直接空冷凝汽器翅片管束表面颗粒沉积的特性研究

发布时间：2018-11-23 19:36

【摘要】：翅片管换热器是直接空冷凝汽器的重要设备之一。颗粒物沉积在翅片管束外表面,不仅影响翅片管换热器的换热效率,而且对机组的安全经济运行起着决定性的作用。通过研究颗粒物在翅片管束外表面的沉积规律,可以为减少颗粒沉积提供可靠的理论依据。本文通过数值模拟的方法对颗粒物在翅片散热管束外表面的沉积规律进行研究,并探究了积灰厚度对翅片管流动换热性能的影响。基于气-固两相流理论,利用Fluent软件对颗粒在翅片管间的沉积过程进行了数值模拟,分析了风速、固相体积分数、翅片间距、翅片厚度及翅片高度等因素对沉积率和翅片管磨损量的影响。结果表明:对颗粒沉积率而言,沉积率随风速的增大而增大,当风速大于1.5m/s时,沉积率的增长率逐渐减小;沉积率随固相体积分数的增加而增加,当固相体积分数大于某一值时,沉积率变小,具有一定的饱和性;随着翅片间距的增加,风速较低时,沉积率减小,风速较高时,沉积率增大;沉积率随翅片厚度的增加而增加;但沉积率随翅片高度的增加而减小。对翅片管磨损量而言,风速越大,碰撞力加大,磨损量增加;固相体积分数越大,碰撞率加大,磨损量增加;翅片间距增大,磨损量减小;翅片厚度增大,阻力变大,磨损量增加;翅片高度小于19mm,磨损量增加,翅片高度大于19mm,磨损量减小。针对翅片管外均匀积灰的情况,分析了积灰厚度对翅片管流动换热性能的影响,得到了翅片管外积灰前后的换热与流动特性,结果表明:随迎面风速的增大,对流换热系数、传热系数、压降均逐渐增大,摩擦系数逐渐减小;同一风速下,随积灰厚度的增加,对流换热系数略微增加,压降与摩擦系数逐渐增大,传热系数逐渐减小。随Re的增大,摩擦系数变小,Nu增大;积灰厚度越大,摩擦系数增加,Nu变小,翅片管的换热性能降低。随管外积灰厚度的增大,翅片管的综合换热流动性能下降。
[Abstract]:Finned tube heat exchanger is one of the important equipments of direct air-cooled condenser. Particles deposited on the outer surface of the finned tube bundle not only affect the heat transfer efficiency of the finned tube heat exchanger, but also play a decisive role in the safe and economical operation of the unit. By studying the deposition rule of particles on the outer surface of finned tube bundles, a reliable theoretical basis can be provided for reducing particle deposition. In this paper, the deposition of particulate matter on the outer surface of fin tube bundle was studied by numerical simulation, and the influence of ash thickness on the heat transfer performance of finned tube was investigated. Based on the gas-solid two-phase flow theory, the deposition process of particles between finned tubes was simulated by Fluent software, and the wind speed, solid volume fraction and fin spacing were analyzed. The influence of fin thickness and fin height on deposition rate and wear quantity of fin tube. The results show that the deposition rate increases with the increase of wind speed, and decreases gradually when the wind speed is greater than 1.5m/s. The deposition rate increases with the increase of solid volume fraction. When the solid volume fraction is greater than a certain value, the deposition rate becomes smaller and has a certain saturation. With the increase of fin spacing, the deposition rate decreases when the wind velocity is lower, and increases with the increase of fin thickness when the wind velocity is higher. However, the deposition rate decreases with the increase of fin height. For finned tube wear, the larger the wind speed, the greater the impact force, the higher the wear amount; the greater the volume fraction of solid phase, the greater the impact rate, the higher the wear rate, the greater the fin spacing, the lower the wear amount. The thickness of the fin increases, the resistance increases and the wear amount increases, the height of the fin is less than 19mm, the wear quantity increases, the height of the fin is larger than 19mm, and the wear quantity decreases. In view of the uniform ash deposition outside the finned tube, the influence of the thickness of the ash deposition on the heat transfer performance of the finned tube is analyzed. The heat transfer and flow characteristics of the finned tube before and after the ash deposition are obtained. The results show that the convection heat transfer coefficient increases with the increase of the facing wind speed. The heat transfer coefficient and pressure drop increased gradually, and the friction coefficient gradually decreased. At the same wind speed, the convection heat transfer coefficient increases slightly, the pressure drop and friction coefficient increase, and the heat transfer coefficient decreases with the increase of ash deposition thickness. With the increase of Re, the friction coefficient becomes smaller and Nu increases, and the thicker the ash deposit, the higher the friction coefficient, the smaller the Nu and the lower the heat transfer performance of the finned tube. With the increase of ash deposition outside the tube, the comprehensive heat transfer performance of the finned tube decreases.
【学位授予单位】：华北电力大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM621

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