Experimental determination of the discharge flow coefficient at a doorway for fire induced flow in natural and mixed convection

摘要

The study is an experimental investigation of the discharge flow coefficient at a doorway-type opening in the case of a fire in an enclosure open to atmosphere. Natural and mixed convection flows are considered with the use of mechanical ventilation. The discharge coefficient is defined as the ratio between the effective flow rate determined experimentally and a theoretical flow rate based on a Bernoulli approach. The effective mass flow rate is obtained from velocity field measured with stereoscopic particle image velocimetry technique. The theoretical flow rate is calculated from vertical temperature profiles measured from both sides of the doorway. Only inflow rate is considered for the calculation of the discharge coefficient. In natural convection mode, a C-D value of 0.54 +/- 0.5 is obtained on a reduced-scale opening (to be compared with 0.68 at large scale). In a mixed convection case, the discharge coefficient is much lower and reaches 0.26 +/- 0.06. This study shows that the discharge coefficient C-D may vary significantly regarding the dimension of the opening and the flow conditions (natural and mixed convection). It illustrates the limits of considering a constant discharge coefficient when dealing with doorway flows in a confined and mechanically ventilated compartment. Copyright (c) 2014 John Wiley & Sons, Ltd.