Flow and Heat Transfer Due to a Buoyant Ceiling Jet Turning Downward at a Corner

An experimental investigation has been carried out on the flow and heat transfer characteristics of a horizontal buoyant ceiling jet that turns downward at a corner to yield a vertical negatively buoyant wall flow. Such flow situations are frequently encountered in thermal energy storage, in electronic systems, and in room fires. However, not much work has been done to understand the basic mechanisms governing such flows, particularly the flow near the corner. In this study, a two-dimensional jet of heated air is discharged adjacent to the lower surface of an isothermal horizontal plate. An isothermal vertical plate is attached at the other end of the horizontal surface, making a right angle corner. The vertical penetration distance of the resulting downward flow is measured and is related to the inflow conditions, particularly to the temperature and velocity at the jet discharge. This penetration distance is found to increase as the distance between the discharge location and the corner is reduced and also as the relative buoyancy level in the inlet flow is decreased. Velocity and temperature measurements are also carried out over the flow region. These indicate that the ceiling flow separates from the horizontal surface just before reaching the corner and then reattaches itself to the vertical wall at a finite distance vertically below the corner. The local surface heat flux measurements show a minimum in the heat transfer rate before the turn, along with a recovery in the heat transfer rate after the turn and the existence of a small recirculation zone near the corner. The net entrainment into the flow and heat transfer rate to the solid boundaries are also measured and correlated with the jet discharge conditions.