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Submitted in fulfillment of the academic requirements for the Masters of Applied Science (Chemistry), Durban University of Technology, Durban, South Africa, 2016. / In this work, the thermodynamic properties for the binary mixtures containing the ionic liquid (IL): 1-ethyl-3-methylimidazolium ethyl sulphate ([EMIM] [EtSO4]) were calculated. The binary systems studied were {pyridine (Py) or ethyl acetoacetate (EAA) or thiophene (TS) + [EMIM] [EtSO4]}. The results were interpreted in terms of the intermolecular interactions between the (pyridine + IL), (ethyl acetoacetate + IL), and (thiophene + IL) molecules. The physical properties: density, speed of sound, and refractive index were measured for the binary mixtures over the complete mole fraction range using an Anton Paar DSA 5000 M vibrating U- tube densimeter and an Anton Paar RXA 156 refractometer, respectively. The measurements were done at T = (298.15, 303.15, 308.15, 313.15, and 318.15) K and at p = 0.1 MPa. The experimental data was used to calculate the derived properties for the binary mixtures namely:- excess molar volume (V E ), isentropic compressibility (ks), molar refractions (R) and deviation in refractive index (Δn). For the binary mixtures, (Py or EAA or TS + IL), V E was negative throughout the whole composition range which indicates the existence of attractive intermolecular interaction between (pyridine + IL) and (ethyl acetoacetate + IL) for (thiophene + IL), V E was negative at low mole fraction of thiophene and became positive at high mole fraction of thiophene. For the binary mixtures (pyridine + IL), (ethyl acetoacetate + IL), ks was positive indicating that the binary mixtures were more compressible than the ideal mixture. For the binary mixture (thiophene + IL) ks was negative at low thiophene composition and positive at high composition indicating that the binary mixture was less compressible than the ideal mixture at low thiophene composition and more compressible at high composition of thiophene. The molar refraction, R, is positive for the (Py or EAA or TS + IL) binary systems at T = (298.15 – 318.15) K, molar refraction decreases as the organic solvent composition increases. For the binary mixture (pyridine + [EMIM] [EtSO4]), Δn is negative at mole fractions < 0.75 of pyridine and positive at mole fractions >0.75 at all temperatures and decreases with an increase in temperature. For the binary system (ethyl acetoacetate + [EMIM] [EtSO4]), Δn values are positive over the entire composition range and at all temperatures and increases with an increase in temperature. Δn values for the (thiophene + IL) system are negative for mole fractions of thiophene < 0.62 and becomes positive for mole fractions of thiophene > 0.62 and Δn increases with an increase in temperature. The Redlich-Kister smoothing equation was used successfully for the correlation of V E and Δn data. The Lorentz- Lorenz equation gave a poor prediction of V E , but a good prediction of density or refractive index. / M

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Thesis (DTech( Mechanical Engineering)-- Cape Peninsula University of Technology, 2014 / Magnetohydrodynamic (MHD) boundary layer flow of an electrically conducting viscous incompressible fluid with a convective surface boundary condition is frequently encountered in many industrial and technological applications such as extrusion of plastics in the manufacture of Rayon and Nylon, the cooling of reactors, purification of crude oil, textile industry, polymer technology, metallurgy, geothermal engineering, liquid metals and plasma flows, boundary layer control in aerodynamics and crystal growth etc. Nanofluid is envisioned to describe a fluid in which nanometer-sized particles are suspended in conventional heat transfer base fluids to improve their thermal physical properties. Nanoparticles are made from various materials, such as metals (Cu, Ag, Au, Al, Fe), oxide ceramics (Al2O3, CuO, TiO2), nitride ceramics (AlN, SiN), carbide ceramics (SiC, tiC), semiconductors, carbon nanotubes and composite materials such as alloyed nanoparticles or nanoparticle core–polymer shell composites. It is well known that, conventional heat transfer fluids, such as oil, water, and ethylene glycol, in general, have poor heat transfer properties compared to those of most solids. Nanofluids have enhanced thermophysical properties such as thermal conductivity; thermal diffusivity, viscosity and convective heat transfer coefficients compared with those of base fluids like oil or water. Owing to their enhanced properties, nanofluids can be used in a plethora of technical and biomedical applications such as nanofluid coolant: electronics cooling, vehicle cooling, transformer cooling, computers cooling and electronic devices cooling; medical applications: magnetic drug targeting, cancer therapy and safer surgery by cooling; process industries; materials and chemicals: detergency, food and drink, oil and gas, paper and printing and textiles.

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A one-dimensional, physical model describing two-phase fluid flow is used to simulate the effect of boiling on silica precipitation in geothermal and epithermal precious metal systems. The extent to which decreasing temperature and fluid vaporization are responsible for quartz precipitation is dependent on three related factors - the temperature of the fluid entering the two-phase system, the change in fluid temperature with respect to distance of fluid travel, and the extent of fluid vaporization in regions of gradual temperature decline. Boiling contributes to significant quartz precipitation in systems with high-temperature basal fluids, and in deeper portions of systems in which extensive vaporization occurs. Temperature reduction is a dominant precipitation mechanism in near- surface regions where temperature reduction is rapid, and in systems with lower temperature fluids. Owing to the small difference in quartz solubility between the liquid and vapor phases at low temperatures, boiling does not contribute to significant quartz precipitation in low temperature, near-surface regions. Quartz precipitation is most intense in systems with high mass flux/permeability ratios and low initial fluid temperatures. Geothermal systems with high mass flux/permeability and moderately low initial fluid temperatures are most effective in producing epithermal systems with abundant gold. Numerical modeling indicates that sufficient copper can be partitioned from a "typical" calc-alkaline melt into an exsolving fluid to produce an economic porphyry copper deposit. Neither non-magmatic sources nor an additional hidden magma source are necessary to provide copper to the system and an elevated initial copper concentration in the melt is not necessary. Melts in shallow systems with initial water concentrations of at least 2.5 wt.% water and Cl/H₂O as low as 0.03 can produce economic deposits with volumes of 50 km³ or less, regardless of copper compatibility. In deeper systems deposits may be produced from melts of less than 30 km³ if copper behaves incompatibly prior to water saturation or if the initial melt is water-rich and requires only minor crystallization to achieve water saturation. If copper behaves compatibly prior to water saturation very large volumes of melt may be required. High salinity fluids may be produced directly from a crystallizing melt and immiscibility is not necessary to produce the high salinities observed in some systems. Depending on the temperature, pressure, initial water content, and the extent of crystallization of the melt, the bulk salinity of the aqueous fluids exsolved from a melt may vary from < 2.0 wt.% NaCl to saturation levels (84 wt.% NaCl at 700°C). Fluid evolution during the magmatic-hydrothermal transition and coincident molybdenite precipitation at Questa, New Mexico, has been traced using fluid inclusion microthermometry. The lack of cogenetic liquid- and vapor-rich inclusions, plus final homogenization of most saline, liquid-rich inclusions by halite dissolution indicate that high-salinity fluids were generated by a mechanism other than fluid immiscibility. Pressure fluctuations, responsible for the formation of a magmatic-hydrothermal breccia, are capable of producing the observed fluids and inclusion behavior. Solubility data indicate that the crystallizing aplite porphyry generated fluids with salinities as high as 57 wt.% NaCl equivalent. / Ph. D.

Steadily increasing heat dissipation in electronic devices has generated renewed interest in direct immersion cooling. The ideal heat transfer fluid for direct immersion cooling applications should be chemically and thermally stable, and compatible with the electronic components. These constraints have led to the use of Novec fluids and fluroinerts as coolants. Although these fluids are chemically stable and have low dielectric constants, they are plagued by poor thermal properties. These factors necessitate the development of new heat transfer fluids with improved heat transfer properties and applicability. Computer Aided Molecular Design (CAMD) approach was used in this work to systematically design novel heat transfer fluids that exhibit significantly better properties than those of current high performance electronic coolants. The candidate fluids generated by CAMD were constrained by limiting their boiling points, latent heat of vaporization and thermal conductivity. The selected candidates were further screened using a figure of merit (FOM) analysis. Some of the fluids/additives that have been identified after the FOM analysis include C₄H₅F₃O, C₄H₄F₆O, C₆H₁₁F₃, C₄ H₁₂O₂Si, methanol, and ethoxybutane. The heat transfer performance of these new fluids/fluid mixtures was analyzed through pool boiling and flow boiling experiments. All the fluid mixtures tested showed an improvement in the critical heat flux (CHF) when compared to the base fluid (HFE 7200). A pool boiling model was developed using the phase field method available in COMSOL. Although these simulations are computationally expensive, they provide an alternate solution to evaluate several candidate fluids generated using the CAMD approach.