【作者】 梅娜；

【导师】 陈亚平；

【作者基本信息】 东南大学 ， 动力机械及工程， 2005， 硕士

【摘要】 管壳式换热器壳侧强化传热问题一直受到专家学者们的重视,人们也在不断探索改进传统管壳式换热器壳侧结构的新方案。近年来,螺旋折流板式换热器的研究引起了众多研究者对旋流强化壳程换热的重视,经研究发现,螺旋流动可以可提高有效传热温差,通道中的速度梯度影响了边界层的形成,使传热系数有较大的增加,且基本不存在流动与传热死区,但其制造比较困难。本文在这样的背景下,展开了新型壳程强化方法—螺旋折流片强化壳侧换热方案的研究与开发。本文在总结和吸取前人成功经验的基础上,提出将管壳式换热器的全部或部分传热管套上螺旋折流片,代替折流板对管束支撑的方案,可诱导形成多个局部螺旋流场,不仅可强化被套的管子本身,而且也强化其周围管子的传热,通过无功强化的方式获得较高的强化传热效果。针对流场的特点,建立单管和四管模型,利用大型计算流体力学软件FLUENT6.0对壳侧流场、温度场进行模拟,着眼于流动与换热的局部细节信息,探讨其强化换热的机理。从不同结构参数的螺旋片对壳侧流动工况适应性的角度,综合分析了其与光管在换热性能上的比较。结果显示,螺旋片所强化的壳程换热系数比光管通道高37.96%～100.06%,平均74.28%;整体上看,大螺旋角度的螺旋片强化换热的效果好,而小螺旋角度的螺旋片适应流速的范围较广,实际应用时,应当结合换热器的实际应用工况来综合评价其优劣。本文的研究工作为旋流强化换热机理的探讨打开了思路,也为该方案后续的理论与实验研究提供了有益的参考,无疑为管壳式换热器开辟了更加广阔的应用空间。更多还原

【Abstract】 A lot of emphases have been focused on the study of the heat transfer enhancement at the shell-side of the shell-tube heat exchangers; researchers are still trying to find new methods to improve the shell-side structure. During recent years, interests on the heat transfer enhancement by helical flow have been aroused by the application of the helical-baffle heat exchangers. Enough results have proved that helical flow can effectively increase the temperature difference and destroy the flow boundary near the wall, which can greatly enhance the heat transfer coefficient. Studies also find that there exist almost no flow and heat transfer stagnant sections in the shell side of such kind of heat exchangers. However, it is quite difficult to design and manufacture the helical baffles, which in turn limited their application.In this thesis, study on the property of a new modification scheme named coil-strip-baffle has been performed, which can also induce the helical or vortex flow in the shell-side. Here the novel coil-strip-baffle scheme is designed by replace the traditional bow baffles or single helical ones with separate coil-strip-baffles around some or all the tubes of the tube bundle. In this way, the coil-strip-baffle can enhance not only the heat transfer of the sleeved tube but also the bared tubes around it. For this reason, high effect of heat transfer enhancement can be gained by use of this simpler method without any added power.Single-tube model and four-tube model have been constituted to simulate the flow and temperature fields by FLUENT6.0 software according to the feature of the flow field. In this study a lot of local detail features of the fluid flow and heat transfer have been caught which make possible to demonstrate its mechanism. Analyses on the property of the coil-strip-baffle with different structure working on a range of different velocities have been made by comparison between the baffled shell side with the bared-tube shell side. The results show that the heat transfer coefficient on thebaffled shell side is higher than the bared-tube shell side by 37.76%～100.06% which means the average value can reaches 74.28%. As a whole, the coil-strip-baffle with bigger helical angle can result in better heat transfer efficiency and also higher flow resistance, which make it necessary to consider the practical working condition during the estimate of its performance in application.The work done here have provided some ideas for the study on the mechanism of heat transfer enhancement by helical flow method and present some valuable results for the further research on this new method which will undoubtedly push forward the more extensive application of shell-tube exchangers.更多还原