Numerical visualization and residence time determination of turbulent reacting duct flow with mass bleed and a backstep on one wall

Liou, Tong‐Miin; Hwang, Po-Wen

doi:10.1016/s0082-0784(98)80515-8

Cited by 6 publications

(2 citation statements)

References 12 publications

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“…Similar numerical studies have been performed in the past few years. Among these, Liou and Hwang [18] used a twodimensional CFD model to study the residence time of tracer particles within the recirculation zone of a backward-facing step. Weller et al [19] applied a large eddy simulation (LES) model to study a premixed turbulent flame stabilized by a backward-facing step.…”

Section: Numerical Modeling and Analysismentioning

confidence: 99%

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Transient application, recirculating pool fire, agent effectiveness screen:

Grosshandler¹,

Hamins²,

McGrattan³

et al. 2001

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NISTIR 6733ii EXECUTIVE SUMMARY * Because of its many positive attributes, halon 1301, or trifluorobromomethane (CF 3 Br), has been used as a fire extinguishing agent in many applications including aircraft, ships, and specialized structures. Due to its high ozone depletion potential, however, world-wide production was halted in 1994. In the search for a long-range replacement, novel types of extinguishing agents and delivery mechanisms are under development. To gauge the suitability of a replacement agent, methods are needed to evaluate the material's suppression effectiveness under conditions that relate to field applications.In this study, a laboratory-scale facility has been developed to screen the suppression effectiveness of agents that are delivered in a transient fashion such as solid propellant gas generators. The transient application, recirculating pool fire (TARPF) agent effectiveness screen features a propane fire stabilized behind an obstruction, which is known to be a highly challenging suppression configuration. The character of the flame and the impact of the air flow, fuel flow, obstruction geometry, and rate of agent addition on the amount of material needed for suppression are evaluated for N 2 , CF 3 Br, and a solid propellant gas generator (SPGG). The importance of the injection process on the flow field and the transport of the agent downstream is examined, and a simple mixing model is used to explain the observed trend of decreasing suppressant mole fraction with increasing injection duration, even for agents as different as CF 3 Br and N 2 . Direct numerical simulation of the suppression event is shown to successfully predict the quantity and rate of N 2 required to extinguish the flame based upon a published global reaction rate for premixed propane/air flame propagation. Important Findings:• The minimum mole fraction of agent for suppression, normalized by the cup burner value, correlates with [1 -exp(-∆ t/ τ )] -1 , where ∆ t is the injection time interval and τ characterizes the mixing time behind the obstacle in the flow.• The general character of the flame and its extinction by a thermal gaseous agent is captured by a direct numerical simulation of the flow based upon single -step chemistry, and numerical experiments have corroborated the simple correlation of the experimental data for N 2 .• The measured difference between the decrease in agent storage bottle pressure and the arrival of the agent at the fire highlight the importance of determining the agent concentration locally and the difficulty in relating changes in bottle pressure to actual mixing conditions. • For the first time, both compressed and solid-propellant generated gases can be compared side by side, and the effect on performance of different formulations, particle loadings and burning rates for various SPGG designs can be unambiguously discriminated.• When the temperature of a hot surface downstream of the pool is above 800 o C, the flame, following suppression, will reignite and stabilize on the hot surface. At ...

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Section: Numerical Modeling and Analysismentioning

confidence: 99%

“…The heat release rate term is (18) where H ∆ is the heat of combustion. Westbrook and Dreyer [24] suggest values for propane of 11 10 6 .…”

Section: Conservation Of Energymentioning

confidence: 99%