The indoor stratified flow in a mechanically extracted room with a doorway and a localised heat source

Abstract This paper investigates the characteristics of stratified flow inside a room with a mechanical extraction ventilation system and a doorway (MEVD), in addition to a localised heat source at the floor level. A combination of theoretical analysis and laboratory experimental observation is used to study the indoor thermal stratified flow pattern. A two-layer stratified flow is developed inside the investigated room due to the interaction between the suction force of the ceiling-level extractor and the buoyancy force of the localised heat source. Based on the stratification interface level, the ventilation flow patterns of the investigated room can be categorized into three regimes: the displacement ventilation regime, the arrested doorway flow regime, and the unbalanced doorway exchange flow regime. When the interface level exceeds the doorway height, the displacement ventilation regime occurs. When the interface level is just below the doorway height, and the flow in the doorway remains unidirectional (the inflow of outdoor ambient fluid), it is referred to as the arrested outflow regime. When the interface level is even lower than the doorway height and bidirectional exchange flow occurs at the doorway (the inflow of outdoor ambient fluid and the outflow of buoyant fluid), it is classified as the unbalanced doorway exchange flow regime. The theoretical models developed in this study successfully predict the important parameters of these three ventilation flow regimes. The predicted interface levels for the three ventilation flow regimes deviate less than 4.65% from those observed in laboratory experiments.