柴油机颗粒过滤器再生时颗粒层氧化燃烧特性探究

基于可视化单通道台架,采用激光位移传感器在线测量再生时过滤壁面上颗粒层厚度,采用电镜离线观测颗粒层形貌,探索已沉积的炭黑颗粒层在柴油机颗粒过滤器(DPF)过滤壁面上的再生氧化过程。结果表明,基于颗粒层厚度变化曲线,再生过程分为3个阶段:第Ⅰ阶段,颗粒层厚度缓慢降低;第Ⅱ阶段,颗粒层厚度快速降低,氧化反应主要发生在DPF孔隙气流处,颗粒层表面出现凹坑形貌;第Ⅲ阶段,颗粒层厚度再次缓慢下降。同时,炭黑颗粒微观形貌由均匀堆积形貌向链状和环状形貌变化,颗粒层随氧化的进行呈现凹坑结构。     

强抗辐射轻型InP光伏太阳电池及其计算机模拟

为了给在高辐射轨道运行的卫星等航天器提供长寿命、强抗辐射太阳电池 ,设计了一种具有最佳结构的n+ i p+InP太阳电池。计算机模拟结果表明 ,即使经 10 17MeV·cm-2 和 10 18MeV·cm-2 的辐射辐照后 ,仍可具有 11%和 7%的转换效率 ;EOL(endoflife)功率质量比可达 10 0W /kg。无需防护罩 ,能够为运行在 32 0 0km极地轨道上的航天器稳定提供十年能量 ,这一指标超过了目前任何一种在研的太阳电池。特别值得一提的是 ,所有这些结果都是基于文中所示的简单结构而获得的。     

Band gap optimization of p–i–n layers of a-Si:H by computer aided simulation for development of efficient solar cell

The p-layer band gap and its thickness strongly influence the efficiency of hydrogenated amorphous silicon (a-Si:H) p–i–n solar cell, i and n-layer band gaps also play key role. In the present work, p, i and n layer band gaps as 2.1 eV (at thickness 10 nm), 1.75 eV (at thickness 400 nm) and 1.95 eV (at thickness 30 nm), respectively and acceptor and donor concentrations as 1 × 10¹⁸ cm^?3and 1 × 10²⁰ cm^?3, respectively, are optimized for obtaining efficient a-Si:H p–i–n solar cell by computer aided one-dimensional AFORS-HET software. It is important to mention that when p-layer thickness is changed to 5 nm, maximum efficiency is obtained at p-layer band gap of 2.2 eV. Such an optimized value would further help to prepare efficient a-Si:H p–i–n solar cells experimentally.     

A-Si:H buffer in a-SiGe:H solar cells

Profiled a-SiGe:H-buffer layers between the doped and the absorption layers of amorphous silicon germanium (a-SiGe:H) solar cells are routinely used to avoid bandgap discontinuities and high-defect densities at the p/i- and i/n interface. Here, we present a much simpler approach replacing the profiled a-SiGe:H-buffer layers at both interfaces by a-Si:H-buffer layers. It is demonstrated that for a-SiGe:H solar cells (thickness of the E_G=1.5 eV part is 54 nm) these structures yield similar open circuit voltage V_OC and fill factor (FF) compared to the bandgap profiled layer at the same short circuit current density j_SC. The influence of thickness, optical bandgap and position of the buffer layers on the solar cell performance is investigated.     

Flow and heat transfer of a third grade fluid past an exponentially stretching sheet with partial slip boundary condition

Non-Newtonian boundary layer flow and heat transfer over an exponentially stretching sheet with partial slip boundary condition has been studied in this paper. The flow is subject to a uniform transverse magnetic field. The heat transfer analysis has been carried out for two heating processes, namely (i) with prescribed surface temperature (PST), and (ii) prescribed heat flux (PHF). Suitable similarity transformations are used to reduce the resulting highly nonlinear partial differential equations into ordinary differential equations. An effective second order numerical scheme has been adopted to solve the obtained differential equations. The important finding in this communication is the combined effects of the partial slip and the third grade fluid parameters on the velocity, skin-friction coefficient and the temperature boundary layer. It is found that the third grade fluid parameter β increases the momentum boundary layer thickness and decreases the thermal boundary layer thickness.     

Experimental investigations of the microscopic features and polarization limiting factors of planar SOFCs with LSM and LSCF cathodes

The paper deals with the microscopic and polarization evaluation of planar circular-shaped seal-less SOFC cells from InDEC^® with an outline of performance limiting factors at reduced temperature. The cells consist of porous NiO–YSZ anode as mechanical support, NiO–YSZ anode active layer, yttria-stabilized zirconia (YSZ) electrolyte, and only differ for the cathode design. A first design (ASC1) with strontium doped lanthanum manganate LSM–YSZ cathode functional layer (CFL) and LSM cathode current collector layer (CCCL); the second design (ASC2) with yttria doped ceria (YDC) barrier layer and lanthanum strontium cobalt ferrite oxide (LSCF) cathode.     

Thermal storage efficiencies of two solar saltless water ponds

A comparative study between two types of solar ponds is presented. The first type has its free surface covered by a thin layer of transparent paraffin oil. The second type is covered by transparent glass floating devices. Each device disposes an air-vacuum chamber. The free water surface between these devices is covered by transparent paraffin oil also. The thermal storage efficiency of each pond is estimated during two time periods: between sunrise and sunset and from midnight to midnight. The calculated efficiency between sunrise and sunset corresponds to the average transmittance–absorptance product. This is estimated using linear regression and also a maximum likelihood identification technique. The behavior of the system was studied by solving numerically the heat transfer equations of the system. Also an ARMAX (AutoRegressivie Moving Average with eXogenous signal) model allowing the assessment of its performance was presented. This efficiency is larger for the first pond during the sunrise to sunset period and smaller when calculated from midnight to midnight. Thus, the first type of pond could be preferred for a use just after the sunset of the same day, while the second for use after one or more days of heat storage.     

Effect of nanostructured anode functional layer thickness on the solid-oxide fuel cell performance in the intermediate temperature

Effect of anode functional layer thickness on the performance of solid-oxide fuel cells (SOFCs) has been investigated in the intermediate temperatures of 600–650 °C. Three types of cells with different thickness (0, 4, 10 micron) of nanostructured anode functional layer (AFL) consisting of Ni-ScSZ (Scandia stabilized zirconia) are prepared. The SOFCs consist of Ni-3YSZ (3 mol% yttria stabilized zirconia) anode tube support with the AFL, ScSZ electrolyte, and LSCF (lanthanum strontium cobalt ferrite) and GDC (gadolinium doped ceria) mixture cathode. It is shown that the performance of the cell is improved as the thickness of the anode functional layer increases. Power densities of the cell with 10 micron thick AFL at 600 and 650 °C are shown to be 0.22 and 0.27 W/cm² at 0.75 V, respectively. According to impedance spectroscopy, improvement of both ohmic and polarization resistances has been observed by increasing the thickness of the AFL, suggesting that the AFL also acts as a better contact layer between the electrolyte and the anode support, and the effectiveness of the AFL by optimizing the thickness.     

Heavily neodymium doped ceria as an effective barrier layer in solid oxide electrochemical cells

10 mol% gadolinium doped ceria (GDC10) is widely used as a barrier layer between oxygen electrode and electrolyte to prevent interfacial reactions. A 50 mol% neodymium doped ceria (NDC50) barrier layer has been proposed and studied in this paper. Symmetrical cells with NDC50 and GDC10 barrier layers, Nd₂NiO_4+δ(NNO)–Ce_0.5Nd_0.5O_2-δ(NDC50) electrode, and YSZ electrolyte have been systematically studied using impedance spectroscopy (EIS) at various temperatures and oxygen partial pressure (pO₂). The NDC50 barrier layer has significantly decreased polarization resistance across a wide temperature and pO₂ range compared to the GDC10 barrier layer. The rare earth C-type structure of the NDC50 barrier layer causes barrier free migration of oxygen ions resulting in improved ionic conductivity compared to GDC10. Distribution of relaxation time (DRT) modeling has been used to obtain insights into the electrode processes.     

TEM and EELS microanalysis of pc-Si thin film solar cells deposited by means of HW CVD

A p–i–n doped pc-silicon thin film grown by means of hot wire chemical vapour deposition (HW CVD) on a zinc oxide film has been investigated by transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS). The structure of both layers, the ZnO substrate layer as much as the silicon thin film and the chemical composition at the interface were the subjects of our investigations. We found that a file of pure silicon with a thickness of about 5 nm covers the substrate surface. A plausible model for getting information on the wavyness of the interface ZnO/pc-Si and the thickness of this pure Si-layer was developed.     

Application of real-time spectroscopic ellipsometry for characterizing the structure and optical properties of microcrystalline component layers of amorphous semiconductor solar cells

Over the past few years, we have applied real-time spectroscopic ellipsometry (RTSE) to probe hydrogenated amorphous silicon (a-Si:H)-based solar cell fabrication on the research scale. From RTSE measurements, the microstructural development of the component layers of the cell can be characterized with sub-monolayer sensitivity, including the time evolution of (i) the bulk layer thickness which provide the deposition rates, and (ii) the surface roughness layer thickness which provide insights into precursor surface diffusion. In the same analysis, RTSE also yields the optical properties of the growing films, including the dielectric functions and optical gaps. Results reported earlier have been confined to p-i-n and n-i-p cells consisting solely of amorphous layers, because such layers are found to grow homogeneously, making data analysis relatively straightforward. In this study, we report the first results of an analysis of RTSE data collected during the deposition of an n-type microcrystalline silicon (μc-Si:H) component layer in an a-Si:H p-i-n solar cell. Such an analysis is more difficult owing to (i) the modification of the underlying i-layer by the H₂-rich plasma used in doped μc-Si:H growth and (ii) the more complex morphological development of μc-Si:H, including surface roughening during growth.     

COMBINED MACROSCOPIC AND MICROSCOPIC ANALYSIS OF THERMOELASTOPLASTIC STRESSES OF A FUNCTIONALLY GRADED MATERIAL PLATE

This article discusses the elastoplastic thermal stresses induced in a ceramic-metal functionally graded material plate (FGP) subjected to a thermal load taking the fabrication process into consideration. The FGP is divided into three regions. The first region near the cooling, metal, surface of the FGP is produced by ceramic particle-reinforced metal; while the second region near the heat-resistant, ceramic, surface is the opposite; and the third middle region is perfectly mixed by the metal and the ceramic. The first and second regions are governed by the particle-reinforced thermoelastoplastic constitutive equation, while the third region is expressed by the macroscopic analysis. Three cases of the temperature condition are studied: cooling from the fabricated temperature to room temperature, heating from the room temperature, and heating after cooling from the fabricated temperature. The temperature-dependent material properties are considered, and the particle volume fraction is assumed to vary according to a power function along the thickness direction of the FGP. The effect of the distribution parameter of the composition on the macroscopic stress, the stress in the matrix, and the stress in the particle in the FGP are discussed and illustrated in figures. Also, the effect of the fabricated temperature on the maximum tensile matrix stress is discussed.     

Contribution of silicon substrates to the efficiencies of silicon thin layer solar cells

Although silicon solar cells based on layers less than 50 μm thick have become very popular, little attention has been paid to the role of the underlying silicon substrate. This treatment uses the device simulation program PC-1D and the ray tracing program SUNRAYS to examine the role of the substrate in contributing to the current and efficiency of textured and non-textured thin layer solar cells. For the case of a heavily doped silicon substrate, substrate contributions can be significant for cells with sufficiently thin base layers. For example, for the case of a silicon thin layer cell with a base layer thickness of 20 μm and a substrate doping of 6 × 10¹⁸ cm⁻³, the substrate contributes no more than 4% of the total short-circuit current. However, decreasing the base width to 5 μm results in an increase in this substrate contribution to 20%. Light trapping tends to alleviate the substrate contribution by increasing the effective path length in the base. Examination of the current components under forward bias reveals that for a thin layer cell with a high quality base and good front surface passivation, back diffusion of electrons into the substrate limits cell performance.     

钙对生物质/塑料混合物共热解特性及动力学的影响

为了探究Ca²⁺对生物质/塑料混合物热解的影响,采用热重分析法研究了Ca²⁺浸渍酸洗玉米秸秆(ACS)/高密度聚乙烯(HDPE)混合物(AHM)的热解特性。结果表明,Ca²⁺的添加,使得AHM的初始分解温度以及第一失重峰对应温度均有所降低;此外,由于Ca²⁺的添加,AHM的第二失重峰对应温度基本不变,最大失重速率有所增加。在430~510℃高温阶段,AHM中ACS和HDPE间存在明显的协同效应(ΔW:-2.2~9.5),且Ca²⁺的添加促进了该协同作用。动力学分析表明,HDPE,ACS以及xCa-ACS可用单个一级反应描述(R²>0.97);xCa-AHM可用3个连续的一级反应来描述(R²>0.95)。此外,Ca²⁺的存在使得AHM第一阶段和第二阶段的活化能降低,第三阶段的活化能增大。     

Energy band structure parameters and their data, derived from the measurements of minority carrier current density in heavily doped emitters of silicon devices

In the n(p)-type heavily doped emitter region (HDER) of silicon devices, at room temperature, we have investigated the minority-carrier lifetime and the energy band structure parameters such as band-gap narrowing, apparent band-gap narrowing, unperturbed Fermi energy shift, optical gap, and reduced interacting density-of-majority conduction (valence) band states effective mass. As used in our previous paper, the present treatment is also based on the two assumptions for minority-carrier transport parameters. Gaussian impurity density profile, and accurate expression for minority-carrier mobility. Our empirical models for minority-carrier lifetime and band-gap narrowing are proposed and determined such that their curves versus the impurity concentration lie in between 3heir existing experimental data. Then, from a conjunction between electrical and optical phenomena, it is found that our theoretical values of such the energy band structure parameters are in good accordance with our own corresponding data, derived from the measurements of minority-carrier saturation current density in the n(p)-type HDER of silicon devices.     

Effects of slip on sheet-driven flow and heat transfer of a third grade fluid past a stretching sheet

The entrained flow and heat transfer of an electrically conducting non-Newtonian fluid due to a stretching surface subject to partial slip is considered. The partial slip is controlled by a dimensionless slip factor, which varies between zero (total adhesion) and infinity (full slip). The constitutive equation of the non-Newtonian fluid is modeled by that for a third grade fluid. The heat transfer analysis has been carried out for two heating processes, namely, (i) with prescribed surface temperature (PST case) and (ii) prescribed surface heat flux (PHF case). Suitable similarity transformations are used to reduce the resulting highly nonlinear partial differential equations into ordinary differential equations. The issue of paucity of boundary conditions is addressed and an effective second order numerical scheme has been adopted to solve the obtained differential equations. The important finding in this communication is the combined effects of the partial slip, magnetic field and the third grade fluid parameter on the velocity, skin-friction coefficient and the temperature field. It is interesting to find that slip decreases the momentum boundary layer thickness and increases the thermal boundary layer thickness, whereas the third grade fluid parameter has an opposite effect on the thermal and velocity boundary layers.     

Stability of transition metals on Mg(0001) surfaces and their effects on hydrogen adsorption

The interactions of a hydrogen atom with clean, vacancied, and transition metal-doped (TM = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, Au, Pt) Mg(0001) surfaces are investigated using first-principles calculations. The H adsorption on Mg(0001) with TMs doped within the second layer is generally more stable than that on clean Mg but clearly weaker than that on Mg surfaces with TM in the first layer. We find, however, that all these TM atoms prefer to substitute for the Mg atoms in the second layer rather than for those in the outermost layer of the Mg surface. To enhance the catalytic effect of the TM dopants, we investigated various co-doping conditions of TMs, and we found that i) Ti is a good “assistant” that stabilizes co-doped Co, Ni, Pd, Ag, Pt, and Au within the first layers and that ii) Ni and Co are more easily incorporated into the first layer of a Mg surface when co-doped with Ti, V, and Nb. These observations may lead to a possible approach to stabilize the TM dopants within the first layer and thus promote the hydrogenation of Mg accordingly.     

Particulate fouling in waste incinerators as influenced by the critical sticking velocity and layer porosity

Fouling of heat transfer surfaces introduces a major uncertainty into the design and operation of heat exchange equipment. Fouling layers as observed on the tube bundles of the economizer in a Dutch waste incinerator were thin and powdery. The fouling layer showed an asymptotic growth rate with a levelling off increase of the thickness. In this study, the influence of the critical sticking velocity on the growth rate of particulate fouling layers is described. The critical sticking velocity of an incident particle hitting a powdery layer is defined as the maximum impact speed at which the particle will stick to the layer. Since the critical sticking velocity is a key parameter in the deposition mechanism, a well-defined experimental set-up has been built to assign it. Experimental results showed that the critical sticking velocity increases with the porosity of the fouling layer. Literature shows that the porosity of a thin sintered powdery layer changes with the layer thickness. Based on the experimental results and the variation of porosity with thickness for a thin sintered powdery fouling layers, a correlation is developed which shows that the sticking velocity decreases exponentially as the fouling layer thickness increases. Therefore, fewer particles are likely to stick as the fouling layer builds up and consequently the deposition rate decreases. The change in the critical sticking velocity as the fouling layer builds up contributes to the explanation of the asymptotic growth of particulate fouling layers on the tube bundle of waste incinerators.     

核电汽轮机低压级内水滴沉积与疏水槽除湿性能研究

采用商用软件CFX对某核电汽轮机低压末三级叶栅通道中的水滴沉积规律进行了三维数值模拟,并初步研究了静／动叶片表面上的水膜流动特性,评估了次次末级后与次末级后疏水槽的除湿性能。结果表明：二次水滴比一次水滴更容易沉积在叶片表面上;水滴在叶片内弧的总沉积水量最多可达到背弧的10倍;静叶片上的水膜厚度沿轴向逐渐变薄,而动叶片上的沿轴向先缓慢变厚再变薄：两个疏水槽的除湿效率在11％左右。     

Optimum design of ordered bulk heterojunction organic photovoltaics

Organic photovoltaics (OPVs) have recently received increasing attention as alternatives to inorganic solar cells because of their light weight, compatibility with flexible electronics, and low production cost. In this work, an ideal device structure for ordered bulk heterojunction (OBHJ) organic photovoltaics is proposed. Also suggested is a parameter related to the power conversion efficiency (PCE) of the devices. Such a parameter could serve as a rule of thumb for researchers. For cases in which it is difficult to reduce the pillar size and spacing, the proposed parameter dictates that an increase in the active layer thickness could be one way to increase the PCE of an OBHJ. To generate maximum PCE, (1) the pillar size and spacing must be two to three times less than the exciton diffusion length and (2) the thickness of the active layer has to be greater than half of the photon mean free path, which is the inverse of the absorption coefficient.