Natural ventilation flows established by a localised heat source in a room with a doorway and a high-level vent

Abstract

Ventilation flows generated by a localised heat source within a room containing two openings to the ambient environment are examined. The openings are representative of a doorway and a high-level vent, and a steady two-layer stratification of well-mixed fluid is established within the room for all cases considered. Classical displacement ventilation flow is observed when the interface between the two layers is above the height of the doorway. Displacement ventilation flow can persist when the interface within the room is below the height of the doorway; in general, however, an unbalanced exchange flow forms across the doorway and the ventilating flow is found to be dependent on the doorway aspect ratio, the doorway height relative to the room height, the effective area of the high-level vent (relative to the square of the room height) and the rate of entrainment into the plume generated by the localised heat source. An analytical model is presented which predicts the ventilation rates and temperature structures within the room for these flows. Results from analogue experiments demonstrate good agreement with the model for a wide range of the parameter space relevant to the full-scale application.