Thesis (doctoral)--Rijksuniversiteit te Groningen, 1995. / Summary in Dutch. Material type: Dissertations. Includes bibliographical references (p. 283-291).

The simple gas turbine engine Operates on the basic Joule-Brayton cycle and it is notorious for its poor thermal efficiency. Several modifications have been made to the simple cycle in order to increase its thermal efficiency but, within the thermal and mechanical stress constrains, the efficiency still ranges between 28 and 35%. However, higher values of energy utilisation efficiency have been claimed in recent years by using low grade heat from the engine exhaust either for district heating or for raising low pressure steam for chemical processes. Both applications are not very attractive in hot countries. The concept of using the low grade thermal energy from the gas turbine exhaust to raise steam in order to drive a steam turbine and generate additional electricity, i. e. the combined power and power or CPP plant would be more attractive in hot countries than the CHP plant. It was hypothesized that the operational parameters, hence the performance of the CPP plant, would depend on the allowable gas turbine entry temperature. Hence, the exhaust gas temperature could not be decided arbitrarily. This thesis deals with the performance of the gas turbine engine operating as a part of the combined power and power plant. In a CPP plant, the gas turbine does not only produce power but also the thermal energy that is required to operate the steam turbine plant at achievable thermal efficiency. The combined gas turbine-steam turbine cycles are thermodynamically analysed. A parametric study for different configurations of the combined gas-steam cycles has been carried out to show the influence of the main parameters on the CPP cycle performance. The parametric study was carried out using realistic values in view of the known constraints and taking into account any feasible future developments. The results of the parametric study show that the maximum CPP cycle efficiency would be at a point for which the gas turbine cycle would have neither its maximum efficiency nor its maximum specific work output. It has been shown that supplementary heating or gas turbine reheating would decrease the CPP cycle efficiency; hence, it could only be justified at low gas turbine inlet temperatures. Also it has been shown that although gas turbine intercooling would enhance the performance of the gas turbine cycle, it would have only a slight effect on the CPP cycle performance. A graphical method for studying operational compatibility, i.e. matching, between gas turbine components has been developed for a steady state or equilibrium operation. The author would like to submit that the graphical method offers a novel and easy to understand approach to the complex problem of component matching. It has been shown that matching conditions between the compressor and the turbine could be satisfied by superimposing the turbine performance characteristics on the compressor performance characteristics providing the axes of both were normalised. This technique can serve as a valuable tool to determine the operating range and the engine running line. Furthermore, it would decide whether the gas turbine engine was operating in a region of adequate compressor and turbine efficiencies. A computer program capable of simulating the steady state off-design conditions of the gas turbine engine as part of the CPP plant has been developed. The program was written in Visual Basic. Also, another program was developed to simulate the steady state off-design operation of the steam turbine power plant. A combination of both programs was used to simulate the combined power plant. Finally, it could be claimed that the computer simulation of the CPP plant makes significant contribution to the design of thermal power plants as it would help in investigating the effects of the performance characteristics of the components on the performance of complete engines at the design and off-design conditions. This investigation of the CPP plant performance can be carried out at the design and engineering stages and thus help to reduce the cost of manufacturing and testing the expensive prototype engines.

Thesis (PhD(Agricultural Economics, Extension and Rural Development))--University of Pretoria, 2007. / Includes bibliographical references.

The emerging general purpose graphics processing units (GPGPU) computing has tremendously speeded up a great variety of commercial and scientific applications. The GPUs have become prevalent accelerators in current high performance clusters. Though the computational capacity per Watt of the GPUs is much higher than that of the CPUs, the hybrid GPU clusters still consume enormous power. To conserve energy on this kind of clusters is of critical significance. In this thesis, we seek energy conservative computing on the GPU accelerated servers. We introduce our studies as follows. First, we dissect the GPU memory hierarchy due to the fact that most of the GPU applications are suffering from the GPU memory bottleneck. We find that the conventional CPU cache models cannot be applied on the modern GPU caches, and the microbenchmarks to study the conventional CPU cache become invalid for the GPU. We propose the GPU-specified microbenchmarks to examine the GPU memory structures and properties. Our benchmark results verify that the design goal of the GPU has transformed from pure computation performance to better energy efficiency. Second, we investigate the impact of dynamic voltage and frequency scaling (DVFS), a successful energy management technique for CPUs, on the GPU platforms. Our experimental results suggest that GPU DVFS is still promising in conserving energy, but the patterns to save energy strongly differ from those of the CPU. Besides, the effect of GPU DVFS depends on the individual application characteristics. Third, we derive the GPU DVFS power and performance models from our experimental results, based on which we find the optimal GPU voltage and frequency setting to minimize the energy consumption of a single GPU task. We then study the problem of scheduling multiple tasks on a hybrid CPU-GPU cluster to minimize the total energy consumption by GPU DVFS. We design an effective offline scheduling algorithm which can reduce the energy consumption significantly. At last, we combine the GPU DVFS and dynamic resource sleep (DRS), another energy management technique, to further conserve the energy, for the online task scheduling on hybrid clusters. Though the idle energy consumption increases significantly compared to the offline problem, our online scheduling algorithm still achieves more than 30% of energy conservation with appropriate runtime GPU DVFS readjustments.

The idea that we can 'save energy' has become a commonplace homily. But with a moment's reflection it is clear there is nothing self-evident about saving energy. Do we save fuel or a system's ability to 'do work'? Do we conserve for perpetuity or to prolong use? Is the motivation resource economy, scarcity, productivity, or - more recently - climate change mitigation? And what stops the fruits of individual parsimony being consumed elsewhere? This thesis offers a history of the idea that we can conserve energy by using it more efficiently. In recounting this story, it is argued that conserved energy is a 'metrological resource' produced by practices of measurement, calculation, and computation. A second argument is that the history of ERC offers an under examined example of a 'resource ontology'; the social processes through which nature is imbued with utility and value. Accordingly, the study of, what is termed, energy resource conservation (ERC herein) involved a novel research method which focused upon the scientific and intellectual processes of resource making, as much as the material. This thesis begins in 1865 with the publication of William Jevons' The Coal Question (1865), in which the resource conservative principles of Classical political economy were overturned. Jevons argued that increased efficiency of coal use would serve only to increase the rate and scale with which coal was used. Proceeding from this anti-thesis, the following chapters outline how, irrespective of Jevons' claim, policies based on the principles of scientific management were applied to the conservation of fuel resources for conserving natural resources. In pre-war America, a complex system of 'pro-rationing' extraction licenses were introduced to conserve the productive capacity of petroleum wells. However, a significant shift occurred during the Cold War, as the conservation of fuel became increasingly conflated with the econometrician's notion of efficient resource allocation. But the most significant developments occurred in the nineteen-seventies, in response to a perceived crisis in energy supply. Fuel policy became a more systemic 'energy policy', which drew on scientific management, graph theory, systems theory, statistical mechanics, and computational econometrics in an attempt to quantify and demonstrate how society could act to conserve energy resources by increasing the efficiency of energy use. The resulting science, and its concomitant policies were an odd mix of cold war rational decision making theories, détente science, scientific radicalism, and liberal economic theory, all given a countercultural and environmentalist gloss in the latter half of the decade. On the basis of this conflation of ideas, a new approach to energy saving that emerged, which transformed the principles of energy resource governance, shifting the onus to conserve from producer to consumer, with distinct implications for post-war theories of political economy.

Orientador: Moacyr Trindade de Oliveira Andrade / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica / Made available in DSpace on 2018-08-12T05:28:32Z (GMT). No. of bitstreams: 1 Castro_RenatoArchanjode_M.pdf: 2548594 bytes, checksum: 5b0406363500b5419ff9f888bb2dac98 (MD5) Previous issue date: 2008 / Resumo: Este trabalho mostra a importância do motor elétrico de indução trifásico rotor gaiola de esquilo, que é o principal responsável pelo consumo de energia elétrica no seguimento industrial, apresenta suas características elétricas, mecânicas e sua evolução ao longo dos anos. Relata ainda a problemática do superdimensionamento destes motores instalados na indústria brasileira, ao qual tem como principal inconveniente a alta requisição de energia reativa nas instalações elétricas, apresenta a forma de faturamento da energia reativa aplicada pelas concessionárias de energia, bem como as principais formas de sua compensação aplicadas atualmente pela indústria nacional e seus efeitos na instalação existente. O trabalho apresenta uma análise comparativa entre o motor Alto Rendimento e o motor Standard, com ênfase na adequação da potência nominal em relação à demanda industrial, bem como em relação ao consumo de energia reativa das opções avaliadas. O suporte proveniente de pesquisas e adequações de instalações industriais aplicada pelo autor, em empresas da região de Americana, em relação à energia elétrica reativa, se constituem como base para o desenvolvimento deste trabalho. A conclusão final busca demonstrar que estas ações de conservação e adequação em motores elétricos industriais, são fundamentais para o processo de eficientização das próprias indústrias, do setor elétrico e da economia do país, de forma geral, uma vez que as mesmas implicam na redução da energia requerida pela indústria sem prover restrições a produção, resultando em significativa economia de recursos no provimento de novas fontes de energia e de melhor utilização do sistema elétrico nacional. / Abstract: This study shows the importance of the electrical engine of triphasic induction rotor (squirrel cage), which is the main responsible for the waste of electrical energy in industry; it presents its electrical and mechanical characteristics and its evolution along the years, as well. The study describes the problem of the super dimensioning of these engines that exist at the Brazilian industry, which has the major inconvenience of the high required of reactive energy in the electrical systems, presenting the way of invoicing the reactive energy applied by the power suppliers, as well as the main ways of its compensation applied presently by the national industry and its consequences for the existent installation. The study presents a comparative analysis between the engine of high efficiency and the Standard engine, focusing the adaptation of nominal power in relation to the industrial demand, as well as in what concerns the waste of reactive energy by the evaluated options. The background for the development of this study came from researches and adaptation of industrial plants applied by the Author in companies of the American region, as far as reactive electrical energy is concerned. The final conclusion tries to demonstrate that these actions of conservation and adaptation in industrial electrical engines are fundamental for the process of improving the efficiency of the very same industries, the electrical sector and the economy of the country as a whole, since that the same actions imply the reduction of the energy required by the industry without restrictions to the production, resulting into a significant saving of resources in what concerns the supply of new sources of energy and a better utilization of the national electrical system. / Mestrado / Mestre em Planejamento de Sistemas Energéticos