The flow characteristics of shell-side fluid in the tube-and-shell heat exchangers with trisection helical baffles with 35° inclined angles are numerically analyzed. The secondary flow distribution of the fluid i...The flow characteristics of shell-side fluid in the tube-and-shell heat exchangers with trisection helical baffles with 35° inclined angles are numerically analyzed. The secondary flow distribution of the fluid in the shell-side channel is focused on. The results on meridian planes indicate that in the shell-side channel, the center part of fluid has an outward tendency because of the centrifugal force, and the peripheral region fluid has an inward tendency under the centripetal force. So in a spiral cycle, the fluid is divided into the upper and lower beams of streamlines, at the same time the Dean vortices are formed near the left baffle, and then the fluid turns to centripetal flow near the right baffle. Finally the two beams of streamlines merge in the main flow. The results of a number of parallel slices between two parallel baffles with the same sector in a swirl cycle also show the existence of the secondary flow and some backward flows at the V-gaps of the adjacent baffles. The secondary flows have a positive effect on mixing fluid by promoting the momentum and mass exchange between fluid particles near the tube wall and in the main stream, and thus they will enhance the heat transfer of the helix heat exchanger.展开更多
The secondary flow within a passage of turbomachinery exhibits a complex flow pattern by the effect of the centrifugal and the Coriolis forces. The passage vortex in this secondary flow generates a major part of the l...The secondary flow within a passage of turbomachinery exhibits a complex flow pattern by the effect of the centrifugal and the Coriolis forces. The passage vortex in this secondary flow generates a major part of the losses. However, the mechanism of the loss generation has not been fully clarified yet. In this point of view, the passage vortex is closely examined by the computational method using the two-dimensional curved square ducts as fundamental models. The inlet boundary layer thickness and the inlet velocity distortion are considered to be the major parameters affecting the generation of passage vortex in the present study. The computed results revealed that the passage vortex gave the predominant effects for the generation of loss not only in the breakdown process but also in the development process.展开更多
基金The National Natural Science Foundation of China (No.50976022)the National Key Technology R&D Program of China during the 11th Five-Year Plan Period (No.2008BAJ12B02)
文摘The flow characteristics of shell-side fluid in the tube-and-shell heat exchangers with trisection helical baffles with 35° inclined angles are numerically analyzed. The secondary flow distribution of the fluid in the shell-side channel is focused on. The results on meridian planes indicate that in the shell-side channel, the center part of fluid has an outward tendency because of the centrifugal force, and the peripheral region fluid has an inward tendency under the centripetal force. So in a spiral cycle, the fluid is divided into the upper and lower beams of streamlines, at the same time the Dean vortices are formed near the left baffle, and then the fluid turns to centripetal flow near the right baffle. Finally the two beams of streamlines merge in the main flow. The results of a number of parallel slices between two parallel baffles with the same sector in a swirl cycle also show the existence of the secondary flow and some backward flows at the V-gaps of the adjacent baffles. The secondary flows have a positive effect on mixing fluid by promoting the momentum and mass exchange between fluid particles near the tube wall and in the main stream, and thus they will enhance the heat transfer of the helix heat exchanger.
文摘The secondary flow within a passage of turbomachinery exhibits a complex flow pattern by the effect of the centrifugal and the Coriolis forces. The passage vortex in this secondary flow generates a major part of the losses. However, the mechanism of the loss generation has not been fully clarified yet. In this point of view, the passage vortex is closely examined by the computational method using the two-dimensional curved square ducts as fundamental models. The inlet boundary layer thickness and the inlet velocity distortion are considered to be the major parameters affecting the generation of passage vortex in the present study. The computed results revealed that the passage vortex gave the predominant effects for the generation of loss not only in the breakdown process but also in the development process.
