The Experts below are selected from a list of 339 Experts worldwide ranked by ideXlab platform

P Adams - One of the best experts on this subject based on the ideXlab platform.

  • allowable Hydrogen permeation rate from road vehicles
    International Journal of Hydrogen Energy, 2011
    Co-Authors: P Adams, B. Cariteau, Alain Bengaouer, Vladimir Molkov, Alexander G. Venetsanos
    Abstract:

    The paper presents an overview of the main results of the European Commission Network of Excellence “HySafe” activity to estimate an allowable Hydrogen permeation rate for automotive legal requirements and standards. A slow, long term Hydrogen release such as that due to permeation from a vehicle into an inadequately ventilated enclosed structure is a potential risk associated with the use of Hydrogen in automotive applications. Due to its small size Hydrogen permeates through the containment materials found in Compressed Gaseous Hydrogen storage systems and is an issue that requires consideration for containers with non-metallic (polymer) liners. Various rates have been proposed in draft legal requirements and standards based on different scenarios and the assumption that permeated Hydrogen disperses homogeneously in a garage like enclosure. This paper focuses on the development of a methodology to estimate an allowable upper limit for Hydrogen permeation in automotive applications, by investigating the behaviour of Hydrogen when released through permeation with a focus on European scenarios. The background to the activity is explained, worst credible scenarios are identified, a methodology proposed and a maximum Hydrogen permeation rate from road vehicles into enclosed structures is estimated.

  • Hydrogen permeation from CGH2 vehicles in garages: CFD dispersion calculations and experimental validation
    International Journal of Hydrogen Energy, 2010
    Co-Authors: Alexander G. Venetsanos, B. Cariteau, P Adams, E. Papanikolaou, Alain Bengaouer
    Abstract:

    Abstract The time and space evolution of the distribution of Hydrogen in confined settings was investigated computationally and experimentally for permeation from typical Compressed Gaseous Hydrogen (CGH2) storage systems for buses or cars. The main goal was to examine whether Hydrogen is distributed homogeneously within a garage-like facility or whether stratified conditions are developed, under certain conditions. The nominal Hydrogen flow rate considered was 1.087 L/min in a bus facility with a volume of 681 m 3 . The release was assumed to be directed upwards from a 0.15 m diameter hole located at the middle part of the bus cylinders casing. Ventilation rates up to 0.03 air changes per hour (ACH) were considered. Simulated time periods extended up to 20 days. The CFD simulations performed with the ADREA-HF code showed that fully homogeneous conditions exist for low ventilation rates, while stratified conditions prevail for higher ventilation rates. Regarding flow structure it was found that the vertical concentration profiles can be considered as the superposition of the concentration at the floor (driven by diffusion) plus a concentration difference between floor and ceiling (driven by buoyancy forces). In all cases considered this concentration difference was found to be less than 0.5%. The dispersion experiments were performed in a large scale garage-like enclosure of 40 m 3 using helium (GARAGE facility). Comparison between CFD simulations and experiments showed that the predicted concentrations were in good agreement with the experimental data. Finally, simulations were performed using two integral models: the fully homogeneous model and a two-layer model and the results were compared both against CFD and the experimental data.

  • HySafe standard benchmark Problem SBEP-V11: Predictions of Hydrogen release and dispersion from a CGH2 bus in an underpass
    International Journal of Hydrogen Energy, 2010
    Co-Authors: Alexander G. Venetsanos, E. Papanikolaou, Olav R. Hansen, Prankul Middha, Javier García, M. Heitsch, D. Baraldi, P Adams
    Abstract:

    One of the tasks of the HySafe Network of Excellence was the evaluation of available CFD tools and models for dispersion and combustion in selected Hydrogen release scenarios identified as “standard benchmark problems” (SBEPs). This paper presents the results of the HySafe standard benchmark problem SBEP-V11. The situation considered is a high pressure Hydrogen jet release from a Compressed Gaseous Hydrogen (CGH2) bus in an underpass. The bus considered is equipped with 8 cylinders of 5 kg Hydrogen each at 35 MPa storage pressure. The underpass is assumed to be of the common beam and slab type construction with I-beams spanning across the highway at 3 m centres (normal to the bus), plus cross bracing between the main beams, and light armatures parallel to the bus direction. The main goal of the present work was to evaluate the role of obstructions on the underside of the bridge deck on the dispersion patterns and assess the potential for Hydrogen accumulation. Four HySafe partners participated in this benchmark, with 4 different CFD codes, ADREA-HF, CFX, FLACS and FLUENT. Four scenarios were examined in total. In the base case scenario 20 kg of Hydrogen was released in the basic geometry. In Sensitivity Test 1 the release position was moved so that the Hydrogen jet could hit directly the light armature on the roof of the underpass. In Sensitivity Test 2 the underside of the bridge deck was flat. In Sensitivity Test 3 the release was from one cylinder instead of four (5 kg instead of 20). The paper compares the results predicted by the four different computational approaches and attempts to identify the reasons for observed disagreements. The paper also concludes on the effects of the obstructions on the underside of the bridge deck.

  • CFD modelling of Hydrogen release, dispersion and combustion for automotive scenarios
    Journal of Loss Prevention in the Process Industries, 2008
    Co-Authors: Alexander G. Venetsanos, P Adams, D. Baraldi, P.s. Heggem, Heinz Wilkening
    Abstract:

    Abstract The paper describes the analysis of the potential effects of releases from Compressed Gaseous Hydrogen systems on commercial vehicles in urban and tunnel environments using computational fluid dynamics (CFD). Comparative releases from Compressed natural gas systems are also included in the analysis. This study is restricted to typical non-articulated single deck city buses. Hydrogen releases are considered from storage systems with nominal working pressures of 20, 35 and 70 MPa, and a comparative natural gas release (20 MPa). The cases investigated are based on the assumptions that either fire causes a release via a thermally activated pressure relief device(s) (PRD) and that the released gas vents without immediately igniting, or that a PRD fails. Various release strategies were taken into account. For each configuration some worst-case scenarios are considered. By far the most critical case investigated in the urban environment, is a rapid release of the entire Hydrogen or natural gas storage system such as the simultaneous opening of all PRDs. If ignition occurs, the effects could be expected to be similar to the 1983 Stockholm Hydrogen accident [Venetsanos, A. G., Huld, T., Adams, P., & Bartzis, J. G. (2003). Source, dispersion and combustion modelling of an accidental release of Hydrogen in an urban environment. Journal of Hazardous Materials, A105, 1–25]. In the cases where the Hydrogen release is restricted, for example, by venting through a single PRD, the effects are relatively minor and localised close to the area of the flammable cloud. With increasing Hydrogen storage pressure, the maximum energy available in a flammable cloud after a release increases, as do the predicted overpressures resulting from combustion. Even in the relatively confined environment considered, the effects on the combustion regime are closer to what would be expected in a more open environment, i.e. a slow deflagration should be expected. Among the cases studied the most severe one was a rapid release of the entire Hydrogen (40 kg) or natural gas (168 kg) storage system within the confines of a tunnel. In this case there was minimal difference between a release from a 20 MPa natural gas system or a 20 MPa Hydrogen system, however, a similar release from a 35 MPa Hydrogen system was significantly more severe and particularly in terms of predicted overpressures. The present study has also highlighted that the ignition point significantly affects the combustion regime in confined environments. The results have indicated that critical cases in tunnels may tend towards a fast deflagration, or where there are turbulence generating features, e.g. multiple obstacles, there is the possibility that the combustion regime could progress to a detonation. When comparing the urban and tunnel environments, a similar release of Hydrogen is significantly more severe in a tunnel, and the energy available in the flammable cloud is greater and remains for a longer period in tunnels. When comparing Hydrogen and natural gas releases, for the cases and environments investigated and within the limits of the assumptions, it appears that Hydrogen requires different mitigation measures in order that the potential effects are similar to those of natural gas in case of an accident. With respect to a PRD opening strategy, Hydrogen storage systems should be designed to avoid simultaneous opening of all PRD, and that for the consequences of the released energy to be mitigated, either the number of PRDs opening should be limited or their vents to atmosphere should be restricted (the latter point would require validation by a comprehensive risk assessment).

Alexander G. Venetsanos - One of the best experts on this subject based on the ideXlab platform.

  • allowable Hydrogen permeation rate from road vehicles
    International Journal of Hydrogen Energy, 2011
    Co-Authors: P Adams, B. Cariteau, Alain Bengaouer, Vladimir Molkov, Alexander G. Venetsanos
    Abstract:

    The paper presents an overview of the main results of the European Commission Network of Excellence “HySafe” activity to estimate an allowable Hydrogen permeation rate for automotive legal requirements and standards. A slow, long term Hydrogen release such as that due to permeation from a vehicle into an inadequately ventilated enclosed structure is a potential risk associated with the use of Hydrogen in automotive applications. Due to its small size Hydrogen permeates through the containment materials found in Compressed Gaseous Hydrogen storage systems and is an issue that requires consideration for containers with non-metallic (polymer) liners. Various rates have been proposed in draft legal requirements and standards based on different scenarios and the assumption that permeated Hydrogen disperses homogeneously in a garage like enclosure. This paper focuses on the development of a methodology to estimate an allowable upper limit for Hydrogen permeation in automotive applications, by investigating the behaviour of Hydrogen when released through permeation with a focus on European scenarios. The background to the activity is explained, worst credible scenarios are identified, a methodology proposed and a maximum Hydrogen permeation rate from road vehicles into enclosed structures is estimated.

  • Hydrogen permeation from CGH2 vehicles in garages: CFD dispersion calculations and experimental validation
    International Journal of Hydrogen Energy, 2010
    Co-Authors: Alexander G. Venetsanos, B. Cariteau, P Adams, E. Papanikolaou, Alain Bengaouer
    Abstract:

    Abstract The time and space evolution of the distribution of Hydrogen in confined settings was investigated computationally and experimentally for permeation from typical Compressed Gaseous Hydrogen (CGH2) storage systems for buses or cars. The main goal was to examine whether Hydrogen is distributed homogeneously within a garage-like facility or whether stratified conditions are developed, under certain conditions. The nominal Hydrogen flow rate considered was 1.087 L/min in a bus facility with a volume of 681 m 3 . The release was assumed to be directed upwards from a 0.15 m diameter hole located at the middle part of the bus cylinders casing. Ventilation rates up to 0.03 air changes per hour (ACH) were considered. Simulated time periods extended up to 20 days. The CFD simulations performed with the ADREA-HF code showed that fully homogeneous conditions exist for low ventilation rates, while stratified conditions prevail for higher ventilation rates. Regarding flow structure it was found that the vertical concentration profiles can be considered as the superposition of the concentration at the floor (driven by diffusion) plus a concentration difference between floor and ceiling (driven by buoyancy forces). In all cases considered this concentration difference was found to be less than 0.5%. The dispersion experiments were performed in a large scale garage-like enclosure of 40 m 3 using helium (GARAGE facility). Comparison between CFD simulations and experiments showed that the predicted concentrations were in good agreement with the experimental data. Finally, simulations were performed using two integral models: the fully homogeneous model and a two-layer model and the results were compared both against CFD and the experimental data.

  • HySafe standard benchmark Problem SBEP-V11: Predictions of Hydrogen release and dispersion from a CGH2 bus in an underpass
    International Journal of Hydrogen Energy, 2010
    Co-Authors: Alexander G. Venetsanos, E. Papanikolaou, Olav R. Hansen, Prankul Middha, Javier García, M. Heitsch, D. Baraldi, P Adams
    Abstract:

    One of the tasks of the HySafe Network of Excellence was the evaluation of available CFD tools and models for dispersion and combustion in selected Hydrogen release scenarios identified as “standard benchmark problems” (SBEPs). This paper presents the results of the HySafe standard benchmark problem SBEP-V11. The situation considered is a high pressure Hydrogen jet release from a Compressed Gaseous Hydrogen (CGH2) bus in an underpass. The bus considered is equipped with 8 cylinders of 5 kg Hydrogen each at 35 MPa storage pressure. The underpass is assumed to be of the common beam and slab type construction with I-beams spanning across the highway at 3 m centres (normal to the bus), plus cross bracing between the main beams, and light armatures parallel to the bus direction. The main goal of the present work was to evaluate the role of obstructions on the underside of the bridge deck on the dispersion patterns and assess the potential for Hydrogen accumulation. Four HySafe partners participated in this benchmark, with 4 different CFD codes, ADREA-HF, CFX, FLACS and FLUENT. Four scenarios were examined in total. In the base case scenario 20 kg of Hydrogen was released in the basic geometry. In Sensitivity Test 1 the release position was moved so that the Hydrogen jet could hit directly the light armature on the roof of the underpass. In Sensitivity Test 2 the underside of the bridge deck was flat. In Sensitivity Test 3 the release was from one cylinder instead of four (5 kg instead of 20). The paper compares the results predicted by the four different computational approaches and attempts to identify the reasons for observed disagreements. The paper also concludes on the effects of the obstructions on the underside of the bridge deck.

  • CFD modelling of Hydrogen release, dispersion and combustion for automotive scenarios
    Journal of Loss Prevention in the Process Industries, 2008
    Co-Authors: Alexander G. Venetsanos, P Adams, D. Baraldi, P.s. Heggem, Heinz Wilkening
    Abstract:

    Abstract The paper describes the analysis of the potential effects of releases from Compressed Gaseous Hydrogen systems on commercial vehicles in urban and tunnel environments using computational fluid dynamics (CFD). Comparative releases from Compressed natural gas systems are also included in the analysis. This study is restricted to typical non-articulated single deck city buses. Hydrogen releases are considered from storage systems with nominal working pressures of 20, 35 and 70 MPa, and a comparative natural gas release (20 MPa). The cases investigated are based on the assumptions that either fire causes a release via a thermally activated pressure relief device(s) (PRD) and that the released gas vents without immediately igniting, or that a PRD fails. Various release strategies were taken into account. For each configuration some worst-case scenarios are considered. By far the most critical case investigated in the urban environment, is a rapid release of the entire Hydrogen or natural gas storage system such as the simultaneous opening of all PRDs. If ignition occurs, the effects could be expected to be similar to the 1983 Stockholm Hydrogen accident [Venetsanos, A. G., Huld, T., Adams, P., & Bartzis, J. G. (2003). Source, dispersion and combustion modelling of an accidental release of Hydrogen in an urban environment. Journal of Hazardous Materials, A105, 1–25]. In the cases where the Hydrogen release is restricted, for example, by venting through a single PRD, the effects are relatively minor and localised close to the area of the flammable cloud. With increasing Hydrogen storage pressure, the maximum energy available in a flammable cloud after a release increases, as do the predicted overpressures resulting from combustion. Even in the relatively confined environment considered, the effects on the combustion regime are closer to what would be expected in a more open environment, i.e. a slow deflagration should be expected. Among the cases studied the most severe one was a rapid release of the entire Hydrogen (40 kg) or natural gas (168 kg) storage system within the confines of a tunnel. In this case there was minimal difference between a release from a 20 MPa natural gas system or a 20 MPa Hydrogen system, however, a similar release from a 35 MPa Hydrogen system was significantly more severe and particularly in terms of predicted overpressures. The present study has also highlighted that the ignition point significantly affects the combustion regime in confined environments. The results have indicated that critical cases in tunnels may tend towards a fast deflagration, or where there are turbulence generating features, e.g. multiple obstacles, there is the possibility that the combustion regime could progress to a detonation. When comparing the urban and tunnel environments, a similar release of Hydrogen is significantly more severe in a tunnel, and the energy available in the flammable cloud is greater and remains for a longer period in tunnels. When comparing Hydrogen and natural gas releases, for the cases and environments investigated and within the limits of the assumptions, it appears that Hydrogen requires different mitigation measures in order that the potential effects are similar to those of natural gas in case of an accident. With respect to a PRD opening strategy, Hydrogen storage systems should be designed to avoid simultaneous opening of all PRD, and that for the consequences of the released energy to be mitigated, either the number of PRDs opening should be limited or their vents to atmosphere should be restricted (the latter point would require validation by a comprehensive risk assessment).

E. Papanikolaou - One of the best experts on this subject based on the ideXlab platform.

  • Hydrogen permeation from CGH2 vehicles in garages: CFD dispersion calculations and experimental validation
    International Journal of Hydrogen Energy, 2010
    Co-Authors: Alexander G. Venetsanos, B. Cariteau, P Adams, E. Papanikolaou, Alain Bengaouer
    Abstract:

    Abstract The time and space evolution of the distribution of Hydrogen in confined settings was investigated computationally and experimentally for permeation from typical Compressed Gaseous Hydrogen (CGH2) storage systems for buses or cars. The main goal was to examine whether Hydrogen is distributed homogeneously within a garage-like facility or whether stratified conditions are developed, under certain conditions. The nominal Hydrogen flow rate considered was 1.087 L/min in a bus facility with a volume of 681 m 3 . The release was assumed to be directed upwards from a 0.15 m diameter hole located at the middle part of the bus cylinders casing. Ventilation rates up to 0.03 air changes per hour (ACH) were considered. Simulated time periods extended up to 20 days. The CFD simulations performed with the ADREA-HF code showed that fully homogeneous conditions exist for low ventilation rates, while stratified conditions prevail for higher ventilation rates. Regarding flow structure it was found that the vertical concentration profiles can be considered as the superposition of the concentration at the floor (driven by diffusion) plus a concentration difference between floor and ceiling (driven by buoyancy forces). In all cases considered this concentration difference was found to be less than 0.5%. The dispersion experiments were performed in a large scale garage-like enclosure of 40 m 3 using helium (GARAGE facility). Comparison between CFD simulations and experiments showed that the predicted concentrations were in good agreement with the experimental data. Finally, simulations were performed using two integral models: the fully homogeneous model and a two-layer model and the results were compared both against CFD and the experimental data.

  • HySafe standard benchmark Problem SBEP-V11: Predictions of Hydrogen release and dispersion from a CGH2 bus in an underpass
    International Journal of Hydrogen Energy, 2010
    Co-Authors: Alexander G. Venetsanos, E. Papanikolaou, Olav R. Hansen, Prankul Middha, Javier García, M. Heitsch, D. Baraldi, P Adams
    Abstract:

    One of the tasks of the HySafe Network of Excellence was the evaluation of available CFD tools and models for dispersion and combustion in selected Hydrogen release scenarios identified as “standard benchmark problems” (SBEPs). This paper presents the results of the HySafe standard benchmark problem SBEP-V11. The situation considered is a high pressure Hydrogen jet release from a Compressed Gaseous Hydrogen (CGH2) bus in an underpass. The bus considered is equipped with 8 cylinders of 5 kg Hydrogen each at 35 MPa storage pressure. The underpass is assumed to be of the common beam and slab type construction with I-beams spanning across the highway at 3 m centres (normal to the bus), plus cross bracing between the main beams, and light armatures parallel to the bus direction. The main goal of the present work was to evaluate the role of obstructions on the underside of the bridge deck on the dispersion patterns and assess the potential for Hydrogen accumulation. Four HySafe partners participated in this benchmark, with 4 different CFD codes, ADREA-HF, CFX, FLACS and FLUENT. Four scenarios were examined in total. In the base case scenario 20 kg of Hydrogen was released in the basic geometry. In Sensitivity Test 1 the release position was moved so that the Hydrogen jet could hit directly the light armature on the roof of the underpass. In Sensitivity Test 2 the underside of the bridge deck was flat. In Sensitivity Test 3 the release was from one cylinder instead of four (5 kg instead of 20). The paper compares the results predicted by the four different computational approaches and attempts to identify the reasons for observed disagreements. The paper also concludes on the effects of the obstructions on the underside of the bridge deck.

Prankul Middha - One of the best experts on this subject based on the ideXlab platform.

  • HySafe standard benchmark Problem SBEP-V11: Predictions of Hydrogen release and dispersion from a CGH2 bus in an underpass
    International Journal of Hydrogen Energy, 2010
    Co-Authors: Alexander G. Venetsanos, E. Papanikolaou, Olav R. Hansen, Prankul Middha, Javier García, M. Heitsch, D. Baraldi, P Adams
    Abstract:

    One of the tasks of the HySafe Network of Excellence was the evaluation of available CFD tools and models for dispersion and combustion in selected Hydrogen release scenarios identified as “standard benchmark problems” (SBEPs). This paper presents the results of the HySafe standard benchmark problem SBEP-V11. The situation considered is a high pressure Hydrogen jet release from a Compressed Gaseous Hydrogen (CGH2) bus in an underpass. The bus considered is equipped with 8 cylinders of 5 kg Hydrogen each at 35 MPa storage pressure. The underpass is assumed to be of the common beam and slab type construction with I-beams spanning across the highway at 3 m centres (normal to the bus), plus cross bracing between the main beams, and light armatures parallel to the bus direction. The main goal of the present work was to evaluate the role of obstructions on the underside of the bridge deck on the dispersion patterns and assess the potential for Hydrogen accumulation. Four HySafe partners participated in this benchmark, with 4 different CFD codes, ADREA-HF, CFX, FLACS and FLUENT. Four scenarios were examined in total. In the base case scenario 20 kg of Hydrogen was released in the basic geometry. In Sensitivity Test 1 the release position was moved so that the Hydrogen jet could hit directly the light armature on the roof of the underpass. In Sensitivity Test 2 the underside of the bridge deck was flat. In Sensitivity Test 3 the release was from one cylinder instead of four (5 kg instead of 20). The paper compares the results predicted by the four different computational approaches and attempts to identify the reasons for observed disagreements. The paper also concludes on the effects of the obstructions on the underside of the bridge deck.

Olav R. Hansen - One of the best experts on this subject based on the ideXlab platform.

  • HySafe standard benchmark Problem SBEP-V11: Predictions of Hydrogen release and dispersion from a CGH2 bus in an underpass
    International Journal of Hydrogen Energy, 2010
    Co-Authors: Alexander G. Venetsanos, E. Papanikolaou, Olav R. Hansen, Prankul Middha, Javier García, M. Heitsch, D. Baraldi, P Adams
    Abstract:

    One of the tasks of the HySafe Network of Excellence was the evaluation of available CFD tools and models for dispersion and combustion in selected Hydrogen release scenarios identified as “standard benchmark problems” (SBEPs). This paper presents the results of the HySafe standard benchmark problem SBEP-V11. The situation considered is a high pressure Hydrogen jet release from a Compressed Gaseous Hydrogen (CGH2) bus in an underpass. The bus considered is equipped with 8 cylinders of 5 kg Hydrogen each at 35 MPa storage pressure. The underpass is assumed to be of the common beam and slab type construction with I-beams spanning across the highway at 3 m centres (normal to the bus), plus cross bracing between the main beams, and light armatures parallel to the bus direction. The main goal of the present work was to evaluate the role of obstructions on the underside of the bridge deck on the dispersion patterns and assess the potential for Hydrogen accumulation. Four HySafe partners participated in this benchmark, with 4 different CFD codes, ADREA-HF, CFX, FLACS and FLUENT. Four scenarios were examined in total. In the base case scenario 20 kg of Hydrogen was released in the basic geometry. In Sensitivity Test 1 the release position was moved so that the Hydrogen jet could hit directly the light armature on the roof of the underpass. In Sensitivity Test 2 the underside of the bridge deck was flat. In Sensitivity Test 3 the release was from one cylinder instead of four (5 kg instead of 20). The paper compares the results predicted by the four different computational approaches and attempts to identify the reasons for observed disagreements. The paper also concludes on the effects of the obstructions on the underside of the bridge deck.