CHARACTERIZATION OF MIXING PATTERNS IN A VENTILATED AIRSPACE WITH A MULTIPLE AIRFLOW REGIONS GAMMA MODEL

Abstract

A model called the multiple airflow regions gamma model (MARGM)was developed based on a continuous distribution of residence time for predictingthe mixing behavior in a ventilated airspace in that data interpretation andmean residence time calculation for a specified output concentration profilecan also be evaluated. The MARGM takes the form of the two-parameter gammadistribution and accounts for different mixing types: complete mixing, nomixing (piston flow), incomplete mixing, and various combinations of the abovetypes. In these combinations, the different mixing types simulated by theMARGM conceptually represent airflow regions in series. The mixing efficiencywas introduced to characterize the extent or degree of mixing in a ventilationsystem. Mixing efficiency equals zero for piston flow (no mixing), unity forcomplete mixing, and a value in between these two extremes for incompletemixing. The MARGM simulates the combinations of complete mixing, incompletemixing, and piston flow. Therefore, seven models are introduced in this effort:complete mixing model, piston flow model, complete-piston flow model, complete-incomplete-pistonflow model (the general model), complete-incomplete mixing model, incomplete-pistonflow model, and incomplete mixing model. The applicability of models was testedby several case studies. Results show that combination models give betterfitting than other simpler models. The MARGM enables building microenvironmentdesigners reconsider the possibilities and consequences of various forms ofincomplete mixing in investigating indoor air quality problems.