulate high heat load conditions representative of regeneratively cooled rocket engines, a high heat flux test facility with cryogenic liquid handing capabilities was developed at the Center for Space Exploration Technology Research. The time history of inlet and outlet fluid temperatures and test section channel wall temperatures were measured at high heat flux conditions (from 1.19 to 3.80 MW/m²) and a Reynolds number (Re) range of 1.88 × 10⁵ to 3.45 × 10⁵. The measured wall temperature data point toward possible film boiling within the test section during certain tests, particularly with higher heat fluxes and lower Reynolds number conditions that resulted in higher wall temperatures. The transient average Nusselt numbers (Nu_L) of the channel obtained from the experimental measurements are lower than those calculated from the Sieder–Tate correlation (Nu_O); however, the ratio (Nu_L/Nu_O) increases with the increase in Reynolds number. The ratio is around 0.25 at the lower end of Re and then increases to 0.7 at the maximum Re studied in the present investigation.     

Influence of T-semi attached rib on turbulent flow and heat transfer parameters of a silver-water nanofluid with different volume fractions in a three-dimensional trapezoidal microchannel

This study aimed at exploring influence of T-semi attached rib on the turbulent flow and heat transfer parameters of a silver-water nanofluid with different volume fractions in a three-dimensional trapezoidal microchannel. For this purpose, convection heat transfer of the silver-water nanofluid in a ribbed microchannel was numerically studied under a constant heat flux on upper and lower walls as well as isolated side walls. Calculations were done for a range of Reynolds numbers between 10,000 and 16,000, and in four different sorts of serrations with proportion of rib width to hole of serration width (R/W). The results of this research are presented as the coefficient of friction, Nusselt number, heat transfer coefficient and thermal efficiency, four different R/W microchannels. The results of numerical modeling showed that the fluid's convection heat transfer coefficient is increased as the Reynolds number and volume fraction of solid nanoparticle are increased. For R/W=0.5, it was also maximum for all the volume fractions of nanoparticle and different Reynolds numbers in comparison to other similar R/W situations. That's while friction coefficient, pressure drop and pumping power is maximum for serration with R/W=0 compared to other serration ratios which lead to decreased fluid-heat transfer performance.     

The numerical investigation of heat transfer and pressure drop of turbulent flow in a triangular microchannel

In this presentation, the flow and heat transfer inside a microchannel with a triangular section, have been numerically simulated. In this three-dimensional simulation, the flow has been considered turbulent. In order to increase the heat transfer of the channel walls, the semi-truncated and semi-attached ribs have been placed inside the channel and the effect of forms and numbers of ribs has been studied. In this research, the base fluid is Water and the effect of volume fraction of Al₂O₃ nanoparticles on the amount of heat transfer and physics of flow have been investigated. The presented results are including of the distribution of Nusselt number in the channel, friction coefficient and Performance Evaluation Criterion of each different arrangement. The results indicate that, the ribs affect the physics of flow and their influence is absolutely related to Reynolds number of flow. Also, the investigation of the used semi-truncated and semi-attached ribs in Reynolds number indicates that, although heat transfer increases, but more pressure drop arises. Therefore, in this method, in order to improve the heat transfer from the walls of microchannel on the constant heat flux, using the pump is demanded.     

超临界压力煤油传热不稳定实验研究

在压力2.5~4 MPa, 质量流量0.7~1.7g/s, 入口温度20~250 ℃的实验条件下, 对煤油在内径1 mm, 长度300 mm竖直上升圆管中的流动及传热不稳定现象进行了实验研究.结果表明, 当热流密度增大到一定程度后, 传热不稳定开始发生.不稳定发生的起始热流密度随压力和流量的增加而增大, 随入口油温的升高而减小, 且当入口油温升高到一定程度后无不稳定现象发生.不稳定发生的初始时刻, 出口油温迅速增加, 管道壁温明显下降, 传热系数增大; 实验段局部流速增大, 进而在管道内部形成压力脉动并产生声音.不稳定结束后, 出口油温几乎保持不变, 壁温会缓慢增加, 直至下一次不稳定发生.      

低压离心压缩系统喘振发生过程的实验观察

在一离心压缩系统喘振实验台上，通过系统各位置及沿叶轮出口圆周上压力波动进行的动态测量，对进入及退出瑞振时的瞬态特性进行了实验观察．实验发现系统的喘振首先发生在储气容腔内，并由下游向上游发展，在此过程中喘振幅度从容腔至进口管呈减小的趋势，且发生时间也逐渐落后．此外，还对喘振的形成和退出过程及其相应特性也进行了观察．     

5×5棒束CFD模拟计算域和网格标准

采用不可压N-S方程、标准k-ε湍流模型、SIMPLE算法,对某压水堆的两跨距5×5燃料组件的水循环区域流动进行数值分析.对比流道横截面上的压降、速度及其横向分量的相对误差,得到计算域的进出口段长度、网格形式、网格尺寸的选取标准.结果显示：计算域的进口段、出口段长度不宜过短或过长,分别为2.0倍、2.3~2.8倍格架中心距长度;格架区宜采用非结构蜂窝网格,光棒区宜采用结构网格;格架区网格尺寸可取0.3 mm,最大不宜超过0.35 mm,而结构网格横向尺寸可取0.3 mm~0.5 mm,纵向稀疏比应小于1.5为宜.满足上述标准,数值分析能保证较高的可信度,同时保持可接受的计算量.     

Numerical investigation of supersonic flow breakdown at the inlet duct throttling

The work presents the results of investigating the process of supersonic flow deceleration in a duct of the two-dimensional inlet throttled by variation of the outlet cross-sectional area. An inlet with three external compression shock waves designed for the freestream Mach number M_d = 7 was considered as an example for the investigation. A one-dimensional analysis of the conditions for realization of the supersonic flow deceleration regimes in the inlet duct with two throats — in the inlet entrance and at the inlet duct outlet, has been carried out. The parametric numerical computations of two-dimensional inviscid or turbulent flows in the inlet were performed with the use of the Euler and Navier—Stokes codes of the program package FLUENT. The critical conditions for the nonuniform flow in the outlet throat bringing to choking the inlet duct were determined.     

微尺度扩散火焰特性的数值解析

本文以均匀空气流中圆管形成的甲烷射流扩散火焰为对象,用数值解析的方法研究了微尺度扩散火焰的火焰结构和燃烧特性。燃烧反应采用甲烷/空气一步总包反应,喷管壁面采用绝热条件。在Re一定情况下,改变喷口尺寸和喷口流速考察了微扩散火焰的结构和火焰熄灭的尺度效应。数值结果表明,随着喷口直径的增大,微火焰的上方出现回流; Re=12条件下,在喷口直径=0.07 mm时存在熄灭极限;稳定燃烧区的最小发热率约为0.5 W;微尺度条件下,Da数对火焰结构和火焰的熄灭有一定的影响。