Transactions of the ASABE Vol. 55(4): 1597-1607 © 2012 American Society of Agricultural and Biological Engineers ISSN 2151-0032 1597 MODELING AMMONIA MASS TRANSFER PROCESS FROM A MODEL PIG HOUSE BASED ON VENTILATION CHARACTERISTICS C. K. Saha, G. Zhang, P. Kai 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 ve- locity, and constant inlet momentum. Due to the symmetrical nature of the airflow pattern in the scale model, the investi- gation 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, giv- en 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 val- ues 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. Keywords. Air velocity, Ammonia emission, Jet momentum number, Model pig house, Turbulence intensity, Ventilation rate. mmonia emissions to the atmosphere are envi- ronmentally important, not only because of the effects of air pollutants in the atmosphere but al- so because of the undesirable ecological effects of nitrogen compounds when deposited onto land and water bodies (Phillips et al., 2000). Approximately 75% of the ammonia emissions in Europe originate from livestock production (Webb et al., 2005). In the Netherlands, Den- mark, and France, approximately 50% of the NH 3 emis- sions from pig production are from pig housing and slurry storage (van der Peet-Schwering et al., 1999). In Denmark as in other countries, the floors of pig pens are fully or par- tially slatted, with shallow slurry pits underneath. Thus, an understanding of the processes leading to ammonia emis- sions is critical in order to reduce the potential environmen- tal impact of livestock production. Ammonia is mainly re- leased from the surface of the slurry (Sommer et al., 2006) and the fouled floor surfaces. Ammonia gas at the liquid-air interface is transported through the laminar boundary layer by molecular diffusion and then by turbulent diffusion and advection (Ni, 1999; Sommer et al., 2006). The transfer of gas between the slurry surface and the airstream depends mainly on the dynamic structure of the flow in the bounda- ry layer (Bird et al., 2007) and the airflow pattern (Morsing et al., 2008). The airflow pattern is affected by several fac- tors, such as ventilation rate (Strom et al., 2002), inlet air- jet momentum (Zhang et al., 2008), floor design (Morsing et al., 2008), height of the pit headspace (Buiter and Hoff, 1998; Ye et al., 2008a), partitions in the room, heat pro- duced by the animals, and animal behavior (Bjerg et al., 2000; Zhang and Strom, 1999). The effects of air velocity and air temperature on am- monia emission in a scale model of a dairy cow house were evaluated by Elzing and Monteny (1997) and Wang et al. (2006). Morsing et al. (2008) found that the ammonia emission was significantly affected by the different airflow patterns created by the floor type and the slurry channel layout. The mass transfer coefficient increased as the venti- lation rate increased, and the turbulence intensity had a significant effect on the mass transfer coefficient at lower Submitted for review in December 2010 as manuscript number SE 8945; approved for publication by the Structures & Environment Divi- sion of ASABE in June 2012. The authors are Chayan Kumer Saha, Doctoral Student, Department of Engineering, Aarhus University, Aarhus, Denmark, Research Scientist, Department of Engineering for Livestock Management, Leibniz Institute for Agricultural Engineering Potsdam-Bornim (ATB), Postdam, Germany, and Associate Professor, Department of Farm Power and Machinery, Bangladesh Agricultural University, Mymensingh, Bangladesh; Guoqiang Zhang, Senior Scientist, and Peter Kai, ASABE Member, Scientist, De- partment of Engineering, Aarhus University, Aarhus, Denmark. Corre- sponding author: Guoqiang Zhang, Department of Engineering, Faculty of Sciences and Technology, Aarhus University, Blichers Alle 20, 8830 Tjele, Denmark; phone: +45-8715-7735; e-mail: guoqiang.zhang@ agrsci.dk. A