Effect of velocity non-uniformity of supply air on the mixing characteristics of push-pull ventilation systems

The aim of this paper is to investigate the effect of the supply air velocity profile and direction on the mixing characteristics of push-pull ventilation systems. An experiment was set up to validate the numerical simulation. Then, numerical simulations were performed to investigate five velocity profile models (uniform, parabolic, linear-down, linear-up and side) and four flow direction models. Mixing fraction e and mixing rate(-) epsilon were proposed as evaluating indexes of the mixing amount of ambient air. The simulation results indicated that the mixing fraction distribution can visually show the mixing characteristics of the ambient air under different air supply conditions. Secondly, when there is airflow escape at the pull hood, the effect of the supply air velocity profile and direction on the mixing amount should be taken seriously. On the other hand, when there is no airflow escape, the mixing amount along the flow path increases linearly, and the effect of the velocity profile and direction on the mixing amount is small. Finally, the mixing amount along the flow path has a minimum value at a certain flow ratio. The results of the present study have certain guiding significance for the design of push-pull ventilation systems. (C) 2019 Elsevier Ltd. All rights reserved.