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Rejeb Ben Maad - One of the best experts on this subject based on the ideXlab platform.

  • Characterisation of a Thermal Plume evolving in a confined environment: application to fire in tunnel
    International Journal of Engineering Systems Modelling and Simulation, 2015
    Co-Authors: Hatem Saafi, Ahmedou Ould Mohamed Mahmoud, Rejeb Ben Maad
    Abstract:

    This investigation analyses the behaviour of a turbulent Thermal Plume evolving in a horizontal tunnel. The Thermal Plume is created by a hot disk. First, we studied the evolution of the Thermal Plume without ventilation system. The study of the average and fluctuating Thermal and dynamic fields shows three zones during the vertical evolution of the free Plume. A first zone close to the source, serving to the Plume supply in fresh air, is characterised by the apparition of three exhausts of the Thermal Plume. Followed by a second zone where the main escape undergoes a contraction. Finally, a third zone where the Thermal Plume accumulates and undergoes a flow upstream named backlayering and a flow downstream that borders the ceiling to leave by the free part of the tunnel. We then determined the effects of the source site and longitudinal ventilation on the Plume structure.

  • Experimental Study of a Thermal Plume Evolving Inside a Rectangular Tunnel: Effects of the Source Height
    2014
    Co-Authors: Hatem Saafi, Ahmedou Ould Mohamed Mahmoud, Rejeb Ben Maad
    Abstract:

    The aim of this work is to simulate experimentally a Plume of fire placed at different heights evolving inside a horizontal tunnel, in order to determine the effect of the source site on the Plume structure. The Plume is produced from an electrically heated disc at a constant and uniform temperature. It is then placed inside the tunnel. First, we studied the evolution of the Thermal Plume while placing the source at a height above the ground. The study of the Thermal and dynamic fields of the flow shows the existence of 3 zones during the vertical evolution of the Thermal Plume. In the first zone, the flow is strongly influenced by the presence of the Thermal Plume generating source. Followed by a second zone where the Plume undergoes a contraction which prepares the flow to be passed in a third zone where the Thermal Plume divides into 2 parts by touching the ceiling. The first part (backlayering) moves towards the side blocked by the blower and the second moves towards the free side while going along the ceiling. We then determined the effect of the source site compared to the ground level on the behavior of the Thermal Plume inside the tunnel. For that, 3 sites of the source (h = 2 cm, h = 7, 5 cm and h = 15 cm) were studied. The comparative study shows that the structure of the flow is influenced by the site of the hot source. doi: 10.14456/WJST.2015.15

  • Experimental study of the structure of a Thermal Plume inside a rectangular tunnel
    IOSR Journal of Applied Physics, 2013
    Co-Authors: Hatem Saafi, Ahmedou Ould Mohamed Mahmoud, Rejeb Ben Maad
    Abstract:

    The objective of this work is to experimentally simulate a Plume developing inside a horizontal tunnel. The experimental device used in this simulation is essentially constituted of a hot disk, a rectangular tunnel and a ventilation system. The hot disk is heated by Joule effect to a constant and uniform temperature, and placed inside the tunnel. The hot source generates a Thermal Plume. We first studied the evolution of the Thermal Plume without ventilation system. The study of the average and fluctuating Thermal and dynamic fields shows three zones during the vertical evolution of the free Plume. A first zone close to the source, serving to the Plume supply in fresh air, is characterized by the apparition of three escapes of the Thermal Plume. Followed by a second zone where the main escape undergoes a contraction. Finally, a third zone where the Thermal Plume accumulates and undergoes a flow upstream named backlayering and a flow downstream that borders the ceiling to leave by the free part of the tunnel. Keywords Fire Plume, Fire tunnel, Thermal Plume, turbulent natural convection. I. INTRODUCTION The Thermal Plume model is an experimental methodology usable easily to simulate the fire Plume (1, 2). The Thermal model contributes to better understand many practical fire problems such as problems associated with fire tunnel and flow encountered in fires of structural elements of buildings. The interaction of these material surroundings with the fire Plumes reveals very complex physical mechanisms. From a fundamental viewpoint, the study of the interaction of the Thermal Plume with the vertical walls that surrounds it began with Agator's work (3) on the influence of a wall placed in the vicinity of the Plume source. He noted that the Plume is attracted toward the wall. A. O. M. Mahmoud and al. (4, 5, 6) are the first who were studied the evolution of a Thermal Plume in semi-confined geometry. They studied the evolution of a Thermal Plume produced by a flat disc heated at 300° C and placed at the entrance of an open-ended vertical cylinder. They noted that the Plume interacts narrowly with the thermosiphon flow which develops along the internal wall of the cylinder. Contrary to previous works (7, 8, 9, 10), they noticed the appearance of a supplementary zone in addition to the two classic zones which characterize the vertical evolution of the free Plume. Just above of the source, the instability zone is characterized by the formation of rotating rolls and by the existence of three extrema of temperature and velocity profiles. Higher, a second zone of turbulence pre- established followed by a last zone where the turbulence is fully established. J. Zinoubi et al. (11, 12) continued this experimental work by studying the form factors effect of the Plume evolution inside a vertical cylinder. Using the visualization and analysis of the Thermal and dynamic profiles of the flow, they showed the existence of three zones described previously. By studying the influence of the cylinder height, J. Zinoubi et al. (13) noted a blocking of the ascending flow in the third zone due to the lateral expansion of the Plume. They also showed that a choice of the cylinder height not exceeding the second zone of the flow let us avoid this blocking. In order to determine the geometry effect, N. Taoufik et al. (14) studied the evolution of a Thermal Plume generated by a flat disc inside an open-ended rectangular canal. They noted the existence of the three zones observed in the cylindrical geometry. Also, they noticed the contraction of the rotating rolls size located in the first zone of the flow. Recently, A. O. Mahmoud et al. (1) studied the effects of source air entrainment on the flow structure induced by two heat sources, one placed at ground level, the other at a height above the ground. The experimental results permitted to specify that the additional vertical contribution of the air entrainment especially entails a substantial change of the flow structure of the Plume, an important elongation of the height of the Plume spread, a considerable increase of the flow rate of the Plume and an important elevation of the Thermal flux absorbed by the air. It is clear that these works were essentially interested to the determination of the effects of the emplacement, the heat release of the fire and the tunnel geometry on the critical ventilation velocity. The physical structure of the Plume inside tunnel has not been studied. A fire Plume inside tunnel has very complex

  • Experimental characterization of a free Thermal Plume and in interaction with its material environment
    Applied Thermal Engineering, 2010
    Co-Authors: Taoufik Naffouti, Jamil Zinoubi, Rejeb Ben Maad
    Abstract:

    Abstract This investigation analyses the behaviour of a turbulent Thermal Plume evolving in a neutral environment and in interaction with its surrounding material. The Thermal Plume is created by a rectangular hot source. This source is placed at the entry of a vertical parallelepipedic canal opened at the ends. Firstly, we studied the behaviour of a free Thermal Plume. The flow visualization and the analysis of the Thermal and dynamic fields enabled us to detect the existence of two zones during the vertical evolution of the Plume. A first zone of Plume development followed by a zone of established turbulence. Secondly, we described the structure of a Thermal Plume produced by the same source inside the vertical canal. In this case the experimental results show clearly a change of the turbulent structure of the flow in comparison with the free Plume. This difference is especially characterized by the appearance of a supplementary zone just above the source that is added to the two zones described previously. In addition, the comparison of the two studied configurations showed that the structure of the Plume is narrowly affected by the confinement. In order to better define the fine structure of the flow, the temperature fluctuations spectra are analyzed. This spectral analysis enables us to show the fast destruction of the big structures vortexes by the confinement effect to give a smaller structure.

  • Experimental study of the effects of a Thermal Plume entrainment mode on the flow structure: Application to fire
    Fire Safety Journal, 2009
    Co-Authors: Ahmedou Ould Mohamed Mahmoud, Jamel Bouslimi, Rejeb Ben Maad
    Abstract:

    Abstract The aim of this work is to experimentally simulate two heat sources of fire, one placed at ground level, the other at a height above the ground, in order to determine the effect of source air entrainment on the resulting flow structure. The development of a free Thermal Plume was examined by generating a Plume produced from an electrically heated disk at a constant temperature. We first studied the behavior of a Thermal Plume induced by a disk embedded in a horizontal plate placed at the level of the ground. This configuration ensured a regular lateral entrainment of air to the Plume. The analysis of the average fields as well as the axial evolution of velocity and temperature showed an important widening of the profiles that encouraged a faster spread of the Plume. We then determined the structure of the Thermal Plume generated by the same source placed at a height above the ground, ensuring simultaneous vertical and lateral entrainment of air into the resulting Plume. Results obtained reveal a vertical elongation of the average profiles that limits the lateral extension of the Plume flow. Comparison of the Plumes produced from the two configurations showed that the flow structure is strongly influenced by the nature of the source of air entrainment. An additional vertical contribution of air entrainment caused the location of the maximum axial velocity above the source to be raised, with the flow rate and the Thermal flux absorbed by the air experiencing a relative increase of the order of 14% and 34%, respectively.

Patrice Joubert - One of the best experts on this subject based on the ideXlab platform.

  • numerical study of an unsteady confined Thermal Plume under the influence of gas radiation
    International Journal of Thermal Sciences, 2020
    Co-Authors: Ying Wang, Anne Sergent, Didier Saury, Denis Lemonnier, Patrice Joubert
    Abstract:

    Abstract Influence of gas radiation on a Thermal Plume initiated by a linear heat source in a confined cavity is investigated through numerical simulations. A 2D pure convection case is first considered to validate the numerical code by comparing the critical Rayleigh number against literature results. Then, simulations are extended to 3D configurations for three different values of the Rayleigh number: 10 6 , 1.2 × 10 6 and 1.2 × 10 7 . The evolution of the Plume is analyzed and shows that the transition to unsteadiness appears much earlier for 3D case. Periodic solutions in time exhibit a stationary plane wave which is further broken in the chaotic regime. Finally, gas radiation is introduced at R a = 1.2 × 10 7 by considering different gaseous media: on one hand, a gray gas model with various optical thicknesses, and on the other hand, a real gas model for humid air (air - H2O mixture). Results show a strong influence of the radiative transfer on flow regimes. By increasing the optical thickness, radiation tends to stabilize the Plume and delays the onset of unsteadiness. Comparison of the time-averaged temperature and velocity distributions for the considered gas models indicates that gas radiation reduces the spatial spreading of the Plume but has little effects on the kinetic field.

  • Numerical study of an unsteady confined Thermal Plume under the influence of gas radiation
    International Journal of Thermal Sciences, 2020
    Co-Authors: Ying Wang, Anne Sergent, Didier Saury, Denis Lemonnier, Patrice Joubert
    Abstract:

    Influence of gas radiation on a Thermal Plume initiated by a linear heat source in a confined cavity is investigated through numerical simulations. A 2D pure convection case is first considered to validate the numerical code by comparing the critical Rayleigh number against literature results. Then, simulations are extended to 3D con­ ars much earlier for 3D case. Periodic solutions in time exhibit a stationary plane wave which is further broken in the chaotic regime. Finally, gas radiation is introduced at Ra = 1,2 10**7 by considering different gaseous media: on one hand, a gray gas model with various optical thicknesses, and on the other hand, a real gas model for humid air (air - H 2 O mixture). Results show a strong influence of the radiative transfer on flow regimes. By increasing the optical thickness, radiation tends to stabilize the Plume and delays the onset of unsteadiness. Comparison of the time-averaged temperature and velocity distributions for the considered gas models indicates that gas radiation reduces the spatial spreading of the Plume but has little effects on the kinetic field.

Ying Wang - One of the best experts on this subject based on the ideXlab platform.

  • numerical study of an unsteady confined Thermal Plume under the influence of gas radiation
    International Journal of Thermal Sciences, 2020
    Co-Authors: Ying Wang, Anne Sergent, Didier Saury, Denis Lemonnier, Patrice Joubert
    Abstract:

    Abstract Influence of gas radiation on a Thermal Plume initiated by a linear heat source in a confined cavity is investigated through numerical simulations. A 2D pure convection case is first considered to validate the numerical code by comparing the critical Rayleigh number against literature results. Then, simulations are extended to 3D configurations for three different values of the Rayleigh number: 10 6 , 1.2 × 10 6 and 1.2 × 10 7 . The evolution of the Plume is analyzed and shows that the transition to unsteadiness appears much earlier for 3D case. Periodic solutions in time exhibit a stationary plane wave which is further broken in the chaotic regime. Finally, gas radiation is introduced at R a = 1.2 × 10 7 by considering different gaseous media: on one hand, a gray gas model with various optical thicknesses, and on the other hand, a real gas model for humid air (air - H2O mixture). Results show a strong influence of the radiative transfer on flow regimes. By increasing the optical thickness, radiation tends to stabilize the Plume and delays the onset of unsteadiness. Comparison of the time-averaged temperature and velocity distributions for the considered gas models indicates that gas radiation reduces the spatial spreading of the Plume but has little effects on the kinetic field.

  • Numerical study of an unsteady confined Thermal Plume under the influence of gas radiation
    International Journal of Thermal Sciences, 2020
    Co-Authors: Ying Wang, Anne Sergent, Didier Saury, Denis Lemonnier, Patrice Joubert
    Abstract:

    Influence of gas radiation on a Thermal Plume initiated by a linear heat source in a confined cavity is investigated through numerical simulations. A 2D pure convection case is first considered to validate the numerical code by comparing the critical Rayleigh number against literature results. Then, simulations are extended to 3D con­ ars much earlier for 3D case. Periodic solutions in time exhibit a stationary plane wave which is further broken in the chaotic regime. Finally, gas radiation is introduced at Ra = 1,2 10**7 by considering different gaseous media: on one hand, a gray gas model with various optical thicknesses, and on the other hand, a real gas model for humid air (air - H 2 O mixture). Results show a strong influence of the radiative transfer on flow regimes. By increasing the optical thickness, radiation tends to stabilize the Plume and delays the onset of unsteadiness. Comparison of the time-averaged temperature and velocity distributions for the considered gas models indicates that gas radiation reduces the spatial spreading of the Plume but has little effects on the kinetic field.

J.c. Elicer-cortés - One of the best experts on this subject based on the ideXlab platform.

  • Temperature spectra from a turbulent Thermal Plume by ultrasound scattering
    Experimental Thermal and Fluid Science, 2004
    Co-Authors: J.c. Elicer-cortés, R. Contreras, Denis Boyer, M. Pavageau, R. H. Hernández
    Abstract:

    Abstract This paper reports the results of a study on temperature inhomogeneities conducted on a Thermal Plume by using ultrasound scattering as a non-intrusive measurement technique. The Plume rises from a metallic disk which can be heated up to 800 °C. The working fluid is air at atmospheric pressure. In the measurement technique, an incoming ultrasound wave is emitted towards the Thermal Plume. The incident wave is scattered because of non-linear couplings with the flow instabilities present in the measurement region. The scattered wave carries information about those flow instabilities. The technique allows for the retrieving of this information. The shape of the obtained spectrum of temperature fluctuations as a function of wave vector modulus | q → |=q is consistent with previous theoretical analysis. Three qualitatively different regions were identified: first, a production region characterized by a q 2 law; secondly, a region with behavior as per q −3 associated with a buoyancy region and; finally, a dissipation region associated with a q −7 law. These spectral regions characterize the energy transfers mechanisms among the length scales of flow investigated here. A coefficient of anisotropy γ was defined to analyze anisotropic features of the flow.

  • Detection and estimation of the istropy degree of temperature scales in a turbulent Thermal Plume by ultrasound scattering
    International Communications in Heat and Mass Transfer, 2003
    Co-Authors: J.c. Elicer-cortés, J. Tapia, M. Pavageau
    Abstract:

    A non-intrusive acoustical approach was used to characterize fine structure of temperature and the isotropy degree in a turbulent Thermal Plume. For this a suitable coefficient y was defined. Results give indication about anisotropy over the whole scale range considered in this study, which is attributed to shear stress for larger scales while buoyancy acts on smaller temperature scales

M. Pavageau - One of the best experts on this subject based on the ideXlab platform.

  • Temperature spectra from a turbulent Thermal Plume by ultrasound scattering
    Experimental Thermal and Fluid Science, 2004
    Co-Authors: J.c. Elicer-cortés, R. Contreras, Denis Boyer, M. Pavageau, R. H. Hernández
    Abstract:

    Abstract This paper reports the results of a study on temperature inhomogeneities conducted on a Thermal Plume by using ultrasound scattering as a non-intrusive measurement technique. The Plume rises from a metallic disk which can be heated up to 800 °C. The working fluid is air at atmospheric pressure. In the measurement technique, an incoming ultrasound wave is emitted towards the Thermal Plume. The incident wave is scattered because of non-linear couplings with the flow instabilities present in the measurement region. The scattered wave carries information about those flow instabilities. The technique allows for the retrieving of this information. The shape of the obtained spectrum of temperature fluctuations as a function of wave vector modulus | q → |=q is consistent with previous theoretical analysis. Three qualitatively different regions were identified: first, a production region characterized by a q 2 law; secondly, a region with behavior as per q −3 associated with a buoyancy region and; finally, a dissipation region associated with a q −7 law. These spectral regions characterize the energy transfers mechanisms among the length scales of flow investigated here. A coefficient of anisotropy γ was defined to analyze anisotropic features of the flow.

  • Detection and estimation of the istropy degree of temperature scales in a turbulent Thermal Plume by ultrasound scattering
    International Communications in Heat and Mass Transfer, 2003
    Co-Authors: J.c. Elicer-cortés, J. Tapia, M. Pavageau
    Abstract:

    A non-intrusive acoustical approach was used to characterize fine structure of temperature and the isotropy degree in a turbulent Thermal Plume. For this a suitable coefficient y was defined. Results give indication about anisotropy over the whole scale range considered in this study, which is attributed to shear stress for larger scales while buoyancy acts on smaller temperature scales