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.

"A flow control method for minimizing losses in a highly loaded compressor blade was analyzed. Passive and active flow control experiments with vortex generator jets were conducted on a seven blade linear compressor cascade to demonstrate the potential application of passive flow control on a highly loaded blade. Passive flow control vortex generator jets use the pressure distribution generated by air flow over the blade profile to drive jets from the pressure side to the suction side. Active flow control was analyzed by pressuring the blade plenum with an auxiliary compressor unit. Active flow control decreased profile losses by approximately 37 % while passive flow control had negligible impact on the profile loss of a highly loaded blade. Passive flow control was able to achieve a jet velocity ratio, jet velocity to upstream velocity, of 0.525. The success of active flow control with a velocity ratio of 0.9 suggests there is potential for passive flow control to be effective. The research presented in this thesis is motivated by the potential savings in the applications of passive flow control in gas turbine axial compressors by increasing the aerodynamic load of each stage. Increased stage loading that is properly controlled can reduce the number of stages required to achieve the desired pressure compression ratio."

Made available in DSpace on 2016-12-12T17:38:35Z (GMT). No. of bitstreams: 1 Claudio Bruning.pdf: 22335027 bytes, checksum: fe824200f322a8e500ff651ebdad0fcd (MD5) Previous issue date: 2015-09-23 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / In 2017 the standards organization(s) in the North American and European markets are reducing the allowable limits for harmonic distortion which may increase the need for PFC circuits; therefore, this paper presents study on a rectifier design with high power factor applied in a home appliance refrigerator that meets the requirements of North American and European markets. The electronic board must drive a refrigerator compressor that uses a linear technology. A comparison between different solutions is presented from which two were selected for implementation. These solutions, known as bridgeless PFC, integrate the rectification and the CC-CC conversion in the same stage reducing the conduction losses. The One Cycle Control (OCC) technique was selected due to its simpler auxiliary circuit requirements. Dynamic modeling and quantitative analysis of the converter was performed and a design methodology was derived. This methodology was used to design and build a 300𝑊 prototype with a bus voltage of 390𝑉 and input voltage with two different ranges, 97𝑉 up to 140𝑉 and 180𝑉 up to 264𝑉 . The results include steady state and transient analyses, efficiency, thermal performance and harmonics standards analyses. / Este trabalho apresenta o estudo de um retificador com elevado fator de potência no controle eletrônico de um refrigerador destinado aos mercados norte-americano e europeu, o qual faz uso de um compressor com tecnologia linear. A demanda decorre dos requisitos normativos exigidos por estes mercados, os quais possivelmente a partir de 2017 só poderão ser atendidos com a utilização de circuitos retificadores com elevado fator de potência. Apresenta-se uma comparação entre diferentes soluções, dentre as quais duas foram selecionadas mantendo-se a mesma plataforma. Estas soluções são conhecidas como bridgeless e integram as etapas de retificação e conversão CC-CC em um único estágio, possibilitando a diminuição das perdas por condução. Foi selecionada a técnica conhecida como One Cycle Control (OCC) devido a simplificação dos circuitos auxiliares necessários. Para a implementação do protótipo, é realizada a modelagem dinâmica e a análise quantitativa dos conversores, bem como a definição de todos os componentes necessários. Os conversores são desenvolvidos para atuar até 300 𝑊 com tensão de barramento de 390 𝑉 e tensão eficaz de entrada entre 97 𝑉 140 𝑉 e 180 𝑉 −264 𝑉 . O protótipo é avaliado em condições de regime permanente, transitória, verificação da eficiência, avaliação térmica e atendimento das normas necessárias.

Made available in DSpace on 2016-12-12T17:38:37Z (GMT). No. of bitstreams: 1 Paulo Sergio Dainez - resumo.pdf: 31972 bytes, checksum: 94a24928564b90b196513e814cfe09a3 (MD5) Previous issue date: 2010-06-25 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / In the resonant linear compressor the piston is drive by a linear actuator and a resonant mechanical spring directly in the reciprocating motion, this is a mass spring resonant system, eliminating bearing and crank of the conventional reciprocating compressors, and the friction loss has a significant reduction. The maximum displacement of the piston is regulating by the equilibration between the power supply by the actuator and the power transfer to the gas compression process. This type of the compressor is design to work at the resonant frequency of the mass spring system, in this condition the efficiency is maximum. Then the control must drive the linear actuator in the maximum displacement of the piston and adjust the drive frequency at the system resonant frequency. For enable of this process is necessary that piston position is known with precision, however the installation of a sensor have same difficulty, since the refrigeration compressor is hermetic system, and it have high pressure and temperature, with wide range of variation. This work develop the implementation of a full order linear observer to estimate the displacement and the velocity of the piston of the resonant linear compressor, and a control system able to drive the compressor in the maximum piston displacement and in the resonant frequency, and only measured a current of the linear actuator, without sensor inside de compressor. For this a nonlinear model of the compressor and a linear model with variable coefficients for the observer are develop, also a simulator of the system is develop, where the compressor model is controlled by the displacement and the velocity signals calculate by observer, demonstrated the feasibility of the proposed technique in the present work. / Nos compressores lineares ressonantes o pistão é acionado por um atuador linear e molas diretamente no sentido do seu movimento alternativo, formando um sistema massa-mola ressonante, eliminando assim os mancais mecânicos e o sistema biela e manivela dos compressores convencionais, reduzindo de forma significativa as perdas por atrito. A amplitude do deslocamento do pistão é regulada pelo equilíbrio da potência fornecida pelo atuador e a potência transferida para o processo de compressão do gás. Estes compressores são projetados para funcionar na frequência de ressonância do sistema massa-mola, nesta condição a eficiência do sistema é máxima. Assim, o controle deve acionar o atuador linear na máxima amplitude de deslocamento do pistão e ajustar a frequência de acionamento na frequência de ressonância do sistema. Para viabilizar este processo é necessário que o curso do pistão seja conhecido com precisão, porém a instalação de um sensor apresenta dificuldades, pois os compressores de refrigeração são herméticos e estão sujeitos a pressões e temperaturas elevadas e com grande faixa de variação. Este trabalho propõe a implementação de um observador de estados de ordem plena, para estimar o deslocamento e a velocidade do pistão do compressor linear ressonante, e um sistema de controle capaz de acionar o compressor no deslocamento máximo e na frequência de ressonância, medindo somente a corrente no atuador linear, sem a necessidade de sensores instalados dentro do compressor. Para isto desenvolve-se um modelo não linear do compressor e um modelo linear equivalente de coeficientes variáveis para o projeto do observador, também é desenvolvido um simulador do sistema, onde o modelo do compressor é controlado pelos sinais de deslocamento e velocidade calculados pelo observador, demonstrando a viabilidade da técnica proposta no presente trabalho.

This report documents the experimental study for four different three-dimensional turbulent flows. The investigation focuses on near wall measurements in these flows. Several experimental techniques are used in the studies; however, the bulk of the investigation focuses on a three-orthogonal-velocity-component fiber-optic laser Doppler anemometer (3D-LDA) system. The control volume of the 3D-LDA is on the order of 50 micro-meter in size, or a y⁺ distance of around 2.3 units (using average values of U_&#964 and ν from the experiment). An auxiliary small boundary layer wind tunnel (auxiliary tunnel) and a low speed linear compressor cascade wind tunnel (cascade tunnel) are utilized in this study. One of four flow experiments is done in the auxiliary tunnel the other three are in the cascade tunnel. The first three-dimensional turbulent flow is a vortical flow created by two half-delta wing vortex generators. Near wall secondary flow features are found. The second flow is an investigation of the first quarter chord tip gap flow in the cascade tunnel. Strong three-dimensional phenomena are found. The third flow investigated is the inflow to the compressor cascade with the moving wall. The experiment records shear layer interaction between the upstream flow and moving wall. Finally the fourth flow investigated is the inflow to the compressor cascade with the moving wall with half-delta wing vortex generators attached. Phase-averaged data reveal asymmetrical vortex structures just downstream of the vortex generators. This is the first time any near wall data has been taken on any of these flows. / Master of Science

Cryocoolers are closed cycle devices which produce cooling below 120 K. Usually, one or two linear motors are used to drive one pulse tube cryocooler. Cryocoolers are used for various applications like, cooling of infra red detectors, cryo surgical knife, cryogen recondenser etc. In this thesis the design development and testing of Twin Pulse Tube Cryocooler (TPTC) are discussed. TPTC consists of two pulse tubes driven by dual piston head linear compressor. This dual piston linear compressor is operated using single linear motor. Using this configuration, cooling power is doubled with reduced cost of compressor. The design, fabrication and testing of Linear Moving Magnet Synchronous Motor (LMMSM) based dual piston head linear compressor are carried out indigenously. Finite Element Method (FEM) analysis is used for estimating eddy current loss and flux distribution pattern in various mover configurations of the linear motor. The developed fabrication and assembly procedure of linear motor are discussed in detail. The mover of linear motor is supported by using a pair of cross armed C – type flexures. These flexures are designed using FEM and are fabricated indigenously. The flexure pairs are tested for 108 cycles with ± 3 mm stroke length of linear motor before assembling compressor. Linear motor is usually required to be operated at different frequencies. Thus, a variable frequency and variable voltage Pulse Width Modulated (PWM) based power supply is designed using analog circuits like Op-Amps. This cost effective power supply is capable of delivering 27 A at 100 V with frequency range of 25 Hz to 80 Hz continuously. Sage software was used to carry out 1-D simulation and obtain dimensions of various Pulse Tube Cryocooler (PTC) components. Various pulse tube configurations like Joint Twin PTC, Twin PTC with buffer volume and single PTC with buffer volume were carried out. A Computational Fluid Dynamics (CFD) Fluent 2-D analysis was carried out for single PTC with buffer volume. The fabrication and assembly procedure of PTC is discussed in detail. A novel method of heat exchanger fabrication was developed and analyzed using FEM and its performance is tested experimentally. The twin PTC is operated at 34 bar and 48 Hz. A light weight High Temperature Superconductor (HTS) based level sensor is developed to monitor the cryogen level. The developed sensor was calibrated against discrete diode array and pre-calibrated continuous capacitance type level sensor. The calibrations were carried out in indigenously designed and fabricated 4-wall cryostat using Liquid Nitrogen (LN2) and LOX as cryogen. LabVIEW software based data acquisition was designed for testing, recording and monitoring the performance of twin PTC and level sensors during experiments.