Numerical predictions on heat transfer characteristic, flow topology and thermal performance assessment in a square duct are presented. The passive technique; insertion of the vortex generator, is opted to develop the heat transfer rate in the square duct heat exchanger. The vortex generator of the present research is Double V-Orifice (DVO). The square duct equipped with DVO is tested with various parameters. The influences of DVO configurations, placement and flow directions on flow pattern and heat transfer profile are considered for laminar flow regime. The Reynolds number based on the hydraulic diameter of the square duct around 100 – 2000 is discussed. The numerical model is solved with the commercial program (finite volume method). As the numerical result, the square duct inserted with the DVO offers greater heat transfer rate than the plain duct around 1.00 – 14.80 times. The maximum of TEF for the square duct inserted with the DVO is found to be around 3.60 depended on s/H, b/H and flow direction. The flow and heat transfer profiles in the square duct inserted with the DVO are also illustrated.