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Advances in mathematical modelling and the availability of high speed computers with considerable memory size is making it possible to study the hydraulics of border irrigation in a greater depth than every before. A zero inertia mathematical model was found to be reliable and inexpensive among the models available in border irrigation hydraulics and was used for this study to simulate free outflow flowing border irrigation. Special emphasis was given to the runoff produced from such a system. This study dealt particularly with, the identification of pertinent open channel variables affecting runoff in border irrigation, presentation of predictive graphical and mathematical solution to quantify runoff, and with utilization of these solutions in developing reuse system design criteria. Inflow rate, surface resistance, border slope, soil infiltration characteristics, application time (time of cutoff and length of run of the border) were among other variables studied. As one might expect, runoff was found to increase with slope, flow rate, application time and decrease with increase in infiltration rate, length of run and bed and vegetation drag. Considering the number of variables affecting runoff characteristics from a given irrigation, it was obvious to see a thorough examination of each variable in dimensional terms was practically impossible. Also, presentation of the results would have required too many graphs. Dimensional anslysis was used to solve this problem and in developing dimensionless runoff curves. The ability to quantify runoff made it possible to develop reuse system design formula for proper sizing of reuse systems under several operational requirements. Shape function for the ultimate infiltrated depth profile was used to get times of runoff and also calculate various efficiencies which are useful for evaluating the system. The study shows, through the use of reuse system, the potential application efficiency can be changed from present values of 60 percent to 90 percent in Arizona. It also can be used to demonstrate the saving in energy that can be realized through such system. Step by step procedures for the design of reuse system using graphical and mathematical solutions are presented with a sample problem worked out. It is expected that the result of this study can be used by designers as well as operators of border irrigation systems without any difficulty with the aid of a simple pocket calculator. Other uses of the study include getting optimal design for the system itself by evaluating various possible designs and classroom instruction on the application of dimensional analysis to open channel hydraulics problems and design of reuse systems.

Forest fuels can be recovered, stored and handled in several ways and these different ways have different implications for CO2 emissions. In this thesis, comparative analyses were made on different forest-fuel systems. The analyses focused on the recovery and transport systems. Costs, primary energy use, CO2 emissions, storage losses and work environment associated with the use of forest fuel for energy were examined by using systems analysis methodology in a life cycle perspective. The bundle system showed less dry-matter losses and lower costs than the chip system. The difference was mainly due to more efficient forwarding, hauling and large-scale chipping. The potential of allergic reactions by workers did not differ significantly between the systems. In difficult terrain types, the loose material and roadside bundling systems become as economical as the clearcut bundle system. The stump and small roundwood systems showed the greatest increase in costs when the availability of forest fuel decreased. Stumps required the greatest increase in primary energy use. Forest fuels are a limited resource. A key factor is the amount of biomass recovered per hectare. Combined recovery of logging residues, stumps and small roundwood from thinnings from the same forest area give a high potential of reduced net CO2 emissions per hectare of forest land. Compensation fertilization becomes more cost-effective and the primary energy use for ash spreading becomes low – about 0,25‰. The total amount of available forest fuel in Sweden is 66 TWh per year. This would cost 1 billion €2007 to recover and would avoid 6.9 Mtonne carbon if fossil coal were replaced. In southern Sweden almost all forest fuel is obtainable in high-concentration areas where it is easy to recover. When determining potential CO2 emissions avoidance, the transportation distance was found to be less important than the other factors considered in this work. The type of transportation system did not have a significant influence over the CO2 avoided per hectare of forest land. The most important factor analysed here was the type of fossil fuel (coal, oil or natural gas) replaced together with the net amount of biomass recovered per hectare of forest land. Large-scale, long-distance transportation of biofuels from central Sweden has the potential to be cost-effective and also attractive in terms of CO2 emissions. A bundle recovery system meant that more biomass per hectare could be delivered to end-users than a pellet system due to conversion losses when producing pellets.

Please read the abstract in the section 00front of this document / Dissertation (MSc (Agronomy))--University of Pretoria, 2006. / Plant Production and Soil Science / unrestricted

Please read the abstract in the section, 00front of this document / Dissertation (MEng (Environmental Engineering))--University of Pretoria, 2008. / Chemical Engineering / MEng / Unrestricted

A lot has been said about change. For example, it is widely recognised that the only constant is change (Heraclitus, 470 BC). As such, no sensible decision can be made any longer without taking into account not only the world as it is, but the world as it will be (Isaac Asimov). As regards this, a bulk of existing researches have been aimed at understanding the triggers for change and the extent or degree to which individuals, organisations, systems or entities have to change. Generally, results from such studies vary. With specific relations to organisations, organisations are advised of the need to develop added adaptive and dynamic capabilities. One of such added adaptive and dynamic capabilities is organisational resilience. In the literature, organisational resilience has been successful linked with organisations ability to maintain long term performance. Hence, the research is not about re-examining the relationship between organisational resilience and organisations ability to maintain long term performance. This research focuses on exploring the critical success factors required to maintain long term performance and building adequate resilience into systems undergoing changes. The investigation was conducted in three phases, namely: (a) the exploratory phase; (b) the descriptive phase; and the empirical phase. The exploratory phase involved identifying the critical factors essential to maintain long term performance and at the same time build resilience into their systems after undergoing organisation-wide changes. In order to make out these critical, a pilot study was conducted. 21 persons occupying senior managerial positions in different organisations were interviewed. The interview data were transcribed, coded and analysed using coding and thematic analysis to identify five common themes, namely (a) employees readiness to support ongoing organisation-wide changes; (b) development of targeted organisational adaptive capacity; (c) the provision of individualised and social support; (d) the use of stress coping mechanisms; and (e) the existence of organisational resilience strategies. The second phase of the research entailed conducting case study research with the intention of describing the identified critical success factors. The final phase entailed conducting empirical analyses and cross case analysis. Results from the cross case study analyses indicated that both resilience building at the individual level and organisational level is needed for organisations to build in resilience into their systems especially after undergoing organisation-wide changes. Three factors (i.e. employees readiness to support ongoing organisation-wide changes, the provision of individualised and social support and the use of stress coping mechanisms) were found to be more pronounced at the individual level. The remaining two factors namely development of targeted organisational adaptive capacity and the existence of organisational resilience strategies are essentially carried out at the organisational level. The research has contributed to the current body of knowledge on how organisations can strive to maintain long term performance, especially for a country like Nigeria where there still remains a dearth of such related studies. Each of the research hypotheses were either confirmed or non confirmed. This will give the practitioners, academicians and managers of Nigerian organisations the opportunity to understand how each of the sub factors of the five critical success factors can influence on attempts to build organisational resilience. In addition, specific actions that managers can follow over the life of an organisation-wide change project that will improve the resilience of systems undergoing change. In addition, differences in how varied control factors can influence resilience building in organisations were explored and validated based on the results of the Mann Whitney test results. At the end of the thesis, recommendations for future practice and research were made. One of such is that resilience building at both levels be done concurrently and given equal prominence.

Graduation date: 1990

Waste heat recovery is a multi-billion-dollar industry with a compound annual growth rate of 8.8% assessed between 2016 to 2024 and low-grade waste heat (< 230^oC ± 20^oC) makes up 66% of this ubiquitous resource. Thermoelectric generators are preferred for the recovery process because they are cheap and are well suited for this temperature range. They generate power by converting thermal potential to electric potential, known as the Seebeck effect. Since they have no moving parts, they are inherently immune to mechanical failure or an intermittent need for maintenance. However, the challenge has been to effectively harvest waste heat with these modules to generate power, using passive processes. This work is focused on designing a device for optimized harvesting of waste energy from the ambient with a custom, evaporatively-cooled heat sink. This heat sink is designed to passively handle the cooling of the other side of the thermoelectric module so as to enable the attainment of a minimum of 5V, which is the minimum voltage required to power small mobile devices. The heat sink model is similar to a loop heat pipe but engineered for compactness. To ensure this level of efficacy is attained, several studies are made to optimize the wick. Non-metal wicks were considered as they do not contribute to an increase in temperature of the compensation chamber in loop heat pipes. A non-metal wick integrated with nanoparticles is tested and results show a clear thermal management enhancement over similar but virgin non-metal wicks, at over 16%. The heat source section of the device is optimized for energy-harvesting in low grade temperature regimes by incorporating a near-black body coating on the metal heat source section. Experimental results show that both the heat source and sink sections were able to induce sufficient thermal potential for the thermoelectric modules to passively generate up to 5V using eight 40mm by 40mm Bismuth Telluride modules in 3.5 minutes. The prototype is relatively cheap, inherently reliable and presents the possibility of passively harvesting low-grade waste heat for later use, including powering small electronic devices.