NT-87-27-1 — Computation of Discharge Coefficients for Laminar Flow in Rectangular and Circular Openings

An equation was developed to directly compute the discharge coefficient of an opening of arbitrary cross section as a function of the three-dimensional geometry, the pressure difference, the total minor loss coefficient, and the air properties. The experimenta] investigation involved the application of the theory to short rectangular and cylindrical openings with cross-sectional dimensions similar to those common to air infiltration in structures as well as a few cases of natural ventilation. It was determined that the contribution of the flow length to the total resistance of an opening should be included in the modeling of structural leakage. A modeling procedure was developed which may be used to determine the cross-sectional area and the three-dimensional get, hetty of an equivalent straight rectangular opening that would provide the same airflow as the modeled structural leakage component.