The introduction of phase change material fluid and nanofluid in micro-channel heat sink design can significantly increase the cooling capacity of the heat sink because of the unique features of these two kinds of fluids. To better assist the design of a high performance micro-channel heat sink using phase change fluid and nanofluid, the heat transfer enhancement mechanism behind the flow with such fluids must be completely understood. A detailed parametric study is conducted to further investigate the heat transfer enhancement of the phase change material particle suspension flow, by using the two-phase non-thermal-equilibrium model developed by Hao and Tao (2004). The parametric study is conducted under normal conditions with Reynolds numbers of Re=600-900 and phase change material particle concentrations ¡Ü0.25 , as well as extreme conditions of very low Reynolds numbers (Re < 50) and high phase change material particle concentration (0.5-0.7) slurry flow. By using the two newly-defined parameters, named effectiveness factor and performance index, respectively, it is found that there exists an optimal relation between the channel design parameters, particle volume fraction, Reynolds number, and the wall heat flux. The influence of the particle volume fraction, particle size, and the particle viscosity, to the phase change material suspension flow, are investigated and discussed. The model was validated by available experimental data. The conclusions will assist designers in making their decisions that relate to the design or selection of a micro-pump suitable for micro or mini scale heat transfer devices. To understand the heat transfer enhancement mechanism of the nanofluid flow from the particle level, the lattice Boltzmann method is used because of its mesoscopic feature and its many numerical advantages. By using a two-component lattice Boltzmann model, the heat transfer enhancement of the nanofluid is analyzed, through incorporating the different forces acting on the nanoparticles to the two-component lattice Boltzmann model. It is found that the nanofluid has better heat transfer enhancement at low Reynolds numbers, and the Brownian motion effect of the nanoparticles will be weakened by the increase of flow speed.

Energy storage with the help of different materials is something that has been around for a long time. Structures such as concrete or brick use their high thermal mass to store energy in the form of temperature increase, sensible heat, of the respective material. Energy storage in the form of sensible heat is relatively small in capacity, which means that large masses of building material are required to give a significant effect. Concrete, for example, requires 4 kJ/kg to increase in temperature by 1 °C. Now society has begun to look more closely at other materials that can be used for energy storage and temperature stabilization in buildings. Phase change materials are unique materials that use the change in phases between different aggregation states to store energy in the form of latent heat. It is mainly phase change between solid and liquid that is used since gaseous form would involve large volume changes. An everyday example of a material that undergoes a phase change is water. Water requires 334 kJ/kg to go from 0 ˚C ice (solid) to 0 ˚C water (liquid).  Water is a very powerful phase change material but cannot be used in buildings as it melts at 0 ˚C. Therefore, other materials have been developed to meet the requirement that the melting take place at the desired temperature, usually room temperature. The different phase change materials can be divided into three different groups: organic, inorganic and eutetic materials. All groups come with their own advantages and disadvantages. Organic materials are stable materials in the sense that they can phase change in repeated cycles which makes them the popular choice when it comes to buildings. One disadvantage that most organic materials possess is that they are flammable. The choice of phase change material will affect the quality of the building and it is therefore important that the knowledge about these materials is adopted before they become more widespread.

>Magister Scientiae - MSc / Phase change material (PCM) through latent heat of molten salt, is a convincing way for thermal energy storage in CSP applications due to its high volume density. Molten salt, with (60% NaNO3 and 40% KNO3) has been used extensively for energy storage however; the low thermal conductivity and specific heat have limited its large implementation in solar applications. For that, molten salt with the additive of silver nanowires (AgNWs) was synthesized and characterized. This research project aims to investigate the thermophysical properties enhancement of nanosalt (Mixture of molten salt and silver nanowires). The results obtained showed that by simply adjusting the temperature, Silver nanowires with high aspect ratio have been synthesized through the enhanced PVP polyol process method. SEM results revealed a network of silver nanowires and TEM results confirmed the presence of silver nanowires with an average diameter of 129 nm and 16 μm in length.

Nowadays continuous increase of energy consumption increases the importance of replacing fossil fuels with renewable energy sources so the CO2 emissions can be reduced. To use the energy in a more efficient way is also favorable for this purpose. Thermal Energy Storage (TES) is a technology that can make use of waste heat, which means that it can help energy systems to reduce the CO2 emissions and improve the overall efficiency. In this technology an appropriate material is chosen to store the thermal energy so it can be stored for later use. The energy can be stored as sensible heat and latent heat. To achieve a high energy storage density it is convenient to use latent heat based TES. The materials used in this kind of storage system are called Phase Change Materials (PCM) and it is its ability of absorbing and releasing thermal energy during the phase change process that becomes very useful. In this thesis a simulation model for a system of thermal energy transportation has been developed. The background comes from district heating systems ability of using surplus heat from industrials and large scale power plants. The idea is to implement transportation of heat by trucks closer to the demand instead of distributing heat through very long pipes. The heat is then charged into containers that are integrated with PCM and heat exchangers. A mathematical model has been created in Matlab to simulate the system dynamics of the logistics of the thermal energy transport system. The model considers three main parameters: percentage content of PCM in the containers, annual heat demand and transport distance. How the system is affected when these three parameters varies is important to visualize. The simulation model is very useful for investigation of the economic and environmental capability of the proposed thermal energy transportation system. Simulations for different scenarios show some expected results. But there are also some findings that are more interesting, for instance how the variation of content of PCM gives irregular variation of how many truck the system requires, and its impact on the economic aspect. Results also show that cost for transporting the heat per unit of thermal energy can be much high for a small demands compared to larger demands.

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京都大学 / 0048 / 新制・論文博士 / 博士(工学) / 乙第12983号 / 論工博第4130号 / 新制||工||1637(附属図書館) / 32453 / 台湾国立成功大学大学院工学研究科建築学専攻 / (主査)教授 鉾井 修一, 教授 原田 和典, 教授 神吉 紀世子 / 学位規則第4条第2項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

The major challenge associated with renewable-energy systems especially solar, is the supply intermittency. One effective solution is to incorporate thermal energy storage components utilizing phase change materials (PCMs). These materials have the potential to store large amounts of energy in relatively small volumes and within nearly an isothermal storage process. The primary drawback of today’s PCMs is that their low thermal conductivity values critically limit their energy storage applications. Also, this grossly reduces the melting/ solidification rates, thus making the system response time to be too long. So, the application of heat transfer enhancement is very important. To improve the PCM storage performance, an efficient performing containment vessel (triplex-tube) along with applications of various heat transfer enhancement techniques was investigated. The techniques were; (i) dispersion of solid nanoparticles, (ii) incorporation of metal foam with nanoparticle dispersion, and (iii) insertion of longitudinal fins with nanoparticle dispersion. Validated simulation models were developed to examine the effects of implementing these techniques on the PCM phase-change rate during the energy storage and recovery modes. The results are presented with detailed model description, analysis, and conclusions. Results show that the use of nanoparticles with metal foam or fins is more efficient than using nanoparticles alone within the same volume usage. Also, employing metal foam or fins alone results in much better improvement for the same system volume.

京都大学 / 新制・課程博士 / 博士(工学) / 甲第24645号 / 工博第5151号 / 新制||工||1983(附属図書館) / 京都大学大学院工学研究科化学工学専攻 / (主査)准教授 渡邉 哲, 教授 佐野 紀彰, 教授 河瀬 元明 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

<p>Surfactant is a type of surface-active molecule with wide industrial applications, such as personal care products, antibacterial products, surface modification, etc. Due to environmental concerns, biobased surfactants derived from renewable sources are of great interest. In the first part of this work, biobased quaternary ammonium (QA) amphiphiles are synthesized from soybean oil via a two-step reaction. For example, fatty acid amides (FAAms) were first synthesized through direct amidation of soybean oil. The FAAms exhibited different liquid-solid phase transition behavior depending on their saturation and chain length. A general trend of increasing enthalpy of fusion, narrower phase transition temperature range, higher melting temperature, and better thermal stability was observed with increasing chain length and saturation. Overall, fifteen green, organic PCMs were synthesized with the comparable latent heat of fusion to petroleum based PCMs. </p> <p>Biobased QA surfactants were successfully synthesized with comparable surface activity to cetyltrimethylammonium bromide (C16TAB) by alkylating FAAms into quaternary ammonium (QA) compounds.  The water solubility of long-chain (C18) QA surfactants was improved by introducing two or more QA groups in the headgroup, or unsaturation in the tail group. All the surfactants exhibited positive charge with high stability against varying pH. Surfactants derived from fully hydrogenated soybean oil (FHS) and diethylenetriamine (DETA) showed lower critical micelle concentration (CMC) and surface tension in water (SFT) than C16TAB. All the other five surfactants had surface activity comparable to C16TAB and C12TAB. These biobased surfactants are potential alternatives to commercial petroleum-derived QA surfactants. </p> <p>The second part of this work is devoted to understanding the effect of mixed surfactant composition on emulsion stability, and formation is beneficial for optimizing the wastewater treatment process. Emulsion behavior in a saline environment was studied with mixed anionic and nonionic surfactants: sodium laureth sulfate (SLES) and Triton X-100. It was found 500 ppm total surfactant concentration was sufficient to stabilize 5 wt. % mineral oil against coalescence, regardless of the surfactant ratio. Compared to Triton X-100-rich emulsions, SLES-rich ones had higher stability against flocculation and creaming. SLES-rich emulsions had twice as much remnant oil in the subnatant as Triton X-100-rich samples, which is undesirable in wastewater treatments. The relation between spontaneous emulsion behavior and the HLD model was studied with SLES-Span-80 surfactant mixtures. The influence of salinity, oil type, and surfactant composition was investigated. Spontaneous emulsification could only be observed when the systems have HLD values close to 0 (-0.96 ~ 1.04). A combined effect of bicontinuous-phase formation and ultra-low interfacial tension led to spontaneous emulsification. This work proposes a practical approach to predict emulsion compositions that result in spontaneous emulsification.</p>

Idag står världen inför en rad olika miljörelaterade problem. Ett av dessa och det kanske mest omtalade är hur utsläpp av växthusgaser sakta men säkert höjer planetens medeltemperatur. Hållbar utveckling är ett begrepp som driver diskussionen framåt om vad vi behöver göra och hur vi behöver förändras för att lösa problemen. Växthusgaserna och deras hot mot klimatet är starkt relaterat till energi. Förnyelsebara energikällor skulle kunna vara en dellösning på problemet men de kräver energilagring av olika former för att kunna ersätta sina fossila konkurrenter. Termisk energilagring är ett sätt att lagra energi på och kan delas upp i tre olika grupper. Dessa är sensibel, latent och termokemisk värmelagring. Syftet med denna litteraturstudie var att kartlägga olika applikationer av latent värmelagring som kan bidra till ett mer hållbart samhälle i framtiden. Resultatet visar att det finns många olika typer av så kallade fasomvandlingsmaterial (PCMs). Beroende på vid vilka temperaturer värme ska lagras vid används olika PCMs. PCMs kan användas för latent värmelagring inom många olika områden. Byggnader är ett av dessa områden där PCMs kan användas för att kyla och värma utrymmen antingen genom integration i ventilationssystem eller i själva byggnadsmaterialen. Latent värmelagring kan också användas i termiska solkraftverk. Latent värmelagring har på senare tid fått stor uppmärksamhet tack vare PCMs förmåga att lagra värme i små volymer och under konstant temperatur. Dock möter tekniken problem vid värmeöverföringen vilket t.ex. är fallet i lagring av termisk solenergi. Forskning pågår därför för att generellt höja PCMs termiska egenskaper. Ett exempel på detta är Nano-PCM. Resultatet visar även att latent värmelagring idag används av företag som affärsidé för olika tillämpningar. Från resultatet går det att dra slutsatsen att latent värmelagring används idag men att det krävs ytterligare forskning för att tekniken ska kunna konkurrera med andra värmelagringsmetoder. / Today, the world faces a number of environmental-related problems. One of these and perhaps most discussed is how emissions of greenhouse gases slowly but surely raise the planet’s average temperature. Sustainable development is a concept that drives the discussion forward and tells us what we need to do and how we need to change to solve the problems. Greenhouse gases and their threats to the climate are strongly related to energy. Renewable sources of energy could be a partial solution to the problem, but they require energy storage of different forms to replace their fossil competitors. Thermal energy storage is a way of storing energy and can be divided into three different groups. These are sensible, latent and thermochemical heat storage. The purpose of this literature study was to map different applications of latent heat storage that can contribute to a more sustainable society in the future. The result shows that there are many different types of phase changing materials (PCMs). Depending on the temperature at which heat is to be stored, different PCMs are used. PCMs can be used for latent heat storage in many different areas. Buildings are one of these areas where PCMs can be used to cool and heat spaces either through integration into ventilation systems or in the building materials itself. Latent heat storage can also be used in thermal solar power plants. Latent heat storage has recently received great attention thanks to PCMs ability to store heat in small volumes and under constant temperature. However, the technology is experiencing problems in the heat transfer, such is the case in the storage of thermal solar energy. Research is therefore ongoing to generally increase PCMs thermal properties. An example of this is Nano-PCM. The result also shows that latent heat storage today is used by companies as a business concept for various applications. From the result, it can be concluded that latent heat storage is used today, but that further research is required for the technology to compete with other heat storage methods.