Thermal Modeling of a Hybrid Thermoelectric Solar Collector with a Compound Parabolic Concentrator

In this study radiant light from the sun is used by a hybrid thermoelectric (TE) solar collector and a compound parabolic concentrator (CPC) to generate electricity and thermal energy. The hybrid TE solar collector system described in this report is composed of transparent glass, an air gap, an absorber plate, TE modules, a heat sink to cool the water, and a storage tank. Incident solar radiation falls on the CPC, which directs and reflects the radiation to heat up the absorber plate, creating a temperature difference across the TE modules. The water, which absorbs heat from the hot TE modules, flows through the heat sink to release its heat. The results show that the electrical power output and the conversion efficiency depend on the temperature difference between the hot and cold sides of the TE modules. A maximum power output of 1.03 W and a conversion efficiency of 0.6% were obtained when the temperature difference was 12°C. The thermal efficiency increased as the water flow rate increased. The maximum thermal efficiency achieved was 43.3%, corresponding to a water flow rate of 0.24 kg/s. These experimental results verify that using a TE solar collector with a CPC to produce both electrical power and thermal energy seems to be feasible. The thermal model and calculation method can be applied for performance prediction.     

Thermal and Mechanical Characteristics of a Multifunctional Thermal Energy Storage Structure

Thermal energy storage (TES) sandwich-structures that combine the heat storage function with structural functionality are described. The structure consists of a thermal interface (TI) connected to a hollow plate lamination. Each laminate is a hollow aluminum plate having a series of mm-scale channels or compartments that are filled with phase change material (PCM). Heat storage is via the latent heat of the PCM. A generalized thermal response model that is applicable to a wide range of channel geometrical configurations is described. The model couples the thermal response of the TI to the hollow aluminum plate/PCM-volume. The temporal response of the system is easily obtained via numerical solution of two ordinary differential equations, which can be solved to give closed-form solutions subject to a simple assumption. Thermal analysis delineates geometrical configurations that have good thermal response characteristics. The mechanical properties of the laminated structure are determined experimentally. Four-point bending experiments are conducted using specimens made with three layers of hollow plates laminated using a structural adhesive. An energy method is developed to model both the deformation and strength of the laminated structure. The energy method is developed based on the assumption that plane cross sections of the structure remain plane under bending, a condition that is valid for both linear and nonlinear materials. The energy method can provide deformation of the aluminum laminates comparable with the experiments. Experiments and modeling indicate that these laminated structures have an excellent performance-to-weight ratio.      

Modeling Thermal Effects in Nanodevices

In order to investigate the role of self-heating effects on the electrical characteristics of nanoscale devices, we implemented a 2D Monte Carlo device simulator that includes the self-consistent solution of the energy balance equations for both acoustic and optical phonons. The acoustic and optical phonon temperatures are fed back into the electron transport solver through temperature-dependent scattering tables. The electrothermal device simulator was used in the study of different generations of nanoscale fully depleted silicon-on-insulator devices that are either already in production or will be fabricated in the next five to ten years. We find less degradation due to self-heating in very short channel device structures due to the increasing role of nonstationary velocity-overshoot effects which are less sensitive to the local temperature.     

Modeling of Buffer Storage in Video Transmission

In video applications, the storage requirement is considerably large and hence they require large amount of network resources for their transmission. For transmitting the videos through a physical channel, there are two types of channelization-constant bandwidth and variable bandwidth channelization. It has been reported that using variable bandwidth channelization the buffer storage requirement is less than that of constant bandwidth channelization. Therefore, using variable bandwidth channelization a stochastic model is proposed for estimating the buffer storage so that the continuous delivery of the video data can be provided to the users.     

Modeling Communication Networks With Hybrid Systems

This paper introduces a general hybrid systems framework to model the flow of traffic in communication networks. The proposed models use averaging to continuously approximate discrete variables such as congestion window and queue size. Because averaging occurs over short time intervals, discrete events such as the occurrences of a drop and the consequent reaction by congestion control can still be captured. This modeling framework, thus, fills a gap between purely packet-level and fluid-based models, faithfully capturing the dynamics of transient phenomena and yet providing significant flexibility in modeling various congestion control mechanisms, different queueing policies, multicast transmission, etc. The modeling framework is validated by comparing simulations of the hybrid models against packet-level simulations. It is shown that the probability density functions produced by the ns-2 network simulator match closely those obtained with hybrid models. Moreover, a complexity analysis supports the observation that in networks with large per-flow bandwidths, simulations using hybrid models require significantly less computational resources than ns-2 simulations. Tools developed to automate the generation and simulation of hybrid systems models are also presented. Their use is showcased in a study, which simulates TCP flows with different roundtrip times over the Abilene backbone.     

用于脉冲负载的光伏-混合储能系统

数字式雷达属于一种典型的脉冲负载,其具体特点表现为周期性的功率突增突减。光伏设备中的蓄电池由于充放电速率较慢,对于脉冲负载频繁的功率突变往往无法快速响应;而超级电容凭借其比功率大、充放电速度快的特点可以对尖峰功率做出快速补偿。基于此,文中提出利用混合储能的方法来解决脉冲负载供电中存在的问题。在Matlab/ Simulink软件中搭建脉冲负载和光储系统的仿真模型,对比分析了蓄电池对脉冲负载单独储能和混合储能时系统运行参数。仿真结果表明:混合储能方案能有效且稳定地供电。     

混合电路贮存可靠性及评价方法

系统地分析和总结了混合电路在贮存中的失效模式及机理,温度、湿度以及化学等导致贮存失效的主要因素,论述了缺陷消除或控制法、贮存寿命加速试验法、标准单元结构评估预计法、自然贮存试验法等评价贮存可靠性的方法,为评估/评价混合电路贮存可靠性提供了思路和参考。     

LED散热器热分析建模方法

针对LED散热器热分析常用的热传导分析模型与流固耦合分析模型存在适用面窄与计算量大的不足,研究了LED散热器热分析的建模方法.提出了一种可以用热传导分析模型等效简化流固耦合分析模型的方法,该方法能快速得到散热器的温度状态并能从等效换热系数h获得LED散热器所需风扇的技术参数即风扇流量,有助于风扇规格的选择.以一款LED车灯风冷散热器的热分析为例,表明提出的等效简化建模方法不仅可以提高分析计算效率,而且具有良好的实用价值.     

Modeling and Simulation of Electric and Hybrid Vehicles

This paper discusses the need for modeling and simulation of electric and hybrid vehicles. Different modeling methods such as physics-based Resistive Companion Form technique and Bond Graph method are presented with powertrain component and system modeling examples. The modeling and simulation capabilities of existing tools such as Powertrain System Analysis Toolkit (PSAT), ADvanced VehIcle SimulatOR (ADVISOR), PSIM, and Virtual Test Bed are demonstrated through application examples. Since power electronics is indispensable in hybrid vehicles, the issue of numerical oscillations in dynamic simulations involving power electronics is briefly addressed     

基于SMP集群的MPI+OpenMP混合编程模型及有效实现

SMP集群混合了两个内存模型：每个节点是一个共享存储的多处理器，而节点间使用分布存储。这一多级体系结构引起了编程模型和性能方面的问题。文章讨论了MPI＋OpenMP混合编程模型的性能和不同的实现方法，提出了多粒度MPI＋OpenMP混合编程方法。建立了对称三对角特征问题的多粒度混合并行算法．并在深腾6800超级计算机上同纯MPI算法作了性能方面的比较。结果表明，该混合并行算法具有更好的扩展性和加速比。     

Modeling of Thermal Conductivity of Graphite Nanosheet Composites

Recent experiments demonstrated a very high thermal conductivity in graphite nanosheet (GNS)/epoxy nanocomposites; however, theoretical analysis is lacking. In this letter, an effective medium model has been used to analyze the effective thermal conductivity of the GNS/polymer nanocomposites and has shown good validity. Strong influences of the aspect ratio and the orientation of the GNS are evident. As expected, interfacial thermal resistance still plays a role in determining the overall thermal transport in the GNS/polymer nanocomposites. In comparison with the interfacial thermal resistance between carbon nanotubes and polymers, the interfacial thermal resistance between GNS and polymers is about one order of magnitude lower, the reason for which is discussed.     

太阳能热利用储热材料的研究与应用

储热材料在太阳能热利用过程中发挥着重要作用,本文综述了各类储热材料的研究与应用。从显热储热和相变储热两个方面分别介绍了低温和中高温储热材料的研究进展,分析了各类储热材料的特点,并展望了今后太阳能热利用储热材料的应用前景及研究方向。     

混合储能在风光互补发电系统中的能量管理与控制策略

储能技术在风光互补发电技术中的应用使得风光互补发电技术得到了进一步完善,各个部分的控制更加合理、有效,系统更加稳定、安全,并且使用效率及寿命得到了提高。通过仿真验证了一种蓄电池与超级电容混合储能结构,在这种结构中通过控制DC/DC变换器将蓄电池的高能量密度及超级电容的高功率密度的特点相结合,并且运用滑动滤波器进行二者的能量分配,同时通过DC/DC变换器达到对各储能部分实时控制的目的,从而提高了混合储能系统的灵活性与实用性。     

Rechargeable Sodium-Based Hybrid Metal-Ion Batteries toward Advanced Energy Storage

Growing demands on energy storage devices have inspired a tremendous amount of research on rechargeable batteries. Future generations of rechargeable batteries are required to have high energy density, long lifespan, low cost, high safety, low environmental impact, and wide commercial affordability. To achieve these goals, significant efforts are underway to focus on electrolyte chemistry, electrode engineering, and new designs for energy storage systems. Herein, a comprehensive overview of an innovative sodium-based hybrid metal-ion battery (HMIBs) for advanced next-generation energy storage is presented. Recent advances on sodium-based HMIBs from the development of reformulated or novel materials associated with Na⁺ ions and other metal ions (such as Li⁺, K⁺, Mg²⁺, Zn²⁺, etc.), are summarized in this work. Daniell cell and “rocking-chair” type batteries are covered. Finally, the current challenges and future remedies in terms of the design and fabrication of new electrolytes, cathodes, and anodes for advanced HMIBs are discussed in this report.     

适用于高速PCB的三维热设计模块

随着高速PCB设计的数量不断增加,对确保布线、信号完整性和热设计要求造成了很大的困难。为了能够应付这一现象,美国CiscoSystems公司已经推出了一款可以进行温度预测设计流量的产品,它能够极大的改善电路设计师和机械设计师之间的共同设计协调性。设计师们可以通过PCB设计软件进行相关信息的交流,以有助于热分析工作的开展。     

针对更精确电迁移预测应用的热耦合模型建模

基于先进逻辑CMOS工艺平台,构建了集成电路热耦合模型,为后端金属线电迁移预测提供更精确的温度变化和分布信息。在建模过程中,为了提高建模和仿真效率,对金属线网络和晶体管有源区进行简化,并用热传输比率对热耦合进行表征。考虑到晶体管参数、金属线走向、金属线之间相对位置对热传输比率的影响,模型中引入相关因子对热传输比率做进一步修正。最后,将该热传输模型嵌入到商用仿真软件中。结果表明,热传输比率(即温度)的仿真值与基于工艺平台流片的实测值吻合良好,验证了模型的准确性。     

基于FPGA的多路并行混合数据存储系统

为了解决多路信号并行混合采集存储的问题,文中设计了一种以FPGA为控制芯片的多路并行采集存储系统。该系统选用XC6SLX163CSG324I为主控芯片,设计包括数据采集接收模块、数据存储模块、数据回读模块。数据接收模块包括16路模拟量数据、导引头(DYT)数据、脉冲编码调制(PCM)数据和控制命令数据。该系统充分利用FPGA可重构的优势,对内部资源合理利用,降低了硬件资源开销,对所接收数据进行多路并行采集存储;利用握手原则,减少了数据的丢失。实验结果表明,该系统存储速率最高可达25 Mbyte/s,且备用口回读数据时,帧计数连续,该系统准确性较高。     

基于热效应的动态耳机模型

提出了采用耳机热效应模型来预测耳机声圈阻值在工作中的变化，从分析耳机工作中的热传递和蓄热机制出发构建了耳机的热效应模型，分频段对模型作了适当简化并确定出模型参数。中频和高频模型能很好地预测声圈阻值的变化，据此补偿耳机响应，改善耳机的听觉效果。