This paper examines experimentally the burning behaviors of thin-layer transformer oil on a water... more This paper examines experimentally the burning behaviors of thin-layer transformer oil on a water layer. A series of transformer oil pool fire experiments with different initial fuel thicknesses was performed. The burning process, burning rate, liquid temperature and radiative heat flux were measured. The experimental results show that the whole process can be divided into five typical phases: (1) rapid growth burning, (2) steady burning, (3) short boilover burning, (4) continuous boilover and (5) fire decay. The appearance of the middle three phases (2-4) depends on initial fuel thickness. The steady burning rate is found to be independent of the fuel thickness but slightly higher than that of burning without a water layer, because of the decrease in the boiling point of the fuel-water mixture. A critical fuel thickness was found to determine whether continuous boilover or short boilover will occur. The results also show the intensity of the initial boilover increases with increasing fuel thickness but the intensity of subsequent boilover of thin-layer burning can surpass that of thick-layer burning for some cases. A linear correlation was found between the time to boilover and fuel initial thickness in agreement with literature findings. The present results are of practical importance in situ-burning and thermal hazard analysis for fire accidents due to leakage of liquid fuels on water.
Radiolysis gas (2H2+O2) can accumulate in BWR steam piping in case of steam condensation. An ensu... more Radiolysis gas (2H2+O2) can accumulate in BWR steam piping in case of steam condensation. An ensuing detonation of the radiolysis gas is the likeliest cause of a pipe and/or valve damage. In the current work we investigate a typical BWR exhaust pipe, which connects the high pressure steam piping with the ambient atmosphere, under the following “worst case” scenario: (a) accumulation of radiolysis gas in an exhaust pipe, (b) fast valve opening to the high pressure system with steam at 70 bar, and (c) adiabatic pressurization of the radiolysis gas by the steam. Taking into account a water surface level of 6 m from the open end this leads to an equilibrium state of 20 bar pressure and 602 K temperature for the pressurized radiolysis gas. The main purpose of the current work was an experimental and numerical evaluation of the maximum pressure load and the integrity of the BWR exhaust pipe in case of a detonation of the pressurized radiolysis gas.
A set of experiments performed at Karlsruhe Institute of Technology (KIT) in the framework of the... more A set of experiments performed at Karlsruhe Institute of Technology (KIT) in the framework of the LACOMECO European project is devoted to flame propagation in an obstructed large scale facility A3 (of 8 m height and 33 m3 volume) with initially vertical hydrogen concentration gradients. Almost linear positive and negative (relative to gravity) concentration gradients are created prior to ignition in the range from 4% to 13%, and the process of flame acceleration is investigated depending on hydrogen concentration gradient and ignition positions. In this paper we describe the A3 facility and analyse the experimental data obtained during the project. The results of numerical simulation performed using Europlexus code are presented together with the critical discussions and conclusions.
The Proceedings of the International Conference on Nuclear Engineering (ICONE), 2007
INTRODUCTION Recently two accidents with radiolytic gas explosions occurred in Boiling Water Reac... more INTRODUCTION Recently two accidents with radiolytic gas explosions occurred in Boiling Water Reactors (BWR). The in-depth analysis of these accidents showed that an extraordinary large pressure rise due to high speed combustion of radiolytic gas inside the pipes caused ductile material failure. The pipe deformations were analyzed in great detail after the accidents to examine the dynamic response of the pipe structure to the radiolytic gas detonation loads (Nakagami , 2002).
Journal of Loss Prevention in The Process Industries, Mar 1, 2013
This paper presents results of an experimental investigation on the deflagration and deflagration... more This paper presents results of an experimental investigation on the deflagration and deflagration-to-detonation transition (DDT) in an obstructed (blockage ratio BR = 50%), semi-confined flat layer filled with uniform hydrogen–air mixtures. The effect of mixture reactivity depending on flat layer thickness and its width is studied to evaluate the critical conditions for sonic flame propagation and the possibility for detonation onset. The
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
h i g h l i g h t s We study spherical and cylindrical H 2 /air flames in un-and semi-confined ge... more h i g h l i g h t s We study spherical and cylindrical H 2 /air flames in un-and semi-confined geometries. A large-scale shadowgraphy for high-speed applications used to measure visible flame. Mixture specific flame acceleration observed for spherical flame propagation. A spherical burning velocity S (sph) for undisturbed flame propagation was derived. The model is in agreement with experimental data for spherical flame propagation.
See separate metadata file. The experimental data provided in three separate parts. Concentration... more See separate metadata file. The experimental data provided in three separate parts. Concentration data and flow-field data given in excel datasheets and CAD drawing files of the facility inside a zip folder.
Experiments were performed on the influence of oxidants (air, pure oxygen O2 and pure nitrous oxi... more Experiments were performed on the influence of oxidants (air, pure oxygen O2 and pure nitrous oxide N2O at atmospheric pressure) in the straight expansion tube after the burst disk on the hydrogen spontaneous ignition. The lowest pressure at which the spontaneous ignition is observed has been researched for a 4 mm diameter tube with a length of 10 cm for the two oxidant gases. The ignition phenomenon is observed with a high speed camera and the external overpressures are measured. Numerical simulations have also been conducted with the high resolution CFD approach detailed chemistry formerly developed by Wen and co-workers. Comparison is made between the predictions and the experimental data.
A series of experiments on hydrogen flame propagation in a thin layer geometry is presented. Prem... more A series of experiments on hydrogen flame propagation in a thin layer geometry is presented. Premixed hydrogen-air compositions in the range from 6 to 15%(vol.) H2 are tested. Semi-open vertical combustion chamber consists of two transparent Plexiglas side walls with main dimensions of 90x20 cm with a gap from 1 to 10 mm in between. Test mixtures are ignited at the open end of the chamber so that the flame propagates towards the closed end. Ignition position changes from top to bottom in order to take into account an effect of gravity on flame propagation regimes. High-speed shadow imaging is used to visualize and record the combustion process. Thermal-diffusion and Darrieus-Landau instabilities are governing the general flame behavior. Heat losses to side walls and viscous friction in a thin layer may fully suppress the flame propagation with local or global extinction. The sensitivity to heat losses can be characterized using a Peclet number as a ratio of layer thickness to lamina...
As a part of a German nuclear safety project on the combustion behavior of hydrogen-carbon monoxi... more As a part of a German nuclear safety project on the combustion behavior of hydrogen-carbon monoxide-air mixtures small scale experiments were performed to determine the lower flammability limit and the laminar burning velocity of such mixtures. The experiments were performed in a spherical explosion bomb with a free volume of 8.2 liter. The experimental set-up is equipped with a central spark ignition and quartz glass windows for optical access. Further instrumentation included pressure and temperature sensors as well as high-speed shadow-videography. A wide concentration range for both fuel gases was investigated in numerous experiments from the lower flammability limits up to the stoichiometric composition of hydrogen, carbon monoxide and air (H2-CO-air) mixtures. The laminar burning velocities were determined from the initial pressure increase after the ignition and by using high-speed videos taken during the experiments.
Experiments in an obstructed semi-confined vertical combustion channel with a height of 6 m (cros... more Experiments in an obstructed semi-confined vertical combustion channel with a height of 6 m (cross-section 0.4 Â 0.4 m) inside a safety vessel of the hydrogen test center HYKA at the Karlsruhe Institute of Technology (KIT) are reported. In the work, homogeneous hydrogen-air-mixtures as well as mixtures with different well-defined H 2-concentration gradients were ignited either at the top or at the bottom end of the channel. The combustion characteristics were recorded using pressure sensors and sensors for the detection of the flame front that were distributed along the complete channel length. In the tests slow subsonic and fast sonic deflagrations as well as detonations were observed and the conditions for the flame acceleration (FA) to speed of sound and deflagration-to-detonation transition (DDT) are compared with the results of similar experiments performed earlier in a larger semi-confined horizontal channel.
A series of experiments in a thin layer geometry performed at the HYKA test site of the KIT. Expe... more A series of experiments in a thin layer geometry performed at the HYKA test site of the KIT. Experiments on different combustion regimes for lean and stoichiometric H 2 /air mixtures were performed in a rectangular chamber with dimensions of 200 Â 900 x h mm 3 , where h is the thickness of the layer (h ¼ 1, 2, 4, 6, 8, 10 mm). To model a gap between a fuel cell assembly and a metal housing, three different layer geometries were investigated: (1) a smooth channel without obstructions; (2) a channel with a metal grid filled 25% of chamber length and (3) a metal grid filled 100% of chamber length. The blockage ratio of metal grid has changed from 10 to 60% of cross-section. Detail measurements of H 2 /air combustion behavior including flame acceleration (FA) and DDT in closed rectangular channel have been done. Five categories of flame propagation regimes were classified. Special attention was paid to analysis of critical condition for different regimes of flame propagation as function of layer thickness and roughness of the channel. It was found that thinner layer suppresses the detonation onset and even with a roughness, the flame may quench or, in thicker layer, is available to accelerate to speed of sound. The detonation may occur only in a channel thicker than 4 mm.
This paper examines experimentally the burning behaviors of thin-layer transformer oil on a water... more This paper examines experimentally the burning behaviors of thin-layer transformer oil on a water layer. A series of transformer oil pool fire experiments with different initial fuel thicknesses was performed. The burning process, burning rate, liquid temperature and radiative heat flux were measured. The experimental results show that the whole process can be divided into five typical phases: (1) rapid growth burning, (2) steady burning, (3) short boilover burning, (4) continuous boilover and (5) fire decay. The appearance of the middle three phases (2-4) depends on initial fuel thickness. The steady burning rate is found to be independent of the fuel thickness but slightly higher than that of burning without a water layer, because of the decrease in the boiling point of the fuel-water mixture. A critical fuel thickness was found to determine whether continuous boilover or short boilover will occur. The results also show the intensity of the initial boilover increases with increasing fuel thickness but the intensity of subsequent boilover of thin-layer burning can surpass that of thick-layer burning for some cases. A linear correlation was found between the time to boilover and fuel initial thickness in agreement with literature findings. The present results are of practical importance in situ-burning and thermal hazard analysis for fire accidents due to leakage of liquid fuels on water.
Radiolysis gas (2H2+O2) can accumulate in BWR steam piping in case of steam condensation. An ensu... more Radiolysis gas (2H2+O2) can accumulate in BWR steam piping in case of steam condensation. An ensuing detonation of the radiolysis gas is the likeliest cause of a pipe and/or valve damage. In the current work we investigate a typical BWR exhaust pipe, which connects the high pressure steam piping with the ambient atmosphere, under the following “worst case” scenario: (a) accumulation of radiolysis gas in an exhaust pipe, (b) fast valve opening to the high pressure system with steam at 70 bar, and (c) adiabatic pressurization of the radiolysis gas by the steam. Taking into account a water surface level of 6 m from the open end this leads to an equilibrium state of 20 bar pressure and 602 K temperature for the pressurized radiolysis gas. The main purpose of the current work was an experimental and numerical evaluation of the maximum pressure load and the integrity of the BWR exhaust pipe in case of a detonation of the pressurized radiolysis gas.
A set of experiments performed at Karlsruhe Institute of Technology (KIT) in the framework of the... more A set of experiments performed at Karlsruhe Institute of Technology (KIT) in the framework of the LACOMECO European project is devoted to flame propagation in an obstructed large scale facility A3 (of 8 m height and 33 m3 volume) with initially vertical hydrogen concentration gradients. Almost linear positive and negative (relative to gravity) concentration gradients are created prior to ignition in the range from 4% to 13%, and the process of flame acceleration is investigated depending on hydrogen concentration gradient and ignition positions. In this paper we describe the A3 facility and analyse the experimental data obtained during the project. The results of numerical simulation performed using Europlexus code are presented together with the critical discussions and conclusions.
The Proceedings of the International Conference on Nuclear Engineering (ICONE), 2007
INTRODUCTION Recently two accidents with radiolytic gas explosions occurred in Boiling Water Reac... more INTRODUCTION Recently two accidents with radiolytic gas explosions occurred in Boiling Water Reactors (BWR). The in-depth analysis of these accidents showed that an extraordinary large pressure rise due to high speed combustion of radiolytic gas inside the pipes caused ductile material failure. The pipe deformations were analyzed in great detail after the accidents to examine the dynamic response of the pipe structure to the radiolytic gas detonation loads (Nakagami , 2002).
Journal of Loss Prevention in The Process Industries, Mar 1, 2013
This paper presents results of an experimental investigation on the deflagration and deflagration... more This paper presents results of an experimental investigation on the deflagration and deflagration-to-detonation transition (DDT) in an obstructed (blockage ratio BR = 50%), semi-confined flat layer filled with uniform hydrogen–air mixtures. The effect of mixture reactivity depending on flat layer thickness and its width is studied to evaluate the critical conditions for sonic flame propagation and the possibility for detonation onset. The
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
h i g h l i g h t s We study spherical and cylindrical H 2 /air flames in un-and semi-confined ge... more h i g h l i g h t s We study spherical and cylindrical H 2 /air flames in un-and semi-confined geometries. A large-scale shadowgraphy for high-speed applications used to measure visible flame. Mixture specific flame acceleration observed for spherical flame propagation. A spherical burning velocity S (sph) for undisturbed flame propagation was derived. The model is in agreement with experimental data for spherical flame propagation.
See separate metadata file. The experimental data provided in three separate parts. Concentration... more See separate metadata file. The experimental data provided in three separate parts. Concentration data and flow-field data given in excel datasheets and CAD drawing files of the facility inside a zip folder.
Experiments were performed on the influence of oxidants (air, pure oxygen O2 and pure nitrous oxi... more Experiments were performed on the influence of oxidants (air, pure oxygen O2 and pure nitrous oxide N2O at atmospheric pressure) in the straight expansion tube after the burst disk on the hydrogen spontaneous ignition. The lowest pressure at which the spontaneous ignition is observed has been researched for a 4 mm diameter tube with a length of 10 cm for the two oxidant gases. The ignition phenomenon is observed with a high speed camera and the external overpressures are measured. Numerical simulations have also been conducted with the high resolution CFD approach detailed chemistry formerly developed by Wen and co-workers. Comparison is made between the predictions and the experimental data.
A series of experiments on hydrogen flame propagation in a thin layer geometry is presented. Prem... more A series of experiments on hydrogen flame propagation in a thin layer geometry is presented. Premixed hydrogen-air compositions in the range from 6 to 15%(vol.) H2 are tested. Semi-open vertical combustion chamber consists of two transparent Plexiglas side walls with main dimensions of 90x20 cm with a gap from 1 to 10 mm in between. Test mixtures are ignited at the open end of the chamber so that the flame propagates towards the closed end. Ignition position changes from top to bottom in order to take into account an effect of gravity on flame propagation regimes. High-speed shadow imaging is used to visualize and record the combustion process. Thermal-diffusion and Darrieus-Landau instabilities are governing the general flame behavior. Heat losses to side walls and viscous friction in a thin layer may fully suppress the flame propagation with local or global extinction. The sensitivity to heat losses can be characterized using a Peclet number as a ratio of layer thickness to lamina...
As a part of a German nuclear safety project on the combustion behavior of hydrogen-carbon monoxi... more As a part of a German nuclear safety project on the combustion behavior of hydrogen-carbon monoxide-air mixtures small scale experiments were performed to determine the lower flammability limit and the laminar burning velocity of such mixtures. The experiments were performed in a spherical explosion bomb with a free volume of 8.2 liter. The experimental set-up is equipped with a central spark ignition and quartz glass windows for optical access. Further instrumentation included pressure and temperature sensors as well as high-speed shadow-videography. A wide concentration range for both fuel gases was investigated in numerous experiments from the lower flammability limits up to the stoichiometric composition of hydrogen, carbon monoxide and air (H2-CO-air) mixtures. The laminar burning velocities were determined from the initial pressure increase after the ignition and by using high-speed videos taken during the experiments.
Experiments in an obstructed semi-confined vertical combustion channel with a height of 6 m (cros... more Experiments in an obstructed semi-confined vertical combustion channel with a height of 6 m (cross-section 0.4 Â 0.4 m) inside a safety vessel of the hydrogen test center HYKA at the Karlsruhe Institute of Technology (KIT) are reported. In the work, homogeneous hydrogen-air-mixtures as well as mixtures with different well-defined H 2-concentration gradients were ignited either at the top or at the bottom end of the channel. The combustion characteristics were recorded using pressure sensors and sensors for the detection of the flame front that were distributed along the complete channel length. In the tests slow subsonic and fast sonic deflagrations as well as detonations were observed and the conditions for the flame acceleration (FA) to speed of sound and deflagration-to-detonation transition (DDT) are compared with the results of similar experiments performed earlier in a larger semi-confined horizontal channel.
A series of experiments in a thin layer geometry performed at the HYKA test site of the KIT. Expe... more A series of experiments in a thin layer geometry performed at the HYKA test site of the KIT. Experiments on different combustion regimes for lean and stoichiometric H 2 /air mixtures were performed in a rectangular chamber with dimensions of 200 Â 900 x h mm 3 , where h is the thickness of the layer (h ¼ 1, 2, 4, 6, 8, 10 mm). To model a gap between a fuel cell assembly and a metal housing, three different layer geometries were investigated: (1) a smooth channel without obstructions; (2) a channel with a metal grid filled 25% of chamber length and (3) a metal grid filled 100% of chamber length. The blockage ratio of metal grid has changed from 10 to 60% of cross-section. Detail measurements of H 2 /air combustion behavior including flame acceleration (FA) and DDT in closed rectangular channel have been done. Five categories of flame propagation regimes were classified. Special attention was paid to analysis of critical condition for different regimes of flame propagation as function of layer thickness and roughness of the channel. It was found that thinner layer suppresses the detonation onset and even with a roughness, the flame may quench or, in thicker layer, is available to accelerate to speed of sound. The detonation may occur only in a channel thicker than 4 mm.
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