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Comparison of mathematical models for exposure assessment with computational fluid dynamic simulation
J S Bennett1, C E Feigley, J Khan
1Department of Environmental Health Sciences, University of South Carolina, Columbia, USA.
Applied Occupational and Environmental Hygiene
|March 11, 2000
Summary
Mathematical models for estimating airborne contaminant exposure have limitations. This study compared three models (CM-1, CM-2, UD) against computational fluid dynamics (CFD), finding UD most accurate for breathing zone concentrations near the source.
Area of Science:
- Occupational hygiene
- Environmental engineering
- Industrial toxicology
Background:
- Airborne contaminant exposure is traditionally assessed via air or biological monitoring.
- Mathematical models are increasingly used in occupational settings for exposure assessment, process design, and epidemiological studies.
- However, the accuracy of these models, which simplify airflow and contaminant transport, has not been systematically evaluated.
Purpose of the Study:
- To systematically evaluate the errors of single-zone completely mixed (CM-1), two-zone completely mixed (CM-2), and uniform diffusivity (UD) models.
- To compare model predictions against detailed concentration fields generated by computational fluid dynamics (CFD).
- To assess model performance under various source locations, ventilation rates, and emission profiles.
Main Methods:
- Computational fluid dynamics (CFD) simulations were performed using Fluent V4.3 to generate detailed workroom concentration fields.
- Numerical experiments included factorial combinations of source locations, dilution air flow rates, and emission rate profiles (constant and time-varying).
- Exposure estimates from CM-1, CM-2, and UD models were compared against CFD predictions to quantify model "error".
Main Results:
- Exposure estimates were dependent on receptor and source location for both constant and time-varying emission sources.
- For constant sources, ventilation rate did not significantly impact CM-1 model error.
- The uniform diffusivity (UD) model demonstrated the closest agreement with CFD for near-source breathing zone concentrations, while CM-1 performed better for a broader plane of possible breathing zones.
- CM-2 showed intermediate agreement, and CM-1 underestimated near-source exposure.
- For time-varying sources, CM-1 model error decreased with increasing ventilation rate.
Conclusions:
- Different mathematical models exhibit varying degrees of accuracy when compared to CFD simulations.
- The UD model shows promise for accurately estimating near-source breathing zone concentrations.
- Model error is influenced by source characteristics, receptor location, and ventilation rates, particularly for time-varying emissions.