环境因素对直接空冷机组的影响

直接空冷机组的运行状况受周围环境的影响很大,不同的风速、风向不仅会影响到机组运行的经济性,甚至还会造成掉闸停机事故。本文在总结火力发电厂空冷系统特点的基础上,对现场环境及所采集数据进行了系统分析,重点研究了环境作用对直接空冷机组空冷风机吸入风量和入口温度以及空冷机组背压影响,同时分析了环境温度的变化对空冷机组供电煤耗的影响。     

Numerical simulation of the casting process of a wind turbine rotor hub

An integrated numerical model was applied to simulate the mold filling and solidification process as well as predict the occurrence of relative casting defects for a rotor hub casting. The goal was to conduct a numerical experimentation to obtain an optimal alloy design of ductile cast iron for the rotor hub casting. A computer‐aided engineering software based on the finite element method was employed in this study. Numerical simulations were conducted for the rotor hub casting with two different types of alloy composition for ductile cast iron. The mold filling and solidification process were examined to predict the occurrence and extent of casting defects and a better alloy design was then proposed based on the simulated results to alleviate casting defects of the rotor hub casting. Copyright © 2010 John Wiley & Sons, Ltd.     

结晶器用铜板强化技术的研究进展

铜及铜合金具有优良的导电导热性能,其在钢铁冶炼过程中的连铸结晶器上起着举足轻重的关键作用.然而结晶器所在的恶劣服役条件却限制了其性能的发挥,较常见的损耗形式为结晶器铜板内表面弯月面处的热裂纹及结晶器铜板下部的摩擦磨损,这些损耗形式在一定程度上大大缩短了结晶器的使用寿命,针对此现象综述了国内外不同表面改性强化技术在结晶器铜板上的应用,通过不同表面改性强化处理,可提高结晶器铜板耐磨性、耐热冲击及耐腐蚀性能,从而提高铸坯质量、延长结晶器使用寿命及降低生产成本的目的.     

特殊钢生产技术的发展及对内燃机零件用钢选择的思考

机电产品大量使用各种特殊钢。随着特殊钢的冶炼、铸坯、成型技术发展,不同铸坯方式的结晶学特征以及最终材料的质量,发生了显著的变化。对铸锭-开坯-轧(锻)制成材与连铸连轧成材的工艺特点和钢材的质量进行比较,对钢材的选择提出一些应考虑的问题。     

Penetration of molten silicon into a bed of fines

During the casting process of silicon the mould must be buffered from the high temperatures of the molten silicon to prevent the mould melting and this is typically done by the operators laying down a layer of crushed silicon particles (fines) prior to pouring of the molten silicon. It is useful for operators to know how deep they should make the layer the fines so as to adequately separate the molten silicon from the mould. In this paper, we consider a model for the penetration of molten silicon into the pre-laid layer of silicon fines, which provides a predictive tool for estimating the necessary depth of fines in order to prevent the molten silicon touching the mould. The mathematical model developed here considers the flow of molten silicon as a Darcy flow and solidification due to heat flow as a one-phase Stefan problem. We are able to find a numerical solutions to this model, and from this we are able to extract data regarding the penetration depth of the molten silicon into the fines before solidification occurs. Our model and numerical solution can been seen as a first step toward understanding this important part of the casting process for silicon.     

初轧均热炉节能与技术进步

我国产钢近50％铸成大钢锭后加工成材,就当前的经济实力而言,短期内不可能取消初轧工序。因此,充分发挥现有模铸系统作用,对其进行技术改造,形成有中国特色的钢铁工业后步工序,使之在经济效益上可与连铸系统相媲美。近年来初轧均热炉技术进步的成绩显著,其主要经验是:1.改造设备;2.改进操作;3.科学管理;4.抓系统节能;5.抓基础理论。     

Thermoelectric air-cooling module for electronic devices

This article investigates the thermoelectric air-cooling module for electronic devices. The effects of heat load of heater and input current to thermoelectric cooler are experimentally determined. A theoretical model of thermal analogy network is developed to predict the thermal performance of the thermoelectric air-cooling module. The result shows that the prediction by the model agrees with the experimental data. At a specific heat load, the thermoelectric air-cooling module reaches the best cooling performance at an optimum input current. In this study, the optimum input currents are from 6 A to 7 A at the heat loads from 20 W to 100 W. The result also demonstrates that the thermoelectric air-cooling module performs better performance at a lower heat load. The lowest total temperature difference-heat load ratio is experimentally estimated as ?0.54 W K^?1 at the low heat load of 20 W, while it is 0.664 W K^?1 at the high heat load of 100 W. In some conditions, the thermoelectric air-cooling module performs worse than the air-cooling heat sink only. This article shows the effective operating range in which the cooling performance of the thermoelectric air-cooling module excels that of the air-cooling heat sink only.     

大功率柴油机飞轮壳优化设计

针对某柴油机飞轮壳由铸铁件改为铸铝件,装机300 h复合循环试验后,飞轮壳出现多处明显裂纹的故障,从理论和试验两方面对飞轮壳断裂的原因进行分析。分析结果显示:飞轮壳的结构设计不合理和铸造缺陷是造成飞轮壳断裂的主因。据此,改进了飞轮壳的结构设计和铸造方法,成功解决了飞轮壳断裂问题。     

GROWTH INSTABILITY DURING PLANAR SOLIDIFICATION WITH A MOLD OF FINITE THERMAL CAPACITY

The temperature and the stress fields in the solidified layer and in the mold of finite thickness for a unidirectional casting process are investigated. Earlier solutions are extended to include the effect of the thermal capacity of the mold on the freezing front growth instability. A numerical solution is obtained for both the heat conduction and the residual stress problem. The results show that the perturbation in contact pressure tends asymptotically to a maximum value at larger times for the lower values of the thermal capacities of the mold materials. The magnitude of the contact pressure perturbation is decreased by the inclusion of the thermal capacity of the mold material, and this effect is enhanced for less distortive and thicker molds. The present article assumes that the thermal and mechanical problems are uncoupled along the casting mold interface. Despite this limitation, the results presented in this article indicate that a mold with a higher thermal capacity (or lower thermal diffusivity) might be less susceptible to thermoelastic instabilities associated with the contact pressure and its dependence on the thermal contact resistance at the casting mold interface.     

Numerical Method for Calculation of Complete Casting Processes—Part I: Theory

This article presents a method for calculation of the complete casting process, including the pouring of the liquid metal into the mold, its solidification, the deformation of the solidified cast, the formation of airgaps between the cast and the mold and their influence on the heat transfer, and the residual stresses. An original phase-change procedure is developed, valid for an arbitrary number of pure metals and/or alloys. A collocated version of a segregated finite-volume method is used to calculate both the liquid metal flow and the deformations and stresses in solids.     

火电机组直接空冷系统初始温差的优选

分析了影响火电机组直接空冷系统初始温差优选的主要因素,阐述了初始温差优选的原理和计算步骤,讨论了空冷凝汽器管束迎面风速选定的依据;结合某电厂的厂址气象条件和运行要求,对300MW机组直接空冷系统的年总费用进行经济性分析,给出直接空冷系统初始温差优选的计算结果。     

大型柴油机气缸套离心铸造

从铸件的设计、离心浇铸装置、工艺参数的选择以及浇铸过程的控制等几方面,介绍了大型柴油机气缸套的离心浇铸技术,在成功浇铸气缸套的基础上,总结了离心铸造气缸套的优点。     

直接空冷系统初始温差值的优化设计

直接空冷系统设计,核心之一是最佳初始温差值ITD的优化设计。文中介绍了直接空冷系统初始温差值的优化理论,探讨了优化过程和计算方法,由于初始温差和空气侧流速大小关系到空冷系统造价和系统运行费用,所以以这两者作为设计变量,以空冷系统年总费用为目标函数,对某一空冷机组进行了分析,优化设计了机组ITD值,得到系统最小年总费用和最佳ITD值。     

直冷式空冷机组燃料BTU实时校正方法研究

煤质的频繁变化严重影响着直冷式空冷机组的特性和效率。火电厂来煤不稳定且实际煤种发热量很难实时准确的得到,给机组协调控制系统的设计带来很大困难。对此,针对直冷式空冷机组研究了一种基于模型的燃料BTU校正方法,用机组负荷实际值与机组模型负荷预测值的比值来反映实际煤种发热量与设计煤种发热量的关系,实时校正进入锅炉的燃料量,消除入炉煤质变化对机组协调控制系统的影响。经仿真实验和实际数据验证:在煤质频繁波动情况下协调控制系统控制品质良好,煤质稳定情况下不会对协调控制产生影响;得到的BTU校正系数不受模型输入信号的影响,能实时准确反映实际煤发热量的变化。该方法可行且有效,可适应现场煤质频繁变化的情况。     

An Efficient Summer Operation Scheme for a Thermal Power Plant Air Cooling System based on Electric Peak Shaving

We proposed a novel efficient operation scheme for a thermal power plant’s air-cooling system based on peak shaving, in order to cope with high ambient temperature in summer. We introduced an absorptiongeneration equipment with water/lithium working pairs into the air cooled condenser(ACC) to reconstruct the traditional thermal power plant, and established a dynamic thermodynamic model adopting Ebsilon code. We studied the thermodynamic performance variation of the reconstructed thermal power plant throughout a 24-hour cycle and found that the fluctuation ratio of the turbine back pressure decreased to 6% from 78%, which is beneficial for the stable and safe operation of the electric power system. The thermal performance improvement benefited from the exploitation of the heat transfer potential of ACC, which realized via cold duty schedule throughout the day, under different ambient temperature conditions. In this system, the generated power was higher at relatively high ambient temperature than that at relatively low ambient temperature, which solved the electricity demand-supply imbalance problem under high ambient temperature. Finally, the same optimization effects for power thermal plants with an indirect air-cooling system were obtained using the same operation scheme.     

应用冷芯制芯中心,迈向现代精益铸造

在三乙胺冷芯工艺的基础上,集成制芯中心,导入PROFIBUS总线控制,提高自动化和安全系数,减少无效劳动,降低劳动强度,提升砂芯表面质量,保证铸件内腔质量,使传统铸造转向现代精益铸造。     

发动机隔热用排气道钢壳的CAD/CAM

为了降低发动机气缸盖的热负荷,在气缸盖排气道内铸入外壁喷涂陶瓷的钢壳。钢壳的形状尺寸及厚度均匀性要求严格。应用计算机建立精确的三维数学模型,并用高精度数控铣床加工出铸造用模具。最后,用精密熔模铸造法加工出符合要求的不锈钢钢壳。     

Development of a Theoretical Process Map for Laser Cladding Using a Three-Dimensional Conduction Heat Transfer Model

In this article, a three-dimensional conduction heat transfer model is developed to predict the clad geometry (e.g., height, width, and dilution) and microstructure (scale and morphology) of the solidified layer for a laser cladding process. The effect of controllable input process parameters like absorbed laser power, powder deposition rate, and processing speed on the clad characteristics is critically assessed with the help of dimensionless parameters. A process map is developed which enables operators to pick up the proper process parameters for a feasible laser cladding process with desirable characteristics. The present conduction model is solved using the finite-volume method in a multiblock, nonorthogonal grid system. The effect of melt pool convection is taken care of by introducing an enhanced thermal conductivity factor for the molten pool.     

INTEGRATED FINITE ELEMENT MODEL FOR TRANSIENT FLUID FLOW AND THERMAL STRESSES DURING CONTINUOUS CASTING

A finite element computational methodology is presented for predicting the temperature distribution, fluid flow, and thermal stresses evolving in a solidifying ingot, which itself is growing in length, during the start-up phase of a continuous casting process, with a particular reference to aluminum casting. The approach is based on the coupling of a thermal and flow model with a stress model, The thermal flow model is developed using a deforming finite element method with an Eulerian-Lagrangian transformation to account for the fact that the ingot itself is also growing at a prescribed casting speed. The stress model is developed also by the finite element method, with mechanical deformations in the solidifying materials described by a hypoelastic-viscoplastic constitutive relation. The integrated model has been applied to study the dynamic development of temperature, flow, and stresses in the solidifying ingot during the start-up phase for continuous casting of aluminum. The results show that the fluid flow and temperature distribution experience a rapid change at the initial stage but that the change slows down later in the process as it approaches to the steady state. Computed results compare reasonably well with experimental measurements for temperature distributions in the ingot. It is found that the thermal stresses in general evolve from small to big in magnitude and from compressive to tensile in the solidifying ingot. The hoop stress is larger than other stress components, in particular in the outer surface region. The air gap formed between the ingot and the bottom block increases initially and decreases afterward as a result of stress relaxation.