1,720,973 research outputs found
Development of a multi-purpose twin-screw extruder
No full textThesis (M.Ing. (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2009.The extrusion market of South Africa has a smaller demand for products than
most of the First World countries in which mainly single process twin-screw
extruders are used. This leaves a void for the development for a multi-purpose
twin-screw extruder. This will enable companies to manufacture a greater
diversity of products with one machine, not only in South Africa, but in the rest of
Africa as well.
Africa has one of the biggest rates of poverty and famine in the world . The
famine crisis in Africa is mainly due to the lack of food with a high nutritional
value. The conventional cooking method currently used, that of preparing food
over an open fire, causes the loss of most of the vitamins and essential
nutritional values in the food .
Extrusion is the process whereby high quality food is manufactured by using
simple raw materials. The raw material goes through a process of heating, mixing
and shearing to produce a high quality end product.
The main disadvantage of extruders currently available on the market is their
cost. Extruders are currently manufactured in the First World countries. This
causes that the machines are too expensive and unaffordable for most of the
African markets. This creates the opportunity for an affordable extruder to be
manufactured and maintained in Africa.
This study provides an introduction to extrusion. Chapter 2 contains a literature
study on the various extruders and their respective available sub-components. It
also discusses the differences between different extruders. In Chapter 3 a
generic approach to the design and manufacturing of an extruder unit is
formulated and discussed. Chapter 4 is dedicated to the explanation of basic
screw geometry and designs. Chapter 5 contains case studies on two types of
barrels designed and tested during this study. It also provides the best choices of
designs for various components. In Chapter 6, a case study of a fully operational
twin-screw food extruder is discussed. This extruder was manufactured in Africa,
and maintained in Africa. Recommendations and conclusions of this study are
summarized in Chapter 7.Master
An integrated approach to implement and sustain energy efficiency and greenhouse gas mitigation in South Africa
Full text linkThesis (Ph.D. (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2005.South Africa is one of the most industrialised countries in Africa. The country is extremely
energy-intensive for a number of reasons, which include a lack of awareness of energy
efficiency and demand-side management (DSM), the low cost of electricity, the absence of energy conservation regulations and standards, lack of driving force, limited experience and track record of energy service companies as well as the financial viability of projects. It is anticipated that South Africa will have run out of excess capacity by 2007, a fact that is forcing Eskom to take action to reduce peak demand by means of certain initiatives. This in turn
has led to electricity becoming more expensive during certain periods of the day. The result is an increasing need for energy efficiency and demand-side management by end users, regulating bodies and Government. It is, however, critical that projects, implemented under the above-mentioned barriers, deliver impacts that can be sustained over time, otherwise the
benefits would only be short-term and of no value to the stakeholders. Measurement and verification are important and necessary aspects of any energy-efficiency, demand-side management or dean development mechanism (CDM) project. It allows for the
objective quantification of the project's impacts by a third party, thus lending credibility to the project outcomes. Its greatest benefit, if conducted correctly, is the increased sustainability of projects and their impacts. Energy efficiency also makes a direct contribution to the reduction of greenhouse gas emissions. The fact that South Africa is able to participate in greenhouse gas (GHG) mitigation through the clean development mechanism offers an opportunity to increase the financial viability of energy-efficiency projects, whilst achieving GHG mitigation. Once again measurement and verification would be critical to the success and sustainability of these energy-related greenhouse gas mitigation projects over time. A need was subsequently identified to develop an integrated approach that provides a clear methodology that could be applied to accurately quantify and verify the savings and impacts that emanate from energy efficiency, demand-side management and greenhouse gas mitigation projects. If applied correctly, the integrated approach would help with the sustainable implementation of energy efficiency, demand-side management and greenhouse gas mitigation projects in South Africa. This study proposes such an integrated approach that provides a methodology that builds on
international protocols. It provides a flexible, clear, accurate and transparent methodology to assist in the sustainable implementation of projects. The integrated methodology has been accepted as the standard by which South Africa's parastatal utility, Eskom, prefers implementation together with measurement and verification on their DSM-funded projects. The approach has proved to be flexible, transparent and replicable.
It has facilitated better project implementation on a number of occasions and proved to provide accurate and verified results to all the stakeholders, which include the demand impact during each time-of-use (TOU) period, the impact on electricity consumption, the impact on the monthly
and annual electricity accounts of end users and the environmental impacts such as GHG
emissions and water consumption.Doctora
Development, characterisation and verification of an integrated design tool for a power source of a soya business unit
No full textThesis (M.Ing. (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2008.Selecting a suitable power source, during the design process, for a stand-alone soya business unit is challenging and complex. Especially with the aim of optimizing electrical and thermal energy, as well as minimizing the life cycle cost. During the design and development of a soya business unit it was realized that a design tool is needed to assist with the decision making process when selecting a power source. Waste heat can be recovered from either or both the exhaust gas and cooling system of the power source and can be utilized in the soya process. Research of available literature revealed no design tool to assist with the decision making process of the stand-alone business unit and consequently lead to this study. This dissertation presents different possible power sources that could be utilized in supplying energy to the business unit, as well as design tools available. Advantages and disadvantages of the different power sources are discussed. The shortfalls of a number of the available design tools are also discussed. A diesel generator set was selected as the preferred power source for the business unit. Criteria for this selection included the price per kWhe generated, the ease of maintenance, the availability of the diesel generators in rural areas and the availability of diesel as a fuel. The diesel engine was characterized through experimental work for a more in depth understanding of the energy profile of the engine at part load conditions. These results were used as guidelines in the development of the design tool. The design tool was developed with the aim of being user friendly and versatile. The time intervals of the required load of the business unit are flexible. Different types of power sources and fuels can be used within the design tool. User defined heat exchangers are utilized to calculate the possible heat recovery from the power source. The design tool matches the available energy of different power sources at part load conditions with the required load profile of the soya business unit. It then eliminates power sources that would not be able to deliver the minimum required energy. The running cost is calculated for each of the remaining power sources and the power source with the minimum annualized cost, which includes capital cost, maintenance cost and fuel cost, is suggested.
The design tool was verified against a base load condition of the soya business unit and the suggested power source showed a saving of 31,4% in electrical energy, an increased overall efficiency of 24,9% and a saving in annualized cost of 27,3%. The design tool can be used to optimize specific components and design options within a combined heat and power system. Sensitivity analysis can be performed with the design tool to determine various influences on the designed system.Master
The use of neural networks to determine the long-term impact of demand side management
Full text linkThesis (M.Ing. (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2004.Eskom, South Africa national electricity provider, estimates that in the year 2006
South Africa will experience a capacity shortage. One way to address this problem is through the implementation of Demand-Side Management (DSM) in various sectors, ranging from the commercial to the industrial. For Eskom to succeed in their vision of implementing DSM, a tool has to be developed that can illustrate the long-term impact of various DSM options for a region. This tool could then be used to illustrate the various role players the advantages of implementing DSM. The purpose of this study was to test if Neural Networks (NN's) can be applied in the construction of an hourly baseline for a region. This baseline could then be used to illustrate the Long-term impact of various DSM options. In this study a technique was developed using hourly data to construct a baseline model for the calculation of the long-term impact of DSM. This technique was then tested and evaluated on a case study. To achieve this goal, an investigation was launched to determine which inputs
have an influence on the energy use of a region. The different variables that
influence the neural network topology were also investigated. This information was then used to develop a technique that models the energy use of the area. To determine accuracy of the simulated energy use, a verification procedure was developed based on an internationally accepted verification model, using data the NN did not "learn" on. Sufficient accurate results were obtained using the defined indices. Thus NN can be used to model the energy use of a region. The major disadvantage of this technique is that hourly data for the whole year was used to train the model on. The question arises into just how much information is needed to model the NN. Subsequently an investigation was launched to determine the minimum data set needed to model the energy use. It was found that a full factorial data set is the minimum set of data that a NN needs to train on. In choosing this data, a study has to be conducted on previous data to determine exactly when the best combination could be obtained. The results indicated that the data could not be minimised due to the configuration of input data. For this study, the months of the year were encoded. This aided the NN in learning the relationship between the various inputs and the energy use. It was found that this is a crucial step in aiding the NN. Thus the NN could not simulate accurate enough results without the encoded data. This results that the number of months cannot be minimised with the current technique used. The model then can be used to evaluate different DSM options by subtracting the
hourly differences from the baseline. This information is then used to evaluate the
options using various indices. The indices included monthly energy use, maximum demand, the energy use during the various time of use periods and the impact of greenhouse gasses. The concept was illustrated by an actual case study. The use of NN for modelling the baseline for the forecasting of the long-term impact of DSM is considerable faster than current techniques with a timesaving element of up to 90 %. The use of NN is thus a viable technique to model the baseline. The results indicate that NN can successfully be used for cases with a high diversity in the
load, and with little or no knowledge of the underlying systems.Master
A methodology to identify, quantify and verify the cost benefits of energy and process improvements on a ferro-metal production plant
Full text linkThesis (M.Ing. (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2005.South Africa has an energy intensive economy with a high dependency on local mining and base metal industries. Furnace plants, which form part of the metal industry, are energy intensive as a result of the actual melting processes which require a great amount of energy. The high electricity and energy usage translates into high operating costs for these plants which in turn reduces the profitability of the plants.
South Africa's ferrochrome industry supplies about 60% of the world's ferrochrome demand and holds around 80% of the world's chrome reserves. This makes South Africa one of the key ferrochrome producers in the world. There is however a need to reduce the cost of production of these plants to ensure competitiveness and profitability within the world market. This dissertation starts by providing an introduction to the problem and then defining the objective and scope of the study. The need for a methodology to identify, quantify and
verify energy and process improvement opportunities in Ferro-metal production plants is highlighted. This need exists because there is a lack of adequate methods for an integrated approach. Three main barriers to energy projects were identified in this study, namely: institutional, technological and financial barriers. The opportunities for energy management and process improvements are investigated, including opportunities to overcome the barriers identified in the study. A methodology, which is developed to incorporate both increased production and energy efficiency scenarios, is then provided. The methodology is firstly aimed at identifying possible opportunities and then quantifying them in terms of financial benefits for the plant. This is necessary to establish whether it will be worth while to explore the opportunities further. Benchmarking is also included in the methodology as this helps to track the performance of the plant over time. A process was developed to enable accurate measurement and verification of energy
related projects in order to evaluate the effectiveness or success of implemented projects. This process is necessary to enhance the credibility of energy related projects by providing an accurate and transparent evaluation of the project's performance. This in turn provides the stakeholders with invaluable information regarding their investments in energy projects. The developed methodology was applied to a case study of a Ferro-metal production plant in order to evaluate the methodology. The case study revealed that the methodology can successfully identify and quantify potential opportunities. The no-cost and low-cost opportunities identified, showed a maximum possible annual saving of up to R925,500 depending on the specific options implemented. Load control opportunities in peak periods revealed an estimated annual cost saving of up to R3,767,400 per year. A possible estimated annual energy consumption saving worth R22,629,900 was identified by a Cusum analysis. This analysis was also used to examine the benefit of a production
gain instead of energy efficiency which showed a possible increase in production of
60,300 tomes per year. The measurement and verification process was then used to determine the impact that an upgrade of a furnace, aimed at increasing production, had on the actual performance of the furnace. The verification process showed an increase in production worth over R3million and an energy saving of over R1 million as a direct result of the upgrade. The process showed that the upgrade did indeed achieve a production gain and therefore the upgrade is considered to be a success.Master
Development of a twin screw extruder with an integrated cooling roller system
Full text linkThesis (MIng (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2012.The Center for Advanced Manufacturing at the Potchefstroom campus of the North West University aims to develop a twin screw extruder that is able to process powder coating resin. The facility has thus far produced various components and sub systems for local and international manufacturers of extrusion products. The research presented in this thesis aims to both develop a twin screw extruder with an
integrated cooling roller system and to investigate of the performance of a twin screw extruder. The development of a twin screw extruder consists of the selection of the drive section of the extruder, the complete design of a twin screw extruder gearbox, the investigation and design of
a suitable barrel for the manufacturing of powder coatings as well as the development of a unique cooling roller unit for the forming of the processed product when exiting the extruder. The extruder was manufactured from the designed components and systems. It was found on
further testing that it was capable of producing a powder coating resin of good quality. In order to evaluate the performance of an extruder, the transfer of energy through the extruder needs to be understood. Furthermore it is necessary to understand the theory behind each type
of energy being consumed by the extruder, as well as the factors influencing the usage of that energy. The theories investigated were verified in practice by measuring the energy consumption of a twin screw extruder operated under various conditions. These tests provided a correlation between the consumption of mechanical and electrical energy. The results gave an indication of the effectiveness of the screw configuration of the processing section of the extruder, making it possible to determine how the configuration should be amended in order to improve the performance of the extruder. The two aims of the thesis were satisfactory completed. The developed twin screw extruder is able to manufacture powder coatings of good quality and the performance evaluation of a twin screw extruder was also successfully completed. It enables the manufacturer to measure and
evaluate the energy consumption of the process in order to improve the performance of the extruder.Master
The development of a control system for gravimetric feeding of a twin screw extruder
Full text linkThesis (MIng (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2012.The control of gravimetric feeding is generally done by control systems which utilize feedback control. The main problem with these control systems is that they generally revert to volumetric feeding during the refilling cycle. Furthermore the control system software is proprietary information and therefore not in the public sector and also very expensive. The main purpose of the study was therefore to review the basics of gravimetric feeding and to apply the knowledge in the design of a control system with applicable software for gravimetric feeding which is not affected by material bulk density variations, targeting food
extrusion applications. It is also aimed at producing a test bench to test the control system and the developed software. The developed control system is a programmable logic controller (PLC) based control system. This allows for the control system to be easily integrated into any PLC controlled
twin screw extruder. The control system was extensively tested to verify the developed
gravimetric control algorithms. The results from the experimental tests illustrated that a fully functional gravimetric feeding system had been developed. Most importantly also that the volumetric characteristics of a material can be used, to assist a PI–controlled gravimetric feeding system in both the feeding cycle and the refilling cycle.Master
Effective control of a low-cost twin-screw food extruder
Full text linkThesis (M.Ing. (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2007.Africa has one of the largest rates of poverty and famine. The hunger crisis in
Africa is due to poverty as well as the little availability of nutritional food. Many locally grown crops are available in Africa but are not used to their fullest potential.
There is a huge demand for proper food production methods. The food crops
in Africa are still cooked in traditional methods by using wood and coal. This
method of cooking produces food of very low quality and nutritional value. The
reason for this is the over-cooking of food, breaking down proteins and other
nutritional components. Extrusion is the process whereby high quality food is manufactured by using simple raw materials. Food extrusion is a process in which a food material is forced to flow, under one or more conditions of simultaneous mixing, heating and shearing, through a die, which is designed to form and/or puff-dry the
ingredients. The main disadvantage of extruders available on the market today is the cost per unit. Extruders are currently manufactured in the USA, Europe and the
Far East. These machines are very expensive and unaffordable for the
African market. The first barrier to overcome is to find a high quality extruder that is affordable for the African economy. This dissertation will provide an introduction to extrusion technology and the application of an effective control system. Chapter 2 contains a literature
study of the types of extruders available and discusses the different components of the extrusion process of the co-rotating twin-screw food extruder. The different needs and barriers for developing extrusion technology in developing countries will also be discussed. In Chapter 3 we will discuss the different components that form a control system and the various control modes that can be implemented to improve the control system, reduce offset and enhance stability. Chapter 4 discusses the purpose of each component of the extrusion process, PLC implementation and control-philosophy of each component. Chapter 5 involves a short case study of a corn grit extrusion process. In this chapter we will discuss three basic stages in the extrusion process and the corresponding input parameters for each stage. The relation between extruder screw speed, feeder screw and percentage of water injected into the extruder process, will be investigated. Recommendations and conclusions of this study will be summarised in Chapter 6.Master
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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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