Theoretical predictions of transient natural displacement ventilation

The transient natural displacement ventilation driven by a localized heat source at the floor of a room is examined to understand the airflow behavior and the relevant thermal stratification characteristic. Two modified theoretical models are developed on the basis of classical plume theory and Kaye and Hunt’s model. The buoyant layer is modeled as composed of a near-ceiling layer and a warm layer rather than being well-mixed. Some assumptions on the buoyancies of the near-ceiling layer and the outflow through the upper opening are made in the two modified models for simplicity. Comparisons are made between the predictions of Kaye and Hunt’s model and the two modified models and experimental data reported in the literature. Two modified models are shown to perform better than Kaye and Hunt’s model. Meanwhile, the predictions of the modified model I seem to agree slightly better with the experimental data than those of the modified model II. Typically, the average relative deviation between the three models’ predictions of the lowest interface height and the experimental data are about 4.2% (modified model I), 4.6% (modified model II), and 4.9% (Kaye and Hunt’s model).