Study of the importance of non-uniform mass density in numerical simulations of fire spread over MDF panels in a corner configuration

Zeinali, Davood; Gupta, Ankur; Maragkos, Georgios; Agarwal, G. S.; Beji, Tarek; Chaos, Marcos; Wang, Yi; Degroote, Joris; Merci, Bart

doi:10.1016/j.combustflame.2018.11.020

Cited by 29 publications

(15 citation statements)

References 32 publications

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“…Nine layers is therefore considered a good representation of the density profile of MDF. The increase in mass loss rate by 9% for 9 layers and 12% for 18 layers is in good agreement with Zeinali et al [46]. In an independent study, published during the review of this paper, they found that simulations of the heat release rate of MDF in a corner test increases by 20% when taking into account the non-uniform density.…”

Section: Influence Of Non-uniform Density At Two Different Moisture Csupporting

confidence: 89%

Ignition and Burning of Fibreboard Exposed to Transient Irradiation

et al. 2020

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Natural materials like wood are increasingly used in the construction industry, making the understanding of their ignition and burning behaviour in fires crucial. The state of the art of wood flammability is based mostly on studies at constant heating. However, accidental fires are better represented by transient heating. Here, we study the piloted ignition and burning of medium density fibreboard (MDF) under transient irradiation. Experiments are conducted in a Fire Propagation Apparatus under parabolic heat flux pulses with peak irradiation ranging from 30 to 40 kW/m 2 and time-to-peak irradiation from 160 to 480 s. The experimental results reveal that the critical conditions for ignition of fibreboard vary over wide ranges: mass flux between 4.9 to 7.4 g/m 2-s, surface temperature between 276 to 298°C, and heat flux between 29 to 40 kW/m 2. Flameout conditions are studied as well, with observations of when it leads either to extinction or to smouldering combustion. We explored the experiments further with a one-dimensional pyrolysis model in Gpyro and show that predictions are accurate. Assuming a non-uniform density profile (a realistic assumption) improves the predictions in comparison to a uniform density profile by increasing the mass loss rate by 12%, decreasing the temperatures by 45%, and increasing the ignition time by 20 s. These results further support previous findings that a single critical condition for igntion or flameout established under constant irradiation does not hold under transient irradiation which indicates that ignition and extinction theories need improvements.

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Section: Influence Of Non-uniform Density At Two Different Moisture Csupporting

confidence: 89%

Ignition and Burning of Fibreboard Exposed to Transient Irradiation

et al. 2020

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“…The effect of mass transpiration (i.e., blockage of convective heat transfer with increasing mass transfer rates) has been reported experimentally in the past for upward spread scenarios over vertical PMM slabs [20]. Additionally, the inclusion of mass transpiration effects has also been considered when modelling flame spread using the approaches based on the law of the wall (e.g., [50]), based on the stagnant film theory (e.g., [12]) as well as on the convective heat transfer model of FireFOAM 2.2.x (e.g., [61][62][63]).…”

Section: Blowing Effectmentioning

confidence: 99%

“…whereṁ pyrol is the mass loss rate due to pyrolysis of the solid fuel,q c, laminar = −αρc p ∂T ∂s is the convective heat flux calculated based on the molecular thermal diffusivity (positive for heating up of the wall, i.e., T g > T w ), s is the direction normal to the wall,q c, threshold is a threshold value (e.g., in the range of 0.5 kW/m 2 [61]),q c, f lame is the maximum value (e.g., in the range of 15 kW/m 2 [61]) of the convective heat flux without mass transfer (i.e., calculated based on an average temperature difference and a convection coefficient value) and f blowing is a correction for the 'blowing' effect (i.e., see Section 4.2). This approach, does not directly take into account the local properties of the flow and considers that the convective heat fluxes remain relatively constant with elevation (i.e., the convective heat transfer coefficient, h, is not calculated).…”

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confidence: 99%

“…The first part of the wall function is employed in the early stages of flame spread when pre-heating of the virgin material occurs and there is no (substantial) burning. In this case, a linear function will assign a fraction of the a priori-determined convective heat flux in the fuel surface based on the fire intensity (i.e., determined by the resolved convective heat flux) in this area [61,62]. The convective heat transfer approach used in FireFOAM 2.2.x has some deficiencies.…”

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confidence: 99%

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Review of Convective Heat Transfer Modelling in CFD Simulations of Fire-Driven Flows

Maragkos

Beji

2021

Applied Sciences

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Progress in fire safety science strongly relies on the use of Computational Fluid Dynamics (CFD) to simulate a wide range of scenarios, involving complex geometries, multiple length/time scales and multi-physics (e.g., turbulence, combustion, heat transfer, soot generation, solid pyrolysis, flame spread and liquid evaporation), that could not be studied easily with analytical solutions and zone models. It has been recently well recognised in the fire community that there is need for better modelling of the physics in the near-wall region of boundary layer combustion. Within this context, heat transfer modelling is an important aspect since the fuel gasification rate for solid pyrolysis and liquid evaporation is determined by a heat feedback mechanism that depends on both convection and radiation. The paper focuses on convection and reviews the most commonly used approaches for modelling convective heat transfer with CFD using Large Eddy Simulations (LES) in the context of fire-driven flows. The considered test cases include pool fires and turbulent wall fires. The main assumptions, advantages and disadvantages of each modelling approach are outlined. Finally, a selection of numerical results from the application of the different approaches in pool fire and flame spread cases, is presented in order to demonstrate the impact that convective heat transfer modelling can have in such scenarios.

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“…The approach also considers mass transpiration effects which tend to reduce the convective heat flux in regions where there is mass transfer. Consideration of mass transpiration effects, while modelling of convective heat transfer, has been included to a certain extent in the literature in the past (e.g., [8,9,10]) but is not necessarily standard practice in fire modelling (e.g., it is not considered by default in FDS [11]). Additional modelling aspects can also be important with respect to accurate (convective) heat flux predictions.…”

Section: Introductionmentioning

confidence: 99%