Mixed Convective Heat Transfer in a Horizontal Channel Heated Periodically From Below

Two-dimensional Navier-Stokes and energy equations are numerically solved for laminar flow in a horizontal channel with localized heating from below. The relative strength of the forced flow and buoyancy effects are examined for a wide range of Rayleigh Ra, Reynolds Re, and Prandtl Pr numbers. For a fixed geometry and a given Rayleigh number, a complicated solution structure is observed upon increasing the Reynolds number. For Re = 0 (i.e., in the case of pure free convection), a steady symmetric flow pattern is obtained. This pattern becomes asymmetric for Re below a critical value, but the rolls remain attached to the heating elements. Above the critical Re, the rolls are carried downstream with a time-dependent velocity, and the flow becomes periodic in time.