Experimental study of transition phenomena in buoyancy-induced natural ventilation

Experiments were carried out to study transition phenomena in buoyancy-induced natural ventilation in a relatively large-scale enclosure equipped with a localized heat source and two openings (upper and lower) on one of the sidewalls. The process studied is transition from the mixing to the displacement ventilation mode realized by opening the lower vent to different heights while keeping the upper vent fully open. Measurements included inside vertical temperature profiles and air velocity through the upper vent. Results show that if the height of the lower vent is small in comparison to that of the upper vent, ventilation takes place by a combined mode of mixing and displacement. The location of the neutral level at the upper vent, defined here as the level separating between inflow and outflow, depends on R, the ratio between the opening heights of the lower and upper vents. When R = 0.43, ventilation takes place by a combined mode of mixing and displacement, while for 0.43 < R = 1, the displacement mode dominates the ventilation process.