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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.

Acoustic droplet vaporization (ADV) is a process in which a phase shift of a liquified droplet into a gaseous microbubble, is triggered using an ultrasonic wave. In contrast to utilizing conventional contrast agents in ultrasound, the phase change contrast agents used in ADV can extravasate into tumor tissue, and they offer a greater circulatory lifespan, thereby increasing the potential applications in which they can be utilized. In this project, the impact of different ultrasound parameters on the efficiency of ADV was investigated, using a programmable ultrasound system. Two different ultrasound sequences were designed, for imaging and vaporization of droplets. Furthermore, three different sets of experiments were performed. Firstly, the vaporization effect of different imaging voltages was investigated, whereby a setting of 15V was identified as an able voltage for the remaining experiments. Secondly, experiments concerning the effect of vaporizing frequency on the ADV efficiency were performed, including the use of single and dual frequencies. Lastly, different frequency settings were combined with varying the number of cycles, to assess how the choice of pulse length influences the vaporization. The results from the project indicate that no substantial difference in ADV efficiency is achieved when using different frequency settings for perfluoropentane droplets encapsulated by cellulose nanofibers. However, the results provide clear indications of the benefit of using longer pulse durations on the vaporization efficiency. In conclusion, further studies are required before ADV can be translated into a clinical setting.

Ultrasound-mediated drug delivery has been proposed as a safe and non-invasive method to achieve localized drug release. Drug-loaded microbubbles are injected in the vascular system and ultrasound waves are then used to localize and burst the microbubbles at a specific targeted area. The relatively large size of microbubbles however limits both their lifetime and their reach in the human body. Phase-change liquid droplets can extend the use of ultrasound contrast agents for localized drug delivery. Their smaller size provides several advantages. The droplets can reach smaller capillaries, such as those in tumors vasculature. Their lifetime is also considerably prolonged. Through the phenomenon of Acoustic Droplet Vaporization (ADV), triggered by ultrasound stimulation, the liquid-filled droplets experience a phase change and are converted into gas-filled microbubbles. The newly created microbubbles can then be disrupted by further stimulation and release their drug load in the tumor tissue. In this project, a protocol to image and burst perfluoropentane-based micro-sized droplets using a single transducer is developed using the Verasonics Ultrasound System. The pulse sequences are developed to allow close monitoring of the drug delivery by capturing a series of images before and after the vaporization or destruction of the droplets. The droplets response was assessed for different pulse voltages and durations. Mean pixel value was calculated for the regions of interest, using the images captured before and after delivery of the ultrasound pulse. Vaporization of the droplets can be achieved with low voltage (10V), whereas high voltage (50V) triggers their destruction. Combined with high voltage, pulse duration affects the rate at which droplets can be destructed.

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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.

The transient thermal response of a 15-cell, 48 volt, lithium-ion battery pack for an unmanned ground vehicle was simulated with ANSYS Fluent. Heat generation rates and specific heat capacity of a single cell were experimentally measured and used as input to the thermal model. A heat generation load was applied to each battery and natural convection film boundary conditions were applied to the exterior of the enclosure. The buoyancy-driven natural convection inside the enclosure was modeled along with the radiation heat transfer between internal components. The maximum temperature of the batteries reached 65.6 °C after 630 seconds of usage at a simulated peak power draw of 3,600 watts or roughly 85 amps. This exceeds the manufacturer's maximum recommended operating temperature of 60 °C. The pack was redesigned to incorporate a passive thermal management system consisting of a composite expanded graphite matrix infiltrated with a phase-changing paraffin wax. The redesigned battery pack was similarly modeled, showing a decrease in the maximum temperature to 50.3 °C after 630 seconds at the same power draw. The proposed passive thermal management system kept the batteries within their recommended operating temperature range.