Heat transfer enhancement of finned oval tubes with staggered punched longitudinal vortex generators

Punched longitudinal vortex generators in form of winglets in staggered arrangements were employed to enhance heat transfers in high performance finned oval tube heat exchanger elements. Three-dimensional hydrodynamically and thermally developing laminar flow (Re=300) and conjugate heat transfer in finned oval tubes were calculated by solving the Navier–Stokes and energy equations with a finite-volume method in curvilinear grids. Velocity field, pressure distribution, vortex formation, temperature fields, local heat transfer distributions and global results for finned oval tubes with two to four staggered winglets (β=30°, Λ=2, h=H) were presented and compared. Winglets in staggered arrangement bring larger heat transfer enhancement than in in-line arrangement since the longitudinal vortices from the former arrangement influence a larger area and intensify the fluid motion normal to the flow direction. For Re=300 and Fi=500, the ratios of heat transfer enhancement to flow loss penalty (j/j0)/(f/f0) were 1.151 and 1.097 for a finned oval tube with two and four staggered winglets, respectively.