Browsing by Author "Franssen, Jean Marc"
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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.Item A Simple Model for the Fire Resistance of Axially Loaded Members - Comparison with Experimental Results(1996-05) Franssen, Jean Marc; Schleich, Jean Baptiste; Cajot, Louis Guy; Azpiazu, Wenceslao; Centros PRE-FUSION TECNALIA - (FORMER)A general model, i.e. a non linear computer code, has been extensively used to determine the buckling load of axially loaded members, considering that the material model behaves at elevated temperatures according to the hypotheses of Eurocode 3 Part 1.2, and the main results of this numerical investigation are summarised in this paper. The main parameters and the results of 59 experimental tests found in the literature are reported, as well as the results of 21 original tests made within this research project. Those test results are used to evaluate the severity factor of the analytical formula deduced from the numerical simulations. This factor is chosen in order to obtain an analytically calculated ultimate load which is, in the average, the same as the experimental load. The ultimate load or ultimate temperature can be determined by the proposed analytical formula or directly by interpolation in tables which give the ratio between the ultimate load and the plastic load at room temperature.