Investigating a selection of mixing times for transient pollutants in mechanically ventilated, isothermal rooms using automated computational fluid dynamics analysis

Abstract

a b s t r a c tUnderstanding mixing times for transient pollutants in mechanically ventilated rooms is important for resilience and safety planning for accidental releases of toxic material. There is a lack of information on the ability of simple models available to predict these times for ventilated spaces with different geometries and ventilation configurations. Three analytical mixing time models, including a novel jet transit based approach, have been selected for comparison with computational fluid dynamics (CFD) predictions for a wide range of cuboidal rooms with ceiling ventilation. A modelling tool has been developed, using open source and open source based software, to automatically build and run a large number of Reynolds averaged Navier-Stokes CFD models. The tool has been used to study the dependence of the chosen mixing metrics on room geometry and ventilation parameters, such as the air change rate, for a transient pollutant entering the room via the ventilation system. The room volume, shape, air change rate and vent layout were varied for each room using a Sobol sequence experimental design. The CFD tool has been used to assess the validity of the analytical mixing time models and to derive parameters for the scenarios of interest.Crown

The effect of the contaminant emission rate on the velocity field and contaminant distribution with the presence of an obstacle in a large space

“…It is unrealistic to assume that the pollutant concentration is well-mixed due to the dimensions for large spaces. The significant spatial variations in contaminant concentration have been investigated in many studies in manufacturing plants and other laboratory experiments [1][2][3][4][5]. However, the effect of gas buoyancy is rarely taken into account, which will influence the flowfield and the concentration field.…”