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Numerical Modeling of Heat Transfer and Water Shedding in Automotive Evaporator Louvered Fins 汽车蒸发器百叶翅片换热与疏水的数值模拟
Pub Date : 2000-11-05 DOI: 10.1115/imece2000-1530
Deming Wang, Chao Zhang
A mathematical model has been developed to simulate mass and heat transfer of humid air flows at the airside of automobile air conditioning evaporators. The phenomenon of water condensation and water shedding in louvered fins are modeled based on extension of the existing Eulerian two-fluid method which treats water and air as two continuous media. A species transport equation for the mass fraction of water vapor in humid air is solved. The condensation of water from the air mixture translates into a sink term for the vapor transport equation and an equal source in the continuity equation for the volume fraction of liquid water in the two-fluid system of equations. A critical element in modeling the condensate transport in louvered fins calls for a surface tension force sub-model, since the surface tension force is the primary resistance against water shedding and draining. A formulation is proposed to evaluate the surface tension force based on searching for the most probable liquid-air interface where sharp gradient of water volume fraction exists. Numerical aspect of the implementation is discussed. In order to validate the model and demonstrate the applicability of the present methodology, a six-louver two-dimensional test case is established. The relative influence of the stopping force on liquid distribution pattern and flow was illustrated. The simulation is then carried out on a full-scale 2-D louvered fin design for different operating conditions. This study has demonstrated the feasibility of modeling “wet” heat transfer and water shedding in evaporator fins with an Eulerian two-fluid based method.
建立了模拟汽车空调蒸发器空侧湿气流传质传热的数学模型。对现有的欧拉双流体方法进行了扩展,将水和空气作为两种连续介质,对百叶翅片中的冷凝水和水脱落现象进行了建模。求解了湿空气中水蒸气质量分数的物质输运方程。在双流体方程组中,空气混合物中水的冷凝转化为蒸汽输送方程中的汇项和液态水体积分数连续性方程中的相等源。对百叶窗翅片中冷凝水输送进行建模的一个关键因素需要一个表面张力子模型,因为表面张力是防止水脱落和排水的主要阻力。提出了一种基于寻找最可能存在水体积分数急剧梯度的液气界面来计算表面张力的公式。数值方面的实施进行了讨论。为了验证该模型并证明本方法的适用性,建立了一个六百叶窗二维测试用例。说明了停止力对液体分布形态和流动的相对影响。然后在不同工况下的全尺寸二维百叶翅上进行了仿真。本研究证明了用欧拉双流体方法模拟蒸发器翅片“湿”传热和水脱落的可行性。
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引用次数: 0
Stacked Microchannel Heat Sinks for Liquid Cooling of Microelectronic Components 用于微电子元件液体冷却的堆叠微通道散热器
Pub Date : 2000-11-05 DOI: 10.1115/1.1647124
Xiaojin Wei, Y. Joshi
A novel heat sink based on a multi-layer stack of liquid cooled microchannels is investigated. For a given pumping power and heat removal capability for the heat sink, the flow rate across a stack of microchannels is lower compared to a single layer of microchannels. Numerical simulations using a computationally efficient multigrid method [1] were carried out to investigate the detailed conjugate transport within the heat sink. The effects of the microchannel aspect ratio and total number of layers on thermal performance were studied for water as coolant. A heat sink of base area 10 mm by 10 mm with a height in the range 1.8 to 4.5 mm (2–5 layers) was considered with water flow rate in the range 0.83×10−6 m3/s (50 ml/min) to 6.67×10−6 m3/s (400 ml/min). The results of the computational simulations were also compared with a simplified thermal resistance network analysis.
研究了一种基于多层液冷微通道堆叠的新型散热器。对于给定的泵送功率和散热器的散热能力,与单层微通道相比,通过一堆微通道的流速更低。采用计算效率高的多网格方法[1]进行了数值模拟,研究了散热器内部的详细共轭输运。研究了以水为冷却剂的微通道长径比和总层数对热工性能的影响。考虑底座面积为10mm × 10mm,高度为1.8 ~ 4.5 mm(2-5层),水流量为0.83×10−6 m3/s (50 ml/min) ~ 6.67×10−6 m3/s (400 ml/min)。并将计算模拟结果与简化的热阻网络分析结果进行了比较。
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引用次数: 154
Analysis of RELAP5 Drift-Flux Model for Vertical Subcooled Boiling Flow at Low Pressure Conditions 低压条件下垂向过冷沸腾流动RELAP5漂移通量模型分析
Pub Date : 2000-11-05 DOI: 10.1115/imece2000-1535
B. Končar, I. Kljenak, B. Mavko
The RELAP5/MOD3.2.2 Gamma code was assessed against low pressure boiling flow experiments performed by Zeitoun and Shoukri (1997) in a vertical annulus. The predictions of subcooled boiling bubbly flow showed that the present version of the RELAP5 code underestimates the void fraction increase along the flow and strongly overestimates the vapor drift velocity. It is shown that in the calculations, a higher vapor drift velocity causes a lower interphase drag and may be a possible reason for underpredicted void fraction development. A modification is proposed, which introduces the replacement of the EPRI drift-flux formulation, which is currently incorporated in the RELAP5 code, with the Zuber-Findlay (1965) drift-flux model for the experimental low pressure conditions of the vertical bubbly flow regime. The improved experiment predictions with the modified RELAP5 code are presented and analysed.
根据Zeitoun和Shoukri(1997)在垂直环空进行的低压沸腾流动实验,对RELAP5/MOD3.2.2伽玛码进行了评估。对过冷沸腾气泡流的预测表明,目前版本的RELAP5程序低估了沿流动的空隙率增加,而严重高估了蒸汽漂移速度。计算结果表明,较高的气相漂移速度会导致较低的相间阻力,这可能是空化率发展被低估的原因。提出了一项修改,将目前纳入RELAP5规范的EPRI漂通量公式替换为Zuber-Findlay(1965)漂通量模型,用于垂直气泡流状态的实验低压条件。提出并分析了改进后的RELAP5代码的实验预测结果。
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引用次数: 1
A Fully Eulerian Approach to Particle-Laden Compressible Flows 满载粒子的可压缩流动的全欧拉方法
Pub Date : 2000-11-05 DOI: 10.1115/imece2000-1525
A. Dolatabadi, J. Mostaghimi, Mihajlo Ivanovic
Dense particles in highly compressible gas flows are analyzed using the Eulerian-Eulerian approach. Simulations are applied to a High Velocity Oxy-Fuel (HVOF) thermal spray torch. In this analysis, by using a fully Eulerian approach, the dispersed flow like the continuous flow is considered in the Eulerian frame whereby most of the physical aspects of the gas-particle flow in the HVOF process can be incorporated. These two phases are coupled through momentum and energy exchanges that are expressed in the form of source terms appearing in the governing equations. The numerical simulations show large variations in gas velocity and temperature both inside and outside the torch due to flow features such as mixing layers, shock waves, and expansion waves. The characteristics of the particles such as velocity and temperature are analyzed.
采用欧拉-欧拉方法对高可压缩气体流中的致密颗粒进行了分析。对高速氧燃料(HVOF)热喷枪进行了仿真研究。在本分析中,通过使用完全欧拉方法,在欧拉框架中考虑了像连续流动一样的分散流动,从而可以纳入HVOF过程中气-颗粒流动的大多数物理方面。这两个阶段通过动量和能量交换耦合在一起,以控制方程中出现的源项的形式表示。数值模拟表明,由于混合层、激波和膨胀波等流动特征,火炬内外的气体速度和温度都发生了很大的变化。分析了颗粒的速度、温度等特性。
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引用次数: 0
Theoretically-Based Leidenfrost Point Model 基于理论的莱顿弗罗斯特点模型
Pub Date : 2000-11-05 DOI: 10.1115/imece2000-1502
J. Bernardin, I. Mudawar
This study presents a theoretically-based model of the Leidenfrost point (LFP); the minimum liquid/solid interface temperature required to support film boiling on a smooth surface. The model is structured around bubble nucleation, growth, and merging criteria, as well as surface cavity size characterization. It is postulated that for liquid/solid interface temperatures at and above the LFP, a sufficient number of cavities (about 20%) are activated and the bubble growth rates are sufficiently fast that a continuous vapor layer is established nearly instantaneously between the liquid and the solid. The model is applicable to both pools of liquid and sessile droplets. The effect of surface cavity distribution on the LFP predicted by the model is verified for boiling on aluminum, nickel and silver surfaces, as well as on a liquid gallium surface. The model exhibits good agreement with experimental sessile droplet data for water, FC-72, and acetone. While the model was developed for smooth surfaces on which the roughness asperities are of the same magnitude as the cavity radii (0.1–1.0 μm), it is capable of predicting the boundary or limiting Leidenfrost temperature for rougher surfaces with good accuracy.
本文提出了一个基于理论的Leidenfrost点(LFP)模型;支持薄膜在光滑表面上沸腾所需的最低液/固界面温度。该模型围绕气泡成核、生长和合并标准以及表面空腔尺寸表征进行构建。假设在LFP及以上的液/固界面温度下,有足够数量的空腔(约20%)被激活,气泡生长速度足够快,几乎在液体和固体之间瞬间建立了连续的蒸汽层。该模型既适用于液体池,也适用于固体液滴。在铝、镍和银表面以及液镓表面的沸腾实验中,验证了表面空腔分布对模型预测的LFP的影响。该模型与水、FC-72和丙酮的实验数据吻合良好。虽然该模型适用于粗糙度与腔半径大小相同(0.1 ~ 1.0 μm)的光滑表面,但对于较粗糙的表面,该模型能够以较好的精度预测边界或限制莱顿弗罗斯特温度。
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引用次数: 0
Transient Axial Free Jet Impinging Over a Flat Uniformly Heated Disk: Solid–Fluid Properties Effects 瞬态轴向自由射流撞击均匀加热的平面:固体-流体特性影响
Pub Date : 2000-11-05 DOI: 10.1115/imece2000-1543
A. Bula, M. M. Rahman, J. Leland
Transient conjugate heat transfer process during axial free jet impingement on a solid disk of finite thickness was considered. As the fluid reached steady state, power was turned on and a uniform heat flux was imposed on the disk at its opposite surface. The numerical model considered both solid and fluid regions. Equations for conservation of mass, momentum, and energy were solved in the liquid region taking into account the transport processes at the inlet and exit boundaries, as well as at the solid-liquid and liquid-gas interfaces. Inside the solid, only the heat conduction equation was solved. The shape and location of the free surface (liquid-gas interface) was determined iteratively as a part of the solution process by satisfying the kinematic condition as well as the balance of normal and shear forces at this interface. A non-uniform grid distribution, captured from a systematic grid-independence study, was used to adequately accommodate large variations near the solid-fluid interface. Computed results include the simulation of six different substrate materials namely, aluminum, constantan, copper, diamond, silicon, and silver, and three different impinging liquids, FC - 77, Mil - 7808, and water. The solids and fluids selected covered a wide range of possibilities of conjugate heat transfer phenomena. The analysis performed showed that the thermal storage capacity, defined as density times specific heat, is an important factor defining which material will attain steady state faster during conjugate heat transfer process, like the thermal diffusivity does it for pure conduction heat transfer.
研究了轴向自由射流冲击有限厚度固体圆盘时的瞬态共轭传热过程。当流体达到稳定状态时,电源被打开,均匀的热流被施加到磁盘对面的表面上。数值模型同时考虑了固体区域和流体区域。在考虑了进口和出口边界以及固液和液气界面的输运过程的情况下,求解了液体区域的质量、动量和能量守恒方程。在固体内部,只求解了热传导方程。作为求解过程的一部分,通过满足运动学条件以及该界面处法向力和剪力的平衡,迭代确定了自由表面(液气界面)的形状和位置。从系统网格独立研究中获得的非均匀网格分布用于充分适应固液界面附近的大变化。计算结果包括六种不同的衬底材料的模拟,即铝、康铜、铜、金刚石、硅和银,以及三种不同的冲击液体FC - 77、Mil - 7808和水。所选择的固体和流体涵盖了广泛的共轭传热现象的可能性。分析表明,蓄热能力(定义为密度乘以比热)是决定材料在共轭传热过程中更快达到稳态的重要因素,就像纯传导传热中的热扩散率一样。
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引用次数: 0
Thermal Spreading Resistance of Eccentric Heat Sources on Rectangular Flux Channels 偏心热源在矩形通量通道上的热扩散阻力
Pub Date : 2000-11-05 DOI: 10.1115/1.1568125
Y. Muzychka, J. Culham, M. Yovanovich
A general solution, based on separation of variables method for thermal spreading resistances of eccentric heat sources on a rectangular flux channel is presented. Solutions are obtained for both isotropic and compound flux channels. The general solution can also be used to model any number of discrete heat sources on a compound or isotropic flux channel using superposition. Several special cases involving a single and multiple heat sources are presented.
提出了一种基于分离变量法求解矩形磁通管内偏心热源热扩散阻力的通解。得到了各向同性和复合通量通道的解。通解也可用于用叠加法对复合或各向同性通量通道上任意数量的离散热源进行建模。提出了几个涉及单个热源和多个热源的特殊情况。
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引用次数: 205
ATR Flow Blockage Tests and CFD Simulations ATR气流阻塞测试和CFD模拟
Pub Date : 2000-11-05 DOI: 10.1115/imece2000-1532
Chang H. Oh, S. A. Atkinson
Steady state flow channel blockage tests were conducted at the Idaho National Engineering and Environmental Laboratory (INEEL) as part of the safety basis upgrade program for the Advanced Test Reactor (ATR). The tests were sponsored by the U.S. Department of Energy (DOE). This study was aimed at carrying out flow blockage tests, establishing a base case to compare test results with numerical results using a computational fluid dynamics code, calculating temperature profiles for blockage cases, and determining whether or not the ATR core would be exposed to core melting due to blockage of the inlet of a fuel cooling channel. The test section consisted of three parallel channels and two side channels along the side plate. Three cases were selected to evaluate flow blockage events in the channels. A base case with all the channels open, Case 1 where the inlet of the middle channel is blocked, and Case 2 where both the middle channel and the side channel are blocked. Laser Doppler anemometer (LDA) was used to measure velocities in the channel. Velocities were measured at 2.54-mm intervals in the channel width, and every 1.27-mm around side windows in the flow direction for three parallel channels. LDA measured velocity profiles for the base case and Case 1 indicated good agreement with predicted velocity profiles from the CFD model. The channel velocity in the blocked channel is about 70% of the velocity in the unblocked, adjacent channel in between the top and second side channel vents. Additional flow redistribution occurs into the blocked channel at the second side channel vent. Temperature calculations for the base case were made to compare with benchmark temperatures calculated with the ATR SINDA model and CFD calculations underpredicted benchmark plate temperatures by less than 10% while it predicted bulk temperatures very well. The same heat flux and boundary conditions were incorporated for Case 1 and Case 2. The results for both cases indicated that core melt would not occur in the postulated ATR flow channel blockage events simulated for this study. Peak fuel plate temperature is about 20% greater than the peak temperature for the unblocked case just upstream of the second side channel vent.
作为先进试验堆(ATR)安全基础升级计划的一部分,稳态流道堵塞试验在爱达荷州国家工程与环境实验室(INEEL)进行。这些测试由美国能源部(DOE)赞助。本研究的目的是进行流动阻塞试验,建立一个基本情况,使用计算流体动力学代码将试验结果与数值结果进行比较,计算阻塞情况下的温度分布,并确定ATR堆芯是否会因燃料冷却通道入口阻塞而暴露于堆芯熔化。试验段由三个平行通道和沿侧板的两个侧通道组成。选取了三个案例来评估通道内的水流阻塞事件。所有通道打开的基本情况,中间通道的入口被阻塞的情况1,中间通道和侧通道都被阻塞的情况2。激光多普勒风速仪(LDA)用于测量通道内的速度。在通道宽度上,以2.54 mm的间隔测量速度,在三个平行通道的流动方向上,沿侧窗每隔1.27 mm测量速度。LDA测量的基本情况和情况1的速度曲线与CFD模型预测的速度曲线吻合良好。堵塞通道中的通道速度约为顶部和第二侧通道通风口之间未堵塞的相邻通道速度的70%。额外的流动再分配发生在阻塞通道的第二侧通道通风口。将基准工况的温度计算与ATR SINDA模型计算的基准温度进行比较,CFD计算对基准板温度的预测低于10%,而对体温度的预测非常好。对于情形1和情形2,采用了相同的热通量和边界条件。这两种情况的结果都表明,在本研究模拟的ATR流道阻塞事件中,不会发生堆芯熔化。燃油板的峰值温度比第二侧通道通风口上游未堵塞的情况下的峰值温度高20%左右。
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引用次数: 0
Modeling and Simulation of Subcooled Turbulent Boiling Flow 过冷湍流沸腾流的建模与仿真
Pub Date : 2000-11-05 DOI: 10.1115/imece2000-1531
J. A. Zarate, R. Roy, S. Kang, Andre Laporta
Modeling and numerical simulation of turbulent sub-cooled boiling flow of refrigerant-113 through a vertical concentric annular channel with its inner wall heated are reported. The two-fluid model conservation equations were solved. The Reynolds stresses in the liquid phase momentum equation were closed using the gradient transport approximation. The turbulent viscosity was considered to be comprised of shear-induced and bubble-induced components. Boiling at the inner wall was described by a wall heat transfer model which splits the wall heat flux into convective, quenching, and vaporization heat flux components. This model was modified to reflect our measurement of the radial turbulent heat flux in the liquid phase near the wall. In addition, new wall laws for the liquid phase mean temperature and axial velocity were used. The computational results are compared with our measurements wherever possible.
本文报道了制冷剂-113在管内加热的垂直同心环形通道内的湍流过冷沸腾流动的模型和数值模拟。求解了双流体模型守恒方程。采用梯度输运近似封闭了液相动量方程中的雷诺应力。湍流粘度被认为是由剪切诱导和气泡诱导组成的。内壁沸腾用壁面传热模型来描述,该模型将壁面热流分为对流热流、淬火热流和汽化热流。对该模型进行了修改,以反映我们对壁面附近液相径向湍流热通量的测量。此外,采用了新的液相平均温度和轴向速度的壁律。尽可能地将计算结果与我们的测量结果进行比较。
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引用次数: 1
Steady-State Operation of a Loop Heat Pipe With Analytical Prediction 循环热管的稳态运行与分析预测
Pub Date : 2000-11-05 DOI: 10.1115/imece2000-1551
H. Watson, C. Gerhart, G. Mulholland, D. Gluck
The steady-state performance of an 800W, sintered nickel powder wick, loop heat pipe (LHP) has been analyzed using a modified Dynatherm LHP Thermal Model. Results from characterization tests of this LHP performed at the Air Force Research Laboratory in Albuquerque, NM are used as the basis for comparison and discussion of results for the analytical model. The analytical predictions gave excellent correlation to the measured data for power levels ranging from 50 to 1500W at condenser chiller settings between −40°C and 20°C, with the LHP in a horizontal orientation.
采用改进的Dynatherm LHP热模型对800W烧结镍粉芯环形热管(LHP)的稳态性能进行了分析。在新罕布什尔州阿尔伯克基的空军研究实验室进行的LHP特性测试的结果被用作分析模型结果比较和讨论的基础。在- 40°C至20°C的冷凝器制冷机设置下,LHP处于水平方向,分析预测与功率水平范围为50至1500W的测量数据具有良好的相关性。
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引用次数: 2
期刊
Heat Transfer: Volume 4
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