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题名	汽轮发电机蒸发内冷系统中两相流摩擦压降及不稳定性的基础研究; 汽轮发电机蒸发内冷系统中两相流摩擦压降及不稳定性的基础研究
作者	1董海虹,电工研究所
学位类别	博士
答辩日期	2009-06-01
授予单位	中国科学院电工研究所
导师	1顾国彪,电工研究所
关键词	汽轮发电机 蒸发冷却技术 汽液两相流动 摩擦压降 不稳定性 不可逆性 turbine generator, evaporative cooling technique, liquid and gas two-phase flow, frictional resistance, irreversibility
其他题名	汽轮发电机蒸发内冷系统中两相流摩擦压降及不稳定性的基础研究
中文摘要	蒸发冷却技术利用介质流动沸腾换热的方式对电机进行冷却，与传统电机冷却方式相比，在安全性、可靠性、冷却效果、运作维护等方面具有突出的优势，颇具发展前景。蒸发冷却技术在水轮发电机方面的应用研究已日益成熟，成功典例较多，而在汽轮发电机方面的应用还存在一些问题尚待解决。汽轮发电机定子空心导线较长，管径较小，介质在其中的流动阻力较大，因而采用强迫循环方式，以泵作为系统的驱动力。介质在空心导线内的流态为气液两相流动，而两相摩擦阻力的研究一直是蒸发冷却技术研究的核心问题之一。能否对电机空心导线中的两相压降进行准确的预算，关系到蒸发冷却系统能否合理循环，是系统实际正常运行的理论保证，对两相压降的准确预算结果可对实际应用起到有效的指导作用。两相流阻力变化复杂，因而在运行中可能会产生一定的不稳定性，这对蒸发冷却系统的实际运行是不利的，然而在以往的蒸发冷却研究中，还没有对这方面展开具体的实验和理论研究。本文依据300MW汽轮发电机定子蒸发内冷系统实际运行工况，对电机空心导线内的两相流摩擦压降及不稳定性进行了实验与理论研究。 本文设计并搭建了水平两相流摩擦压降研究实验台、具有高差的三根水平并联空心导线内两相流不稳定性研究实验台，并开发了实验采集系统，以R113为实验冷却介质进行了两相流摩擦压降和不稳定性实验研究与理论分析；对300MW汽轮发电机定子蒸发内冷系统工作特性的进行了实验与模拟研究；利用热力学第二定律对强迫蒸发冷却循环的热力过程进行了分析。 两相摩擦压降研究结果表明，使用本文所提出的流量当量直径，对空心导线进行单相阻力计算精度高于使用水力直径的计算结果；相同条件下，矩形空心导线内的两相摩擦阻力要大于与其流量当量直径相等的圆管内的两相摩擦阻力；均相模型、L－M－N、Chisholm－B、Friedel等经验算法不能对空心导线内的两相摩擦压降进行较准确的预测；修正后的Chisholm－B算法计算结果与实验数据的平均相对误差小于8％。 具有高差的三根水平并联空心导线内两相流不稳定性研究结果表明，对于300MW汽轮发电机定子蒸发内冷系统，实际工况下空心导线内的两相流动不会 出现密度波不稳定性；对于静态不稳定性来说，只要在起初设计时，注意泵的压头－流量曲线与管路阻力特性曲线的流量匹配问题即可避免。 汽轮发电机定子蒸发内冷系统工作特性研究结果表明，热负荷增加时，空心导线内总压降变化曲线的峰值和谷值都向着流量增大的方向偏移，曲线变化趋于平缓；随着流量的减小或者热负荷的增加，蒸发点温度、介质出口温度、壁温最高点皆升高，且温度分布均匀性降低；空心导线内过冷沸腾段相对较长，不可轻易忽略；进口温度的升高，可使相变换热优势增强，且不会对温度分布均匀性造成不利影响；出口压力的升高使两相段变短，削弱了相变换热比例，但同时又使过冷沸腾段增长，增强了相变换热比例。 汽轮发电机定子蒸发内冷系统的热力过程分析结果表明，强迫蒸发冷却循环实质为只有泵功输入，无有用功输出的蒸汽动力循环，其不可逆性受到热源温度、泵功、系统与热源和冷源之间的传热温差以及介质两相流动特点等多方面因素的影响；实际循环驱动力应为泵功和自身产生有用功之和；两相换热段越长，越能使蒸发冷却循环的热力性能得到提高。 The heat generated by generator, can be carried off by the evaporative cooling technique, through the phase changing heat transfer of the work media. Compared with the traditional cooling methods, the evaporative cooling technique has outstanding advantages for its security, reliability, perfect cooling effects, easy maintenance and etc., and it has good development prospects. The evaporative cooling technique applied in hydro generators has been developing mature and there are many successful application examples. But there are still some unresolved problems in the evaporative cooling technique researches on application in turbine generators. The evaporative cooling system circulation in turbine generator’s stator is the forced circulation mode driven by pump, because the length of the hollow conductors are too long, its diameter is too small and the work media’s flowing resistance in the hollow conductors is so big. The work media’s flow state in hollow conductors is two-phase flow. The two-phase flow frictional resistance in hollow conductors is always one of the core issues in the evaporative cooling technique researches. The accuracy of the two-phase flow frictional resistance forecast computation is related to the reasonability of the evaporative cooling circulation. The accurate forecast computation can play an effective role in guiding the application. There can be some instability phenomena occurring in the actual operation for the complexity of the two-phase flow resistance variation and it’s to the applications’ disadvantage. The study on the two-phase flow instability has not been carried out in the evaporative cooling technique previous researches. In this paper, the two-phase flow frictional resistance and instability in hollow conductors were researched through experiments and theoretical analysis, based on the actual work conditions of the evaporative inner cooling system in 300MW turbine generator stator. In this paper, the horizontal two-phase flow frictional resistance research experiment table and the two-phase flow instability research table about three horizontal parallel hollow conductors with certain vertical distance, were designed and established, the experimental data collection system was developed, and R113 was chosen as the experiment work media. Based on the experiment, the two-phase flow frictional resistance and instability were researched and the experiment results were analyzed theoretically. The work characteristics of evaporative inner cooling system in 300MW turbine generator stator were researched through experiments and theoretical analysis. And the thermodynamic processes of the forced evaporative cooling system were analyzed by the second law of the thermodynamics. The research results of two-phase flow frictional resistance in hollow conductors show that the accuracy of liquid flow resistance computation results can be increased by using the equivalent flow resistance diameter put forward in this paper, comparing with using the equivalent hydraulic diameter. And under the same work condition, the two-phase flow frictional resistance in rectangular hollow conductor is larger than that in the equivalent hydraulic diameter pipe. From the comparison results between simulation results and experiment data, it can be concluded that the tradition two-phase flow frictional resistant experience calculation method, such as homogeneous model correlation, L-M-N correlation, Chisholm－B correlation and Friedel correlation, are not suitable for the rectangular hollow conductor, but the modified Chisholm－B correlation is better, and its average error is 8%. The research results of two-phase flow instability in three horizontal parallel hollow conductors research results, show that there will be not density wave instability occurring under the actual work condition, in the 300MW turbine generator stator’s evaporative cooling system and the flow drift instability can be avoid by matching reasonably the hollow conductor resistance characteristic curve and the pump characteristic curve, during designing at first. The research results of work characteristics of evaporative inner cooling system in 300MW turbine generator stator, show that under the same heat load, the peak and valley values of the total pressure drop curves in the hollow conductors will increase towards the direction of bigger flux and the curves trend to smooth. With the flux decreasing or heat load increasing, the saturated boiling point temperature, inlet and outlet temperature, and the maximum wall temperature will be increasing, and the uniformity of temperature distribution becomes bad. Through simulating, it can be concluded that the length of subcooled boiling in hollow conductor is relatively long and it should not be neglected. With the inlet temperature increasing, the advantage of phase change heat transfer will be enhanced and the uniformity of temperature distribution will not be influenced. With outlet pressure increasing, the length of two-phase flow becomes shorter and the advantage of phase change heat transfer is weakened, but at the same time, the length of subcooled boiling becomes longer and the proportion of phase change heat transfer will be increased to some extent. Through analyzing the thermodynamic processes of the forced evaporative cooling system by the second law of the thermodynamics, it can be concluded that the forced evaporative cooling system is a kind of steam power cycle, which has no usable power outputted to the external environment with the usable power inputted by the pump. The irreversibility of the forced evaporative cooling system can be influenced by the heat source temperature, input power, the differential of heat and cold source temperature, the two-phase flow characteristics and etc. The power consumed by the system is the sum of the input power by pump and the usable power generated by the system itself. The results of analyzing the performance evaluation function show that the thermodynamic performance can be enhanced by making the two-phase flow longer through some measures.
语种	中文
公开日期	2010-10-18
页码	134
分类号	TM3;TM5
内容类型	学位论文
源URL	[http://ir.iee.ac.cn/handle/311042/6796]
专题	电工研究所_其他部门_其他部门_博士学位论文
推荐引用方式 GB/T 7714	1董海虹,电工研究所. 汽轮发电机蒸发内冷系统中两相流摩擦压降及不稳定性的基础研究, 汽轮发电机蒸发内冷系统中两相流摩擦压降及不稳定性的基础研究[D]. 中国科学院电工研究所. 2009.

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