Thermal design of automobile exhaust based thermoelectric generators: Objectives and challenges

The potential for thermoelectric power generation (via waste heat recovery onboard automobiles) to displace alternators and/or provide additional charging to a vehicle battery pack has increased with recent advances in thermoelectric material processing. In gasoline fueled vehicles (GFVs), about 40% of fuel energy is wasted in exhaust heat, while a smaller amount of energy (30%) is ejected through the engine coolant. Therefore, exhaust-based thermoelectric generators (ETEG) have been a focus for GFV applications since the late 1980s. The conversion efficiency of modern thermoelectric materials has increased more than three-fold in the last two decades; however, disputes as to the thermal design of ETEG systems has kept their overall efficiency at limited and insufficient values. There are many challenges in the thermal design of ETEG systems, such as increasing the efficiency of the heat exchangers (hot box and cold plate), maintaining a sufficient temperature difference across the thermoelectric modules during different operating conditions, and reducing thermal losses through the system as a whole. This paper focuses on a review of the main aspects of thermal design of ETEG systems through various investigations performed over the past twenty years. This paper is organized as follows: first, the construction of a typical ETEG is described. The heat balance and efficiency of ETEG are then discussed. Then, the third section of this paper emphasizes the main objectives and challenges for designing efficient ETEG systems. Finally, a review of ETEG research activities over the last twenty years is presented to focus on methods used by the research community to address such challenges.     

无背索斜拉桥钢-混凝土组合脊骨主梁的关键受力分析

根据无背索斜拉桥中大悬臂钢-混凝土组合脊骨主梁的结构和受力特点,采用空间有限元法分析了混凝土桥面板徐变对组合脊骨梁内力分配的影响、钢箱梁扭转效应、组合悬臂挑梁受力及荷载横向分布、桥面板剪力滞效应等几个关键性受力问题,并利用外国规范验算了钢箱梁承压板的局部稳定性。由分析可知,混凝土徐变导致脊骨梁中钢箱梁应力增加,混凝土板应力下降;钢箱梁的扭转翘曲正应力可达到弯曲正应力的10%;大悬臂组合行车道板的横向分布计算取3片梁模型即可,且施工中采取预弯措施可防止组合挑梁的混凝土板受拉开裂;《本四桥规》中承压板容许应力计算公式约具有2.0的安全度;混凝土行车道板的剪力滞效应明显,塔梁固结处的行车道板还出现了负剪力滞现象。上述结论可为同类结构设计提供参考。     

连续刚构拱梁组合桥梁应力横向分布与温度应力分析

连续刚构拱梁组合桥梁,兼有连续刚构桥刚度大与拱桥跨越能力大的优点。以某连续刚构拱桥为研究对象,应用ANSYS软件建立起该桥的三维有限元模型,研究该桥箱梁应力的横向分布规律与全桥的温度应力。     

涡河连续刚构桥结构静载试验分析

以涡河大桥成桥静载试验为例,通过实测与理论计算进行比较,分析该桥箱梁部分实际受力性能,结果表明该桥的强度和刚度满足设计要求.在试验控制截面选择、试验工况确定、试验布载和测点布置方法上具有一定的借鉴意义.     

承台大体积混凝土水化热分析与施工控制

结合援孟加拉国中孟友谊六桥主桥承台设计与施工,利用Midas/Civil有限元计算分析软件对承台大体积混凝土水化热进行仿真分析,掌握水化热变化规律及其应力影响,据此指导现场施工控制。结果表明:仿真分析很好地反映了水化热变化规律及其应力影响,混凝土质量优良,没有出现温度裂缝,可供类似大体积混凝土设计与施工借鉴。     

预应力束张拉顺序对锚下局部应力影响分析

预应力混凝土构件中通常布置有多束预应力束,在施工设计中需要考虑预应力束的张拉顺序,合理的进行预应力筋的张拉。采用有限元程序ANSYS对不同的预应力束张拉顺序下某大桥主粱被动锚固区的局部应力进行分析计算,计算结果对同类桥梁的设计施工有一定的参考价值。     

干燥细砂破坏形式试验分析

土体破坏不是偶然的现象,受控于多种因素,而这些因素均为变量,不能精确地知道它们的数值。土体的结构是指土颗粒或集合体的大小和形状、表面特征、排列形式及它们之间的连接特征,也是影响土体破坏的多种因素之一。文章通过模型试验发现细砂的破坏是多种形式的综合体,其中土体的密实度、颗粒大小、级配等均是影响土体破坏形式的重要因素。     

Mechanical properties of asphalt pavement structure in highway tunnel

A linear full 3D finite element method （FEM） was performed in order to present the key design parameters of highway tunnel asphalt pavement under double-wheel load on rectangular loaded area considering horizontal contact stress induced by the acceleration/deceleration of vehicles. The key design parameters are the maximum horizontal tensile stresses at the surface of the asphalt layer, the maximum horizontal tensile stresses at the bottom of the asphalt layer and the maximum vertical shear stresses at the surface of the asphalt layer were calculated. The influencing factors such as double-wheel weight; asphalt layer thickness; base course stiffness modulus and thickness; and the contact conditions among the structure layers on these key design parameters were also examined separately to propose construction procedures of highway tunnel asphalt pavement.     

Reliability analysis of repairable systems using stochastic point processes

In order to analyze the failure data from repairable systems, the homogeneous Poisson process(HPP) is usually used. In general, HPP cannot be applied to analyze the entire life cycle of a complex, re-pairable system because the rate of occurrence of failures (ROCOF) of the system changes over time rather thanremains stable. However, from a practical point of view, it is always preferred to apply the simplest methodto address problems and to obtain useful practical results. Therefore, we attempted to use the HPP model toanalyze the failure data from real repairable systems. A graphic method and the Laplace test were also usedin the analysis. Results of numerical applications show that the HPP model may be a useful tool for the entirelife cycle of repairable systems.     

SEAM沥青混合料的试验结果与技术性能分析

对SEAM沥青混合料的试验结果与技术性能进行了分析。