Results 1 - 10 of 19
Results 1 - 10 of 19. Search took: 0.022 seconds
|Sort by: date | relevance|
[en] The thermal diode is a device which allows heat to be transferred in one direction, and blocks heat flow in the opposite direction. Most thermal diode designs have been based on the fact that heat usually can be transferred more efficiently by convection than by conduction. This study has been carried out to develop a Loop-type thermal diode solar space heating system, which is capable of adjusting the direction of heat flow and the solar absorption. It can be used for space heating in winter and for cooling load reduction of buildings in summer. This system exploits the sun's thermal energy more aggressively than the existing solar systems by adjusting itself appropriately to the direction of heat flow and insolation conditions. Also, by replacing curtain wall(nonstructural walls) of the building, the system could improve the utilization efficiency of building space. It is expected that the system could be applied broadly to public buildings, office accommodation, or residential buildings
[en] An excessive use of fossil fuel leads to the limitation of coal deposits and carbon dioxide accumulation that accelerates the global warming, so the international environment regulation becomes more strict to control the greenhouse gas emission. Many researches are being made on alternative energy development to cut down fossil fuel and to decrease carbon dioxide. During the last decade, there have been active tries to utilize the solar energy that is unlimited and clean . The application of solar energy to heating and cooling of the building has much improved the economical efficiency and function with the development of high-technology materials, and it is not rare to find the recently built houses and commercial buildings equipped with solar energy systems. In particular, the advanced countries such as USA and Japan attempt the remarkable reduction of energy consumption in heating and cooling of buildings. For this, they are searching for the more effective application of various alternative energies including the solar energy. In addition, they are trying to realize the distinct zero energy conception by applying the new techniques and materials to the existing buildings. In developing the new techniques of solar energy application to heating and cooling system, the economic problems hire to be addressed, The typical problems encountered in applying the solar energy are insufficient design concept for HVAC(heating, ventilation, and air conditioning) system and low reliability, Further, the economical efficiency of the solar energy is still low to compete with the oil, and there are many limits on the realization of the actual system in a building, e.g. spatial alignments and exterior appearances. The purpose of this study is to find the improved method to increase the heat transfer efficiency of the solar energy system that are to be installed in houses and commercial buildings. For this, a series of experiments using the bi-directional thermo diode system (Smart Module System) were made. Six kinds of working fluids were used to investigate their effects on the thermal performance of a bi-directional solar thermo diode. Two kinds of thermo diodes were studied. The first one is the mono-directional thermo diode that allows heat flow in the desired direction but blocks in the opposite direction. The second one is the bi-directional thermo diode of which the direction of heat flow, surface absorptivity and heat capacity of the module can be adjusted for maximum energy efficiency. This hi-directional can be used both for the summer cooling and winter heating of buildings and shelters. Usually, the thermo diodes are simple beam shape, but in this study, they were redesigned as two L-shaped loops mounted between a collector plate and a Storage tank. Rotable joints between the horizontal and inclined segments of the loop enable easy alteration of geat transfer direction. The loops and tank were filled with a working fluid for effective heat transfer when the solar thermo diode was forwarded biased. The solar thermo diode was heated by a radiant heater that consisted of 20 halogen lamps that generates a heat flux of about 1000W/m2 on the collector surface. The working fluids used in the study were water, acetone, ethylalcohol. In addition, three kinds of silicon oil with different viscosity were studied. And three mixtures of water and ethylalcohol of different volume ratio were used. Finally, the nano fluids were also studied. Working fluids were tested with thermal conductivity values ranging from 0.1 to 0.56 W/m- .deg. C, thermal expansion coefficient values ranging from 1.8 x 10-4 to 1.3 x 10-3 K-1, and kinematic viscosity values ranging from 0.65 x 10-6 to 100 x 10-6 m2/s. Through the study, it was found that the circulation point(CP) at the onset of fluid flow is very important. for a given working fluid, the heat transfer and heated stability of the system depends strongly on the circulation point of the fluid stream. Also, the circulation point are different each other for different working fluids. In summary, the circulation point is the function of working fluid, geometrical characteristics of the thermodiodes and flow conditions such as flow velocity and flow rate. The earlier occurrence of circulation point at a lower temperature leads the stable distribution of the temperature. With this respect, the working fluid of water-ethylalcohol mixture whose volume ratio is 2 to 8 were found to yield the most stable heat transfer
[en] Nature has been giving us energy from the beginning of the world. But human hardly use it. Solar energy is a kind of energy from the nature. This study has been carried out to study the use of solar energy as it is harnessed in the form of thermal energy. Solar energy is one of the most promising energy resources on earth and in space, because it is clean and inexhaustible. Heat for comfort in buildings can be provided from solar energy by systems that are similar in many respects to the water heater systems. To utilize the solar energy, we can not only solve the problem of energy shortage, but also can protect the environment and benefit the human beings. We must think about how to absorb the solar energy more efficiently, how to store more energy, and other problems such as additional electrical-heating system. This study deals with the collection of solar energy and its storage in all-glass solar vacuum tubes for different types of header design, flow passage and heat transfer devices. In order to elicit the most efficient combination of header design, flow passage, heat transfer hardware and operating conditions, we have studied four different types of solar collectors utilizing vacuum tubes. We selected the evacuated solar collector with metal cap and the all-glass evacuated solar collector. These collectors are more efficient than flat-plate collectors in both direct and diffuse solar radiation. The all-glass evacuated collector have been widely utilized due to their high efficiency, low heat losses, long lifetime and low costs. The evacuated solar collector in the present study uses a single vacuum solar collector either with a heat pipe (SEIDO 5) or with a 'dual pipe' flow passage (SEIDO 2). The one with heat pipe is designed such that the condensing section of heat pipe is inserted into a pipe header where the water from the storage tank is constantly circulated. Solar energy is transferred in the form of heat as it is ultimately saved in the storage tank. Similar principle is applied in the 'dual pipe' type where cold water enters the inner pipe and flows along the outer pipe raising its temperature thanks to the irradiation of solar energy. Different from these in its design and heat collection mechanism, all glass solar vacuum collector is utilized more efficiently and more conveniently in harnessing the solar energy. The 'U-pipe' type is one of those methods, which became quite popular recently with the usage of all glass solar vacuum tubes. Water is heated as it flows through the U-shaped copper pipe placed inside the vacuum tube. A rolled copper sheet tightly inserted along the inner surface of inner tube enhances heat transfer between the heated collector surface and the water contained in the U-shaped copper pipe. This study has been carried out a series of tests under the same conditions to elicit the most suitable model, which deems to enhance heat transfer and improve its durability in utilizing solar vacuum tubes
[en] Small-medium reactors have been highly evaluated to have more safe characteristics than those of large reactors. In addition, it could be used for a variety of purposes, such as small-scale power production in mountainous of island area, seawater desalination, regional heating system. For a higher safety, studies about a way of using natural circulation have being conducted around world. CAREM(Argentina), AST- 500(Russia), and NHR-200(china) etc. According to this tendency, REX- 10(Regional Energy rX-10) is designed in Korea for regional heating and small-scale power production. To investigate the thermal-hydraulic behavior of REX-10, we designed Rex-10 Test Facility (RTF), simulating REX-10, by using the scaling law. The scaling ratios of length, volume and power were set with 1/1, 1/50 and 1/50, respectively. The diameter and total length of RTF are 40 cm and approximately 6 m, respectively. The facility is composed of various components, which are a core in the bottom part, a heat exchanger in the middle part, a pressurizer and hot legs in the upper part, and chillers outside the facility. The test instrumentation is also designed to measure temperatures, flow rates, pressures, and pressure drop. The experiment parameters were adopted based on the 1-dimensional approach. There are a variety of parameters which influence natural circulation behavior such as heater power, overall flow resistance parameter, the distance between the center of the heat exchanger and the core. As the experimental geometries are fixed, it is found that the most important parameter is the heater power under the experimental conditions. In addition, to evaluate the effect of heater power, some experiments were conducted at varying heater power condition (from 70 kW to 170 kW) under constant primary pressure (2.0 MPa) and secondary flow rate (4.5 liter per minute). As the results of the experiments, the temperature and flow rate increase with increasing heater power. The flow rate is particularly proportional to heater power to the one third. These results show good agreement in terms of the governing equation of steady state natural circulation. In conclusion, it was evaluated that RTF is satisfied with the safety of a natural circulation system. The outlet temperature of the core at 200 kW heater power did not exceed the boiling temperature at 2.0 MPa, and the heat generated in the reactor core was removed by the coolant in the secondary loop
[en] The utilization of microencapsulated phase change materials(PCMs) provides several advantages over conventional PCM application. The heat storage system, as well as heat recovery system, can be built to a smaller size than the normal systems for a given thermal cycling capacity. This microencapsulated PCM technique has not yet been commercialized, however. In this work sodium acetate trihydrate(CH3COONa · 3H2O) was selected for the PCM and was encapsulated. This microencapsulated PCM was mixed with cement mortar for utilization as a floor heating system. In this experiment performed here the main purpose was to investigate the thermal performance of a storage brick with microencapsulated PCM concentration. The thermal performance of this storage brick is dependent on PCM concentration, flow rate and cooling temperature of the heat transfer fluid, etc. The results showed that cycle time was shortened as the PCM content was increased and as the mass flow rate was increased. The same effect was obtained when the cooling temperature was decreased. For each thermal storage brick the overall heat transfer coefficient(U-value) was constant for a 0% brick, but was increased with time for the bricks containing microencapsulated PCM. For the same mass flow rate, as the cooling temperature decreased, the amount of heat withdrawn increased, and in particular a critical cooling temperature was found for each thermal storage brick. The average effectiveness of each thermal storage brick was found to be approximately 48%, 51% and 58% respectively
[en] An overview of the possible positional disturbances of a stationary satellite or a space vehicle and of the necessary corrections is first presented. The characteristic properties of fluids used for space propulsion are then described. Several types of low-thrust propulsion systems (electro-thermal and radio-thermal types) are described and compared.
[fr]Apres avoir donne un apercu sur les perturbations de position possibles d'un satellite stationnaire ou d'un vehicule spatial et sur les corrections necessaires, on presente les proprietes caracteristiques de fluides utilises pour la propulsion dans l'espace. On decrit plusieurs types de propulseurs a faible poussee par fluide et on les compare en vue de leur utilisation.
[en] In the first chapters of thesis I am going to show the importance of research of civil use of fusion energy. Then I will give a short introduction in fusion physics and plasma physics, because the method of fusion used here (Tokamak) is based on plasma physics. After that I am going to present a more detailed picture of a state of the art tokamak and its heating systems. Different confinement modes (low confinement mode and high confinement mode - H-mode and L-Mode) will also be explained. And the most important instability in the high confinement mode (the Edge Localize modes or ELMs) will be discussed. Later on I will give an introduction to plasma diagnostics and probe physics. After this general part I will show details on our measurement system and explain the physics and abilities of our probe head. And show how it can survive temperatures up to several tens or hundreds of thousands degrees. In the next chapters some more direct measurements (like density and poloidal rotation measurements) will be presented. After this the radial transport of poloidal momentum will be defined and will be shown and discussed in detail during different operational modes (L-modes and H-modes) and time intervals (ELM and inter ELM intervals). Various statistical methods (like PDF generation, classical and robust statistical moments) will be applied on the momentum transport. In the end the given results will be interpreted and an outlook for further experiments will be given. (author)
[de]Im ersten Kapitel dieser Arbeit werde ich zeigen, warum die zivile Nutzung von Fusionsenergie wichtig für unsere Zukunft ist. Im Folgenden werde ich eine kurze Einführung in die Fusions- und Plasmaphysik geben, da die verwendeten Fusionsmaschinen (Tokamaks) auf Plasmaphysik basieren. Anschließend werde ich eine detailliertere Beschreibung eines modernen Tokamaks und seiner Heizsysteme vorlegen. Auch die unterschiedlichen Einschlussszenarien, wie H-mode und L-mode werden diskutiert. Im Folgenden werden die wichtigsten Instabilitäten (Edge localised modes (Randschichtmoden) erklärt und klassifiziert. Abschließend für diesen allgemeinen Teil werde ich noch eine Einführung in Plasmadiagnostik (im speziellen Sondendiagnostik) geben. Anschließend werde ich unser Messsystem im Detail beschreiben und die zu Grunde liegende Physik und die Möglichkeiten unseres Sondenkopfes diskutieren, und zeigen wie er mehrere Zehn- bis Hunderttausende Grad überstehen kann. Im nächsten Kapitel werden direktere Messungen wie etwa Plasmadichte und poloidale Rotation präsentiert. Der wichtigste Teil wird die Definition und Messung des radialen Transportes von poloidalem Impuls sein. Messungen während H- und L-Mode so wie während und zwischen ELMs werden präsentiert und im Detail analysiert. Verschiedene statistische Methoden wie etwa Wahrscheinlichkeitsdichte sowie klassische und robuste statistische Momente werden benutzt, um den Transport und seine Komponenten zu untersuchen. Zum Ende hin werden die Ergebnisse interpretiert und eine Ausblick auf zukünftige Forschung gegeben. (author)
[en] The reliability and sustainability of future fusion power plants will highly depend on the aptitude of materials to withstand severe irradiation conditions induced by the burning plasma in reactors. The so-called reduced-activation ferritic-martensitic (RAFM) steels are the current promising candidates for the structural applications considering the reactor's first wall. These steels exhibit irradiation embrittlement and hardening for defined irradiation conditions that are mainly characterized by the irradiation temperature and the irradiation dose. A proper characterization of such irradiated steels implies the use of adapted mechanical testing tools. In the present study, the instrumented indentation technique makes use of a post-processing tool based on neural networks. This technique has been selected for its ability to examine tensile properties by multistage indents on miniaturized irradiated metallic samples. The steel specimens studied in this project have been neutron-irradiated up to a dose of 15 dpa. They have been subsequently tested at room temperature in a Hot Cell by means of an adapted commercial indentation device. The significant irradiation-induced hardening effect present in the range of 250-350 deg C could be observed in the hardness and material's strength parameters. These two material parameters show a similar evolution with increasing irradiation temperatures. Post-irradiation annealing treatments of Eurofer97 have been realized and leads to a partial recovery of the irradiation damage. Considering the demands for characterization in irradiated steels at high temperature and for post-irradiation annealing experiments, the existing instrumented indentation device has been further developed during this work. A conceptual design has been proposed for an indentation testing machine, operating at up to 650 deg C, while remaining the critical temperature limit for tensile strength of the newly developed oxide dispersion strengthening ferritic-martensitic (ODS-RAFM) steel. A heating system as well as an optical sensing system have been both conceived for the high temperature testing facility. The former system relies on the use of cartridge heaters heating the sample and the indenter by thermal conductivity, and is further investigated by numerical analyses. The latter system is used for measuring the indentation depth at displacement resolutions up to 20nm and is based upon an existing method of digital image processing. Two main parts feature the design suggested for the machine. The first one stands for the basic structure and the force application system, while the second makes the connection between the vacuum chamber, the heating-cooling and the sample positioning systems. The integrated vacuum chamber acts for a significant diminution of oxidation at the specimen and the tip. The final design of the machine takes into account the spatial constraints existing in a Hot Cell.
[en] Fermi National Accelerator Laboratory will be conducting the high energy particle physics experiment Muons to Electrons (Mu2e). In this experiment, physicists will attempt to witness and understand an ultra-rare process which is the conversion of a muon into the lighter mass electron, without creating additional neutrinos. The experiment is conducted by first generating a proton beam which will be collided into a target within the production solenoid (PS). This creates a high-intensity muon beam which passes through a transport solenoid (TS) and into the detector solenoid (DS). In the detector solenoid the muons will be stopped in an aluminum target and a series of detectors will measure the electrons produced. These components have been named the DS train since they are coupled and travel on a rail system when being inserted or extracted from the DS. To facilitate the installation and removal of the DS train, a set of external stands and a support stand for the instrumentation feed-through bulkhead (IFB) have been designed. Full analysis of safety factors and performance of these two designs has been completed. The detector solenoid itself will need to be maintained to a temperature of 22°C ± 10°C. This will minimize thermal strain and ensure the accurate position of the components is maintained to the tolerance of 2 mm. To reduce the thermal gradient, a passive heating system has been developed and reported.
[en] Energy and natural resources are essential prerequisites for the maintenance of the life and the development of human civilization. With the advancement of technology is more emphasis on energy efficiency and reducing carbon dioxide emissions. Energy efficiency is using less power without reducing the quality of life. Almost half of the energy used is devoted to buildings, including heating and cooling. Buildings are a major source of CO_2 emissions in the atmosphere. Reducing the impact of buildings on the environment and the development of renewable energy, energy solutions are key factor in terms of sustainable development. Energy and geothermal pumps posts represent effective solutions for large facilities for heating and cooling. Geothermal energy piles represent a system of pipes that circulate thermal fluid and embedded in earth, thus extracting heat from the bearing to satisfy the needs for heating and cooling. Experience has shown that this type of energy piles can save up to two thirds of the cost of conventional heating, while geothermal pump has the ability to low temperature resources (such as groundwater and earth) to extract energy and raise the higher level needed for heating buildings. Their implementation is supported by an active group of researchers working with industry to demonstrate the benefits of dual benefit performance at the foundations. Initiative for renewable heat and potential for further adoption of solutions with these technologies is rapidly expanding. The use of this source of energy has great potential due to environmental, economic and social benefits. (author)