Multiple papers have been published which attempt to predict the thermal conductivity or thermal diffusivity of graphite “nanofluids” 1–6. In each of the papers empirical methods (with no consideration of quantum mechanical principles or a structural reference) are employed in an attempt to understand and predict the heat transfer characteristics of a nanofluid. However, the results of each of these papers vary considerably. The primary reason for this may relate to the inability to construct a representative material model (based on the chemical structure), that can accurately predict the thermal enhancement properties based on the intercalated adsorption of a fluid with a noticeable heat capacity 3. This project has strived to simulate the interaction of (nano-scale) graphite particles “dispersed” in water (at the structural level of effective surface “wetting”). The ultimate purpose is to enhance the heat conduction capacity. The strategy was to initially focus on the structural properties of the graphite powder, followed by incremental exposure to water molecules to achieve a representative model. The procedure followed includes these experimental steps: a) Molecular resolution porosimetry (i.e. BET) experiments, to determine the graphene “platelet” surface area to correlate with the minimum crystallite size (where a single graphite crystal is made up of multiple unit cells) of the graphite powder samples. b) Powder X-ray diffraction (PXRD) analyses of the graphite powder samples each supplied by different manufacturers in order to determine their respective crystallographic structures. c) Infrared (IR) and Raman vibrational spectra characterisation of all of the graphite powder samples for further structure confirmation. d) Thermo-gravimetric analysis (TGA) of graphite powder and water mixture samples, to try and determine the point at which the bulk water has separated and evaporated away from the graphite powder/water mixture, resulting in a minimum layer of water adsorbed on the graphite surface and inter-/intra-particle graphite spaces. e) Differential scanning calorimetry (DSC) of the “dry” and “surface-wetted” graphite samples to determine their specific heat capacities. f) Laser flash analysis (LFA) of the “dry” and “surface-wetted” graphite samples to determine their thermal diffusivity and thermal conductivity. g) The computer simulated analysis of the graphite powder exposed to water by means of computational modelling, to elucidate the various conformational approaches of water onto the graphite surface and the associated thermodynamic behaviour of water molecules ad/absorbed at the graphite surface. Data from the TGA measurements allowed for the determination of the appropriate amount of water required in order to not only experimentally prepare graphite “surface-wetted” samples, but also to determine the effective amount of absorbed water to be considered in the computational models. For experimental verification, both dry and wet graphite samples should then be used in a laser flash analysis (LFA), in order to elucidate the effect the interfacial layer of water has on the thermal properties of graphite. A computerised model of a single graphite crystal exposed to water was created using the MedeA (v. 2.14) modelling software. The conformational behaviour and energy states of a cluster of water molecules on the graphite surface were then analysed by using the VASP 5.3 software (based on a periodic solid-state model approach with boundary conditions), to determine the energetics, atomic structure and graphite surface “wetting” characteristics, at the atomistic level. The results of the computerised model were correlated to the physical experiments and to previously published figures. Only once a clear understanding of the way in which water molecules interact with the graphite surfaces has been obtained, can further investigation follow to resolve the effect that exposure of larger graphite surfaces to polar solvents (such as water and lubricants) will have on the heat conductance of such ensembles. This scope of further work will constitute a PhD study. / Dissertation (MEng)--University of Pretoria, 2015. / tm2015 / Mechanical and Aeronautical Engineering / MEng / Unrestricted

Superhydrophobic surfaces have gained attention as a potential mechanism for increasing condensation heat transfer rates. Various aspects related to condensation heat transfer are explored. Adiabatic, air-water mixtures are used to explore the influence of hydrophobicity on two-phase flows and the hydrodynamics which might be present in flow condensation environments. Pressure drop measurements in a rectangular channel with one superhydrophobic wall (cross-section approximately 0.37 X 10 mm) are obtained, revealing a reduction in the pressure drop for two-phase flow compared to a control scenario. The observed reduction is approximately 10% greater than the reduction that is observed for single-phase flow (relative to a classical channel). Carbon nanotubes have been used to create superhydrophobic coatings due to their ability to offer a relatively uniform nanostructure. However, as-grown carbon nanotubes often require the addition of a thin-film hydrophobic coating to render them superhydrophobic, and fine control of the overall nanostructure is difficult. This work demonstrates the utility of using carbon infiltration to layer amorphous carbon on multi-walled nanotubes to achieve superhydrophobic behavior with tunable geometry. The native surface can be rendered superhydrophobic with a vacuum pyrolysis treatment, with contact angles as high as 160 degrees and contact angle hysteresis less than 2-3 degrees. Drop-size distribution is an important aspect of heat transfer modeling that is difficult to measure for small drop sizes. The present work uses a numerical simulation of condensation to explore the influence of nucleation site distribution approach, nucleation site density, contact angle, maximum drop size, heat transfer modeling to individual drops, and minimum jumping size on the distribution function and overall heat transfer rate. The simulation incorporates the possibility of coalescence-induced jumping over a range of sizes. Results of the simulation are compared with previous theoretical models and the impact of the assumptions used in those models is explored. Results from the simulation suggest that when the contact angle is large, as on superhydrophobic surfaces, the heat transfer may not be as sensitive to the maximum drop-size as previously supposed. Furthermore, previous drop-size distribution models may under-predict the heat transfer rate at high contact angles. Condensate drop behavior (jumping, non-jumping, and flooding) and size distribution are shown to be dependent on the degree of subcooling and nanostructure size. Drop-size distributions for surfaces experiencing coalescence-induced jumping are obtained experimentally. Understanding the drop-size distribution in the departure region is important since drops in this size are expected to contribute significantly to the overall heat transfer rate.

Surface-bound particulates containing radionuclides in the environment can become airborne through the process of resuspension. Once airborne, these radionuclides can be inhaled or ingested to deliver an internal dose of ionizing radiation. To that end, the resuspension factor method is a powerful tool for predicting a person's exposure to airborne particles from surface contaminations, and therefore is used to determine protective and intervening measures. The resuspension factor is calculated as the ratio measured airborne to surface mass concentration and has been found to generally decrease exponentially with time. Current models of the resuspension factor are empirical and have failed to predict recent measurement, motivating a stronger basis and physical model for the system. Additionally, federal guidances conservatively suggest an unphysical model of particulate radioactivity impact wherein the entirety of the radiation is absorped. For this dissertation, two- and three-compartment catenary models were derived which build on measured resuspension rate constants under various influences. These models were fit to a set of historic observations of resuspension factors using an instrumental uncertainty-weighting to resolve the large variances early in time which otherwise inflate calculations. When compared to previous resuspension models, our physical models better fit the data achieving reduced-chi-squared closer to 1. An experiment was undertaken to validate our basic environment resuspension models in an urban environment without wind. A resuspension chamber is constructed by placing an acrylic tube atop a poured concrete surface and lowering a low-volume air sampler head from above. Europium oxide powder was dispersed upon the surface or from above the air sampling height to emulate ideal compartmentalized release scenarios, and air is sampled on an hourly, daily, or weekly basis. Sampler filters then were evaluated for Europium content using neutron activation and gamma spectroscopy. Hourly measurements following airborne release are within an order of magnitude of early-timeframe historic resuspension factors (~10^−6 m^−1), whereas daily and weekly measurements from surface release demonstrate a gradual decrease in resuspension factor (∼10^−8 m^−1). These results support a need to critically assess the resuspension factor definition and its relationship to "initial suspension" and the indoor background, non-anthropogenic resuspension. Finally, a simulated model was generated to demonstrate loss of alpha radiation from relevant transuranic radioparticles. This was accomplished using the Geant4 Monte Carlo particle transport code. This basic model demonstrated a clear loss of average intensity and energy of exiting particles which are both directly related to the absorped dose. The data shows a loss from 10 to 90% of intensity to occur at particle sizes approaching the range of alphas within them, and a loss of roughly half the initial alpha energy at around the same particle sizes. The results establish a first-order baseline for a particulate self-absorption model which complement existing dosimetry models for inhaled radionuclides.

Includes bibliography. / The study takes the work of three teachers to examine whether the popular belief of "small is better" is substantiated in the practice of these teachers. The study observes and analyses the classroom instruction of each of these teachers in a small class as well as in a large class. The observation is done with the use of an observation schedule, and the analysis of data is done within a Vygotskian framework. The study shows that the pedagogy and the teaching style of the three teachers does not change when they teach differently sized classes. In other words, their classroom practice is the same for both the small and large classes. The study further shows that the pedagogy of the teacher determines the effectiveness or quality of instruction, and that class size does not impact, either positively (in the case of the small class) or negatively (in the case of a large class) on the effectiveness or quality of instruction.

Organic-inorganic hybrid perovskites (OIHPs), which are promising materials for electronic and optoelectronic applications (1-10), have made into layered organic-inorganic hybrid perovskites (LOIHPs). These LOIHPs have been applied to thin-film transistors, solar cells and tunable wavelength phosphors (11-18). It is known that devices fabricated with single crystal exhibit the superior performance, which makes the growth of large-sized single crystals critical for future device applications (19-23). However, the difficulty in growing large-sized LOIHPs single crystal with superior electrical properties limits their practical applications. Here, we report a method to grow the centimeter-scaled LOIHP single crystal of [(HOC2H4NH3)2PbI4], demonstrating the potentials in mass production. After that, we reveal anisotropic electrical and optoelectronic properties which proved the carrier propagating along inorganic framework. The carrier mobility of in-inorganic-plane (in-plane) devices shows the average value of 45 cm2 V–1 s–1 which is about 100 times greater than the record of LOIHP devices (15), showing the importance of single crystal in device application. Moreover, the LOIHP single crystals show its ultra-short carrier lifetime of 42.7 ps and photoluminescence quantum efficiency (PLQE) of 25.4 %. We expect this report to be a start of LOIHPs for advanced applications in which the anisotropic properties are needed (24-25), and meets the demand of high-speed applications and fast-response applications.

Porous materials are implemented in several industrial applications such as water desalination, gas separation and pharmaceutical care which they are mainly governed by the pore size and the PSD. Analyzing shale reservoirs are not excluded from these applications and numerous advantages can be gained by evaluating the PSD of a given shale reservoir. Because of the limitations of the conventional characterization techniques, novel methods for characterizing the PSD have to be proposed in order to obtain better characterization results for the porous materials, in general, and shale rocks in particular. Thus, permporosimetry and evapoporometry (EP) technologies were introduced, designed and utilized for evaluating the two key parameters, pore size and pore size distribution. The pore size and PSD profiles of different shale samples from Norway and Argentina were analyzed using these technologies and then confirmed by mercury intrusion porosimeter (MIP). Norway samples showed an average pore diameter of 12.94 nm and 19.22 nm with an average diameter of 13.77 nm and 23.23 nm for Argentina samples using permporosimetry and EP respectively. Both techniques are therefore indicative of the heterogeneity of the shales. The results from permporosimetry are in good agreement with those obtained from MIP technique, but EP for most part over-estimates the average pore size. The divergence of EP results compared to permporosimetry results is referred to the fact that the latter technique measures only the active pores which is not the case with the former technique. Overall, both techniques are complementary to each other which the results from both techniques seem reasonable and reliable and provide two simple techniques to estimate the pore size and pore size distributions for shale rocks.

In this work the differences between and characteristics of water and high solids, heated black liquor sprays from air-assist atomizers are examined. Sprays were imaged with a high speed camera and the images analyzed with computer code to produce droplet size data and macroscopic spray characteristics such as mass distribution. Fluid flow rates were measured to allow relevant dimensionless groups for the spray to be calculated. A 1000 degree C tubular furnace was placed around the spray to determine the effect of industrially relevant temperatures on the droplet formation process, relative to room-temperature conditions. It was found that high solids black liquor forms long, thin ligaments rather than droplets. In high-temperature surroundings the size of these ligaments increases, which from a comparison with theory in the literature was attributed to enhanced skin-formation driven by heat transfer. The data suggest that this skin formation may prevent secondary breakup. All sprays for both fluids produced droplet size mass distributions that were well described by the square-root normal distribution. The normalized width (s*) of these distributions was similar for all sprays and consistent with literature data for other nozzle designs (0.24 < s* < 0.38). The image analysis method assumed droplets were spheres with the same projected area. When this assumption was changed for black liquor sprays to a cylindrical droplet assumption, the shape and normalized width of the resulting mass distributions remained the same, but the representative diameter (calculated from surface area to volume ratios) decreased. Based on the agreement between the normalized distribution width in this work and that in the black liquor spraying literature it was concluded that the addition of atomizing air cannot be considered a means to narrow a droplet size distribution independent of droplet size. The results also indicate the importance of including the effects of skin formation and temperature- and time-dependent fluid properties in spray modeling. It is intended that these results contribute to increased understanding of the black liquor atomization process and lead to improved computational modeling of the same.

Loess is an unique record of the paleoclimate of the Quaternary. Because it is directly deposited from the atmosphere, it can be used as a proxy for wind speed and circulation patterns. It can also be directly dated using luminescence. The site of the loess being investigated for this paper is PrimelTrégastel (Brittany), which lies in north-western France of the shore to the English Channel. The English Channel may be one of the sources for loess of the last glaciation, the Wichselian, and is the reason for choosing Primel-Trégastel to investigate. It is the purpose of this paper to investigate the climate of the time the loess was formed at Primel-Trégastel using grain-size distribution analysis, as well as comparing its properties to other loess sites in north-western Europe. The results show that the loess of Primel-Trégastel is coarse and have a relatively high sand content. That may imply that the loess was deposited during cold and arid conditions by high wind speeds, and at that it may have had a relatively close source. The results also exhibit cycles in the coarseness of the grain-size, indicative of the climate varying between cold and relatively warmer, resulting in relatively higher and lower wind speeds respectively. The loess of Nantois and Pegwell Bay are also relatively coarse, and the loess of Pegwell Bay also have a high sand content. The loess of Nussloch was in comparison more unlike the one of Primel-Trégastel, possibly due to the lack of a local source of sand at Nussloch.

The content of the thesis is a proposal for a business plan. The thesis is divided into a theoretical and practical part. In the theoretical part is described the business intention briefly characterized business plan. The business plan is presented in a practical part and deals in detail with market analysis, marketing plan, business size, placement, personnel resources and financial plan. As part of the business plan, a marketing survey, financial plan and financial analysis are set out. Based on these factors, the profitability of the enterprise and the reality of the business plan are determined at the end of the work.

This study is designed to try to determine if faculty productivity as measured by the average number of student credit hours produced by each faculty member in selected units of two private universities of similar size is a significant variable in the financial conditions of the two institutions. The data are collected from the two institutions. The data are collected from the two institutions for the second semester of the 1970-71 academic year.