Numerical Study On Laminar Flow And Heat Transfer Characteristics In Pyramid-shaped Tube

Shell and tube heat exchanger is the most widely used heat exchanger type because of its simple structure,high temperature and high pressure resistance and other advantages.To improve the heat transfer performance of shell and tube heat exchanger and to develop a new generation of strengthening elements of shell and tube heat exchanger are of great significance to reduce the cost and save resources.With the progress of science and technology,the heat supply load of heat exchanger in the aspect of temperature is gradually increased.Because the traditional structure of heat exchanger and working medium can not meet the high temperature requirements of heat exchanger within the limited heat exchange area,so in order to effectively improve the overall heat transfer performance of heat exchanger,fin or strengthened round tube are used in various heat exchangers.Most of the existing heat exchangers strengthen the heat transfer on the fin side by strengthening the fin or increasing the heat transfer range of the fin or increasing the airflow disturbance on the air side,ignoring the role of the heat transfer tube.But as the most suitable for the shell and tube heat exchanger in the strengthening of the heat exchange tube has a variety of shortcomings.Therefore,in order to increase the heat exchange area of the heat exchange tube,accelerate the disturbance of the fluid in the tube,develop the heat exchange tube with anti-scaling function and realize the simplification of the structure and manufacturing process,the existing heat exchange tube was improved.On the basis of the existing heat exchange tube,a kind of gold-shaped pyramid strengthened tube was obtained.In this paper,using the method of numerical simulation,the 3D full length modeling and simulation of the pyramidal rough element reinforced pipe with water as the medium are carried out.In terms of flow characteristics,the velocity field,velocity vector diagram and flow diagram of the pyramid-type toughened tube and the corresponding smooth circular tube were compared and analyzed to study the heat transfer mechanism of the pyramid-type toughened tube.In terms of heat transfer characteristics,the temperature fields of the pyramid-type toughened tubes and the smooth round tubes were compared.The local Nu number distribution of the pyramid-type toughened tubes was studied,and the average Nu number of the two heat exchange tubes was compared.The effects of pyramidal rough element structure,Re number and vortex on the heat transfer performance of pyramidal rough element reinforced tubes are discussed.In order to find the best heat transfer efficiency which affects the heat transfer performance of the reinforced tubes with pyramidal rough elements,the geometrical structure of the reinforced tubes with pyramidal rough elements was optimized by taking the length L,the elevation Angle and the height H of the pyramids as variable parameters.The findings:In this paper,the flow and heat transfer characteristics in the tube strengthened by the tower rough element are numerically simulated.By comparing with the traditional tube,the influence of the tower rough element on the flow and heat transfer characteristics in the tube is analyzed.The influence of different structural parameters on the fluid flow and heat transfer characteristics in the tube is analyzed.The findings:(1)The maximum and minimum values of local Nu number appear at the pyramid element,respectively.The maximum heat transfer coefficient is 2.7 times that of the smooth round tube,while the average heat transfer coefficient is 2 times that of the smooth round tube.(2)Pyramid stiffened tube is more suitable for higher Reynolds number;(3)The optimization of the structure of the pyramid can increase the maximum heat transfer1.2 and the resistance 1.56 times;(4)The optimal value of the relative length L/D of the pyramid is between 0.79 and 1.05,the optimal value of the elevation Angle is between 39.80 and 450,and the optimal value of the relative height H/D is between 0.09 and 1.(5)The rent reduction effect of the reinforced tube with small pyramid is more obvious;(6)The influence of the structural parameters of the pyramidal rough element on the transverse vortex is greater;(7)The maximum heat transfer enhancement can be 2.54 times compared with that of the gold-shaped pyramid reinforced tube of the internal disturber element,and 2.9 times compared with that of the smooth round tube;(8)In the range of Re = 50 ～ 200,the comprehensive enhanced heat transfer ability of the reinforced tubes with pyramidal is better;In the range of Re = 200 ～ 500,the comprehensive enhanced heat transfer ability of the hollow torsion vortex generator inserted into the tube strengthened by the pyramid is better.(9)The errors of the fitting relations with absolute vortex flux are all within 10%.