Airflow and concentration characterisation and ammonia mass transfer modelling in wind tunnel studies

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 m2 cross section wind tunnel at 0.1–0.4 m s−1 mean wind velocities and 11%–30% reference turbulence intensities. A 0.1-m thick ammonia concentration boundary layer and 0.03–0.1 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.

Research highlights
► Wind velocities and turbulence intensities inversely correlated in wind tunnel.
► Thickness of ammonia concentration boundary layer approximated 0.1 m above emission surface.
► Ammonia mass transfer affected by wind tunnel size.