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微尺度通道内流动沸腾研究综述 总被引:1,自引:0,他引:1
阐述了微尺度通道内传热问题出现的工程背景——高密度微电子器件的冷却。对当前国内外微尺度通道内流动沸腾换热特性的研究现状进行了归纳。突出分析了工质种类、微尺度通道的几何参数和工质的工况参数等对微尺度通道内流动沸腾换热特性的影响。同时分析了微尺度通道内流动沸腾换热的强化机理、流动阻力特性、压降关联式和沸腾换热关联式的理论和实验研究。最后根据分析对今后的工作提出了一些建议。 相似文献
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提出了一种用于超临界液化天然气换热的微小通道换热器整体性能提高的被动式强化技术并进行了数值模拟验证和设计优化。在普通的矩形微小通道内利用3D激光打印技术在壁面加工横向圆弧形微沟槽以强化换热能力。首先对圆弧形微沟槽的槽深、槽宽和相邻两槽道中心距等几何尺寸进行了优化计算,然后讨论了在使用强化技术后工质温度在跨越临界温度的120.000~250.000 K的换热强化和流动特性,进一步考察了工质温度、质量流量(雷诺数)和进口压力对传热系数(努塞尔数)、摩擦因子和综合效益系数的影响。此外,通过微沟槽附近的局部流动特性分析强化换热机理,数值模拟结果表明带有横向微沟槽的紧凑式换热器的综合换热效益得到30%左右增加,显示了优异的换热强化综合效果。 相似文献
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提出了一种用于超临界液化天然气换热的微小通道换热器整体性能提高的被动式强化技术并进行了数值模拟验证和设计优化。在普通的矩形微小通道内利用3D激光打印技术在壁面加工横向圆弧形微沟槽以强化换热能力。首先对圆弧形微沟槽的槽深、槽宽和相邻两槽道中心距等几何尺寸进行了优化计算,然后讨论了在使用强化技术后工质温度在跨越临界温度的120K-250K范围内的换热强化和流动特性,进一步考察了工质温度、质量流量(雷诺数)和进口压力对换热系数(努塞尔数)、摩擦因子和综合效益系数的影响。此外,通过微沟槽附近的局部流动特性分析强化换热机理,数值模拟结果表明带有横向微沟槽的紧凑式换热器的综合换热效益得到30%左右增加,显示了优异的换热强化综合效果 相似文献
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在综合流向微槽表面流动及传热特性的基础上,结合涡轮叶冷却通道内的流动和换热特性,提出了将流向微槽表面应用于涡轮叶片的冷却通道,分析研究流向微槽的影响,以期为涡轮叶片的冷却寻找更有效的技术。 相似文献
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本研究对微小通道内氢气/空气预混火焰进行了数值模拟。考察了微小通道内贴壁处壁面反应对微小通道内火焰燃烧特性的影响,在此基础上考察了不同微小尺度下壁面反应作用的程度。研究结果表明:微小通道贴壁处壁面反应能够抑制通道内的气相燃烧反应,其中H自由基是参与壁面反应最重要的自由基。当微小通道壁面间距为3 mm时,壁面反应的作用不太明显,但当壁面间距减少到0.4 mm时,壁面反应的作用已经不可忽视,此时必须要考虑到壁面反应的影响。 相似文献
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《热能动力工程》2016,31(6)
为了研究流体流经半圆形微通道的传热与流动特性,对去离子水、Cu-水纳米流体及Al-水纳米流体在21个当量直径为612μm的平行半圆形微通道热沉(微型散热片)中的流动与对流换热特性进行了实验研究。研究发现:与截面为矩形的常规形状相比,半圆形微通道也具有很好的换热效果,与去离子水相比,添加Al和Cu纳米颗粒的纳米流体压降损失增大。当纳米流体的质量浓度为0.5%时,在微通道换热器中的纳米流体效应由于粘度过大等原因发生了恶化,并且这种恶化在高流速下也出现了。根据实验数据得到了半圆形微通道内低浓度纳米流体的层流对流换热以及摩擦阻力系数关联式,对热性能系数的分布曲线进行了综合分析,研究结果对于集成高效芯片散热系统设计具有重要意义。 相似文献
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对梯形截面微通道内去离子水的不可压缩充分发展的流动建立数学模型,采用二维SIMPLE算法求解通道横截面上的流向速度分布.对特定几何尺寸的通道内水的充分发展流动在实验雷诺数范围内进行数值模拟,并计算充分发展段的阻力系数,将模拟所得阻力系数随雷诺数的变化关系与有关实验结果进行了对比,得到了较好的一致性.从而表明:N-S方程仍然适用于微通道内去离子水的层流流动的数值模拟. 相似文献
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ABSTRACTThe thermal performance of the rotating U-shaped mini/micro/macrochannels is numerically investigated (Re = 125–20000). To compare the performance of different types of channels, the macrochannel passage with a square cross-section (D*D) is replaced by an array of parallel rectangular micro/mini channels with sides of D*D/12.5 (mini) and D*D/50 (micro). The results show that using nanofluid and converting the macrochannel to a parallel arrangement of minichannels considerably improve heat transfer enhancement and consequently a large volume reduction of up to about 70% for similar heat transfer. Also, in contrast to the macrochannel, adding ribs to the minichannels cannot improve their thermal performance. 相似文献
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Pietro Asinari 《International Journal of Heat and Mass Transfer》2005,48(18):3864-3879
A new approach to take into account the effects of variable physical properties on turbulence is suggested. It allows to choose freely the turbulent closure model for conventional terms due to velocity fluctuations and to describe coherently the additional terms due to density fluctuations. Numerical calculations based on the suggested approach have been performed for carbon dioxide flowing within mini/micro channels under cooling conditions. The numerical predictions show that the effects due to density fluctuations are smaller than it could have been initially supposed and that the heat transfer impairment for mini/micro channels, which some experiments seem to highlight, is not completely explained by the considered model. 相似文献
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This second part of a two-part study concerns heat transfer characteristics for FC-72 condensing along parallel, square micro-channels with a hydraulic diameter of 1 mm, which were formed in the top surface of a solid copper plate. Heat from the condensing flow was rejected to a counter flow of water through channels brazed to the underside of the copper plate. The FC-72 condensation heat transfer coefficient was highest near the channel inlet, where the annual liquid film is thinnest. The heat transfer coefficient decreased along the micro-channel because of the film thickening and eventual collapse of the annular regime. Notable heat transfer enhancement was observed for annular flow regions of the micro-channel associated with interfacial waves. Comparing the present data to predictions of previous annular condensation heat transfer correlations shows correlations intended for macro-channels generally provide better predictions than correlations intended specifically for mini/micro-channels. A new condensation heat transfer coefficient correlation is proposed for annular condensation heat transfer in mini/micro-channels. The new correlation shows excellent predictive capability based on both the present FC-72 data and a large database for mini/micro-channel flows amassed from eight previous sources. 相似文献
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An empirical approach is proposed to estimate the bulk temperature in practical laminar tube flow. To examine the correlation, heat transfer in different types of tubes with wall conduction and uniform constant heat flux at tube outer wall surface is numerically investigated. The predictions from the proposed correlation match well with the numerical results in all the cases studied for air flow in the Pe range from 105 to 1032 and for water flow in the Pe range from 70 to 700. The method is further testified via comparison with experimental data and numerical results of mini (micro)-channel water flow available in literature. 相似文献
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Manu Mital 《Applied Thermal Engineering》2013,50(1):429-436
Thermal management issues are limiting barriers to high density electronics packaging and miniaturization. Liquid cooling using micro and mini channels is an attractive alternative to large and bulky aluminum or copper heat sinks. These channels can be integrated directly into a chip or a heat spreader, and cooling can be further enhanced using nanofluids (liquid solutions with dispersed nanometer-sized particles) due to their enhanced heat transfer effects reported in literature. The goals of this study are to evaluate heat transfer improvement of a nanofluid heat sink with developing laminar flow forced convection, taking into account the pumping power penalty. The phrase heat transfer enhancement ratio (HTR) is used to denote the ratio of average heat transfer coefficient of nanofluid to water at the same pumping power. The proposed model uses semi-empirical correlations to calculate nanofluid thermophysical properties. The predictions of the model are found to be in good agreement with experimental studies. The validated model is used to identify important design variables (Reynolds number, volume fraction and particle size) related to thermal and flow characteristics of the microchannel heat sink with nanofluids. Statistical analysis of the model showed that the volume fraction is the most significant factor impacting the HTR, followed by the particle diameter. The impact of the Reynolds number and other interaction terms is relatively weak. The HTR is maximized at smallest possible particle diameter (since smaller particles improve heat transfer but do not impact pumping power). Then, for a given Reynolds number, an optimal value of volume fraction can be obtained to maximize HTR. The overall aim is to present results that would be useful for understanding and optimal design of microchannel heat sinks with nanofluid flow. 相似文献
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《传热工程》2012,33(3):288-301
AbstractWettability plays an important role during flow boiling inside micro and mini channels. The present work focuses on the flow boiling heat transfer characteristics inside copper minitube (inner diameter of 3?mm) coated internally to render the inside surface nearly hydrophobic. Electroless Galvanic Deposition technique is employed for hydrophobic coating inside the copper tube. Both single phase heat transfer and two-phase flow boiling heat transfer and pressure drop characteristics were investigated in regular and internally coated hydrophobic copper minitubes. The experiments were performed with deionized water as a working fluid and the mass flux was varied from 100 to 650?kg/m2s. The two-phase heat transfer characteristics was observed to be both functions of mass flux as well as heat flux. The two phase heat transfer has been observed to be augmented due to the wettability within the tubes. The two-phase pressure drop has also been observed to increase when compared to the regular, uncoated tube; however, the proportional increment is lower than the augmentation achieved in two-phase heat transfer. The enhanced heat transfer effects observed have been explained on the basis of wetting physics. 相似文献
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Friction factors in smooth trapezoidal silicon microchannels with different aspect ratios 总被引:3,自引:0,他引:3
An experiment has been conducted to measure the friction factor of laminar flow of deionized water in smooth silicon microchannels of trapezoidal cross-section with hydraulic diameters in the range of 25.9-291.0 μm. It is shown that the friction constant of these microchannels is greatly influenced by the cross-sectional aspect ratio, Wb/Wt. Based on the 334 data points, a correlation equation for the friction constant of a fully developed laminar flow of water in these microchannels is obtained in terms of the cross-sectional aspect ratio. The experimental data is found to be in good agreement with an existing analytical solution for an incompressible, fully developed, laminar flow under no-slip boundary condition. It is confirmed that the Navier-Stokes equations are still valid for the laminar flow of deionized water in smooth silicon microchannels having hydraulic diameter as small as 25.9 μm. For smooth channels with larger hydraulic diameters of 103.4-291.0 μm, transition from laminar to turbulent flow is found at Re=1500-2000. 相似文献