The Optimum Angle of Attack of Delta Winglet VortexGenerators on Heat Transfer Performance of Finned Flat Tube Bank with Considering Nonuniform Fin Temperature

Abstract

To investigate the effects of the angle of attack of delta winglet vortex generators (VGs) on heat transfer performance and pressure drop penalty of finned flat tube bank, local and average heat transfer characteristics were studied by using analogy between heat and mass transfer with naphthalene sublimation experiments. In order to consider nonuniform fin temperature, the heat transfer rate from fin surfaces was investigated by solving the conduction equation in the fin with a Finite Volume Method on curvilinear coordinate systems based on experimental results of local heat transfer. Three angles of attack (> = 25°, 35°, 45°) are investigated. Without considering the nonuniform fin temperature, increasing the angle of attack, average Nusselt number and friction factor are increased, the heat transfer enhancement on fin surface without mounted VGs is reduced, but the heat transfer enhancement on fin surface mounted with VGs is less affected. Considering the nonuniform fin temperature, the heat transfer enhancement becomes weak as the angle of attack greater than certain value. The numerical calculation shows that the total heat transfer rate from the fin surface mounted with VGs is larger than the total heat transfer rate from the fin surface constructing the same flow channel. Based on a dimensionless factor of the larger the better, JF, the results show that the angle of attack, 40°, has better heat transfer performance for the configurations discussed in this article.