Study and set-up of a wind tunnel for assessing ammonia emissions from the field

Livestock and agricultural activities contribute significantly to atmospheric ammonia emission in Europe. The volatilization process depends on many factors especially the wind speed and rainfall. The most important methods to evaluate ammonia volatilization are the dynamic flux chamber and micrometeorological method. The chambers are more flexible and simple to use in every situation. Few studies have been carried out to determine, which conditions are established inside the tunnel and how they could influence the measurements. For that purpose, in this paper an assessment of the effects of the wind tunnel configuration and flow rate was performed with CFD simulations and wind speed measurements in order to verify that airflow is completely developed. The wind tunnel consists in a mixing chamber situated between a divergent and a convergent duct, on which is possible to mount an axial fan. Each part of the tunnel is equipped with sampling points and measurements were performed with a portable anemometer. During the test the tunnel is flushed with incoming air, for simulating the wind action on the soil surface. Two conditions were accomplished: air blowing and air suction. The vertical profiles of the air velocity in three cross sections were then investigate with more measurements made in the vicinity of the emitting surface. Results of velocity profiles demonstrate that the wind tunnel works better in the air suction conditions, for which there is less influence of the geometry of wind tunnel on the air flux.