To explore the interaction of the vortical flow generated by punched delta-winglet pairs (DWPs) with in-line arrange ment and to explore their influence on the heat transfer enhancement (HTE) and onflow loss penalty (FLP) in a high performance finned oval tube (FOT) heat exchanger element, three-dimensional flow and conjugate heat transfer in an FOT were calculated for a thermally and hydrodynamically developing laminar flow (Re = 300) by solving the Navier-Stokes and energy equations with a Finite-Volume Method in body-fitted grids. The conjugate heat transfer was realized by iterations of the energy equation in the flow field and the conduction equation in the fin; FOT with one to three inline DWPs (beta = 30 degrees, Lambda = 2, h = H) were investigated. Velocity and temperature fields, vortex formation, local heat transfer distributions and global results were presented. The LVs of the incoming flow intensified the LVs downstream of the second and the third winglet. For Re = 300 and Fi = 500, the ratios of HTE to FLP (j/j(0))/(f/f(0)) were 1.04, 1.01 and 0.97 for an FOT with one, two and three DWPs in-line respectively.