Flow And Geometric Conditions For Stable G(?)rtler Vortices In Spiral Smooth Channel

Energy plays an extremely important role in human society.With the progress of science and technology,energy consumption is increasing day by day.However,a large amount of energy consumption has brought about a series of environmental problems,and energy saving has become an important means to protect the environment.Heat exchanger is commonly used in industrial heat exchange equipment,in the use of its auxiliary equipment such as fans on the consumption of electric energy is huge.Improving heat transfer performance of heat exchanger can not only reduce energy consumption,but also reduce the volume of heat exchanger to meet the needs of various occasions,so it is concerned by the majority of scholars.Spiral plate heat exchanger is a kind of high efficiency heat exchanger with spiral heat transfer channel.The current related research focuses on the influence of structural parameters on heat transfer performance,and ignores the flow heat transfer mechanism in the channel.In order to optimize the design of spiral plate heat exchanger and improve its heat transfer efficiency,it is very necessary to analyze the complex flow and heat transfer process in the channel.In the process of analysis,the first thing to do is to analyze the G（?）rtler vortices which is widely existed in the spiral channel and generated in the boundary layer of the concave wall.Since G（?）rtler vortices often improve the heat transfer performance of heat exchangers,it is very important to determine the flow and geometric conditions for stable G（?）rtler vortices in spiral smooth channel.In this paper,the motion of G（?）rtler vortices in spiral smooth channel and the flow and heat transfer of fluids in the presence of G（?）rtler vortices are analyzed by numerical methods.The effects of flow parameters and geometric parameters on the motion and generation of vortices are determined.Finally,the flow and geometric conditions for stable G（?）rtler vortices in spiral smooth channel are solved.The specific research is as follows:（1）The dimensionless number Se of the secondary flow intensity was determined as the descriptive parameter of the intensity of G（?）rtler vortices.Based on the change of Se along the main flow direction,the velocity distribution of the fluid and the Se_local distribution on the cross section,the motion of G（?）rtler vortices along the main flow direction was divided into three stages:generation,development and decay.The generation stage refers to the process from the entrance to the generation of G（?）rtler vortices;the development stage refers to the process from the generation of G（?）rtler vortices to the maximum intensity of G（?）rtler vortices;the decay stage refers to the process of continuous decay after the maximum intensity of G（?）rtler vortices.The flow and heat transfer of the fluid in the presence of G（?）rtler vortices in the channel are revealed.The flow trajectory of the fluid particle in the channel is not a standard spiral,and the fluid particle rotates forward around the direction of the main flow.Near the G（?）rtler vortices in the channel,the low-temperature fluid located in the center of the channel flows to the wall,and the high-temperature fluid close to the wall is away from the wall,which enhances the convective heat transfer between the fluid and the wall and improves the heat transfer efficiency.（2）The flow parameter in this paper is determined to be Reynolds number Re_m,and the geometric parameter is the inlet curvature radius R_i,channel width b and channel height h,and its influence on the motion and generation of G（?）rtler vortices is explored.The results show that:With the increase of Re_m,the generation of G（?）rtler vortices is advanced,vortex intensity and vortex interaction are also enhanced,and no vortices are generated at smaller Re_m;With the increase of R_i,the generation of G（?）rtler vortices is delayed,vortex intensity and vortex interaction are also weakened,and no vortices are generated at larger R_i;The influence of b on G（?）rtler vortices is a limitation that vortices can be developed more fully at larger b,and correspondingly,the decaying range of vortices is larger in the decay stage,and no vortices are generated at smaller b;h only influences the vortex interaction and has no influence on the generation of vortices.（3）By analyzing the change of Se along the main flow direction under different vortex states,the first condition for stable G（?）rtler vortices in spiral smooth channel is determined to satisfy the Se_max or （?） greater than 0 in the function obtained by fitting the parameter points in the interval of existing vortices,and the second condition is that the flow state is laminar.And research to improve the accuracy of the first condition,it is found that （?） is more stable than Se_max and is not susceptible to vortex interaction,and the parameter points with smaller （?） values should be selected when fitting the function.Finally,the flow and geometric conditions for stable G（?）rtler vortices in spiral smooth channel with certain reliability are obtained.