1,720,981 research outputs found
A biomass-fueled combined steam and sCO2 heat and power cycle for Southern African conditions
Get PDFBiomass is a renewable, cost-efficient, carbon-neutral fuel obtained from agricultural waste streams or energy crops that can be combusted in a furnace to co-generate electricity and heat. Integrating a supplementary high efficiency cycle, such as the supercritical-CO2 (sCO2) Brayton cycle, with an existing industrial Rankine cycle and a biomass fired boiler may be an economical option to increase overall thermal efficiency and net generation. However, the integration of sCO2 heaters within the biomass boiler presents challenges related to operating philosophies and component specifications. The focus of this research was to investigate the integration of a sCO2 Brayton cycle with a combined heat and power steam cycle with a modular biomass boiler firing typical Southern African bagasse fuel. A quasi-steady state 1D thermofluid network-based process model of the sCO2, steam and flue gas cycles was developed for nominal and partial load analysis. It accounts for the detailed component characteristics for the Rankine and Brayton cycles, as well as the biomass boiler, together with the complex interactions between all of the components in the different cycles. To facilitate the analysis of these intricate systems, a sophisticated simulation code was developed to allow for necessary customization and enforcement of required boundary conditions and control parameters. The network model solves the mass, energy, momentum, and species balance equations for the various fluid streams, accounting for radiative and convective heat transfer phenomena in the boiler. Due to the novelty of the proposed integrated cycle, high-fidelity 3D CFD modelling was then also used to validate the heat uptakes for the sCO2 heaters in the biomass boiler. Two configurations with the sCO2 heater/s situated within the flue gas flow path were investigated, namely a single convective-dominant heater, and a dual heater configuration with a radiative and a convective heater. At nominal load, the network model results show the required rate of overfiring for the sCO2 configurations, with a 15.3% increase in fuel flow rate resulting in an additional 21.2% in net power output. The impact of the sCO2 heaters situated in the gas flow path was quantified, with reduced heat uptakes for downstream steam heat exchangers offset by increased furnace waterwall heat transfer. At partial loads, between 100%-60%, inventory control proves to be the better performing control strategy for load following, maintaining high thermal efficiency across partial loads. Notably, at 60% load, the sCO2 compressor inlet conditions are near the pseudo-critical point, which requires careful management of inventory control. The boiler CFD modelling highlighted lower heat uptakes for sCO2 heaters compared to the 1D model, exacerbated at lower loads, particularly for the dual heater configuration. The 1D model was consequently calibrated based on these results. The single sCO2 heater configuration is recommended as the preferred configuration to minimise adverse impacts on the Rankine cycle superheaters. Further iterations between the 1D process model and CFD model are recommended
Key factors influencing the outcome of Energy Projects procured using Public Private Partnerships in South Africa
Get PDFProcesses required for the procurement of construction projects by the public and private sectors must comply with many requirements and incentives, not least of which is usually the requirement to provide value for money. However, large capital works construction projects, particularly those undertaken by the public sector, have a tendency to over-run both their construction schedules and their budgets. This is amply demonstrated in South Africa by the construction of the Medupi and Kusile coal fired power stations by Eskom, the South African national power utility, which are both running over schedule and are projected to be over budget by 52% and 48% respectively. In contrast, Public Private Partnership contracts between the private sector and the South African government were recently used to construct large, utility scale renewable energy facilities in South Africa, with a total capacity equivalent to that of Medupi power station, on time and on budget. This research study considers the various procurement options in use globally for the construction of capital projects, before looking in detail at the Public Private Partnerships approach for infrastructure procurement, both globally and in the South African context for energy projects. The research study and aims to answer the questions, “What are the key factors that influence the outcome of energy projects procured using public private partnerships in South Africa?” and “What interventions could improve the success rates of projects procured using public private partnership contracts in South Africa?”. A social constructionist epistemology was adopted to guide the research, as the context of the research questions is complex requiring flexible research approaches, able to consider matters such as the perceptions of stakeholders involved in energy projects. The research study makes use of a systematic literature review of international publications, and a survey of individuals working in the South African renewable energy industry. The data was analysed using qualitative content analysis to identify themes, and further coded to identify the factors. The research study aims to contribute to the body of knowledge on the use of the effectiveness of the Public Private Partnerships approach used for the procurement of energy projects in South Africa as there appears to have been little research undertaken in this area to date
Enabling 'growth mindsets' in engineering students
Get PDFStudent failure is often attributed to a lack of work by students. While this view has some merit, it implies that only students need to change and reduces the incentive for lecturers, curricula, assessment practices to be interrogated. In this thesis, I take a comprehensive look into why students do not work. Firstly, I place social psychology factors in context with other factors that impact student success and show how beliefs about academic ability underpin the academic behaviour that leads to success. By placing a learning theory lens on six characteristics of fixed mindsets (beliefs that ability can only be developed to an individually pre-determined level) and growth mindsets (beliefs that that effective effort will lead to unlimited self-improvement), I develop a theoretical framework that explains how both fixed and growth mindsets can be encouraged by teaching practices. As students with fixed mindsets may be more vulnerable to dropping out of university, lecturers should be aware of the mindset messages they are sending to students through their words, actions and choice of activities and assessment practices. To address the question of how growth mindsets can be developed, I present results from a systematic literature review of growth mindset interventions aimed at engineering students, drawing on databases in education, engineering, and psychology. The findings show that most interventions involved informing students about mindsets and asking students to reflect on or teach others about mindsets, using personal examples. An intervention was devised to develop growth mindsets in engineering students through tutoring groups on the social media platform WhatsApp. Poor group functioning was addressed using a design-based research approach for the establishment of effective groups. Unexpectedly, assessments of engineering students' mindsets through surveys and interviews showed very low numbers of students with fixed mindset views. Reasons for this result are explained by categorizing growth mindset enablers identified from literature and comparing the literature findings with interview data from engineering students. The thesis culminates by contributing a critique on mindset assessment and a framework for creating learning environments conducive to student success
Numerical optimisation and theoretical analysis of complex microchannel heat exchangers
Get PDFThe purpose of this study is to evaluate the performance of the geometries in forced convective heat transfer and steady state laminar incompressible fluid flow. Microchannel heat sinks used were numerically modelled from highly conductive (aluminium) solid material substrate. ANSYS FLUENT Response Surface Optimisation Tool (RSO) was used to numerically optimise and compare the performance of combined microchannel heat sinks with perforated, solid, half-hollow and hollow fins. The simulation began by optimising a typical microchannel heat sink geometry before fin-bars were inserted into the cooling channel to augment heat transfer. Furthermore, solid and perforated fins were modelled and added on the top of the typical heat sink. The performance of the various configurations was then compared. A novel combined microchannel design with circular micro fins was modelled with a circular flow channel. Additionally, a hybrid model was developed, incorporating circular fins on a microchannel heat sink with a rectangular flow channel. The third design featured rectangular fins mounted on a microchannel with a rectangular flow channel. The combined microchannels, featuring circular and rectangular fins, were cooled by water flowing through the channels and internally along the fin inner surface walls to dissipate heat. These designs were then integrated into the computational domain and subjected to cooling using both water and an air stream. The water flows through the flow channel while air flows over the vertical fins to remove excess heat from the external wall surfaces of the fins in forced convection laminar flow condition. Theoretical analysis (intersection of asymptotes method) was carried out in the cooling channels (circular and rectangular). The theoretical analysis results indicated the presence of an optimal geometry among the various cross-sectional shapes, effectively cooling a volume with a uniformly distributed heat flux. A comparison of the analytic findings with the numerical results demonstrates that an optimal design is possible. The numerical cooling processes were carried out in parallel and counter flows. These findings demonstrate that an optimal design can be realised with a combination of Computational Fluid Dynamics and geometric modelling techniques
Workplace learning through structured interactions
No full textIncludes abstract.Includes bibliographical references (leaves 102-114).Individuals need to keep learning to stay employable and compete in today’s job market, and organisations need to keep learning in order to maintain a competitive advantage in the economy. The workplace is thus being recognised as a legitimate environment for learning new skills and knowledge, through participation in everyday work activities. This recognition has led to numerous studies that connect learning and the workplace, giving rise concepts such as ‘the learning organisation’, ‘organisational learning’, ‘workplace learning’ and ‘informal learning’. All of which have created confusion, uncertainty and complexity in understanding how learning takes place. In order to understand how individuals learn in the workplace, and thus understand how organisations can enhance such learning, this study investigates individuals’ perceptions of their workplace as a learning environment and their experiences of learning through participation in work activities
Kolb Interrupted : An investigation into students' experience of an experiential learning approach to entrepreneurship education
No full textEntrepreneurial activity is widely regarded as a primary driver of socio-economic development. Alongside structural and systemic support, entrepreneurship education is a critical factor in improving entrepreneurial activity. While entrepreneurship education initiatives abound, little is understood about the effectiveness and pedagogical basis of these programmes, especially from the perspective of the student. This thesis focuses on a case study of a South African programme of entrepreneurship education designed around Kolb's Experiential Learning Cycle. The research employs a phenomenographic framework to identify the qualitatively different ways in which students experience this experiential learning approach to entrepreneurship education. This research shows that students' ways of experiencing learning can be characterised in one of two ways; a superficial way of experiencing learning in which students takes on a less sophisticated and surface view of learning, and an immersed way of experiencing learning in which students' engage in a deep and sophisticated manner. These ways of experiencing learning suggest two ways in which Kolb's Experiential Learning Cycle is interrupted; firstly, at the point of concrete experience, and secondly, at the point of reflective observation. This study makes a contribution to knowledge by examining experiential learning from the perspective of the student, and shows how programmes of entrepreneurship education can be better designed, in order to have an impact on entrepreneurial activity and socio-economic development
Pupils' experiences of technology : exploring dimensions of technological literacy
No full textIncludes bibliographical references (leaves 155-162).Technology is the driving force behind much of the change taking place in the world today. Consequently, across society, calls are being made to ensure technological literacy is a meaningful and central part of schooling to adequately prepare pupils to become part of an increasingly technologically driven world. However, studies have shown that large parts of society perceive technology primarily in terms of computers
Considering two audiences when recording lectures as lecturecasts
Get PDFThis article presents the outcome of an investigation into the provision of lecturecasts to students. The objective was to ensure that both those who attended live lectures of a second-year engineering course and/or watched recorded versions of the lectures had an experience that supported their learning. A range of data was drawn on including the personal reflection of the lecturer of the course, questionnaires, and student interviews. The qualitative data were analysed through an inductive process that drew on the principles of grounded theory and the findings that emerged included the role of the ‘talking head’ in recordings, balancing the needs of the live and recorded audience, the importance of digital annotation using e-ink, content navigation using index markers, the availability of the lecturecasts, and the importance of considering intellectual property. These findings demonstrate how the design and implementation of lecturecasting can be improved to ensure that students have the best possible experience of the material being presented
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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