CFD Simulation Of Shell-and-tube Heat Exchanger With Helical Baffles

Shell and tube heat exchanger with helical baffles is superior to that with segmental baffles in improving the heat transfer performance, reducing pressure drop, eliminating dead zone, preventing deposit and lowering the risks of vibration of tube bundle. And it has been used more and more widely in engineering.The computational fluid dynamics method(CFD) is adopted in the present work to simulate the flow and heat transfer in the helical baffle heat exchanger. And the heat transfer coefficient per pressure drop is employed to assess the integrative performance of the heat exchanger. The results reveal that, the heat transfer coefficient per pressure drop of the helical baffle heat exchanger is 1.3~1.5 times larger than that of the segmental baffle heat exchanger. Baffle shape and helix angle are the key factors to influence the performance of helical baffle heat exchanger. In the range of helix angles 10°~40°, 1/4 sector helical baffle heat exchanger shows the best integrative performance. As for the effects of helix angles, the optimum value varies on the flow rates. When the flow rate is smaller than 1 kg/s, the heat exchanger performed best at 30°. As the flow rate increased to 1 kg/s, the exchanger performed well at 20° as at 30°.Comparisons of single helix and double helix were numerically studied. The results show that the double helix not only enhances the role of fluid diversion, but also can improve the integrative performance of the helical baffle heat exchanger when using a relative big helix angle(30°~40°). Leakage zones exist in the central part of the heat exchanger with discontinuous helical baffles, which would reduce the efficiency of heat transfer. A novel baffle type which combines helical baffle with rhombus baffle is proposed in this paper to solve this problem. The simulation results indicate that the improved helical baffle not only helps avoid leakage zones, but also can improve the integrative performance of the helical baffle heat exchanger at a bigger helix angle. And this novel baffle is also convenient for the manufacture and engineering application.Condensation of vapor in the shell side of helical baffle heat exchanger is simulated with combination of CFD and Lee model. The calculated results show that the condensation rate is 20% lower than theoretical value at a small flow rate. The deviation will increase as the flow rate increases. The main reason for inducing this deviation is the failure to accurately calculate the intrinsic condensation heat transfer rate around the wall region using CFD method.A novel method combined Fluent and HTRI is proposed for the simulation of condensation process to overcome the drawback mentioned above. The results indicate that the liquid concentrates at the bottom of condenser forming a liquid region when the inlet flow rate is relative low and this region move towards the outlet as the inlet flow increases.In the present work, the calculated results are useful for the design of those kind of heat exchangers. And the methods to simulate the condensation can be used in the future work.