A. Gourbil - Academia.edu (original) (raw)
Papers by A. Gourbil
OATAO is an open access repository that collects the work of Toulouse researchers and makes it fr... more OATAO is an open access repository that collects the work of Toulouse researchers and makes it freely available over the web where possible. This is an author-deposited version published in : http://oatao.univ-toulouse.fr/ Eprints ID : 16112 To cite this version : ABSTRACT Forced-convection boiling is experimentally studied in a two-dimensional heat-generating model porous medium. Visualizations of the two-phase flow and thermal measurements inside the test section are performed. Boiling curves show that the critical heat flux on a specific heating element decreases as the global thermal power released by the porous medium increases. Also, visualizations show that the void fraction in the test section increases with the global heating power. An image processing program was developed to measure the void fraction, in order to investigate its influence on the critical heat flux. Such a measurement is validated using a second test section where air is injected at a known flow rate insid...
International Journal of Heat and Mass Transfer, 2016
Experimental Thermal and Fluid Science
Dryout experiments are performed in a quasi two-dimensional heat-generating model porous medium, ... more Dryout experiments are performed in a quasi two-dimensional heat-generating model porous medium, with bottom flooding. The test section is composed of an array of heating cylinders placed between two ceramic plates. It is held vertically and a liquid (HFE-7000) is injected from bottom at a controlled flow rate, pressure and temperature. Dryout incipient power is investigated by applying an increasing thermal power to a bundle of heating cylinders until a dry zone is detected. The liquid inlet mass fluxes range from 1.0 kg m s 2 1 to 10.5 kg m s 2 1 and the heat fluxes are between 195 kW m 2 and 1086 kW m 2. Two kinds of dryout phenom-enology are observed. First, at low liquid injection rate (below 4.2 kg m s 2 1 inlet mass flux), reaching the dryout power results into a liquid front receding from the top of the test section to the upper limit of the heated zone, while downstream the heated zone, the porous medium is vapour-saturated. Second, at higher flow rate (over 5.2 kg m s 2 1 inlet mass flux), the boiling crisis happens at the surface of a single heating element, resulting in a local film boiling, whereas a two-phase flow still go through the whole test section. In both cases, high-speed visualizations allow characterizing 8 boiling/flow regimes, depending on the inlet mass flux, the power released by the heated zone, and the location inside the porous medium. In particular, when reaching the dryout incipient power, the existence of a pulsed flow regime is highlighted. Such a characterization of boiling/ flow regimes might be helpful in improving dryout models.
This paper presents a pore-scale experimental study of the reflooding of a two-dimensional model ... more This paper presents a pore-scale experimental study of the reflooding of a two-dimensional model porous medium. The objective is to better understand the reflooding mechanisms in play in the context of nuclear reactor safety. The hot debris bed that forms in a nuclear reactor following a loss of coolant accident is comparable to a heat-generating porous medium. Its cooling by water reflooding involves intense boiling mechanisms that must be modeled properly to assess mitigation procedures. The experimental study presented in this paper focuses on the phenomenology of reflooding of a model porous medium composed of a bank of mm-scale heating cylinders placed between two ceramic plates. A Fluorinert TM liquid, HFE-7000, is injected at a temperature close to saturation into the dry and super-heated porous medium. Each cylinder of the test section is used both as a heating element and a temperature probe, which enables to track the evolution of the three different macroscopic zones identified during cooling of the system. The reflooding dynamics, in particular the cooling fronts velocities, are thus determined thanks to pore-scale thermal measurements together with direct visualizations. The influence of the injection flow rate and of the heating power are studied in a parametric way.
OATAO is an open access repository that collects the work of Toulouse researchers and makes it fr... more OATAO is an open access repository that collects the work of Toulouse researchers and makes it freely available over the web where possible. This is an author-deposited version published in : http://oatao.univ-toulouse.fr/ Eprints ID : 16112 To cite this version : ABSTRACT Forced-convection boiling is experimentally studied in a two-dimensional heat-generating model porous medium. Visualizations of the two-phase flow and thermal measurements inside the test section are performed. Boiling curves show that the critical heat flux on a specific heating element decreases as the global thermal power released by the porous medium increases. Also, visualizations show that the void fraction in the test section increases with the global heating power. An image processing program was developed to measure the void fraction, in order to investigate its influence on the critical heat flux. Such a measurement is validated using a second test section where air is injected at a known flow rate insid...
International Journal of Heat and Mass Transfer, 2016
Experimental Thermal and Fluid Science
Dryout experiments are performed in a quasi two-dimensional heat-generating model porous medium, ... more Dryout experiments are performed in a quasi two-dimensional heat-generating model porous medium, with bottom flooding. The test section is composed of an array of heating cylinders placed between two ceramic plates. It is held vertically and a liquid (HFE-7000) is injected from bottom at a controlled flow rate, pressure and temperature. Dryout incipient power is investigated by applying an increasing thermal power to a bundle of heating cylinders until a dry zone is detected. The liquid inlet mass fluxes range from 1.0 kg m s 2 1 to 10.5 kg m s 2 1 and the heat fluxes are between 195 kW m 2 and 1086 kW m 2. Two kinds of dryout phenom-enology are observed. First, at low liquid injection rate (below 4.2 kg m s 2 1 inlet mass flux), reaching the dryout power results into a liquid front receding from the top of the test section to the upper limit of the heated zone, while downstream the heated zone, the porous medium is vapour-saturated. Second, at higher flow rate (over 5.2 kg m s 2 1 inlet mass flux), the boiling crisis happens at the surface of a single heating element, resulting in a local film boiling, whereas a two-phase flow still go through the whole test section. In both cases, high-speed visualizations allow characterizing 8 boiling/flow regimes, depending on the inlet mass flux, the power released by the heated zone, and the location inside the porous medium. In particular, when reaching the dryout incipient power, the existence of a pulsed flow regime is highlighted. Such a characterization of boiling/ flow regimes might be helpful in improving dryout models.
This paper presents a pore-scale experimental study of the reflooding of a two-dimensional model ... more This paper presents a pore-scale experimental study of the reflooding of a two-dimensional model porous medium. The objective is to better understand the reflooding mechanisms in play in the context of nuclear reactor safety. The hot debris bed that forms in a nuclear reactor following a loss of coolant accident is comparable to a heat-generating porous medium. Its cooling by water reflooding involves intense boiling mechanisms that must be modeled properly to assess mitigation procedures. The experimental study presented in this paper focuses on the phenomenology of reflooding of a model porous medium composed of a bank of mm-scale heating cylinders placed between two ceramic plates. A Fluorinert TM liquid, HFE-7000, is injected at a temperature close to saturation into the dry and super-heated porous medium. Each cylinder of the test section is used both as a heating element and a temperature probe, which enables to track the evolution of the three different macroscopic zones identified during cooling of the system. The reflooding dynamics, in particular the cooling fronts velocities, are thus determined thanks to pore-scale thermal measurements together with direct visualizations. The influence of the injection flow rate and of the heating power are studied in a parametric way.