Scale model experiments to determine the effects of internal airflow and floor design on gaseous emissions from animal houses

摘要

Odours and gases emitted from animal houses are strongly related to airflows. Knowledge of the exchange mechanisms between air and the manure surface in the slurry pit, and between air and the soiled surfaces and animals within the building may lead to novel and efficient ways of reducing the odour emission. To investigate the effects of airflow patterns, and floor and slurry channel designs, on gaseous emissions, four 1:10 scale models were bui each identical except for their floor and slurry channel layouts. The floor types investigated were two configurations of partly solid and two configurations of fully slatted floors. Ammonia water was circulated from a storage tank to a reservoir of ammonia water at the bottom of each model with an air space between the water surface and the floor. Provision was made for enough ammonia to be available for prolonged evaporation. Ventilation air was supplied under the ceiling at one end wall. The air outlet was placed in the ceiling halfway between the two end walls and about 1/3rd from one of the sidewalls. Ammonia concentration was measured in the outlet air. The results showed that the average NH sub(3) concentration in the outlet air was significantly affected by the different airflow patterns created by the floor type and slurry channel layout. Using a partly solid, dry floor as a reference the effect of soiling the solid floor resulted in more than double the NH sub(3) concentration in the outlet air. The use of fully slatted floors with slurry channels parallel to the supply air jet resulted in a 57% increase in the emission values compared with the reference model whilst using slurry channels under the fully slatted floor perpendicular to the supply air jet increased the emission values by only 22%. It is hypothesised that the effects on gas emissions are as a consequence of changing airflow patterns and different types of flow in the boundary layer between the slurry and ventilation air. The results from the scale model experiments need to be validated with full-scale experiments.