聚合物电导率对0-3型压电复合材料极化性能的影响

建立了0-3型压电复合材料的等效电学模型.分析了聚合物电导率对复合材料极化性能的影响，研究了聚苯胺改性0-3型锆钛酸铅/聚偏氟乙烯复合材料极化性能与聚合物电导率之间的关系.理论分析和实验结果均表明，提高聚合物电导率可以提高复合材料的极化性能. 关键词： 压电复合材料 电导率 极化 聚偏氟乙烯     

一种混合WDMA-OCDMA系统归一化吞吐量性能研究

理论分析了一种混合WDMA-OCDMA系统的归一化吞吐量性能.研究了光差拍噪声对系统归一化吞吐量性能的影响.提出了BCH信道编码的方案来改善系统性能.结果表明,当系统负载较轻时,归一化吞吐量略微下降;但当系统负载中等或较重时,归一化吞吐量明显提高.同时,BCH信道编码提高了WDMA-OCDMA系统的归一化吞吐量峰值.     

一种多波长OCDMA解码器方案及其性能分析

提出了一种多波长OCDMA（MW OCDMA）系统的光解码器方案,通过多个光硬限幅器来抑制多用户干扰.分析了使用该解码器的MW OCDMA误码率性能、频谱效率和归一化吞吐量性能.分析结果表明,该方案能有效改善MW OCDMA系统的误码率性能,在要求的误码率条件下增加同时用户数,从而能有效改善MW OCDMA系统的频谱效率.同时,采用光硬限幅器的MW OCDMA 系统的归一化吞吐量性能明显提高,特别是归一化吞吐量峰值提高了约一倍.     

一种新型重力热管传热性能研究

提出了带内循环管的新型重力热管,通过内循环的引入提高了液体的有效提升高度,增大了换热面积;而且在蒸发段实现了降膜蒸发,大大提高了热管的传热传质性能,最终提高了其热传导性能.内循环管的引入也消除了常规重力热管的携带限和沸腾限的约束,提高了热管的工作温度范围.对相同规格的常规重力热管和新型重力热管分别建立数学模型,分析其传热传质性能.结果表明,与常规重力热管比,新型重力热管蒸发段的导热系数和相当导热系数分别提高了11.5～13倍和386～563倍.     

基于ANSYS的芯片冷却器传热分析

针对微槽式芯片冷却器,建立三维仿真模型,分析其稳态工况下的传热情况,获得其温度和热应力分布.分析了五种不同结构形式芯片冷却器工作性能的影响,比较了纯铜和氮化硅复合物两种材质对散热性能的影响.结果表明,铜质冷却器散热性能较好,但内部热应力却高于复合材质冷却器.通过将原冷却通道分割成两个相同的小通道,可提高冷却性能,且应将...     

四翼梁式次镜支撑结构的研究

为了优化大型望远镜次镜支撑结构的静力学和动力学性能,采用有限元分析的方法,计算了次镜支座最大变形与次镜支座的偏置角、四翼梁叶片厚度的关系;分析了四翼梁结构的频率与叶片偏置角的关系.分析证明当次镜支座偏置一定角度时能改善结构的静力学性能;当相对的两片叶片从直径线上错开一定的距离,对提高望远镜的谐振频率是十分有利的,在两者之间综合取舍确定了四翼梁的优化形式.分析结果表明,优化后的四翼梁结构的静力学和动力学性能均有提高.     

提高轻板隔墙的隔声性能

影响轻板隔墙隔声性能的因素是多方面的.本文着重研究了降低龙骨的传声、附加构造的作用以及墙板的选择等方面.文中通过理论分析和实验比较,说明这些措施对提高轻板隔墙的隔声性能是有效而可行的.     

0-3型压电复合材料覆盖层水下 吸声性能的理论研究

目前压电分流阻尼技术在振动和噪声领域的应用得到了广泛的关注. 本文尝试将压电分流阻尼技术应用于水下吸声领域, 以提高覆盖层的吸声性能. 将压电覆盖层厚度模态的机电方程和声波传播的传递矩阵相结合, 建立一维电声模型. 该模型可以用于分析多层压电和非压电水下吸声覆盖层的吸声性能. 采用该模型分析了0-3型压电复合材料覆盖层的水下吸声性能. 压电复合材料的参数是采用Furukawa的模型计算的. 研究结果表明, 采用合适的分流电阻, 负电容分流电路可以在较宽的频率范围显著提高覆盖层的吸声性能. 其原理可以从阻抗匹配的角度解释, 负电容分流电路可以调整压电覆盖层的表面声阻抗, 使之与水的特性声阻抗相匹配.     

Factors affecting focusing performance of continnous phase plate concentration

为提高惯性约束聚变系统中聚焦光斑的能量集中度,分析了在应用过程中影响连续相位板性能的主要误差来源,并建立了相应的数学模型.通过分析得出存在误差时远场焦斑的能量集中度和均方根值,且口径误差、对准误差、振幅畸变误差对连续相位板的聚焦性能影响很小,波前畸变影响能量集中度的权重最大.进一步分析可知:当畸变波前相关长度与连续相位板的最小空间周期(10 mm左右)相当时,畸变波前极大地影响激光的聚焦性能,提高惯性约束聚变系统中畸变波前的相关长度是提高聚焦光斑的能量集中度的有效方法.     

圆管内插入环状多孔介质的换热性能研究及其场协同分析

本文运用数值计算的方法,以空气为流动介质,研究了圆管内插入环状多孔介质在充分发展的层流区的换热及流动综合性能,并进行了场协同分析.结果表明,在圆管内插入环状多孔介质可以有效提高换热与流动的综合性能,其PEC值随Re数的增大呈现缓慢增大的趋势.多孔材料的孔隙率对综合性能的影响最为明显,孔隙率越高,综合性能越好.     

Experimental Heat Transfer Coefficients of Waste Heat Recovery Unit in Detergent Manufacturing Process

The waste heat recovery unit is one of the most important units in the chemical process. It recovers waste heat from the exhaust gas of the process resulting in the reduction of heat loss. In the detergent manufacturing process, the particulate air leaving the spray dryer is the exhaust gas containing the large amount of heat. Therefore, a waste heat recovery unit can significantly reduce heat loss. In this work, heat transfer coefficients of a waste heat recovery unit in the detergent manufacturing process were studied. Waste heat from the particulate air is recovered in the shell and coiled tube heat exchanger. The particulate air flows in the shell side, and water flows in the tube side. Four coiled tubes with different coil pitches were investigated. The results show that the tube-side heat transfer coefficient increases as the coil pitch decreases. Loading ratio also has an important effect on heat transfer coefficients. The increase of loading ratio leads to a lower value of the overall heat transfer coefficient. From 100 experiments, empirical correlations for the prediction of tube-side and shell-side heat transfer coefficients were proposed. The results indicate that the predicted heat transfer coefficients agree well with the experimental values.     

雾化喷射冷却的机理及模型研究

雾化喷射冷却的换热机理十分复杂,目前其研究还很不成熟。本文从喷射雾滴的特性参数出发,以被冷却表面上形成的喷射液膜为对象,考虑了冷却液体向环境的散热,建立质量、能量守恒方程,得到半经验半解析的雾化喷射换热模型。其中,本文提出真换热系数和显换热系数的概念,认为显换热系数受空间散热影响,而真换热系数只与喷雾动量有关。最后设计了雾化喷射局部换热实验,对模型进行检验,结果表明,该模型能够较好地符合实验所得的换热系数及加热面表面温度沿喷射半径的分布趋势。     

Heat pumps in industrial processes—An optimization methodology

The optimal integration of heat pumps in industrial processes has not yet been fully understood. In this paper an optimization methodology and a method which uses the composite curves as a guideline to the correct choice of heat pump type are outlined. The selection is done by matching the shape of the composite curves against the specific characteristics of several heat pump types. Furthermore, a methodology for the optimization of the most important parameters in a heat pump system is presented. In the optimization methodology the annual cost is minimized by varying heat source and heat sink temperatures, the heat pump size and the stream or streams to be utilized as heat source and heat sink.To reveal the potential for electrically driven compression heat pumps two different examples were studied with the methodology. The first example had close composite curves and was thought to be a poor heat pump candidate. The second one had open composite curves and was thought to be a promising example. The results showed that for both examples, heat pump installations were advantageous under good economic conditions for the heat pump, i.e. low electricity price, high fuel price and low investment costs. Also reasonable payback periods were achieved. With more unfavourable conditions the payback period increased, and in extreme cases a heat pump was no longer a better alternative than pure heat exchange. This decline in potential for heat pumping was much less in the example with open composite curves than in the example with closed ones. However, the conclusion to be drawn is that there exists today a potential for heat pumps in industrial processes.     

Experimental and numerical investigation of heat transfer in a miniature heat sink utilizing silica nanofluid

In this paper, heat transfer characteristics of a miniature heat sink cooled by SiO₂–water nanofluids were investigated both experimentally and numerically. The heat sink was fabricated from aluminum and insulated by plexiglass cover plates. The heat sink consisted of an array of 4 mm diameter circular channels with a length of 40 mm. Tests were performed while inserting a 180 W/cm² heat flux to the bottom of heat sink and Reynolds numbers ranged from 400 to 2000. The three-dimensional heat transfer characteristics of the heat sink were analyzed numerically by solving conjugate heat transfer problem of thermally and hydrodynamically developing fluid flow. Experimental results showed that dispersing SiO₂ nanoparticles in water significantly increased the overall heat transfer coefficient while thermal resistance of heat sink was decreased up to 10%. Numerical results revealed that channel diameter, as well as heat sink height and number of channels in a heat sink have significant effects on the maximum temperature of heat sink. Finally, an artificial neural network (ANN) was used to simulate the heat sink performance based on these parameters. It was found that the results of ANN are in excellent agreement with the mathematical simulation and cover a wider range for evaluation of heat sink performance.     

基于原油最高温度点变化规律分析停输相变传热

采用分区法数学模型,利用等价比热容法处理析蜡潜热问题,追踪停输相变过程中管道内原油最高温度点位置的变化轨迹,确定管道内原油最终凝固位置,提出管道内原油全凝的判断依据。基于最高温度点位置的变化规律将传热过程分为四个阶段,重点讨论了各阶段中自然对流、潜热释放、传热方式转化对最高温度位置点变化的影响,结合Ra数变化分析了自然对流换热影响从强到弱的变化过程。深入探讨了停输相变过程中管道内固相率的变化及不同位置处原油温降曲线的特点。     

利用高翅管换热器提高压力恢复系统效率

为提高压力恢复系统效率,设计并制造了一台高翅管换热器。采用滚扎而成的整体式螺旋高翅片管,代替套片式圆形普通翅片管,翅片管材料为紫铜,管束按等腰三角形叉排布置,管内强制水冷。测试了高翅管换热器的阻力特性,对比分析了加入换热器前后压力恢复系统性能的变化。结果表明:随着背压的提高,该换热器流阻逐渐降低,当背压达到9.366kPa时,换热器流阻为0.133kPa,仅占换热器入口激光尾气压力的1.4%;与不加换热器相比,加入高翅管换热器后的引射器混合室入口压力降低了12.95%,压力恢复系统的效率得到了提高。     

微尺度水平单管内流动沸腾特性实验研究

对非共沸混合工质R134a/R32(75/25)在水平微尺度管道内的流动沸腾换热实验结果进行了分析和讨论,以探究微细通道内流动沸腾换热的主导机制。对影响其换热的多种因素(热流密度、质量流量和质量干度)进行了分析,实验得出,当质量干度较低时,热流密度和质量流量共同控制着微尺度管内的换热方式,当热流密度的影响占主导地位时,管道内的换热以核态沸腾为主;当质量流量的影响占主导地位时,管道内的换热以强制对流为主。     

An Experimental Study on Heat Transfer Coefficients of a CO2-Filled Thermosyphon

Abstract

Because carbon dioxide is ozone friendly and has negligible global warming potential, it has received renewed interest in recent years as an important alternative refrigerant. In this article, the heat transfer characteristics of a carbon dioxide-filled two-phase closed thermosyphon were investigated experimentally, and the empirical heat transfer correlations are reported. The heat transfer data were analyzed, and heat transfer coefficients were compared with conventional heat transfer correlations. The results represent that heat transfer correlation of the heated section can be expressed with Kutatelatze's correlation, and heat transfer coefficients of the condenser section are found to be in reasonable agreement with the Nusselt equation.     

Forced convection heat transfer from porous heat sinks placed in partially open cavity: Some case studies

In this present study, the forced convection heat transfer from aluminum foam heat sinks with 10, 20, 40 PPI pore density placed in a discrete form in a partially open cavity were experimentally investigated. Air was used as working fluid. The uniform heat flux was applied to 3 × 3 array of foam heat sinks horizontally mounted in the cavity. The experimental studies were performed for the 3363–9743 range of Reynolds number and the 2.7 x 10⁶ and 7.5 x 10⁶ range of modified Grashof number. The effects of the Reynolds number, the modified Grashof number and the pore density of foam heat sink on the heat transfer were investigated. The results obtained were compared with the results obtained without foam heat sink cases. In addition, the most heated elements within the cavity were identified and solution proposals were presented. In addition, the most heated elements within the cavity were identified and solution proposals were presented.     

微小圆通道内流动沸腾换热特性的研究

微小通道内相变换热具有热流密度高、单位体积内换热面积大、结构紧凑等特点,成为高效紧凑式换热器设计的重要途径。本文以氟利昂R113为工质,完成了0.7、1.1和1.4 mm的圆形小通道内的流动沸腾实验,对小通道内流动沸腾换热特性进行了分析,拟合了计算沸腾换热特性的实验关联式,为工程实际应用提供参考。