Abstract:The effect of Prandtl number of mixed convection heat and mass transfer in a triangular enclosure with heated and concentrated circular obstacle is analyzed by solving mass, momentum, energy and concentration balance equations. The left lower middle and right upper middle walls are kept at low temperature and concentration. All others wall are assumed to be adiabatic. The lower wall is moving in the +x direction and all others walls are maintained at no-slip condition. Moreover, Galerkin Weighted Residuals finite element method is applied to solve the governing equations. The study is performed for different values of Prandtl number, Richardson number and buoyancy ratio. A simple transformation is employed to transfer the governing equations into a dimensionless form. The result shows that at high Pr heat transfer rate increase rapidly and at low Pr it increases linearly with the increase of Ri. However, buoyancy ratio and Lewis number plays an important role for the flow, temperature and concentration fields.