Instability and heat transfer in mixed-convection flow in a horizontal duct with discrete heat sources

Three-dimensional mixed-convection flow in a horizontal rectangular duct at low Reynolds numbers has been investigated numerically. Multiple strip heat sources are flush-mounted on the bottom surface, modeling integrated circuit chips on printed circuit boards, and the fluid considered is air. According to the stability diagram presented, four different flow patterns might exist. The discontinuous thermal boundary condition on the bottom makes the longitudinal rolls expand and shrink periodically, and also helps in the generation of transverse rolls. The steady transverse rolls were found even at subcritical Rayleigh numbers for relatively low Reynolds numbers. The implications of these observations to the cooling of electronic equipment are discussed.