Heat transfer to and ignition of ceiling by an impinging diffusion flame

Matti Kokkala

Research output: Book/ReportReport

Abstract

This work is an experimental study of the heat transfer to and the ignition of a ceiling surface exposed by an impinging buoyant jet diffusion flame. Natural gas flames in the range of 2.9 kW to 10.5 kW on a burner of a diameter of 64 mm were used. The shapes of these flames are described with appropriate temperature and species concentration measurements. The gas temperature below and the total heat flux to the stagnation point were found to be functions of the ratio of the ceiling height to the flame height. In the intermittent flame region the stagnation point heat flux was found to be higher than given by You and Faeth, but to approach their results in the plume region. For these flames, the ignition of a PMMA ceiling was found to occur only if the visible flame touches the ceiling at least 50 % of the time, i.e., if the average flame height is bigger than the ceiling height. The critical heat flux was between 20 kW/m2 and 30 kW/m2 depending, e.g., on the size of the flame. These values are higher than the critical radiative heat flux for piloted ignition of the same material. The sustained ignition of PMMA required a surface temperature in the range of 380 °C to 410 °C. After turning the gas burner off, the flames on the surface extinguished repeatably as the surface temperature decreased to 320 °C.
Original languageEnglish
Place of PublicationEspoo
PublisherVTT Technical Research Centre of Finland
Number of pages80
ISBN (Print)951-38-3255-4
Publication statusPublished - 1989
MoE publication typeD4 Published development or research report or study

Publication series

SeriesValtion teknillinen tutkimuskeskus. Tutkimuksia - Research Reports
Number586
ISSN0358-5077

Fingerprint

Ceilings
Ignition
Heat flux
Heat transfer
Gas burners
Temperature
Fuel burners
Enthalpy
Natural gas
Gases

Keywords

  • ceilings
  • diffusion flames
  • heat transfer
  • heat flux
  • ignition
  • fire tests

Cite this

Kokkala, M. (1989). Heat transfer to and ignition of ceiling by an impinging diffusion flame. Espoo: VTT Technical Research Centre of Finland. Valtion teknillinen tutkimuskeskus. Tutkimuksia - Research Reports, No. 586
Kokkala, Matti. / Heat transfer to and ignition of ceiling by an impinging diffusion flame. Espoo : VTT Technical Research Centre of Finland, 1989. 80 p. (Valtion teknillinen tutkimuskeskus. Tutkimuksia - Research Reports; No. 586).
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Kokkala, M 1989, Heat transfer to and ignition of ceiling by an impinging diffusion flame. Valtion teknillinen tutkimuskeskus. Tutkimuksia - Research Reports, no. 586, VTT Technical Research Centre of Finland, Espoo.

Heat transfer to and ignition of ceiling by an impinging diffusion flame. / Kokkala, Matti.

Espoo : VTT Technical Research Centre of Finland, 1989. 80 p. (Valtion teknillinen tutkimuskeskus. Tutkimuksia - Research Reports; No. 586).

Research output: Book/ReportReport

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PY - 1989

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N2 - This work is an experimental study of the heat transfer to and the ignition of a ceiling surface exposed by an impinging buoyant jet diffusion flame. Natural gas flames in the range of 2.9 kW to 10.5 kW on a burner of a diameter of 64 mm were used. The shapes of these flames are described with appropriate temperature and species concentration measurements. The gas temperature below and the total heat flux to the stagnation point were found to be functions of the ratio of the ceiling height to the flame height. In the intermittent flame region the stagnation point heat flux was found to be higher than given by You and Faeth, but to approach their results in the plume region. For these flames, the ignition of a PMMA ceiling was found to occur only if the visible flame touches the ceiling at least 50 % of the time, i.e., if the average flame height is bigger than the ceiling height. The critical heat flux was between 20 kW/m2 and 30 kW/m2 depending, e.g., on the size of the flame. These values are higher than the critical radiative heat flux for piloted ignition of the same material. The sustained ignition of PMMA required a surface temperature in the range of 380 °C to 410 °C. After turning the gas burner off, the flames on the surface extinguished repeatably as the surface temperature decreased to 320 °C.

AB - This work is an experimental study of the heat transfer to and the ignition of a ceiling surface exposed by an impinging buoyant jet diffusion flame. Natural gas flames in the range of 2.9 kW to 10.5 kW on a burner of a diameter of 64 mm were used. The shapes of these flames are described with appropriate temperature and species concentration measurements. The gas temperature below and the total heat flux to the stagnation point were found to be functions of the ratio of the ceiling height to the flame height. In the intermittent flame region the stagnation point heat flux was found to be higher than given by You and Faeth, but to approach their results in the plume region. For these flames, the ignition of a PMMA ceiling was found to occur only if the visible flame touches the ceiling at least 50 % of the time, i.e., if the average flame height is bigger than the ceiling height. The critical heat flux was between 20 kW/m2 and 30 kW/m2 depending, e.g., on the size of the flame. These values are higher than the critical radiative heat flux for piloted ignition of the same material. The sustained ignition of PMMA required a surface temperature in the range of 380 °C to 410 °C. After turning the gas burner off, the flames on the surface extinguished repeatably as the surface temperature decreased to 320 °C.

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KW - fire tests

M3 - Report

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T3 - Valtion teknillinen tutkimuskeskus. Tutkimuksia - Research Reports

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Kokkala M. Heat transfer to and ignition of ceiling by an impinging diffusion flame. Espoo: VTT Technical Research Centre of Finland, 1989. 80 p. (Valtion teknillinen tutkimuskeskus. Tutkimuksia - Research Reports; No. 586).