Experimental study on flow behavior of breathing activity produced by a thermal manikin

Breathing is the most common but essential activity of human body. People can't leave without breathing. The breathable air quality around the occupant should be maintained high to avoid the respiratory diseases transmission. This paper reports an experimental study on the flow behavior of breathing activity produced by a thermal manikin. Measurements were performed in the breathing zone of the manikin by employing particle image velocimetry (PIV) system, and the temporal and spatial distributions of breathing airflows both with and without the convective boundary layer (CBL) were characterized by use of phase averaging approach. In addition, a quadruple decomposition methodology extended from proper orthogonal decomposition (POD) was adopted to divide the instantaneous flow fields of breathing airflows into four parts, the flow characteristics as well as cycle-to-cycle variations upon each part studied respectively. The results showed that the breathing flow at different phases presented different flow behaviors during breathing process. CBL had a larger influencing area and played a key role in promoting the upward spread and transmission of exhaled contaminants, which cause the inhaled flow mainly come from more the lower jaw region and block the contaminants inhaled from other directions, thus reducing the risk of infection. It was found through the POD results that CBL enlarged the scale and magnified the energy of coherent structures at the transition stage between expiration and inspiration, and the large scale coherent structures were dominant and made more contribution to the contaminant dispersion in the entire breathing process.