潜热型热功能流体强化换热分析

本文建立了分析带有相变微胶囊的潜热型热功能流体的流动和换热过程数理模型,应用有限差分法和移动热源法进行联合求解。计算结果表明,相变微胶囊的加入:较好地提高了流体的换热性能。获得了相变颗粒大小和体积分数对强化换热影响等结果。计算结果对该类流体的设计和应用提供了理论依据。     

圆管内潜热型功能流体对流换热的实验研究

本文实验研究了由正十四烷和尿素甲醛树脂制成的相变微胶囊和水混合组成的潜热型功能流体流过等热流圆管时的对流换热特性。相变微胶囊的加入可以显著增强流体与壁面间的对流换热,显著降低壁面温度和流体温度;在融化段对流换热系数呈增加分布,流体和壁面温度各自基本稳定在相应的温度值。强化对流换热的效果主要在融化段,并随流体中相变微胶囊浓度的增大而增强,也随R-eynolds数的增大而增强。     

微针肋槽道内去离子水换热特性

设计了槽肋比为1:2和2:1的矩形大长宽比微针肋散热器,并实验研究了去离子水在其内的流动换热性能。结果表明：当进口温度为40 ℃、微针肋槽道在雷诺数小于650、最高壁面温度低于77 ℃时,单位面积散热量可达21.32 W/cm²。当雷诺数一定时,同一个槽道壁面温度沿着流动方向不断增加、同一个位置壁面温度随着加热功率的增加而增大,局部努谢尔数沿着流动方向先减小后逐渐增加并趋于定值。当针肋流动换热长度较长时,其入口效应可以忽略,槽道平均努谢尔数随着雷诺数的增大而增大,与加热功率无关;为了更好地表达微针肋槽道内的换热特性,考虑了槽肋比、流动雷诺数等影响,拟合了去离子水在微针肋槽道内的对流换热关系式。     

流体横掠圆形微针肋热沉流动与传热特性

本文以去离子水为冷却工质,对流体横掠当量直径为90～200 μm的圆形微针肋阵列热沉的流动与传热特性进行了实验研究.实验数据显示:对于叉排实验件热沉,摩擦阻力系数对雷诺数的依变关系在Re=100前后发生转变;端壁效应、高径比和布置方式对摩擦阻力系数有很大影响;努塞尔特数随雷诺数的增大显著增大,其依变关系在双对数坐标下呈现较好的线性关系.     

水平圆管内磁性潜热型功能流体对流换热特性的数值模拟

建立磁场作用下水平圆管内磁性潜热型功能流体对流换热的数学物理模型,分析磁场强度、磁性相变微胶囊体积分数、流体质量流量等因素对流体对流换热的影响.磁场对磁性潜热型功能流体的对流换热具有显著的强化作用,磁场强度愈大强化作用愈明显,强化原因是磁性相变微胶囊受到磁力作用产生扰动.     

流体横掠微针肋阵列热沉的阻力特性

本文以去离子水作为冷却工质,研究了在低Re下流体横向冲刷微针肋阵列时的阻力特性,所用微针肋阵列肋高200μm,直径120μm,为转置正方形叉排结构.实验结果与可利用关联式的对比表明,现存宏观尺度上的关联式不能很好地预测流体横掠微针肋阵列热沉的阻力特性,特别是在Re大于140时,实验结果要高于关联式预测值.     

肋端间隙对微针肋热沉流体流动和传热的影响

本文针对微针肋顶端间隙诱导产生的加速流对流体流动和传热的影响,采用计算流体力学（CFD）模拟与分析软件进行了三维数值模拟。模型采用有限体积法离散、SIMPLEC算法进行层流计算。模拟结果表明,不同肋端间隙对针肋内部流体流动和传热特性有重要影响。在本文的模拟条件下,定流量和定泵功下的最优无量纲间隙（肋端州隙比肋茸径）分别...     

流体横掠方形微针肋阵列热沉的传热特性

本文以去离子水为冷却工质,对流体横向冲刷方形微针肋阵列热沉的传热特性进行了实验研究.结果表明流体横掠微针肋热沉具有优越的换热特性.实验得出,冷却液的雷诺数对热沉的换热性能影响显著;总热阻随着泵功的增大而降低;对流换热热阻在总热阻中所占比例较小,流体吸热焓变热阻成为影响热沉性能的主导因素.     

内肋套管管内流动与换热特性研究

利用实验和数值模拟方法考察了含水原油在内肋套管内的流动与传热性能,指出了在 Re=200～1200 时管子结构尺寸(肋片高度、肋片宽度和肋片长度)对传热性能的影响,并进行了实验验证.     

一类潜热型功能液固两相流体的定压比热研究

应用两相流与热物理理论，严格推导出一类潜热型功能液固两相流体的定压比热计算公式．     

Heat transfer in lattice BGK modeled fluid

The thermal lattice BGK model is a recently suggested numerical tool aiming at solving problems of thermohydrodynamics. The quality of the lattice BGK simulation is checked in this paper by calculating temperature profiles in the Couette flow under different Eckert and Mach numbers. A revised lower order model is proposed to improve the accuracy and the higher order model is proved to be advantageous in this respect, especially in the flow regime with a higher Mach number.     

微结构表面封闭式喷雾冷却传热特性

以蒸馏水为工质,在闭式循环喷雾冷却系统上,变化喷雾流量,研究了表面几何结构对喷雾传热性能的影响。从对流换热和相变换热比例关系的角度,对喷雾换热机理进行了实验研究。结果表明：与光滑表面相比,微结构表面可明显增强喷雾换热强度,这主要归因于相变换热的增强。表面温度较低时,直肋面换热效果最好 ;增大流量,光面换热增强,而直肋面变化不明显。表面温度较高时,方肋面换热效果最好;随着流量增大,所有面换热均增强。对于微结构表面,相变换热份额均大于50%,故而以相变换热为主;而光滑表面,即使在温度较低时,相变换热份额也大于20%。临界热流密度与三相接触线长度正相关,流量为15.9 mL/min时,方肋面、直肋面和光面的临界热流密度依次为159.1,120.2,109.8 W/cm2,蒸发效率分别为96.0%,72.5%,67.1%。     

微结构表面封闭式喷雾冷却传热特性

以蒸馏水为工质,在闭式循环喷雾冷却系统上,变化喷雾流量,研究了表面几何结构对喷雾传热性能的影响。从对流换热和相变换热比例关系的角度,对喷雾换热机理进行了实验研究。结果表明:与光滑表面相比,微结构表面可明显增强喷雾换热强度,这主要归因于相变换热的增强。表面温度较低时,直肋面换热效果最好 ;增大流量,光面换热增强,而直肋面变化不明显。表面温度较高时,方肋面换热效果最好;随着流量增大,所有面换热均增强。对于微结构表面,相变换热份额均大于50%,故而以相变换热为主;而光滑表面,即使在温度较低时,相变换热份额也大于20%。临界热流密度与三相接触线长度正相关,流量为15.9 mL/min时,方肋面、直肋面和光面的临界热流密度依次为159.1,120.2,109.8 W/cm2,蒸发效率分别为96.0%,72.5%,67.1%。     

Experimental study on the heat transfer characteristics of a new type flat micro heat pipe heat exchanger with latent heat thermal energy storage

An experimental energy storage system has been designed using a new type flat micro heat pipe heat exchanger that incorporates a moderate-temperature phase change material paraffin with a melting point of 58°C. The basic structure, working principles, and design concept are discussed. The heat transfer process during the charging and discharging of the heat exchanger under various operating conditions has been experimentally investigated. Results show that the performance of the new type flat micro heat pipe was steady and efficient during charging and discharging. The average thermal storage power and absorption efficiency have been determined to be approximately 537 W and 92.5%, respectively.     

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。     

矩形微槽道纳米流体沸腾传热压降特性研究

为研究纳米流体微尺度沸腾传热流阻及压降特性,文中以体积浓度为0.2％的水基Al2O3纳米流体为试验工质,在尺寸为0.6mm×2mm矩形微槽道中进行沸腾传热实验,建立实验模型,分析纳米流体沸腾传热两相摩擦乘子的影响因素及进出口压降组成,并将本实验的两相摩擦压降值与现有理论模型及参数修正后理论模型预测值进行比较.结果显示,在本实验给定的条件下,实验段两相流压降中88.6％为两相摩擦压降.与L-M模型相比,M-H修正模型和Z-M修正模型都能较好地预测实验结果.其中经M-H修正模型能更好地预测本实验的实验值,使得平均误差减小为21.2％,大大降低了原L-M模型的误差.     

Heat and mass transfer characteristics during rapid solidification of Fe-Cu peritectic alloys

The viscose flow and microstructure formation of Fe-Cu peritectic alloy melts are investigated by analyzing the velocity and temperature fields during rapid solidification, which is verified by rapid quenching experiments. It is found that a large temperature gradient exists along the vertical direction of melt puddle, whereas there is no obvious temperature variation in the tangent direction of roller surface. After being sprayed from a nozzle, the alloy melt changes the magnitude and direction of its flow and velocity rapidly at a height of about 180 μm. The horizontal flow velocity increases rapidly, but the vertical flow velocity decreases sharply. A thermal boundary layer with 160–300 μm in height and a momentum boundary layer with 160–240 μm in thickness are formed at the bottom of melt puddle, and the Reynolds number Re is in the range of 870 to 1070 in the boundary layer. With the increase of Re number, the cooling rate increases linearly and the thickness of thermal boundary layer increases monotonically. The thickness of momentum boundary layer decreases slowly at first, then rises slightly and decreases sharply. If Re < 1024, the liquid flow has remarkable effects on the microstructure formation due to dominant momentum transfer. The separated liquid phase is likely to form a fiber-like microstructure. If Re>1024, the heat transfer becomes dominating and the liquid phase flow is suppressed, which results in the formation of fine and uniform equiaxed microstructures. Supported by the National Natural Science Foundation of China (Grant Nos. 50121101 and 50395105)     

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.     

微通道冷却器内流动和传热特性的数值模拟

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。