O objetivo deste trabalho é realizar uma análise paramétrica do processo de desumidificação de ar comprimido em trocadores de calor compactos com superfícies intensificadoras do tipo aletas deslocadas. A umidade contida no ar comprimido precisa ser retirada do sistema para evitar a formação de condensado nas linhas de distribuição, nos atuadores ou nos dispositivos finais. Utiliza-se o processo de desumidificação por resfriamento onde a temperatura do ar é diminuída até alcançar o ponto de orvalho, resultando em formação de condensado. O desumidificador é constituído por dois trocadores de calor (recuperador e evaporador), sendo cada um deles dividido em duas regiões. Realizou-se a modelagem do processo de transferência de calor para cada um dos trocadores. Utilizou-se o método do potencial de entalpias para determinar os coeficientes globais de transferência de calor de cada trocador. Para a realização da simulação numérica, foi implementado um programa utilizando como ferramenta computacional o programa “Engineering Equation Solver" (EES). O estudo foi feito variando-se os parâmetros geométricos do trocador de calor e verificando sua influência nos coeficientes de transferência de calor, nos calores trocados e nas condições de saída do ar. Primeiramente, cada parâmetro foi analisado individualmente e depois com algumas combinações. Concluiu-se que as dimensões das aletas no recuperador e os comprimentos do recuperador e do evaporador são os parâmetros que mais influenciam nas propriedades do ar comprimido na saída do desumidificador. / The objective of this work is to conduct a parametric analysis of the dehumidification process of compressed air in compact heat exchangers with Offset Strip Fins. The humidity carried by the compressed air should be removed from the system to prevent the condensation in the distribution lines and in the actuators or the final devices. The dehumidification process by cooling occurs when the temperature of the air is diminished until reaching the dew point, resulting in condensation of water vapor. The dehumidifier is constituted by two heat exchangers (recuperator and evaporator), each one of them being divided in two regions. A modeling of the heat and mass transfer process for each heat exchangers, was performed. The enthalpy driving potential method was used to determine the overall heat transfer coefficients of each heat exchanger. The numerical simulation was implemented by using the computational software "Engineering Equation Solver"(EES). The study was made varying the geometric parameters of the heat exchanger and verifying its influences on the heat transfer coefficients, the heat transfer and pressure drop, and the air exit conditions. First, each parameter was analyzed individually and then with some combinations. Its was concluded that the fins dimensions in both regions of the lengths of the recuperator and the evaporator are the parameters that have larger influence on the exit compressed air properties.

O torneamento radial é um processo de usinagem usado na indústria metal mecânica para o corte de peças, abertura de canais ou faceamento. Esta pode ser considerada uma operação crítica devido à forma geométrica da ferramenta e aos movimentos de corte. Isto gera a necessidade de aplicação de fluidos de corte, normalmente em abundância, na região de corte. Considerando como funções destes fluidos o arrefecimento, a lubrificação e a expulsão do cavaco, sua aplicação durante essa operação é de suma importância. Várias pesquisas visam restringir o uso de tais fluidos, seja por critérios econômicos, ambientais ou sanitários. Neste contexto, o uso da técnica de mínima quantidade de lubrificante (MQL) vem ganhando espaço nos meios produtivos. Embora seja aplicada há anos em diferentes processos de usinagem, existem poucos relatos sobre a aplicação de MQL em operações de torneamento radial; no mesmo seguimento, a aplicação de ar comprimido (ACO) vai ao encontro do conceito de usinagem ambientalmente amigável. Assim, este trabalho apresenta uma análise comparativa na aplicação de lubrificantes em abundância (ABD), em MQL e o uso de ACO no torneamento radial do aço SAE 1045 para diferentes condições de corte. Na investigação, foram consideradas as forças geradas durante o processo, as rugosidades e o desvio dimensional das superfícies usinadas, e o desgaste da ferramenta. Observou-se que os esforços gerados com MQL foram similares ou inferiores aos gerados com ABD. A mesma tendência foi observada no perfil de rugosidade, predominando valores inferiores. O MQL possibilita um corte mais estável durante a vida da ferramenta, reduzindo a ocorrência de desgaste e prolongando sua vida útil, minimiza a oscilação axial e a flexão da ferramenta, reduz as rugosidades e minimiza os desvios dimensionais. Assim, pode-se afirmar que a aplicação da técnica por MQL é viável no torneamento radial do aço SAE 1045. / Radial turning is a machining process used in the metalworking industry for parting off, grooving or facing operations. This can be considered a critical operation due to the geometric shape of the tool and the cutting movements. This generates the need for application of cutting fluids, usually in abundance, in the cutting region. Considering as functions of these fluids the cooling, lubrication and expulsion of the chip, their application during this operation is of paramount importance. Several researches aim to restrict the use of such fluids, either by economic, environmental or sanitary criteria. In this context, the use of the minimum quantity of lubricant (MQL) technique has been gaining ground in the productive media. Although it has been applied for years in different machining processes, there are few reports on the application of MQL in radial turning operations; at the same time, the application of compressed air (ACO) meets the concept of environmentally friendly machining. Thus, this work presents a comparative analysis on the application of abundant lubricants (ABD) in MQL and the use of ACO in radial turning of SAE 1045 steel for different cutting conditions. In the investigation, the forces generated during the process, the roughness and the dimensional deviation of the machined surfaces and the tool wear were considered. It was observed that the machining forces generated with MQL were similar or inferior to those generated with ABD. The same tendency was observed in the profile of roughness, predominating lower values. MQL enables a more stable cut during tool life, reducing the occurrence of wear and extending tool life, minimizes axial oscillation and tool flexion, reduces roughness and minimizes dimensional deviations. Thus, it can be indicated that the application of the technique by MQL is feasible in the radial turning of SAE 1045 steel.

As energy systems shift away from fossil-fuel based electricity, the non-dispatchability of renewable energy converters (REC) continue to stress the grid infrastructure and conventional thermal generating units. These hybrid electricity systems require energy storage systems to buffer the variabilities of electricity supply and demand. Regenerative air energy storage (RAES) is an emerging technology that shows promise to overcome the barriers of REC variability. RAES uses a novel compressor/expander that approaches isothermal operation by spraying water into the piston/cylinder to absorb/release heat. RAES can be sized for power and energy independently, and has a high round-trip efficiency that can be boosted using low grade waste heat. Because of its novelty, new numerical models are necessary to investigate the sizing and performance of RAES systems. In this thesis a numerical simulation tool is developed to allow flexible and intuitive analysis of a range of hybrid energy systems involving RAES.

The demand for electricity in South Africa has grown faster than the increase in generation capacity. However, it is expensive and time consuming to commission new power stations. Another approach is to reduce electricity demand through the implementation of energy efficiency projects. This alternative is usually less expensive. Compressed air on South African mines is a large electricity consumer with a reputation of wastage. This allows significant potential for electrical and financial savings. A typical mine compressed air system consists of multiple compressors at various locations, surface connection networks, underground distribution systems, thousands of users and leaks. The size, complexity and age of these systems provide a major challenge for electricity saving efforts. Simulating such an intricate system is difficult as it is nearly impossible to accurately gather all the required system parameters. Some initiatives focused on subsections of mine compressed air systems. This is not the best approach as changes to one subsection may adversely affect other systems. A new approach to simplify mine compressed air systems was developed to identify saving opportunities and to assess the true impact of saving efforts. This new approach enables easier system analysis than complex simulation models. Techniques to gather critical system information are also provided. A new implementation procedure was also developed to integrate different energy saving strategies for maximum savings. An electrical power saving of 109 MW was achieved through the implementation of the integrated approach on twenty-two mine compressed air systems. The savings is equivalent to a reduction of 0.96 TWh per annum that relates to a saving of 0.4% of South Africa’s total electricity consumption. Average compressor power consumption was reduced by 30%. The power consumption reduction relates to an estimated annual electricity cost saving of R315 million. A saving of 0.96 TWh per annum is equivalent to a carbon dioxide emission reduction of 0.98 million tonne. The implementation of the integrated approach could be applied to other industrial compressed air systems. A reduction in electricity consumption of 30% on all industrial compressed air systems has the potential to reduce global electricity demand by 267 TWh per annum. That is more than the total amount of electricity consumed in South Africa. / Thesis (PhD (Electrical Engineering))--North-West University, Potchefstroom Campus, 2013

In 2011 South Africa's main electricity supplier, Eskom, experienced a peak electricity demand of 89% of their total installed generation capacity. The high utilisation rate makes it difficult to perform essential maintenance on the system. Eskom implements Demand-Side Management (DSM) projects in various industries, in order to reduce the demand and to ensure sustainable electricity supply. The mining sector consumes 14.5% of the total amount of electricity generated by Eskom. Mine compressed air systems can consume as much as 40% of a mine's total electricity requirements. This makes mine compressed air systems an ideal target for DSM. Electricity load seems to be reduced, but many DSM savings are not sustained throughout the project lifetime. An existing project feedback method of a specific Energy Services Company (ESCo) includes the manual collection of data from the mines and manual generation of reports. These reports show energy savings of the DSM projects to help the ESCo and their clients to improve and sustain the performance of the projects. A great amount of man-hours is used which results in large time delays in the feedback-loop. In order to address this, the need for a new automatic feedback reporting system was identified. This study mainly focusses on the development and implementation of a new method to monitor DSM savings on mine compressed air systems. It includes the reliable collection of data from mines, processing and storing of the data in a central database and generating savings reports. This is done automatically on a daily basis. In order to complete the feedback-loop, the reports are verified and emailed to clients and ESCo personnel on a daily basis. The new reporting system is implemented at a number of mines. Four of these project implementations are used as case studies to measure and interpret the effectiveness and value of this system. It saves a significant amount of man-hours and proves to be of great value in the sustainability of DSM project savings. Both Eskom and mining companies benefit from the efficient monitoring of mine compressed air savings. / Thesis (MIng (Computer and Electronic Engineering))--North-West University, Potchefstroom Campus, 2013.

Growing demand for electricity forces suppliers to expand their generation capacity. Financing these expansion programmes results in electricity cost increases above inflation rates. By reducing electricity consumption, additional supply capacity is created at lower costs than the building of conventional power stations. Therefore, there is strong justification to reduce electricity consumption on the supplier and consumer side. The mining and industrial sectors of South Africa consumed approximately 43% of the total electricity supplied by Eskom during 2012. Approximately 10% of this electricity was used to produce compressed air. By reducing the electricity consumption of compressed air systems, operating costs are reduced. In turn this reduces the strain on the South African electricity network. Previous energy saving projects on mine compressed air systems realised savings that were not always sustainable. Savings deteriorated due to, amongst others, rapid employee turnover, improper training, lack of maintenance and system changes. There is therefore a need to improve projects that have already been implemented on mine compressed air systems. The continuous improvement of equipment (such as improved control valves) and the availability of newer technologies can be used to improve existing energy saving strategies. This study provides a solution to reduce the electricity consumption and operating costs of a deep level mine compressed air system. This was achieved by modernising and improving an existing underground compressed air saving strategy. This improvement resulted in a power saving of 1.15 MW; a saving equivalent to an annual cost saving of R4.16 million. It was found that the improved underground compressed air DSM project realised significant additional electrical energy savings. This resulted in ample cost savings to justify the implementation of the project improvements. It is recommended that opportunities to improve existing electrical energy saving projects on surface compressed air systems are investigated. / MIng (Mechanical Engineering), North-West University, Potchefstroom Campus, 2014

The demand for electricity in South Africa has grown faster than the increase in generation capacity. However, it is expensive and time consuming to commission new power stations. Another approach is to reduce electricity demand through the implementation of energy efficiency projects. This alternative is usually less expensive. Compressed air on South African mines is a large electricity consumer with a reputation of wastage. This allows significant potential for electrical and financial savings. A typical mine compressed air system consists of multiple compressors at various locations, surface connection networks, underground distribution systems, thousands of users and leaks. The size, complexity and age of these systems provide a major challenge for electricity saving efforts. Simulating such an intricate system is difficult as it is nearly impossible to accurately gather all the required system parameters. Some initiatives focused on subsections of mine compressed air systems. This is not the best approach as changes to one subsection may adversely affect other systems. A new approach to simplify mine compressed air systems was developed to identify saving opportunities and to assess the true impact of saving efforts. This new approach enables easier system analysis than complex simulation models. Techniques to gather critical system information are also provided. A new implementation procedure was also developed to integrate different energy saving strategies for maximum savings. An electrical power saving of 109 MW was achieved through the implementation of the integrated approach on twenty-two mine compressed air systems. The savings is equivalent to a reduction of 0.96 TWh per annum that relates to a saving of 0.4% of South Africa’s total electricity consumption. Average compressor power consumption was reduced by 30%. The power consumption reduction relates to an estimated annual electricity cost saving of R315 million. A saving of 0.96 TWh per annum is equivalent to a carbon dioxide emission reduction of 0.98 million tonne. The implementation of the integrated approach could be applied to other industrial compressed air systems. A reduction in electricity consumption of 30% on all industrial compressed air systems has the potential to reduce global electricity demand by 267 TWh per annum. That is more than the total amount of electricity consumed in South Africa. / Thesis (PhD (Electrical Engineering))--North-West University, Potchefstroom Campus, 2013

In 2011 South Africa's main electricity supplier, Eskom, experienced a peak electricity demand of 89% of their total installed generation capacity. The high utilisation rate makes it difficult to perform essential maintenance on the system. Eskom implements Demand-Side Management (DSM) projects in various industries, in order to reduce the demand and to ensure sustainable electricity supply. The mining sector consumes 14.5% of the total amount of electricity generated by Eskom. Mine compressed air systems can consume as much as 40% of a mine's total electricity requirements. This makes mine compressed air systems an ideal target for DSM. Electricity load seems to be reduced, but many DSM savings are not sustained throughout the project lifetime. An existing project feedback method of a specific Energy Services Company (ESCo) includes the manual collection of data from the mines and manual generation of reports. These reports show energy savings of the DSM projects to help the ESCo and their clients to improve and sustain the performance of the projects. A great amount of man-hours is used which results in large time delays in the feedback-loop. In order to address this, the need for a new automatic feedback reporting system was identified. This study mainly focusses on the development and implementation of a new method to monitor DSM savings on mine compressed air systems. It includes the reliable collection of data from mines, processing and storing of the data in a central database and generating savings reports. This is done automatically on a daily basis. In order to complete the feedback-loop, the reports are verified and emailed to clients and ESCo personnel on a daily basis. The new reporting system is implemented at a number of mines. Four of these project implementations are used as case studies to measure and interpret the effectiveness and value of this system. It saves a significant amount of man-hours and proves to be of great value in the sustainability of DSM project savings. Both Eskom and mining companies benefit from the efficient monitoring of mine compressed air savings. / Thesis (MIng (Computer and Electronic Engineering))--North-West University, Potchefstroom Campus, 2013.

Unreliable and unsustainable electricity supply has been experienced in South Africa since 2007. Eskom implemented Demand Side Management (DSM) as a short-term solution to alleviate this problem. Several compressed-air DSM projects were implemented to help reduce the strain on the electrical network. Compressed air is an integral part of production in deep-level mining, and is extensively utilised. Problems are encountered with the effective management and repairing of leaks, since the majority of mines have little to no procedures in place for leak management. Awareness of the condition of the compressed-air system and leaks needed to be created at management level in order to achieve the best results. The purpose of this study is to investigate the effect of proper leak management on compressed-air systems in the mining industry. Peak-clipping DSM projects implemented in the mining industry were used for evaluation of results. Contribution to the sustainability of compressed-air DSM projects savings through successful leak documentation was the prime focus of this study. This was achieved through the development of a Compressed Air Leakage Documentation System (CALDS). This entailed the electronic field-data capture and record keeping of field data, using rugged PDA devices suitable for the extreme environmental conditions encountered in deep-level mining. Report generation on the status of detected leaks created awareness of compressedair- system performance and leak-repair tracking at management level. Audible detection was sufficient for this study, since the focus was on the larger more-severe leaks. Leaks were expressed in monetary terms to indicate the severity. It was found that successful management of leaks could contribute to an increase of as much as 85% in project savings. The results also showed that creating awareness through documentation of leaks, and the effect this has on the system, resulted in regular repairing of these leaks. Sustainability of projects was maintained during an evaluation period of ten months, with projects achieving on average 125% of target savings. The study showed that effective reporting on compressed-air leaks resulted in increased system efficiency and sustainable DSM project savings. It was also seen that leak detection by outsourced companies did not necessarily result in financial savings. When the mine took responsibility for its own leak detection and repairs, significant savings were realised. / Thesis (M.Ing. (Electrical and Electronic Engineering))--North-West University, Potchefstroom Campus, 2011.

Demand Side Management (DSM) is one of the most viable and sustainable short term methods to address the shortfall in electricity generation in South Africa. This is because DSM projects can be implemented relatively quickly and inexpensively when compared with alternative generation options. This specifically applies to the mining industry. South African mines presently consume 15% of Eskom-generated electricity. Mine compressed air systems are some of the biggest users, consuming approximately 21% of mine electricity consumption. Electricity savings on compressed air systems are therefore important. With this study, various Energy Efficiency methods on compressed air systems were investigated. These methods include variable speed drives on compressor motors, temperature control of compressor discharge, minimising pressure drops in the air distribution systems, eliminating compressed air leaks, and optimising compressor selection and control. The most efficient strategies were identified, taking into account factors such as financial viability, sustainability, and ease of implementation. The best strategies were found to be the optimised control and selection of compressors, minimising compressed air leaks, and the optimal control of system pressure. These strategies were implemented and tested on large compressed air systems in gold and platinum mines. Savings of between 10% and 35% on the maximum demand of the systems were achieved. In present monetary terms this translates to as much as R108 million savings for the mines per year at the end of 2009 tariffs. If total mine compressed air electricity consumption can reduce by 30%, it will result in nearly a 1% reduction in total Eskom demand. This shows that mine compressed air savings can make a significant contribution to the drive for Energy Efficiency in South Africa. / Thesis (M.Ing. (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2010.