01. Experimental/Computational Fluid Dynamics

This study investigates the indoor airflow characteristics of a room with a localized heat source at the floor level, and a hybrid extraction ventilation (HEV) system. The HEV system consists of two vents, one located at the floor level and the other at the ceiling level, along with a mechanical extraction device at the ceiling level. A baffle board is installed at the vents' indoor side to reduce the outdoor ambient fluid's inflow vertical momentum. Mathematical models are developed by considering the buoyant source's buoyancy flux, the effective vent opening area, the extraction flow rate, and the room's geometry. The mathematical predictions are compared with salt-bath experimental measurements to ensure their validity. This study observed a two-layer stratification flow pattern inside a room with a HEV system. The upper layer is formed by ascending buoyant fluid, while the lower layer is formed by replacement fresh ambient fluid. Two flow modes, i.e. the forward and reverse flow modes, were observed in the analogous experiments with the low and high extraction flow rates. Two flow modes are separated by a critical flow rate. In the forward flow mode, a HEV room with a larger floor-level vent always has a higher interface height and a lower reduced gravity of buoyant fluid than those in the room with a larger ceiling-level vent at the same extraction flow rate and with the fixed total effective vent opening area of two vents. In the reverse flow mode, a room with a larger floor-level vent opening area only raises the interface height without influencing the reduced gravity of the buoyant fluid. This study suggests that the HEV system with a larger floor-level vent opening area in the forward flow mode provides a higher flow rate and a lower reduced gravity of the buoyant fluid in a room.