电子器件用液冷冷板的竖向流道优化设计

设计了用于电子器件散热的竖向冷板。采用ANSYS软件模拟的方式,对不同结构的冷板流场、压力场、温度场进行了分析,梳理了设计中遇到的问题及解决的方式,得出设计中侧重点的不同导致的结果差异,这也为以后的工程实践提供一定的参考。     

空气强制对流冷却工况下多芯片散热过程数值模拟

建立强制空气对流冷却多个电子芯片的理论模型,采用控制容积法离散控制方程组并进行数值求解,得到芯片和固体基板的温度场,分析了冷却空气流过电子芯片的流场,同时在考虑芯片与基板的接触热阻的情况下,计算了芯片的温度分布,并与不考虑其接触热阻的数值模拟结果进行了比较。研究表明离冷却空气进口最远的芯片温度最高;空气在芯片之间流动会产生回流现象;当电子芯片与固体基板接触热阻较小时,芯片工作产生的热量能很好地通过固体基板传递出去,而当电子芯片与固体基板接触热阻较大时,热量传递会相对困难,使得芯片工作时产生的热量不能及时带走,芯片容易超温工作。     

有源相控阵天线阵面冷板设计与优化

针对有源相控阵天线阵面散热问题,设计了一种冷板作为热沉、子阵外壳为均温板的散热结构,通过热仿真分析和试验测试该冷板的散热性能,在此基础上对冷板结构进行优化,采取冷板作为流量分配网络、子阵盲配通液的散热结构改善散热性能,结果表明,优化后散热结构相对原散热结构的冷板散热性能有较大提升,子阵外壳与冷板的温度和温差有较大改善,为冷板的结构设计提供一定的参考意义。     

用于高热流密度器件冷却的热管散热器实验研究

针对大型计算机服务器CPU的耗能量,探讨了一种新的热管排布方式的散热器,并对其散热性能进行了实验研究.研究结果表明,采用此种热管散热器,最高热流密度为74.3W/cm2,其冷却风速控制在4m/s即可满足芯片冷却要求.同时根据模拟计算得到的散热器底板温度分布,可有助于对热管排布方式的优化设计.     

基于遗传算法的金属辐射冷板换热性能优化研究

通过对金属辐射冷板传热数学模型的简化,得出影响辐射冷板换热性能的五个重要参数(冷水供回水平均温度、水流速度、管径、板厚、管间距)的数学描述。其次通过编写MATLAB遗传算法的金属辐射冷板目标函数优化代码,经遗传迭代求出辐射冷板换热性能目标函数的最值,及其对应的最优解组合。通过分析可知遗传算法能够有效的搜索到目标函数最优解,由于数学问题的提出是基于金属辐射冷板的基本原理,因此该算法具有一定的推广性,可用于多种形式的辐射冷板设计,能够有效、方便的提高辐射冷板的换热性能。     

辐射冷板性能测试标准对比分析

该文主要介绍了国外现行辐射冷板测试标准:欧洲标准EN 14240和美国标准ASHRAE 138。通过对比分析这两个标准之间的区别,对我国辐射冷板性能测试提供参考和建议。     

基于遗传算法的金属辐射冷板换热性能优化研究北大核心

通过对金属辐射冷板传热数学模型的简化,得出影响辐射冷板换热性能的五个重要参数(冷水供回水平均温度、水流速度、管径、板厚、管间距)的数学描述。其次通过编写MATLAB遗传算法的金属辐射冷板目标函数优化代码,经遗传迭代求出辐射冷板换热性能目标函数的最值,及其对应的最优解组合。通过分析可知遗传算法能够有效的搜索到目标函数最优解,由于数学问题的提出是基于金属辐射冷板的基本原理,因此该算法具有一定的推广性,可用于多种形式的辐射冷板设计,能够有效、方便的提高辐射冷板的换热性能。     

水射流冷却过程中表面热流密度的预测

建立了由内部一点测量温度值,选取多个时间步长计算未知的表面热流密度与换热系数的导热反问题算法。该算法采用有限容积法离散方程,附加源项法处理边界条件。将该计算模型应用于求解浸没水射流冷却过程中表面热流密度,将计算温度值与实验测温值进行比较验证了算法的正确性。在此基础上分析了水射流冲击过程中薄钢片表面热流密度随表面温度与时间的变化特性。     

GaN芯片阵列射流冷却技术研究

针对高热流密度GaN芯片局部点热流的散热特点,采用射流冷却传热方法,对340 W/cm~2的高热流密度进行了冷却,热源以4×4点阵形式存在,实验分析了工质流量、热负荷等因素对系统换热性能的影响。以水为冷却工质,工质流量≤4.47 L/min,试验测得点热源温度低于78.8℃。     

Bright thermal atomic beams by laser cooling: A 1400-fold gain in beam flux

Using a three-step transverse laser cooling scheme, a strongly diverging flow of metastable Ne(3s ³ P ₂] atoms is compressed into a well-collimated, small diameter atomic beam (e.g., 1.4 mrad HWHM divergence at 3.6 mm beam diameter) with an unmodified axial velocity distribution centered at 580 m/s. The maximum increase in beam flux 1.04 m downstream of the source is a factor 1400; the maximum increase in phase space density, i.e., brightness, is a factor 160. The laser power used is only 140 mW. The scheme is extendable to a large variety of atomic species and enables the application of bright atomic beams in many areas of physics.     

Design of a high flux VUV beamline for low energy photons

A VUV beamline at the Shanghai Synchrotron Radiation Facility (SSRF) for angle-resolved photoelectron spectroscopy (ARPES) measurements is designed. To increase the resolution and bulk sensitivity, a photon energy as low as 7 eV is desired. Because the reflectivity for p-polarized photons strongly decreases when the photon energy is below 30 eV, the design of a high flux beamline for low energy VUV photons is a challenge. This work shows a variable including angle Varied Line-space Plane-Grating Monochromator (VLPGM) with varied grating depth (VGD) which can achieve both high resolution and high flux with broad energy coverage.     

磁驱动加载装置负载区降温系统设计及应用

在材料物性研究中,压力和温度是两个基础的物理量,国内磁驱动加载装置具有压力调节能力,暂不具备样品降温控制技术,针对这一现状设计了一套配合磁驱动加载装置负载区的样品初始降温系统,结合设计的电极板结构和测试探针工装,使负载区电极板与样品、样品与探针固定于设定位置;通过往电极板和探针工装形成的密闭气室内注入压缩低温液氮达到对样品降温的目的;通过真空泵,抽出电极板和探针工装形成的密闭气室内的空气,避免测速探针由于低温凝结空气中的水汽而无法工作。基于该系统开展了低温下铋的斜波压缩实验,获得了?80 ℃初始温度下铋的动力学响应数据,验证了降温系统的可靠性。     

高极化纯度的超表面透镜设计与应用

针对超表面在透镜方面的应用,基于各向异性超表面单元设计了一款高极化纯度的聚焦超表面透镜,并探讨了其在高增益高极化纯度天线方面的应用.设计了一款具有极化滤波特性的各向异性超表面单元,单元对x极化波保持高透性的同时,对y极化波保持近乎为零的透射率.利用该型单元设计了焦距为30 mm、阵列大小为105 mm×105 mm、单元数为21×21的聚焦超表面透镜.根据光路可逆原理,焦点处发出的球面波被超表面透镜有效转化为平面波,从而达到提高天线增益的目标.实验中分别用不同极化形式的球面波照射聚焦超表面来研究超表面对不同极化波的控制特性.结果表明,x极化波照射时,超表面工作于透镜模式,球面波转化为平面波,天线增益大大提高;y极化波照射时,超表面类似于金属板,将入射波全部反射;x/y极化混合波照射时,天线增益大大提高,且极化隔离度高于25 dB,充分说明设计的聚焦超表面在提高x极化波增益的同时可高效滤除y极化波,达到了高增益高极化纯度的目标.     

Instrument for thermal radiation flux measurement in high temperature gas flow (Cuernavaca instrument)

A new instrument for hemispherical radiation heat flux measurement is proposed. It is based on the theory of blow of the boundary layer, taking into account that at the critical mass flow rate through the porous surface the thermal boundary layer is blown off and only radiation flux high temperature gases reaches the porous surface. With the measurement of blow of gas flow and the temperature of the porous material, the respective heat flux is obtained.     

Multi-layer flows of immiscible fractional Maxwell fluids with generalized thermal flux

Unsteady laminar flows and heat transfer of n-immiscible fractional Maxwell fluids in a channel are investigated under influence of time-dependent pressure gradient. The isothermal channel walls have translational motions in their planes with time-dependent velocities. Governing equations of the mathematical model are based on the generalized constitutive equations for shear stress and thermal flux described by the time-fractional Caputo derivative. Analytical and semi-analytical solutions for velocity, shear stress, and temperature fields are obtained by using finite sine-Fourier and Laplace transforms. In the case of semi-analytical solutions, the inverse Laplace transforms are obtained numerically by employing the Talbots algorithms. Using the software Mathcad, numerical calculations have carried out and results are presented in graphical illustrations in order to analyze the memory effects on the fluid temperature and motion. It is found that in fluids with thermal memory the heat transfer is slower compared with the ordinary fluid, while the fractional velocity parameters act as braking/accelerating factors of the fluids.     

Dynamics of flux lines: thermal fluctuations

A relaxational dynamics for ad-dimensional model of flux lines is investigated. The flux lines are subject to thermal fluctuations such that they form a flux liquid rather than a flux lattice. We find that the density-density auto correlation function decays as (logt/t ²)² for large timest. In contrast, this correlation function decays for point-like vortices ast ^–2. At the transition to an empty lattice (Abrikosov-Meissner transition), the auto correlation function decays as a power law with dimension-dependent exponentsd+2 for flux lines andd for point-like vortices. Therefore, the fluctuations and the interactions of long flux lines have an accelerating effect on the relaxation.     

Optimization of the focused flux of high harmonics

Following the theoretical predictions [1], the observation of two-photon processes by interaction of vacuum ultraviolet (VUV) radiation with inner-shell levels of atoms requires focused intensities in the 10¹³-10¹⁴ W/cm² range. Our aim is to reach this regime in order to study non-linear optics at these wavelengths. We first optimized the high harmonic conversion efficiency in argon by studying the best experimental conditions for phase-matching, concentrating on focus geometry related to laser energy, cell length and position relative to the focus. We then studied the resulting harmonic beam focusability by a toroidal mirror (f=10 cm) and made an image of the harmonic focus. We conclude with an evaluation of the focused intensity that we are able to reach experimentally.Received: 28 January 2003, Published online: 24 April 2003PACS: 32.80.Rm Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states) - 42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation     

高变倍比红外变焦距光学系统设计

 采用长波160×120元非制冷焦平面阵列探测器,设计了工作于8μm～12μm波段折射式红外连续变焦光学系统,该系统具有大相对孔径,F数为1.2,变倍比10×,高成像质量等特点。系统使用锗和氯化钾两种普通红外材料,通过引入非球面校正系统轴外像差和高级像差,在中焦时采用平滑换根快速提高变倍比。系统在空间频率17lp/mm处,全焦距范围内调制传递函数（MTF）均在0.55以上,接近衍射极限;系统在接收半径17μm的探测器敏感元内,能量集中度大于72%,表明该系统具有良好的成像质量。     

Ion wind generation and the application to cooling

Ion Wind Generation (IWG) based cooling systems portend a new type of cooling for mobile electronics. However, the actual application of IWG cooling is still limited because a few important parameters are still unclear: maximum wind velocity, minimum operational voltage, degradation of corona-discharging electrodes, and optimum electrode geometries. We report on experimental investigation on these parameters based on a prototype IWG system consisting of wire electrodes and semi-cylindrical contour-shaped electrodes. We tested various IWG system designs with different electrode diameters, electric configurations, and operational conditions. The experimental studies could provide better understanding of IWG cooling systems and accelerate its application.