The present numerical work explores the mixed convective flow and heat transfer analysis in top lid driven square cavity containing heated triangular block with constant heat flux (CHF) thermal condition. The fluid flow in the cavity is driven by top moving wall in +x direction, while all other walls are stationary. Governing equations are solved by using finite volume method (FVM) and SIMPLE scheme for range of pertaining parameters such as, Reynolds number (Re = 1, 10, 50, 100, 500 and 1000), Prandtl number (Pr = 1, 50, 100), and Grashof number (Gr = 0, 10(2), 10(3), 10(4) and 10(5)). The influence of size of blockage (b =10%, 20% and 30%) on momentum and heat transfer characteristics has also been explored. The physical insights of systems are delineated by analyzing variation of streamlines and isotherm contours; while the heat transfer characteristics are explored by using dimensionless heat transfer coefficient or Nusselt number (local as well as averaged values). It is observed that increase in Reynolds number enhances the heat transfer rate (Nusselt number) only up to Re = 180-220, later, deterioration of heat transfer rate is observed. The critical (Rear) as well as stagnant (Re-stag) Reynolds number of heat transfer for present case are identified. (C) 2016 Elsevier Ltd. All rights reserved.