Browsing by Author "Karlsson, Bjorn"
Now showing 1 - 2 of 2
Results Per Page
Sort Options
Item Influence of gas species on backdraft probability using a diffusion flame limits criterion(2009-03) Pérez Jiménez, Christian; Franssen, Jean Marc; Karlsson, Bjorn; Tecnalia Research & InnovationBackdraft is a limited-ventilation fire phenomenon closely linked to the unburnt gases accumulated in the fire compartment just before creating an opening that allows a new supply of oxygen to enter the compartment. The aim of this article is to help understanding the influence of gas species such as hydrocarbon CmHn, water, carbon dioxide, oxygen, and nitrogen on backdraft probability. The influence of increasing the number of moles of the above gas species as well as the number of atoms of carbon, hydrogen, and oxygen in the fuel composition is analyzed. For this purpose, a diffusion flame limit criterion based on Le Chatelier's rule is used. In order to verify the obtained results, validation with 41 backdraft experiments is carried out.Item Influence of obstacles on the development of gravity current prior to backdraft(2009) Pérez-Jiménez, Christian; Guigay, Georges Jan; Karlsson, Bjorn; Eliasson, Jonas; Horvat, Andrej; Sinai, Yehuda; Franssen, Jean Marc; Tecnalia Research & InnovationThe phenomenon of backdraft is closely linked to the formation of a flammable region due to the mixing process between the unburned gases accumulated in the compartment and the fresh air entering the compartment through a recently created opening. The flow of incoming fresh air is called the gravity current. Gravity current prior to backdraft has already been studied, Fleischmann (1993, Backdraft phenomena, NIST-GCR-94-646. University of California, Berkeley) and Fleischmann (1999, Numerical and experimental gravity currents related to backdrafts, Fire Safety Journal); Weng et al. (2002, Exp Fluids 33:398-404), but all simulations and experiments found in the current literature are systematically based on a perfectly regular volume, usually parallelipedic in shape, without any piece of furniture or equipment in the compartment. Yet, various obstacles are normally found in real compartments and the question is whether they affect the gravity current velocity and the level of mixing between fresh and vitiated gases. In the work reported here, gravity current prior to backdraft in compartment with obstacles is investigated by means of three-dimensional CFD numerical simulations. These simulations use as a reference case the backdraft experiment test carried out by Gojkovic (2000, Initial Backdraft. Department of Fire Safety Engineering, Lunds Tekniska Högskola Universitet, Report 3121). The Froude number, the transit time and the ignition time are obtained from the computations and compared to the tests in order to validate the model.