10 research outputs found
Etude expérimentale d’une interaction thermique au sein d’un fluide
No full textDuring a reactivity insertion accident, the temperature and the pressure rapidly increase inside the rod and can lead to the rupture of the clad and the ejection of fuel toward the coolant. Since the fuel could be finely fragmented, the thermal interaction between fuel and coolant (FCI) could create a pressure wave as well as a large vapor volume. Safety-related consequences of the FCI may be related to both phenomena. Past experimental studies concerning such a RIA related FCI are in-pile experiments in thermal hydraulics conditions that differ from PWR conditions. Therefore validation of a simulation tool from these data and extrapolation to reactors conditions is subject to uncertainties. This experimental study is devoted to the violent thermal interaction between a hot material and a fluid. An experimental bench has been designed. It is mainly a cylindrical tube, where the interaction takes place, connected to a larger vessel as a compressibility tank. To reduce the required level of energy as well as temperature and pressure conditions, liquid carbon dioxide has been chosen to simulate water in PWR conditions. Respect of thermodynamics similarity criteria allows to lower pressure by a factor 3 and energy per unit mass fluid by a factor 5. To produce the energy pulse, a tungsten wire is heated by Joule effect from the discharge of a 27 mF capacity. Design of the tank allows for a relatively long mechanical relaxation of the coolant with regards to the heat transfer kinetics. The pressure wave is recorded thanks to four dynamic pressure sensors along the tube. Two dual tip fiber optical probes allow characterizing the kinetics of vapor formation near the wire. The data acquisition system operates with a required frequency of the MHz range. This test bench allows to record the local behavior of the fluid such as the pressurization of the liquid. A very clear pressure wave have been recorded just after weak energy pulse around 0.2 kJ. The influence of some major parameters on these quantities have been studied. For example, the liquid level in the tank is increased between two tests up to be totally fu ll, so, the influence of the compressibility is highlighted. Also, three different wire diameters have been used to modify the heat transfer kinetics. Finally, several intensities of the energy pulse have been considered. All these studies help to improve the understanding on the thermal interaction potentially involved in the nuclear reactor safety context.Un accident d’insertion de réactivité (RIA) dans un cœur nucléaire pourrait provoquer la rupture d’une gaine et l’éjection d’une fine poudre de combustible chaud dans le caloporteur. La réponse du fluide peut être violente. L’étude de cette interaction (Fuel/Coolant Interaction FCI) est importante pour la sûreté nucléaire. Plusieurs études et expériences ont été menées avec de l’eau ou du sodium ou sont prévues dans le cadre des essais intégraux du programme international dans le réacteur CABRI. Cependant, les conditions complexes ne permettent pas la mesure des grandeurs locales nécessaires à l’étude de la dynamique de vaporisation. En effet, effectuer des expériences de vaporisation violente avec de l’eau requiert beaucoup d’énergie et des équipements résistant aux hautes pressions, notamment pour reproduire les conditions de fonctionnement d’une centrale nucléaire de type REP. Il est ainsi intéressant d’utiliser un autre fluide, tel que le dioxyde de carbone, dont les propriétés thermodynamiques (pression critique, enthalpie de vaporisation...) réduisent ces contraintes. Néanmoins, afin de pouvoir comparer et utiliser les observations de l’expérience, il est indispensable d’établir et de vérifier des lois de similitudes entre les deux fluides. L’étude de ces similarités entre l’eau et le dioxyde de carbone a établi qu’en conservant la pression réduite ainsi que le titre thermodynamique, on obtient des rendements similaires pour la conversion de l’énergie thermique en travail avec des énergies mises en jeu divisées par cinq. Ceci a permis d’envisager la conception et la réalisation d’un banc d’essais pour provoquer l’interaction thermique violente au sein d’un fluide. Afin de reproduire la cinétique de l’interaction, la géométrie du système a été adaptée. L’impulsion d’énergie au sein du fluide est générée à l’aide d’un filament de tungstène subissant la décharge d’une batterie de condensateurs à l’extrémité basse d’un cylindre. Au-dessus de ce cylindre, un réservoir de grand volume offre une source de compressibilité. L’enceinte contenant le CO2 liquide aux conditions thermodynamiques adaptables est instrumentée à l’aide de capteurs de pression le long du tube et des sondes optiques pour repérer la phase vapeur. Ce banc expérimental a permis d’acquérir des observations locales de la réaction telle que la montée en pression du liquide. Un pic de pression franc a été observé pour des impulsions d’énergie relativement faible, de l’ordre de 0,2 kJ. Plusieurs études sur les paramètres d’influences ont été menées. Notamment, l’influence de l’énergie, du diamètre du fil et du sous-refroidissement
Experimental study of a solid/liquid thermal interaction
No full textUn accident d’insertion de réactivité (RIA) dans un cœur nucléaire pourrait provoquer la rupture d’une gaine et l’éjection d’une fine poudre de combustible chaud dans le caloporteur. La réponse du fluide peut être violente. L’étude de cette interaction (Fuel/Coolant Interaction FCI) est importante pour la sûreté nucléaire. Plusieurs études et expériences ont été menées avec de l’eau ou du sodium ou sont prévues dans le cadre des essais intégraux du programme international dans le réacteur CABRI. Cependant, les conditions complexes ne permettent pas la mesure des grandeurs locales nécessaires à l’étude de la dynamique de vaporisation. En effet, effectuer des expériences de vaporisation violente avec de l’eau requiert beaucoup d’énergie et des équipements résistant aux hautes pressions, notamment pour reproduire les conditions de fonctionnement d’une centrale nucléaire de type REP. Il est ainsi intéressant d’utiliser un autre fluide, tel que le dioxyde de carbone, dont les propriétés thermodynamiques (pression critique, enthalpie de vaporisation...) réduisent ces contraintes. Néanmoins, afin de pouvoir comparer et utiliser les observations de l’expérience, il est indispensable d’établir et de vérifier des lois de similitudes entre les deux fluides. L’étude de ces similarités entre l’eau et le dioxyde de carbone a établi qu’en conservant la pression réduite ainsi que le titre thermodynamique, on obtient des rendements similaires pour la conversion de l’énergie thermique en travail avec des énergies mises en jeu divisées par cinq. Ceci a permis d’envisager la conception et la réalisation d’un banc d’essais pour provoquer l’interaction thermique violente au sein d’un fluide. Afin de reproduire la cinétique de l’interaction, la géométrie du système a été adaptée. L’impulsion d’énergie au sein du fluide est générée à l’aide d’un filament de tungstène subissant la décharge d’une batterie de condensateurs à l’extrémité basse d’un cylindre. Au-dessus de ce cylindre, un réservoir de grand volume offre une source de compressibilité. L’enceinte contenant le CO2 liquide aux conditions thermodynamiques adaptables est instrumentée à l’aide de capteurs de pression le long du tube et des sondes optiques pour repérer la phase vapeur. Ce banc expérimental a permis d’acquérir des observations locales de la réaction telle que la montée en pression du liquide. Un pic de pression franc a été observé pour des impulsions d’énergie relativement faible, de l’ordre de 0,2 kJ. Plusieurs études sur les paramètres d’influences ont été menées. Notamment, l’influence de l’énergie, du diamètre du fil et du sous-refroidissement.During a reactivity insertion accident, the temperature and the pressure rapidly increase inside the rod and can lead to the rupture of the clad and the ejection of fuel toward the coolant. Since the fuel could be finely fragmented, the thermal interaction between fuel and coolant (FCI) could create a pressure wave as well as a large vapor volume. Safety-related consequences of the FCI may be related to both phenomena. Past experimental studies concerning such a RIA related FCI are in-pile experiments in thermal hydraulics conditions that differ from PWR conditions. Therefore validation of a simulation tool from these data and extrapolation to reactors conditions is subject to uncertainties. This experimental study is devoted to the violent thermal interaction between a hot material and a fluid. An experimental bench has been designed. It is mainly a cylindrical tube, where the interaction takes place, connected to a larger vessel as a compressibility tank. To reduce the required level of energy as well as temperature and pressure conditions, liquid carbon dioxide has been chosen to simulate water in PWR conditions. Respect of thermodynamics similarity criteria allows to lower pressure by a factor 3 and energy per unit mass fluid by a factor 5. To produce the energy pulse, a tungsten wire is heated by Joule effect from the discharge of a 27 mF capacity. Design of the tank allows for a relatively long mechanical relaxation of the coolant with regards to the heat transfer kinetics. The pressure wave is recorded thanks to four dynamic pressure sensors along the tube. Two dual tip fiber optical probes allow characterizing the kinetics of vapor formation near the wire. The data acquisition system operates with a required frequency of the MHz range. This test bench allows to record the local behavior of the fluid such as the pressurization of the liquid. A very clear pressure wave have been recorded just after weak energy pulse around 0.2 kJ. The influence of some major parameters on these quantities have been studied. For example, the liquid level in the tank is increased between two tests up to be totally fu ll, so, the influence of the compressibility is highlighted. Also, three different wire diameters have been used to modify the heat transfer kinetics. Finally, several intensities of the energy pulse have been considered. All these studies help to improve the understanding on the thermal interaction potentially involved in the nuclear reactor safety context
Thermal characterization of a solid-solid phase change material for energy storage application
No full textInternational audienceThermal energy represents half of the primary energy used in Europe and is one of the main contributor of greenhouse gas emission. Integration of renewable thermal energy sources, such as biomass, solar thermal, geothermal or wasted heat is then a major stake for near future. Thermal Energy Storage (TES) is one of the key component that can help the development of renewable thermal energy in domains like urban heating network or industrial processes, allowing to smooth peaks of demand, to manage the balance with the supply and then to minimize the use of fossil energy.Most of the TES currently operated in the world are based on sensible heat by increasing and decreasing the temperature of a material such as water, thermal oil, molten salt, rock…The use of Phase Change Materials (PCM) as storage medium enable to reach higher energy density for a large temperature range (i.e. 30°C to 1 000 °C [1]). Current technologies use solid-liquid phase PCM as TES medium and reach energy densities from 100 MJ.m-3 for paraffin to 1 000 MJ.m-3 for salt hydrates. These systems show some drawbacks like the presence of a liquid phase which may imply leakage, undercooling or large volume variation of about 10 to 20%V/V upon phase transformation [2] which leads to mechanical stresses for the storage vessel. An alternative solution consists in using solid-solid PCM with about 5-10%V/V phase change variation [1] and that could even later be used as structural material of the TES systems.This study proposes to investigate and compare the thermal behavior of a classical solid-liquid paraffin and a polyalcohol as a solid-solid PCM. Both materials have first been analyzed by calorimetry and then characterized into a thermal bench.The bench used is composed of two thermal loops, a heat exchanger with circular metallic fins composes the former test section. PCM fills the space between the fins. Temperature into the section is measured and used to calculate the heat flux and the energy stored into the system to compare the properties of the solid-solid PCM with the solid-liquid classical paraffin as reference. Latent heat, energy density and thermal conductivity are compared. Furthermore, several thermal cycles are done to study the effect of the aging on both materials
Thermal characterization of a solid-solid phase change material for energy storage application
No full textInternational audienceThermal energy represents half of the primary energy used in Europe and is one of the main contributor of greenhouse gas emission. Integration of renewable thermal energy sources, such as biomass, solar thermal, geothermal or wasted heat is then a major stake for near future. Thermal Energy Storage (TES) is one of the key component that can help the development of renewable thermal energy in domains like urban heating network or industrial processes, allowing to smooth peaks of demand, to manage the balance with the supply and then to minimize the use of fossil energy.Most of the TES currently operated in the world are based on sensible heat by increasing and decreasing the temperature of a material such as water, thermal oil, molten salt, rock…The use of Phase Change Materials (PCM) as storage medium enable to reach higher energy density for a large temperature range (i.e. 30°C to 1 000 °C [1]). Current technologies use solid-liquid phase PCM as TES medium and reach energy densities from 100 MJ.m-3 for paraffin to 1 000 MJ.m-3 for salt hydrates. These systems show some drawbacks like the presence of a liquid phase which may imply leakage, undercooling or large volume variation of about 10 to 20%V/V upon phase transformation [2] which leads to mechanical stresses for the storage vessel. An alternative solution consists in using solid-solid PCM with about 5-10%V/V phase change variation [1] and that could even later be used as structural material of the TES systems.This study proposes to investigate and compare the thermal behavior of a classical solid-liquid paraffin and a polyalcohol as a solid-solid PCM. Both materials have first been analyzed by calorimetry and then characterized into a thermal bench.The bench used is composed of two thermal loops, a heat exchanger with circular metallic fins composes the former test section. PCM fills the space between the fins. Temperature into the section is measured and used to calculate the heat flux and the energy stored into the system to compare the properties of the solid-solid PCM with the solid-liquid classical paraffin as reference. Latent heat, energy density and thermal conductivity are compared. Furthermore, several thermal cycles are done to study the effect of the aging on both materials
First characterization of two phase phenomena occurring during a rapid energy discharge in saturated carbon dioxide
No full textInternational audienceThe aim of this paper is to characterize two-phase phenomena occurring for a rapid energy discharge in the fluid leading to explosive vapour expansion. This study was motivated by the lack of macro-scale experiments characterizing those transient phenomena at high reduced pressure. For that purpose, a complete test section was designed based on the Joule effect to deliver the energy discharge. CO2 was chosen as working fluid, allowing to work at saturation and under saturation conditions. Equipped with pressure sensors and a high-speed camera, the complete process is recorded during few seconds. The thermal shock in the carbon dioxide creates transientpressure peaks and sudden vapour production. The first observed pressure wave is well described as acoustics. This first wave is followed by a quick (60 ms) generation of vapour.The maximum volume of vapour produced is extracted from pressure fluctuations and matches the theoretical value. Following their creation, the bubbles flow upward in the test section as bubbly flow. Visual observation allows the characterization of the shape and the velocity of pertinent bubbles as part of a wobbling flow. This project, motivated by the so-called Fuel Coolant Interaction (FCI) nuclear safety related problematic, brings consistent data allowing to better characterize thesmall scale processes for such transient vaporization phenomena. This paper focuses on a single test performed under saturated conditions
