自然对流板肋热沉的三维数值结构优化

为提高热沉自然对流换热性能,利用ICEPAK软件对基板水平放置和基板竖直放置的两种放置取向的板肋热沉进行了数值模拟和结构优化。首先,通过与前人的实验结果进行对比,验证了数值模型的合理性;然后对一系列不同结构参数的热沉进行数值模拟,通过对比其散热性能寻找最优的热沉结构。热沉几何参数变化范围为肋片厚度1~15mm,肋片间隙6.75~33.75mm,肋片高度55~1395mm。结果表明在每个肋片高度下都有一组最优的肋厚t和肋间隙s值;当肋片高度超过720mm值时,基板水平放置热沉的热阻趋于一个稳定值;基板竖直放置热沉的热阻随肋片高度的增加一直在减小。     

带有双弯曲肋片的细通道流动与传热的数值模拟

为了强化细通道的传热性能,设计了一种带有双弯曲肋片的细通道。采用数值模拟的方法研究双弯曲肋片对于细通道中流体的流动特性、传热特性以及综合特性的影响。分析了进口雷诺数、肋片的半径大小对于细通道热沉中的摩阻系数、努塞尔数以及综合传热因子的影响。结果表明:细通道的摩阻系数与努塞尔数随着肋片半径的增大而增大,热阻随其增大而减小;在设置的雷诺数范围内,综合性能最好的为MCDR-0.4。证明双弯曲肋片的添加可以有效地提升细通道的综合性能。     

微肋渐扩细通道流动与传热特性分析

为进一步提高渐扩细通道热沉的综合性能,设计了3种微肋渐扩细通道,分别为:矩形肋、圆形肋和三角形肋渐扩细通道。采用CFD软件对不同结构微肋渐扩细通道的流动和传热特性进行数值研究,并将结果与光滑的渐扩细通道和直细通道进行对比。结果表明:微肋能有效地提高渐扩细通道的传热性能,但同时也增大其流动压降。在所研究的微肋渐扩细通道及工况范围内,矩形肋渐扩细通道的传热系数最高,其传热系数分别比直细通道和渐扩细通道平均高104.01%和119.1%。圆形肋渐扩细通道的压降最小,其压降分别比直细通道和渐扩细通道平均高190.65%和287.43%。此外,圆形肋渐扩细通道的综合性能最好,在所研究的工况范围其综合传热强化因子的范围为1.16—1.47,比渐扩细通道平均高28.59%。     

半导体激光器低热阻液冷热沉研究现状与展望

近年来,半导体激光器输出功率持续增加,引发热负载受限问题。热负载使芯片有源区产生温升,进一步影响芯片温度分布,导致半导体激光器(Laser diode, LD)芯片性能逐渐劣化。而对于确定的封装形式,热沉热阻成为控制温升的决定性因素。因此,降低热沉热阻对提升半导体激光器输出能力与光束性质具有重要意义。液冷热沉可以有效降低热阻,本文从液冷热沉材料、液冷热沉结构和液冷冷媒性质三个方面,回顾了近30年LD液冷热沉热阻演变进程,总结了液冷热沉发展过程中热阻的影响因素,进一步探讨了降低热阻的发展方向与应用前景。     

基于热阻网络模型的硅基微槽热沉多目标优化设计

微槽热沉具有传热效率高、可靠性强的优点,可用于对微尺度高热流密度电子元件进行冷却。为满足其性能需求和控制成本,在对微槽热沉进行设计时需要对其传热能力和流动阻力同时进行优化。传统研究采用的热阻网络模型较为简单,不能很好地反映热阻和流动阻力对微槽道截面形状拓扑变化的响应,且其优化对象通常为既定截面的形状尺寸。为此提出一种基于离散化方法的单层硅基微槽热沉热阻网络模型,将热沉鳍片细分为厚度较小的微元,根据微元热阻对微元宽度的响应及微元热阻对整体热阻的贡献来描述微槽道的整体热阻。以微泵输出功率为优化边界条件,压降和热阻为优化目标,通过SQP（sequential quadratic programming,序列二次规划）方法对层流状态下四边形等截面硅基微槽热沉进行尺寸优化,利用CFD（computational fluid dynamics,计算流体动力学）对优化结果进行模拟和验证。结果表明,当鳍片高度较低时,鳍片截面形状为矩形,随着鳍高增加,截面形状有向三角形发展的趋势。在设计区间内,微槽道截面为梯形、鳍片截面为三角形时传热效率与压降相对占优。用边界点法和理想点法优化模型求得微槽道高度、鳍底宽、槽底宽、槽顶宽的优化结果分别为500,50,64.5,114.5 μm和500,50,50,100 μm。该方法能根据设计需求调整评价函数,同时计算结果具有重要工程意义,为微槽热沉设计人员提供参考。     

用结构函数法测量GaN HEMT与夹具的界面层热阻

为准确测量Ga N HEMT与夹具界面层的热阻,在两种不同的管壳界面材料条件下,利用经过改进的显微红外热像仪测量Ga N HEMT的降温曲线。采用结构函数算法对两种降温曲线进行分析,得到反映器件各层材料热阻的积分结构函数曲线。利用JESD51-14中的方法分别确定结壳热阻分离点和夹具到热沉的热阻分离点,得到结壳热阻Rj-c为1.078 K/W,夹具到热沉的热阻Rf-s为0.404 K/W。利用两种条件下的总热阻减去结壳热阻和夹具到热沉的热阻得到管壳界面材料热阻,导热硅脂热阻为0.657 K/W,空气介质热阻为1.105 K/W。依据该方法可以实现对界面层热阻的测量。     

大功率LED灯具封装结构的散热分析及优化

通过对大功率LED多层材料的封装结构进行建模及数值分析,得到稳态的温度场分布、芯片最高温度与环境温度、LED功率的变化关系,并利用热阻模型对材料散热效率进行了优化。对于单一肋片,存在一个使其热阻最小的最佳肋厚。对于肋片组散热器,肋片数量较少时也能使散热器总热阻较小,且应尽量使肋片厚度接近单个肋片热阻最小时的厚度,以更少的肋片数量获得较小的散热器总热阻,这样既能控制芯片的最高温度,又可有效地节约成本。     

网阵结构对变压吸附装置性能的影响

对变压吸附制氧装置吸附床结构进行改进,加入金属肋片构成网阵,并根据PSA气体分离理论对改进后的吸附床进行吸附以及解吸过程的数值计算,分析了空气流过加入金属肋片的吸附床时,金属肋片结构对吸附性能的影响。采用局部能量平衡方程以及吸附动力学方程作为数学模型,对吸附反应器的主要设计参数进行分析。改变网状结构尺寸以及内表面接触热阻,通过计算机模拟得到金属肋片结构参数与吸附动力的关系,以及对提高吸附反应器工作效率的影响。     

3ω法测量钛酸钡薄膜的热导率

电子设备小型化带来的热效应问题,使得提高薄膜材料热导率和降低薄膜与基底的界面热阻成为提高薄膜器件可靠性的关键因素,因此测量薄膜器件热性能成为了电子工业中愈发重要的课题。钙钛矿结构的钛酸钡作为一种高介电常数材料,在电子工业中被广泛使用。通过建立一套3ω法测试系统,测试了使用高分子辅助沉积法在SiO_2薄膜上沉积的钛酸钡薄膜样品的热导率,并通过不同厚度薄膜热阻与热导率的关系,计算出钛酸钡薄膜的热导率为5.63 W/mK,钛酸钡与SiO_2的界面热阻为2.13×10~(-8)m~2W/K。     

叶脉型微通道热沉设计及散热特性分析

为改善相控阵天线多热源阵面温度的均匀性,基于植物叶脉优良的传质特性,提出一种用于相控阵多热源阵面的叶脉型微通道热沉。首先,对叶脉型微通道热沉的流动特性和散热特性进行仿真分析,得到热沉的热源温度分布。然后,以热源温度标准差最小化为目标,进一步优化叶脉型微通道结构,得到了非对称叶脉型微通道拓扑结构。最后,采用金属3D打印加工了铝基微通道热沉样件并进行散热性能测试。数值仿真结果表明,相比于传统平行微通道热沉,叶脉型微通道热沉不仅强化了传热,而且使得热源温度更均匀,压力损失更小;实验结果验证了叶脉型微通道热沉优良的散热性能。研究结论可为相控阵多热源阵面的热沉设计提供依据。     

Strength variation of gas cooling turbine blade pin‐fin with different array

As an important measure of cooling, the pin fin array has been widely used in the cooling blade of turbine. However, most of the cracks in turbine blade are found near the pin fin due to stress concentration. In order to study the strength variations of pin fin in various shapes and with various longitudinal and transverse pitches, this paper establishes 10 rectangular, 3 elliptical and 1 diamond‐shaped slab models of pin fin array. The results indicate the existence of high stress area and low stress area around the pin fin. In the rectangular pin fin model, the maximum equivalent stress is detected on the side perpendicular to the load applied, the low stress area is on the side parallel to the load applied, and the high and low stress areas are semi‐elliptically distributed along their own track. For a rectangular pin fin array, the equivalent stress along each side of the bottom first increases and then decreases, with the maximum equivalent stress at the corners and the minimum at mid‐point of each side; along the height direction, the minimum equivalent stress of a rectangular pin fin array is near the ends while that of a square pin fin array is at the mid‐points. Under the same conditions, the stress of the rectangular pin fin array decreases with the decrease of the aspect ratio (h₁/b). The position of the maximum stress around the elliptical pin fin array varies from the two axis ratio (a/b). When a/b is 2, the maximum equivalent stress around the bottom is at the positions with a horizontal angle of 75°/120°/255°/300°; when a/b is 1, the maximum equivalent stress is at the positions with a horizontal angle of 60°/135°/240°/315°; and when a/b is 0.5, the maximum equivalent stress is at the positions with a horizontal angle of 45°/150°/220°/330°. Under the same conditions, the stress of a round pin fin array is smaller than that of a square one. In all the analytical models, the diamond‐shaped pin fin array presents the largest equivalent stress and the highest stress concentration.     

Heat transfer during reflux condensation of R134a inside a micro-fin tube with different tube inclinations

This study presents an experimental investigation of the heat transfer occurring during reflux condensation of refrigerant R134a in an inclined micro-fin tube (0.008 m OD, 0.5 m length). The experiments were carried out at a system pressure of 0.74 MPa and at inclination angles of 30°, 38°, 45°, 60° and 90° from the horizontal. The experiments indicated that the inclination angle has a significant effect on heat transfer during reflux condensation. The maximum reflux heat transfer coefficient was found at 30° inclination angle. At this arrangement, the heat transfer increased by a factor of 2.45 compared to the vertical case. A comparison with previous studies suggests that the heat transfer in a micro-fin tube is 2.2 times better than that in a plain tube, and 1.34 times better than that in a plain rectangular channel both at 30° inclination.     

Thermal Performance of a Functionally Graded Radial Fin

This paper investigates the steady-state thermal performance of a radial fin of rectangular profile made of a functionally graded material. The thermal conductivity of the fin varies continuously in the radial direction following a power law. The boundary conditions of a constant base temperature and an insulated tip are assumed. Analytical solutions for the temperature distribution, heat transfer rate, fin efficiency, and fin effectiveness are found in terms of Airy wave functions, modified Bessel functions, hyperbolic functions, or power functions depending on the exponent of the power law. Numerical results illustrating the effect of the radial dependence of the thermal conductivity on the performance of the fin are presented and discussed. It is found that the heat transfer rate, the fin efficiency, and the fin effectiveness are highest when the thermal conductivity of the fin varies inversely with the square of the radius. These quantities, however, decrease as the exponent of the power law increases. The results of the exact solutions are compared with a solution derived by using a spatially averaged thermal conductivity. Because large errors can occur in some cases, the use of a spatially averaged thermal-conductivity model is not recommended.     

超疏水表面融霜演化行为及排液特性

及时脱除热力除霜后冷表面残留液滴,可以延缓二次结霜。本文对室温环境下超疏水表面融霜演化行为进行了微观可视化观测,对比分析了表面倾角对裸铝表面(接触角88. 0°)及超疏水表面(接触角151. 1°)融霜排液的影响。实验结果表明,水平超疏水表面融霜过程存在单液膜卷曲收缩及多液滴合并两种行为,较大的静态接触角及较小的接触角滞后是促使多液滴合并的主要原因。与倾斜裸表面融霜过程存在大量残留液滴不同,超疏水表面融霜液可实现自排除;当表面倾角>30°时,超疏水表面排液率可达90%以上。结合表面润湿特性及表面倾角推导出表面液滴临界脱落半径,与实验结果吻合较好。     

Experimental study on control fins of a small flying vehicle using piezo-composite actuators

A camber morphing control fin design and an all-moving control fin design using piezo-composite unimorph actuators are presented in this paper. The control fin of a small flying object is usually actuated using a servo motor system with an electromagnetic motor. Much research has been conducted to solve the structural complexity of servo actuation systems to convert the rotation of a servo motor to a linear actuation motion. To simplify this structural complexity, several types of smart actuators have been developed, such as bimorph or unimorph actuators with piezoelectric material layers and shape memory alloy actuators. In this study, a camber morphing type control fin and an all-moving type control fin actuated using piezo-composite actuators are designed to evaluate their ability to simplify the structural complexity of the gear transmission and electromagnetic servo motor system or hydraulic actuator system. Within the skin of the control fin, a piezo-composite actuator is mounted and the other end inserted in a slot of the control fin. As the piezo-composite actuator is excited by an electric field, the pitch angle of the control fin is changed. Experimental testing for the pitch rotation angle of a control fin in a 450 V electric field showed the deflection angle of the camber morphing control fin was 1.4° and the rotational angle of the all-moving control fin was 5.4°, which is obtained from the rotation angle magnification linkage structural system.     

Multi-objective optimization of a rectangular micro-channel heat sink using the augmented ε-constraint method

ABSTRACT

This article proposes the use of an improved version of the ?-constraint method for the design and optimization of a rectangular micro-channel heat sink. This study aims to optimize the geometric parameters describing the micro-channel, namely its width, its fin width and its depth. The thermal resistance and the pumping power, considered as indicators of the thermal performance, have been approximated by surrogated models based on response surface approximation. The optimization task is formulated as a nonlinear programming problem. This approach has been implemented in GAMS. Sufficient details on both the single-criterion and multi-criteria formulation of the problem have been provided. The implications of the mathematical modelling formulation and the interrelationship between criteria and estimated quantities have been clarified. The use of the augmented ε-constraint method for the multi-objective optimization of a rectangular micro-channel heat sink constitutes the main contribution of this work.     

工艺参数对EB-PVD制备YSZ涂层的影响

为探讨电子束物理气相沉积(EB-PVD)制备8 mol.%氧化钇稳定氧化锆(8YSZ)涂层过程中工艺参数对涂层致密性、表面粗糙度和晶粒择优取向生长的影响,利用扫描电镜、原子力显微镜和X射线衍射技术对涂层的上述性能进行了分析.分析结果表明,随沉积速率由750 nm/min下降至20 nm/min,YSZ涂层的晶粒逐渐聚合长大,晶粒之间的孔隙减少,涂层的气体扩散系数相应地由2.41×10-4cm4/(N·s)下降至6.56×10-5cm4/(N·s).YSZ涂层的表面粗糙度随靶基距的提高逐渐降低,涂层的晶体学取向随蒸汽粒子入射角的改变而改变,入射角为30°时(111)晶面具有平行于涂层表面排列的趋势,入射角为45°时(311)和(420)晶面具有平行于表面排列的趋势,而入射角为60°时(220)和(331)晶面具有平行于表面排列的趋势.     

Effect of Bubble Size and Angle of Tapering Upriser Pipe on the Performance of Airlift Pumps

Airlift pumps are devices with the ability to lift liquid phase by injecting the gas phase. Parameters that affect the performance of these pumps are divided into two groups. The first group contains design parameters such as diameter of the pipe, tapering angle of the upriser pipe, and the submergence ratio, which is the ratio of immersed length to the total length of the upriser. The second group includes operating parameters such as the gas flow rate, bubble diameter, bubble distribution, and inlet gas pressure. In this research, the performance of an airlift pump is investigated numerically for different submergence ratios and different diameter of the upriser pipe. For this purpose, an airlift pump with a riser length of 914 mm and different diameters (6, 8, and 10 mm) and seven tapering angles (0°, 0.25°, 0.5°, 1°, 1.5°, 2°, and 3°) is numerically modeled and analyzed. Different submergence ratios are used: 0.4, 0.6, and 0.8. The numerical results are compared with the existing experimental data in the literature and show reasonable agreement. The results indicate that decrease in size of the bubble diameter increases mass flow rate of liquid at constant submergence ratios. The present study reports the improved performance of this pump with decrease in bubble size and increase in angle of tapering upriser pipe. Moreover, the results show that the tapering upriser pipe with 3° tapering angle gives the highest efficiency at nearly all submergence ratios. Further, the highest efficiency of the pump is shown to be at the largest submergence ratio.     

基于2-PSR/UPU并联机构的旋盖装置设计及性能分析

目的针对生产线上的旋盖工序,提出一种基于2-PSR/UPU并联机构的旋盖装置,解决生产线上不同倾角斜面上的旋盖问题。方法建立2-PSR/UPU并联机构模型;根据定杆长约束条件求解机构的位置反解,并通过相应的运动算例验证其反解位姿,通过对多个反解位姿进行对比,从中得出有效解;利用三维坐标搜索法求解工作空间。结果该并联机构动平台下方10 mm参考点工作空间连续且没有出现空洞,能适应0~35°范围斜面上的旋盖问题,给出了该并联机构在25°,30°,35°斜面情况下旋盖的实例。结论基于2-PSR/UPU并联机构的旋盖装置结构简单,机构具有可调性,可以在生产线上实现精准控制。该并联机构一移两转的特性能适应不同倾斜角斜面的旋盖任务。     

单面波浪平板脉动热管的传热性能

对一种单面波浪平板脉动热管的传热性能进行了实验研究,分析在空气强制对流冷却条件下充液率、加热功率、倾角等因素对其传热性能的影响。研究结果表明,除0°倾角外,脉动热管的最佳充液率为20%～30%,倾斜角度对脉动热管传热性能的影响很小,但90°时相对最好。脉动热管在0°放置时其传热性能较差,在低充液率的情况下甚至丧失脉动效果,主要是工质回流不畅的原因,与平板脉动热管的槽道设计有很大关系。此外低加热功率时热管传热性能存在波动,有时甚至不能启动。