Using equilibrium molecular dynamics simulations, an analysis of the key thermophysical properties critical to heat transfer processes is performed. Replication of thermal conductivity and shear viscosity observations found in experimental investigations were performed using a theoretical nanopthesis-fluid system and a novel colloid-fluid interaction potential to investigate the key nanofluid parameters. Analysis of both the heat current (thermal conductivity) and stress (shear viscosity) autocorrelation functions have suggested that the dominant physical mechanisms for thermal and momentum transport arises from enhancements to the longitudinal and transverse acoustic modes energy transfer brought about by the increased mass ratio of the nanopthesis to the fluid. This conclusion was further supported by analysis of the local density fluctuations surrounding increasing nanopthesis diameters where the longitudinal acoustic mode characteristics for density fluxes were seen to be enhanced by the presence of the heavier platinum nanopthesiss. It is then concluded that the key macroscopic characteristic in obtaining the largest thermal energy transfer enhancement is through the mass of the nanopthesis relative to the base fluid. Also, the small local density effects in the nanofluid are greatly affects the viscosity calculations. These conclusions provide the theoretical framework for many of the experimental results obtained.

Thermodynamics is important for the design of amine scrubbing CO₂ capture processes. CO₂ solubility and amine volatility in aqueous amines were measured at high temperature and pressure. A rigorous thermodynamic model was developed for MEA-CO₂-H₂O in Aspen Plus®. CO₂ solubility at 80-190°C was obtained from total pressure measurements. Empirical models as a function of temperature and loading were developed for CO₂ solubility from 40 to 160°C in aqueous monoethanolamine (MEA), piperazine (PZ), 1-methylpiperazine (1MPZ), 2-methylpiperazine (2MPZ), PZ/2MPZ, diglycolamine® (DGA®), PZ/1MPZ/1,4-dimethylpiperazine (1,4-DMPZ), and PZ/methyldiethanolamine (MDEA). The high temperature CO₂ solubility data for MEA is comparable to literature and compatible with previous low temperature data. For MEA and PZ, amine concentration does not have obvious effects on the CO₂ solubility. The heat of CO₂ absorption derived from these models varies from 66 kJ/mol for 4 m (molal) PZ/4 m 2MPZ and to 72, 72, and 73 kJ/mol for MEA, 7 m MDEA/2 m PZ, and DGA. The heat of absorption estimated from the total pressure data does not vary significantly with temperature. At 0-0.5 loading ([alpha]), 313-413 K, 3.5-11 m MEA (mol fraction x is 0.059-0.165), the empirical model of MEA volatility is ln(PMEA/xMEA) = 30.0-8153/T-2594[alpha]²/T. In 7 m MEA with 0.2 and 0.5 loading, PMEA is 920 and 230 Pa at 120°C. At 0.3-0.5 loading, the enthalpy of MEA vaporization, -[Delta]Hvap,MEA, is about 70-73 kJ/mol MEA. At 0.25-0.4 loading, 313-423 K, 4.7-11.3 m PZ (x is 0.078-0.169), the empirical model of PZ volatility is ln(PPZ/xPZ) = -123+21.6lnT+20.2[alpha]-18174[alpha]²/T. In 8 m PZ with 0.3 and 0.4 loading, PPZ is 400 and 120 Pa at 120°C, and 2620 and 980 Pa at 150°C. At 0.25-0.4 loading, -[Delta]Hvap,PZ is about 85-100 kJ/mol PZ at 150°C and 66-80 kJ/mol PZ at 40°C. [Delta]Hvap,PZ has a larger dependence on CO₂ loading than [Delta]Hvap,MEA in rich solution because of the more complex speciation/reactions in PZ at rich loading. Specific heat capacity of 8 m PZ is 3.43-3.81 J/(g•K) at 70-150°C. Two new thermodynamic models of MEA-CO₂-H₂O were developed in Aspen Plus® starting with the Hilliard (2008) MEA model. One (Model B) includes a new species MEACOOH and it gets a better prediction than the other (Model A) for CO₂ solubility, MEA volatility, heat of absorption, and other thermodynamic results. The Model B prediction matches the experimental pKa of MEACOOH, and the measured concentration of MEACOO-/MEACOOH by NMR. In the prediction the concentration of MEACOOH is 0.1-3% in 7 m MEA at high temperature or high loading, where the heat of formation of MEACOOH has effects on PCO₂ and CO₂ heat of absorption. Model B solved the problems of Model A by adding MEACOOH and matched the experimental data of pKa and speciation, therefore MEACOOH may be considered an important species at high temperature or high loading. Although mostly developed from 7 m MEA data, Model B also gives a good profile for 11 m (40 wt%) MEA. / text

In the first part of this thesis, we present results from extensive molecular dynamics simulations of the collapse transitions of hydrophobic polymers in explicit water. The focus is to understand the roles that curvature and interactions associated with the polymer-water “interface” have on collapse thermodynamics. We show that model hydrophobic polymers can have parabolic, protein-like, temperature-dependent free energies of unfolding. Analysis of the water structure shows that the polymer-water interface can be characterized as soft and weakly dewetted. We also show that an appropriately defined surface tension for the polymer-water interface is independent of the attractive polymer-water interactions. This helped us to develop a perturbation model for predicting the effect of attractions on polymer collapse thermodynamics. In the second part, we explore connections between structure, thermodynamics, and dynamics of inhomogeneous fluids. First, we use molecular dynamics simulations and classical density functional theory (DFT) to study the hard-sphere fluid at approximately 103 equilibrium state points, spanning different confining geometries and particle-boundary interactions. We provide strong empirical evidence that both excess entropy and a new generalized measure of available volume for inhomogeneous fluids correlate excellently with self-diffusivity, approximately independent of the degree of confinement. Next, we study via simulations how tuning particle-wall interactions to flatten or enhance the particle layering of a model confined fluid impacts its self-diffusivity, viscosity, and entropy. Interestingly, interactions that eliminate particle layering can significantly reduce confined fluid mobility, whereas those that enhance layering can have the opposite effect. Excess entropy helps to understand and predict these trends. Finally, we explore the relationships between the effective interparticle interactions, static structure, and tracer diffusivity of a solute in a mixture. We show that knowledge of these relationships can allow one to “tune” the effective interparticle interactions of the solute in a way that increases its tracer diffusivity. One interesting consequence is that the mobility of a hard-sphere solute can be increased by adding a soft-repulsion to its interaction, effectively making it bigger. / text

We have performed a series of experiments developing the techniques of volumetric, isochoric heating of matter to high energy density states, and the subsequent probing of the release isentrope. Using ultrafast, ultra intense laser systems with pulse lengths from 100fs - 1ps and pulse energies between 2 J and 100 J, we generated strong secondary radiation, in the form of K[subscript alpha] x-rays and directed proton beams, which we used to rapidly heat a foil sample to temperatures from ~ 1 eV to ~ 25 eV at solid density, thus entering the strongly coupled, partially ionized regime of warm dense matter, in which the equation of state is poorly understood. The first set of experiments examines the possibility of using laser generated K[subscript alpha] x-rays in isochoric heating experiments and concludes that this technique will require the use of higher energies and higher Z materials than were used in this thesis to achieve warm dense matter conditions. In the second set of experiments, we used an ultrafast, lasergenerated proton beam with a temperature of ~ 2 MeV and cutoff energy of ~ 40 MeV to volumetrically and isochorically heat a sample foil to > 20 eV. With singleshot diagnostics, we measured the evolution of the temperature with 3:3 ps resolution over the _rst 35 ps of expansion by streaked optical pyrometry, and measured the evolution of the target expansion over the same timescale with sub-ps resolution by chirped pulse interferometry. In this way we were able to verify the equation of state and ion-balance in the SESAME equation of state tables with a Saha ionization model and distinguish this as more accurate than other, simpler models. This thesis establishes an experimental framework for acquiring equation of state data in the regime of warm dense matter that is distinct and complimentary to that acquired by the techniques of shock heating. / text

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Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(エネルギー科学) / 甲第19092号 / エネ博第316号 / 新制||エネ||64 / 32043 / 京都大学大学院エネルギー科学研究科エネルギー基礎科学専攻 / (主査)教授 木下 正弘, 教授 森井 孝, 教授 片平 正人 / 学位規則第4条第1項該当

The objective of this thesis is to evaluate the potential for wind as an alternative energy source to replace fossil fuels and reduce global CO2 emissions. From 1995 to 2007, fossil fuels as the major energy source accounted for an addition of 89.3 Gt of carbon to the atmosphere over this period, 29 % of which was transferred to the ocean, 15 % to the global biosphere, with the balance (57 %) retained in the atmosphere. Building a low-carbon and climate-friendly energy system is becoming increasingly urgent to combat the threat of global warming. / Engineering and Applied Sciences

The knowledge of physicochemical properties of organic compounds becomes increasingly important. In this study, we developed UPPER (Unified Physical Property Estimation Relationships), a comprehensive model for the estimation of 20 physicochemical properties of organic compounds. UPPER is a system of thermodynamically sound relationships that relate the various phase-transition properties to one another, which includes transition heats, transition entropies, transition temperatures, molar volume, vapor pressure, solubilities and partition coefficients in different solvents and etc. UPPER integrates group contributions with the molecular geometric factors that affect transition entropies. All of the predictions are directly based on molecular structure. As a result, the proposed model provides a simple and accurate prediction of the properties studied. UPPER is designed to predict industrially, environmentally and pharmaceutically relevant physicochemical properties of organic compounds. It also can be an aid for the efficient design and synthesis of compounds with optimal physicochemical properties.

Calibrated, multiband radiometric measurements of the optical radiation emitted by rocket-triggered lightning (RTL) have been made in the ultraviolet (UV, 200-360 nm), the visible and near infrared (VNIR, 400-1000 nm), and the long wave infrared (LWIR, 8-12 µm) spectral bands. Measurements were recorded from a distance of 198 m at the University of Florida International Center for Lightning Research and Testing (ICLRT) during the summers of 2011 and 2012. The ICLRT provided time-correlated measurements of the current at the base of the RTL channels. Following the onset of a return stroke, the dominant mechanism for the initial rise of the UV and VNIR waveforms was the geometrical growth of the channel in the field-of-view of the sensors. The UV emissions peaked about 0.7 µs after the current peak, with a peak spectral power emitted by the source per unit length of channel of 10 ± 7 kW/(nm-m) in the UV. The VNIR emissions peaked 0.9 µs after the current peak, with a spectral power of at 7 ± 4 kW/(nm-m). The LWIR emissions peaked 30-50 µs after the current peak, and the mean peak spectral power was 940 ± 380 mW/(nm-m), a value that is about 4 orders of magnitude lower than the other spectral band emissions. In some returns strokes the LWIR peak coincides with a secondary maximum in the VNIR band that occurs during a steady decrease in channel current. Examples of the optical waveforms in each spectral band are shown as a function of time and are discussed in the context of the current measured at the channel base. Source power estimates in the VNIR band have a mean and standard deviation of 2.5 ± 2.2 MW/m and are in excellent agreement with similar estimates of the emission from natural subsequent strokes that remain in a pre-existing channel which have a mean and standard deviation of 2.3 ± 3.4 MW/m. The peak optical power emitted by RTL in the UV and VNIR bands are observed to be proportional to the square of the peak current at the channel base. The same trend was found for natural lightning using peak currents estimates provided by the National Lightning Detection Network. Ratios of the optical power to the electromagnetic power emitted at the time of peak current suggest the radiative efficiency in the VNIR band is a few percent during the early onset of a return stroke. The majority of return strokes in RTL are found to emit most of their optical energy during the initial impulse phase.

Since boiling heat transfer affords a very effective means to transfer heat, it is implemented in numerous technologies and industries ranging from large power generation plants to micro-electronic thermal management. Although having been a subject of research for several decades, an accurate prediction of boiling heat transfer is still challenging due to the complexity of the coupled mechanisms involved. It appears that the boiling heat transfer coefficient is intimately related to bubble dynamics (i.e. bubble nucleation, growth and detachment) as well as factors such as nucleation site density and interaction between neighbouring and successive bubbles. In order to contribute to the understanding of the boiling phenomenon, an experimental investigation of saturated pool boiling from a single or two neighbouring artificial nucleation sites on a polished copper surface has been performed. The bubble growth dynamics has been characterized for different wall superheats and a experimental growth law has been established. The interaction between successive bubbles from the same nucleation site has been studied, showing the bubble shape oscillations that can be caused by these interactions. The forces acting on a growing bubble has been reviewed, and a complete momentum balance has been made for all stages of bubble growth. The curvature along the interface has been measured, and indications concerning the mechanism of bubble detachment have been suggested. The rise of bubble after detachment has been investigated, and the maximum velocity reached before a change of direction has been estimated and compared to existing models from the literature. The interaction between bubbles growing side by side has been studied: the generation and propagation of a wave front during the coalescence of two bubbles has been highlighted. As boiling heat transfer enhancement techniques are being imagined and developed, this study also focuses on the electrohydrodynamic enhancement technique. Boiling experiments have been performed in the presence of electric fields, and their effects on heat transfer and bubble dynamics have been characterized. Although the volume of the bubbles at detachment and the relationship between the bubble frequency and the wall superheat were not affected, the bubble growth curve was modified. The bubbles were elongated in the direction of the electric field, and this elongation was estimated and compared to other studies from the literature. The rising velocity of the bubble was reduced in the presence of electric field, and the behaviour of bubbles growing side by side was modified, the electric field causing the bubbles to repeal each other. These results, obtained in a fully controlled environment, provide compelling evidence that electric fields can be implemented to alter the bubble dynamics and subsequently heat transfer rates during boiling of dielectric fluids.