【作者】 李红霞；

【导师】 李蔚；

【作者基本信息】 浙江大学 ， 热能工程， 2013， 硕士

【摘要】 据调查,90%以上的换热设备都存在不同程度的污垢问题,一旦出现污垢沉积现象,将给换热器运行带来很大影响,造成能量损失。因此,近年来换热器的污垢问题日益受到人们的重视。本文在分别完成了3中典型的直肋管和波纹板式换热器,以流动特性分析为基础,结合冯卡门传热传质类比通过数值方法结合实验数据对比讨论了强化传热表面几何特性、流动速度等参数对污垢热阻值的影响。结果如下：(1)文章利用的研究方法是依据kern-seaton污垢模型,结合冯卡门类比通过选取合适的数值模拟方案获得其相关换热表面污垢特性。通过与相关实验数据的对比验证发现,文章的数值分析结果误差均在接收范围内,说明选取的研究方法是合理的。(2)通过分析直肋管的各个几何参数(肋高、肋间距和肋片厚度)对流型、壁面剪切力和污垢热阻渐进值的影响发现,肋间距是影响直肋管污垢特性的重要参数。在管型设计和应用选择中,肋间距即不能太大,要避免流动的重新附和,流体重新附着区的剪切力要比分离区小得多；又不能太小,间距越小流体流过肋片之后的分离强度也会越小,从而壁面剪切力也会越小,结垢越严重。(3)对3不同结构参数(板式换热器波纹高度、波纹间距、波纹角度、面积扩展系数等)板片的努塞尔数、摩擦因子和传质系数的数值结果均与实验结果一致。板式换热器的努塞尔数随雷诺数增加而增加,但增加速度减慢；BRM01因其具有最紧凑的几何结构(V形角65°,板片间距7mm),换热性能最好。(4)板式换热器的污垢热阻渐进值与板片间的流速成反比,但流速越大污垢热阻渐进值减少的速度越慢。在板式换热器的运行中,如果运行速度太小,换热效果差且易结垢；如果运行速度太大,消耗的泵功却不能有效提高换热和抑垢效果,得不偿失。因此,应结合板式换热器应用场合,根据污垢热阻渐进值与雷诺数的变化趋势选择一个最佳的运行速度,文章推荐此雷诺数在2500左右。更多还原

【Abstract】 Fouling in enhanced heat exchangers is a comprehensive and complex problem, which has many influential factors, so more investigations are needed in the detail researches of heat transfer and fouling performance in heat exchangers, which have substantial significances and actual applications. From mass balance and numerical simulation in the investigation on the flow and heat transfer performance of enhanced heat exchangers, this paper uses Von-Karman analogy to predict the fouling performance in three internal repeated rib tubes and three corrugated plate heat exchangers with different geometries. Additionally, the influences of fluid velocity and geometries have been discussed and compared with experimental data, which can be used to optimize the designs of heat exchangers generally and broaden its further applications. Results are as follows:(1) The turbulent model with non-equilibrium wall functions is used in the3D numerical simulation to obtained Nusselt number and wall shear stress, while the Von-Karman analogy is used to obtain mass transfer coefficient. By comparing the results with experimental data, the investigation method the paper used is right.(2) The different geometry parameters of internal repeated rib tubes are investigated to find their influence on stream line, wall shear stress and fouling resistance. To explain the diversity of anti-fouling performance in different tubes, the rib distance is the most important parameter. If it is too large for the stream line to develop or too small to disturb the reattachment, the wall shear stress will not big enough to peel off the fouling deposition, which can results a poor fouling performance.(3) The Nusselt number, friction factor and wall shear stress is calculated in the three corrugated plate heat exchangers with different geometries parameters including plate height, plate spacing and plate angle. The Nusselt numbers in the three PHEs are all increased with the velocity, but the increasing rate is declined. BRM01has the best heat transfer performance because of its most compact geometry design, the largest plate angle65°nd smallest corrugation pitch7mm.(4) The fouling resistance is reduced with the increase of velocity, but the reduction rate reduces when velocity increases. So in the operation of PHE, an optimum velocity may exist. If the velocity is too small, the fouling resistance can be too large to have a good heat transfer performance. And the continued increasing of velocity will demand a high pumping cost while has little improvement in fouling performance. Re=2500is recommended according to this paper.更多还原