HiGtech är en projektgrupp på Högskolan i Gävle vilka konstruerar och bygger energisnåla tävlingsfordon. Ett av fordonen tävlar i Shell Eco Marathons prototypklass för bensindrivna förbränningsmotorer och drivs av en på högskolan konstruerad motor. Motorns effekt överförs till en kedjetransmission via en inköpt och modifierad centrifugalkoppling. Den nuvarande centrifugalkopplingen väger cirka 1,5 kg. Då en stor faktor för tävlingsresultatet är fordonets rullmotstånd, vilken beror av fordonets vikt, har målet med detta arbete varit att konstruera en specialanpassad centrifugalkoppling, vars vikt endast är hälften så stor som motorns nuvarande koppling. Experiment på motorn, en undersökning av befintliga centrifugalkopplingar samt en litteraturstudie har utförts vilket gav indata för konstruktionsarbetet. Centrifugalkopplingens diameter har optimerats med avseende på låg vikt, där massan av kopplingens nav, trumma och backar tagits fram och jämförts för olika diametrar. Backarnas massa har beräknats med en framtagen beräkningsmodell och navets samt trummans massor har tagits fram genom 3D-modellkoncept. Vidare har en centrifugalkoppling konstruerats av stål, anpassad för tävlingsfordonets motor med individuell justering av ingreppsvarvtalet för dess backar. Centrifugalkopplingens optimala diameter beräknades till 110 millimeter, vilket har resulterat i en totalvikt på den utvecklade kopplingen på cirka 730 g. En specifikationslista har tagits fram på lämpligt friktionsmaterial, dock krävs vidare tester för att säkerställa att önskad funktion uppnås på grund av vibrationer som kan uppstå, något som avgränsats bort i detta arbete. / HiGtech is a project group at the University of Gävle, in which students design and build energy efficient vehicles to compete with around the world. One of the vehicles is competing in the Shell Eco Marathon prototype class for gasoline-powered internal combustion engines and is driven by an on campus designed engine. The engine's power is transmitted to a chain transmission via a purchased and modified centrifugal clutch. The current centrifugal clutch weighs about 1.5 kg. An important factor for the outcome in the competition is the rolling resistance of the vehicle, which depends on its weight, the aim of this work has been to design a customized centrifugal clutch, whose weight is only half as large as the engine’s current clutch. Experiments on the engine, a survey of centrifugal clutches and a literature study has been performed which gave input for the design work. The diameter of the centrifugal clutch has been optimized for low weight, where the mass of the clutch hub, drum and shoes has been compared for the different diameters. The shoe mass has been calculated using a developed model and the hub and drum masses have been developed through a 3D model concept. Furthermore, a centrifugal clutch out of steel, adapted for the engine of the competing vehicle, has been developed, with individual adjustments of the engagement speed of its shoes. The optimal diameter of the centrifugal clutch was calculated to 110 millimeters, resulting in a total weight of the developed clutch of about 730 g. A list of specification has been developed for an appropriate choice of friction material, however, further testing is required to ensure that the desired functionality is achieved due to vibrations that may occur, this was however demarcated in this work.

No description available.

South Africa experienced a severe shortfall in electricity supply during 2008. Eskom, the national electricity supplier, implemented several strategies to alleviate the situation. The Power Conservation Programme set the mining sector a mandatory target to reduce its annual power consumption by 10%. The quickest way to achieve these savings is by optimising the largest power consumers on the mines. Compressed air is one of these, constituting approximately 40% of total electricity consumption on platinum mines. Several methods to reduce power consumption on compressed air systems were investigated. The investigation revealed that centrifugal air compressors on the mines are typically manually operated at a fixed delivery output. Attempts to reduce electricity consumption by reducing air demand will therefore not necessarily lead to savings. A control system that will enable the compressor to automatically match the supply with system demand is required. An optimised control strategy was then developed and implemented on three compressed air systems. Measurements demonstrated savings between 13% and 49%. With the Eskom tariffs proposed for 2010, this implies a total saving of R 46 million per year for these three case studies. This will achieve, and may even exceed, the mandatory reduction in electricity consumption of the mines. These results demonstrate that one of the quickest ways to reduce energy consumption on South African mines is by implementing optimised compressor controls. / Thesis (M.Ing. (Electrical Engineering))--North-West University, Potchefstroom Campus, 2010

South Africa experienced a severe shortfall in electricity supply during 2008. Eskom, the national electricity supplier, implemented several strategies to alleviate the situation. The Power Conservation Programme set the mining sector a mandatory target to reduce its annual power consumption by 10%. The quickest way to achieve these savings is by optimising the largest power consumers on the mines. Compressed air is one of these, constituting approximately 40% of total electricity consumption on platinum mines. Several methods to reduce power consumption on compressed air systems were investigated. The investigation revealed that centrifugal air compressors on the mines are typically manually operated at a fixed delivery output. Attempts to reduce electricity consumption by reducing air demand will therefore not necessarily lead to savings. A control system that will enable the compressor to automatically match the supply with system demand is required. An optimised control strategy was then developed and implemented on three compressed air systems. Measurements demonstrated savings between 13% and 49%. With the Eskom tariffs proposed for 2010, this implies a total saving of R 46 million per year for these three case studies. This will achieve, and may even exceed, the mandatory reduction in electricity consumption of the mines. These results demonstrate that one of the quickest ways to reduce energy consumption on South African mines is by implementing optimised compressor controls. / Thesis (M.Ing. (Electrical Engineering))--North-West University, Potchefstroom Campus, 2010

Thesis (M.S.)--University of Alabama at Birmingham, 2008. / Description based on contents viewed July 8, 2009; title from PDF t.p. Includes bibliographical references (p. 47).

Thesis (Ph. D.)--University of Texas at Austin, 2006. / Vita. Includes bibliographical references.

Low-temperature energy systems are processes that operate below ambient temperatures and make use of refrigeration cycles, where the main energy consumption is due to the shaft work required to drive the compressors. Very-low-temperature energy systems, also known as cryogenic processes, operate at around -150°C and below. Due to increasing demand of products from cryogenic processes and tighter environmental regulations, existing plants need to be revamped to increase their energy efficiency or adapt to new processing capacities. So, accurate models of the performance of cryogenic processes are needed in order to optimise their operation. The present work proposes a new approach for optimising the operating conditions of existing refrigeration cycles in cryogenic processes, using pure refrigerants, for different plant operating conditions. In this work, the process conditions are considered as given and not considered as variables during the optimisation. The operational optimisation is achieved by integrating models for the part-load performance of centrifugal compressors and models for the simulation of plate-fin heat exchangers (PFHEs), into a single optimisation approach. An optimisation approach similar to the one proposed in this work was not found in the open literature. The optimisation approach varies the refrigerant evaporation temperatures, flow rates and cooling duties, minimum temperature difference in PFHEs, and rotational speed of compressors. The objective function seeks to minimise shaft work demand and the constraints consider the operational limitations of centrifugal compressors (minimum and maximum flow rates) and PFHEs (no temperature crosses and meeting the target temperatures of the process streams). In order to explore the solution space that is generated by the complex interactions between the variables and find an approximation to a global optimum, a multistart optimisation algorithm is implemented. The part-load centrifugal compressor model implemented in this work uses regressed data from their performance curves together with the fan laws. The proposed simulation model of PFHEs represents these units as a ‘fictitious’ heat exchanger network of two-stream matches. The simulation model accounts for single and two-phase streams and for the temperature-dependent physical properties of pure refrigerants (e.g. viscosity, heat capacity, etc.). In addition to the simulation model, design and rating models for PFHEs with single and two-phase streams are also proposed. The examples presented in this work for the design, simulation and rating of single and two-phase streams in PFHEs show that the models proposed can find feasible designs, and can predict the outlet temperature of the process streams within ±3°C for different inlet conditions. The example presented in this work for the operational optimisation of refrigeration cycles shows that savings of around 3% in shaft work consumption (up to £0.86 million per year), for different process throughput, can be achieved using the proposed methodology.

Made available in DSpace on 2014-06-11T19:28:33Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-12-16Bitstream added on 2014-06-13T20:18:22Z : No. of bitstreams: 1 goncalves_cg_me_guara_parcial.pdf: 217661 bytes, checksum: c20902856040fbee187ead0ee3cb00b5 (MD5) Bitstreams deleted on 2015-06-25T13:01:15Z: goncalves_cg_me_guara_parcial.pdf,. Added 1 bitstream(s) on 2015-06-25T13:03:30Z : No. of bitstreams: 1 000679599_20151231.pdf: 217896 bytes, checksum: cf025ea71faace9e52cbc1051e6f88a1 (MD5) Bitstreams deleted on 2016-01-04T10:26:26Z: 000679599_20151231.pdf,. Added 1 bitstream(s) on 2016-01-04T10:28:17Z : No. of bitstreams: 1 000679599.pdf: 1039378 bytes, checksum: fb5a9506ef24ceed88e78978a6f9f073 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Este estudo mostra as variáveis dinâmicas do processo de fundição centrífuga de cilindros de laminação, que são utilizados para realização de conformação em gaiolas de laminação. O objetivo desse estudo é analisar as principais variáveis dinâmicas do processo de fundição centrifugada de cilindros de laminação e estudar as relações entre estas variáveis. Os processos de fundição centrífuga podem ser classificados em fundição centrífuga vertical e horizontal. Para a fundição centrífuga vertical, são elaborados os envelope de carga de dois modelos de máquinas centrífugas verticais existentes na literatura, onde se consegue determinar o tipo de rolamento de apoio utilizado na máquina. Para a fundição centrífuga horizontal, são estudadas variáveis como rotação, razão G, “aspect ratio”, espessura e vibração de uma amostra de aproximadamente 1.000 cilindros de ferro fundido, aço rápido e aço alto cromo. Desta amostra, verifica-se que a causa de sucateamento de parte dos cilindros não está ligada a adoção de variáveis dinâmicas incorretas no processo. Também é visto que diferentemente do alumínio, os cilindros de ferro fundido, aço rápido e aço alto cromo exigem maior rotação quanto maior a espessura da casca fundida. / This paper shows the dynamic variable of centrifugal casting process of rolling mill rolls which are used to compress the metal in rolling mill process. The main goal is to analyze the main dynamic variable and to study its relation in the process. There are two type of centrifugal casting: horizontal and vertical. For the horizontal centrifugal casting, two load envelopes are done, being possible to determine the bearing model used on the vertical centrifugal casting machine. For the horizontal centrifugal casting, variable such as rotating, ratio G, aspect ratio, thickness and vibration are studied to a sample of 1,000 casting rolls made of casting iron, high speed steel and high chromium steel. From this sample, it is seen that the cause of scrapping is not related to incorrect adoption of dynamic variables in the process. It is also verified that differently from the aluminum, cast iron, high speed steel and high chrome steel rolls demand greater speed with the increasing the shell casting thickness.

Made available in DSpace on 2014-10-09T12:25:28Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:02:56Z (GMT). No. of bitstreams: 0 / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Made available in DSpace on 2014-10-09T12:33:48Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:03:59Z (GMT). No. of bitstreams: 0 / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP