缠绕管式换热器内流场模拟与传热过程强化

发布时间：2018-04-16 02:27

本文选题：缠绕管式换热器 + 数值模拟　；参考：《青岛科技大学》2017年硕士论文

【摘要】：缠绕管式换热器是一种高效的管壳式换热器,具有结构紧凑、杂质沉积率小、管内操作压力高、换热效率高的优点。本文采用三维建模软件SolidWorks建立了缠绕管式换热器的物理模型,利用Fluent流场模拟软件,对换热器内部流场进行了数值模拟,研究了缠绕管式换热器内部流场及传热特性。针对缠绕管式换热器壳程压降大的缺点,提出了新型水滴型截面换热管并进行了数值模拟。研究工作可对缠绕管式换热器的设计开发提供指导。(1)考察了不同入口流速不同截面处的缠绕管式换热器壳内流体的流动特性,结果表明:管程流体中,由于缠绕半径小,内层管相比外层管的PEC指数高11.7%,具有更好的换热效果;壳程内,在缠绕管间存在着由外侧高速区向内层缠绕管运动的径向流,径向流有助于促进外层冷流体与换热管管壁间的热量交换,且随着入口流速的增大,径向流也逐渐增大,当入口流速为0.7m/s时,径向流速可达1.2m/s。随着入口流速的增加,壳程的湍动强度更高,入口流速为0.5m/s时,湍动能最大为0.03m2/s2,提高了壳程的传热效果。(2)建立了平行排列、交叉排列和错位排列三种不同的缠绕管排布方式,考察了缠绕管式换热器内管排列方式及入口流速对壳侧流动、传热性能的影响。模拟结果表明:交叉排列具有更高的阻力系数,大约比其它两种排列高出10%;与平行排列方式相比,采用错位排列方式时由于缠绕管的导流作用,管间存在较大的径向速度,促进缠绕管外侧流体与缠绕管周围流体的混合,管后低速区面积亦大大减少,强化了流体传热,PEC指数大约高出25%;温度分布也更加均匀。(3)对新型水滴形截面换热管的换热器,通过数值模拟,结果表明:与普通圆管的换热器的对比,水滴形换热管的管内流体分布更均匀;高速流体和高温流体分布更均匀,有利于热量的传递。壳程内,虽然水滴形管的换热器的努塞尔数Nu有一定的降低,但其阻力系数f和压降有大幅度减小,当入口流速为0.4m/s时,水滴形管的努塞尔数Nu是圆管的94.2%,而其阻力系数f只有圆管的75%,PEC指数提高了5%,大大减小了由于壳程阻力带来的压力损失。
[Abstract]:Winding tube heat exchanger is an efficient tube and shell heat exchanger with the advantages of compact structure, low impurity deposition rate, high operating pressure and high heat transfer efficiency.In this paper, the physical model of the winding tube heat exchanger is established by using the three-dimensional modeling software SolidWorks, and the flow field and heat transfer characteristics of the winding tube heat exchanger are numerically simulated by using the Fluent flow field simulation software.Aiming at the disadvantage of large pressure drop in the shell side of the winding tube heat exchanger, a new type of water droplet cross section heat transfer tube is proposed and numerically simulated.The research work can provide guidance for the design and development of the winding tube heat exchanger. (1) the flow characteristics of the fluid in the shell of the winding tube heat exchanger with different inlet velocity and different cross section are investigated. The results show that the winding radius is small in the pipe side fluid.The inner tube has a better heat transfer effect than the outer tube with a PEC index of 11.70.There is a radial flow from the outer high speed region to the inner winding tube in the shell side.The radial flow can promote the heat exchange between the outer cold fluid and the tube wall, and the radial flow increases gradually with the increase of the inlet velocity. When the inlet velocity is 0.7m/s, the radial velocity can reach 1.2 m / s.With the increase of inlet velocity, the turbulent intensity of shell side is higher. When the inlet velocity is 0.5m/s, the maximum turbulent kinetic energy is 0.03m2 / s ~ 2, which improves the heat transfer effect of shell side.The effects of inner tube arrangement and inlet velocity on shell flow and heat transfer performance were investigated.The simulation results show that the cross arrangement has a higher resistance coefficient, which is about 10% higher than that of the other two kinds of arrangement. Compared with the parallel arrangement, there is a larger radial velocity between the two tubes due to the flow conduction of the winding tube when the misaligned arrangement is adopted.By promoting the mixing of the fluid outside the winding tube and the fluid around the winding tube, the area of the low speed zone behind the tube is greatly reduced, and the PEC index of the enhanced fluid heat transfer is about 25% higher than that of the tube, and the temperature distribution is also more uniform. 3) for the heat exchanger of the new type of water droplet section heat exchanger,Through numerical simulation, the results show that the fluid distribution in the tube is more uniform than that in the conventional round tube, and the distribution of high speed fluid and high temperature fluid is more uniform, which is beneficial to the heat transfer.In the shell side, although the Nusselle number Nu of the water droplet tube heat exchanger decreases to a certain extent, the resistance coefficient f and the pressure drop of the heat exchanger decrease greatly. When the inlet velocity is 0.4m/s,The Nusselle number Nu of the water droplet tube is 94.2g of the circular tube, and its resistance coefficient f only increases the 75 PEC index of the circular tube, which greatly reduces the pressure loss caused by the shell resistance.
【学位授予单位】：青岛科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TQ051.5

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