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1.
Jean-Alain Le Duff Pascal Ould Jean-Louis Bernard 《International Journal of Pressure Vessels and Piping》1996,65(3):241-253
The determination of fatigue life of components containing defects usually takes into account crack propagation only. In a real situation, a number of cycles are often required to reach fatigue crack initiation and predictive evaluation of fatigue crack initiation phases of real defects in austenitic stainless steel welded joints are presented. Fatigue crack growth rates in wrought and cast austenitic stainless steels and associated welds are also presented. Effects of various mechanical parameters (R ratio and variable amplitude loading) of a PWR environment and of metallurgical factors (δ ferrite content and ageing in cast austenitic stainless steels) are discussed. 相似文献
2.
Surface and through thickness residual stress measurements were performed on an aged cast austenitic-ferritic stainless steel pipe and on an orbital TIG weld representative of those of primary coolant pipes in pressurized water reactors. An abrasive-jet hole drilling method and a block removal and layering method were used. Surface stresses and through thickness stress profiles are strongly dependent upon heat treatments, machining and welding operations. In the aged cast stainless steel pipe, stresses ranged between −250 and +175 MPa. On and near the orbital TIG weld, the outside surface of the weld was in tension both in the axial and hoop directions, with maximum values reaching 420 MPa in the weld. On the inside surface, the hoop stresses were compressive, reaching −300 MPa. However, the stresses in the axial direction at the root of the weld were tensile within 4 mm depth from the inside surface, locally reaching 280 MPa. 相似文献
3.
K. Kussmaul D. Blind J. Jansky 《International Journal of Pressure Vessels and Piping》1984,17(2):83-104
The present paper deals with cracking in ferritic pipework of light water reactor (BWR) feedwater systems whose causes are unsuitable design and manufacture and, at least occasionally, unsuitable water quality. Thus in two BWR plants in the German Federal Republic large circumferential cracks have been found in the circumferential welds in the main feedwater pipelines immediately adjacent to the reactor pressure vessel, and in a further BWR large longitudinal cracks have been found in pipe bends of the reactor water purification pipework connected to the main feedwater pipelines.The piping regions near the reactor pressure vessel feedwater nozzles represent a boundary region of varying thermodynamic states of the pressurised water. The reactor pressure vessel is heated to saturation temperature by the radioactive decay heat, and then cooler water, and sometimes (during start-up) cold water is injected into the reactor pressure vessel in order to maintain a constant water level about 2 m above the upper edge of the feedwater nozzles. In order to improve the state of knowledge regarding the stressing conditions under prevailing operating conditions, extensive strain and temperature measurements have been carried out. The results of these measurements carried out in several BWRs confirm the occurrence of rapid temperature changes in the feedwater pipework in the regions where it connects to the reactor pressure vessel, leading to varying stresses which at times reach the plastic region. These processes are triggered by special operating states such as start-up and shut-down or hot standby operation with feedwater flows smaller than 6% relative to normal operation under full load. 相似文献
4.
Hydrogen is considered today a promising environmental friendly energy carrier for the next future, since it produces no air pollutants or greenhouse gases when it burns in air, and it possesses high energy capacity. In the last decades great attention has been devoted to hydrogen production from water splitting by photocatalysis. This technology appears very attractive thanks to the possibility to work under mild conditions producing no harmful by-products with the possibility to use renewable solar energy. Besides, it can be combined with the technology of membrane separations making the so-called photocatalytic membrane reactors (PMRs) where the chemical reaction, the recovery of the photocatalyst and the separation of products and/or intermediates simultaneously occur. In this work the basic principles of photocatalytic hydrogen generation from water splitting are reported, giving particular attention on the use of modified photocatalysts able to work under visible light irradiation. Several devices to achieve the photocatalytic hydrogen generation are presented focusing on the possibility to obtain pure hydrogen employing membrane systems and visible light irradiation. Although many efforts are still necessary to improve the performance of the process, membrane photoreactors seem to be promising for hydrogen production by overall water splitting in a cost-effective and environmentally sustainable way. 相似文献
5.
D. Bockelmann R. Goslich D. Bahnemann D. Weichgrebe 《Solar Energy Materials & Solar Cells》1995,38(1-4)
Solar detoxification of a pure model compound (dichloroacetic acid) as well as of real waste waters was studied. Different types of reactors, light concentrating and non-concentrating were used and their advantages and disadvantages were compared and discussed. For this purpose a dimensionless number, the photoreactor number was introduced. Also the influence of different electron accepters (hydrogen peroxide and oxygen) on the degradation process was studied, both in the model system and the real waste water system. 相似文献
6.
C. Agrafiotis A.G. Konstandopoulos L. Nalbandian C. Sattler A.M. Steele 《Solar Energy》2005,79(4):409-421
The present work proposes the exploitation of solar energy for the dissociation of water and production of hydrogen via an integrated thermo-chemical reactor/receiver system. The basic idea is the use of multi-channelled honeycomb ceramic supports coated with active redox reagent powders, in a configuration similar to that encountered in automobile exhaust catalytic aftertreatment.Iron-oxide-based redox materials were synthesized, capable to operate under a complete redox cycle: they could take oxygen from water producing pure hydrogen at reasonably low temperatures (800 °C) and could be regenerated at temperatures below 1300 °C. Ceramic honeycombs capable of achieving temperatures in that range when heated by concentrated solar radiation were manufactured and incorporated in a dedicated solar receiver/reactor. The operating conditions of the solar reactor were optimised to achieve adjustable, uniform temperatures up to 1300 °C throughout the honeycomb, making thus feasible the operation of the complete cycle by a single solar energy converter. 相似文献
7.
A solar photoreactor operated in the batch, recirculating mode is analyzed in terms of very simple observable variables such as the impinging photon flux, the incident area, the initial concentration, the flow rate, the reactor volume and a property defined as the Observed Photonic Efficiency. The proposed equipment is made of a tubular reactor, a tank, a pump and the connecting pipes. The analysis is formulated in terms of the photon input corresponding to an equivalent batch system that is derived as a new reaction coordinate for photoreactions. Employing several plausible approximations, the pollutant concentration evolution in the tank is cast in terms of very simple analytical solutions.Process photonic efficiencies are defined for the system operation and calculated with respect to the maximum achievable yield corresponding to the differential operation of the solar recirculating reactor. 相似文献
8.
A dynamic, heterogeneous, two-dimensional model for packed-bed water gas shift reactors is presented. It can be applied to both high and low temperature shifts, and at scales ranging from industrial (for power plant applications) to small (such as automotive fuel cell applications). The model is suitable for any catalyst for which kinetic data are available, and shows excellent agreement with available experimental data for non-equilibrium conditions. The model is applied to an IGCC-TIGAS polygeneration plant to examine the dynamic behavior of the WGS units. The development of catalyst hot-spots is predicted during start-up or transition between steady states under certain conditions. 相似文献
9.
R. Gharari H. Kazeminejad N. Mataji Kojouri A. Hedayat 《International Journal of Hydrogen Energy》2018,43(4):1939-1965
Progress of severe accident (SA) can be divided into core degradation and post core meltdown. An important phenomena during severe accidents is the hydrogen generation from exothermal reaction between oxidation of core components, and molten core concrete interaction (MCCI). During the severe accidents, a large amounts of hydrogen is produced, deflagrated and consequently the containment integrity is violated. Therefore, the main objectives of this study is to highlight the source of hydrogen production during SA. First, a thorough literature review and main sources of hydrogen production, hydrogen reduction systems are introduced and discussed. Based on the available results, the amount of produced hydrogen in a typical pressurized water reactor (PWR) and a boiling water reactor (BWR) are estimated to be 1000 and 4000 kg, respectively during in-vessel phase. The average rate of hydrogen production is about 1 kg/s during reflooding of a degraded core. Also, about 2000 kg hydrogen is produced during MCCI for a PWR. The lower and upper range of hydrogen required to initiate combustion is 4.1 and 74 vol percent, respectively. In this paper a review is provided of what has been done in the literature with regard to hydrogen generation in severe accidents of nuclear power plants. In addition, the review identifies the literature gaps and underlines the need of developing a systematic hydrogen management strategy. A hydrogen management strategy is proposed in order to maintain the containment integrity against the probable combustion or hydrogen explosion loads. 相似文献
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11.
H2-based membrane biofilm reactor (MBfR), a kind of autotrophic denitrification system, is a novel and special membrane bioreactor using hydrogen as inorganic electron donor to reduce nitrate and nitrite in water and wastewater. In this paper, the state of the art of recent research on denitrification through H2-based MBfRs is reviewed, including theoretical fundamentals, key influencing factors, possible problems and applications. Hydrogen/nitrate counter-diffusion has been described as Dual substrates limitations. The denitrifying bacteria in H2-based MBfR were summarized. The key factors affecting the performance of H2-based MBfR were listed in terms of substrate concentrations, membrane materials, reactor types, biofilm management and operation conditions. The pH value, salinity, dissolved oxygen, HRT (hydraulic retention time) and carbon source have been identified as main operational conditions affecting H2-MBfR performance. Furthermore, membrane fouling in H2-based MBfRs was emphasized. H2-MBfR was proved excellent in denitrification based on its high performance for groundwater, IX brine and aquaculture wastewater treatment. Several aspects may be considered in future works were proposed. 相似文献
12.
The concentration of dissolved oxygen in water, in equilibrium with atmospheric air (ca. 8 ppm at 20 °C), defines the limits of all practical oxidizing processes for removing pollutants in photocatalytic reactors. To solve this limitation, an alternative approach to that of a continuously aerated reactor is the use of a recirculating system with aeration performed after every cycle at the reactor entering stream. As defined by the nature of a single recirculating step (the need of a reactor operation at a rather low concentration range), this procedure results in a very low photonic efficiency (thus requiring a large photon collecting area and consequently increasing the capital cost). The design engineer will have to resort to a series of several reactors with recirculation. This solution may then lead to a very high Photonic Efficiency for the entire process (i.e., a reduced light harvesting area) at the price of an increase in the required capital cost (due to the larger number of reactors). This paper provides a very simple analysis and analytical expressions that can be used to estimate, for a desired degree of degradation, a trade-off solution between a high number of reactors and a very large surface area to collect the solar photons. 相似文献
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14.
蓄光型自发光材料又称为光致光超长余辉蓄光材料、非放射性蓄光材料、无电源自发光材料等。该材料主动吸蓄太阳光、灯光、紫外光、杂散光等可见光5~10分钟后,就可在黑暗中持续发光12小时以上,并可根据实际需要,使其发出红、绿、蓝、黄、紫等多种彩色光。目前,蓄光型自发光材料制品有发光涂料、油漆、发光油墨、发光釉料、发光塑料、发光橡胶、发光皮革、发光玻璃、发光陶瓷、发光装饰石、发光铝塑复合板、发光工艺品等。由于其 相似文献
15.
C. Tablero P. Palacios J.J. Fernndez P. Wahnn 《Solar Energy Materials & Solar Cells》2005,87(1-4):323
Intermediate Band Materials (MIB) have been proposed in previous works as a new kind of photovoltaic materials. These materials are principally characterized by an intermediate partially occupied band, isolated from the valence and conduction bands of the host semiconductor. These materials have a theoretical efficiency greater than that of conventional solar cells because they can absorb photons with a lower energy than the bandgap of the original host semiconductor. However, although the operation of these solar cells has been described, it is necessary to use a method to be able to propose the material which has these properties. In this work, a theoretical study of the electronic and optoelectronic properties using quantum-mechanics calculations is presented. The results confirm that MIB are able to absorb photons of lower energy than the host semiconductor. 相似文献
16.
Separator materials suitable for use in industrial alkaline water electrolysers are surveyed, including both inorganic and organic materials. The properties which make asbestos diaphragms unsuitable for use above 100°C are also reviewed.In summary, potassium titanate and polyantimonic acid separator materials perform well in high-temperature alkali. Oxide-coated metallic diaphragms merit further attention. Polysulfone and polyphenylene sulfide polymers are promising, but will need definite improvement in their wettability. Asbestos stabilization by silicate electrolyte additions may be viable. 相似文献
17.
This study presents numerical studies of hydrogen production performance via water gas shift reaction in membrane reactor. The pre-exponential factor in describing the hydrogen permeation flux is used as the main parameter to account for the membrane permeance variation. The operating pressure, temperature and H2O/CO molar ratio are chosen in the 1–20 atm, 400–600 °C and 1–3 ranges, respectively. Based on the numerical simulation results three distinct CO conversion regimes exist based on the pre-exponential factor value. For low pre-exponential factors corresponding to low membrane permeance, the CO conversion approaches to that obtained from a conventional reactor without hydrogen removal. For high pre-exponential factor, high CO conversion and H2 recovery with constant values can be obtained. For intermediate pre-exponential factor range both CO conversion and H2 recovery vary linearly with the pre-exponential factor. In the high membrane permeation case CO conversion and H2 recovery approach limiting values as the operating pressure increases. Increasing the H2O/CO molar ratio results in an increase in CO conversion but decrease in H2 recovery due to hydrogen permeation driving force reduction. As the feed rate increases in the reaction side both the CO conversion and hydrogen recovery decrease because of decreased reactant residence time. The sweep gas flow rate has a significant effect on hydrogen recovery. Low sweep gas flow rate results in low CO conversion H2 recovery while limiting CO conversion and hydrogen recovery can be reached for the high membrane permeance and high sweep gas flow rate cases. 相似文献
18.
The optical transmittance properties, under diffuse light, of semitransparent materials used to fabricate photovoltaic devices have been investigated by using an apparatus provided with two “coupled” integrating spheres, one for producing the incident diffuse light and the other for collecting the transmitted light. A detailed analysis of the measurement conditions has been performed taking into account the perturbing effect each sphere produces on the other, and a final expression for the correct transmittance of the sample is derived. 相似文献
19.
This paper reviews the fitness-for-purpose of commonly used materials and possible alternative materials for all components of solar heating systems for domestic hot water. Optimum materials are recommended where possible. A conclusion of the survey of materials which has been carried out is that, using current technology, reliable, durable solar heating systems can be built. The cost of such systems is high, due to the use of expensive materials (such as copper and stainless steel) and the systems are unlikely to be cost-effective in the long term. Costs can be reduced by the use of lower cost materials such as the polymerics for many of the components, but as yet there are insufficient materials performance data to ensure long-term reliability. 相似文献
20.
O.A. McLoughlin S.C. Kehoe K.G. McGuigan E.F. Duffy F. Al Touati W. Gernjak I. Oller Alberola S. Malato Rodríguez L.W. Gill 《Solar Energy》2004,77(5):657-664
This paper compares three different collector shapes for the disinfection of water heavily contaminated with Escherichia coli (K-12). Tests were carried out in real sunlight using laboratory scale reactors to determine the performance of different reflector profiles. The reactors were constructed using Pyrex tubing and aluminium reflectors of compound parabolic, parabolic and V-groove profiles. Results have shown that the compound parabolic reflector promoted a more successful inactivation of E. coli than the parabolic and V-groove profiles. Tests were also carried out to assess the improvement to disinfection which could be achieved using TiO2 coated Pyrex rods fixed within the reactors. This technique, however, yielded a slight enhancement in the compound parabolic reactor but no benefit to overall disinfection performance in either the parabolic or V-groove reactors.These results show that the use of UV sunlight to disinfect contaminated drinking water in a full-scale continuous flow solar reactor is both promising and an appropriate technology for developing countries but that the inclusion of a fixed photocatalyst within the reactor tubes has yet to prove any significant improvement. 相似文献