Research Paper Airflow and concentration characterisation and ammonia mass transfer modelling in wind tunnel studies Chayan Kumer Saha a, *, Guoqiang Zhang a , Ji-Qin Ni b a Department of Biosystems Engineering, Faculty of Agricultural Sciences, Aarhus University, Blichers Alle 20’, P.O. Box 50, 8830 Tjele, Denmark b Department of Agricultural and Biological Engineering, Purdue University, 225 S University Street, West Lafayette, IN 47906, USA article info Article history: Received 2 March 2010 Received in revised form 27 August 2010 Accepted 24 September 2010 Published online 25 October 2010 Ammonia mass transfer was modelled by investigating the airflow characteristics above ammonia release surfaces in a wind tunnel and evaluating the effect of wind tunnel dimensions on ammonia emission and the mass transfer process. A laboratory experiment was conducted using a 0.35  0.35 m 2 cross section wind tunnel at 0.1e0.4 m s 1 mean wind velocities and 11%e30% reference turbulence intensities. A 0.1-m thick ammonia concentration boundary layer and 0.03e0.1 m thick wind velocity boundary layers were observed at the tested velocities and turbulence intensities. Increases in wind velocity did not significantly affect ammonia concentration profiles, but they reduced tunnel outlet ammonia concentrations and increased emissions. An inverse-relationship between turbulence intensities and wind velocity was also observed. The highest turbulence intensities were located close to the ammonia release surface where wind velocities were the lowest. An ammonia mass transfer coefficient model was developed as a function of wind velocity and turbulence intensity. Comparisons with two similar studies revealed that characteristics of wind velocity and ammonia emission were significantly affected by wind tunnel geometric dimensions. ª 2010 IAgrE. Published by Elsevier Ltd. All rights reserved. 1. Introduction Ammonia (NH 3 ) in and from animal houses at high concen- trations and emission rates is one of the most important agricultural environmental problems related to human and animal health since it causes ecological damage, loss of nitrogen from manures as fertiliser, causes changes in biodi- versity, and produces malodorous emissions (e.g., Aneja et al., 2008; Bull & Sutton, 1998; Portejoie, Martinez, & Landmann, 2002; Webb et al., 2005). Approximately 50% of the NH 3 emis- sions in the Netherlands, Denmark, and France were estimated as coming from pig housing and slurry storage (van der Peet-Schwering, Aarnink, Rom, & Dourmad, 1999). Ammonia release from liquid slurry in animal buildings and open fields is a process of convective mass transfer that allows dissolved ammonia to be transferred from immediate liquid surface into free air stream. Ammonia emission is a process of ammonia emanating from an enclosure, to outside the enclo- sure or to atmosphere (Ni, 1999). Identification and quantifi- cation of different factors that are involved in these processes are important for modelling agricultural ammonia emissions and helping to develop emission abatement technologies. Significant progress in studying ammonia transfer from liquid animal slurry has been made since the first research was conducted in the early 1970s (Hashimoto & Ludington, 1971). Transfer of gaseous ammonia from the immediate * Corresponding author. Tel.: 45 30318008. E-mail addresses: chayan.saha@agrsci.dk (C.K. Saha), Guoqiang.zhang@agrsci.dk (G. Zhang), jiqin@purdue.edu (J.-Q. Ni). Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/issn/15375110 biosystems engineering 107 (2010) 328 e340 1537-5110/$ e see front matter ª 2010 IAgrE. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.biosystemseng.2010.09.007