凝汽器水侧流动的三维数值模拟

运用计算流体力学的方法,采用多孔介质模型对凝汽器水侧流场进行了数值模拟.从计算所得三维流场可清楚地掌握影响凝汽器工作的重要因素：该凝汽器进口水室漩涡的存在使流动阻力增加,流动恶化;高速流体集中于水室中心区域,会影响换热器的换热性能.其整体阻力特性与试验数据吻合较好,表明该模型和计算方法正确.解决了凝汽器水侧数值计算建模的困难和网格数量问题,为动力装置冷却水系统整体的数值模拟提供基础.图6参5     

凝汽器水侧的数值研究及改造

引入多孔介质,采用k-ε湍流模型,利用二维数值计算方法对一双流程凝汽器的水侧流体流动进行了计算与分析。针对凝汽器水侧由于设计缺陷,存在漩涡及流动死区的情况,提出在凝汽器前后水室安装导流板,对凝汽器前后水室流体流动进行引导改善。改进后,凝汽器水侧流动漩涡以及流动死区完全消失,凝汽器水室的流动漩涡以及流动死区消失、流动阻力下降,水侧冷却水分布更加合理,凝汽器换热效果有所提高。     

考虑物性变化的凝汽器水侧流场数值研究

在管束区域采用多孔介质模型的基础上,通过考虑冷却水吸热升温后物性的变化,对凝汽器水侧流动特性的数值模拟进行一定的改进。对某电厂双流程凝汽器水侧流场数值模拟的结果对比表明:冷却水温度变化对凝汽器水侧流动特性存在一定的影响,主要表现在冷却水密度的变化引起进水室和下流程的流动阻力的变化。此外,分析表明考虑冷却水温升与否对管束区速度分布均匀性的模拟影响不大。     

基于冷却水流速分布模拟的凝汽器性能数值分析

冷却水流速是影响凝汽器性能的主要因素之一,为了实现基于冷却水流速实际分布的凝汽器性能模拟,借鉴多孔介质的阻力源项加载思想提出了基于冷却管入口实体建模的凝汽器水侧流动计算模型,以某600MW火电机组的低压凝汽器为例,在设计工况下对该凝汽器水侧流动进行了数值模拟,获得了凝汽器水侧管束截面上的冷却水流速分布,并基于上述冷却水流速分布的模拟结果,分别数值计算了冷却水流速均匀分布和不均匀分布两种情况下凝汽器汽侧的蒸汽流动,获得了相应情况下的凝汽器性能。计算结果表明：对于本文研究的凝汽器,基于多孔介质模型和基于冷却管入口实体建模的凝汽器水侧流动模拟得到的管束截面上的冷却水流速分布在流动细节上存在差异;冷却水流速均匀分布和不均匀分布两种情况下获得的凝汽器性能有差异,凝汽器压力相差10.9Pa,总平均传热系数相差12.6W/（m²·K）。建议对于冷却水流速不均匀分布比较严重的情况,在研究凝汽器性能时考虑冷却水流速不均匀分布的影响。     

600MW机组电站凝汽器水侧流动的分析

选取某电厂600MW机组凝汽器水侧流场进行数值模拟,研究流体的流动状况。模拟结果显示,凝汽器进口水室内存在涡旋,涡旋的存在增加了流体的流动阻力,使流动恶化,流量分布的不均匀,严重影响了设备的换热性能。在使用过程中,应采取措施减小涡旋,计算结果可以为凝汽器设计和改进提供参考。     

凝汽器水侧流动的三维数值模拟

建立了某一凝汽器实际管束的流动计算模型,运用计算流体力学的方法,对该凝汽器水侧流场进行了三维数值模拟。采用分区对称计算方法,大大降低网格数量,从而详细预测了凝汽器水侧进出口水室以及其连接管和冷却水管束内的流动特性。计算结果可以清楚地表明:该凝汽器进口水室存在大量漩涡,使流动阻力增加,流动恶化;水室速度分布不均匀,进口水室管板中心区域流体流速较高而边缘区域较低,结构上存在一定问题;而出口水室的结构较为合理。这与采用多孔介质模型模拟的结论一致,进一步验证了采用多孔介质模型对凝汽器进行计算是正确可行的。计算结果同时表明,冷却水管束内流量和流速的分布是不均匀的,位于中心位置的冷却水管流量较大,而周边区域较小,最大流量差别可达到38%,且相邻管路的流量减小幅度与冷却水管布置有关。冷却水管内冷却水流量和流速的差异将会影响换热器的换热性能。计算结果可为分析研究管排流动不均而引起的换热效率问题提供条件,也可为凝汽器设计和结构优化提供依据。     

电站凝汽器水侧流场均匀性的定量分析

尝试了一种定量计算凝汽器管程流场均匀性的方法:采用多孔介质模型及数值模拟方法对凝汽器水室流场进行数值分析;然后采用速度相对标准偏差对凝汽器管程的流场分布进行定量计算,将上述方法在某双流程凝汽器水侧流动的分析上进行了应用,结果表明管程流场均匀性定量分析方法可以对凝汽器管程流场的均匀性进行定量计算;文章所分析的双流程凝汽器第一流程的均匀性差于第二流程。     

双流程电站凝汽器水室的流动分析与改造

为能够准确预测凝汽器水侧流动特性,应用计算流体力学商用软件,管束区域采用多孔介质模型,对某电厂双流程凝汽器水室流场进行了数值分析。结果表明:该电站双流程凝汽器入口水室结构存在一定的缺陷,导致冷却水在局部产生了较大的阻力,形成了明显漩涡。针对凝汽器水室中漩涡产生的原因,对凝汽器水室结构进行了优化改造,并且在此基础上提出了更多合理的建议。     

基于FLUENT的凝汽器壳侧流动模拟边界条件设置探讨

基于FLUENT平台探讨了凝汽器壳侧流动数值模拟边界条件的设置,改进了多抽气口凝汽器壳侧流动出口边界条件的设置。首先讨论了实现凝汽器壳侧流动模拟的进、出口边界条件的若干设置组合,明确了在不同工况下更容易开展凝汽器壳侧流动模拟的进、出口边界条件组合。然后将该进、出口边界条件组合应用于某单抽气口凝汽器性能的数值模拟上,获得理想的模拟结果;对某多抽气口凝汽器性能的数值模拟的应用表明,需对计算区域出口边界的设置进行一定的改进,将压力出口边界设在抽气管内壁面可以获得有参考价值的模拟结果。为凝汽器工程设计人员在FLUENT平台上实现各种形式管束模块凝汽器壳侧流动的数值模拟,准确获得凝汽器性能的变化提供有益的参考。     

基于喉部出口不均匀流场的电站凝汽器性能数值研究

壳侧入口流动条件的给定会影响凝汽器壳侧流场的数值模拟结果，为进一步改进凝汽器性能的分析手段，以两台电站凝汽器为对象，分别在壳侧入口流场均匀分布和不均匀分布两种条件下对凝汽器壳侧的蒸汽流动进行数值模拟，其中不均匀入口条件基于对凝汽器喉部流场的模拟获得，进而通过数据提取获得两台凝汽器的性能曲线，并对不同入口条件下模拟得到的凝汽器性能进行了对比，模拟结果表明：凝汽器喉部出口流场具有较强的不均匀性；壳侧入口均匀条件下模拟得到的凝汽器性能好于入口不均匀条件，建议在研究凝汽器性能时尽可能地考虑入口蒸汽流场不均匀分布的影响。     

黏土矿物在电池领域的应用研究进展

黏土矿物是一类含水硅酸盐矿物,主要含铝、镁等元素,在我国储量丰富、价格低廉。基于其晶体结构、微观形态和物化特性,黏土矿物可用于制备电池材料,改善电池性能。本文简述了凹凸棒石(坡缕石)、海泡石、蒙脱石等黏土矿物在电池电解质、电极材料中的研究进展,对存在的问题进行了分析,为下一步的研究提出了建议。     

Impact of the price of energy on the use of conservation tillage in agriculture in the USA

The relationship between energy expenditure and the use of conservation tillage is of special importance in addressing concerns about the impact of agricultural production on the environment in the US. After establishing that a relationship exists between the price of energy and the use of conservation tillage via the Granger causality, the relationship is quantified. It is shown that while the real price of crude oil, the proxy used for the price of energy, does not affect the rate of adoption of conservation tillage, it does impact upon the extent to which it is used. Finally, there is no structural instability in the relationship between the relative use of conservation tillage and the real price of crude oil over the period 1963–1997.     

叶片动应力计算的重要改进及其在不调频叶片设计上的应用

叶栅流场中的叶片受流道中汽流力的作用，同时也承受了流道中谐波汽流力的激振。由于谐波汽流力沿周向波动，其对叶片的激振力应该是流道宽度内谐波激振力的积分。本着这一观念对ASME早期发表的动应力基本方程进行改进，重新作了推导，并指出了降低叶片共振应力的途径。多年来已取得了成功应用，其中涉及带冠单叶片的动强度特性及不调频叶片事故处理的材料综合抗振强度对比分析，对工程实践具有一定的参考借鉴的价值。     

Perspectives of solar cooling in view of the developments in the air-conditioning sector

Changes in the standards of thermal comfort in the urban microclimate and in the capital cost of air-conditioning equipment have drastically increased the energy consumption in the building sector over the last decade. At the same time, the integration of renewable energy systems, mainly active solar ones, in buildings has been an area of intense research over the last 30 years. This has also been the case in the field of solar refrigeration, mainly in the field of sorption systems. The analysis discussed in the paper is focused on the state of the art of thermal solar systems use and on the possibilities of combining those with state of the art technologies in sorption refrigeration, in order to cover the cooling demand of residential and commercial buildings. This was done by assessing the available solar and refrigeration technologies as well as by highlighting the situation in the building market, as this is still the dominant factor for the propagation of such systems.     

Efficiency of destruction of waste used in the co-incineration in the rotary kilns

This work presents a study about the efficiency of destruction of industrial waste, used in the co-incineration in rotary kilns of the cement industry, considering the principle of the chemistry equilibrium and the kinetic of the reactions. As an example, it has analysed the burn of one hazardous waste which has in its composition toluene, xylene and dicloroethane. The temperatures of the transformation and the time of the reaction to the formation of sub-products which will originate CO₂, H₂O and HCl, are evaluated. Thus, the formation of the pollutants in the kiln is preliminary estimated and the different forms to control the emissions is also discussed.     

某舰主锅炉筒身内壁裂缝起因分析

本文介绍某舰中修时发现锅炉汽水联箱水部筒壁及锅炉汽筒产生裂缝情况。分析了产生这种情况的原因,主要是由腐蚀性疲劳和腐蚀性热应力所致。并对此提出一些合理化建议,供有关人员参考。     

Modelling of Heat Transfer in the Evaporator and Condenser of the Working Fluid in the Heat Pipe

The aim of this paper is to point out possible solutions to the further development of heat pipes by numerical modelling of phase-change heat transfer. Numerical modelling has now become a standard method that helps to reduce the economic costs of research and development of new and innovative devices. The article describes the procedures for using numerical simulation in phase-change heat transfer that occurs due to evaporation and condensation of the working fluid. The suggested procedure enables modelling of gravitational heat pipe under different changes in its geometry or under changes in the working fluid. From the simulation results we can find out how the heat pipe behaves under different geometric changes and how much heat output it transfers. The paper presents results obtained from modelling of heat pipes, such as classical gravitational heat pipe, heat pipe with capillary geometry, and closed loop pulsating heat pipe. The results gathered from numerical simulation of heat pipes were compared with measurement results.     

冠状动脉导丝、球囊技术在左锁骨下动脉闭塞介入治疗中的应用

【摘要】 目的 探讨冠状动脉导丝、球囊技术在左锁骨下动脉闭塞介入治疗中的应用。方法 采用冠状动脉导丝、球囊技术行血管内支架成形治疗11例左锁骨下动脉闭塞患者。结果 冠状动脉导丝、球囊技术血管内支架成形治疗锁骨下动脉闭塞患者,手术成功率高,10例左锁骨下动脉血流完全通畅,椎动脉正向血流方向恢复;局部并发症少。结论 冠状动脉导丝、球囊技术治疗锁骨下动脉闭塞患者效果可靠,操作相对简单、安全,并发症少。

     

Excel软件在煤炭检测报告中的应用

煤炭分析结果的计算工作量大、繁琐费时。在煤炭检测报告中应用Excel软件,只要输入几个原始测定数据,Excel软件将会在瞬间完成全部计算工作并自动生成一份完整漂亮的检测报告。简化了工作程序,节省了时间,提高了工作效率。Excel软件不仅是财务、统计人员的好帮手,在理化检测工作中也大有用武之地。     

Developments in the scale-up of the vortex-pyrolysis system

Fundamental and applied research and engineering development over the past 13 years has demonstrated that continuous reactors could be used with very fast heating rates and short residence times to produce high yields of liquids from biomass. The National Renewable Energy Laboratory developed the ablative pyrolysis system and Interchem Environmental is commercializing this technology. Interchem designed and built a first generation, 32.7 tonnes (36 tons) per day, prototype ablative pyrolysis system in Missouri. The system was operated for 15 months with varying degrees of success. A second generation plant was designed based on the operating data collected from the first plant and on NREL's design for the vortex reactor. This facility is currently being built in Kansas City, KS. This paper discusses the design and operation of the first generation prototype facility and the design of the second generation system. The second plant is designed to produce 70% oil, 15% char and 15% non-condensible gases from the incoming wood. The oil will be sold as boiler fuel, the char sold as a feedstock to charcoal briquette manufacturers and the gases burned to provide process heat. Upon successful commercialization of this process, agricultural and forest residues can be converted into valuable products. In addition, the process offers a mechanism to use biomass as a feedstock for chemical production rather than relying on petroleum feedstocks.