CFD Simulation For Heat Transfer And Mixing Equipment

The heat transfer and mixing are the common unit operations in the chemical production process. It is of vital significance in optimizing the equipment's structure and improving the equipment performance to take the study on heat transfer and mixing device as well as the devices'operational principle and the rules of how their structural parameters influence the equipment performance.Numerical simulation methods are adopted in this paper. Through three-dimensional simulation of the heat exchangers (bow-shaped baffle heat exchanger,Helical baffle heat exchanger) and mixing facilities (static mixer),which was calculated by FLUENT software, the equipments within flow field information and the influencing rules that structural parameters impact on the performance are obtained.The main work involves in the following aspects:1. The simulation of shell side field on the segmental baffle board heat exchangers and helical supporting board heat exchanger using the full-scale model was made in this paper. The intuitionistic character of the flowing state in the two heat exchangers was obtained by the software's post-process function. The results obtained showed that in the segmental baffle board heat exchangers, there existed large scale of dead zone of flowing and heat transfer on the back of segmental baffle board, especially in the intersection between segmental baffle board and the cylinder while in the helical supporting board heat exchangers, the flowing state of fluid turned out to be spiral. There was a large radial velocity gradient which caused the turbulence on the surface of the tube. It helped thinning the boundary layer, which was benefit for the heat transfer. Through the study on the effects of structure parameters of heat exchanger shell on the characteristics of flow field, it could be figured out that the dead zone could be decreased by reducing the board space in segmental baffle board heat exchangers. The results obtained in this paper could be used as the theoretical basis in the optimal designing for heat exchangers.2. Through comparison on the turbulent kinetics energy, pressure drop and heat transfer coefficients in the two kind of heat exchangers, it could be figured out that compared with the segmental baffle board heat exchangers, the heat transfer coefficients under shell pressure drop of helical supporting heat exchangers could be enhanced by 0.6-2 times while the loss of pressure drop could be reduced 30%~60%.3. The characteristics of longitudinal flow heat exchangers were simulated using periodic unit ducts model. The effect of percentage of orifice and its opening way on the characteristics of heat exchangers was studied. The results obtained showed that under the percentage to be lower than 0.2, a higher heat exchanger coefficients could be reached in a large hole while it would be benefit for heat exchange and reducing the heat loss when a small hole is adopted.4. The flow field distribution in the static mixer is found through simulation carried out on SK static mixer. It could be seen that besides the motion along helical ribbon, the fluid inside the static mixer also did spinning motion around the hydraulic center in the cross-section.5. The effects of rotation angle, length/diameter ratio, setting angle of the adjacent torsion slips and the number of mixed units on the performance of mixers were studied in this paper, and the optimal designing parameters were determined to be: rotation angle 180 degree, length/diameter 1.5 and the rotation angle between the two adjacent torsion slips 90 degree.6. The results obtained through simulation on the two-phase flow mixing process in mixer using the Euler model showed that the single-phase volume fraction is changing along with the time variation. Through simulation, the time needed for mixing as well as the number of mixing units could also be obtained.