The similarity hypothesis applied to turbulent flow in an annulus

The velocity distribution in fully developed turbulent flow in an annulus is investigated using Goldstein's [1] extension of the similarity hypothesis of von Kármán. The theoretical result is compared with the experimental data of various investigations. The validity of the similarity theory in the study of turbulent flow in an annulus is examined using the measurements of the turbulence characteristics of Brighton and Jones [2]. The results indicate that the adoption of the theory is justified in the outer region of the flow only, i.e. outside the radius of maximum velocity. A particular form of the theory, which was found [1] to predict the velocity distribution accurately in the simpler pipe flow geometry, is used in the annulus study. The analysis of the annular flow is such that the computed results for the pipe can then be used to advantage.

The simpler correlations for the velocity distribution in the form of the “law of the wall” are briefly discussed, and the inadequacy of these in the inner region of the flow, i.e. inside the radius of maximum velocity, is pointed out. For completeness, a simple modified equation of a semi-empirical nature is presented. The final result for the inner region is compatible with the results for the limits of the annular geometry, viz. the pipe and the parallel wall channel. It is noted that the velocity distribution in the outer region of the annulus is accurately described using the simple logarithmic laws.     

The effect of bottom reflectivity on the performance of a solar pond

The reflectivity of the bottom of a solar pond increases on account of the accumulation of dirt or the presence of undissolved salt. The effect of the reflection of the solar radiation at the bottom of the pond on the seasonal performance of the pond has been studied using a three zone model. The spectral reflectivity of dirt and common salt were measured in the laboratory and used in the analysis. The results obtained from the analysis show that the presence of dirt at the bottom of the pond does not affect the performance of the pond substantially. On the other hand, the presence of undissolved salt at the bottom of the pond results in substantial deterioration of the pond performance.     

50MW抽汽冷凝式汽轮机叶片断裂原因分析

阐明了50MW抽汽冷凝式汽轮机转子动叶片对汽轮机组安全稳定运行的重要性、分析了引起汽轮机叶片断裂的多种原因，根据上海石化热电一站50MW抽汽冷凝式汽轮机在运行工况下叶片断裂的症状，以及在汽轮机检修过程中对叶片断裂截面的剖析，着重分析了热电一站汽轮机历年叶片断裂的原因，认为提高汽轮机叶片设计可靠性，加强汽轮机叶片的特性监控，以及控制运行中汽轮机中压缸的蒸汽流量，是防止50MW抽汽冷凝式汽轮机叶片断裂的主要手段。     

Evidence of the illegitimacy of the additive approach to the determination of the thermophysical properties of coal-water fuel with glycerol

For the fuel ignition, the thermal conductivity and heat capacity are the key properties that determine the pre-ignition behavior of the drop of the fuel. The classic monophase fuels, such as natural gas, liquid propellants, or solid one-component fuels, have been investigated for a long time; and their thermophysical properties are well known in most of the cases. Composite fuels, which have recently attracted the attention of the researchers, have complex contents. In many cases, composite fuel is a mixture of solid and liquid components in the form of a slurry. Coal-water fuel and its derivatives with different additives are examples of such type fuels. For those fuels, the thermophysical properties are usually unknown. Nowadays, researchers use simple additivity theory for the calculation of the thermophysical properties of complex fuels for the first approach. Authors of this research believe that the simple additivity approach is not correct and can lead to the wrong results in the case of the numerical research of the ignition and burning processes of such a fuel. In the present research, the thermophysical properties of coal-water fuel with glycerol additives were experimentally obtained. It was found that the coefficient of thermal conductivity increases with temperature and varies in the range of 0.45 to 0.53 W/(m·K). The heat capacity of the fuel also increases with the temperature and varies from 4.7 to 5.5 kJ/kg·K. The higher the glycerol content, the lower the thermal conductivity and heat capacity of the composite fuel in the investigated temperature range. The results confirm the failure of the approach of the additivity law usage. Neither, thermal conductivity coefficient or heat capacity of the coal-water fuel with the addition of up to 20% glycerol complies with the additivity law. Differences between real values of the thermophysical properties and calculated ones are more than 30% to 50%. Empirical expressions for calculation of the thermophysical properties of coal-water fuel with the addition of up to 20% glycerol are presented.     

State of the art of the virtual utility: the smart distributed generation network

The world of energy has lately experienced a revolution, and new rules are being defined. The climate change produced by the greenhouse gases, the inefficiency of the energy system or the lack of power supply infrastructure in most of the poor countries, the liberalization of the energy market and the development of new technologies in the field of distributed generation (DG) are the key factors of this revolution. It seems clear that the solution at the moment is the DG. The advantage of DG is the energy generation close to the demand point. It means that DG can lower costs, reduce emissions, or expand the energy options of the consumers. DG may add redundancy that increases grid security even while powering emergency lighting or other critical systems and reduces power losses in the electricity distribution. After the development of the different DG and high efficiency technologies, such as co‐generation and tri‐generation, the next step in the DG world is the interconnection of different small distributed generation facilities which act together in a DG network as a large power plant controlled by a centralized energy management system (EMS). The main aim of the EMS is to reach the targets of low emissions and high efficiency. The EMS gives priority to renewable energy sources instead of the use of fossil fuels. This new concept of energy infrastructure is referred to as virtual utility (VU). The VU can be defined as a new model of energy infrastructure which consists of integrating different kind of distributed generation utilities in an energy (electricity and heat) generation network controlled by a central energy management system (EMS). The electricity production in the network is subordinated to the heat necessity of every user. The thermal energy is consumed on site; the electricity is generated and distributed in the entire network. The network is composed of one centralized control with the EMS and different clusters of distributed generation utilities and heat storage tanks. Each of these clusters is controlled by a local management station (LMS). Every LMS has information about the requirements (heat, cold and electricity) of the users connected to its cluster and the state of the utilities and water level of the storage tanks in its cluster. The EMS receives the information from the LMSs and sets the electricity input or output of every cluster in the network. With the information ordered by the EMS, the LMS set the run or stand‐by of the utilities of its cluster. The benefits of the VU are the optimization of the utilization yield of the whole network, the high reliability of the electricity production, the complete control of the network for achieving the main aim of the EMS, the high velocity for assuming quick changes in the demand of the system and high integration of renewable energy sources, plus the advantages of the DG. This paper indicates the state of the art of the VU concept, analyses the projects that are being developed in this field and considers the future of the VU concept. Copyright © 2004 John Wiley & Sons, Ltd.     

The effect of current density and thickness of the active mass upon the corrosion rate of the spines of lead-acid battery plates

The effect of current density and the thickness of the active mass upon the corrosion of the spines of tubular lead-acid batteries has been determined by measuring the corrosion rate by the weight loss method. The presence of antimony in the alloy decreases the overvoltage of the corrosion reaction. Study of electrodes of different active mass layer thickness shows that with increase in thickness the corrosion rate decreases. If the thickness is above 3 mm, the corrosion rate remains constant, and is affected only by the nature of the alloy. The density of the active mass does not affect the corrosion behaviour of the electrodes. The experimental results confirm the validity of the oxygen corrosion model.     

Shallow solar pond: State-of-the-art

This review article deals with the various aspects of shallow solar ponds (SSP) suitable for domestic purposes and for supplying industrial process heat. The introduction gives a general idea of the status of the SSP technology among various solar energy applications. This part also surveys designs and performance of both water bag type and large scale SSP, already experimentally studied by other workers. The analysis of thermal process of SSP takes the input energy, the mechanism of thermal absorption and various losses in the system, into consideration. The methods for the improvement of the system performance suggests the materials that can be used and designs that can be incorporated in the various components of SSP. Here, a detailed study of the module, the glazing, the glazing supports and the insulation is done. The auxiliary systems viz, the mode of water transfer and water storage, play an important part in the optimum performance of the SSP systems. The “modes of operation” gives an account of the three different ways of circulating the liquid through the system-batch heating, closed cycle continuous flow heating, and open cycle continuous cycle flow heating. The theoretical analysis of the thermal performance of the SSP is done by making use of the Hottel-Willier-Bliss model for the flat plate collectors. A computation based on this model is employed in evaluating the values of monthly average daily collections efficiency with respect to the ambient temperatures for various initial water temperatures. The results obtained from the experiments conducted by Lawrence Livermore Laboratory, gives an idea of the system performance. The review also looks into the effects of various parameters, such as, the mass flow rate of the liquid, the total mass of water required per day, water depth, radiation intensity, average day-time ambient temperature, number of glazings, total heat loss coefficient, etc. The different modes of flow of the liquid are compared. An incorporation of the reflector in the SSP by various workers proved to provide a marked improvement in the system performance. The aspects such as, the cost effectiveness, maintenance and reliability of the SSP are briefly dealt with. It was felt that the review would be incomplete without a mention of the limitations and potential applications of the SSP. Based on these studies on SSP, done by various workers, the conclusion was that the performance of the system can be improved by the proper choice of the material, and by optimizing the design and the modes of operation.     

干湿循环条件下裂缝对土体吸力影响的机制研究

受干旱影响,土体会出现干缩裂缝,基质吸力的变化是分析裂缝开展的关键点,而裂缝的产生影响着基质吸力的变化,因此基于室内模型研究了干湿循环条件下不同位置土体开裂情况及对应部位基质吸力的时空演化规律。结果表明,斜坡中部裂缝更易发育,受旱过程中当裂缝存在时顶部土体的基质吸力增长滞后于坝坡中部土体的基质吸力增长;降雨后再干燥时段除底部外土体各处基质吸力受裂隙影响在较短时间快速增大,多次干湿循环后土体裂缝发展形态基本保持不变,此时同一部位基质吸力变化趋势基本相同,而不同部位因裂缝开展差异吸力变化有所不同。根据吸力变化情况绘制出的土水特征曲线反映出不同形态的裂缝存在对周边土体的影响(渗透系数)。研究成果可为维护坝坡稳定提供指导。     

Influence of the pro-ecological tax on the market prices of fuels and electricity

The proposed pro-ecological tax should be proportional to the cumulative consumption of non-renewable natural exergy burdening the considered product. It should replace the existing value-added tax (VAT). The income of the state after introducing the new tax, should remain without any change. That principle determines the coefficient of proportionality between the cumulative consumption of non-renewable exergy and the value of the tax. The total value of the tax should be paid to the state after extracting the minerals and fuels from nature and importing the fuels and semi-finished products, then transferred to the subsequent products in a form of their elevated price. Hence, the tax is eventually paid by the consumers in the form of an elevated price of goods and services. The total income of the society should remain without any changes. The largest price increase will appear in the case of fuels and electricity. The prices of electricity produced from renewable resources are calculated too, taking into account the accompanying unavoidable consumption of non-renewable exergy for the construction of the power plant. The new VAT should enhance the economy of the most energy-consuming products, stimulate the mitigation of the total consumption level of the society and increase the application of the renewable energy resources.     

Experimental characterization of a free thermal plume and in interaction with its material environment

This investigation analyses the behaviour of a turbulent thermal plume evolving in a neutral environment and in interaction with its surrounding material. The thermal plume is created by a rectangular hot source. This source is placed at the entry of a vertical parallelepipedic canal opened at the ends. Firstly, we studied the behaviour of a free thermal plume. The flow visualization and the analysis of the thermal and dynamic fields enabled us to detect the existence of two zones during the vertical evolution of the plume. A first zone of plume development followed by a zone of established turbulence. Secondly, we described the structure of a thermal plume produced by the same source inside the vertical canal. In this case the experimental results show clearly a change of the turbulent structure of the flow in comparison with the free plume. This difference is especially characterized by the appearance of a supplementary zone just above the source that is added to the two zones described previously. In addition, the comparison of the two studied configurations showed that the structure of the plume is narrowly affected by the confinement.In order to better define the fine structure of the flow, the temperature fluctuations spectra are analyzed. This spectral analysis enables us to show the fast destruction of the big structures vortexes by the confinement effect to give a smaller structure.     

Solar energy trial in Folovhodwe South Africa: Lessons for policy and decision-makers

In Mutale Local Authority of South Africa, a photovoltaic pilot project was commissioned to provide off-grid electricity to 582 households residing in Folovhodwe village. The aim was to try a renewable source of energy supply in a rural settlement area. The Beneficiaries Assessment method was used to assess the problems of the implementation and operation of the solar energy project in Folovhodwe. The project initiators did not realize that there would be the problem of the sustainable implementation of the project. The problem of sustainability was related to the inadequate definition of the role of each stakeholder. For example the end users were not taught how to properly operate and repair faulty equipment because it was not built into the planning and implementation stages of the project. Skill acquisition through capacity building for the end users can promote the sustainability of the project on a long-term basis. In Folovhodwe, improper planning and implementation of the project was responsible for the failure of the project. The project initiators did not foresee the problem of theft of materials, problems related to the procurement of spare parts and who would bear the cost of maintenance of the facilities. The failure of the project was also related to the inability of the policy makers to tackle the question of the role that each stakeholder should play to ensure the success of the project in a rural setting. The suggestion to policy and decision-makers is that pilot projects with relatively new technology input in a rural area should reconsider the importance of culture, capacity development and the level of income of the end users at the initial planning stage and implementation.     

Effects of swirl on the stability of jet diffusion flames

An experimental study was made, using a double-swirl burner, of the stability of swirling-fuel-jet diffusion flames in swirling air streams. The fuels were hydrogen and methane. The primary variables studied were swirl intensities of the fuel jet and the air stream. It was found that the stability of flame depended on the swirl intensity of both the fuel jet and the air stream. The application of swirl to the fuel jet decreased the rim stability of the flame, but increased the blowout stability of the lifted diffusion flame. For low swirl intensity of the air stream, the effect was similar to that of the fuel jet. At higher swirl intensities of the air stream, above a critical value, the flame stability increased noticeably because of the formation of a recirculation zone near the injector exit. Even in strongly swirling air streams, the favorable effect of fuel swirl on stability of the lifted flame was evident, particularly for the methane flame.     

Simulation Studies of the Transients of Squirrel-Cage Induction Motors

A new simulation approach is proposed in consideration of a saturation and a deep bar effect for the study of transients of three-phase squirrel-cage type induction motors. The mathematical model of an induction motor is expressed by the six differential equations of three-phase instantaneous voltage and current. The torque of an electric equation is related to the motion equations of motor and driven machine in the mathematical model. The values of reactance of stator and rotor are changed by the saturation of core caused by starting current. Also both the values of reactance and resistance of rotor bar are varied by the deep bar effect in the rotor core during starting. The calculation method of circuit constant that adds the influence of saturation and deep bar effect is proposed in this paper. The circuit constant of simulation model in consideration of saturation and the deep bar effect are decided by these computation methods in accordance with the conditions of rotation speed and current. If the large current flows, the leakage reactance of the stator and the rotor decreases by saturation. Moreover, the resistance of the rotor gradually decreases when the rotational speed rises from stop to synchronous speed, and the leakage reactance increases gradually. The calculated values were compared with the observed values of the examination machine of 1100 kW4P and an excellent agreement was obtained demonstrating the accuracy of the proposed simulation. Consequently, it is shown that the saturation and the deep bar effect are the essential factors to perform the accurate simulations of the induction motor. After checking the validity of the proposed approach, the simulation of the grounding faults was performed. In this study, all the simulation programs have been developed in the Matlab/Simulink environment.     

抽水蓄能电站甩负荷球阀动水关闭过程流固耦合研究

抽水蓄能电站甩负荷过渡过程中,内部流场与外部结构双向作用,对球阀安全运行造成不良影响。为探讨抽水蓄能电站甩负荷工况球阀动态关闭过程中流场演变对球阀关键部件的影响,基于流固耦合理论,建立球阀系统离散角度有限元仿真模型,以多角度结构分析近似模拟球阀在动水关闭过程中的结构瞬态过程,反映球阀流道的分布特点及薄弱环节的数据特征。为此,先对某抽水蓄能电站进行数值模拟,提取甩负荷过渡过程关键参数,根据仿真结果确定球阀流场边界条件;然后计算球阀流道内流场压力与速度分布;最后基于流场仿真结果建立球阀结构流固耦合模型,求解球阀瞬态过程结构强度相关参数分布。结果表明,甩负荷过渡过程中,在水流三维瞬变流动的影响下,球阀结构的应力分布具有明显规律性,工作密封与检修密封的过流面积突变,导致应力极大值出现在基座与枢轴部位。流场作用于球阀壁面的变形量叠加,球阀总变形量呈现由上游至下游逐渐递增的趋势。     

催化裂化装置长周期运行的问题及对策

洛阳石化2号催化裂化装置设计加工规模为1.4Mt/a,设计运行时数为8400h/a.大检修期间,针对该装置主要改造内容,以及开工后实际运行状况,找到了影响装置长周期运行的4条主要因素:装置的进料主要由加氢蜡油和闪蒸塔底油组成,闪蒸塔底油的掺炼比例高达70％,装置运行负荷高达110％,由于进料性质差,加工负荷高,操作调整较为频繁;由于原料变劣,硫、氮含量上升,反应过程中形成的硫化物、氮化物协同待生催化剂进入再生系统,在再生系统的低温部位发生低温硫酸、硝酸、氰酸露点腐蚀;随着原料逐渐变劣、变重,装置结焦倾向增加,重点围绕沉降器汽提段格栅及分馏塔进行问题说明;实际生产中,催化剂单耗逐渐增加,平衡剂中重金属含量略有上升,其中镍含量上升明显,平衡剂0～40μm的细粉含量也逐步上升.结合以上问题,提出相应的建议与对策.     

基于ArcGIS和Matlab程序的岩体裂隙方向性研究

岩体裂隙的方向性研究为裂隙几何描述的突破口,而裂隙玫瑰花图是裂隙方向统计数据的主要表达方式之一,过去大多采用人工统计手工绘制的方式实现,效率低。因此,按裂隙宽度将裂隙分为大、中、小、微小裂隙,借助ArcGIS和Matlab程序实现对裂隙方向数据的自动提取、玫瑰花图绘制、裂隙方向分组及裂隙分布函数的拟合。最后,对贵州省普定实验站的典型裂隙剖面的应用结果表明,该实测剖面的裂隙方向服从正态分布,且裂隙按隙宽分类得到的4种类型裂隙与整体裂隙的玫瑰花图、分布函数基本一致,增进了对裂隙方向统计分布的认识。     

天然河道与矩形水槽交汇口水面形态特性差异分析

鉴于天然河道与矩形水槽交汇口水面形态变化规律一致,定量分析上存在差异的问题,基于MIKE21FM建立天然河道阜新细河与支流汤头河交汇口的水动力数学模型,模型应用有限体积法求解浅水方程,通过对比模拟水面线与实测洪痕推算水面线,表明该模型能较好地模拟交汇口水流运动过程。利用该模型模拟不同分流比条件下天然河道交汇口水流运动,分析交汇口处的水面横比降、纵比降、分离区特征值与已有矩形水槽研究结果的差异。结果表明,天然河道断面形态由单一的横比降向凸脊形过渡发生在汇流比为0.5时,大于矩形水槽汇流比0.4;随着汇流比的增大,天然河道上游干流纵比降减小速率与矩形水槽基本一致,支流上游纵比降增大速率小于矩形水槽,干流下游纵比降增大速率大于矩形水槽;天然河道分离区的形状指标与收缩系数均大于矩形水槽,并给出了形状指标、收缩系数与汇流比的一般关系式。研究结果可用于指导河道整治、河网和河道设计等领域的实际工作。     

Comprehensive assessment of system efficiency and competitiveness of nuclear power plants in combination with hydrogen complex

The strategy provides construction and commissioning of a number of new nuclear power units for the development of nuclear energy in Russia. The share of nuclear power plants increase in the energy systems of Russia is predicted from 19 to 22% in the future, up to 2050. Nuclear power plants planned to involve in the primary frequency control at the same time. All these circumstances exacerbate the problem of providing nuclear power plants with a basic electrical load in the night period, including during the daily period. The energy strategy of Russia provides for the production of hydrogen by low-carbon methods, one of which is water electrolysis using nuclear power. Hydrogen production is included in the development strategy of the at operating Russian NPPs. Hydrogen production planned at the Kola NPP by water electrolysis. Thus, the article provides a rationale for the effectiveness of combining nuclear power plants with a hydrogen complex based on the production of hydrogen by electrolysis of water. The effectiveness substantiated of the new principle of combination with overheating of the working fluid steam turbine cycle of the NPP taking into account the safety of handling hydrogen. A new system proposed for the combustion of hydrogen in oxygen, which makes it possible to overheat the working fluid of the NPP steam turbine cycle with undissociated steam, which significantly reduces the content of unreacted hydrogen in the working fluid flow. In addition, a system was developed and proposed for removing unreacted hydrogen and oxygen from the steam phase of the working fluid of the NPP steam turbine cycle. Thermodynamic and technical-economic new estimates are presented and analyzed of the efficiency of combining NPP with a hydrogen complex.     

Computer simulation of the performance of a solar pond in the southern part of Iran

In this study a computer model of a solar pond to be built in the southern part of Iran is developed. The input to the program is the daily solar radiation, ambient temperature, evaporation rate, etc. The temperature rise of the pond for various rates of energy removal is the output of the program. A parametric study on such a computer simulation for optimization of performance of the actual solar pond is quite economical. Several computer experiments are carried out for various conditions of interest of the area around Shiraz in the southern part of Iran. Temperature rise of the bottom of the pond is calculated for different rates of energy removal. It is observed that after a few months of operation, the temperature of the bottom of the pond becomes sufficiently high to allow energy extraction from the pond. The temperature variation of the pond for different overall efficiencies of the pond under various conditions are also obtained and discussed. The response of the pond to several consecutive days of cloudiness is also studied. It is concluded that solar ponds are also reliable solar collector-storage systems for this part of the world.     

浊度和池底反射率对太阳池热性能的影响

提出了同时考虑浊度和池底漫反射的太阳池辐射透射模型和热效率模型,计算分析了浊度和池底反射 率对太阳池热性能的综合影响。模拟计算表明,浊度一定时,热性能总是随着池底反射率的增大而降低。计算 还表明,存在一个临界池底反射率,当池底反射率小于临界值时,浊度的增大导致太阳池热性能的下降;当池 底反射率超过临界值时,一定范围内浊度的增加反而有利于太阳池热性能的提高;当池底反射率在临界值附近 时,浊度的变化对太阳池热性能的影响很小。通过模拟计算得出了典型情况下的临界池底反射率,在太阳池的 实际研究和设计中可供参考。