Abstract
This paper presents an analytical model able to explore the design method of natural smoke evacuation through an exhaust vent subject to wind pressure. The proposed model can be used to determine the flow rate of smoke and the optimal section of the exhaust vent according to the geometric parameters of the room, the heat release rate and the pressure exerted by the wind forces at the exhaust vent. The numerical resolutions of the mathematical equations of the model were performed using the dichotomy method. The proposed analytical approach is built progressively by, (i) the examination of interaction forces between buoyancy forces and wind pressure forces, (ii) a numerical validation of the analytical model using the numerical simulation software Fire Dynamics Simulator, and (iii) proposal of a method of approximation of the optimal section of the exhaust vent for a maximum smoke evacuation rate. The results show very satisfactory and provide adequate prediction of the optimal size of the exhaust vent between the theoretical approximation and various configurations of numerical simulation. The feasibility and effectiveness of the proposed approach lead to an accurate and reliable analytical model able to analyze the influence of the size of natural smoke evacuation vents subjected to the pressure of wind forces.
Highlights
Fire safety engineering [1], which identifies the risks and their mitigation, owes its success to modeling the development of flames, fumes and criteria associated with safety objectives such as heat flow, the clearance height, evacuation outside the fumes, heat, gases and unburned products, etc. [1, 2]
The purpose of this study is to propose an analytical model for controlling the design parameters of the smoke exhaust vent under the influence of wind pressures, to improve the fire engineering zone-codes
We can apply Archimedes' theorem to the volume of outside air surrounding the geometry of the studied room to estimate the variation of pressure forces between the smoke exhaust vent surface, which is subject to the forces of the wind, and air inlet opening, which is not subject to the forces of wind pressure
Summary
Fire safety engineering [1], which identifies the risks and their mitigation, owes its success to modeling the development of flames, fumes and criteria associated with safety objectives such as heat flow, the clearance height, evacuation outside the fumes, heat, gases and unburned products, etc. [1, 2]. Natural smoke extraction facilities [5] are fixed equipment that are activated by the effect of thermal ascendancy to evacuate and direct smoke and heat to the outdoors in a controlled way These devices serve to protect buildings in case of excessive heat stress. The analysis process is built by (1) a simulation of a case study, (2) development of an analytical model giving the optimal section of the smoke exhaust vent for a maximum extraction flow while taking into account the wind speed, and Rachid Fakir et al.: Natural Ventilation of Smoke Subject to Wind Pressure within Fire Safety Engineering Approach (3) an analysis of the results of the simulations and discussion, to show the advantages and disadvantages of using zone-codes vis-a-vis CFD codes for different wind speeds
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