Browsing by Author "Nechab, Khadouma"
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- Dynamics in fire-induced ceiling-jetPublication . Nechab, Khadouma; Piloto, P.A.G.; Abdallah, BenarousThe aim of this thesis is to test the ability of some correlative models to recover both dynamic and thermal characteristics of a fire induced ceiling-jet flow. The flow occurs when the fire plume impinges the ceiling and develops in the radial direction of the fire axis. These correlative models were also compared with a two-zone model (CFAST) and with an advanced calculation method (Computational Fluid Dynamics) for the calculation of the temperature and velocity near the ceiling. These calculations were developed inside an open car park, using different fire events (localized fires). Both temperature and velocity predictions are decisive for sprinklers positioning, fire alarms positions, detectors positions and activation times and back-layering predictions. Simple graphs were depicted for the time of the fire event and another ones were depicted for the maximum value expected during the fire event. Some correlative models agree well with the results obtained with CFAST. The CFD results over predicted the dynamics of the fire events.
- Fire dynamics in open compartmentsPublication . Piloto, P.A.G.; Possoli, Ketlen; Junior, Luiz C.M.; Nechab, Khadouma; Benarous, AbdallahWith the aim to increase fíre safety in open compartments, such as open car parks, some correlative models were used to test the ability to recover both dynamics and thermal characteristics ofa ceiling-jet flow. The flow occurs when the fire plume impinges the ceiling and develops in the radial direction ofthe fire axis. Both temperature and velocíty predictions decisive for sprinklers positioning, fire alarms positions, detectors (heat, smoke) position and activation times and back-layering predictions. This investigation deals with a parametric analysis using different fire events, fíre scenarios and correlative formulations (Alpert, Cooper, Heskestad and Delichatsios, Motevalli and Marks). An advance calculation method (CFAST) based on a two zone model fonnulation was used to compare the results.
- Fire dynamics in open compartmentsPublication . Piloto, P.A.G.; Possoli, Ketlen; Junior, Luiz C.M.; Nechab, Khadouma; Benarous, AbdallahFire events in car parks have been a major problem for buildings,vehicles and humans.The main cause for fire propagation are the combustible materials of the vehicles. Ceiling jet flow occurs when the fire plume impinges the ceiling and develops in the radial direction. Both temperature and velocity prediction sare decisive for sprinklers positioning,fire alarms positions,detectors (heat,smoke) positions and activation times and back-layering predictions.
- Fire dynamics in open compartmentsPublication . Piloto, P.A.G.; Possoli, Ketlen; Junior, Luiz C.M.; Nechab, Khadouma; Benarous, AbdallahWith the aim to increase fire safety in open compartments, such as open car parks, some correlative models were used to test the ability to recover both dynamics and thermal characteristics of a ceiling-jet flow. The heat flow, coming from a burning vehicle, occurs when the fire plume impinges the ceiling and develops in the radial direction of the fire axis. Both temperature and velocity predictions are decisive for sprinklers positioning, fire alarms positions, detectors (heat, smoke) position and activation times and back-layering predictions. This investigation deals with a parametric analysis using different fire events (class of the vehicle) and two fire scenarios. Some correlative formulations were used: Alpert, Cooper, Heskestad & Delichatsios and Motevalli & Marks. An advance calculation method (CFAST) based on a two-zone model formulation was used to compare the results, as well as the CFD software ANSYS Fluent, based on the finite volume method. A total of 16 simulation results were obtained taking into consideration 2 different heights for the compartment (H=3m and H=5m), 4 different car classes (fire events), 6 radial positions (R) and two software (CFAST and ANSYS Fluent). The correlative model from Motevalli & Marks overestimates the dynamic characteristics in small compartments. The two zone model overestimates the maximum temperature in the biggest compartment and the CFD results for temperature and velocity are always higher than the other calculation methods.
- Numerical prediction of the incoming heat fluxes on firefighter protective clothingPublication . Dahamni, Salim; Nechab, Khadouma; Benarous, Abdallah; Piloto, P.A.G.Improving the performances of a firefighter protective clothing requires a better understanding of the conjugated thermal exchanges in the ambient-garment-body assembly [1]. As the protective clothing is believed to ensure, as long as possible, a skin temperature below the injury threshold, it is mandatory to quantify accurately the instantaneous thermal loadings provided by the fire source. Indeed, protective garments are commonly designed for incoming heat flux values that are recorded during isolated tests, under quasi-steady fire conditions [2]. Moreover, the scarce unsteady investigations devoted to heat flux predictions are based on presumed temporal laws for fire heat release and do not account for natural or mechanical ventilation effects on fire development.
- Numerical prediction of the incoming heat fluxes on firefighter protective clothingPublication . Dahamni, Salim; Nechab, Khadouma; Benarous, Abdallah; Piloto, P.A.G.The present study is a numerical attempt for the prediction of the incoming thermal flux on a firefighter protective clothing. The study focuses on ventilation conditions impact on the incident fluxes reaching the external garment’s face. A radiative and convective transfer modelling is considered for a 3D geometry compartment, equipped with a door, a window and subject to a localized fire, with stationary heat release rate (HRR) during a prescribed exposure time. An additive constraint on oxygen mass fraction threshold is considered to account for flame extinction. The outer layer of the protective garment is modeled as a solid medium, featuring both front (chest F) and rear (back R) sensors. The baseline case corresponds to a situation where the external temperature of the protective clothing and that of the fresh air adjacent to the firefighter's body are maintained at 25 °C. Despite the importance of mechanical ventilation devices in smoke clearance and temperature attenuation, critical values for ventilation flow rates may lead to tremendous heat fluxes revealing the apparition of backdraft situations
- Simulação numérica de fluxos de calor recebidos em vestuário de proteção de bombeiroPublication . Dahamni, Salim; Nechab, Khadouma; Benarous, Abdallah; Piloto, P.A.G.Neste estudo é apresentada uma simulação numérica para determinar o fluxo térmico recebido pelo vestuário de proteção individual utilizado pelos bombeiros. O estudo é centrado no impacto das condições de ventilação dos compartimentos nos fluxos incidentes que atingem a superfície exterior do de proteção individual (EPI). É apresentada uma simulação de transferência de calor por radiação e por convecção para um compartimento com geometria definida a três dimensões, constituído por uma porta, uma janela e sujeito a uma fonte de calor ocalizada, caracterizado por uma taxa estacionária de liberação de calor (HRR) durante um tempo de exposição prescrito. É considerada uma restrição aditiva no limiar da fração mássica de oxigênio responsável pela extinção da chama.