Effect of Fin Heat Conduction on the Performance of Punched Winglets in Finned Oval Tubes

Abstract

Wing-type longitudinal vortex generators were employed for performance enhancement of finned tube heat exchanger elements. The effect of finite fin heat conduction on the performance of fins and longitudinal vortex generators was considered. Three-dimensional developing laminar flows and conjugate heat transfer in high performance finned oval tube elements, with and without punched deltawinglets, were studied numerically with a Finite-Volume Method. Body-fitted grids were used to satisfy exactly the thermal and hydrodynamic boundary conditions. The conjugate heat transfer was realized by iterations of convection in the flow field and conduction in the fin. Reynolds numbers of 100<Re<500, and fin conduction parameters of 100<Fi<1000 were varied. Temperature fields, local fin heat transfers and fin efficiencies were presented. Performance of finned oval tube elements with up to four in-line or staggered winglets was evaluated. For the investigated base configuration, performance enhancement through winglets increased with increasing Reynolds number and fin conductivity. For performance comparisons of different configurations, results of isothermal fins could be transferred to non-isothermal fins. The performance enhancement by winglets for fins with finite conduction may be reduced by about 20% in practical applications compared to that for isothermal fins.