Impurity effects in BWR water chemistry

In this paper impurity effects are discussed from the viewpoint of intergranular stress corrosion cracking (IGSCC) of sensitized austenitic stainless steels in simulated reactor water. By using constant elongation rate tensile (CERT) testing it is demonstrated that low concentrations of certain, commonly encountered impurities may have a large effect on the tendency for IGSCC. This is especially true for sulfate and chloride ions and also, but to a smaller degree, for nitrate and carbonate. The effect of chloride is enhanced by copper ions and by hydrogen peroxide in start-up environment.     

防止酸洗引起的爆管事故

对酸洗引起的锅炉爆管事故进行了原因分析,提出了检验方法及处理措施。     

在绝热流动情况下非球形水滴的运动特性

采用非球形颗粒的阻力系数关联式，建立了水滴在绝热逆流空气中的动力学方程，得出了水滴所受阻力及其最终沉降速度的计算方法。在此基础上，分析了水滴变形程度和内部流动对水滴运动特性的影响，结果表明水滴变形程度增加使得水滴受到的空气阻力增大，而最终沉降速度减小，水滴的内部流动导致其受到的空气阻力减小，计算条件下最大偏差可达15％。     

Measurement of leak-rate through fatigue-cracks in pipes under four-point bending and BWR conditions

Leak-rate tests were performed using 114 mm and 165 mm (4 and 6 in) diameter, schedule 80 pipes made of austenitic stainless steel SUS304 and carbon steel STS42. Each pipe contained a through-wall fatigue crack and was mounted on a four-point bending machine of 400 kN maximum loading. Tests were done under a pressure of 7 MPa, with a subcooling temperature. The leak rate was measured by a Venturi flow meter and a differential pressure transducer attached to the pressure vessel. Comparisons of the effect of pipe material, diameter and crack angle were made. This paper shows that from a Leak-Before-Break viewpoint, the stainless-steel pipe is superior to the carbon-steel one, and that the pipe with the larger diameter is better than the one with the smaller diameter. No unstable fracture was observed in the tests.     

Performance penalties caused by thermal coupling in solar piping loops

Solar heating systems often employ conduits to carry cool fluid to the collector array and to carry the heated fluid back to the storage tank. In systems in which these two conduits are bundled together in one cover (in what has come to be known as the “life-line”) there is a thermal performance penalty caused by heat transfer from the hot conduit to the cold conduit. This cross heat transfer results in a penalty in system performance, and this paper is about evaluating this penalty. We show that the standard Hottel-Whillier-Bliss (HWB) equation can be modified to simultaneously take into account both the pipe heat losses to the ambient environment and the cross heat transfer between the hot and cold streams. Parameters in these equations are the thermal resistances between the fluids and between each fluid and the ambient. Methods are presented for both calculating and measuring these thermal resistances. We carry out sample calculations of the parameters in the modified HWB equation for a representative solar DHW system equipped with either of two different life-lines of commercial design. System simulations using these parameters reveal that the thermal effects of these life-lines are to reduce the net delivered solar energy by 6–14%, and that heat loss to the ambient is more detrimental to the system performance than heat transfer from the hot to the cold conduit.     

Modeling the effects of loading scenario and thermal expansion coefficient on potential failure of cryo-compressed hydrogen vessels

A multiscale thermomechanical model for a simplified Type-3 cryogenic, compressed-hydrogen (H₂) storage vessel is described in this paper. The model accounts for the temperature-dependent elastic-plastic behavior of the vessel's carbon/epoxy composite overwrap and aluminum alloy liner. The homogenized thermo-elastic-plastic behavior for the individual laminae of the vessel layup is obtained using an incremental Eshelby-Mori-Tanaka approach associated with a micromechanical failure criterion to predict laminar failure while a standard elastic-plastic constitutive model is used to describe the behavior of the typical aluminum alloy assumed for the liner. The vessel's response to external loadings is modeled using a finite element method. Four loading scenarios, representing four thermomechanical cycles applied to the vessel, are analyzed to evaluate constituent and laminar stresses as well as the associated failure criterion during the cycle according to these scenarios. The model can provide helpful guidance to mitigate thermal stresses by selecting a suitable loading scenario, optimizing the layup, and tailoring the thermomechanical properties of the resin matrix.     

Study over thermal state of gas turbine engine metal-ceramic rotor blades and nozzle guide vanes under thermal shock and thermal-cyclic loading conditions

To ensure a reliable operation of the 2.5 MW gas turbine engine (GTE- 2.5) with the inlet gas temperature TIT = 1623 K, studies were performed over the thermal state of the nozzle guide vanes and rotor blades with the temperatures, rates and flows of the working media and cooling air simulating all the potential turbine stage operating duties. The steady state and thermal-cyclic tests having been accomplished, there was no visible defect on the rotor blades and the nozzle vanes. Afterwards, they survived the endurance tests at the rated cooling. Therefore, the functionality of the shell thin-wall hybrid nozzle vanes and rotor blades under the variable operating duties of the gas turbine at the "shock" and "cyclic" loads of the working media temperature variations has been demonstrated.     

Dynamics of copper–water nanofluid with the significance of prescribed thermal conditions

In this study, unsteady bidirectional stretched flow and heat transport of a Cu–water nanomaterial in the presence of a magnetic environment embedded in a porous medium occupying boundary-layer region is investigated. Moreover, heat transport investigation is conceded out by simultaneous heat sources, namely, prescribed surface temperature and prescribed heat flux. The considered problem is converted into a set of four coupled differential equations with the help of a suitable combination of variables. The Keller–Box method is then implemented to get the numerical solution for velocity components and temperature distributions. Nanomaterial volume fraction $\psi$ impact on the velocity components and temperature distributions are studied. Through reduced skin friction coefficients and Nusselt numbers, it is detected that the heat transport capacity of nanomaterial is better than that of the base fluid. An exponentially decaying behavior of velocity components and temperature distributions is observed at far-field for various amounts of involved flow parameters.     

Effects of diesel/water emulsion on heat flow and thermal loading in a precombustion chamber diesel engine

An experimental investigation has been carried out to study the effects of using water/diesel emulsion fuel in an indirect injection diesel engine on the heat flux crossing liner and cylinder head, thermal loading and metal temperature distribution. A single cylinder precombustion chamber diesel engine has been used in the present work. The engine was instrumented for performance, metal temperature and heat flux measurements. The pure gas oil fuel and different ratios of water/diesel emulsion were used and their effects on the heat flux level and the injector tip temperature are studied. Two correlation were found for the heat flux crossing the liner and the cylinder head at various water/diesel emulsion ratios, fuelling rate and thermocouple probe locations. It was found that the addition of water to diesel fuel, to control the nitrogen oxides emissions, has great influence on reducing the heat flux, the metal temperatures and thermal loading of combustion chamber components.     

The simulation error caused by input loading variability in offshore wind turbine structural analysis

Stochastic representations of turbulent wind and irregular waves are used in time domain simulations of offshore wind turbines. The variability due to finite sampling of this input loading is an important source of simulation error. For the OC4 reference jacket structure with a 5 MW wind turbine, an error of 12–34% for ultimate loads and 6–12% for fatigue loads can occur with a probability of 1%, for simulations with a total simulation length of 60 min and various load cases. In terms of fatigue life, in the worst case, the lifetime of a joint was thereby overestimated by 29%. The size of this error can be critical, i.e., ultimate or fatigue limits can be exceeded, with probability depending on the choice of number of random seeds and simulation length. The analysis is based on a large simulation study with about 30,000 time domain simulations. Probability density functions of response variables are estimated and analyzed in terms of confidence intervals; i.e., how probable it is to obtain results significantly different from the expected value when using a finite number of simulations. This simulation error can be reduced to the same extent, either using several short simulations with different stochastic representations of the wind field or one long simulation with corresponding total length of the wind field. When using several short‐term simulations, it is important that ultimate and fatigue loads are calculated based on the complete, properly combined set of results, in order to prevent a systematic bias in the estimated loads. Copyright © 2014 John Wiley & Sons, Ltd.     

Thermal waves propagation in porous material undergoing thermal loading

A model for predicting thermal waves within a surface-heated porous structure has been developed. The relevant phenomena for the moisture, pressure and temperature fields are coupled. Considering mass and energy transfer processes, a set of governing differential equations is presented. The solution of the problem has been obtained with a finite difference scheme.     

Production of hydrogen by direct thermal decomposition of water

This paper reports the first results of a study on the feasibility of producing hydrogen by direct thermal splitting of water by use of concentrated radiation. Relative amounts of H, O, OH, H₂, O₂ and H₂O have been computed between 1500 and 4000 K at thermodynamic equilibrium. In addition, the rate of the overall reaction has been estimated assuming a kinetic model: 90% of equilibrium concentrations are reached after about 10^?2, 10^?3 and 10^?4s at 2200, 2500 and 3000 K respectively. The dissociation experiments have been carried out in an image furnace, simulating the future use of a solar furnace. Water is injected through a zirconia nozzle heated at the focus. The hot jet containing active species is then quenched by turbulent cold jets in order to minimize recombinations. Several shapes of zirconia nozzles and quenching devices have been tested in order to maximize the net production of hydrogen, which reaches 1.7 STP l. h^?1 in continuous operation. Modelling of the hot nozzle allows the calculation of the gas temperature and shows that thermodynamic equilibrium conditions are reached under certain conditions. Parallel experiments show that cooling rates up to 10⁶ Ks^?1 can be obtained by quenching.     

Estimation of lateral water flow in an aquifer by thermal logging

Temperature logs in an old brine-disposal well reveal a large thermal anomaly in and around the disposal aquifer. The shape and rate of decay of the anomaly permit comparison with a numerical model of the system, to give estimates of the initial amplitude of the anomaly and the rate at which the injected brine is being swept laterally from the injection zone centred on the well. It is found that the water in a portion of the Mannville Group near Regina is moving with a lateral flow rate of 2.6 m/yr, with a limit of probable error of 15%. It is not possible to determine the direction of movement by this method. The limited pressure data available suggest that flow of this rate may be greater than the mean regional flow.     

Numerical simulation of thermal loading produced by shaped high power laser onto engine parts

Recently a new method for simulating the thermal loading on pistons of diesel engines was reported. The spatially shaped high power laser is employed as the heat source, and some preliminary experimental and numerical work was carried out. In this paper, a further effort was made to extend this simulation method to some other important engine parts such as cylinder heads. The incident Gaussian beam was transformed into concentric multi-circular patterns of specific intensity distributions, with the aid of diffractive optical elements (DOEs). By incorporating the appropriate repetitive laser pulses, the designed transient temperature fields and thermal loadings in the engine parts could be simulated. Thermal–structural numerical models for pistons and cylinder heads were built to predict the transient temperature and thermal stress. The models were also employed to find the optimal intensity distributions of the transformed laser beam that could produce the target transient temperature fields. Comparison of experimental and numerical results demonstrated that this systematic approach is effective in simulating the thermal loading on the engine parts.     

对一起由内燃机车故障引起接触网烧损事故的分析

1 事故概况 2007年8月19日,配属济南西机务段的DF8B型5254号内燃机车,运行至淄博站时,发生柴油机差示压力计动作停机故障,乘务员做正常检查后重新起机继续运行.     

Hydrogen production by splitting water on solid acid materials by thermal dissociation

Conventionally, there have been three basic ways of research on H₂ production from H₂O-splitting with solar energy: photo-catalytic, photo-electrochemical and thermochemical. Among them the thermal dissociation of H₂O has been considered the most efficient, because it is a single step energy conversion process and gives much higher conversion efficiency than those resulted from other methods. However, the major stumbling block of thermal dissociation of H₂O has been the requirement of a high dissociation temperature which causes problems both with materials for the reactor and with energy conversion efficiency for the process. In this study, we show that the dissociation temperature can be drastically lowered when H₂O is thermally dissociated on solid acid materials. A probable mechanism of the thermal H₂O-splitting on solid acid materials is also presented, based on some experimental results of this study and reports in the literature.     

Estimation of boundary conditions in the presence of unknown moving boundary caused by ablation

Ablative materials can sustain very high temperatures in which surface thermochemical processes are significant enough to cause surface recession. Existence of moving boundary over a wide range of temperatures, temperature-dependent thermophysical properties of ablators, and no prior knowledge about the location of the moving surface augment the difficulty for predicting the exposed heat flux at the receding surface of ablators. In this paper, the conjugate gradient method is proposed to estimate the unknown surface recession and time-varying net surface heat flux for these kinds of problems. The first order Tikhonov regularization is employed to stabilize the inverse solution. Considering the complicated phenomena that are taking place, it is shown via simulated experiment that unknown quantities can be obtained with reasonable accuracy using this method despite existing noises in the measurement data.     

热压、风压共同作用下自然通风效果的CFD预测

自然通风效果与热压、风压强度及建筑物结构形式密切相关.对有平面热源及两个通风口的建筑模型进行了CFD研究.本研究涵盖了平面热源、风速及风口位置等三个因素:平面热源功率范围100～500 W/m2,进风速度范围0.25～1.25 m/s,进风口位置相对高度(进风口位置中心高度/房间高度)范围0.13～0.9.通过分析平面热源、进风口位置、进风速度等对室内温度场分布的影响,初步得出了风压与热压共同作用时室内温度场的分布规律.研究表明,当热压与风压共同作用时,室内存在一个温度相对较低的过渡区,且该过渡区有助于有效利用自然通风降低室温,提高通风效果.     

环境条件和冷却水流量对光伏光热系统的性能影响

环境条件对光伏光热(PV/T)系统性能的影响十分显著。文章通过改变实验室内部的环境条件,对比分析了通风、密闭条件下,不同冷却水流量对PV/T系统的输出性能以及光伏组件温度的影响。实验结果表明:密闭条件下PV/T组件工作温度与周围环境温度的平均值比通风条件下高出约7℃;密闭条件下PV/T系统的输出功率、热效率比通风条件下分别增大约3.5%,13%。     

冷冻水冷器水垢影响电费水费损失的评估

介绍了冷冻系统水冷器污垢影响的对比试验实测和评估,粗略计算了水垢 造成我国冷冻水冷器运行电费水费的损失每年高达３０亿元．因此,建议重视自动 清洗技术的应用。