An application of ultrasonic tomographic imaging to study smoldering combustion

Tse, Stephen D.; Anthenien, Ralph A.; Fernandez‐Pello, A. C.; Miyasaka, Kenji

doi:10.1016/s0010-2180(98)00053-4

Cited by 21 publications

(10 citation statements)

References 24 publications

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“…The ultrasound technique follows the same approach as that of Tse et al [11] and uses speakermicrophone pairs to track the progress of the smolder reaction (because the char is more permeable than the virgin foam) and to observe the evolution of the char. The acoustic attenuation coefficient α of the porous medium can be approximated [11] as being inversely proportional to the square root of the permeability K, by α = A/K 1/2 , where A is a constant dependant on the ultrasonic frequency, the medium porosity, and several fluid properties, giving:…”

Section: Ultrasound Probing Systemmentioning

confidence: 99%

“…The acoustic attenuation coefficient α of the porous medium can be approximated [11] as being inversely proportional to the square root of the permeability K, by α = A/K 1/2 , where A is a constant dependant on the ultrasonic frequency, the medium porosity, and several fluid properties, giving:…”

Section: Ultrasound Probing Systemmentioning

confidence: 99%

“…Ultrasound probing offers a non-intrusive means of monitoring the changing structure of a smoldering sample's interior and tracking the smolder front, because the smolder reaction leaves behind a char of higher permeability than the unreacted foam [10,11]. Tse et al developed an ultrasound imaging technique [11] to determine the permeability of a sample from the attenuation of the ultrasound signal. The char was found to continue reacting (SCO) after the passage of the smolder front, resulting in the formation of pores in the char region, thereby allowing greater oxidizer supply and potentially triggering a gas-phase ignition.…”

Section: Introductionmentioning

confidence: 99%

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The role of secondary char oxidation in the transition from smoldering to flaming

Putzeys

Bar-Ilan

Rein

et al. 2007

Proceedings of the Combustion Institute

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TitleThe role of secondary char oxidation in the transition from smoldering to flaming AbstractThe transition from forward smoldering to flaming in polyurethane foam is observed using indepth thermocouples and ultrasound probing. The experiments are conducted with small parallelepiped samples vertically placed in an upward wind tunnel. Three of the vertical sample sides are maintained at elevated temperature and the fourth is exposed to an upward oxidizer flow and a radiant heat flux. An ultrasound probing technique is used to measure the line-of-sight average permeability of the sample at the same heights as the thermocouples. The smolder front propagation is tracked by both the thermocouples and ultrasound data, which show an increase in temperature and permeability upon passage of the smolder front. The permeability data also show that the transition to flaming is preceded by rapid fluctuations in permeability in the char region below the smolder front, indicating the formation of pores by secondary char oxidation. The pores provide locations for the onset of gas-phase ignition (i.e. transition to flaming).The results from all the tests indicate that the formation of pores is a necessary but not sufficient condition for the transition to flaming. Two novel measures of the intensity of the secondary char oxidation are introduced: the time derivative of permeability, and the secondary char oxidation velocity. The time derivative of permeability, which provides a measure of the pore formation rate, is found to increase as the oxygen concentration and/or radiant heat flux increase, and to indicate the likelihood of the transition to flaming. The permeability data offers a means to track the propagation of the secondary char oxidation, and to calculate the secondary char oxidation velocity, which is found to be strongly correlated to the transition to flaming. A simplified energy balance model is able to predict the dependence of the secondary char oxidation velocity on oxygen concentration and radiant heat flux.

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Section: Ultrasound Probing Systemmentioning

confidence: 99%

Section: Ultrasound Probing Systemmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The role of secondary char oxidation in the transition from smoldering to flaming

Putzeys

Bar-Ilan

Rein

et al. 2007

Proceedings of the Combustion Institute

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“…In addition to the thermocouples, a novel technique has been developed and applied to image the interior of the reaction by use of ultrasonic pulses as described by Tse et al [6]. A set of 5 ultrasonic speaker/microphone transducer pairs are fixed lengthwise along the centerline of the sample to obtain line-of-sight average permeability data.…”

Section: Flight Hardwarementioning

confidence: 99%

Forced forward smoldering experiments in microgravity

Bar-Ilan

Rein

Fernandez‐Pello

et al. 2004

Experimental Thermal and Fluid Science

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Results from two forward forced-flow smolder tests on polyurethane foam using air as oxidizer conducted aboard the NASA Space Shuttle (STS-105 and STS-108 missions) are presented in this work. The two tests provide the only presently available forward smolder data in microgravity. A complimentary series of ground-based tests were also conducted to determine, by comparison with the microgravity data, the effect of gravity on the forward smolder propagation. The objective of the study is to provide a better understanding of the controlling mechanisms of smolder for the purpose of control and prevention, both in normaland microgravity. The data consists of temperature histories from thermocouples placed at various axial locations along the fuel sample centerline, and of permeability histories obtained from ultrasonic transducer pairs also located at various axial positions in the fuel sample. A comparison of t he tests conducted in normal-and microgravity indicates that smolder propagation velocities are higher in microgravity than in normal gravity, and that there is a greater tendency for a transition to flame in microgravity than in normal gravity. This is due primarily to the reduced heat losses in the microgravity environment, leading to increased char oxidation. This observation is confirmed through a simplified one-dimensional model of the forward smolder propagation. This finding has important implications from the point of view of fire safety in a space-based environment, since smolder can often occur in the forward mode and potentially lead to a smolder-initiated fire.

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“…The UIS system is thoroughly outlined in Tse et al [11] and is therefore only shown here as 3) The received RMS waveform strength is digitally sampled and stored. It can be seen that the steep rise in transmission of the UIS signal at a given location correlates with a measured temperature of -290-300°C, corresponding to the pyrolysis temperature of the polyurethane foam [12].…”

mentioning

confidence: 99%