Theoretical study of a thermoelectric-assisted vapor compression cycle for air-source heat pump applications

This paper proposes a thermoelectric-assisted vapor compression cycle (TVCC) for applications in air-source heat pump systems which could enhance the heating capacity of the system. Performances of TVCC are calculated and then compared with that of basic vapor compression cycle (BVCC). The simulation results show that when coefficients of performance (COPs) of the two cycles are almost equal, the TVCC under maximum COP condition of the thermoelectric modules still performs better than BVCC by 13.0% in heating capacity through selecting the appropriate intermediate temperature. In addition, the TVCC can also achieve an improvement of 16.4%–21.7% in both the heating COP and capacity when compared with the BVCC with an assistant electric heater that is provided with the equivalent power input of thermoelectric heat exchanger. Thus, the TVCC could be beneficial to the applications in small heat pumps if there is always need for auxiliary electric heat.     

The shear strength of nano-Ag sintered joints and the use of Ag interconnects in the design and manufacture of SiGe-based thermo-electric modules

Thermo-electric modules (TEMs) can be used to convert heat into electricity by utilizing the Seeback effect. It is now possible to buy BiTe thermo-electric modules that can operate up to temperatures of around 300 °C. However, many applications, such as the harvesting of excess gas turbine heat, may occur at higher temperatures. Therefore, new materials and manufacturing processes need to be developed to produce packaged TEMs that can operate at a maximum operating temperature of 650 °C. Two critical areas in the manufacture of a SiGe TEM are the choice and strength of materials used to both sintered joint the TE material to the rest of the module and the metal used for the interconnects. The interconnection material needs to be sufficiently strong to withstand large temperature fluctuations while maintaining a low contact resistance, as well as being compatible with the nano-Ag sintered joint. Shear force tests of the sintered thermo electrical leg material showed that the joints are brittle when sintered to W metallized AlN substrates are used and ductile fracture behavior when sintered to Cu metallized AlN substrates using the NanoTach K nano silver paste. Almost all of the joints were found to be brittle when using the NachTach X nano silver paste. Shear testing of the sintered joints showed that the X paste joints were variable in strength and stiffness, having a typical Young’s modulus between 10 and 100 MPa at room temperature. The K paste joints were stiffer, but had a similar strength as compared to the X paste joints.     

以任意高维纠缠态为量子信道的受控隐形传态

目的是利用高维量子纠缠态为量子信道，讨论未知单粒子态的受控隐形传输问题。以三维量子纠缠态为信道，提出一个二维任意单粒子态的受控隐形传输协议。提出了以任意[d]-维量子纠缠态为量子信道，[t]-维任意单粒子态的隐形传输协议[(t相似文献   

Numerical investigation of thermal and electrical management during hydrogen reversible solid-state storage using a novel heat exchanger based on thermoelectric modules

In order to reduce the costs generated by the hydrogen solid storage tank's accessories such as the heat exchanger, this work was carried out. It shows thermal and electrical investigations of transient hydrogen (H₂) solid storage in a tank filled with porous medium (LaNi₅) to activate a potential PEM automotive fuel cell. For this purpose, we use a novel heat exchanger with a heat sink combined with thermoelectric modules (TEMs). We realize a simulation that helps us verify if thermoelectric exchanger will be an alternative to the conventional ones. The main results are that a thermoelectric cooler and heater with 127 couples of semiconductors coupled with 19 fins heat sink could be used during the reversible hydrogen solid storage. Also, results show that we can avoid the water freezing at negative temperatures when using a conventional heat exchanger by using TEM during hydrogen absorption. Finally, during the endothermic desorption of the hydrogen, TEG use can avoid boiling water used in the heating system. Also, the hydrogen tank will be lighter and compact without fins and water tubes.     

Fast power cycling protocols implemented in an automated test bench dedicated to IGBT module ageing

This paper presents fast test protocols for ageing IGBT modules in power cycling conditions, and a monitoring device that tracks the on-state voltage V_CE and junction temperature T_J of IGBTs during ageing test operations. This device is implemented in an ageing test bench described in previous papers, but which has since been modified to perform fast power cycling tests.The fast test protocols described here use the thermal variations imposed on IGBT modules by a test bench operating under Pulse Width Modulation conditions. This test bench reaches the maximal values of power cycling frequencies attainable with a given module packaging in order to optimize test duration.The measurement device monitors V_CE throughout the ageing test that is needed to detect possible degradations of wire bonds and/or emitter metallization. This requires identifying small V_CE variations (a few dozen mV). In addition, the thermal swing amplitude of power cycling must be adjusted to achieve a given ageing protocol. This requires measuring junction temperature evolution on a power cycle, which is carried out by means of V_CE measurement at a low current level (100 mA).Experimental results demonstrate the flexibility of this test bench with respect to various power cycling conditions, as well as the feasibility of the proposed on-line monitoring methods.     

等效变形模量的非线性特征分析

在瞬时沉降或最终沉降计算中，都要用到土的变形模量Ｅ０，由于室内试验和原位测试方面存在的困难，过去对变形模量研究的报导有限。本文用载荷试验结果证明了变形模量具有非线性特征。在此基础上，通过北京地区三类土的原位平板载荷试验的压力－变形曲线的数学表达式及其特征值分析了等效变形模量Ｅ０，ｅｑ随压力的变化特征，并推导出相应的表达式。     

三次透视投影变换图像拼接

为了减少带有路面信息的建筑物图像的拼接中产生的图像失真并提高拼接速度,基于局部变形方法并结合建筑物和路面纹理信息的不同提出了三次投影变换图像拼接方法。该方法根据图像内容将图像分割成不同子图像,然后拼接图像内容相同的子图像,最后实施总体拼接。为了改善当前全局投影变换带来的图像形状失真或扭曲问题,整个拼接过程采用三次局部的透视投影图像变换方法。由于是在传统的透视投影变换的基础上基于图像内容分割后再拼接,故拼接结果比传统方法更精确、更真实。实验结果表明:采用提出的图像拼接方法克服了路面部分纹理信息过少导致图像失真的缺陷,拼接速度比相关拼接方法提高了20%~40%。该方法能快速得到清晰无缝的拼接图像,基本满足拼接速度快、真实度高的要求。     

超混沌系统的动力学性质及同步问题的研究

选取一个超混沌Qi系统,详细分析其动力学性质。采取基于观测器的方法来实现系统在不同初值条件下的同结构投影同步,并采用反馈法的思想设计合适的控制器,以实现Qi系统和Liu系统不同结构之间的完全同步。通过Lyapunov稳定性定理证明控制器的合理性,并对两种同步方法进行数值仿真来证明其可行性和有效性。     

Visualizing the performance loss of solar cells by IR thermography — an evaluation study on CIGS with artificially induced defects

Local electric defects may result in considerable performance losses in solar cells. Infrared (IR) thermography is one important tool to detect these defects on photovoltaic modules. Qualitative interpretation of IR images has been carried out successfully, but quantitative interpretation has been hampered by the lack of “calibration” defects. The aims of this study are to (i) establish methods to induce well‐defined electric defects in thin‐film solar cells serving as “calibration” defects and to (ii) assess the accuracy of IR imaging methods by using these artificially induced defects. This approach paves the way for improving quality control methods based on imaging in photovoltaic. We created ohmic defects (“shunts”) by using a focused ion beam and weak diodes (“interface shunts”) by applying a femto‐second laser at rather low power on copper indium gallium selenide cells. The defects can be induced precisely and reproducibly, and the severity of the defects on the electrical performance can be well adjusted by focused ion beam/laser parameters. The successive assessment of the IR measurement (ILIT‐Voc) revealed that this method can predict the losses in P_mpp (maximal power extractable) with a mean error of below 10%. Copyright © 2016 John Wiley & Sons, Ltd.     

Compendium of photovoltaic degradation rates

Published data on photovoltaic (PV) degradation measurements were aggregated and re‐examined. The subject has seen an increased interest in recent years resulting in more than 11 000 degradation rates in almost 200 studies from 40 different countries. As studies have grown in number and size, we found an impact from sampling bias attributable to size and accuracy. Because of the correlational nature of this study we examined the data in several ways to minimize this bias. We found median degradation for x‐Si technologies in the 0.5–0.6%/year range with the mean in the 0.8–0.9%/year range. Hetero‐interface technology (HIT) and microcrystalline silicon (µc‐Si) technologies, although not as plentiful, exhibit degradation around 1%/year and resemble thin‐film products more closely than x‐Si. Several studies showing low degradation for copper indium gallium selenide (CIGS) have emerged. Higher degradation for cadmium telluride (CdTe) has been reported, but these findings could reflect a convolution of less accurate studies and longer stabilization periods for some products. Significant deviations for beginning‐of‐life measurements with respect to nameplate rating have been documented over the last 35 years. Therefore, degradation rates that use nameplate rating as reference may be significantly impacted. Studies that used nameplate rating as reference but used solar simulators showed less variation than similar studies using outdoor measurements, even when accounting for different climates. This could be associated with confounding effects of measurement uncertainty and soiling that take place outdoors. Hotter climates and mounting configurations that lead to sustained higher temperatures may lead to higher degradation in some, but not all, products. Wear‐out non‐linearities for the worst performing modules have been documented in a few select studies that took multiple measurements of an ensemble of modules during the lifetime of the system. However, the majority of these modules exhibit a fairly linear decline. Modeling these non‐linearities, whether they occur at the beginning‐of‐life or end‐of‐life in the PV life cycle, has an important impact on the levelized cost of energy. Copyright © 2016 John Wiley & Sons, Ltd.