【摘要】：翅片管換熱器是直接空冷凝汽器的重要設(shè)備之一。顆粒物沉積在翅片管束外表面,不僅影響翅片管換熱器的換熱效率,而且對機組的安全經(jīng)濟運行起著決定性的作用。通過研究顆粒物在翅片管束外表面的沉積規(guī)律,可以為減少顆粒沉積提供可靠的理論依據(jù)。本文通過數(shù)值模擬的方法對顆粒物在翅片散熱管束外表面的沉積規(guī)律進行研究,并探究了積灰厚度對翅片管流動換熱性能的影響�；跉�-固兩相流理論,利用Fluent軟件對顆粒在翅片管間的沉積過程進行了數(shù)值模擬,分析了風(fēng)速、固相體積分數(shù)、翅片間距、翅片厚度及翅片高度等因素對沉積率和翅片管磨損量的影響。結(jié)果表明:對顆粒沉積率而言,沉積率隨風(fēng)速的增大而增大,當(dāng)風(fēng)速大于1.5m/s時,沉積率的增長率逐漸減小;沉積率隨固相體積分數(shù)的增加而增加,當(dāng)固相體積分數(shù)大于某一值時,沉積率變小,具有一定的飽和性;隨著翅片間距的增加,風(fēng)速較低時,沉積率減小,風(fēng)速較高時,沉積率增大;沉積率隨翅片厚度的增加而增加;但沉積率隨翅片高度的增加而減小。對翅片管磨損量而言,風(fēng)速越大,碰撞力加大,磨損量增加;固相體積分數(shù)越大,碰撞率加大,磨損量增加;翅片間距增大,磨損量減小;翅片厚度增大,阻力變大,磨損量增加;翅片高度小于19mm,磨損量增加,翅片高度大于19mm,磨損量減小。針對翅片管外均勻積灰的情況,分析了積灰厚度對翅片管流動換熱性能的影響,得到了翅片管外積灰前后的換熱與流動特性,結(jié)果表明:隨迎面風(fēng)速的增大,對流換熱系數(shù)、傳熱系數(shù)、壓降均逐漸增大,摩擦系數(shù)逐漸減小;同一風(fēng)速下,隨積灰厚度的增加,對流換熱系數(shù)略微增加,壓降與摩擦系數(shù)逐漸增大,傳熱系數(shù)逐漸減小。隨Re的增大,摩擦系數(shù)變小,Nu增大;積灰厚度越大,摩擦系數(shù)增加,Nu變小,翅片管的換熱性能降低。隨管外積灰厚度的增大,翅片管的綜合換熱流動性能下降。
[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.
【學(xué)位授予單位】：華北電力大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TM621

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