In this work, we propose a numerical study of the thermal-hydraulic performance in a novel flat heat exchanger tube with discrete inclined ribs. Analysis of flow structures shows that four longitudinal swirl flows are induced in the flat tube. These swirl flows lead to adequate fluid mixing between the core flow and the near wall regions, and consequently, improve the heat transfer performance significantly. To determine the effects of parameters such as Reynolds number (300 <= Re <= 1500), the rib pitch ratio (0.6 <= P* <= 1.8), and the rib height ratio (0.06 <= H* <= 0.18) on the thermal and flow performance, a sensitivity analysis has been carried out by means of Response Surface Methodology. It is found that a reducing of P* and an increase in H* causes an increment in the Nusselt number and friction factor. The highest values of the Nusselt number and friction factor are achieved at P* = 0.6 and H* = 0.18 when Re is held at 900. Besides, the Nusselt number is more sensitive to Re and H* while the friction factor is more sensitive to P*. The findings from this work may provide useful guidelines for engineers and researchers to design efficient heat exchangers. (C) 2017 Elsevier Ltd. All rights reserved.