Contaminant transport by human passage through an air curtain separating two sections of a corridor: Part II – Two zones at different temperatures

Abstract

Air curtains are installed in open doorways of a building to reduce buoyancy-driven exchange flows across the doorway. Although an air curtain allows an unhampered passage of humans and vehicles, the interaction of this traffic with an air curtain is not well understood. In this study, we investigate the problem of the simultaneous interaction between the air curtain, the wake of a moving person and the buoyancy-driven flow arising due to the density difference across the doorway. To this end, we conduct small-scale waterbath experiments with fresh water and salt water solutions to achieve different fluid densities. As a model of human passage, a vertical cylinder is pulled through a planar jet representing an air curtain and separating two zones at different densities. For a fixed travel distance of the cylinder before and after the air curtain, the average infiltration flux of dense fluid into the light fluid side increases with increasing cylinder velocity. Remarkably, we find that the infiltration flux is independent of the density difference across the doorway and is mainly due to the interaction between the air curtain and the cylinder wake with negligible effects from the buoyancy-driven flow. Furthermore, the infiltration flux is also independent of the travel direction of the cylinder. As a consequence, the sealing effectiveness of an air curtain reduces with an increasing cylinder speed and this reduction is independent of the direction of the buoyancy-driven flow. We provide a theoretical explanation for the observed changes in the effectiveness curve of the air curtain as the function of the deflection modulus. Dye visualisations of the air curtain and the cylinder wake are used to examine the re-establishment process of the air curtain after its disruption by the cylinder. We observe that the re-establishment time of the air curtain and the infiltration in the cylinder wake increases with an increasing cylinder speed.