Pour être utilisé en réfrigération secondaire comme matériau à changement de phase dans un fluide frigoporteur, un hydrate doit posséder une enthalpie de dissociation élevée, à une température adaptée à l’application (positive pour de la climatisation) et à une pression acceptable pour une installation industrielle. De plus, le mélange diphasique doit présenter de bonnes conditions d’écoulement et d’échanges thermiques. Un dispositif dynamique constitué d'un réacteur agité et d'une boucle de circulation, placé dans une chambre climatique, a été développé pour l’étude de coulis d’hydrates de dioxyde de carbone. Pour ce dispositif, un protocole a été mis en œuvre pour le refroidissement d’une solution chargée en CO2, générant des coulis d'hydrate à taux d’hydrate allant jusqu'à 25°% véhiculant une chaleur latente importante (374 kJ.kg-1). Une étude cinétique sur la formation des hydrates de CO2 dans le réacteur agité à été réalisé et montre que la cinétique de formation de ces hydrates est de 2 %.h-1 dans le réacteur pour une pression, une température, et une vitesse d'agitation de départ de 3 MPa, 12 °C et 1042 tr/min et pour une température de consigne du groupe froid de -1 °C. L’étude rhéologique du coulis a permis de mettre en place une corrélation empirique de type Herschel-Bulkley en fonction du taux d’hydrates qui permet une caractérisation satisfaisante du comportement rhéologique du fluide. Les résultats de l’étude thermique ont permis d’établir des corrélations entre les nombres de Nusselt et de Reynolds qui caractérisent les régimes de fonctionnement thermique du système. / To be used as phase change material in a secondary refrigerant, a hydrate must enclose a high dissociation enthalpy, at a temperature adapted to the application (positive for air-conditioning) and a pressure suitable for an industrial facility. Moreover, the two-phase mixture must present good conditions of flowing and heat exchange. A dynamical set-up with a stirred tank reactor with a loop of circulation, placed in a thermostated room, was developed for the study of carbon-dioxide-hydrate slurries. In this set-up, one protocol was carried out: by cooling of a water-CO2 solution, generating slurries hydrate rates 25 %, conveying a high latent heat (374 kJ.kg-1). A study of CO2 hydrate formation kinetics was lead in the tank reactor and the results showed the CO2 hydrate formation kinetics is 2 %.h-1 for a pressure, temperature and a stirring rate at the begin of 3 MPa, 12°C and 1042°rpm and a temperature of the chiller about -1°C. A study rheological allows the development of an empirical Herschel-Bulkley-type correlation as a function of the hydrate rate was achieved for rheological characterization of the fluid behavior. The thermal results obtained allow establishing correlation as a function of Nusselt and Reynolds number which characterize operational regimes of the system thermal.

Incorporating insulation material with phase change materials (PCMs) could help enhance the insulation capability for further building energy savings by reducing the HVAC loadings. During the phase change process between the solid and liquid states, heat is being absorbed or released by PCMs depending on the surrounding temperature. This research explores the benefits of a polyurethane (PU)-PCM composite insulation material through infiltrating paraffin wax as PCM into PU open cell foam. The new PU-PCM composite provides extra shielding from the exterior hot temperatures for buildings. Through this study, it was demonstrated that PU-PCM composite insulation could potentially help building energy savings through reducing the loads on the HVAC systems based on the building energy modeling using EnergyPlus. The Zero Energy Lab (ZØE) at the University of North Texas was modeled and studied in the EnergyPlus. It is a detached building with all wall facades exposed to the ambient. It was determined that the new PU-PCM insulation material could provide 14% total energy saving per year and reduce the electricity use due to cooling only by around 30%.

The theoretical part of the diploma thesis deals with introduction to the issue of refrigeration systems with thermal energy storage. Possibilities of thermal energy storage with phase change are introduced. The thermodynamic principle of functioning of the particular refrigeration system type is explained here as well as its coefficient of performance and fundamental components. In addition, several examples of ice-making systems are discussed. In the practical part the design of a particular refrigeration system is calculated. The main part of the design is the cold evaporator with direct evaporation and the possibility of ice production and its usage for thermal energy storage. The calculation of the overall two-phase heat transfer is carried out.

Cette thèse a été réalisée initialement dans le cadre du projet Stockage Thermique Appliqué à l’extension de Production d’énergie Solaire thermodynamique (STARS) soutenu par l'Agence De l'Environnement et de la Maîtrise de l'Energie (ADEME).L’objectif du projet est de développer une solution de stockage thermique adaptée à la technologie Fresnel à génération directe de vapeur avec une zone de stockage de chaleur latente. Dans une unité de stockage latent, le nitrate de sodium (NaNO3) a été choisi comme matériau à changement de phase (MCP) et l’acier faiblement allié a été envisagé comme matériau de structure du conteneur et de l’échangeur thermique. La contribution de la thèse se positionne au niveau de l’étude de la corrosion et de la durabilité des matériaux de structure (conteneur et échangeur) en contact avec le MCP. L’objectif est de déterminer une loi de vitesse de corrosion qui permettrait de dimensionner les parois de l’échangeur et de développer des protocoles utilisant les techniques électrochimiques afin de suivre in-situ l’état de la corrosion au sein de l’unité de stockage. Les travaux présentés dans ce manuscrit portent sur l’étude expérimentale de la corrosion de l’acier dans le nitrate de sodium fondu à 340°C en fonction des paramètres expérimentaux tels que la présence d’impuretés (oxydes, chlorures), l’atmosphère gazeuse et le cyclage thermique. L’étude par mesures gravimétriques met en évidence la formation d’une couche de corrosion protectrice en surface de l’acier et la production de nitrite de sodium (NaNO2) par la réaction de corrosion. Cette couche constituée principalement de Fe2O3 (insoluble dans NaNO3 fondu) a été caractérisée par différentes méthodes d’analyse de surface (DRX, XPS). L’évolution de l’épaisseur de la couche de corrosion obtenue par cette technique montre une cinétique de corrosion logarithmique dans NaNO3 pur et une cinétique linéaire en présence d’une teneur importante en impuretés chlorures (10 mol%). L’étude électrochimique a apporté des indications sur le comportement du fer (et de l’acier) dans NaNO3 fondu. En combinant ces données avec les observations expérimentales issues des essais de corrosion nous avons pu proposer un mécanisme réactionnel pour la corrosion de l’acier en milieu nitrate fondu. L’étude par spectroscopie d’impédance électrochimique a permis de valider le mécanisme réactionnel proposé. A l’aide de ce mécanisme, les paramètres cinétiques puis la valeur du courant de corrosion ont été déduits par simulation des diagrammes d’impédance. L’analyse de la variation du courant de corrosion en fonction du temps permet de calculer l’épaisseur de la couche de corrosion et de la comparer à celle obtenue par gravimétrie. Un bon accord entre les valeurs obtenues par différentes techniques a été observé.Au cours de ce travail, nous avons également montré la possibilité d’utiliser les techniques électrochimiques pour l’instrumentalisation des installations industrielles afin de suivre in-situ l’évolution de la composition du MCP et l’état d’avancement de la corrosion de l’acier.Enfin, ce travail a montré que l’acier faiblement allié est adapté pour être utilisé dans une unité de stockage latent avec le nitrate de sodium comme matériau à changement de phase. / This thesis was originally performed as part of the STARS project (Stockage Thermique Appliqué à l’extension de Production d’énergie Solaire thermodynamique) which was supported by ADEME (l'Agence De l'Environnement et de la Maîtrise de l'Energie). The objective is to develop a thermal storage system using latent heat from a phase change material (PCM) in order to match with Fresnel technology using direct steam generation. Sodium nitrate (NaNO3) has been selected as PCM and low-alloy steel has been considered as candidate material to build the container and the heat exchanger of a latent heat storage system. The contribution of this thesis is to provide better understanding of the corrosion of the candidate material in contact with the PCM. This thesis aims to determine a corrosion rate law which helps design the thickness of the heat exchanger’s wall and to develop protocols using electrochemical technics to follow in-situ corrosion process in the latent heat storage system. The work presented in this manuscript focuses on experimental study of corrosion of low-alloy steel in molten NaNO3 (340°C) in function of different parameters: presence of impurities (oxides, chlorides), atmosphere and thermal cycling. Gravimetric measurements reveal the formation of a protective corrosion layer on the steel’s surface and the production of sodium nitrite (NaNO2) by corrosion reaction. The corrosion layer consisting mainly of Fe2O3 (insoluble in molten NaNO3) was characterized by surface analytical methods (XRD, XPS). Variation of the thickness of corrosion layer obtained by gravimetric methods shows logarithmic kinetics in pure NaNO3 and linear kinetics in the presence of 10mol% of impurity chlorides. Electrochemical study has provided indications on the iron (and steel) behavior in molten NaNO3. By combining results of this study with experimental observations from gravimetric study, we were able to propose a corrosion mechanism of the steel in molten NaNO3. This mechanism was then validated by electrochemical impedance spectroscopy study. Kinetics parameters and value of corrosion current were deduced by the simulation of impedance diagrams using the proposed mechanism. The thickness of corrosion layer was calculated by analyzing the variation of the corrosion current with time. These values present a good agreement with values obtained by gravimetric study.In this work, we also show the possibility of using electrochemical measurements at industrial scale to follow in-situ the evolution of the PCM's composition and the corrosion state. Finally, this work has shown that low-alloy steel is suitable for using in a latent heat storage system with NaNO3 as phase change material.

In this research thermal properties enhancement of phase change material (PCM) using boron nitride nanomaterials such as nanoparticles and nanotubes is studied through experimental measurements, finite element method (FEM) through COMSOL 5.3 package and molecular dynamics simulations via equilibrium molecular dynamics simulation (EMD) with the Materials and Process Simulations (MAPS 4.3). This study includes two sections: thermal properties enhancement of inorganic salt hydrate (CaCl2∙6H2O) as the phase change material by mixing boron nitride nanoparticles (BNNPs), and thermal properties enhancement of organic phase change material (paraffin wax) as the phase change material via encapsulation into boron nitride nanotubes (BNNTs). The results of the proposed research will contribute to enhance the thermal transport properties of inorganic and organic phase change material applying nanotechnology for increasing energy efficiency of systems including electronic devices, vehicles in cold areas to overcome the cold start problem, thermal interface materials for efficient heat conduction and spacecraft in planetary missions for efficient thermal managements.

The thesis deals with the integration of phase change materials (PCMs) into building structures. The basic requirement is improved thermal stability during the summer season without using an air conditioner. This can be achieved by increasing the thermal storage capacity of the building structures. If the thermal capacity cannot be increased on the level of weight, phase change materials can be used. These materials are capable of storing latent heat and thus increasing the thermal storage capacity of the building. In the thesis the phase change materials were investigated in a thermal incubator by thermal analysis and, above all, in full-scale experiments using comparative measurements. The comparative measurements were carried out in two attic rooms at the Faculty of Civil Engineering, Brno University of Technology, where in one was used as a reference and the other for the experiment. Manufactured heat storage panels were installed in the experimental room. These panels are composed of a base plate; the capillary tubes placed on it are coated with modified plaster. The gypsum plaster is modified with micro-capsules paraffin for improving the thermal storage capacity. This system is connected to a thermal air-water pump, by which the storage panels can be additionally cooled or heated. In the experimental measurements, different operating modes were investigated and their effect on the indoor environment was evaluated. Thermal storage in PCMs dampens the temperature amplitude in the building during the summer season and, at the same time, allows the stored heat to be discharged during the night. Moreover, the time interval of withdrawing electric energy from the supply mains is much shorter than in the case of air conditioning. A conventional air conditioner must operate simultaneously with the thermal load, i.e. at the time of peak consumption of electric energy. Thanks to the set regimes, the installed system is capable of responding to external thermal condit

No description available.

<p dir="ltr">Ice thermal energy storage (ITES) systems have long been an economic way to slash cooling costs in the commercial sector since the 1980s. An ITES system generates cooling in the formation of ice within a storage tank. This occurs during periods of the day when the cost of electricity is low, normally at night. This ice is then melted to absorb the energy within the conditioned space. While ITES systems have been prosperous in the commercial sector, they have yet to take root in the residential sector.</p><p dir="ltr">The U.S. Department of Energy (DoE) has published guidelines for TES. The DoE guidelines include providing a minimum of four hours of cooling, shifting 30-50% of a space’s cooling load to non-peak hours, minimizing the weight, volume, complexity, and cost of the system, creating a system than operates for over 10,000 cycles, enacting predictive control measures, and being modular to increase scale for larger single-family and multi-family homes [1]. The purpose of this research is to develop a model that meets these guidelines.</p><p dir="ltr">After extensive research in both experimental data, technical specifications, existing models, and best practices taken from the works of others a MATLAB model was generated. The modeled ITES system is comprised of a 1m diameter tank by 1m tall. Ice was selected as the PCM. A baseline model was constructed with parameters deemed to be ideal. This model generated an ITES system that can be charged in under four hours and is capable of providing a total of 22.18 kWh of cooling for a single-family home over a four-hour time period. This model was then validated with experimental data and found to have a root mean squared error of 0.0959 for the system state of charge. During the validation both the experimental and model estimation for the water/ice within the tank converged at the HTF supply temperature of -5.2°C.</p><p dir="ltr">With the model established, a parametric analysis was conducted to learn how adjusting a few of the system parameters impact it. The first parameter, reducing the pipe radius, has the potential to lead to a 152.6-minute reduction in charge time. The second parameter, varying the heat transfer fluid (HTF) within the prescribed zone of 0.7 kg/s to 1.2 kg/s, experienced a 4.8-minute increase in charge time for the former and a decrease in charge time by 5.4 minutes for the latter. The third parameter, increasing the pipe spacing and consequently increasing the ratio of mass of water to mass of HTF, yielded a negative impact. A 7.1mm increase in pipe spacing produced a 16.6-minute increase in charge time. Meanwhile, a 14.2mm increase in pipe spacing created a 93.3-minute increase in charge time and exceeded the charging time limit of five hours.</p><p dir="ltr">This functioning model establishes the foundation of creating a residential-scale ITES system. The adjustability and scalability of the code enable it to be modified to user specifications. Thus, allowing for various prototypes to be generated based on it. The model also lays the groundwork to synthesize a code containing an ITES system and a heat pump operating as one. This will aid in the understanding of residential-scale ITES systems and their energy effects.</p>

<p>This research is concerned with CFD modelling of thermal energy storage tanks containing water with submerged phase change materials (PCM). Under appropriate operating conditions, the energy density of this hybrid system can be significantly increased (two to five times) relative to a system containing water only. However, due to low thermal conductivity of phase change materials, the geometry and configurations of the PCM capsules in the tank should be optimized. This research focused on the assessment of flat plate PCM modules submerged in a rectangular water tank. The encapsulation of the PCM within the slender flat plates resulted in a large PCM surface area and a reduction in the internal heat transfer resistance. The water was heated by coils placed at the bottom of the tank. The resulting natural convection currents acted to transfer heat from the hot coils to the PCM modules which were treated as isothermal at the PCM melt temperature. It is concluded that the charge rate of the system increases to 2.8 times by increasing the PCM volume percentage from 2.5% to 15%. However for PCM volume percentages of more than 15%, the area of the PCM became much more than the area of the coil (around 15 times) in a way that the charge rate of the system started to be controlled by the coil. In this stage, the charge rate of the system remained constant, and adding modules to the system only increased the heat capacity of the system. Therefore the charge rate of the system could only increase if the coil surface area was increased. The heat transfer coefficients of the PCM modules and coil tubes were higher than those evaluated by the experimental correlations for natural convection. This was due to the recirculation of the flow in the tank “pumping effect” created by the coil for PCM modules and by the PCM modules for the coil. It was also concluded that superheating of the PCM surface temperature decreases the heat transfer rate to the PCM significantly, and the charge rate of the system varies linearly with the temperature difference between the PCM modules and the coil.</p> / Master of Applied Science (MASc)

<p>Electrohydrodynamics (EHD) was used to enhance the thermal performance of a latent heat thermal storage cell by reducing the charging time for a given amount of latent heat stored. Paraffin wax, which is an organic dielectric commercially available material was selected as the phase change material (PCM).</p> <p>Electric field was applied into the cell by using 9 electrodes kept at -8 kV in an effort to establish EHD forces inside the PCM. The EHD effect was studied in an originally conduction dominated melting environment. That was achieved by the cell design which promoted unidirectional melting downwards to prevent natural convection from occurring by assuring a thermally stratified molten phase. The target was to study the EHD mechanisms of enhancement with less interfering physics.</p> <p>Melting was studied under constant heat flux boundary condition. The temporal thermal profile of the surface heater and the melt front location were used to assess the EHD effect by comparing it to a 0 kV (no EHD) case.</p> <p>It was found that by using EHD (-8 kV), the time required to melt 7 mm thickness of the PCM can be reduced by 40 % when compared to 0 kV case. Through a four hour experiment time, the amount of molten PCM can be increased by 29 % by using EHD compared to 0 kV. The EHD power consumption was less than 0.17 W which is equivalent to 2.4 % of the thermal energy stored in the PCM.</p> <p>A new phenomena was discovered when applying EHD in the tested cell, which is Solid Extraction, where the solid dendrites within the mushy zone were extracted from the mushy zone into the liquid bulk towards regions of higher electric field.</p> <p>A new criteria was developed to quantify the EHD enhancement level and was called EHD enhancement factor. An enhancement factor up to 13 could be reached by using EHD. The effect of changing the heat flux on the enhancement factor was investigated, and it was found that the enhancement factor decreased by increasing the heat flux.</p> <p>Numerical simulations were performed in an effort to understand the EHD mechanisms of enhancement. The static electric field distribution, the interfacial extraction forces and the body forces acting on suspended dendrites were evaluated. The results of numerical simulations were supported by the high speed imaging and the experimental data to explain the EHD mechanisms of enhancement and the regions where solid dendrites extraction happened.</p> <p>Finally an analytical model was developed to estimate the energy stored in the different components of the tested latent heat storage cell and to estimate the amount of energy lost to the surroundings in order to quantify the accuracy of the experiment and a maximum of 18 % heat loss was estimated.</p> / Master of Applied Science (MASc)