Possible Air Pumping Action in a Room Fire

Abstract

The air pumping effect of a fire plume, proposed years ago, to give a higher air intake rate through vertical openings in a compartment fire is further investigated in this paper. Equations for the air intake rate through vertical openings found in the literature are reviewed. As most of the reported correlation expressions were derived empirically from experiments, results might be different if the fire geometry, fuel type and ambient conditions are different. Furthermore, most of the data on heat release rates in earlier experiments were measured from the mass loss rate of fuel, not by the oxygen consumption method. Values used therefore might deviate from the actual heat release rates. Aerodynamic flow through a doorway, induced by a compartment fire, is commonly simulated by Computational Fluid Dynamics (CFD). Factors which are difficult to control in experiments but affecting the doorway airflow can be studied more easily with CFD.In the study presented in this paper a two-room structure with a fire room connected to an adjacent room through a door was selected. Different door widths linking the two rooms were set to give different ventilation factors. A total number of 16 simulations using the popular CFD software, Fire Dynamics Simulator, based on large eddy simulations, were carried out with different heat release rates of a fire in the fire room. Predicted horizontal velocity components were used to estimate the air intake rates through the door to justify the air pumping action. It appears that there is an air pumping effect of the fire plume for cases with lower ventilation factors, even for pre-flashover fires. Results further confirmed earlier experimental data on post-flashover fires. Therefore, further study on possible air pump effects in a room fire is strongly recommended.