Mixed convection flow fields and heat transfer of partially enclosed axial and radial laminar jets impinging on a heated flat plate have been investigated from the numerical solution of incompressible unsteady Navier-Stokes and energy equations with a Boussinesq approximation. For mixed convection flow at Re = 200, steady flow has not been observed for either the radial or the axial jet. For the smallest Crashof number (Gr = 10,000), periodic solutions have been obtained. With Gr = 40,000, nonsteady nonperiodic (chaotic) flow appears. Free convection may increase the heat transfer by more than 200 %.