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The spreading of small liquid drops over thin and thick porous layers (dry or saturated with the same liquid) has been investigated in the case of both complete wetting (silicone oils of different viscosities) and partial wetting (aqueous SDS solutions of different concentrations). Consideration has been carried out from both experimental and theoretical points of view. Nitrocellulose membranes of different porosity and averaged pore size were used as a model of thin porous layers, glass and metal filters were used as a model of thick porous substrates. It has been shown, that the spreading process follows the power law in time in the case of spreading of silicon oil drops over porous substrate saturated with the same oil. The liquid flow in the spreading drop has been matched with the flow in the porous substrate. Both the exponent and the pre-exponential factor of the power law have been predicted and compared with our experimental data, which shows the good agreement. An effective lubrication coefficient has been introduced, which accounts for an effective slippage of liquids over porous substrates. This coefficient has been both theoretically predicted and experimentally verified.

The atomization and spray forming of liquid metals was studied. Melt break up algorithms were developed to predict the size distribution of the spray generated as well as secondary aspects of the atomization phenomena. In the model, which is based on the Surface Wave Formation (SWF) theory, the relative velocity between the gas and melt phase was thought to induce a sinusoidal disturbance on the surface of the melt column. Depending on the flow conditions such a disturbance could grow in amplitude and cause certain parts of the surface to be torn off the liquid column. A number of different approaches to the problem of drop disintegration were also considered. Based on experimental observations of the critical Weber number made by other authors, a criterion was formulated, which allowed the secondary break up of drops to be predicted. In addition, an analytical model originally presented by Wolf and Andersen (1965), which was intended to describe the stripping mode of secondary disintegration, was also revised and incorporated into a computer routine. Finally a comparison of the models was made against the predictions of the empirical Lubanska (1970) equation. High Speed Photography studies of a water column atomized by gas revealed that the formation of a surface wave was the prominent mechanism perturbing and finally disintegrating the column into a fine spray of drops. Phase Doppler Anemometry studies of the water/gas jet produced during the atomization of a water column indicated that there was a gradient of particle sizes across the spray. The finer fragments were found in the close proximity of the centre axis of the conical flow, with particles becoming larger in size as the distance from the centre increased. Vaporization of the water drops near the centre due to the high gas velocities should be taken into account when interpreting these results. The break up algorithms were tested against experimental data for a number of different A1 and Fe alloys with various solute elements, obtained using a close coupled atomization facility. Case studies were made for the effects of gas injection pressure, initial melt stream diameter, initial melt stream exit velocity and number of atomizing gas jets on the mean powder particle size produced. The algorithms could predict the distribution of drop sizes in space, a feature that enabled the simulation of spray forming runs and the direct comparison of the numerical predictions to experimental data. The shapes of the Al-1.6wt%Hf and the Al-1.6wt%Hf-3.2wt%Li alloy preforms and the particle distribution along the radial direction of the Al-1.6wt%Hf preform were calculated and compared favourably with experimental data. Microscopic observation of Al-1.6wt%Hf and Al-1.6wt%Hf-3.2wt%Li preforms indicated that there was a variance of particle size as well as grain size along the radial direction of the spray. The grain size was found to decrease with increasing distance from the central axis of the preform, while the radial distribution of drop diameters did not reveal a distinct trend.

A Twyman-Green interferometer was used to study the selective transport of ethanol-water mixtures of various concentration across a nonporous homogeneous silicone rubber membrane at 25°C. The instrument developed enabled the measurement of the transient concentration profiles within the boundary layers bathing the membrane. Measurements as close as 5um from the membrane surface were possible. The majority of the reported interferometric studies of liquid/membrane transport have been limited to the observation of the fringes and stop short of a full theoretical analysis. Such analysis is complicated by the optical effects of light deflection and the computational burden involved in the transient solution of the mathematical models required to describe membrane transport. A rigorous treatment of light deflection was developed on the basis of Fermat's principle of least time. The transient numerical solution of the model equations was accomplished by the application of the method of lines. To decouple the equilibrium and kinetic phenomena in membrane transport requires the independent measurement of the sorption isotherm. Traditional techniques for measuring the extent and composition of the imbibed phase involve removing the membrane from the liquid and are therefore limited by the inherent difficulties of obtaining a 'clean' separation. This was circumvented by measuring the excess (relative) sorption isotherm without removing the membrane from the liquid. The data was analysed in terms of Flory-Huggins thermodynamics which was fitted to the measured excess isotherm across the entire concentration range. For a binary mixture, transport across a homogeneous membrane involves two simultaneous fluxes which can be coupled through kinetic and/or equilibrium interactions. A measure of the extent of coupling was obtained by comparing the results from a simplified 'decoupled' flux model with those based on a 'coupled' flux model allowing for equilibrium interactions. Such interactions were found to have little effect on the flux of ethanol but strongly influenced the flux of water across silicone rubber. In particular, coupling through equilibrium interaction was found to be responsible for as much as 75% of the total flux of water. The diffusion coefficients of both ethanol and water in silicone rubber were shown to decrease strongly with alcohol concentration.

Experiments on helium film flow over a stainless steel beaker rim were carried out in the temperature region 1.63K to 11mK. No previous measurements have been made below 35mK. The results of other studies of film flow below 1K are mutually conflicting; this is thought to originate from poor temperature stability, inadequate vibration isolation and contamination of the substrate. Careful attention was paid to these points in the design and construction of a demagnetisation cryostat, full details of which are given. Flow experiments from initial level differences of ~8mm confirmed the existence of a range of metastable transfer rates at all temperatures. The variation of the mean rate with rim height suggests that the film profile should be calculated using a van der Waals' exponent, n, of 2.85 ± .25. The low temperature increase in transfer rate reported by others was observed, but did not extend below 1K. Instead, the mean transfer rate was approximately constant from 1K to 400mK, in direct conflict with the predictions of thermal fluctuation theories of superfluid dissipation. Below 250mK the results corroborated closely those of Crum et al in that the transfer rate fell sharply with decreasing temperature. Discrepancies arose between runs below 60mK, some showing the transfer rate to decrease monotonically with temperature down to 20mK whilst others indicated a levelling out of the transfer rate, followed by a slight increase at the lowest temperatures. These effects were thought to originate from changes in the concentration of the 3He impurity in the film. Steady state driven flow experiments at level differences of < 500μm provided the first evidence for the existence of dissipation at subcritical transfer rates at temperatures below 1K. That is, superfluid flow was shown to be never strictly frictionless. Above 1K, the form of the subcritical dissipation curve conformed to the predictions of thermal fluctuation theories, but the values of the parameters 3 and f0 for flow over stainless steel were considerably smaller than those reported for flow over glass. The parameter f0 was also found to be strongly temperature dependent. Below 1K, the onset of dissipation was seen to be much more gradual, and the form of the subcritical dissipation curve was independent of temperature down to 20mK. These findings were corroborated by measurements of the damping of the inertial oscillations occurring at the end of each flow experiment. At the lowest temperature attained, 11mK, a change in subcritical dissipative behaviour was observed; exponential damping of the oscillations indicated that the frictional force on unit mass of superfluid was now directly proportional to the superfluid velocity, and was of magnitude (4.56 ± .28) x 10−3 dynes g−1 cm −1 s. Exponential damping was also observed at temperatures above 1K, where Robinson type thermal dissipation was the dominant mechanism at small transfer rates.

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This thesis reports the investigation of liquid-to-gas and liquid-to-solid phase transitions of liquid hydrocarbon fuels and their ethanol blends, both in the bulk phase and as single droplets. The key point has been to develop an understanding of the fuels' macroscopic behavior by studying them at the molecular and at the single droplet level. A key work in this thesis is the investigation of different ratio ethanol/gasoline blends at the molecular level. At the macroscopic level, the vapor pressure, and hence the evaporation of the blends, is influenced by the strength of intermolecular interactions. Thus, information on the molecular interactions between ethanol and gasoline are inferred by using IR and excess IR spectroscopy. The spectroscopic data suggest that the hydrogen bonding between ethanol molecules is weakened upon gasoline addition, but the hydrogen bonds do not disappear. This can be explained by a formation of small ethanol clusters that interact via Van der Waals forces with the surrounding gasoline molecules. In addition, Raman spectroscopy is performed on the same blends, and the Raman spectra are compared with the IR ones. Two different approaches for data evaluation, with the scope of determining the ethanol content in the blends, are tested and compared: Firstly, the calibration of the intensity ratio of characteristic peaks as function of composition; secondly, a principal component regression (PCR). Both methods are found to have comparable uncertainty. For the evaluation of the Raman spectra, the PCR method yielded better accuracy than the intensity ratio approach. In addition, a detailed investigation of the influence of noise in the signal is presented. When the full IR spectra were evaluated by PCR, even high noise levels did not reduce the measurement accuracy significantly. Later, with the aim of studying the evaporation dynamics of fuel blends, at the single droplet level, electrodynamic balance (EDB) and optical tweezers are used to trap ethanol/gasoline droplets, containing different ethanol percentages. A longer lifetime is observed for droplets containing a greater fraction of ethanol. In order to explain the experimental evaporation trends obtained, a theoretical model is used to predict the evaporation rates of pure ethanol and pure gasoline droplets in dry nitrogen gas. Also a theoretical estimation of the saturation of the environment, with other aerosols, in the tweezers is carried out. Lastly, the liquid-to-solid phase transition of some long chain alkanes, commonly present in diesel or gasoline, is investigated both at the molecular and at the single droplet level. Firstly, by using Raman spectroscopy the solidification of these hydrocarbons in the bulk phase is observed. Distinctive features associating the solid even hydrocarbons to a triclinic structure and the odd ones to an orthorhombic structure can be observed in the spectra. Secondly, the liquid-to-solid phase transition of single hydrocarbons droplets is investigated. Freezing time and surface area resulted to be inversely proportional in dodecane droplets. This might suggest a surface freezing mechanism. Furthermore, differences in the scattering patterns, depending on the freezing mechanism, are pointed out. Droplets freezing homogeneously show a different scattering pattern with respect to droplets that froze heterogeneously.