VENTCF2: An algorithm and associated FORTRAN 77 subroutine for calculating flow through a horizontal ceiling/floor vent in a zone-type compartment fire model

An algorithm and associated FORTRAN 77 subroutine, called VENTCF2, for calculating the effects on two-layer compartment fire environments of the quasi-steady flow through a circular, shallow (i.e. small ratio of depth-to-diameter), horizontal vent connecting two spaces is presented. The two spaces can be either two inside rooms of a multi-room facility or one inside room and the outside ambient environment local to the vent. The flow is determined by consideration of standard orifice-type flows driven by cross-vent pressure differences and, when appropriate, the combined pressure- and buoyancy-driven flows which occur when the density configuration across the vent is unstable, i.e. a relatively cool, dense gas in the upper space overlays a less dense gas in the lower space. The algorithm calculates rates of flow exchange between the two spaces based on previously reported model equations. Characteristics of geometry and the instantaneous environments of the two spaces are assumed to be known and specified as inputs. Outputs calculated are the rates and properties of the vent flow at the elevation of the vent as it enters the top space from the bottom space and/or as it enters the bottom space from the top space. Rates of mass, enthalpy and products of combustion extracted by the vent flows from upper and lower layers of inside room environments and from outside ambient spaces are determined explicitly. VENTCF2 is an advanced version of the algorithm /subroutine VENTCF in that it includes an improved theoretical and experimental basis. The subroutine is completely modular and it is suitable for general use in two-layer, multi-room, zone-type fire model computer codes. It has been tested numerically over a wide range of input variables and the results of some of these tests are described.