Mass flow rate through a horizontal opening at small pressure differences

Abstract

The smoke and air flow through a horizontal opening was investigated using a model-scale room equipped with a horizontal opening on the ceiling. A smoke layer was created under the ceiling using a small gas burner. The pressure difference across the horizontal opening was changed by controlling the air supply to and exhaust from the space above the opening. Smoke and air flow patterns were either downward uni-directional flow of air, bi-directional flow of air and smoke or uni-directional flow of smoke upward. By changing the pressure difference across the opening, critical pressure differences to cause uni-directional flow were determined. It was found that the critical pressure was 0.98 of the smoke layer buoyancy for the onset of upward uni-directional smoke flow, and 0.47 for downward uni-directional air flow. From the measured carbon dioxide concentration, the mass flow rates of smoke and air were calculated and correlated with the non-dimensional pressure difference in the case of bi-directional flows.