Atomic diffusion phenomena were examined in a metal-alloy nuclear fuel system composed of δ-phase U-50wt%Zr fuel in contact with either Zr-10wt%Gd or Zr-10wt%Er. Each alloy was fabricated from elemental feed material via melt-casting, and diffusion samples of nominal 1.5 mm thickness were prepared from the resulting alloy slugs. The samples were assembled into diffusion couples and annealed for periods of 14, 28, and 56 days at temperatures of 550°C, 600°C, and 650°C. Thus, the U-50Zr/Zr-10Er system and the U-50Zr/Zr-10Gd system were each annealed for three different time periods at each of three different temperatures, for an initial total of 18 diffusion interfaces that were to be studied. In practice, data was collected from only 12 of the 18 interfaces. At 650°C, the U-50wt%Zr alloy exists in the γ-phase region, which enabled the comparison of diffusion behavior between the δ phase and γ phase. Diffusion samples were examined by collecting composition profiles across the diffusion interface for each element via electron probe microanalysis. From the resulting experimental data diffusion coefficients were evaluated. Diffusion coefficients were found to be on the order of 10^-19 m2/s in the δ-phase systems, and 10^-17 m^2/s in the γ-phase systems. It was observed that atomic mobility of all diffusing species was generally greater in the U-50Zr/Zr-10Gd system than in the U-50Zr/Zr-10Er system; furthermore, it was found that diffusion rates were considerably higher above the phase transformation temperature into the γ phase, as indeed would be expected in the more open structure of the body-centered cubic γ phase, as compared to the hexagonal δ-phase U-Zr. However, values for diffusion coefficients measured in this study were considerably smaller than those found in past studies of δ-phase U-Zr, which are on the order of 10^-17 m^2/s. It is likely that diffusion was inhibited by the formation of stable metal oxides resulting from oxygen contamination; it is also possible that diffusion was suppressed by the presence of the erbium and gadolinium.

An experimental study was conducted in order to investigate the two-phase-flow phenomena in a mini-size, horizontal impacting tee junction. The test section was machined in an acrylic block with a rectangular cross-section of 1.87-mm height × 20-mm width on the inlet and outlet sides. Air-water mixtures at 200 kPa (abs) and room temperature were used as the test fluids. Four flow regimes were identified visually: bubbly, plug, churn, and annular over the ranges of gas and liquid superficial velocities of 0.04 ≤ JG ≤ 10 m/s and 0.02 ≤ JL ≤ 0.7 m/s, respectively, and a flow regime map was developed. The present flow-regime map was compared with several experimental maps. It is thought from those comparisons that the channel height has a more significant role in determining the flow-regime boundaries than the hydraulic diameter. The two-phase fully-developed pressure gradient was measured in the inlet and the outlet sides of the junction for six different inlet conditions and various mass splits at the junction. Comparisons were conducted between the present data and former correlations. The correlations that agreed best with the present data were identified. Five single-phase test sets were performed. In each set of experiments, the pressure distribution was measured for the whole range of the mass split ratio, Wi/W1. The pressure drop at the junction at each value of Wi/W1 was calculated. Values of the pressure-loss coefficient, , were calculated at various Wi/W1 and inlet Reynolds number. The pressure-loss coefficient was strongly dependent on the inlet Reynolds number in the laminar region, while the results for the turbulent region were almost coincident. Numerical simulations of single-phase flow in an impacting tee junction of identical dimensions to that of the present test-section were performed to confirm the results of the experiments. Phase-redistribution experiments were conducted covering all four inlet flow regimes and models were proposed for predicting the experimental data. Good agreement in terms of magnitude and trend was obtained between the present experimental data and the proposed model. New correlations were developed for the single- and two-phase pressure drop in the junction.

Energy shortages around the world necessitated research into alternative energy sources especially for domestic applications to reduce the load on conventional energy sources. This resulted in research done on the possibility of integrating solar energy with an aqua-ammonia diffusion absorption cycle specifically for domestic applications. The bubble pump can be seen as the heart of the diffusion absorption cycle, since it is responsible, in the absence of a mechanical pump, to circulate the fluid and to desorb the refrigerant (ammonia) from the mixture. It is thus of paramount importance to ensure that the bubble pump is designed efficiently. Various bubble pump simulation models have been developed over the years, but it was found that none of the existing models served as a good basis for application-specific design. Most of the models constrained too many parameters from the outset which made the investigation of the effects of certain parameters on the bubble pump’s performance impossible. According to the research, no bubble pump model investigated the effect of such a wide variety of factors including tube diameter, heat flux, mass flux, generator heat input and system pressure on the bubble pump’s lift height. A simulation model for a bubble pump for integration with a solar-driven aqua-ammonia diffusion absorption cycle was developed. It serves as a versatile design model to optimise the bubble pump for a large variety of conditions as well as changes in parameters. It was achieved by constraining the bubble pump dimensions and parameters as little as possible. A unique feature of this model was the fact that the bubble pump tube was divided into segments of known quality which made the length of the pipe completely dependent on the flow inside the pipe. It also made the demarcation of the flow development inside the tube easier. The model attempted to incorporate the most appropriate correlations for pressurised two-phase aqua-ammonia flow. The most appropriate void fraction correlation was found to be Abstract The design and optimisation of a bubble pump for an aqua-ammonia diffusion absorption heat pump the Rouhani-Axelsson (Rouhani I) correlation. It was mainly due to its exclusive use of thermophysical properties and the vapour quality. The most appropriate heat transfer coefficient that predicted the most realistic wall temperature, was the correlation from Riviera and Best (1999) which was the only correlation found in the literature developed with aqua-ammonia in mind. It was found that the published correlation could not reproduce their experimental results, and a modification of their correlation was made after which the simulation model’s results correlated well with the experimental values of Riviera and Best (1999). The main goal of the simulation model was to determine the height that the bubble pump was capable of lifting at the slug to churn flow transition under various conditions. The effect of varying a variety of parameters on the bubble pump lift height was also investigated. The results from Shelton & White Stewart (2002) were compared to the outputs of the simulation model, and it was found that their constraining of the submergence ratio limited their outputs, and that their heat inputs under different conditions was a bit optimistic. The simulation model’s outputs correlated well at higher tube diameters with the results from Shelton & White Stewart (2002), but at the lower diameters which was used in their study it was impossible to compare data, since their diameters was already in mini flow and micro flow regions. The temperatures also correlated well, all within 2% of the results from Shelton & White Stewart (2002). It was found that there couldn’t be just one set of optimised conditions and values for the bubble pump, but that each cycle with differing specifications and operating conditions would yield a unique set of optimised parameters. It was for that reason very important not to constrain parameters beforehand without investigating its effect on the bubble pump first. / Thesis (MIng (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2013.

Energy shortages around the world necessitated research into alternative energy sources especially for domestic applications to reduce the load on conventional energy sources. This resulted in research done on the possibility of integrating solar energy with an aqua-ammonia diffusion absorption cycle specifically for domestic applications. The bubble pump can be seen as the heart of the diffusion absorption cycle, since it is responsible, in the absence of a mechanical pump, to circulate the fluid and to desorb the refrigerant (ammonia) from the mixture. It is thus of paramount importance to ensure that the bubble pump is designed efficiently. Various bubble pump simulation models have been developed over the years, but it was found that none of the existing models served as a good basis for application-specific design. Most of the models constrained too many parameters from the outset which made the investigation of the effects of certain parameters on the bubble pump’s performance impossible. According to the research, no bubble pump model investigated the effect of such a wide variety of factors including tube diameter, heat flux, mass flux, generator heat input and system pressure on the bubble pump’s lift height. A simulation model for a bubble pump for integration with a solar-driven aqua-ammonia diffusion absorption cycle was developed. It serves as a versatile design model to optimise the bubble pump for a large variety of conditions as well as changes in parameters. It was achieved by constraining the bubble pump dimensions and parameters as little as possible. A unique feature of this model was the fact that the bubble pump tube was divided into segments of known quality which made the length of the pipe completely dependent on the flow inside the pipe. It also made the demarcation of the flow development inside the tube easier. The model attempted to incorporate the most appropriate correlations for pressurised two-phase aqua-ammonia flow. The most appropriate void fraction correlation was found to be Abstract The design and optimisation of a bubble pump for an aqua-ammonia diffusion absorption heat pump the Rouhani-Axelsson (Rouhani I) correlation. It was mainly due to its exclusive use of thermophysical properties and the vapour quality. The most appropriate heat transfer coefficient that predicted the most realistic wall temperature, was the correlation from Riviera and Best (1999) which was the only correlation found in the literature developed with aqua-ammonia in mind. It was found that the published correlation could not reproduce their experimental results, and a modification of their correlation was made after which the simulation model’s results correlated well with the experimental values of Riviera and Best (1999). The main goal of the simulation model was to determine the height that the bubble pump was capable of lifting at the slug to churn flow transition under various conditions. The effect of varying a variety of parameters on the bubble pump lift height was also investigated. The results from Shelton & White Stewart (2002) were compared to the outputs of the simulation model, and it was found that their constraining of the submergence ratio limited their outputs, and that their heat inputs under different conditions was a bit optimistic. The simulation model’s outputs correlated well at higher tube diameters with the results from Shelton & White Stewart (2002), but at the lower diameters which was used in their study it was impossible to compare data, since their diameters was already in mini flow and micro flow regions. The temperatures also correlated well, all within 2% of the results from Shelton & White Stewart (2002). It was found that there couldn’t be just one set of optimised conditions and values for the bubble pump, but that each cycle with differing specifications and operating conditions would yield a unique set of optimised parameters. It was for that reason very important not to constrain parameters beforehand without investigating its effect on the bubble pump first. / Thesis (MIng (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2013.

The distinctive architecture of the stratum corneum with its unique nature of an interstitial lipoidal environment plays the major role in regulating the barrier function of the skin. The major problem with the transdermal delivery of 5-fluorouracil or idoxuridine is the permeation of sufficient amounts to the deeper layers of the skin and into the systemic circulation. In an attempt to enhance the transdermal permeability of 5-fluorouracil and idoxuridine, the aim of this study was to evaluate two lamellar gel phase systems (Physiogel dermaquadrille® and Physiogel NT®) and Emzaloids® as transdermal delivery vehicles for the two actives. Lamellar gel phase systems (LGPS) and Emzaloids® are both novel drug delivery systems. The epidermis of female abdominal skin was used in vertically mounted Franz diffusion cell experiments. An average amount of 250 mg of the 1% m/m LGPS was applied to cover the entire diffusion area of 1,075 cm2 of the skin, which contained 2,5 mg of the active. Samples of the actives in Emzaloids® were prepared and applied in the same way. The control solutions of the actives in water were prepared so that 1 ml of the applied solution contained the same amount of drug that was applied to the experimental cells. The entire receptor phase of the cells was removed at 2,4,6, 8, 10, 12 and 24 hours and was replaced with fresh 37°C receptor phase. The amount of active in the receptor phase was determined by HPLC analysis. Graphs of the cumulative amount of the active that permeated the skin over the 24 hour period were drawn and the slope of the graphs represented the flux in µg/ml/h. The average flux values of six experimental cells and six control cells were compared. Entrapment of the actives in the Emzaloid® vesicles was confirmed with the use of confocal laser scanning microscopy. Results for the LGPS indicate an enhancement ratio in the order of 4,2 for 5-fluorouracil and 1,7 for idoxuridine when compared to the control cells. There were no viscosity changes in the LGPS samples containing 1% m/m of the active when compared with the blank LGPS samples, suggesting that no change in the internal structure of the LGPS occurred after the addition of the actives to it. There were also no significant changes in the pH of the samples. Entrapment of the actives in the Emzaloid® vesicles occurred readily. The Emzaloid® vehicle showed a lower rate of release for idoxuridine than the LGPS did during the VanKel dissolution experiments. This suggests that higher flux values would be obtained with the LGPS for idoxuridine than with the Emzaloid® formulation, since more drug was available for permeation through the skin. This was, however, not the case. The Emzaloid® formulation showed much higher flux values, showing that even with a smaller amount of active available to permeate the skin higher flux values were obtained. Enhancement ratios of 20,33 and 3,50 were achieved with the Emzaloid® formulation for 5-fluorouracil and idoxuridine respectively. The internal LGPS structure which mimics the skins lipid components remained unchanged after the addition of the actives. Greater success might be achieved with the LGPS for different model drugs, since the drugs' physicochemical properties play an important part in its permeation through the skin. The Emzaloid® formulation, which is closely related to liposomes and transfersomes, showed great potential for commercially marketable formulations for the drugs tested but further research on the formulation has to be done. / Thesis (M.Sc. (Pharmaceutics))--North-West University, Potchefstroom Campus, 2005.

The removal of heat from the containment building is an important consideration in the design of a nuclear power plant. In this investigation a simple rectangular natural circulation loop was simulated to determine whether it could possibly be used to remove usable quantities of heat from a containment building. The loop had a vertical pipe on the inside and outside of the containment building. These pipes acted as heat exchangers. Single phase and two phase cases were simulated by imposing a temperature on the respective vertical leg pipe walls and determining the heat absorption from the containment building. The heat was conveyed from the inside of the building to the outside via the natural circulation phenomenon. A literature study was done to cover topics relevant to this investigation. A theoretical model using conservation equations and control volumes was derived. This model was based largely on knowledge gleaned from the literature study. The theoretical model was a simple homogenous model, which was sufficiently detailed for a conceptual investigation. The theoretical model was then manipulated into a form suitable for use in a computer simulation program. Simplifications were made to the simulation model and underlying theory due to the nature of the investigation. The simulation model was validated against published experimental results. During the simulation phase a number of cases were investigated. These cases were divided into base cases and parametric studies. During the base case simulations the change of key fluid variables along the loop was examined. During the parametric studies the hot and cold leg inside wall temperatures, loop geometry and pipe diameter were varied. The effect of these parameters on the heat absorption from the containment was determined. The simulations showed that with the current assumptions about 75 to 120 of the natural circulation loops are needed depending on their geometry and containment conditions. The heat removal rates that were calculated varied from 50 kW to 600 kW for a single loop. As explained in the final chapter, there are many factors that influence the results obtained. The natural circulation concept was deemed to be able to remove usable quantities of heat from the containment building. / Thesis (M.Ing. (Nuclear Engineering))--North-West University, Potchefstroom Campus, 2012.

According to the National Curriculum Statement (NCS) of South Africa cognitive development is a prominent matter which should already commence at pre-school teaching and learning. The NCS envisages learners who will develop to maturity, take their place in society and solve problems by means of critical and creative thinking. Accordingly, teachers are challenged to create teaching and learning environments that stimulate and encourage intellectual openness. This study was undertaken in an attempt to determine to which extent thinking skills in the Foundation Phase, with specific reference to Grade 3 learners, are developed. The study also sought to establish the potential of a self developed, curriculum-based co-operative teaching-learning intervention programme for the development and/or improvement of the thinking skills of Grade 3 learners. The nature of cognitive development, the importance of co-operative learning for cognitive development and the thinking skills that Grade 3 learners should possess, were researched by means of a literature study. A quasiexperimental study followed, using a sequential mixed-method research design. By means of a pre-test the cognitive development levels of two experimental groups, namely experimental group A and experimental group B, comprising thirty learners each, were determined. Thereafter, both groups were exposed to a co-operative teaching-learning intervention programme on a rotational basis to determine the impact of the cooperative teaching-learning intervention programme on the thinking skills of the learners. Data was collected by means of testing and semi-structured interviews with the class teachers of the experimental groups A and B prior to and after the completion of the intervention, focus-group interviews with the learners after the intervention and observation during the implementation of the intervention. Based on the results, it appeared that in accordance with the vision of the NCS, trouble is being taken with the development of the thinking skills of the Foundation Phase learners who took part in the study, and that co-operative learning possesses the latent potential to further develop and promote thinking skills. / Thesis (Ph.D. (Learning and Teaching)--North-West University, Vaal Triangle Campus, 2010.

According to the National Curriculum Statement (NCS) of South Africa cognitive development is a prominent matter which should already commence at pre-school teaching and learning. The NCS envisages learners who will develop to maturity, take their place in society and solve problems by means of critical and creative thinking. Accordingly, teachers are challenged to create teaching and learning environments that stimulate and encourage intellectual openness. This study was undertaken in an attempt to determine to which extent thinking skills in the Foundation Phase, with specific reference to Grade 3 learners, are developed. The study also sought to establish the potential of a self developed, curriculum-based co-operative teaching-learning intervention programme for the development and/or improvement of the thinking skills of Grade 3 learners. The nature of cognitive development, the importance of co-operative learning for cognitive development and the thinking skills that Grade 3 learners should possess, were researched by means of a literature study. A quasiexperimental study followed, using a sequential mixed-method research design. By means of a pre-test the cognitive development levels of two experimental groups, namely experimental group A and experimental group B, comprising thirty learners each, were determined. Thereafter, both groups were exposed to a co-operative teaching-learning intervention programme on a rotational basis to determine the impact of the cooperative teaching-learning intervention programme on the thinking skills of the learners. Data was collected by means of testing and semi-structured interviews with the class teachers of the experimental groups A and B prior to and after the completion of the intervention, focus-group interviews with the learners after the intervention and observation during the implementation of the intervention. Based on the results, it appeared that in accordance with the vision of the NCS, trouble is being taken with the development of the thinking skills of the Foundation Phase learners who took part in the study, and that co-operative learning possesses the latent potential to further develop and promote thinking skills. / Thesis (Ph.D. (Learning and Teaching)--North-West University, Vaal Triangle Campus, 2010.

An experimental study was conducted in order to investigate the two-phase-flow phenomena in a mini-size, horizontal impacting tee junction. The test section was machined in an acrylic block with a rectangular cross-section of 1.87-mm height × 20-mm width on the inlet and outlet sides. Air-water mixtures at 200 kPa (abs) and room temperature were used as the test fluids. Four flow regimes were identified visually: bubbly, plug, churn, and annular over the ranges of gas and liquid superficial velocities of 0.04 ≤ JG ≤ 10 m/s and 0.02 ≤ JL ≤ 0.7 m/s, respectively, and a flow regime map was developed. The present flow-regime map was compared with several experimental maps. It is thought from those comparisons that the channel height has a more significant role in determining the flow-regime boundaries than the hydraulic diameter. The two-phase fully-developed pressure gradient was measured in the inlet and the outlet sides of the junction for six different inlet conditions and various mass splits at the junction. Comparisons were conducted between the present data and former correlations. The correlations that agreed best with the present data were identified. Five single-phase test sets were performed. In each set of experiments, the pressure distribution was measured for the whole range of the mass split ratio, Wi/W1. The pressure drop at the junction at each value of Wi/W1 was calculated. Values of the pressure-loss coefficient, , were calculated at various Wi/W1 and inlet Reynolds number. The pressure-loss coefficient was strongly dependent on the inlet Reynolds number in the laminar region, while the results for the turbulent region were almost coincident. Numerical simulations of single-phase flow in an impacting tee junction of identical dimensions to that of the present test-section were performed to confirm the results of the experiments. Phase-redistribution experiments were conducted covering all four inlet flow regimes and models were proposed for predicting the experimental data. Good agreement in terms of magnitude and trend was obtained between the present experimental data and the proposed model. New correlations were developed for the single- and two-phase pressure drop in the junction.

The removal of heat from the containment building is an important consideration in the design of a nuclear power plant. In this investigation a simple rectangular natural circulation loop was simulated to determine whether it could possibly be used to remove usable quantities of heat from a containment building. The loop had a vertical pipe on the inside and outside of the containment building. These pipes acted as heat exchangers. Single phase and two phase cases were simulated by imposing a temperature on the respective vertical leg pipe walls and determining the heat absorption from the containment building. The heat was conveyed from the inside of the building to the outside via the natural circulation phenomenon. A literature study was done to cover topics relevant to this investigation. A theoretical model using conservation equations and control volumes was derived. This model was based largely on knowledge gleaned from the literature study. The theoretical model was a simple homogenous model, which was sufficiently detailed for a conceptual investigation. The theoretical model was then manipulated into a form suitable for use in a computer simulation program. Simplifications were made to the simulation model and underlying theory due to the nature of the investigation. The simulation model was validated against published experimental results. During the simulation phase a number of cases were investigated. These cases were divided into base cases and parametric studies. During the base case simulations the change of key fluid variables along the loop was examined. During the parametric studies the hot and cold leg inside wall temperatures, loop geometry and pipe diameter were varied. The effect of these parameters on the heat absorption from the containment was determined. The simulations showed that with the current assumptions about 75 to 120 of the natural circulation loops are needed depending on their geometry and containment conditions. The heat removal rates that were calculated varied from 50 kW to 600 kW for a single loop. As explained in the final chapter, there are many factors that influence the results obtained. The natural circulation concept was deemed to be able to remove usable quantities of heat from the containment building. / Thesis (M.Ing. (Nuclear Engineering))--North-West University, Potchefstroom Campus, 2012.