Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: The purpose of this investigation is to determine the performance of an axial ow compressor operating in a closed loop helium cycle under high through- ow conditions. The GTHTR300 four-stage helium test compressor was chosen for this investigation. Limited information on the helium test compressor's blade pro les are available, therefore a mathematical model was developed to calculate the blade geometries based on the theory of Lieblein and Aungier. A locally available three-stage compressor was used to con rm whether the mathematical model calculated the blade pro le geometries correctly. The Stellenbosch University Compressor Code (SUCC), an axisymmetric inviscid through- ow code, was used to compare the performance of the calculated three-stage compressor blade geometries with available experimental data. Excellent correlation was obtained, thus it was concluded that the mathematical model as well as the SUCC could be used to predict the performance of an axial ow compressor. The blade geometries of the helium test compressor were calculated and the pressure ratio and e ciency predictions of the SUCC correlated well with the experimental data. The helium test compressor was simulated to verify the calculated blade geometries further using the Computational Fluid Dynamics (CFD) package NUMECA FINE /Turbo. The FINE /Turbo pressure ratio and e ciency predictions compared adequately with the SUCC and available experimental data, especially in the design region. At high mass ow rates the stator blade row experiences negative incidence stall which results in a large recirculation zone in the stator blade wake. / AFRIKAANSE OPSOMMING: Die doel van hierdie ondersoek is om vas te stel wat die werkverrigting is van 'n aksiale kompressor in 'n geslote lus helium siklus onderhewig aan hoë deurvloei kondisies. Die GTHTR300 vier-stadium helium toets kompressor is gekies vir die ondersoek. Daar is egter beperkte inligting oor die helium kompressor se lem geometrie, dus is 'n wiskundige model ontwikkel om dit te bereken gebaseer op die werk van Lieblein en Aungier. Om te bevestig dat die lem geometrie akkuraat was, was die lem geometrie van die 'n plaaslike beskikbare drie-stadium kompressor bereken. Die Stellenbosch University Compressor Code (SUCC), 'n aksisimmetriese nie-viskeuse deurvloei kode, is gebruik om die prestasie van die berekende lem geometrie met beskikbare eksperimentele data te vergelyk. Uitstekende korrelasie is verkry vir die drukverhouding en benuttingsgraad resultate, dus is die gevolgtrekking gemaak dat die wiskundige model sowel as die SUCC gebruik kon word om die lem geometrie en werkverrigting van aksiale kompressors te bereken en voorspel. Die helium toets kompressor is gesimuleer met behulp van die numeriese vloei-dinamika pakket NUMECA FINE /Turbo om die berkende lem geometrie verder te veri eer. Die FINE /Turbo drukverhouding en benuttingsgraad resultate het goed gekorreleer met beide die SUCC resultate en eksperimentele data, veral in die ontwerpsgebied. Teen hoë massa vloei tempo's vind daar groot wegbreking teen negatiewe invalshoek plaas in die stator lemry en dit veroorsaak 'n hersirkulasie sone in die naloop van die stator lem.

There is a need to improve the capabilities of cooling technology to dissipate increasingly high heat fluxes (approaching 200 W/cm²) from electronic components in order to maintain acceptable operating temperatures. The linear compressor with clearance seal and flexure spring which has been used for many years for space application, is an attractive proposition for vapour compression refrigeration (VCR) systems in electronics cooling applications because it offers several advantages over traditional compressor technology. This thesis introduces a novel design of oil-free linear compressor and investigates the performance of the linear compressor system and the key issues with respect to the operations of the compressor. A comprehensive system analysis has been carried out for the linear compressor regarding the moving magnet motor characteristics, spring stiffness, damping, imbalance of current in coils, DC offset and leakage across the clearance seal. To measure the performance of the linear compressor, an experimental apparatus and a data acquistion system have been built. A harmonic fitting approach has been proposed to reconstruct current, voltage and displacement signals using fast Fourier transform (FFT) and minimisation algorithms. The piston dynamics have been modelled to infer pressure-volume (P-V) diagrams. Preliminary measurements of the linear compressor at resonance using nitrogen show that an adiabatic efficiency of 42% - 60% and a motor efficiency of 71% - 89% are maintained over a wide range of operating parameters, indicating that systems using this type of compressor could have good part load efficiency. At the design point (a pressure ratio of 3.0 and a stroke of 13 mm), pressure drop loss is responsible for 27% of the total losses and the most significant loss is the copper loss (34%). A commercial crank-drive compressor with comparable properties has also been evaluated for comparison, showing that the prototype linear motor has a much higher efficiency than the rotary induction motor, particularly at low electrical power inputs while the volumetric efficiencies in the crank-drive compressor are about 20% higher. The linear compressor in a refrigeration system using R134a has been measured for different strokes under each pressure ratio with a fixed condenser outlet temperature of 50°C and evaporator temperature ranging from 6°C to 27°C. A model of the resonant frequency using discharge and suction pressures and the stroke has been validated. A coefficient of performance (COP) of 3.2 has been achieved at a cooling capacity of 384 W and an evaporator temperature of 20°C. This is assumed to be a typical CPU cooling condition. A Proportional-Integral-Derivative (PID)/Pulse-Width-Modulation (PWM) control system using a solenoid operated valve has been developed for DC offset and clearance control. Operation of the linear compressor with a fixed clearance of 0.8 mm using nitrogen has been carried out in comparison with the fixed zero DC offset operation. When operated with a fixed clearance, the volumetric efficiency increases with a decreasing stroke but the fixed clearance operation requires a higher power input. This provides evidence that the piston control in a refrigeration system with capacity control should be for a zero DC offset.

The research work disclosed in this publication is partially funded by the Strategic Educational Pathways Scholarship Scheme (Malta). The scholarship is part-financed by the European Union – European Social Fund under Programme II – Cohesion Policy 2007-2013. / This dissertation documents a compressor preliminary design study conducted by the author in fulfilment of his MSc thesis requirements. The compressor is intended for a new development engine within the 20Klbf thrust category, planned to be used on a short-haul aircraft, namely the ERJ-190. A market research suggests that there exists a definite opportunity for a commercially profitable engine within this thrust class. Furthermore, the proposed new engine is projected to outperform current production engines on critical issues such as fuel efficiency and operability. By and large, the objectives of this work have been achieved and a compressor design and layout is suggested, which matched or exceeded all the initial requirements. The quality of the results from this study are thought to be of sufficient detail to allow a further, more detailed development study to resolve some subtle pending issues. It is expected that, some compressor stages may have to be altered slightly during detailed design to augment their performance and ease of manufacture and assembly. Throughout this study, the importance of the compressor design figure of merits, pertaining to a short haul engine, has been outlined and their interaction on the design process is well documented. Furthermore, some rather unorthodox objectives such as compressor performance retention and reliability have been discussed. The author approached these subjects in an innovative way due to the limited non-proprietary knowledge available on these issues, especially considering their implications within preliminary design. Furthermore, the author developed and tested a new preliminary turbomachinery design code, named Turbodev, which can be used as an aid in future compressor design endeveours. Turbodev can handle most types of compressor layouts and generates an overall aerodynamic assessment of the turbomachinery performance. In conclusion; this documentation and the associated literature review aim to provide the reader with an overview of the work done and yield a better understanding of the decisions that face any design bureau when developing a new or modified engine component.

In Taiwan, most of the energy relies on imports due to few natural resources. Further more, scientists estimate that crude oil will be depleted within 40 years. A high cost energy era has arrived. Skyrocketing oil prices have a severe negative impact on the cost structure of the Taiwan Power Company (TPC), which has an estimated deficit of NT$70 billion in 2007. TPC has faced a difficult dilemma: whether to raise the electricity rate or become bankrupt. Eventually, the government has to intervene. The Kyoto Protocol was in effect in February 2005. It is expected that the environmental convention of reducing of CO2 will become an international movement following ISO14000. With every one kilowatt hour of electricity is generated by TPC, 638g of CO2 were produced. The products of made-in-Taiwan will not received international approval and will be boycotted by the International market if the energy efficiency of national enterprise is too low. Air compressor system, which is as important as water and electricity, is popularly used in almost all industries. However, its high energy-consumption and low efficiency system is seldom noticed. The energy cost of air compressor system is about 80% of the total operational cost which includes the electricity costs of all the machinery and lightings. How to improve air compressor efficiency plays an important role in the manufacture¡¦s production cost and its competition against other industries. Facing fierce competition and low profit, the industries must not only continuously innovate and reduce the cost to enhance competition ability for keeping market share, but also increase energy efficiency and reduce the emission of greenhouse gases by the green production method meeting the environmental requirement. The report is the summary of the interviews with many industry leaders who are involved in the air compressor production or the government officials who are in charge of energy-saving promotion. It also combines with the data of actual measurement of the compressor systems to research if the investment willingness of manufacturers is reflected by their operation cost, operation strategy, the risky consideration when facing law and the information getting of compressor energy-saving. The results of the study are: Clarify the main factors which influence the investment willingness to compressor energy-saving. (A) The cost side: The investment willingness is influenced by the cognition of the leaders of manufacturer unit or business owner to compressor system cost. (B) The strategy side: The investment willingness is influenced by the cognition of the leaders of manufacturer unit or business owner to the operation strategy on compressor system. (C) The legal side: The investment willingness is influenced by the cognition of the leaders of manufacturer unit or business owner to the legal affection to business. (D) The information side: The investment willingness is influenced by getting the information of energy-saving of compressor system. Finally, the study proposes a feasible project to the industries and the government officials who promote energy saving.

In this investigation, casing mounted high frequency response pressure transducers are used to characterize the flow behavior near the aerodynamic stability limit of a low speed single stage axial flow compressor. Time variant pressure measurements are acquired at discrete operating points up to the stall inception point and during the transition to rotating stall, for a length of time no shorter than 900 rotor revolutions. The experimental data is analyzed using multiple techniques in the time and frequency domains. Experimental results have shown an increase in the breakdown of flow periodicity as the flow coefficient is reduced. Below a flow coefficient of 0.40 a two node rotating disturbance develops with a propagation velocity of approximately 23% rotor speed in the direction of rotation. During rotating stall, a single stall cell is present with a propagation velocity of approximately 35% rotor speed. The stall inception events present are indicative of a modal stall inception.

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The master's thesis deals with compressor turbochargers used for supercharging of combustion engines. The aim of the thesis is feasibility study of compressor surge limit simulation. First of all the principle and purpose of supercharged combustion engines is described and the compressors' types using for supercharging are mentioned as well. The main part of the thesis is focused on flow instabilities and their influence on compressor operating zone. There are mentioned some possibilities of operating zone extension. The practical part comprises the simplified computation of a one stage of centrifugal compressor and flow analysis by means of CFD simulation.

Using an inverter-driven compressor in variable capacity heat pump systems has a main drawback, which is the extra loss in the inverter. The present experimental study aims to recover the inverter losses by using brine-cooled and water-cooled inverters, thereby improving the total efficiency of the heat pump system. In order to achieve this goal, a test rig with the air-cooled, water-cooled and brine-cooled inverters is designed and built, and a comparative analysis of the recovered heat, inverter losses and system performance is conducted when the compressor is driven by the water-cooled, brine-cooled and air-cooled inverters at three different switching frequencies for each inverter. The experimental results show that the inverter losses as a magnitude and as a ratio of the total consumed power are lowest in the brine-cooled inverter and highest in the air-cooled one at all the compressor speeds and all the inverter switching frequencies. Moreover, the recovered energy varies between 45 and 125 (W) in the water-cooled inverter, which corresponds to 63 and 69 (%) of the inverter losses; while it varies between 61 and 139 (W) in the brine-cooled inverter, which corresponds to 79 and 90 (%) of the inverter losses. It is also proved that the improvement of the system coefficient of performance (COPsys) is almost the same when the water-cooled or the brine-cooled inverter is used and varies between 0.54 and 3 (%) in comparison with using the air-cooled one. Indeed, the total isentropic efficiency of the compressor is improved slightly when using the water-cooled inverter and little more when using the brine-cooled one at the same running conditions. In addition, the total isentropic efficiency of the compressor is improved by increasing the inverter switching frequency when any of the inverters is used. The experimental results also show that cooling the inverter by the water, which comes out from the condenser, increases the maximum temperature of the base plate of the inverter about 10 °C which could cause a two-fold deterioration in the inverter median life in comparison with cooling the inverter by air. On the contrary, using the brine for cooling the inverter decreases the maximum temperature of the base plate of the inverter about 30 °C which could cause about a six-fold improvement in the inverter median life. / Capacity-controlled Ground Source Heat Pump single-family dwellings

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No description available.