Studies On The Heat Transfer Enhancement At Novel Scheme Of Coil-Strip-Baffle Heat Exchanger

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.