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 predicting the mixing behavior in a ventilated airspace in that data interpretation and mean residence time calculation for a specified output concentration profile can also be evaluated. The MARGM takes the form of the two-parameter gamma distribution and accounts for different mixing types: complete mixing, no mixing (piston flow), incomplete mixing, and various combinations of the above types. In these combinations, the different mixing types simulated by the MARGM conceptually represent airflow regions in series. The mixing efficiency was introduced to characterize the extent or degree of mixing in a ventilation system. Mixing efficiency equals zero for piston flow (no mixing), unity for complete mixing, and a value in between these two extremes for incomplete mixing. The MARGM simulates the combinations of complete mixing, incomplete mixing, and piston flow. Therefore, seven models are introduced in this effort: complete mixing model, piston flow model, complete-piston flow model, complete-incomplete-piston flow model (the general model), complete-incomplete mixing model, incomplete-piston flow model, and incomplete mixing model. The applicability of models was tested by several case studies. Results show that combination models give better fitting than other simpler models. The MARGM enables building microenvironment designers reconsider the possibilities and consequences of various forms of incomplete mixing in investigating indoor air quality problems.

Keywords:

• Mixing
• Indoor air quality
• Residence time distribution
• Ventilation

Acknowledgments