Mass flow rate through a horizontal opening at small pressure differences

• Published in: Fire safety journal Vol. 120; p. 103050
• Main Authors: Harada, Kazunori, Nii, Daisaku
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier Ltd 01.03.2021; Elsevier BV
• Subjects: Air flow; Air supplies; Bi-directional flow; Carbon dioxide; Carbon dioxide concentration; Critical pressure; Critical pressure differences; Flow distribution; Flow rates; Fluctuating flow; Horizontal opening; Mass flow rate; Pressure; Smoke; Fluctuating flow; Bi-directional flow; Horizontal opening; Mass flow rate; Critical pressure differences
• ISSN: 0379-7112; 1873-7226
• DOI: 10.1016/j.firesaf.2020.103050

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. •A series of model scale experiments were carried out to investigate the flow through and around a horizontal opening.•The critical pressure differences for uni-directional flow were correlated with the buoyancy of the smoke layer.•Engineering relationships for mass flow rate under bi-directional flow were developed by comparison with experiments.