Study Of Flow And Enhanced Heat Transfer Characteristics Of Pyramidal Shaped Tube Built-in Vortex Generator

In this paper,the physical model of the pyramidal shaped tube is established based on Fortran language using a self-programming method and the meshing of this model is also realized.The mesh of the built-in vortex generator part is divided using ICEM software and the mesh of the built-in vortex generator model of the pyramidal shaped tube is generated by combining the meshes using the mesh stitching method.With the equal wall temperature（UWT）boundary condition,Re=15000～55000,ANSYS Fluent numerical simulation software was used to firstly study the effects of three structural parameters of pyramidal rough element on the turbulent flow and heat transfer characteristics of the fluid inside the pyramidal shaped tube;the relative height,relative width and relative length of the pyramidal rough element were compared and analyzed when the relative height,relative width and relative length of the pyramidal rough element were taken at different ratios,the heat transfer characteristics of the fluid inside the shaped tube The effects of the average characteristics,local heat transfer characteristics and secondary flow intensity of fluid transfer inside the pyramidal shaped tube when the relative height,relative width and relative length of the pyramidal rough element are taken to different ratios are compared and analyzed,and the effects of the pyramidal shaped tube with different shapes of vortex generators on the average characteristics,local heat transfer characteristics and secondary flow intensity of fluid transfer inside the tube are studied,and the following conclusions are drawn:（1）The smaller the relative length L/D of the pyramidal rough element,the smaller the relative width W/D of the pyramidal rough element,and the larger the relative height H/D of the pyramidal rough element,the larger the value of the JF value of the comprehensive enhanced heat transfer factor of the shaped tube,but in order to ensure the shape of the pyramidal shaped tube,the selected structural parameters should not be too large or too small;at L/D of 0.53,W/D of 0.77,H/D of 0.089,the maximum average Nusselt number of the pyramidal shaped tube is 2.15 times that of the smooth circular tube;（2）With the increase of Re,the influence of vortex generator on convective heat transfer inside the pyramidal shaped tube gradually decreases;in comparison,it is found that the heat transfer capacity of the built-in rectangular wing vortex generator of the pyramidal shaped tube is the strongest,followed by the built-in isosceles right-angle trapezoidal wing vortex generator and parallelogram wing vortex generator,and the heat transfer capacity of the built-in isosceles trapezoidal wing vortex generator is the worst;the heat transfer capacity of the built-in rectangular hollow vortex generator of the pyramidal shaped tube is the strongest,followed by the built-in isosceles right-angle trapezoidal hollow vortex generator and parallelogram hollow vortex generator,and the heat transfer capacity of the built-in isosceles trapezoidal hollow vortex generator of the pyramidal shaped tube is the worst;（3）With the increase of Re,the shape of the built-in vortex generator has less and less influence on the integrated strengthening factor JF inside the pyramidal shaped tube,and the value of the strengthening heat transfer factor JF is decreasing;it is found that the pyramidal shaped tube built-in rectangular wing vortex generator>pyramidal shaped tube built-in isosceles right-angle trapezoidal wing vortex generator>pyramidal shaped tube built-in parallelogram wing vortex generator>pyramidal isosceles trapezoidal wing vortex generator built into the profile tube;isosceles right-angle trapezoidal hollow vortex generator built into the pyramidal profile tube>parallelogram hollow vortex generator built into the pyramidal profile tube>rectangular hollow vortex generator built into the pyramidal profile tube>isosceles trapezoidal hollow vortex generator built into the pyramidal profile tube;（4）The local Nu_local value of the wall surface of the pyramidal shaped tube built-in vortex generator shows periodic changes with the angleθ.The trend of the Nu_local on the wall surface of the pyramidal shaped tube is basically the same,and the peak size of the Nu_local on the wall surface of the pyramidal shaped tube is different due to the influence of the shape of the vortex generator;（5）Pyramidal shaped tube with built-in vortex generator causes the fluid flow in the tube to show rotational flow,and this rotational flow induces a strong secondary flow in the pyramidal shaped tube,which makes the fluid velocity and temperature distribution in the tube more uniform;the velocity and temperature fields in the core region are shaped differently by the shape of the vortex generator;（6）The intensity of secondary flow Se and the average Nusselt number Nu_m in the tube of pyramidal shaped tube with built-in vortex generator increase with the increase of Re,but there is no consistency in the trend of the two;the pyramidal shaped tube with built-in vortex generator can cause greater secondary flow than the pyramidal shaped tube without vortex generator;in addition,the intensity of secondary flow caused by different shapes of vortex generator in the center of the tube of pyramidal shaped tube is different,which is caused by the different shapes of vortex generator.