12 research outputs found
Design and experimental analysis of an Integral Collector Storage (ICS) prototype for DHW production
No full textThis paper presents an innovative solar ICS (Integral Collector Storage) for the production of Domestic Hot Water (DHW). The novelty consists in combining an absorbent surface, heat pipes and a storage cavity made up of a phase change material (PCM) within a single compact casing. The energy performance of the system was experimentally studied in different seasons of the year, with and without domestic hot water production. The temperatures inside the collector were monitored using K-type thermocouples and their trends were analysed and discussed. During the experimental phase, the thermal storage reached the maximum temperature of 79.3 °C, exploiting the latent heat of the PCM. Overall performances demonstrated good agreement with results available in the literature in terms of efficiency and energy storage. A specific heat flux of 2.64 kW·m−2 was achieved in DHW production, with a water flowrate of 0.87 kg·min−1. The 0.02 m3 PCM section was able to store 24.57 kWh of thermal energy along a monitored month. Future developments of this new technology include new experimental tests with larger prototypes and the coupling with a real user
Multiple states of finger propagation in partially occluded tubes
No full textRecent experiments by Pailha et al. [Phys. Fluids24, 021702 (2012)10.1063/1.3682772] uncovered a rich array of propagation modes when air displaces oil from axially uniform tubes that have local variations in flow resistance within their cross-sections. The behaviour is particularly surprising because only a single, symmetric mode has been observed in tubes of regular cross-section, e.g., circular, elliptical, rectangular, and polygonal. In this paper, we present experimental results describing a new mode, an asymmetric localised air finger, that persists in the limit of zero propagation speed. We show that the experimental observations are consistent with a model based on capillary static calculations within the tube's cross-section, and the observed bistability is a consequence of the existence of multiple solutions to the Young-Laplace equations. The model also provides an upper bound for the previously reported symmetry-breaking bifurcation [A. de Lózar, A. Heap, F. Box, A. L. Hazel, and A. Juel, Phys. Fluids21, 101702 (2009)10.1063/1.3247879]. © 2013 AIP Publishing LLC
Etude des écoulements de convection naturelle et mixte pour le développement de séchoir et d'enveloppes solaires
No full textLa croissance démographique rapide et l'industrialisation ont entraîné une augmentation significative de la demande énergétique à l'échelle mondiale, malgré une baisse de 1 % en 2020 due à la pandémie de COVID-19. Malgré les progrès réalisés dans le domaine des énergies renouvelables, les combustibles fossiles restent prédominants. Le secteur du bâtiment, troisième consommateur d'énergie, contribue largement aux émissions de CO2. Les systèmes de chauffage, ventilation et climatisation (HVAC) représentent 50 à 60 % de la consommation d'énergie. L'intégration de la technologie photovoltaïque (PV) dans les bâtiments via le BIPV ou le BAPV permet de réduire la demande énergétique et les émissions de CO2. Cependant, l'efficacité des cellules PV est limitée par la génération de chaleur, ce qui rend nécessaire des méthodes de refroidissement passif telles que la convection naturelle pour maintenir les performances et la durabilité. Des technologies passives telles que les doubles façades, les murs Trombe et les cheminées solaires utilisent l'énergie solaire pour améliorer la ventilation dans les bâtiments. En particulier, les cheminées solaires murales offrent un refroidissement et une ventilation efficaces. S'appuyant sur le projet NAMICO, une cheminée solaire murale intérieure attenante à une pièce a été fabriquée à l'échelle au LOCIE pour recueillir des données fiables sur les systèmes BIPV double façade connectés à l'espace habitable via une ouverture d'entrée horizontale.Cette thèse évalue un banc d'essai modulaire en établissant des protocoles et des critères expérimentaux. Est investigué l'effet de la position et de la taille des fenêtres sur les performances de la cheminée solaire et du système de ventilation de la pièce. Sont également étudiés les effets de l'émissivité de surface, (0,08 ou 0,96) et du flux de chaleur injecté depuis le mur d'entrée du canal en forme de L(110 W/m², 235 W/m²). Les performances thermiques et cinématiques du canal sont évaluées en analysant les données de température des parois et en effectuant des mesures PIV une fois que le banc d'essai de la cheminée a atteint un état quasi stable. Le flux d'air moyenné dans le temps est mesuré et visualisé en deux dimensions spatiales. L'effet de la position et de la taille de la fenêtre de la pièce sur la ventilation est évalué en mesurant la température de l'air et en traçant la circulation de l'air avec un générateur de fumée. Un modèle simplifié unidimensionnel (SHBM) a également été développé. Il est validé à l'aide de données expérimentales.En conclusion, la géométrie de l'entrée de la cheminée affecte le champ thermique et la topologie du flux dans le canal vertical. L'augmentation du flux de chaleur renforce le champ thermique sur les parois et le flux d'air dans la cheminée sur les parois à émissivité faible et élevée. Une émissivité de surface plus élevée améliore le transfert de chaleur radiatif de paroi à paroi, modifiant les profils thermiques des parois et les flux d'air en passant d'un chauffage à une paroi à un chauffage asymétrique du canal. Par conséquent, la température de la paroi chauffée diminue d'autant que la température de la paroi opposée, recevant le rayonnement, augmente. De plus, le débit volumique d'air sortant de la cheminée est calculé comme étant plus élevé aux parois de cheminée à ε = 0,96 par rapport à ε = 0,08 sous le même flux de chaleur. Les arêtes des murs de l'entrée créent des zones de recirculation, la taille de ces structures étant affectée par le flux de chaleur et l'émissivité. Il a également été étudié que la taille et le placement de la fenêtre sur le mur de la pièce n'ont aucun effet notable sur les performances de la cheminée mais influencent la distribution de la température. L'approche de modélisation développée aide à prédire la ventilation mais surestime les températures des parois de la cheminée.Rapid population growth and industrialization have led to a significant rise in energy demand globally, though a 1% drop occurred in 2020 due to the COVID-19 pandemic. Despite advancements in renewables, fossil fuels remain predominant. The building sector, ranking third in energy consumption, contributes heavily to CO2 emissions, with HVAC systems alone accounting for 50-60% of energy usage. Integrating photovoltaic (PV) technology into buildings via BIPV or BAPV offers a promising solution to reduce energy demand and CO2 emissions. However, the efficiency of PV cells is limited by heat generation, requiring passive cooling methods like natural convection, especially in BIPV systems, to maintain performance and longevity. Solar-assisted passive technologies like double-skin façades, Trombe walls, and solar chimneys utilize solar energy to enhance air ventilation in buildings. Among these, wall-mounted solar chimneys offer effective cooling and ventilation. Building upon NAMICO project, a unique indoor wall-mounted solar chimney with scaled-down room model have been fabricated at LOCIE for gathering reliable data on BIPV systems integrated on double-skin façade connected via horizontal inlet opening with the dwelling space.This doctoral research assesses a modular test bench in a lab setting, establishing protocols and criteria for experiments. The research explored the impact of window position and size on the performance of the solar chimney and room ventilation system. Experiments also investigate the effects of varying surface emissivity, set at either 0.08 or 0.96, and uniform heat flux injected solely from the inlet-forming wall of the L-shaped channel, at rates of 110 W/m² or 235 W/m². The top window of the room remains open while maintaining constant aspect and extension ratios of the channel. Thermal and kinematic performance of the L-shaped channel is assessed by analysing wall temperature data and conducting PIV measurements on whole channel once the solar chimney test rig reached quasi-steady state. The 2D time-averaged flow field within the channel was measured, and spatial flow structures were visualized. Additionally, the impact of room window placement and aperture size on ventilation was evaluated by measuring room air temperature and observing airflow patterns using a smoke generator. A simplified one-dimensional model, the Steady Heat Balance Model (SHBM), is also developed to predict the thermal and ventilation performance, validated using experimental data.it has been concluded chimney inlet geometry affects thermal field and flow topology in the vertical channel. Increasing heat flux boosts thermal field on walls and flow field within the chimney on both low and high emissive walls of the channel. Higher surface emissivity enhances wall-to-wall radiative heat transfer, altering wall thermal profiles and airflow patterns by modifying the thermal conditions from one-wall heating to asymmetrical of the channel. Consequently, the temperature of the heated wall decreases notably while the temperature of the opposing wall, receiving radiation, increases proportionally. Additionally, the volume airflow rate out of the chimney is computed to be higher at ε = 0.96 chimney walls compared to ε = 0.08 under the same heat flux. No reverse is observed at the outlet of the chimney even at low emissive walls of the channel. Sharp corners of the inlet create recirculation zones, the size of these structures are being affected by input heat flux and wall emissivity. It is also investigated that the size and placement of the window on room wall have no visible impact on chimney performance but influences room temperature distribution. Lastly, the modelling approach developed aids in predicting ventilation but overestimates chimney wall temperatures
Stratification Enhancement for an Integrated Collector Storage Solar Water Heater (ICSSWH)
No full textInternational audienceStratification is a key point in increasing performances of storage systems. The experimental study conducted only focuses on the charging of a high aspect ratio cavity representing the storage system of an ICSSWH, and the exchange with the solar collector is modeled by a constant heat flux. Thermal stratifica-tion is enhanced by placing in the system a stratification plate and by changing the position of the heat exchange zone between solar collector and storage. The parameters that vary in this study are the angle of inclination of the system (30, 45 and 60 ° relative to the horizontal), the heat flux imposed (1800, 2700 and 3600 W/m 2) and the length of the stratification plate. The experiments lasted three hours. Satisfying stratification was obtained, mainly due to the reverse flow occurring in the system. However, this phenomenon increases with time and could result in creating a dead volume under the heat exchange area. This aspect will be further studied using CFD models. The impact of a good thermal stratification in the system will also be studied by determining the annual performance of the ICSSWH
Initiation of underwater granular avalanches: Influence of the initial volume fraction
No full textInternational audienc
Experimental study of a partially heated cavity of an integrated collector storage solar water heater (ICSSWH)
No full textInternational audienceAs part of development of a new integrated collector storage, we experimentally studied the convective phenomena in an inclined cavity with a high aspect ratio (height: H = 1.3 m and thickness: L = 0.1 m). This integrated collector storage has a secondary circuit collecting the irradiation and transferring it at the bottom front face of the cavity. This transfer results in the concentration of the solar heat flux. To simulate the storage, the cavity was partially heated with a constant heat flux at the bottom front face over 0.2 m height. We investigated three inclined angles (30°, 45° and 60°) and three heat flux densities, 1800, 3600 and 5400 W m−2. Flow was essentially 2D (two-dimensional) in the lower part of the cavity and 3D (three-dimensional) in the top part. The temperature profiles showed the need to develop a system that improves stratification within the cavity. The addition of a plate parallel to the cavity's front wall creates a channel that separates the upward and downward flows, reduces the mixing effect within the storage and slightly improves the stratification. The plate causes the fluid flow to become 2D in the study plane, allowing the use of 2D numerical models
Study of a New Integrated Solar Collector
No full textAbstractEven though the integration of renewable energies in new buildings is technically easy, the rise of solar thermal systems in the French market of energy renovation is limited by recurring constraints of implementation related to the installation of the storage tank. This is the reason why the Integrated Solar Collector (ISC) constitutes a very promising concept to develop. For both new buildings and renovation of the existing buildings, the ISC gives the opportunity to reduce the cost of installation and operation comparatively to a conventional Solar Domestic Hot Water System, because of their simplicity and passive operating process (without pump, nor controller). This second advantage is extremely important for the development prospects of the solar thermal market which is currently slowed down by the level of investment. The third advantage of our new ISC is the possibility of successful architectural integration, contrary to the currently available solutions with the storage installed on the roof.We developed a new concept of ISC adapted to the energy renovation with a multidisciplinary approach. Its design took into account various aspects: architectural integration (storage bellow the collector), energy performance (solar heat transfer at the bottom of the storage, fully insulated storage) and technological constraints (freezing risk). The project made it possible to study on the one hand its global performance (stratification, solar fraction) and on the other hand the free convective heat transfers inside the storage cavity. The approach used both numerical (architectural draft and design of the prototype, global modelling, and velocity / temperature fields) and experimental tools (test of heat, PIV on a cavity heated at the bottom, test of the prototype). The first prototype of ISC puts forward very satisfactory energy performances. Improvements are possible by enhancing thermal stratification in the storage system. Concerning the heat pipes operation against gravity, the project highlighted the current lack of technological solution adapted to our needs. The study of the building integration showed the architectural opportunities given during the renovation (new volumes) and the technical constraints which were solved (weight, storage insulation, freezing)
Etude des écoulements de convection naturelle et mixte pour le développement de séchoir et d'enveloppes solaires
No full textRapid population growth and industrialization have led to a significant rise in energy demand globally, though a 1% drop occurred in 2020 due to the COVID-19 pandemic. Despite advancements in renewables, fossil fuels remain predominant. The building sector, ranking third in energy consumption, contributes heavily to CO2 emissions, with HVAC systems alone accounting for 50-60% of energy usage. Integrating photovoltaic (PV) technology into buildings via BIPV or BAPV offers a promising solution to reduce energy demand and CO2 emissions. However, the efficiency of PV cells is limited by heat generation, requiring passive cooling methods like natural convection, especially in BIPV systems, to maintain performance and longevity. Solar-assisted passive technologies like double-skin façades, Trombe walls, and solar chimneys utilize solar energy to enhance air ventilation in buildings. Among these, wall-mounted solar chimneys offer effective cooling and ventilation. Building upon NAMICO project, a unique indoor wall-mounted solar chimney with scaled-down room model have been fabricated at LOCIE for gathering reliable data on BIPV systems integrated on double-skin façade connected via horizontal inlet opening with the dwelling space.This doctoral research assesses a modular test bench in a lab setting, establishing protocols and criteria for experiments. The research explored the impact of window position and size on the performance of the solar chimney and room ventilation system. Experiments also investigate the effects of varying surface emissivity, set at either 0.08 or 0.96, and uniform heat flux injected solely from the inlet-forming wall of the L-shaped channel, at rates of 110 W/m² or 235 W/m². The top window of the room remains open while maintaining constant aspect and extension ratios of the channel. Thermal and kinematic performance of the L-shaped channel is assessed by analysing wall temperature data and conducting PIV measurements on whole channel once the solar chimney test rig reached quasi-steady state. The 2D time-averaged flow field within the channel was measured, and spatial flow structures were visualized. Additionally, the impact of room window placement and aperture size on ventilation was evaluated by measuring room air temperature and observing airflow patterns using a smoke generator. A simplified one-dimensional model, the Steady Heat Balance Model (SHBM), is also developed to predict the thermal and ventilation performance, validated using experimental data.it has been concluded chimney inlet geometry affects thermal field and flow topology in the vertical channel. Increasing heat flux boosts thermal field on walls and flow field within the chimney on both low and high emissive walls of the channel. Higher surface emissivity enhances wall-to-wall radiative heat transfer, altering wall thermal profiles and airflow patterns by modifying the thermal conditions from one-wall heating to asymmetrical of the channel. Consequently, the temperature of the heated wall decreases notably while the temperature of the opposing wall, receiving radiation, increases proportionally. Additionally, the volume airflow rate out of the chimney is computed to be higher at ε = 0.96 chimney walls compared to ε = 0.08 under the same heat flux. No reverse is observed at the outlet of the chimney even at low emissive walls of the channel. Sharp corners of the inlet create recirculation zones, the size of these structures are being affected by input heat flux and wall emissivity. It is also investigated that the size and placement of the window on room wall have no visible impact on chimney performance but influences room temperature distribution. Lastly, the modelling approach developed aids in predicting ventilation but overestimates chimney wall temperatures.La croissance démographique rapide et l'industrialisation ont entraîné une augmentation significative de la demande énergétique à l'échelle mondiale, malgré une baisse de 1 % en 2020 due à la pandémie de COVID-19. Malgré les progrès réalisés dans le domaine des énergies renouvelables, les combustibles fossiles restent prédominants. Le secteur du bâtiment, troisième consommateur d'énergie, contribue largement aux émissions de CO2. Les systèmes de chauffage, ventilation et climatisation (HVAC) représentent 50 à 60 % de la consommation d'énergie. L'intégration de la technologie photovoltaïque (PV) dans les bâtiments via le BIPV ou le BAPV permet de réduire la demande énergétique et les émissions de CO2. Cependant, l'efficacité des cellules PV est limitée par la génération de chaleur, ce qui rend nécessaire des méthodes de refroidissement passif telles que la convection naturelle pour maintenir les performances et la durabilité. Des technologies passives telles que les doubles façades, les murs Trombe et les cheminées solaires utilisent l'énergie solaire pour améliorer la ventilation dans les bâtiments. En particulier, les cheminées solaires murales offrent un refroidissement et une ventilation efficaces. S'appuyant sur le projet NAMICO, une cheminée solaire murale intérieure attenante à une pièce a été fabriquée à l'échelle au LOCIE pour recueillir des données fiables sur les systèmes BIPV double façade connectés à l'espace habitable via une ouverture d'entrée horizontale.Cette thèse évalue un banc d'essai modulaire en établissant des protocoles et des critères expérimentaux. Est investigué l'effet de la position et de la taille des fenêtres sur les performances de la cheminée solaire et du système de ventilation de la pièce. Sont également étudiés les effets de l'émissivité de surface, (0,08 ou 0,96) et du flux de chaleur injecté depuis le mur d'entrée du canal en forme de L(110 W/m², 235 W/m²). Les performances thermiques et cinématiques du canal sont évaluées en analysant les données de température des parois et en effectuant des mesures PIV une fois que le banc d'essai de la cheminée a atteint un état quasi stable. Le flux d'air moyenné dans le temps est mesuré et visualisé en deux dimensions spatiales. L'effet de la position et de la taille de la fenêtre de la pièce sur la ventilation est évalué en mesurant la température de l'air et en traçant la circulation de l'air avec un générateur de fumée. Un modèle simplifié unidimensionnel (SHBM) a également été développé. Il est validé à l'aide de données expérimentales.En conclusion, la géométrie de l'entrée de la cheminée affecte le champ thermique et la topologie du flux dans le canal vertical. L'augmentation du flux de chaleur renforce le champ thermique sur les parois et le flux d'air dans la cheminée sur les parois à émissivité faible et élevée. Une émissivité de surface plus élevée améliore le transfert de chaleur radiatif de paroi à paroi, modifiant les profils thermiques des parois et les flux d'air en passant d'un chauffage à une paroi à un chauffage asymétrique du canal. Par conséquent, la température de la paroi chauffée diminue d'autant que la température de la paroi opposée, recevant le rayonnement, augmente. De plus, le débit volumique d'air sortant de la cheminée est calculé comme étant plus élevé aux parois de cheminée à ε = 0,96 par rapport à ε = 0,08 sous le même flux de chaleur. Les arêtes des murs de l'entrée créent des zones de recirculation, la taille de ces structures étant affectée par le flux de chaleur et l'émissivité. Il a également été étudié que la taille et le placement de la fenêtre sur le mur de la pièce n'ont aucun effet notable sur les performances de la cheminée mais influencent la distribution de la température. L'approche de modélisation développée aide à prédire la ventilation mais surestime les températures des parois de la cheminée
