This paper presents numerical prediction of characteristics of laminar, as well as, turbulent flow and heat transfer in a square sectioned duct inserted with a twisted tape, whose width equals the length of the duct side, The heat transfer characteristics are predicted under axially and peripherally constant wall heat flux conditions. As such, the flow and heat transfer are periodically fully developed in axial direction. Correlations for friction factor and Nusselt number are derived from the predicted data. The correlation for friction is compared with the experimental data, which are found to be in reasonably good agreement with each other, for both laminar and turbulent flows.