螺旋折流板管壳式换热器的CFD模拟研究

发布时间：2018-02-24 20:43

本文关键词： 螺旋折流板换热器 CFD 压降传热系数单位压降传热系数冷凝　出处：《天津大学》2015年硕士论文　论文类型：学位论文

【摘要】：与传统的弓形折流板换热器相比,螺旋折流板换热器具有换热效果好、流动死区少、壳侧压降低、不易结垢、管束不易发生诱导振动等优点,在工程中的应用越来越广泛。本文采用计算流体力学的方法对螺旋折流板换热器壳程的流体流动与传热过程进行了模拟研究,并以单位压降传热系数作为评价换热器综合性能的参数。结果表明,螺旋折流板换热器的单位压降传热系数是弓形折流板换热器的1.3~1.5倍。折流板形状和螺旋角度是影响螺旋折流板换热器性能的关键参数。在研究的螺旋角范围内(10°~40°),1/4扇形折流板换热器的单位压降传热系数最高。螺旋角度对单位压降传热系数影响的研究结果表明,最佳螺旋角度应与流体流量相适应,流量较小(0.6~1 kg/s)时,30°下的综合性能最优,当增大至1 kg/s时,20°与30°螺旋角的综合性能均最优。双螺旋与单螺旋结构对换热器性能影响的研究结果表明,双螺旋对流体的导流作用增强,大螺旋角(30°~40°)时,双螺旋结构不仅可以提高壳侧的传热性能,同时能提高换热器的综合性能。针对螺旋折流板换热器内存在的三角漏流区问题,提出了在双螺旋结构的基础上增设一组菱形折流板的新型折流板形式,模拟结果表明,该结构可以完全避免换热器内部流体短路现象。该新型结构易于加工制造,便于工程实施。采用Lee模型对冷凝过程进行模拟的结果表明,流量较小时冷凝量相比理论计算值的计算结果低约20%,随着流量增大,偏差会更大。通过分析发现,导致上述预测失真的主要原因是CFD在冷凝管壁面处不能考虑冷凝过程对传热的强化作用,冷凝传热系数的预测值与单相传热过程的结果接近。这就限制了传热过程的热通量,进而影响到冷凝量的预测。本文提出了Fluent与HTRI相结合的自定义方法研究了不同入口流量对冷凝器速度场和液相分布的影响。结果表明,流量较小时,液相会在冷凝器壳侧底部聚集,导致该区域的速度较小;随着流量的增加,液相将随气相做螺旋状流动,聚集在冷凝器的壳程底部的液体逐渐向前移动,并在冷凝器的出口附近汇集。本文模拟结果可为螺旋折流板换热器的放大设计提供理论依据,模拟冷凝过程的方法可为以后的研究工作提供借鉴。
[Abstract]:Compared with the traditional curved baffle heat exchanger, the spiral baffle heat exchanger has the advantages of better heat transfer effect, less dead zone, lower shell side pressure, less scaling and less induced vibration of tube bundle. In this paper, the fluid flow and heat transfer process of spiral baffle heat exchanger are simulated by the method of computational fluid dynamics (CFD). The heat transfer coefficient per unit pressure drop is taken as the parameter to evaluate the comprehensive performance of the heat exchanger. The heat transfer coefficient per unit pressure drop of the spiral baffle heat exchanger is 1.3 ~ 1.5 times that of the bow baffle heat exchanger. The shape and the helical angle of the baffle plate are the key parameters affecting the performance of the spiral baffle heat exchanger. In the range of helical angle studied, the heat transfer coefficient is 10 掳/ 40 掳/ 1 / 4. The heat transfer coefficient per unit pressure drop of sector baffle heat exchanger is the highest. The effect of spiral angle on unit pressure drop heat transfer coefficient is studied. The optimum spiral angle should be adapted to the flow rate of the fluid, and the comprehensive performance at 30 掳is optimal when the flow rate is smaller than 0.6 kg / s. When the helical angle is increased to 1 kg/s, the comprehensive performance of 20 掳and 30 掳helical angle is optimal. The results of the study on the effect of double helix and single helix structure on the performance of heat exchanger show that the flow conduction effect of double helix on fluid is enhanced, and the large helix angle is 30 掳~ 40 掳. The double helix structure can not only improve the heat transfer performance of the shell side, but also improve the comprehensive performance of the heat exchanger. A new type of baffle with a set of diamond baffles is put forward on the basis of double helical structure. The simulation results show that the new structure can completely avoid the phenomenon of short circuit in the heat exchanger, and the new structure is easy to process and manufacture. The Lee model is used to simulate the condensation process. The results show that the flow rate is about 20% lower than the calculated value of theoretical calculation, and the deviation will be greater with the increase of flow rate. The main reason for the above prediction distortion is that CFD can not consider the enhancement effect of condensation process on the wall of condensing tube, and the predicted value of condensation heat transfer coefficient is close to the result of single-phase heat transfer process, which limits the heat flux of heat transfer process. In this paper, a custom method combined with Fluent and HTRI is proposed to study the effect of different inlet flow rates on the velocity field and liquid phase distribution of the condenser. The results show that the flow rate is small. The liquid phase accumulates at the bottom of the condenser shell, causing the velocity of the region to be small. With the increase of the flow rate, the liquid phase will flow spirally with the gas phase, and the liquid gathered at the bottom of the condenser shell will gradually move forward. The simulation results can provide a theoretical basis for the design of the helical baffle heat exchanger, and the method of simulating the condensation process can be used as a reference for future research.
【学位授予单位】：天津大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TQ051.5

【相似文献】