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高密度、 小体积和高集成的电子元器件散热困难, 易造成过早失效, 采用微通道换热器可以实现小体积内高热流的散热, 但流动阻力很大. 为了保证传热效果, 降低流动阻力, 本文提出了一种新型的微通道结构并对其流动与传热特性进行了数值模拟. 首先研究了微通道形状和结构, 模拟结果表明: 进出口截面宽高比为0.8 的矩形微通道的换热效果最好; 并在此基础上提出一种康托尔分型凹槽结构, 研究了有无康托尔分形以及不同分形级数对流动与传热性能的影响, 综合对比发现: 第二级康托尔分形模型 N2 既能保证热阻显著降低, 又能相比阵列结构降低压降, 具有明显的换热优势; 最后对这种康托尔分形结构的凹槽形状, 尺寸及不同方向上的分形进行研究, 结果表明梯形凹槽的下上表面长度比b/a 为0.6 、 流动方向分形比fx 为1 .25 和通道高度方向分形比fy 为1 .5 时换热流动性能最佳. 相似文献
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《低温与超导》2021,49(7):59-66
微通道内扩缩结构的布置,有利于诱发二次涡流,提高传热性能。基于单侧矩形肋微通道(MC-OSRR),提出了单侧矩形肋和空腔(MC-RR.RC)、单侧矩形肋和扰流柱(MC-RR.RPF)两种组合结构微通道优化模型。在验证数值方法有效性的基础上,以去离子水为流动介质,运用Fluent软件模拟研究了不同体积流量、壁面温度、进口温度条件下扩缩型微通道的流动与传热特性。结果表明,空腔和扰流柱结构的引入,能进一步诱发二次流,促进流动混合,低体积流量下有利于增强单侧矩形肋微通道整体性能;相比空腔结构,布置于通道中央的扰流柱结构对主流体的扰动更为剧烈,高体积流量下无法在控制阻力增加幅度的基础上强化单侧矩形肋微通道传热。 相似文献
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为满足固体激光器用微通道冷却器的换热要求, 根据冷却器结构分别建立了二维和三维物理模型, 利用计算流体力学方法首先对比研究两者的流动特性, 然后考察雷诺数和玻片生热量对微通道流动和传热特性的影响。结果表明:对于类似大平板间的矩形微通道层流流动区域, 其流动及传热特性可直接采用二维简化模型进行模拟分析;对于重点关注的转捩区, 采用三维模型模拟分析更好;当雷诺数增大到转捩点, 流体的传热效果得到明显增强;随着雷诺数的增大, 玻片生热量对通道内最低压力需求的影响逐渐减小;不同玻片生热量对微通道流动影响不可忽略, 对努赛尔数和通道总压降基本无影响。 相似文献
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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。 相似文献
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滑移流区内微环缝槽道中的层流流动与换热 总被引:7,自引:0,他引:7
本文针对微环缝槽道采用速度滑移和温度跳跃边界条件求解了不可压缩气体的N-S方程和能量方程,理论分析了微环缝槽道在单侧或双侧不同热流密度加热条件下的流动与层流换热特性,讨论了Kn数、内外径比对流动阻力及换热特性的影响。结果表明:滑移流区微环继通道内的流阻和Nusselt数明显低于连续流区;且随着Kn数的增加,流阻和Nusselt数均减小;但其随内外径比r*的变化趋势与连续流区相似。 相似文献
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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. 相似文献
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Jun Yao Yufeng Yao Peter J. Mason & Mayur K. Patel 《advances in applied mathematics and mechanics.》2009,1(2):231-241
Numerical simulation of heat transfer in a high aspect ratio rectangular
microchannel with heat sinks has been conducted, similar to an experimental study.
Three channel heights measuring 0.3 mm, 0.6 mm and 1 mm are considered and the
Reynolds number varies from 300 to 2360, based on the hydraulic diameter. Simulation
starts with the validation study on the Nusselt number and the Poiseuille
number variations along the channel streamwise direction. It is found that the predicted
Nusselt number has shown very good agreement with the theoretical estimation,
but some discrepancies are noted in the Poiseuille number comparison. This
observation however is in consistent with conclusions made by other researchers
for the same flow problem. Simulation continues on the evaluation of heat transfer
characteristics, namely the friction factor and the thermal resistance. It is found
that noticeable scaling effect happens at small channel height of 0.3 mm and the
predicted friction factor agrees fairly well with an experimental based correlation.
Present simulation further reveals that the thermal resistance is low at small channel
height, indicating that the heat transfer performance can be enhanced with the
decrease of the channel height. 相似文献
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Fluid flow and heat transfer characteristics of single-phase flows in microchannels for refrigerant R-134a were experimentally investigated. Experiments were conducted using rectangular channels micromilled in aluminum with hydraulic diameters ranging from approximately 112 to 210 w m and aspect ratios that varied from 1.0 to 1.5. Using overall temperature, flow rate, and pressure drop measurements, friction factors and convective heat transfer coefficients were experimentally determined for steady flow conditions. Effects of Reynolds number, relative roughness, and channel aspect ratio are examined in predicting friction factor and Nusselt number for the experiments. Experiment results indicated that transition from laminar to turbulent flow occurred between a Reynolds number of 2,000 and 4,000. Friction factor results were consistently lower than values predicted by macroscale correlations but exhibited the same trends with Reynolds numbers of macroscale correlations. Nusselt number results also exhibited a similar pattern of lower values obtained in the experiments than those predicted by commonly used macroscale correlations. Nusselt number results also indicated that channel size may suppress turbulent convective heat transfer and surface roughness may affect heat transfer characteristics in the turbulent regime. 相似文献
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In this paper, an analytical method of microchannel heat exchanger characteristics optimization is described. An objective function that combines thermal-hydraulic and constructive parameters of a heat-exchanger such as number, diameter, and length of channels, was developed. Limitations on its application were determined. Influence of these parameters on the function’s value was analyzed. It is demonstrated that for each fixed amount of microchannels and its length, an optimal channel diameter exists. Formulas for optimal ratio of length, diameter, and number of microchannels evaluation were derived. It was shown that the maximum value of the objective function corresponds to a thin heat exchange matrix that consists of a large number of short channels with small diameter. 相似文献
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Experiments were carried out to examine the effects of a single porous-type roughness element on the insulated wall opposite the smooth heated plate on the heat transfer. The local heat transfer and drag coefficients depend on the porous diameter and the porosity. The local heat transfer coefficient takes a peak, PI, under the porous element in laminar flow. On the other hand, in turbulent flow, it takes two peaks, PI and P2, under and after the element, respectively. The position of peak P2 varies with the height of the element and the Reynolds number. The drag coefficient of the porous element is lower than that of the solid element. According to thermal performance at constant pumping power, this kind of element should be used in laminar flow. In addition, it is estimated that the porous element should be utilized in the composite effects (the turbulence increase and the thermal radiation shielding effect) of heat transfer in order to apply the element effectively. 相似文献
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Boiling heat transfer in a refrigerant R 21 flow in a microchannel heat sink is studied. A stainless steel heat sink with
a length of 120 mm contains ten microchannels with a size of 640×2050 μm at cross-section with a wall roughness of 10 μm.
The local heat-transfer coefficient distribution along the heat sink length is obtained. The ranges of parameters are: mass
flow from 68 to 172 kg/m2s, heat fluxes from 16 to 152 kW/m2, and vapor quality from 0 to 1. The maximum values of the heat transfer coefficient are observed at the inlet of microchannels.
The heat transfer coefficients decrease substantially along the length of channels under high heat flux conditions and, on
the contrary, change insignificantly under low heat flux condition. A comparison with the well-known models of flow boiling
heat transfer is performed and the range of applicability is defined. 相似文献