Experimental and theoretical radiation damage studies on crystalline silicon solar cells

An experimental facility was developed to asses in situ the degradation of crystalline silicon solar cells, fabricated by the Solar Energy Group of the National Atomic Energy Commission (CNEA), by measuring the current–voltage characteristic curve. The cells were irradiated with 10 MeV protons and fluences between 10⁸ and 10¹³ p/cm², using an external beam of the linear tandem accelerator TANDAR, at CAC-CNEA. Furthermore, theoretical simulations were performed to establish the relation between the variation of the electrical parameters and the degradation of the lifetime of minority carriers in the base. The damage constant for 10 MeV proton irradiated silicon solar cells of n⁺–p–p⁺ structure and 1 Ω cm base resistivity was determined. Finally, a proposal of a new model of radiation damage for silicon solar cells is discussed.     

柴油机燃用柴油-碳酸二甲酯(DMC)混合燃料时缸内辐射传热的变化

研究了柴油机燃用柴油-DMC混合燃料后由于碳粒生成量减少而引起的缸内辐射传热量的变化以及发动机尾气烟度的变化.结果表明,添加DMC后排气烟度能够得到显著改善,并且存在一个最佳添加比例;同时随着添加比例的提高,缸内辐射传热量有所降低;对比尾气烟度和缸内辐射传热量,可以得到碳烟的生成量与缸内辐射传热量呈正比关系.     

Radiation and ionizational nonequilibrium effects on the electron density in a nonequilibrium MHD generator duct

This paper presents an investigation of the radiation and ionizational nonequilibrium effects of charge carriers on the electron density across a nonequilibrium MHD channel. Using the generated and empirical velocity and temperature profiles, the steady and unsteady diffusion equations are solved numerically using an implicit finite difference technique. It is found that, as a result of the radiation effects during ionizational nonequilibrium processes, the electron density is more, in comparison with its equilibrium value, in the boundary layer region, whereas it is less than its equilibrium value in the core.     

Numerical investigation on the creep damage induced by void growth in heat affected zone of weldments

In structural welded joints after long-term service at high temperature, fracture occurs mainly in the fine-grained heat affected zone (HAZ). Recently, the nucleation and growth of creep voids in the fine-grained HAZ of weldments, recognized as Type IV fracture, have become an important problem for low alloy ferritic heat resisting steels. In this paper, a new constitutive model was introduced to analyze the creep damage development in HAZ induced by void growth. This model is based on the equations of continuum damage mechanics (CDM) and combines a micromechanism-based method to account for the void growth process, which is different from the previous studies of creep damage. By coding a user-defined material subroutine (UMAT) in the FEA software ABAQUS, the proposed model was used to investigate the creep damage development in HAZ of a multi-material cross-weld specimen and a medium bore welded branched pipe where four different material properties: base material, coarse-grained HAZ, fine-grained HAZ, and weld material, were taken into account.     

柴油机主要零部件振动特性及辐射噪声分析

本文以95型柴油机为例，用有限元法计算了其传递特性和振动响应；并通过试验记录了各主要外部构件的振动特性，得到了10000Hz以内的频谱图；同时，还用声强法测量了标定工况下的辐射噪声。计算和试验结果显示油底壳、缸体、正时齿轮盖是该机最主要的辐射噪声源。文中还探讨了降低辐射噪声的途径。     

Radiation and mass transfer effects on flow of an incompressible viscous fluid past a moving vertical cylinder

The interaction of free convection with thermal radiation of a viscous incompressible unsteady flow past a moving vertical cylinder with heat and mass transfer is analyzed. The fluid is a gray, absorbing-emitting but non-scattering medium and the Rosseland approximation is used to describe the radiative heat flux in the energy equation. The governing equations are solved using an implicit finite-difference scheme of Crank-Nicolson type. Numerical results for the transient velocity, the temperature, the concentration, the local as well as average skin-friction, the rate of heat and mass transfer are shown graphically. It is found that at small values of the Prandtl number and radiation parameter N, the velocity and temperature of the fluid increases sharply near the cylinder as the time t increase, which is totally absent in the absence of radiation effects.     

Investigation of a platinum catalyst supported on a hydrogen peroxide-treated carbon black

A hydrogen peroxide-treated carbon support was used to prepare electrocatalysts for low temperature fuel cells. The electrochemical stability of the Pt/C catalysts was evaluated by potential scan tests. The results show that the oxidative treatment introduces oxygen-bearing functional groups onto the support surface. These functional groups connect with metal nanoparticles via O atoms so as to alleviate the agglomeration of supported nanocatalysts. During the test, the mean particle size of catalysts increased from 2.5 nm and 2.6 nm to 5.3 nm and 4.8 nm for untreated and treated carbon support, respectively. Electrochemical surface area measurements also show that the oxidative treatment of carbon support enhanced the electrochemical stability of Pt/C catalysts. It is suggested that the chemical interaction between the metal particle and the oxygen-bearing functional group plays an important role in immobilizing catalyst nanoparticles.     

Investigation of the influence of fuel type on energy indicators of an electrochemical generator as a PART of a cogeneration unit

The influence of the type of fuel such as hydrogen, methane, motor diesel fuel, ethanol, motor gasoline and methanol on the fuel utilization ratio, the specific consumption per unit of electrical and heat power generated, the efficiency of the catalytic burner, the solid oxide fuel cell battery and the electrochemical generator has been studied. It has been shown that hydrogen is the best fuel in terms of energy indicators, and methanol is the worst one. For hydrogen, the fuel utilization ratio and specific fuel consumption for the production of electrical power and heat power supplied to heat networks are equal to 1; 0.122 kg r.f./kW·h and 34 kg r.f./GJ, respectively, while for methanol these indicators are 0.359; 0.275 kg r.f./kW·h and 83.7 kg r.f./GJ, respectively. For other types of fuels studied the energy indicators lie between the specified values.     

Effects of different lithium compound electrodes on the electrochemical performance of the ceramic fuel cells

The effects of five different lithium compound electrodes LiNi_0.83Co_0.11Mn_0.06O₂ (LNCM-811), LiNi_0.6Co_0.2Mn_0.2O₂ (LNCM-622), LiNi_0.5Co_0.2Mn_0.3O₂ (LNCM-523), LiMO₄ (LMO) and LiCO₂ (LCO) on the electrochemical performance of the ceramic fuel cells with GDC as the electrolyte were investigated. It is found that the maximum power density (MPD) of the cell with LNCM-811 as the symmetrical electrode is the highest in H₂ at 550 °C among the five cells with different electrodes. The ionic conductivity of the composite electrolyte formed during performance testing in the cell with LNCM-811 as electrode is also the highest. With the decrease of Ni content in LNCM, the MPD of the cells with LNCM as electrode gradually decreases. The MPD of the cell with LCO as electrode was 196.9 mW?cm^?2, and MPD of the cell with LMO as electrode was the lowest, only 4.24 mW?cm^?2. According to the characterization results of SEM, FTIR and XPS of the different lithium compound electrode materials and the cells before and after performance test, it was found that the change law of the amount of molten salts such as LiOH produced by the reduction of lithium compound in H₂ is consistent with the change law of the MPD of the cells. It is proved that in addition to providing enough catalysts such as Ni and Co that can catalyze the electrode reaction, the key to the outstanding power generation performance of the cell is to produce a sufficient amount of lithium compound molten salt after being reduced in H₂.     

Effect of catalyst layer with zeolite on the performance of a proton exchange membrane fuel cell operated under low-humidity conditions

Proton exchange membrane fuel cells (PEMFCs) employ a proton conductive membrane as the separator to transport a hydrogen proton from the anode to the cathode. The membrane's proton conductivity depends on the water content in the membrane, which is affected by the operating conditions. A membrane electrode assembly (MEA) that can self-sustain water is the key component for developing a light-weight and compact PEMFC system without humidifiers. Hence, zeolite is employed to the anode catalyst layer in this study. The effect of the gas diffusion layer (GDL) materials, catalyst loading, binder loading, and zeolite loading on the MEA performance is investigated. The MEA durability is also investigated through the electrochemical impedance spectroscopy (EIS) method. The results suggest that the MEA with the SGL28BCE carbon paper, Pt loadings of 0.1 and 0.7 mg cm^?2 in the anode and cathode, respectively, Nafion-to-carbon weight ratio of 0.5, and zeolite-to-carbon weight ratio of 0.3 showed the best performance when the cell temperature is 60 °C and supplies with dry hydrogen and air from the environment. According to the impedance variation measured by EIS, the MEA with zeolite in the anode catalyst layer shows higher and more stable performance than those without zeolite.     

Experimental and numerical studies of local current mapping on a PEM fuel cell

Local current distribution on a PEM fuel cell has been mapped experimentally by using a special-designed single cell fixture. It is composed of a composite cathodic flow-field plate, a membrane electrode assembly (MEA) and a stainless-steel anodic flow-field plate. An array of 16 individual conductive segments was distributed on the composite plate. A self-made MEA is in direct contact with the segmented current collectors. Regional-averaged current through each segment is determined by using the Hall-effect sensor. To ensure the data reliability, a comparison of polarization curves was made between the composite flow-field plate and the conventional flow-field plate. Then, the effects of flow-field patterns, dew points of the cathodic feedings and cathodic stoichiometrics on the local current distribution were examined. The transient variation of the local current distribution on the cathode under supersaturated conditions was further visualized to illustrate the flooding phenomena in different flow patterns. This technique developed by the present work has contributed to knowledge and understanding the local current distributions in a PEM fuel cell that is helpful in designing the fuel-cell components.     

Biodiesel from low cost feedstocks: The effects of process parameters on the biodiesel yield

Biofuel (e.g. biodiesel) has attracted increasing attention worldwide as blending component or direct replacement for fossil fuel in fuel energized engines. The substitution of petroleum-based diesel with biodiesel has already attained commercial value in many of the developed countries around the world. However, the use of biodiesel has not expanded in developing countries mostly due to the high production cost which is associated with the expensive high-quality virgin oil feedstocks. This research focuses on producing of biodiesel from low cost feedstocks such as used cooking oil (UCO) and animal fat (AF) via alkaline catalyzed transesterification process investigating the effects of process parameters, for example (i) molar ratio of feedstock to methanol (ii) catalyst concentration (iii) reaction temperature and (iv) reaction period on the biodiesel yield. The biodiesel was successfully produced via transesterification process from low cost feedstocks. It was also observed that the process parameters directly influenced the biodiesel yield. The optimum parameters for maximum biodiesel yields were found to be methanol/oil molar ratio of 6:1, catalyst concentration of 1.25 wt% of oil, reaction temperature of 65 °C, reaction period of 2 h and stirring speed of 150 rpm. The maximum biodiesel yields at the optimum conditions were 87.4%, 89% and 88.3% for beef fat, chicken fat and UCO, respectively. The results demonstrate high potential of producing economically viable biodiesel from low cost feedstocks with proper optimization of the process parameters.     

Study of a post-fire verification method for the activation status of hydrogen cylinder pressure relief devices

To safely remove from its fire accident site a hydrogen fuel cell vehicle equipped with a carbon fiber reinforced plastic composite cylinder for compressed hydrogen (CFRP cylinder) and to safely keep the burnt vehicle in a storage facility, it is necessary to verify whether the thermally-activated pressure relief device (TPRD) of the CFRP cylinder has already been activated, releasing the hydrogen gas from the cylinder. To develop a simple post-fire verification method on TPRD activation, the present study was conducted on the using hydrogen densitometer and Type III and Type IV CFRP cylinders having different linings. As the results, TPRD activation status can be determined by measuring hydrogen concentrations with a catalytic combustion hydrogen densitometer at the cylinder's TPRD gas release port.     

Effect of operating conditions on the performance of a direct methanol fuel cell with PtRuMo/CNTs as anode catalyst

PtRu/CNTs and PtRuMo/CNTs catalysts have been synthesized by microwave-assisted polyol process and used as the anode catalysts for a direct methanol fuel cell (DMFC). The catalysts were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectrometry (XPS). The effect of different anode catalysts, membrane electrode assembly (MEA) activation, methanol concentration, methanol flow rate, oxygen flow rate and cell temperature on the DMFC performance has been investigated. The results show that the PtRu or PtRuMo particles with face-centered cubic structure are uniformly distributed on CNTs, and the addition of Mo to PtRu/CNTs makes the binding energies of each Pt species shift to lower values. PtRuMo/CNTs is a promising anode catalyst for DMFCs, and the appropriate operating conditions of the DMFC with PtRuMo/CNTs as the anode catalyst are MEA activation for 10 h, 2.0–2.5 M methanol at the flow rate of 1.0–2.0 mL/min, and oxygen at the flow rate of 100–150 mL/min. The DMFC performance increases significantly with an increase in cell temperature.     

废塑料合理再生利用的探讨

废塑料处理不当,不仅浪费资料,且造成白色污染。为贯彻可持续发展方针,亟待探索废塑料合理再生利用的途径。文章在介绍德国和日本经验的基础上,提出了对我国废塑料合理再生利用的建议。     

木薯干发酵生产燃料乙醇潜力研究

在实验室条件下研究木薯于发酵生产乙醇的潜力,以期为红薯燃料乙醇项目的生产提供相关参考数据。以粉碎后的木薯干为原料,料水比为1：2．8,糖化所用的复合酶添加量为原料质量的0．4％,在35℃±1℃温度下用酵母活化液（干酵母在33℃±1℃、40倍其质量的2％的葡萄糖溶液中活化60min）发酵原料产乙醇,反应周期为70h。在此工艺条件下．酒精度达22．0％,乙醇产率为48．32％,原料的TS和VS利用率分别为75．22％和80．01％。根据实验研究结果,今后在红薯燃料乙醇项目的运行和技改过程中需要根据实际情况确定适宜的料水比范围;酵母生理活性的高低是影响产酒率的重要因素．应根据生产状况对其进行改进或创新,从而取得自己的知识产权：应通过气相色谱法分析液相产物的成分．同时掌握发酵液的残留糖含量和酵渣组成等情况,为副产物的充分利用和开发附加产品做准备。     

A computational study to analyze the effect of equivalence ratio and hydrogen volume fraction on the ultra-lean burning of the syngas-fueled HCCI engine

This computational study investigates the equivalence ratio and hydrogen volume fraction effect on the ultra-lean burning of the syngas-fueled homogeneous charge compression ignition (HCCI) engine. In this research, low calorific syngas, composed of different compositions of H2, CO, and CO2, is used as a fuel in the HCCI engine that is operated under an overly lean air-fuel mixture. ANSYS Forte CFD package with Gri-Mech 3.0 chemical kinetics was used to analyze the in-cylinder combustion phenomena, and the simulation results were validated with experimental tests in the form of in-cylinder pressure and heat release rate at different equivalence ratios.The results indicate that changing the equivalence ratio produces a negligible change in combustion phasing, while it positively impacts the combustion and thermal efficiency of this syngas-fueled HCCI engine under lean conditions due to the high burning rate in the squish region. Moreover, an increased equivalence ratio increases MPRR due to the rich mixture combustion. The results also represent that the high-volume fraction of H2 in syngas fuel causes an advanced burning phase, improves the combustion performance of the HCCI engine at all equivalence ratio conditions, and causes slightly high NOx emissions.     

Effect of hydrogen addition to intake gas on combustion and exhaust emission characteristics of a diesel engine

The present study experimentally investigated the performance and emission characteristics of the diesel engine with hydrogen added to the intake air at late diesel-fuel injection timings. The diesel-fuel injection timing and the hydrogen fraction in the intake mixture were varied while the available heat produced by diesel-fuel and hydrogen per second of diesel fuel and hydrogen was kept constant at a certain value. NO showed minimum at specific hydrogen fraction. The maximum rate of incylinder pressure rise also showed minimum at 10 vol. % hydrogen fraction. However, it is desirable to set the maximum rate of incylinder pressure rise less than 0.5 MPa/deg. to realize low level of combustion noise and NO emission. We attempt to reduce further NO and smoke emissions by EGR. As the result, in the case of the diesel-fuel injection timing of −2 °. ATDC with 3.9 vol. % hydrogen addition, the smoke emission value was 0%, NO emission was low, the cyclic variation was low, and the maximum rate of incylinder pressure rise was acceptable under a nearly stoichiometric condition without sacrificing indicated thermal efficiency.     

Effect of anisotropic thermal conductivity of the GDL and current collector rib width on two-phase transport in a PEM fuel cell

A two-dimensional two-phase model based on the classical two-fluid model is used to analyze electrochemical and thermal transport in a PEMFC. The model is extended to account for the dependence of interfacial area density on liquid volume fraction. At a given fixed voltage, the fuel cell generates maximum current density for low through-plane and high in-plane thermal conductivities at high humidity operating conditions. It is also predicted that for low humidity operating conditions, the fuel cell generates maximum current density if the GDL is tailored to have high through-plane thermal conductivity near the inlet and progressively decreasing through-plane thermal conductivity at distances away from the inlet. At fully humidified cathode inlet conditions, narrower current collector ribs generate higher current densities at all voltages by reducing the resistance to diffusion of reactants and products through the GDL. In order to maximize the current density at low humidities, ribs must be wider near the inlet and narrower away from the inlet. The proposed methodology for tailoring GDL through-plane thermal conductivities and rib widths reduces the risk of membrane dehydration near inlet and also reduces the possibility of excessive liquid accumulation in the region away form the inlet.