Numerical Simulation On Heat Transfer Enhancement By Punched Holes On Vortex Generator Pairs

As a passive component for heat transfer enhancement,vortex generator(VG)has been widely used in various fields since its development.Arranged on the surface of the heat exchanger,the VGs can enhance heat transfer by inducing vortex.When the fluid flows through the VG,the pressure loss affects the comprehensive performance on heat transfer.The shape resistance of the vortex generator is a major factor in generating flow resistance under the condition of angle of attack.VGs with punched holes can effectively reduce the shape resistance,thereby improving the heat transfer performance.Numerical simulations were carried out to investigate the performance of plane and curve trapezoidal wing VGs with different areas and shape of punched holes.The corresponding mechanism of heat transfer is analyzed based on intensity of secondary flow theory.The mechanism of heat transfer enhancement is explored with the help of secondary flow theory.Parametric study on plane trapezoidal winglet pair reveals that larger area generates larger longitudinal vortex intensity.When the curved surface is contact with the fluid,the separation of the fluid boundary layer is delayed.Then the pressure drop reduced.The curved trapezoidal winglet pair provides the best thermo-hydraulic performance.A pair of trapezoidal VG winglet is symmetrically arranged at the bottom of the straight rectangular channel,punching circular holes,triangular holes,rectangular holes and trapezoidal holes,respectively.The punching area ratio is 0.03 to 0.12.The computational fluid dynamics method is used to numerical simulate the heat transfer on the bottom wall of the channel The effects of the these VGs are examined and compared using the dimensionless parameters j/j0,f/f0 and R=(j/j0)/(f/f0),which represent the enhanced heat transfer performance,flow resistance performance and comprehensive heat transfer performance.The simulation results show that the plane trapezoidal VG winglet has larger area and better heat transfer performance than the curve ones;while curved VGs perform better resistance due to the streamlined surface.The bigger punching area is,the lower f/f0.When the punching area ratio is 0.12,plane trapezoidal VGs winglet pair punching rectangular holes show the best thermal hydraulic performance with the value of R ranging from 0.93 to 1.13 under the present conditions;curved trapezoidal winglet pair with trapezoidal hole has the highest comprehensive heat transfer performance with the value of R ranging from 0.97 to 1.21.In this paper,the performance of plane and curve trapezoidal wing VGs with different areas and shape of punched holes are analyzed.The results show that punching holes can effectively reduce flow resistance and gives better thermal-hydraulic performance.