Discharge Coefficients for Adjustable Slot Inlets Used to Ventilate Animal Production Buildings

The purpose of this study was to empirically determine discharge coefficients (Cd) for inlets with an adjustable baffle and to compare the results with published Cd values and equations for airflow per m of slot length. Two types of baffled inlet were included in the study. One was built so as to direct the air jet across the ceiling, and the other was oriented to direct the air jet down the wall. Experiments were conducted using a model ventilation system that contained the two inlets and several fans to vary the airflow rate. The inlet velocity was measured with a hot wire anemometer and the pressure drop across the inlet was measured using a manometer. The airflow per m (Q/L) was calculated from the data and compared with published equations. In addition, the discharge coefficients were determined for 20 inlets with aspect ratios (w/L) ranging from 0.008 to 0.030. It was found that jet orientation did not influence values of Q/L or Cd as has been accepted for many years. The average discharge coefficient for the baffled inlets was 0.50 for aspect ratios of 0.018 or less and was not significantly different from the literature. For aspect ratios between 0.018 to 0.030 the value of Cd increased from 0.50 to 0.62 based on regression analysis. The results of this study will provide better discharge coefficient estimates for inlet sizing for new buildings and to develop better recommendations for retrofitting existing buildings.