Predicting Airflow Rates in the Coarse Layer of Passive Dry Barriers

Laboratory experiments were conducted with steady wind velocities to measure pressure drops in pipes used to ventilate passive dry barriers. Two vent pipe diameters (100 and 150 mm) and several pipe end geometries were tested. Nondimensional ventilator equations were developed using the pressure drop data that, when combined with Darcy’s law, can be used to estimate airflow rates in passive dry barriers. A field experiment was conducted to verify the laboratory results. Comparisons were also made between flow rates predicted using the airflow rate equations and flow rates measured in two field-scale tests of dry barriers, one of which was constructed by the writers. Results of the laboratory tests indicate that a unique ventilator equation exists for each pipe end geometry, and that more than one equation may exist if the pipe end is not symmetrical (i.e., the pressure drop depends on wind direction relative to the pipe end). The field experiment indicated that the equations developed based on the laboratory data are in general agreement with average field conditions, but more scatter exists in the field due to varying wind velocities. Good correspondence exists between predicted flow rates and those measured in the field scale tests of passive dry barriers.