L. Allançon, B. Porterie, R. Saurel and J.C. Loraud
A numerical analysis is given for the prediction of unsteady,two‐dimensional fluid flow induced by a heat and mass source in aninitially closed cavity which is vented when the…
Abstract
A numerical analysis is given for the prediction of unsteady, two‐dimensional fluid flow induced by a heat and mass source in an initially closed cavity which is vented when the internal overpressure reaches a certain level. A modified ICE technique is used for solving the Navier–Stokes equations governing a compressible flow at a low Mach number and high temperature. Particular attention is focused on the treatment of the boundary conditions on the vent surface. This has been treated by an original procedure using the resolution of a Riemann problem. The configuration investigated may be viewed as a test problem which allows simulation of the ventilation and cooling of such cavities. The injection of hot gases is found to play a key role on the temperature field in the enclosure, whereas the vent seems to produce a distortion of the dynamic flow‐field only. When the injection of hot gases is stopped, the enclosure heat transfer is strongly influenced by the vent. A comparison with the results obtained when the radiative heat transfer between the walls of the enclosure is considered, indicate that radiation dominates the heat transfer in the enclosure and alters the flow patterns significantly.
Details
Keywords
D. Morvan, B. Porterie, J.C. Loraud and M. Larini
Reports numerical simulations of an unconfined methane‐air turbulent diffusion flame expanding from a porous burner. Turbulent combustion is simulated using the eddy dissipation…
Abstract
Reports numerical simulations of an unconfined methane‐air turbulent diffusion flame expanding from a porous burner. Turbulent combustion is simulated using the eddy dissipation concept (EDC) which supposes that the reaction rate is controlled by the turbulent structures which enhance the mixing of fuel and oxidant. Two statistical k‐ε turbulence models have been tested: a standard high Reynolds number (HRN) and a more recent model based on the renormalization group theory (RNG). Radiation heat transfer and soot formation have been taken into account using P1‐approximation and transport submodels which reproduce the main phenomena encountered during soot production (nucleation, coagulation, surface growth). The set of coupled transport equations is solved numerically using a high order finite‐volume method, the velocity‐pressure coupling is treated by a projection technique. The numerical results confirm that 20‐25 percent of the combustion heat released is radiated away from the flame. Unsteady and unsymmetrical flame behaviour is observed for small Froude numbers which results from the development of Rayleigh‐Taylor like instabilities outside the flame surface. For higher Froude numbers the steady‐state and symmetrical nature of the solution is recovered.
Details
Keywords
E. Daniel, R. Saurel, M. Larini and J.C. Loraud
This paper investigates the multi‐phase behaviour of dropletsinjected into a nozzle at two separate wall locations. The physical featuresof the droplets (rate of mass, density and…
Abstract
This paper investigates the multi‐phase behaviour of droplets injected into a nozzle at two separate wall locations. The physical features of the droplets (rate of mass, density and radius) at each injector location are identical. This system can be described by a two‐phase Eulerian—Eulerian approach that yields classical systems of equations: three for the gaseous phase and three for the dispersed droplet phase. An underlying assumption in the two phase model is that no interaction occurs between droplets. The numerical solution of the model (using the MacCormack scheme) indicates however that the opposite jets do interact to form one jet. This inconsistency is overcome in the current paper by associating the droplets from a given injection location with a separate phase and subsequently solving equations describing a multiphase system (here, three‐phase system). Comparison of numerical predications between the two‐phase and the multiphase model shows significantly different results. In particular the multiphase model shows no jet interaction.
Details
Keywords
Md Delwar Hossain, Md Kamrul Hassan, Anthony Chun Yin Yuen, Yaping He, Swapan Saha and Waseem Hittini
The purpose of this study is to review and summarise the existing available literature on lightweight cladding systems to provide detailed information on fire behaviour…
Abstract
Purpose
The purpose of this study is to review and summarise the existing available literature on lightweight cladding systems to provide detailed information on fire behaviour (ignitibility, heat release rate and smoke toxicity) and various test method protocols. Additionally, the paper discusses the challenges and provides updated knowledge and recommendation on selective-fire mechanisms such as rapid-fire spread, air cavity and fire re-entry behaviours due to dripping and melting of lightweight composite claddings.
Design/methodology/approach
A comprehensive literature review on fire behaviour, fire hazard and testing methods of lightweight composite claddings has been conducted in this research. In summarising all possible fire hazards, particular attention is given to the potential impact of toxicity of lightweight cladding fires. In addition, various criteria for fire performance evaluation of lightweight composite claddings are also highlighted. These evaluations are generally categorised as small-, intermediate- and large-scale test methods.
Findings
The major challenges of lightweight claddings are rapid fire spread, smoke production and toxicity and inconsistency in fire testing.
Originality/value
The review highlights the current challenges in cladding fire, smoke toxicity, testing system and regulation to provide some research recommendations to address the identified challenges.
Details
Keywords
T. Basset, E. Daniel and J.C. Loraud
Presents validation of the Eulerian approach for unsteady two‐phase flows, whose behaviour depends on the coupling between the two phases, on the basis of the study of…
Abstract
Presents validation of the Eulerian approach for unsteady two‐phase flows, whose behaviour depends on the coupling between the two phases, on the basis of the study of attentuation and dispersion of an acoustic wave propagating into a one dimensional two‐phase flow. This approach and the corresponding numerical aspects are accurate enough for later applications in more complex geometries, where “vortex shedding” phenomena take place. Attenuation and dispersion of a pressure wave in a two‐phase medium of rest was previously studied by Temkin and Dobbins. Present work is an extension of this theory to the case of a two‐phase flow. This theoretical approach leads to a numerical solution of the problem. Compares the derived results with those obtained from a direct numerical simulation based on MacCormack scheme in a finite volume formulation. Verifies that analytical and numerical approaches are in good agreement.
Details
Keywords
Xuehui Wang, Tiannian Zhou, Qinpei Chen and Jian Wang
This study aims to investigate the controlling mechanisms of ambient oxygen and pressure on piloted ignition of solid combustibles under external…
Abstract
Purpose
This study aims to investigate the controlling mechanisms of ambient oxygen and pressure on piloted ignition of solid combustibles under external radiant heating.
Design/methodology/approach
The numerical simulation method was used to model the influence of ambient oxygen concentration on the piloted ignition of a thermally irradiated solid sample in reduced pressure atmospheres. The solid phase decomposition and gas phase kinetics were solved simultaneously.
Findings
It was determined that the elevated oxygen atmospheres resulted in a higher flame temperature and a thicker temperature profile over the solid surface. Also, increasing oxygen and reducing pressure had a similar effect in the decrease of the ignition delay time. The shorter ignition time in reduced pressure was mainly because of the decreasing of convective heat losses from the heated solid. As oxygen was reduced, however, ignition occurred later and with a greater mass loss rate because more volatiles of solid fuel at transient ignition were required to sustain a complete reaction under an oxygen-poor condition.
Research limitations/implications
The results need to be verified with experiments.
Practical implications
The results could be applied for design and assessment of fire-fighting and fire prevention strategies in reduced pressure atmosphere.
Originality/value
This paper shows the effect mechanism of ambient oxygen and pressure on piloted ignition of solid combustibles.