Numerical modeling of melting and dripping process of polymeric material subjected to moving heat flux: Prediction of drop time

Kim, Yangkyun; Hossain, Akter; Nakamura, Yuji

doi:10.1016/j.proci.2014.05.068

Cited by 34 publications

(19 citation statements)

References 7 publications

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“…In the microgravity environment like spacecraft, the melts would not flow away from the flame, but form a spherical shape under the surface tension force 18 , 19 . Only limited numerical works have simulated the dripping behaviors in the wire 20 , 21 and façade panel 10 , but most of them did not include the condensed-phase pyrolysis and gas-phase flame, because of the complexity.…”

Section: Introductionmentioning

confidence: 99%

Critical Drip Size and Blue Flame Shedding of Dripping Ignition in Fire

Huang

2018

Sci Rep

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Dripping of molten fuels is a widely observed fire phenomenon, and, by igniting other fuels, it can promote fire spread and increase fire hazards. In this work, dripping phenomena from fires of horizontally oriented wires, coated with polyethylene (PE), are investigated in the laboratory. It is found that as long as a flame is attached to the drip, thin tissue paper can be ignited by a single drip. Below a minimum diameter (Dmin = 0.63 mm), the drip floats up. Above a critical diameter (Dcrt = 2.3 mm), a flame can remain attached to the drip and ignite tissue paper as it falls through a distance of at least 2.6 m, thereby posing a significant fire hazard. A falling burning drip appears to the eye to be a blue chain of flame as a result of persistence of vision. Photographic evidence identifies a flame-shedding process, most likely associated with continual sequential ignition of fuel vapor within a von Karman vortex street generated behind the falling burning drip. The frequency of flame shedding agrees with both the frequency of modeled vortex shedding and the frequency of the unexpected sound that is heard during the process. This is the first time that combustion characteristics of dripping fire phenomena have been studied in detail, and this helps to better evaluate the risk and hazards of wire and façade fires.

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Section: Introductionmentioning

confidence: 99%

Critical Drip Size and Blue Flame Shedding of Dripping Ignition in Fire

Huang

2018

Sci Rep

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“…Namely, the drop weight depends on the surface tension. The simulations also demonstrate that the dimensionless drop time is linearly correlated with Ca 0.5 /Bond 2 based on a balance between the resistance force (eg, surface tension force acting on the polymer‐air interface and the viscous force in the molten polymer) and the gravitational force, where Ca is the capillary number representing the relative effect of the viscous force versus the surface tension and Bond is the modified Bond number representing force balance between the surface tension and the gravity …”

Section: Introductionmentioning

confidence: 78%

“…Hence, the magnitude of resistance force determines the weight of small drop. The 2‐dimensional numerical simulation results for polymers of random chain scission based on Newtonian fluid assumption reveal that the competition between the surface tension and gravitational force is dominating in the determination of drop volume, whereas the role of viscosity in drop volume is negligible in comparison . Namely, the drop weight depends on the surface tension.…”

Section: Introductionmentioning

confidence: 99%

“…18 Based on the hypothesis that the dripping Newtonian fluid assumption reveal that the competition between the surface tension and gravitational force is dominating in the determination of drop volume, whereas the role of viscosity in drop volume is negligible in comparison. 19 Namely, the drop weight depends on the surface tension. The simulations also demonstrate that the dimensionless drop time is linearly correlated with Ca 0.5 /Bond 2 based on a balance between the resistance force (eg, surface tension force acting on the polymer-air interface and the viscous force in the molten polymer) and the gravitational force, where Ca is the capillary number representing the relative effect of the viscous force versus the surface tension and Bond is the modified Bond number representing force balance between the surface tension and the gravity.…”

Section: Introductionmentioning

confidence: 99%

“…The simulations also demonstrate that the dimensionless drop time is linearly correlated with Ca 0.5 /Bond 2 based on a balance between the resistance force (eg, surface tension force acting on the polymer-air interface and the viscous force in the molten polymer) and the gravitational force, where Ca is the capillary number representing the relative effect of the viscous force versus the surface tension and Bond is the modified Bond number representing force balance between the surface tension and the gravity. 19 Similarly, the large-size dripping should also rely on the balance between the gravity and the forces resisting the deformation driven by the gravity. In this study, we developed a pendant experiment to assess the ability of polymer strand to resist its gravity.…”

Section: Introductionmentioning

confidence: 99%

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Development of a pendant experiment using melt indexer for correlation with the large‐size dripping in the UL‐94 test

et al. 2018

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Summary The dripping phenomena affect fire hazards significantly. In the UL‐94 test, the dripping has been classified into the small‐size dripping due to surface melting and the large‐size dripping originating from bulk softening. Both types of dripping result from the gravity resisted by the forces including the viscous force. Based on the mechanical mechanism, a pendant experiment to reflect the ability of polymer melt to resist the gravity and a simple model equation were developed. The pendant experimental data of 7 polymers verified the model equation, and the regressed model parameter values of activation energy were close to reported data to some extent for most polymers. Correlations between the predicted pendant mass and the dripping behavior featured by the maximum drop mass showed that the pendant mass predicted at the glass transition temperature was proportional to the maximum drop mass. For polymers of large‐size dripping, the pendant mass predicted at typical decomposition temperatures such as the onset decomposition temperature was generally proportional to the maximum drop mass. Moreover, the model equation indicated that for the large‐size dripping the product of drop mass and first dripping time should be proportional to the specimen thickness, which was verified by reported dripping data.

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Melt dripping behavior in the process of flame spread over energized electrical wire at different pressures

Wang

Wei

et al. 2019

Fire and Materials

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SummaryMelt dripping of polymer insulation in electrical wires is impacted by some factors, such as ambient pressure and electric current. The motivation of this paper is to investigate and discuss the effect of these factors on melt dripping characteristics in the process of flame spread over electrical wire. The results show that the number of dripping times and dripping frequency generally increase with ambient pressure reduced. No dripping phenomenon occurs when the ambient pressure is below 40 kPa at any electric current or is above 70 kPa without electric current applied. There is a good parabolic correlation between the ambient pressure and dripping frequency. The equilibrium temperature of conductor resulted by electric current increases with electric current. A critical electric current found to divide the temperature rate into two regimes is about 8 A. The dripping period and dripping frequency depend on the electric current. The dripping frequency fits well with electric current using a power‐law function. The numerical data are consistent with the experimental data. Besides, the decrease in dripping frequency is greater with ambient pressure at reduced electric current, whereas at larger electric current, the electric current, rather than the ambient pressure, dominates the increased dripping frequency.

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Numerical modeling of melting and dripping process of polymeric material subjected to moving heat flux: Prediction of drop time

Cited by 34 publications

References 7 publications

Critical Drip Size and Blue Flame Shedding of Dripping Ignition in Fire

Critical Drip Size and Blue Flame Shedding of Dripping Ignition in Fire

Development of a pendant experiment using melt indexer for correlation with the large‐size dripping in the UL‐94 test

Melt dripping behavior in the process of flame spread over energized electrical wire at different pressures

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