Theoretical modeling of the stratified flow in a hybrid extraction ventilated room with a localized buoyancy source

Abstract

This study develops a set of steady-state theoretical models for the indoor stratified flow driven by the combined effects of the buoyancy force by a localized heat source and the inertial force by an extraction device. The investigation considers an isolated room that has a vent and a mechanical extraction device at the ceiling level and a vent at the floor level. The combined effects of different mechanical extraction flow rates and a fixed buoyancy flux of a localized heat source on the stratified flow are investigated. In addition, various effective vent area ratios are considered as part of this study. Salt bath experiments are conducted in a reduced-scale building model to validate the theoretical models. The interface height and the reduced gravity of the buoyant layer observed in the experiments are in reasonable agreement with those predicted by the theoretical models. In this study, the volumetric flow rates through both the ceiling-level and floor-level openings were not directly measured by using this experimental technique, and the volumetric flow rates are estimated by using experimental data of the interface height and the reduced gravity instead. Two flow regimes are observed, the forward and reverse flow regimes separated by the critical flow rate, in the hybrid extraction ventilated space. In the forward flow regime, the interface height and the reduced gravity of the buoyant layer depend on the extraction flow rate and the effective vent area ratio. These variables still influence the interface height in the reverse flow regime, while the extraction flow rate alone determines the reduced gravity of the buoyant layer.