Numerical Simulation Study Of Heat Exchangers With Continuous Helical Baffles

As a new type of shell-and-tube heat exchangers, the heat exchangers with helical baffles gets fast development, by right of its higher heat transfer coefficient, lower pressure drop, less bypass effects, less shell-side fouling, and prevention of flow induced vibration, compared to the conventional heat exchangers with segmental baffles. Because of the complicated configuration of the heat exchangers with helical baffles, previous studies focused on the experiments of the discontinuous helical baffles in shell-and-tube heat exchangers with small shell diameter and big helical angle, and there is no many researches on its numerical simulation.This paper investigates the continuous helical baffles in shell-and-tube heat exchangers with a big shell diameter and small helical angle by means of CFD. By changing structural parameters and process conditions, this paper investigates flow behavior, heat transfer and resistance performance of shell-and-tube heat exchangers with continuous helical baffles. The main contents are as follows:Mathematical model coupling tube and shell side is established. Segmental baffles heat exchangers and helical baffles heat exchangers of seven different helical angles, which shell diameter is 500mm, are simulated. Realizableκ-εturbulent model is adopted in the numerical simulation.Simulation results indicate that whether working media is water-water or waxoil-water, heat exchangers with helical baffles behaviors more perfectly than with segmental baffles in the aspects of flow behavior, heat transfer and resistance performance.Flow field in shell side of helical baffles heat exchangers shows that in the inlet and outlet of heat exchangers, velocity is lower and velocity gradient is bigger, so flow field needs to be improved. Velocity is lower in the far away from axial direction, so it is necessery to improve the velocity of this region. Temperature gradient is big around heat tubes, while, in the middle of each tube bundle and the region between tube bundle and shell wall, temperature distribution is even and temperature gradient is small. Local heat transfer coefficient distribution along axial and radial direction is similar to velocity distribution along axial and radial direction. Local pressure coefficient distribution is inner lower and outer higher along radial direction and is uniform degressive along axial direction.For the heat exchangers with helical baffles, helical angle has a great effect on the tangential velocity which effects heat transfer and flow resistance performance. With helical angle augmentation, heat transfer coefficient and pressure drop decrease rapidly. While, heat transfer coefficient per pressure drop increases rapidly with helical angle augmentation.There is an analysis about heat transfer, flow characteristics and evaluation for the helical baffles heat exchangers of seven different helical angles. With flow rate augmentation, for two working media, heat transfer coefficient increases and pressure drop also increases. The trend is more obvious when helical angle is small and pressure drop is very close for two working media. Heat transfer coefficient per pressure drop decreases with flow rate augmentation, then becomes smooth.Heat transfer and friction factor correlations of helical baffles heat exchangers of seven different helical angles have been obtained.