Numerical simulation of particulate matter emissions from mechanically ventilated swine barns

摘要

Numerical modeling using computational fluid dynamics (CFD) was applied to predict the transport of particulate matter (PM) in a mechanically ventilated airspace. A three-dimensional model was used to predict the PM concentrations and air velocities at selected locations within the ventilated space using two turbulence models (standard and realizable k-epsilon models) and particle tracking methods (time-averaged and stochastic tracking). The PM concentrations predicted using the realizable k-epsilon model and stochastic particle tracking showed better agreement with experimental data than the standard k-epsilon model and time-averaged particle tracking. The PM concentrations and air velocities at selected points within the exhaust duct were also predicted. The calculated normalized mean square error (NMSE) values ranged from 0.012 to 0.021, indicating close agreement between the corresponding predicted and measured values. The modeling parameters were applied to determine the PM emission rates from a typical swine barn ventilated by a bank of fans. The PM emission rates were calculated based on PM concentrations determined: (a) inside the exhaust duct, (b) at regions near the exhaust, and (c) along the alley. Emission rates based on PM concentrations determined at locations within the barn other than the exhaust could differ (by as much as 40%) from PM emission rates determined at the exhaust. Numerical simulation showed that one possible approach to the measurement of PM emission rates from mechanically ventilated swine barns equipped with multiple fans would be to determine the PM emission rate at one exhaust fan and estimate the emission rates in the other fans based on the airflow rate ratios between the fans.