Modeling Ammonia Mass Transfer Process from a Model Pig House Based on Ventilation Characteristics

Abstract

Airflow characteristics above the emission surface inside animal houses play an important role in gaseous and odor emissions. The influence of airflow characteristics, i.e., air velocities and turbulence intensities, on ammonia mass transfer processes were investigated in a model of a finishing pig house. The 1:6 scale model was 1750 1000 605 mm (L W H) and had two sidewall inlets and an exhaust opening in the middle of the ceiling. Different airflow characteristics were generated by using three ventilation control strategies: constant inlet opening area, constant inlet velocity, and constant inlet momentum. Due to the symmetrical nature of the airflow pattern in the scale model, the investigation was conducted in left half of the model. Nonlinear modeling simulated the ammonia mass transfer coefficient (AMTC) as a function of airflow characteristics and jet momentum number. Changes in ventilation control strategies, given the variation of floor air characteristics, changed the ammonia emissions and AMTC. The mean floor air velocities and the root mean square of the floor air velocity fluctuations were correlated to the jet momentum number to the power of 0.56 and 0.54, respectively. AMTC increased proportionally to floor air velocity and turbulence intensity. The AMTC values determined in this experiment were compared to a published study using a 1:12.5 scale model. The correlation of AMTC and jet momentum number for the two models was similar. The relationships obtained in this study could be helpful in understanding the airflow characteristics in the floor region and simulating emission rates from pig houses, while the dependence of AMTC on jet momentum number was confirmed for two different scale models. There is a need to validate it in full-scale houses since the presence of pigs, slatted floors, and porous partitions could alter the relationship of jet momentum number with AMTC.