Department of Mechanical and Mechatronic Engineering

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16th INTERNATIONAL CONFERENCE ON HEAT TRANSFER, FLUID MECHANICS AND THERMODYNAMICS: 3D PRINTED MINIATURE COOLER FOR ELECTRONICS THERMAL MANAGEMENT ONLINE, 8 – 10 AUGUST 2022
(ASTFE, 2022-08-08) Imtiaz, Nida; Wahid, Mazlan Abdul; Kamaruzaman, Natrah Binti; Ng, Kim Choon; Xu, Ben Bin; Shahzad, Muhammad Wakil
The global Central Processing Units (CPUs) are expected to grow at a significant CAGR of 3.6% by 2028. The major factors driving the growth are increasing demand for high processing power CPUs in various applications such as personal computers, servers, and portable computers, among others; growing adoption of enterprise systems that require high-performance CPUs with faster processing speed; and rise in the number of CPU cores per chip over time. However, thermal management is a crucial issue to maintain their performance with increasing processing speed and number of CPU cores per chip. The conventional fans/blowers are unable to maintain required temperature and hence deteriorate CPU performance. We proposed an innovative miniature indirect evaporator cooler for thermal management and local cooling of electronic boards, CPU and Graphics Processing Unit (GPU). In proposed unit, the humidity of supply air is maintained by separating dry and wet channels via thin copper film that also provide good heat transfer properties. Thin water layer is maintained through wick surface in wet channel to extract heat from supply air flowing in dry channel. In order to achieve the objectives and evaluate the performance, miniature indirect evaporator cooler is designed and most of parts are fabricated using 3D printing facility. Extensive experiments are conducted at assorted temperature to map the performance for various electronic units applications. The result shows that the 200mm x 150mm cell with 5 dry and wet channels can achieve up to 40–45Watt cooling capacity. Based on 3D printed modular design, it has flexibility to improve capacity to match application requirements. The proposed miniature cooler can be employed for electronic thermal management and maintain low temperature to enhance their efficiency and improve processing speed.
A concentrating solar power value proposition for South Africa
(Energy Research Centre, University of Cape Town, 2013) Gauche, Paul; Von Backstrom, Theodore W.; Brent, Alan C.
Concentrating solar power (CSP) offers the potential for a high degree of localization and an alternative strategy to meet electricity demand for South Africa in a future of uncertain conventional resources. The integrated resource plan (IRP) makes strides to introduce renewables to the electricity generation system by 2030, but we argue that the proposed energy mix is too reliant on resources that are not only unsustainable but also at risk in the short to medium term. Coal and other conventional resources may be more limited than originally anticipated, which if true, requires action to be taken soon. CSP is currently the only sustainable and dispatchable energy technology that could domestically supply a significant portion of South Africa’s electricity needs. A balanced mix of PV, wind and CSP can provide the energy supply needed in South Africa, but steps are required soon to take advantage of the localization potential and excellent sustainable energy resources.
Accounting for proof test data in Reliability Based Design Optimization
(Stellenbosch : Stellenbosch University, 2015-03) Ndashimye, Maurice; Venter, Gerhard; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
ENGLISH ABSTRACT: Recent studies have shown that considering proof test data in a Reliability Based Design Optimization (RBDO) environment can result in design improvement. Proof testing involves the physical testing of each and every component before it enters into service. Considering the proof test data as part of the RBDO process allows for improvement of the original design, such as weight savings, while preserving high reliability levels. Composite Over-Wrapped Pressure Vessels (COPV) is used as an example application of achieving weight savings while maintaining high reliability levels. COPVs are light structures used to store pressurized fluids in space shuttles, the international space station and other applications where they are maintained at high pressure for extended periods of time. Given that each and every COPV used in spacecraft is proof tested before entering service and any weight savings on a spacecraft results in significant cost savings, this thesis put forward an application of RBDO that accounts for proof test data in the design of a COPV. The method developed in this thesis shows that, while maintaining high levels of reliability, significant weight savings can be achieved by including proof test data in the design process. Also, the method enables a designer to have control over the magnitude of the proof test, making it possible to also design the proof test itself depending on the desired level of reliability for passing the proof test. The implementation of the method is discussed in detail. The evaluation of the reliability was based on the First Order Reliability Method (FORM) supported by Monte Carlo Simulation. Also, the method is implemented in a versatile way that allows the use of analytical as well as numerical (in the form of finite element) models. Results show that additional weight savings can be achieved by the inclusion of proof test data in the design process.
Adaptive digital image correlation using neural networks
(Stellenbosch : Stellenbosch University, 2023-03) Atkinson, Devan James; Becker, Thorsten Hermann; Neaves, Melody; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
ENGLISH SUMMARY: Subset size selection is crucial to the accuracy and precision of digital image correlation (DIC) measured displacements. Increasing the subset size improves noise suppression (reducing random errors) at the cost of spatial resolution (ability to accurately measure complex displacement fields). The tradition of global correlation parameter assignment is suboptimal because the speckle pattern quality and displacement field complexity can vary spatially. Dynamic subset selection (DSS), which assigns location specific optimal subset sizes, is challenging because the metrological performance of correlation is dictated by complex interactions between correlation parameters (subset size and shape function) and image set properties (noise, speckle pattern and displacement field complexity). This dissertation uses an open-source DIC framework to investigate the potential of artificial neural networks (ANNs) for error prediction and DSS, prior to the DIC process, from purely image information. ANNs are capable of modelling complex relationships within noisy, incomplete data without imposing fixed relationships, inspiring their recent resurgence for DIC applications. Despite the plethora of open-source DIC algorithms available, none offer spatially and temporally independent assignment of correlation parameters. Subsequently, a modular, open-source DIC framework capable of such flexibility is developed. This framework is predominantly consistent with current state-of-the-art practices and performs on par with well-established open-source and commercial DIC algorithms. Drawing direct links between the well-documented theory of DIC and its nuanced practical implementation, bridges this gap in literature which has acted as a barrier to newcomers intending to develop the capabilities of DIC. This framework, implemented in 117 and 202 lines of MATLAB code for 2D and stereo DIC, respectively, is attractive as a starting point to further the capabilities of DIC. The feed-forward ANN developed using this DIC framework, predicts random errors based on the speckle pattern quality (contained within a subset) and standard deviation of image noise more accurately and precisely than established theoretical derivations. A DSS framework is developed which uses this ANN to appoint subset sizes, based on the local speckle pattern, that offer random errors consistent with a stipulated threshold value. Appropriate selection of the random error threshold offers a favourable compromise between noise suppression and spatial resolution for up to moderate displacement gradients. Consequently, in the presence of varying speckle pattern quality this framework outperforms the traditional approach of trialand- error global subset size selection for the same mean subset size. Speckle pattern characteristics outside the training scope reveal the generalisability limitations of the DSS method, and associated ANN, as it performs on par with the traditional global subset size approach, motivating the need to broaden its training scope. Investigation of convolutional neural networks for dynamic shape function selection is initiated, showing they are capable of quantifying displacement field complexity between image pairs to guide spatially and temporally independent shape function assignment. The dissertation reveals that ANNs are an attractive approach to model the correlation parameter assignment. Furthermore, such models facilitate dynamic correlation parameter assignment from purely image information such that they can operate as a pre-process to DIC.
ADHD screening tool: investigating the effectiveness of a tablet-based game with machine learning
(Stellenbosch : Stellenbosch University, 2019-04) Swarts, Romano; Fourie, Pieter Rousseau; Van den Heever, David Jacobus; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering (CRSES)
ENGLISH ABSTRACT: This study investigated the effectiveness of a tablet-based game that incorporated machine learning to screen participants between the ages of six and twelve years for ADHD inattentive subtype. Prior to the design and development of the ADHD screening tool, a thorough investigation of the literature was conducted. Additionally, existing ADHD screening tools and cognitive training tools were identified. This research project implemented lessons learned from the literature, as well as input from medical professionals and the DSM-V diagnostic criteria. The ADHD screening tool presents a patient-testing interface in the form of a tablet-based game with a cloud-based machine learning classifier. The cloud-based classifier is integrated with an algorithm, and together they can discriminate between ADHD and non-ADHD patients with a sensitivity of 100i% and specificity of 87.5i%. The device used for testing was a single, internet connected, commercially available tablet. No additional hardware is required.
Aerodinamiese eienskappe van lugverkoelde warmte-uitruilers
(Stellenbosch : Stellenbosch University, 1996) Duvenhage, Kobus; Kroger, D. G.; Du Toit, C. G.; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
ENGLISH ABSTRACT: The aim of this dissertation is to contribute in solving the problem, due to a lack of knowledge and information, concerning the aerodynamic features of a typical air-cooled heat exchanger (ACHE), numerically and experimentally. Only forced draught ACHE's are considered. The project consists mainly of numerical experimentation, using the general purpose code, PHEONICS.
Aerodynamic characteristics of a mission-adaptive stealthy air inlet
(Stellenbosch : Stellenbosch University, 2003-12) Marais, Louwrens; Thiart, G. D.; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
ENGLISH ABSTRACT: The aerodynamic performance of a mission-adaptive air inlet for a stealthy unmanned aircraft was examined using CFX 5.5, a commercial Computational Fluid Dynamics package. In order to ensure that the numerical results were reliable, the package was validated against a number of flow situations for which previously-known results exist. This was done for both external and internal flow, and in all cases the conclusion could be made that the code produces realistic results. The simulation of the inlet was done in two steps. A first-order design was simulated using robust simulation parameters: the focus was on obtaining a "picture" of the flow into the inlet, not on the quantitative values of flow variables. On account of the results of these simulations, the design was suitably modified. This second-order design was then simulated using more accurate simulation parameters, and the results analysed in detail. Comparative simulations between the two design iterations showed that their pressure recoveries are similar, but that the distortion of the velocity profile at the engine compressor face is lower for the second-order design than for the first-order design over a significant portion of the operational range. When compared with an idealized theoretical analysis, the numerical results showed that the performance of the inlet was severely degraded at most operating conditions. This is mainly due to the effects of flow separation ahead of the inlet capture plane. To alleviate this problem, recommendations for the modification of the design are proposed. This thesis demonstrates that CFD is a valuable tool for both qualitative and quantitative evaluation of performance during the design process of an air inlet.
Aerodynamic damping of an oscillating fan blade: Numerical fluid structure interaction analysis
(Stellenbosch : Stellenbosch University, 2017-03) Peters, Christian Dietrich; Els, D. N. J.; Van der Spuy, S. J.; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
ENGLISH SUMMARY: The thesis’ main objective is to determine the dynamic ﬂow phenomena that dampen a fan blade’s oscillation amplitude using numerical ﬂuid structure interaction (FSI) simulations. The observed ﬂow eﬀects include the formation and shedding of leading edge vortices, downwash and the added mass eﬀect. Leading edge vortices are a major damping contributor and are dependent on the blade’s eﬀective angle of attack. The aim of the thesis is to ﬁnd a suitable method that is capable of simulating the aerodynamic damping of an axial fan used in an air cooled condenser unit. Therefore, three diﬀerent numerical models are used to perform the FSI simulation and are compared according to their accuracy, robustness and computational cost. The aerodynamic damping of an oscillating fan blade was experimentally investigated by Basson (2015) and his results are used to validate the three numerical models. The three methods used are a mesh-based FSI simulation, a simpliﬁed one dimensional beam model coupled with a heuristic ﬂow model and a meshless FSI simulation. The mesh based and meshless FSI simulations are both suitable for modelling the entire air cooled condenser fan unit, whereas the simpliﬁed 1D beam model is incapable of doing so.
Aerodynamic development of a contra-rotating shrouded rotor system for a UAV
(Stellenbosch : Stellenbosch University, 2015-03) Geldenhuys, Heinrich Jacques; Van der Spuy, S. J.; Von Backstrom, T. W.; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
ENGLISH ABSTRACT: Unmanned aerial vehicles with vertical take-off and landing capabilities have received extensive attention worldwide in the last decade. Their low detectability, high manoeuvrability in confined spaces, and their capability for out-of-sight operations make them practical solutions for an array of military and civilian missions. The main advantage of shrouded rotors in hover and low speed conditions is the decreased blade tip induced drag when the tip gap is small enough. A well-designed shroud augments the rotor thrust in hover and low axial flight conditions. It also provides noise reduction and safety. A contra-rotating rotor system eliminates the need for separate anti-torque devices, thus producing a smaller footprint and a more compact vehicle. In this study a more efficient coaxial rotor for the ducted coaxial rotor system as published by (Lee 2010) was developed. The first phase of the design process consisted of the selection and numerical analysis of the best suited parent airfoils for the rotors by using XFOIL and XFLR 5. The second phase dealt with the design of a counter-rotating rotor system for the existing cambered shroud as published by (Lee, 2010), using the DFDC-070ES2a two dimensional code, specifically written for ducted rotor optimization. The final phase of the study dealt with the Computational Fluid Dynamic (CFD) verification of the design in ANSYS-CFX 15.07. A comparison between the CFX predictions of the newly designed rotor system and the reference design indicates a 33% improvement in hover thrust at the design power input.
Aerodynamic optimisation of a small-scale wind turbine blade for low windspeed conditions
(Stellenbosch : Stellenbosch University, 2006-12) Cencelli, Nicolette Arnalda; Von Bakstrom, T. W.; Denton, T. S. A.; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronical Engineering
ENGLISH ABSTRACT: Wind conditions in South Africa determine the need for a small-scale wind turbine to produce useable power at windspeeds below 7m/s. In this project, a range of windspeeds, within which optimal performance o the wind turbine is expected, was selected. The optimal performance was assessed in terms of the Coefficient of Power(Cp), which rates the turbines blade's ability to extract energy form the avalible wind stream. The optimisation methods employed allowed a means of tackling the multi-variable problem such that the aerodynamic characteristics of the blade were ideal throughout the wind speed range. The design problem was broken down into a two-dimensional optimisaion of the airfoils used at the radial stations, and a three-dimensional optimisation of the geometric features of the wind rotor. by means of blending various standard airfoil profiles, a new profile was created at each radial station. XFOIL was used for the two-dimensional analysis of these airfoils. Three-dimensional optimisn involved representation of the rotor as a simplified model and use of the Blade Element Momentum(BEM) method for analysis. an existimg turbine blade, on which the design specifications were modelled, was further used for comparative purposes throughout the project. The resulting blade design offers substantial improvements on the reference design. The application of optimisation methods has successfully aided the creation of a wind turbine blade with consistent peak performance over a range of design prints.
An affordable robotic-assisted rehabilitation device for the treatment of stroke and spinal cord injury.
(Stellenbosch : Stellenbosch University, 2018-03) Basson, Ariel; Muller, Jacobus Hendrik; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
ENGLISH ABSTRACT: Please refer to full text for abstract
Aiming strategies for small central receiver systems
(Stellenbosch : Stellenbosch University, 2015-03) Grobler, Annemarie; Gauche, Paul; Smit, Willie; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
ENGLISH ABSTRACT: Concentrating solar power as a sustainable energy technology is considered favourable in South Africa due to the high solar resource and the integration possibilities with the current electricity grid. Considering the various concentrating solar power technologies, the central receiver system is thought to be one of the most promising due to its high capacity factor and cost-efficient thermal storage capabilities. These thermal systems are able to reach high temperatures (more than 1000°C have been shown), and to obtain such temperatures, a high solar flux is required. This is achievable by aiming all of the heliostats at the centre of the target. High flux gradients over the receiver surface area and between the outer and inner surfaces of the receiver material can exist. These thermal gradients account for differences in temperatures on the receiver which result in thermal stresses leading to elastic and potentially plastic deformation of the material. To eradicate the thermal stresses, the aim points of the heliostats can be managed such that the flux density distribution over the receiver aperture is decreased and homogenised. The primary objective of this thesis is to develop an aiming strategy specifically for small experimental heliostat fields. To reach this objective, a simulation platform was developed to model any heliostat field and receiver, and an analysis was conducted to compare analytical flux prediction methods to ray tracing. At high incidence angles of between 30° and 60°, the standard deviations of the circular Gaussian flux approximation methods were found to differ between approximately 10 % and 30 % from the ray traced results. A novel method, the Gaussian mixture model, was suggested and deviated less than 4 % from the ray traced results when considering the standard deviation of the flux profile. Two basic aiming strategies were developed using the Tabu search and Genetic algorithm optimisation methods. These two strategies make use of approximate method of flux prediction. Experiments were conducted to investigate static aiming strategies on physical systems and to identify factors that could have an effect on the experimental results. Finally a method of implementing the aiming strategy on a dynamic system was proposed. By implementing both optimisation methods to complement each other, a new aiming strategy was developed that proved to provide better homogenisation of the flux distribution than either of the two methods alone. The accuracy of the final predicted flux distribution was improved by using the Gaussian mixture model as the flux distribution approximation method.
Air turbine design study for a wave energy conversion system
(Stellenbosch : University of Stellenbosch, 2010-03) Ackerman, Paul Henry; Von Backstrom, T. W.; Van Niekerk, J. L.; University of Stellenbosch. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
Air-cooled condenser steam flow distribution and related dephlegmator design considerations
(Stellenbosch : Stellenbosch University, 2013-12) Owen, Michael Trevor Foxwell; Kroger, D. G.; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
ENGLISH ABSTRACT: The steam-side side operation of a practical air-cooled steam condenser is investigated using a combination of CFD, numerical, analytical and experimental methods. Particular attention is directed towards the vapor flow distribution in the primary condensers and dephlegmator performance. Analysis of the vapor flow in the distributing manifold, connecting the steam turbine exhaust to the air-cooled heat exchangers, highlights the importance of careful design of the guide vanes in the manifold bends and junctions. Improved guide vane design and configuration can reduce the steam-side pressure drop over the manifold and improve the vapor flow distribution, which may be beneficial to condenser operation. The vapor flow in the primary condensers is shown to exhibit a non-uniform distribution amongst the heat exchanger tubes. The vapor flow distribution is strongly linked to the distribution of tube inlet loss coefficients through the heat exchanger bundles. The non-uniform flow distribution places an additional demand on dephlegmator performance, over and above the demands of row effects in the case of multi-row primary condenser bundles. Row effects are shown to account for as much as 70 % of available dephlegmator capacity in this case. Simultaneously, inlet loss coefficient distributions can account for up to 30 % of dephlegmator capacity. In some situations then, the dephlegmator is fully utilized under ideal operating conditions and there is no margin of safety to cope with non-ideal operation of the primary condensers. The upstream regions of the primary condensers are therefore exposed to a high risk of undesirable noncondensable gas accumulation. Reduced dephlegmator capacity due to insufficient ejector performance may further compound this problem. Single-row primary condenser bundles eliminate row effects and thereby significantly reduce the demands on dephlegmator performance. The use of such bundles in the dephlegmator would also measurably reduce ejector loading. In light of the findings of this study, it is recommended that single-row bundles be considered as the primary option for future air-cooled condenser applications. A hybrid (dry/wet) dephlegmator concept is analysed and shown to be able to provide measurably enhanced dephlegmator performance when operating in wet mode, while consuming only a small amount of water. The enhanced dephlegmator cooling translates to an increase in total air-cooled condenser capacity of up to 30 % at high ambient temperatures in this case. The benefit of this enhanced cooling capacity to steam turbine output may be significant. The hybrid dephlegmator concept therefore offers a simple, cost-effective and sustainable solution to the issue of reduced air-cooled condenser performance during hot periods. Careful design of the first and second stage bundle configurations in the hybrid dephlegmator is necessary to avoid flooding in the first stage during wet operation of the second. Furthermore, the slightly poorer dry-operation performance of the hybrid dephlegmator results in increased risk of non-condensable gas accumulation in multi-row primary condensers. Again, single-row primary condenser bundles would lay rest to such concerns.
Air-cooled heat exchangers and cooling towers : thermal-flow performance evaluation and design
(Stellenbosch : Stellenbosch University, 2004-12) Kroger, Detlev G.; Von Backstrom, T. W.; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
ENGLISH ABSTRACT: During the last 30 years I have been involved in the theory and practice of thermal engineering and in particular, in the areas of air-cooled heat exchangers and cooling towers for the power, refrigeration, process and petrochemical industries in South Africa and internationally. During this period, I have authored and co-authored more than 120 papers that were published in technical journals or presented at conferences nationally or internationally. Most of these papers are included in a manuscript entitled "Air-cooled Heat Exchangers and Cooling Towers", in which Ipresent a systematic approach to the thermal performance evaluation and design of industrial air-cooled heat exchangers and cooling towers. This original publication also includes the relevant practice applicable to the design of cooling systems, based on my experience as a consultant to industry. Design offices throughout the world presently follow our design methods, or at least employ many of our research results. Our work has furthermore contributed to the development of improved cooling system designs (e.g. new dephlegmator header designs), components (e.g. single-row flattened finned tubes) and product improvement and quality control (e.g. performance testing and measurement of thermal contact resistance between fin and tube during production). Many of our research findings have found application in the modification of existing cooling systems. The manuscript has also been used as reference work during the presentation of short courses to practising engineers and consultants in industry and to engineering graduates at the University of Stellenbosch. A two-volume edition of this manuscript was published by PennWell Corp., Tulsa, Oklahoma, USA in 2004.
An algorithm for fast optimal Latin hypercube design of experiments
(Wiley-Blackwell, 2010-04) Viana, Felipe A. C.; Venter, Gerhard; Balabanov, Vladimir
This paper presents the translational propagation algorithm, a new method for obtaining optimal or near optimal Latin hypercube designs (LHDs) without using formal optimization. The procedure requires minimal computational effort with results virtually provided in real time. The algorithm exploits patterns of point locations for optimal LHDs based on the ɸp criterion (a variation of the maximum distance criterion). Small building blocks, consisting of one or more points each, are used to recreate these patterns by simple translation in the hyperspace. Monte Carlo simulations were used to evaluate the performance of the new algorithm for different design configurations where both the dimensionality and the point density were studied. The proposed algorithm was also compared against three formal optimization approaches (namely random search, genetic algorithm, and enhanced stochastic evolutionary algorithm). It was found that (i) the distribution of the ɸp values tends to lower values as the dimensionality is increased and (ii) the proposed translational propagation algorithm represents a computationally attractive strategy to obtain near optimum LHDs up to medium dimensions.
Alternative methods of material handling within a reconfigurable manufacturing station.
(Stellenbosch : Stellenbosch University, 2017-03) Deacon, Matthew Marc; Basson, A. H.; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
ENGLISH ABSTRACT: This thesis contributes to evaluating methods of material handling within a reconfigurable manufacturing station, as alternative to a six degree of freedom articulated robot arm. This research follows the design process of formulating the design requirements, considering different concepts and evaluating them, designing a selected concept in detail, validating the concept using test data and then applying the concept to a broader application. A few material handling methods are briefly considered before focusing on the use of a Cartesian robot. Different configurations of a Cartesian robot were considered. As part of the design analysis, a model was developed which allows for the input of various station parameters and provides an estimate of the station’s throughput and cost. This estimation model was implemented in MathCAD and split into two parts: a throughput estimate and a cost estimate. The inputs into the model are the process module configuration and the target kinematics. The model includes load and force calculations for each axis and component selection, as an input to the cost estimate. A control system was developed, based on the PROSA architecture and implemented in C#. The design and implementation of this control system is discussed in this thesis. To be able to validate the research results, a case study is used as an example implementation of the material handling method. However, the design is not limited to the case study, but rather provides a model for any process station with similar transport requirements. The model was validated using a test setup in the Automation Laboratory that uses Festo components. The model therefore only provides for Festo components at this stage, but can easily be expanded upon if other manufacturers are to be considered. After the model was validated, it was applied to the case study, including drive selection, to provide an estimate throughput and cost. These estimates are then compared to previous research that used a six degree of freedom articulated arm robot for a similar case. Other applications, different from the case study, of the model are also discussed.
Analysing the performance of a compressor impeller for a micro gas turbine
(Stellenbosch : Stellenbosch University, 2019-04) Bindeman, Marco; Van der Spuy, S. J.; Von Backstrom, T. W.; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering (CRSES)
ENGLISH ABSTRACT: This project sets out to numerically evaluate the performance of micro gas turbine (MGT) compressor impellers and to improve the 1-Dimensional (1-D) mean-line code developed for the in-house analysis of these impellers. The objective for the improvement of the code is to accurately predict the performance of both radial flow and mixed-flow impellers. The possible applications for MGTs are numerous. They find specific application for the propulsion of unmanned aerial vehicles (UAVs). Mixed-flow compressors offer the opportunity to reduce the frontal area of a MGT engine while maintaining a high pressure ratio and ensuring a high thrust-to-weight ratio. The use of mixed-flow impellers in MGTs are thus attractive. Although detailed aerodynamic design is normally based on two- and three-dimensional viscous flow analysis, 1-D analysis with empirical work input and loss models is the basis for most aerodynamic performance analyses. Using 1-D mean-line flow analyses also allows the researcher to analyse multiple geometries in a short time span, while only analysing the best performing geometries with 3-D Computational Fluid Dynamics (CFD). Two areas of the mean-line code were identified for improvement. A new slip factor formulation taking both radial and axial flow components into account was implemented. Secondly, an alternative location for the inter-blade throat area was proposed, considering the area between a main blade and splitter blade, as opposed to the area close to the inducer section which is effectively between the main blades. The code was adapted to calculate the throat parameters for the alternative location and two iterations. of the code were subsequently created. The first employing the new slip factor and the second employing both the new slip factor and an alternative throat location. Three diferent impellers, of which one impeller is a mixed-flow impeller, were analysed using the adapted mean-line code and the results were validated with 3- dimensional CFD. The newly adapted 1-D mean-line code was found to predict the performance of the mixed-flow impeller reasonably well. The mean-line code over predicted both the pressure ratio and isentropic efficiency (total-to-total) by 1.6% and 2.8% respectively, while also predicting a larger operating range. The pressure ratio of the centrifugal impellers was under predicted on average by 15%, while the the isentropic efficiency was predicted within 3%. It was however found that a blade outlet angle of 90 adversely affected the performance prediction of the code.
The analysis and optimization of an axial compressor
(Stellenbosch : Stellenbosch University, 2015-12) Hamman, Richard Alan; Venter, Gerhard; Van der Spuy, Johan; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
ENGLISH ABSTRACT: Axial compressors are widely used in a variety of contexts. When compared to centrifugal compressors, axial compressors offer higher pressure ratios and efficiencies. Due to the complex relationship between blade shape and compressor performance, as well as the sensitivity of axial compressors to massflow rates, the design of an axial compressor is a challenging problem. These design difficulties can be circumvented using numerical design optimization. In this work, meta-model based design optimization (MBDO), a variant of numerical design optimization, is used to develop replacement blades for a low speed axial compressor. Two numerical models were developed: a low fidelity, computationally inexpensive single stage model and a high fidelity, computationally expensive three stage model. For reasons of computational cost, the single stage model was used to evaluate the objective function in the optimization process. An optimized blade design was developed, which delivered a 9:83% increase in pressure coefficient over the original design, when evaluated with the single stage model. This increase was not sustained when evaluating the optimized design with the three stage model. After investigation, the cause was found to be a high incidence angle near the hub and shroud, just outside the range in which incidence angle was constrained in the design problem. To compensate for this, the blade angles were manually adjusted, in order to lower the incidence angle. The adjusted blades delivered an increase of 8:54% over the original design, when evaluated with the three stage model.
The Analysis of an organic rankine cycle for smaller concentrated solar powered systems.
(Stellenbosch : Stellenbosch University, 2018-12) Karsten, Louis; Dinter, Frank; Hoffmann, Jaap; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
ENGLISH ABSTRACT: Small-scale energy consumers (500 kWe – 5 MWe), that are situated in off-grid areas are often left reliant on fossil fuels (like diesel generators) to meet their energy needs. The International Energy Association (IEA) however attempts to decarbonise the entire energy system and has set certain goals for the renewable energy sector. Most renewable energy sources offer only intermitted power solutions for small-scale off-grid applications and storing electrical energy for this scale becomes expensive. Concentrated solar power (CSP) can offer a non-intermitted solution by having the added benefit of thermal energy storage (TES). However, the critical barrier to the widespread usage of small-scale CSP is the lack of optimised and economically competitive technology. Steam Rankine cycles are typically integrated with CSP in large-scale applications but the thermodynamic properties of steam however prohibit water being used as suitable working fluid in lower temperature and lower power output applications. The aim of this thesis is therefore to determine whether the integration of an organic Rankine cycle (ORC), with a smaller CSP system can result in a feasible energy solution for off-grid applications. The first step taken was to determine the technical feasibility of solar integrated organic Rankine cycle (SORC) technology. It was proven feasible by the operation of existing small-scale SORC plants. ORC’s and CSP as separate types of technology are being used in various industries. The integration of CSP with an ORC is however considered an immature technology. A small-scale application in the higher DNI region of South Africa was identified to use as case study. Black Mountain mine near the town Aggeneys was selected by using a multi criteria decision analysis tool. Even though Black Mountain mine is grid-connected, it is still a viable case study to analyse whether an SORC can be a feasible solution for a mine. In proving so, the proposition then exists to use a SORC for future mining developments in off-grid areas. A SORC was theoretically analysed by looking at the solar field, TES and power block separately. The theory developed was then combined to create a model for a SORC. The simulation was conducted on MatLab and the design point was resultantly determined at a plant efficiency of 12.8 % and a turbine inlet pressure and evaporating temperature of 2858.8 kPa and 186 °C respectively. The simulation was then expanded to run over a period of one year and a maximum capacity factor of 83 % was recorded. The lowest achievable levelised cost of electricity (LCOE) was 16.7 $c/kWh at a solar multiple (SM) of 1.7 and TES size of 6 hours. The conclusion was reached that SORC’s are economically competitive with diesel generators but cannot solely meet the required energy demand and must therefore utilise auxiliary energy sources.

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