凝汽器的局部强化传热数值计算研究

发布时间：2018-08-16 19:23

【摘要】：凝汽器是凝汽设备的核心设施,是电厂热力循环中处理乏汽的重要环节,是电厂热力循环的"冷端"。凝汽器对电厂热力循环的主要功能是凝结在汽轮机做功发电后被排出的蒸汽,并在电厂热力循环"冷端"建立及并维持一定的真空度。凝汽器真空度,也就是凝汽器压力,是表征凝汽器工作特性的重要指标。如果凝汽器真空度过低,也就是凝汽器压力过高,就会影响汽轮机和回水管路等诸多设备的安全运行。凝汽器内部主要分为两个换热区域,即主凝结区和空冷区。主凝结区的作用是凝结大部分蒸汽,空冷区的作用凝结剩余的蒸汽,冷却蒸汽中夹杂的不凝结气体,减小抽气设备的抽气负荷,维持凝汽器真空度基本不变。蒸汽流经主凝结区,大部分蒸汽凝结成水,于是蒸汽的质量含量随蒸汽凝结而降低,其中夹杂的空气等不凝结气体的质量含量则相应上升。于是空冷区的换热热阻比主凝结区更高,换热系数比主凝结区更低。与主凝结区相比,空冷区成为凝汽器的换热薄弱环节。现有的关于提高凝汽器换热的科研成果主要集中于改变凝汽器的内部结构或采用新型管材,从整体上提高凝汽器的换热效果,或者改良凝汽器配套的抽气设备,提升抽气效果,帮助维持凝汽器真空度。而针对凝汽器的换热薄弱环节空冷区,专门研究空冷区的强化换热,国内外还比较缺乏这样的研究,特别是利用热泵技术对空冷区强化换热,让热泵蒸发器直接介入凝汽器空冷区的换热,这个领域基本还是空白。本研究正是针对凝汽器空冷区,建立凝汽器局部强化传热物理模型,建立凝汽器局部强化传热数学模型,通过数值计算研究了热泵蒸发器管束介入凝汽器空冷区,在空冷区内局部管束设置"急冷区",对凝汽器局部管束强化换热的影响规律。本研究进行的具体工作如下:1.对凝汽器进行了传热分析,特别是分析了空冷区的换热特性。2.根据本科研团队所做的基于热泵技术的凝汽器局部管束强化凝结实验,本文建立了凝汽器局部强化传热物理模型,并根据物理模型建立了凝汽器局部强化传热数学模型。3.使用凝汽器局部强化传热数学模型,对空冷区内"急冷区"的各种不同规模和组态进行数值计算研究。数值计算的结果表明,只要在空冷区内设置"急冷区",那么不论"急冷区"位于空冷区的前段、中段还是后段,不论"急冷区"由一组、两组还是三组换热管组成,空冷区的压力都是有所降低的,空冷区的换热系数都是有所提高的。4.通过数值计算研究在空冷区内设置两组或三组相邻换热管作为"急冷区",数值计算的结果表明,设置三组相邻换热管作为"急冷区'"的换热效果更好,而且将"急冷区"设置在空冷区后段的换热效果更好。5.通过数值计算研究在空冷区内设置两组或三组不相邻换热管作为"急冷区",数值计算的结果表明,设置两组相邻换热管作为"急冷区"的换热效果优于设置三组不相邻换热管作为"急冷区"的换热效果,而且将"急冷区"设置在空冷区后段的换热效果更好。综上所述,在凝汽器空冷区内设置"急冷区",在技术上是可行的,有利于提高凝汽器换热效率,提高电厂经济性。本研究的研究结果可以指导实际电厂凝汽器进行改造,具有重要的工程实践价值。
[Abstract]:The condenser is the core facility of the condenser equipment, is an important link in the thermal cycle of the power plant to deal with exhausted steam, is the "cold end" of the thermal cycle of the power plant. The condenser vacuum degree, i.e. the condenser pressure, is an important index to characterize the condenser performance. If the condenser vacuum degree is too low, i.e. the condenser pressure is too high, it will affect the safe operation of steam turbine and return water pipeline and many other equipment. The condenser is mainly divided into two heat transfer areas, namely the main condensation area and the air-cooled area. The role of the zone is to condense most of the steam. The role of the air-cooled zone is to condense the remaining steam. The inclusion of non-condensable gas in the steam is cooled. The pumping load of the pumping equipment is reduced and the vacuum of the condenser is maintained basically unchanged. The mass content of non-condensable gases such as air inclusion increases correspondingly. Thermal resistance of heat transfer in air-cooled zone is higher than that in main condensation zone, and coefficient of heat transfer is lower than that in main condensation zone. The internal structure of the condenser or the use of new tube, from the overall improvement of the heat transfer effect of the condenser, or the improvement of condenser matched with the extraction equipment, improve the extraction effect, help to maintain the vacuum of the condenser. Especially using heat pump technology to enhance heat transfer in the air-cooled zone, let heat pump evaporator directly into the condenser air-cooled zone heat transfer, this field is basically blank. The heat transfer characteristics of heat pump evaporator tube bundles in the air-cooled zone were analyzed. 2. Based on the research team, the heat transfer characteristics of the air-cooled zone were analyzed. The physical model of local enhanced heat transfer in condenser is established in this paper. The mathematical model of local enhanced heat transfer in condenser is established according to the physical model. 3. The mathematical model of local enhanced heat transfer in condenser is used to numerically simulate various scales and configurations of the "quench zone" in the air-cooled zone. The results show that the pressure in the air-cooled zone decreases and the heat transfer coefficient in the air-cooled zone increases as long as the "quench zone" is set in the air-cooled zone. Two or three groups of adjacent heat exchanger tubes are set as "quench zone" in the air-cooled zone. The results show that the heat transfer effect is better when three groups of adjacent heat exchanger tubes are set as "quench zone", and the heat transfer effect is better when the "quench zone" is set at the rear of the air-cooled zone. Two or three groups of non-adjacent heat exchanger tubes are used as the "quench zone". The numerical results show that the heat transfer effect of setting two groups of adjacent heat exchanger tubes as the "quench zone" is better than that of setting three groups of non-adjacent heat exchanger tubes as the "quench zone", and the heat transfer effect of setting the "quench zone" in the rear section of the air-cooled zone is better. It is technically feasible to set up "quench zone" in the air-cooled zone, which is conducive to improving the heat transfer efficiency of condensers and improving the economy of power plants.
【学位授予单位】：山东大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TK264.11;TM62

【相似文献】