Effect of air stability on the continuous and periodic exhalation flow of a person

The concept of air stability is derived from atmospheric stability, which represents the extent of stability of room air. Experiments on thermal manikin were performed to investigate the effect of air stability on the dispersion of exhaled flow. Seven cases with the combination of three ventilation patterns (no ventilation, mixing ventilation and displacement ventilation) and two breathing modes (continuous and periodic) were applied. The trajectory of exhaled flow was visualized and measured by smoke visualization and velocity measurement, respectively. The results show that both the continuous and periodic exhalation are significantly affected by the air stability with respect to the trajectory and velocity decay. Meanwhile, the turbulence highly develops in the periodic flow, making the contaminant mix well with the ambient air and the flow flatter in comparison with continuous jet. As the stable condition restrains the upward movement of the flow, it becomes flatter under stable condition compared with neutral condition even though they have similar Ar and body plume. In addition, the velocity decay is smaller for stable condition because it entrains less ambient air.