Analysis of the effects of outdoor and accelerated ageing on the optical properties of reflector materials for solar energy applications

Lifetime tests of solar reflector materials are eligible prior to application, to prove the stability of the optical properties. In this work, six reflector materials were aged outdoors and in a climatic test chamber. The surfaces of the samples were inspected using profilometry and optical microscopy. The total and specular reflectance spectra were measured using spectrophotometry and the weighted solar reflectance values were calculated before and after ageing. Reflectors of silvered glass, anodised aluminium, thin film-coated anodised aluminium, and lacquered rolled aluminium withstood accelerated testing well, while a laminated evaporated aluminium reflector, which was specular initially, became diffuse. Laminated and lacquered reflectors withstood outdoor ageing better than expected from accelerated ageing and better than unprotected thin film-coated and anodised aluminium, which degraded significantly outdoors. Thus, optical degradation depends on climatic conditions and on the protective layer, if applicable. The discrepancy between results from outdoor and accelerated ageing shows that a thorough understanding of corrosion processes is necessary for drawing conclusions about long-term performance from accelerated ageing tests.     

Assessment methods of material ageing using Sdobyrev''s creep rupture model

The physical aspects of the activation energy, in higher and high temperatures, of the metal creep process were examined. The research results of creep-rupture in a uniaxial stress state and the criterion of creep-rupture in biaxial stress states, at two temperatures, are then presented. For these studies creep-rupture, taking case iron as an example the energy and pseudoenergy activation was determined. For complex stress states the criterion of creep-rupture was taken to be Sdobyrev's, i.e. σ_red = σ₁ β + (1 − β)σ_i, where: σ₁-maximal principal stress, σ_i-stress intensity, β-material constant (at variable temperature β = β(T)). The methods of assessment of the material ageing grade are given in percentages of ageing of new material in the following mechanical properties: 1) creep strength in uniaxial stress state, 2) activation energy in uniaxial stress state, 3) criterion creep strength in complex stress states, 4) activation pseudoenergy in complex stress states. The methods 1) and 3) are the relatively simplest because they result from experimental investigations only at nominal temperature of the structure work, however, for methods 2) and 4) it is necessary to perform the experimental investigations at least at two temperatures.     

A new model to describe absorption kinetics of Mg-based hydrogen storage alloys

Based on Chou model and unreacted-core model, a new mixed rate controlling kinetic model has been derived in this paper to investigate the adsorption reaction time t for Mg-based hydrogen storage materials as a function of temperature T, particle radius R₀ and reaction fraction ζ. This new model could be predigested into individual single step and mixed two-connection step equations. The characters of this new model have also been discussed. Moreover, the new model is successfully applied for a real case and results indicate that this new model works very well and could reasonably deal with complex kinetics mechanism.     

Unified model of ballistic and diffusive carrier transport: Application to photovoltaic materials

A unified model of one-dimensional ballistic and diffusive carrier transport in semiconductors, valid for arbitrary mean free path and arbitrary shape of the band edge profiles, is applied in a study of the effect of grain boundaries on the transport properties of photovoltaic materials. Adopting the trapping model to describe the grain boundaries, dark conductivities and photoconductivities are calculated as a function of donor density for samples consisting of chains of grains with length comparable to the mean free path. The results of the unified model are found to deviate substantially from those of the purely ballistic and purely diffusive limits.     

An empirical model for predicting the length of a capillary tube

Any refrigerant device consists of several parts, and one of the most significant parts is the expansion device. This expansion device can be classified into several types according to the size of the refrigeration system. The capillary tube is used usually with a small refrigerant system size to reduce the higher pressure in the condenser into the low pressure in the evaporator. In this study, the effect of the capillary tube's diameter and that of the temperature of the condenser and evaporator on the length of such a device has been theoretically studied. Furthermore, a validation between the theoretical analysis and experimental findings from the literature review has been carried out. To achieve the theoretical aspect, MATLAB code has been developed. The results showed that the maximum difference between the theoretical and experimental results regarding temperature and pressure refrigeration is around 5% and 3.4%, respectively. Also, the results depict that the inner diameter and the condenser temperature have an effect on the length of the capillary tube. However, the effect of the inner diameter is higher compared with the condenser temperature. In addition, an equation to predict the length of the capillary tube has been developed with an accuracy of 98%. This equation is created as a function of the capillary tube's diameter and the temperature of the condenser and the evaporator. Moreover, this equation can be used to predict the length of the capillary tube for small refrigeration devices, especially those operating under 10 KW. The findings of this study can help make a mathematical approach used for the design of the capillary tube simpler and easier to apply.     

An empirical exploration of the world oil price under the target zone model

This paper investigates the behavior of the world oil price based on the first-generation target zone model. Using anecdotal data during the period of 1988–1999, we found that OPEC has tried to maintain a weak target zone regime for the oil price. Our econometric tests suggest that the movement of the oil price is not only manipulated by actual and substantial interventions by OPEC but also tempered by market participants’ expectations of interventions. As a consequence, the non-linear model based on the target zone theory has very good forecasting ability when the oil price approaches the upper or lower limit of the band.     

Recent progress in the application of carbon materials to supercapacitors and lead-carbon batteries

新型炭材料是电化学储能领域中非常重要的一类储能材料,目前广泛应用于各种电化学储能器件.本文综述了具有电容特性的高比表面积炭材料在超级电容器与铅炭电池中的应用.采用不同的方法合成具有高比表面积的新型炭材料作为超级电容器电极材料,能够得到较高的比容量.适量高比表面积的炭材料应用于铅酸电池负极,形成铅炭电池,极大地提高了电池的储能特性.论文最后探讨了新型炭材料在超电容以及铅炭电池中应用的发展方向.     

An empirical analysis of the dynamic programming model of stockpile acquisition strategies for China's strategic petroleum reserve

The world's future oil price is affected by many factors. The challenge, therefore, is how to select optimal stockpile acquisition strategies to minimize the cost of maintaining a reserve. This paper provides a new method for analyzing this problem using an uncertain dynamic programming model to analyze stockpile acquisition strategies for strategic petroleum reserve. Using this model, we quantify the impact of uncertain world oil price on optimal stockpile acquisition strategies of China's strategic petroleum reserve for the period 2007–2010 and 2011–2020. Our results show that the future stockpile acquisition is related to oil prices and their probability and, if not considering the occurrence of oil supply shortage, China should at least purchase 25 million barrels when world oil price is at an optimal level. The optimal price of stockpile acquisition of every year has a stronger relationship with the probability of high price; and the optimal expected price and size of stockpile acquisition is different in each year.     

应用尾矿资源生产墙体材料的循环经济新实践

循环经济倡导的是一种建立在物质不断循环利用基础上的经济发展模式。对循环经济和传统经济进行了比较,针对尾矿造成环境污染且存在安全隐患和粘土砖浪费土地资源且建筑耗能大的问题,介绍了利用铜矿尾矿生产新型墙体材料,由此指出,该项目不仅可解决尾矿资源利用问题,而且顺应墙材行业转型改革的形势,是贯彻循环经济理念的新实践。     

Studying the electrochemical response to emulated photovoltaic electrochemical constrains of Li-ion electrode materials at the lab-scale

As part of a research project on new lithium-ion secondary cells to store energy from renewable power sources, this work reports on the development of a new methodology for a laboratory-scale study of electrode materials for these cells under the specific constraints of photovoltaic charging. A first example is that of a cell containing the spinel anode Li₄Ti₅O₁₂, charging under different solar irradiation regimes. This material is well suited to applications under discontinuous charge/discharge conditions. At the end of the test, after about 250 cycles, the two cells tested provide the same capacity and energetic efficiency of about 2.2 mAh and 90%, respectively.     

Influence of intrinsic hydrogenation/dehydrogenation kinetics on the dynamic behaviour of metal hydrides: A semi-empirical model and its verification

Metal hydrides can store hydrogen at low pressures and with high volumetric capacity. For the possible application as storage medium in hydrogen stand-alone power systems, large metal hydride hydrogen storage units are usually required. A reliable and verified kinetic correlation is an important tool in the designing process of a larger storage unit. This paper describes kinetic investigation of a AB₅-type alloy and its corresponding hydride, with the purpose of finding a semi-empirical correlation suitable for use in heat and mass transfer modelling and engineering design of metal hydride storage units.     

The novel use of phase change materials in refrigeration plant. Part 2: Dynamic simulation model for the combined system

A dynamic mathematical model for coupling the refrigeration system and PCMs has been developed in this paper. Overall the model consists of the following basic components: a compressor, a condenser, an expansion valve, an evaporator cooler and a PCM heat exchanger. The model developed here, is based on a lumped-parameter method. The condenser and evaporator were treated as storage tanks at different states, which have a superheat region, a two-phase region and a sub-cooled region. In the single-phase region the parameters are considered homogeneous whereas in the two-phase region, the intensive properties are considered as in thermal equilibrium. The compressor model is considered as an adiabatic process; an isentropic efficiency is employed in this process. The expansion process in the thermostatic expansion valve is considered as an isenthalpic process. The PCM is treated as a one-dimensional heat transfer model. The mathematical simulation in this study predicts the refrigerant states and dynamic coefficient of performance in the system with respect to time. The dynamic validation shows good agreement with the test result.     

Using a model to predict the migration and transformation of chemicals for alkali-surfactant-polymer flooding in soil

In recent years, alkali–surfactant–polymer (ASP) flooding has been widely used in Daqing area. In order to predict the possible impact of leakage accident, this paper not only established a corresponding model to predict the migration of various components of ASP flooding in soil but also calculated the kinetic parameters of the equation and obtained the vertical migration rule of pollutants in the soil through comparative analysis.     

Thermal model for the optimization of a solar rotary kiln to be used as high temperature thermochemical reactor

The present study focuses on a thermal model describing a rotary kiln reactor. Several applications can be foreseen for this reactor, for example high temperature heat storage for thermal solar power plants. The energy is provided by concentrated solar radiation that heats up the cavity walls. A thermal model, describing the reactor behavior, is developed and validated. Particular attention is given to the radiation model, which constitutes the most important heat transfer. An innovative way of modeling the reactor aperture through a fictive surface at an imposed equivalent temperature leads to a significant decrease of the simulation time, without decreasing the precision of the solution. The model is validated by comparison first with other models, which make different assumptions and second with experimental results. After the validation, the model can be used for simulating the behavior under different operating condition or to define the possible improvements by a change of the reactor geometry such as the insulation’s thermal conductivity or thickness.     

Application of an empirical model in CFD simulations to predict the local high temperature corrosion potential in biomass fired boilers

To gain reliable data for the development of an empirical model for the prediction of the local high temperature corrosion potential in biomass fired boilers, online corrosion probe measurements have been carried out. The measurements have been performed in a specially designed fixed bed/drop tube reactor in order to simulate a superheater boiler tube under well-controlled conditions. The investigated boiler steel 13CrMo4-5 is commonly used as steel for superheater tube bundles in biomass fired boilers. Within the test runs the flue gas temperature at the corrosion probe has been varied between 625 °C and 880 °C, while the steel temperature has been varied between 450 °C and 550 °C to simulate typical current and future live steam temperatures of biomass fired steam boilers. To investigate the dependence on the flue gas velocity, variations from 2 m·s⁻¹ to 8 m·s⁻¹ have been considered. The empirical model developed fits the measured data sufficiently well. Therefore, the model has been applied within a Computational Fluid Dynamics (CFD) simulation of flue gas flow and heat transfer to estimate the local corrosion potential of a wood chips fired 38 MW steam boiler. Additionally to the actual state analysis two further simulations have been carried out to investigate the influence of enhanced steam temperatures and a change of the flow direction of the final superheater tube bundle from parallel to counter-flow on the local corrosion potential.     

从含湿气体的热物理特性分析锅炉烟气潜热的利用

通过分析含湿气体的性质,解决气水接触式换热、冷凝式锅炉设计所涉及的含湿气体的含湿量与温度的关系、温焓关系,进而推导出排烟温度与锅炉热效率的关系.明确减少锅炉排烟损失的努力方向.     

Improved safety margins for Belgian nuclear power plants by the application of the Master Curve approach to RPV surveillance materials

In the context of existing regulatory codes, the integrity assessment of the pressure vessel of a nuclear power plant (NPP) is based on the empirical assumption that the fracture toughness of the surveillance materials, expressed in terms of a lower bound curve indexed by a reference temperature RT_NDT, undergoes a shift under irradiation by an amount equal to the increment of the T_41 J index temperature measured from surveillance Charpy tests. Nowadays, an alternative route exists, based on: reconstitution of previously tested specimens; execution of fracture toughness tests in the irradiated condition; Master Curve analysis of the results obtained and finally determination of an alternative toughness-based reference temperature (_RTT0)$({\mathrm{RT}}_{T_0})$, which can be used to index the lower bound K_Ic curve. As we demonstrate in this paper for several surveillance materials extracted from Belgian power plants, this “advanced” approach can provide NPP owners and plant engineers an additional safety margin with respect to the operating limits of the reactor and the pressurized thermal shock (PTS) screening criteria. These additional safety margins have been found particularly significant for older plants, for which the actual fracture toughness in the unirradiated condition is often underestimated by the approach based on RT_NDT.     

Modifying the solar spectrum to enhance silicon solar cell efficiency—An overview of available materials

There are three ways in which the cell efficiency of silicon solar cells may be improved by better exploitation of the solar spectrum: down-conversion (cutting one high energy photon into two low energy photons), photoluminescence (shifting photons into wavelength regions better accepted by the solar cell) and up-conversion (combining low energy photons to one high energy photon). In this paper, we present the state of the art of these three methods and discuss the suitability of materials available today for application to silicon solar cells.     

Using LMDI method to analyze the change of China's industrial CO2 emissions from final fuel use: An empirical analysis

Based on time series decomposition of the Log-Mean Divisia Index (LMDI), this paper analyzes the change of industrial carbon emissions from 36 industrial sectors in China over the period 1998–2005. The changes of industrial CO₂ emission are decomposed into carbon emissions coefficients of heat and electricity, energy intensity, industrial structural shift, industrial activity and final fuel shift. Our results clearly show that raw chemical materials and chemical products, nonmetal mineral products and smelting and pressing of ferrous metals account for 59.31% of total increased industrial CO₂ emissions. The overwhelming contributors to the change of China's industrial sectors’ carbon emissions in the period 1998–2005 were the industrial activity and energy intensity; the impact of emission coefficients of heat and electricity, fuel shift and structural shift was relatively small. Over the year 1998–2002, the energy intensity change in some energy-intensive sectors decreased industrial emissions, but increased emissions over the period 2002–2005. The impact of structural shift on emissions have varied considerably over the years without showing any clear trend, and the final fuel shift increased industrial emissions because of the increase of electricity share and higher emissions coefficient. Therefore, raw chemical materials and chemical products, nonmetal mineral products and smelting and pressing of ferrous metals should be among the top priorities for enhancing energy efficiency and driving their energy intensity close to the international advanced level. To some degree, we should reduce the products waste of these sectors, mitigate the growth of demand for their products through avoiding the excessive investment highly related to these sectors, increasing imports or decreasing the export in order to avoid expanding their share in total industrial value added. However, all these should integrate economic growth to harmonize industrial development and CO₂ emission reduction.