阵列波导光栅中心波长温度稳定性的研究

阵列波导光栅中心波长的温度不稳定性成为限制其应用的主要原因。为了设计温度不敏感阵列波导光栅,结合弹性多层板热应力理论和应力集中效应给出掩埋波导芯层应力的解析解,利用等效折射率法计算阵列波导的有效折射率及其温度系数,考虑波导材料折射率和波导长度随温度的变化得到了硅基二氧化硅阵列波导光栅中心波长的温度系数。并研究了贴有应力板的阵列波导光栅中心波长的温度特性,结果表明在芯片底部贴有0.37 mm厚的铝板时,TE模和TM模中心波长的温度系数分别是5.9 pm/℃和8.0 pm/℃,下降到传统阵列波导光栅中心波长温度系数的一半。     

毫秒脉冲激光辐照硅基PIN的温度场应力场数值分析

为了研究毫秒脉冲激光辐照硅基PIN多层结构产生的温度场和应力场的特点,本文基于热传导理论和弹塑性力学理论,利用等效比热容法处理相变潜热,考虑多个热源,尤其是底层铝电极反射的影响,并考虑硅基PIN探测器每层材料参数的非线性影响,采用有限元模拟软件COMSOL Multiphysics,对毫秒脉冲激光辐照硅基PIN多层结构的过程进行了二维数值模拟,得到了材料表层及内部各层的瞬态温度场与应力场的时空分布和变化规律.结果表明,底层铝电极对激光的反射,使得在底层铝电极处及附近硅层的温度都略有升高.在此基础上,分析了毫秒脉冲激光辐照硅基PIN的硬破坏机理,即熔融前力学损伤导致硅基PIN探测器的功能失常.     

Control of birefringence using polymer as cladding layer in optical planar waveguides

We demonstrate theoretically that a polymer layer, when used as cladding layer for silica-based planar optical waveguides on a silicon substrate, can substantially reduce birefringence. Multilayer planar optical waveguides usually exhibit stresses that are caused by thermal-induced strains that originate from the bonding of the layers, in addition to intrinsic strains. Effect of various intrinsic properties on thermal stress as a function of thickness of the guiding layer is studied. It is shown that it is possible to achieve the thermal stress free and, hence, the stress-induced birefringence free waveguide devices by proper waveguide designs.     

铝纳米颗粒的热物性及相变行为的分子动力学模拟

采用分子动力学方法模拟了纳米金属铝在粒径为0.8-3.2 nm 时的熔点、密度和声子热导率的变化, 研究了粒径为1.6 nm的铝纳米颗粒的密度、比热和声子热导率随温度的变化. 采用原子嵌入势较好地模拟了纳米金属铝的热物性及相变行为, 根据能量-温度曲线和比热容-温度曲线对铝纳米颗粒的相变温度进行了研究, 并利用表面能理论、尺寸效应理论对铝纳米颗粒熔点的变化进行了分析. 随着纳米粒径的不断增大, 铝纳米颗粒的熔点呈递增状态, 当粒径在2.2-3.2 nm时, 熔点的增幅减缓, 但仍处于递增趋势. 随着纳米粒径的增大, 铝纳米颗粒的密度呈单调递减, 热导率则呈线性单调递增, 且热导率的变化情况符合声子理论. 随着温度的升高, 粒径为1.6 nm的铝纳米颗粒的密度、热导率均减小. 该模拟从微观原子角度对纳米材料的热物性进行了研究, 对设计基于铝纳米颗粒的相变材料具有指导意义.     

Numerical study of heat transfer enhancement of counter nanofluids flow in rectangular microchannel heat exchanger

This paper reports a numerical analysis of the performance of a counter-flow rectangular shaped microchannel heat exchanger (MCHE) using nanofluids as the working fluids. Finite volume method was used to solve the three-dimensional steady, laminar developing flow and conjugate heat transfer in aluminum MCHE. The nanofluids used were Ag, Al₂O₃, CuO, SiO₂, and TiO₂ and the performance was compared with water. The thermal, flow fields and performance of the MCHE were analyzed using different nanofluids, different Reynolds numbers and different nanoparticle concentrations. Temperature profile, heat transfer coefficient, pressure profile, and wall shear stress were obtained from the simulations and the performance was discussed in terms of heat transfer rate, pumping power, effectiveness, and performance index. Results indicated enhanced performance with the usage of nanofluids, and slight penalty in pressure drop. The increase in Reynolds number caused an increase in the heat transfer rate and a decrease in the overall bulk temperature of the cold fluid. The increase in nanoparticle concentration also yielded better performance at the expense of increased pressure drop.     

高压热处理对铝青铜热物理性能的影响

在5 GPa压力下对铝青铜进行750℃、保温15 min的高压热处理,对高压热处理前后铝青铜的电导率以及25～600℃温度范围内的热扩散系数、热容和热导率进行测试,结合显微组织的观察结果,探讨了高压热处理对铝青铜热物理性能的影响。研究表明:高压热处理能增大铝青铜的热扩散系数,减小热容;对热导率而言,温度低于400℃时高压热处理能增大铝青铜的热导率,而温度高于400℃时高压热处理能减小铝青铜的热导率。分析认为,产生变化的主要原因是高压热处理使铝青铜的微观组织发生了变化。     

Eliminating the birefringence in silicon-on-insulator ridge waveguides by use of cladding stress

We propose and demonstrate the use of the cladding stress-induced photoelastic effect to eliminate modal birefringence in silicon-on-insulator (SOI) ridge waveguides. Birefringence-free operation was achieved for waveguides with otherwise large birefringence by use of properly chosen thickness and stress of the upper cladding layer. With the stress levels typically found in cladding materials such as SiO2, the birefringence modification range can be as large as 10(-3). In arrayed waveguide grating demultiplexers that were fabricated in a SOI platform, we demonstrated the reduction of the birefringence from 1.2 x 10(-3) (without the upper cladding) to 4.5 x 10(-5) when a 0.8-microm oxide upper cladding with a stress of -320 MPa (compressive) was used. Because the index changes induced by the stress are orders of magnitude smaller than the waveguide core-cladding index contrast, the associated mode mismatch loss is negligible.     

Specific features of waveguide heating due to transmission of high-power microwave signals

Waveguide heating due to transmission of microwave signals is studied. Mathematical models are developed to evaluate heat liberation, and differential equations of thermal balance are derived with allowance for different working conditions of waveguides. The results prove the necessity of the further study of the effect of heat liberation in waveguides on strength and functional characteristics.     

Thermodynamic Performance Analysis of a Waste Heat Power Generation System (WHPGS) Applied to the Sidewalls of Aluminum Reduction Cells

To recover energy from the waste heat of aluminum reduction cells, a waste heat power generation system (WHPGS) with low boiling point working fluid based on Organic Rankine Cycle was proposed. A simplified model for the heat transfer around the walls of aluminum reduction cells and thermodynamic cycle was established. By using the model developed and coded in Matlab, thermal performance analysis of the system was conducted. Results show that the electrolyte temperature and the freeze ledge thickness in the cell can significantly affect the heat absorption of the working fluid in the heat exchange system on the walls. Besides, both the output power and the thermal efficiency of the power generation system increase with the system pressure. The output power and thermal efficiency of the system can also be affected by the type of working fluid used in the system. Working fluids for the best system performance under different output pressures were determined, based on the performance analysis. This WHPGS would be a good solution of energy-saving in aluminum electrolysis enterprises.     

再生冷却红外窗口热响应特性耦合计算研究

本文对强对流加热环境下带再生冷却系统的红外窗口传热和热应力问题进行了数值模拟,采用一维管流假设,管流和固体结构传热采用耦合方式求解.研究表明:(1)在本文计算状态下模型温度和热应力都是随加热时间而增加的,最大温度发生在窗口表面的填充材料和石英玻璃中部,最大热应力发生在合金材料内部;(2)现有冷却管道配置下工质温度没有异常变化;(3)窗口区合金温度一直在升高,若飞行时间进一步延长,要考虑合金温升给窗口防热带来的不利影响;(4)在现有温度分布状态下,内冷管道的引入并未给结构强度造成薄弱环节.     

The role of alumina nanoparticles in epoxy adhesives

Both untreated and calcined fumed alumina nanoparticles were dispersed into an epoxy-based adhesive at various percentages. The glass transition temperature of the nanofilled adhesives increased up to an optimal filler loading and then decreased, probably due to concurrent and contrasting effects of chain blocking and reduction of the crosslinking degree. Tensile modulus, stress at break, and fracture toughness of bulk adhesive were positively affected by the presence of untreated alumina nanoparticles at an optimal filler content. Mechanical tests on single-lap aluminum bonded joints indicated that untreated alumina nanoparticles markedly improved both the shear strength and fatigue life of the bonded joints. In particular, the shear strength increased by about 60% for an optimal filler content of 1 vol.%, and an adhesive failure mechanism was evidenced for all the tested specimens. Concurrently, a relevant decrease of the equilibrium contact angle with water was observed for nanofilled bulk adhesives. In summary, alumina nanoparticles can effectively improve the mechanical performances of epoxy structural adhesives, both by increasing their mechanical properties and by enhancing the interfacial wettability with an aluminum substrate.     

Effects on the evolution of microstructure and properties of low-silicon cast aluminum alloys in service

ABSTRACT

The microstructure evolution and property change of four kinds of low silicon cast aluminum alloy exposed to heat for 0–50?h at 200°C were studied by means of Brinell hardness test, tensile property test, friction and wear property test and XRD analysis. The results show that with increasing thermal exposure time, the tensile strength of each group of samples decreased and the amount of wear increased. The tensile strength of samples with more Si content decreased slowly. When the time increased to 50?h, the increase of wear loss was the largest. The hardness of samples after thermal exposure increases compared with that before thermal exposure. The residual stress of (311) diffraction crystal surface of AlSi3.5Mg0.66 under different thermal exposure time was measured. The type of residual stress changed from residual tensile stress to residual compressive stress after thermal exposure. There is an abnormal phenomenon that the hardness of the sample increased and the amount of wear increased, and it is evident that the distribution of residual stress was inhomogeneous after thermal exposure. It is found that with increasing thermal exposure time to 50?h, the average lattice distortion ε of the low-index crystal plane and the high-index crystal plane in the aluminum alloys gradually increased.     

Laser backwriting process on glass via ablation of metal targets

Ablation of metal targets onto pyrex glass substrates, using a Q-switched Nd:YAG laser working at 355 nm, was used to study the potential of a laser backwriting process for the fabrication of optical waveguides via an index of refraction change. Metal foils of stainless steel, aluminum, copper, brass and gold have been used as blanks and irradiated by focusing the laser beam through a cylindrical lens under continuous movement in a direction perpendicular to the irradiation. An horizontal setup was found suitable to improve the effect of the plume in the sample. Results were obtained for two different configurations. Transversal profiles were analysed using a contact profilometer, comparing results obtained for the different configurations, traverse speeds and metal targets used. Two ablation regimes were identified, which are related to a critical laser fluence value of 2.7 J/cm². Surface micrographs obtained by scanning electron microscopy are discussed, together with the characteristics of the structures attained, taking into account the optical and thermal properties of the ablated metal blanks.     

Thermal Performance of a Capillary Pumped Loop for Automotive Cooling

The design and test results for a capillary pumped loop (CPL) for thermal management of up to 210 W at the source and heat transfer over a distance of 1 m are discussed. The design configuration of the CPL evaporator consists of an internally grooved aluminum evaporator, 31.70-mm outer diameter and 500-mm long, fitted with a porous ultra-high molecular weight polyethylene wick, 8- to 15-μm pore radius, and 38% porous volume. Heat was transferred using a stainless steel tube of 4.5-mm internal diameter for vapor and liquid lines. High-grade acetone (99.99% pure) was used as the heat transfer fluid inside the loop. In the tests, thermal characteristics of the CPL were specifically studied with respect to the temperature control capability using an active thermal device on the reservoir and to the start-up process through pressure priming of the capillary evaporator. The loop was able to start-up successfully at both low and high heat loads, although proper priming of the wick structure before start-up was necessary to attain low evaporator temperatures during steady-state operation. While maintaining constant reservoir temperature through active means, the loop was able to control evaporator temperature within 55 ± 3°C, even with changing input heat from 30 to 210 W. Total thermal resistance from the evaporator surface to the surroundings was 0.19° to 1.15° C/W with the minimum value achieved at the maximum heat load of 210 W. This study is intended to illustrate the thermal potential of the CPL as an effective temperature control device in automotive applications.     

Effects of controllable process factors on Al rear surface bumps in Si solar cells

High efficiency solar cells require good back surface field passivation and high back reflectance in the rear Al region. In module processes, wafer-based solar cell can break through stress during soldering uneven rear aluminum surfaces - a serious problem that affects throughput. This work examined rear surfaces with respect to controllable process factors such as ramping and cooling rates during rapid thermal processing, and the fineness of aluminum powder used in the screen-printed paste. A faster ramp up rate resulted in a uniform temperature gradient between the aluminum and silicon surfaces. As a results, the bumps on the aluminum surface were small and of high density. Fine aluminum metal powder in the paste for screen-printing contact points resulted in large distribution, high density bumps. Bumps formed during cooling in metallization, their sizes and densities were dependent the on uniformity of the aluminum and silicon liquid wetting of the silicon surface.     

A Neural Network-Based Optimization Of Thermal Performance Of Phase Change Material-Based Finned Heat Sinks—An Experimental Study

Experiments are conducted to determine the time to reach a set-point temperature for aluminum finned heat sinks filled with the phase change material n-eicosane. Results thus obtained are integrated with a feed-forward back-propagation artificial neural network to predict operating times. The artificial neural network prediction is then used to determine the optimum configuration that maximizes thermal performance. Four different plate-fin heat sink geometries filled with phase change materials giving rise to different volume fractions of the aluminum were experimentally investigated.     

Economical synthesis of nanocrystalline alumina using an environmentally low-cost binder

Sol-gel, a commonly used technique, involves the formation of an amorphous gel from a precursor solution. In this research nanocrystalline alumina powders have been synthesized through a new sol-gel simplified method. The route involved using an environmentally low-cost binder and aluminum nitrate in an aqueous medium. The added metal ions were dispersed in the gelled binder matrix. The gelled mass was dried and characterized by simultaneous thermogravimetric and differential thermal analysis (TG-DTA) and calcined at 350, 400, 530, 650, and 900 °C for 2 h. The samples were evaluated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The used binder can be applied to form a perfect matrix for the entrapment of metal ions that during heat treatment, gives rise to ultrafine amorphous or crystalline alumina particles. In this study, the transition phases of alumina with particle sizes of 15-25 nm as well as aluminum oxide hydrate phase were produced by the heat treatment of the gelled mass at temperature 650 °C. By increasing the calcinations temperature to 900 °C, alumina transition phases were changed and aluminum oxide hydrate eliminated. The particle sizes at this temperature were obtained in the range 15-30 nm. The particle size and crystallite size of products measured from XRD and TEM were in good agreement.     

SiO2脊形条波导热极化引起的电光效应

通过理论模拟对具有上覆盖层的SiO₂脊形条波导结构进行了优化，在此基础上利用微电子工艺制作了SiO₂脊形波导Mach-Zehnder型电光调制器，并进行热极化引起的电光和非线性效应的研究.热极化过程大幅增强了样品的电光及非线性效应，二次电光系数由热极化前的1.56×10^-22(m/V)²提高到热极化后的8.50×10^-22(m/V)²，极化后得到了0.093pm/V的线性电光系数，对热极化的物理机理进行了理论分析. 关键词： 电光调制器 2光波导')" href="#">SiO₂光波导 电光效应 热极化     

Polymer composites for thermal management: a review

The aim of this review article is to consolidate the important research works dedicated to polymers which are mainly used target material for heat transfer applications. The requirement of present day heat transfer equipment is compactness, lightweight, manufacturability, and lower cost. Materials like copper and aluminum though have better thermal conductivity but they are expensive and also heavy. Polymers are cheaper and easy to manufacture, recycle though they have sufficiently lower thermal conductivity compared to copper and aluminum. Polymer materials are thermally insulating material. It is too difficult to improve the amorphous nature of polymer material in order to achieve high thermal conductivity. One key path to increase the thermal conductivity of a polymer is to reinforce high thermal conductive fillers in the host matrix. In this review paper, an attempt is made to explore and summarize various key paths suggested by the researchers to develop high thermal conductive polymer composites.     

新型沟槽道微热管散热性能实验研究

微热管以其效率高、响应快且无能耗,在高功率集成微电子散热方面应用广泛。针对电子器件的小型化、高能耗发展趋势,本文提出一种新型沟槽道微热管结构,对该沟槽道微热管进行稳态和瞬态热性能实验研究,研究了风速、角度、加热功率等因素对该新型热管的热性能影响规律。结果表明,该微热管在整个散热器传热上起主导作用,性能比达到0.88,冷凝端温差为0.8℃,具有良好的均温性,该微热管加热功率为140 W,空气流速1.5 m/s时,换热系数可达2 359 W/(m^2·℃),热阻为0.27℃/W;高功率状态下可保持良好的热扩散性能,有效避免微热管的热应力集中,有望高效解决集成电子器件的散热问题。