Dissertations / Theses on the topic 'Compression twin'

Failure mechanisms were studied in wrought AZ31B magnesium alloy under different strain paths and various temperatures. Optical micrographs were used to observe the formation of shear bands and regions of high twin density in samples strained under uniaxial, biaxial and plane strain conditions. Interrupted testing at 4% effective strain increments until failure was used to observe the evolution of the microstructure. Results showed that shear bands with a high percentage of twinned grains appeared early in the samples strained under biaxial or plane strain tension. These bands are similar to the failure region in uniaxial tension specimens. A forming limit diagram for AZ31B was developed from the strain data, showing that plane strain and biaxial tension had very similar limit strains, in contrast to materials like steel or aluminum alloys which typically have greater ductility in biaxial tension compared to plane strain tension. When the experiments are repeated at elevated forming temperatures of 75 C and 125 C there is no observable shear band formation. The forming limit diagrams for each temperature were created and showed a marked increase in biaxial tension formability, compared to plane strain tension. Optical microscopy showed no sign of any compression twins and very few tensile twins in samples strained in biaxial or plane strain tension, up to 12% effective strain. The lack of compression twins at these strain levels shows that the effect of temperature on critical resolved shear stress for < c+a > slip is greater than previously expected.

Ce projet de thèse expose des méthodes de traitement, dans le domaine des ondelettes, pour résoudre certains problèmes liés à la mise en oeuvre de l’holographie numérique dans l’axe. Ce developpement utilise des outils de la théorie de l’information et des divers moyens de traitement du signal tels que la séparation aveugle de sources (SAS). Cette technique est exploitée, ici, pour améliorer l’efficacité de l’holographie numérique, tels que la suppression de l’image jumelle, l’estimation de l’indice de réfraction, le codage et la transmission temps réel des hologrammes. Tout d’abord, nous donnons une brève introduction à la configuration dans l’axe de l’holographie numérique telle qu’elle est mise en oeuvre à l’UMR 6614 CORIA: l'explication de l’étape d’enregistrement ainsi que les différentes approches de restitution des hologrammes utilisés dans cette thèse. Ensuite, nous présentons un état de l’art des méthodes permettant de résoudre les deux principaux obstacles rencontrés dans la reconstruction des hologrammes numériques: l’étape de mise au point et la suppression de l’image jumelle. Ensuite, nous expliquons méticuleusement l’outil basé sur la transformée d’ondelettes, pour assurer une décomposition multi résolution de l’image, qui permet la séparation aveugle des images mélangées par un produit de convolution. Notre proposition consiste à utiliser la 2ème génération de la transformée en ondelettes d’une manière adaptative appelée aussi Schéma de lifting en quinconce Adaptif (SLQA). Cette décomposition est couplée à un algorithme de séparation appropriée pour former les trois étapes suivantes : les images d’entrées, mélangées par convolution, sont décomposées par SLQA pour former un arbre d’ondelettes. Ensuite, on applique l’algorithme de séparation sur le noeud le plus parcimonieux, généralement à la résolution la plus élevée, et enfin les images séparées sont reconstruites à l’aide de l’inverse de SLQA. Cet outil est appliqué pour résoudre plusieurs problèmes liés à des applications d’holographie numérique dans l’axe. Dans ce contexte, deux méthodes sont proposées. La première méthode, utilisant l’entropie globale, est développée pour rechercher de manière automatique le meilleur plan de mise au point des images holographiques. La deuxième méthode sert à supprimer l’image jumelle qui accompagne l’image restituée. Cette dernière se base sur la décomposition SLQA avec un algorithme de séparation statistique qui utilise la fameuse technique Analyse en Composantes Indépendantes (ACI). Vu que le formalisme d’un produit de convolution est retenu dans l’étape de formation de l’hologramme, l’outil SLQA et ACI assurent parfaitement la tâche de déconvolution. Les résultats expérimentaux confirment bien que nos deux méthodes proposées sont capables d’estimer le meilleur plan de mise au point et d’éliminer l’effet de l’image jumelle dans l’image restituée. Puis, nous proposons d’estimer l’épaisseur d’un anneau dans une image restituée d’un hologramme contenant la diffraction d’une bulle de vapeur stable dans une gouttelette d’un liquide. La dernière partie met en oeuvre le nouveau concept de Télé-Holographie. Il s’agit de mettre en place un échange de flux interactif entre la chambre d’enregistrement des hologrammes in-situ et un laboratoire distant au sein duquel s’effectue le traitement numérique de ces hologrammes. Pour atteindre cet objectif, nous proposons de réaliser une compression sans perte des hologrammes numériques par transformée en ondelettes. Pour la phase de la transmission progressive, selon la capacité du canal de transmission, nous proposons une manière efficace pour le codage de l’arbre des zéros des coefficients emboités obtenu par la transformée d’ondelette en quinconce (SLQA). Ce codeur nous permet une réduction considérable du débit binaire lors de la transmission des hologrammes. Les premiers tests effectués sur des hologrammes réels, enregistrés au sein du laboratoire CORIA, montrent une amélioration significative des taux de compression totale et de la taille de l’hologramme compressé
The present thesis is meant to develop specific processes, in the realm of wavelets domain, for certain digital holography applications. We mainly use the so-called blind source separation (BSS) techniques to solve numerous digital holography problems, namely, the twin image suppression, real time coding and transmission of holograms. Firstly, we give a brief introduction to in-line configuration of digital holography in flow measurements: the recording step explanation and the study of two reconstruction approaches that have been used during this thesis. Then, we emphasize the two well known obstacles of digital holograms reconstruction, namely, the determination of the best focus plane and the twin image removal. Secondly, we propose a meticulous scrutiny of the tool, based on the Blind Source Separation (BSS), enhanced by a multiscale decomposition algorithm, which enables the blind separation of convolutively mixed images. The suggested algorithm uses a wavelet-based transformer, called Adaptive Quincunx Lifting Scheme (AQLS), coupled with an appropriate unmixing algorithm. The resulting deconvolution process is made up of three steps. In the first step, the convolutively mixed images are decomposed by AQLS. Then, separation algorithm is applied to the most relevant component to unmix the transformed images. The unmixed images are, thereafter, reconstructed using the inverse of the AQLS transform. In a subsequent part, we adopt the blind source separation technique in the wavelet field domain to solve several problems related to digital holography. In this context, we present two main contributions for digital in-line hologram processing. The first contribution consists in an entropy-based method to retrieve the best focus plane, a crucial issue in digital hologram reconstruction. The second contribution consists in a new approach to remove a common unwanted artifact in holography called the twin image. The latter contribution is based on the blind source separation technique, and the resulting algorithm is made up of two steps: an Adaptive Quincunx Lifting Scheme (AQLS) based on the wavelet packet transform and a statistical unmixing algorithm based on Independent Component Analysis (ICA) tool. The role of the AQLS is to maximize the sparseness of the input holograms. Since the convolutive formalism is retained in digital in-line holography, BSS-based tool is extended and coupled with wavelet-based AQLS to fulfill the deconvolution task. Experimental results confirm that convolutive blind source separation is able to discard the unwanted twin image from digital in-line holograms. The last of this part consists in measuring the thickness of a ring. This ring is obtained from an improved reconstructed image of an hologram containing a vapor bubble created by thermal coupling between a laser pulse and nanoparticles in a droplet of a liquid. The last part introduces the Tele-Holography concept. Once the image of the object is perfectly reconstructed, the next objective is to code and transmit the reconstructed image for an interactive flow of exchange between a given laboratory, where the holograms are recorded, and a distant partner research. We propose the tele-holography process that involves the wavelet transform tool for lossless compression and transmission of digital holograms. The concept of tele-holography is motivated by the fact that the digital holograms are considered as a 2D image yielding the depth information of 3D objects. Besides, we propose a quincunx embedded zero-tree wavelet coder (QEZW) for scalable transmission. Owing to the transmission channel capacity, it reduces drastically the bit rate of the holography transmission flow. A flurry of experimental results carried out on real digital holograms show that the proposed lossless compression process yields a significant improvement in compression ratio and total compressed size. These experimentations reveal the capacities of the proposed coder in terms of real bitrate for progressive transmission

L'extraction aqueuse des lipides de la graine de tournesol est étudiée en contacteur agité. La diffusion à l'intérieur des particules est le facteur limitant de l'échange de matière. Les protéines sont impliquées dans l'entraînement et la stabilisation des lipides par l'eau. Le fractionnement de la plante entière est également étudié avec l'eau en extrusion bi-vis. Un extrait et un raffinat sont obtenus séparément et en une seule étape continue. Des rendements d'extraction en huile de 55 % peuvent être obtenus sous forme d'émulsions huile/eau. Leur stabilité est assurée par la présence à l'interface de tensioactifs : les phospholipides et les protéines voire les pectines. Les extraits se composent aussi d'une phase hydrophile. Prépondérante, elle contient des composés hydrosolubles (protéines, pectines…). Riches en fibres, les raffinats présentent une teneur significative en protéines au comportement thermoplastique. Ils peuvent être transformés en agromatériaux par thermomoulage.

Apresentamos neste trabalho o projeto e a construção de um Oscilador Paramétrico Ótico (OPO), demonstrando o caráter quântico da correlação de intensidade dos feixes sinal e complementar nele produzidos a partir de um feixe de bombeio de 532 nm. Estudamos ainda a compressão quântica de ruído no feixe de bombeio refletido por uma cavidade de OPO, obtendo 38 % de redução (abaixo do limite quântico) no ruído de quadratura de um feixe de 1064 nm produzido por um laser de Nd:YAG. Por fim, observamos a formação de estruturas nos feixes de saída para cavidades com modos transversos degenerados (confocal e concêntrica) e demonstramos pela primeira vez o caráter multimodo transverso das correlações quânticas em um OPO com cavidade confocal.
We present in this work the project and construction of an Optical Parametric Oscillator (OPO), showing the quantum behavior in the intensity correlation of signal and idler beams, generated from a 532 nm pump. We have also studied the quantum noise compression in the pump beam reflected from an OPO cavity, obtaining 38 % of noise reduction below the vacuum fluctuations in the quadrature of a 1064 nm beam coming from a Nd:YAG laser. Finally, we observed the pattern formation in the output beams for transverse degenerate cavities (confocal and concentric) and we show, for the first time to our knowledge, the transverse multimode behavior in the quantum correlation of a confocal OPO.

The application of high resolution electron backscatter diffraction (HR-EBSD) techniques has been used in order to study the evolution of geometrically necessary dislocation (GND). The tested materials were taken from AZ31 magnesium sheet which had strong basal texture. Because of low symmetry of the magnesium crystal lattice, the von Mises criteria cannot be satisfied by the three independent, easily activated, basal slips. The strain along the c-axis of the crystal must be accommodated by either twinning and/or slip systems. HR-EBSD data was taken in order to investigate these phenomena. The HR-EBSD results were post processed in order to resolve total GND density onto the observed possible slip systems. The first chapter of the investigation focused on the correlation between resolved GNDs with tensile twin nucleation, and the subsequent propagation path in the microstructure. For this purpose, 2.5 % strain was applied in a uniaxial compression test along the transverse direction (TD). Several fine scan were done at the boundaries where twin formed. The results show that in order for a twin to nucleate spontaneously at the grain boundaries, two criteria should generally be met: high angle grain boundaries (35-45°) and pile ups of basal slip system in neighboring grain at the other side of the boundary. Furthermore, once nucleation has initiated, twin propagation can occur through low angle grain boundaries (15-25°); if a twin reaches a high angle boundary, it will generally terminate at the boundary at low strain levels. A twin may pass through high angle boundaries with further deformation. In the second chapter, deformation of the AZ31 magnesium alloy was study for different strain paths. For this purpose, compression and tension in-situ tests were done and the texture and GND evolutions were investigated. The results show that the load paths, compression and tension, evolve the microstructure in different ways. Massive twin fractions were formed in compression, and higher GND contents were observed in tension tests. It was observed that at higher strain levels GND contents are roughly independent of the initial texture but the activation of slip systems at low strain strongly depends on initial structure. If the samples were loaded along RD, GND density increased sharply at low strain. In contrast, for the samples loaded along TD, GND increased moderately. A small amount of repetition is apparent in the two parts of the thesis due to them being formatted for individual publication as journal papers.

碩士
國立中正大學
機械工程所
96
The thesis focuses on the vibration analysis of twin-screw compressors by using finite element software ANSYS. In the first part, the natural frequency and mode shapes of female and male rotors are investigated individually using ANSYS and the results are validated experimentally by modal testing. The deviations in natural frequency between ANSYS and experiment up to the first six modes all are within 7%. Moreover, results from ANSYS reveal that a torsional mode corresponding to 880 Hz while two rotors is meshing together is much lower than those of the individual modes of female and male rotors, respectively. It implies that this torsional mode plays an important role in the vibration of twin screw compressor. The second part of the thesis studies the vibration response for a twin screw compressor while the varying pressure is taken into consideration in the FEM model. The air pressure is obtained experimentally and then is transferred to the FEM model. Therefore the vibration response of the twin screw compressor is determined semi-empirically. A user-friendly interface is developed to conduct the vibration analysis of twin screw rotor with air pressure included automatically. By simply input the data of rotor profile and the contact line between two rotors, one may utilize this program integrated with ANSYS to determine the mode shapes, bearing forces, and stress distribution of a twin screw rotor.

碩士
國立中正大學
機械系
92
The moving compressed air is one of main sources, which causes the vibration of the twin screw compressors. However the compressed air is also influenced by the mesh between the rotating male and female rotors. In this thesis, the rotors in a twin screw compressor are modeled as two simply supported Timshenko shaft due to the fact that both the male and female rotors are stubby. The displacement responses for both the male and female rotors are represented using assumed mode method and then the equation of motion is derived using the Lagrange method. The dy-namic characteristics that include natural frequencies and the mode shapes are obtained by solving the free vibration of the system. The tran-sient response is also obtained by using the Runge-Kutta method. The displacement responses corresponding to two different tooth profiles are studied. Results show that the tooth file affects the compressed air and thus it influences the associate vibration response of the meshing rotor. The algorithm developed in this thesis provides a tool which predicates the vibration response of the twin screw compressor after the tooth profile of the rotor is determined.

碩士
國立中央大學
機械工程研究所
95
Twin screw rotor compressor has the advantages of simple structure, unique system, and reliable and easy operation; therefore it is widely used in various construction works involving aerodynamics and refrigeration air conditioning, etc., making it a new compressor model with a broad application future. This study intends to determine the three key precision parts of screw compressors by making an in-depth research into the assembly process of the twin screw rotor compressor and the size design of various parts. By utilizing and analyzing the results obtained from the 1-D and 2-D assembly simulation software developed to analyze the assembly process, possible situations and the defective rate that may occur after assembly was obtained. Modification advice was therefore proposed based on the original design and size, in order to improve the yield rate of the twin screw rotor compressor, reduce any difficulties in assembly, and cut down on both labor cost and time, while providing future designers with some reference for shortening the design period.

碩士
國立中正大學
機械工程所
94
The thesis focuses on the investigation of vibration caused by the meshing between the male and female rotors in a twin-screw compressor during operation. The female and male rotors are modeled as two coupled, simply-supported rotating Timoshenko beams due to the fact that both the male and female rotors are stubby. The equations of motion are derived using Lagrange method and then the dynamic characteristics that include natural frequencies and the mode shapes of the meshing rotors subjected to air loading are obtained using Runge-Kutta method. The time and frequency vibration responses caused by the varying meshing stiffness and the unbalance are studied. Moreover, the meshing between the male and female rotors is simulated and the associate contact stress between the meshing teeth and the resulting deformation were investigated using the finite element method package, ANSYS-LSDYNA. Finally, a transfer matrix was developed to model the vibration path from the meshing teeth to the bearing, via the rotating shaft, which can be used as a reference for future experiments.

碩士
國立臺灣大學
機械工程學研究所
87
A theoretical method correlated with experimental data is proposed to investigate the performance of a twin screw compressor. The influences of various design parameters on the performance of the compressor are discussed in particular. The theoretical analysis begins with the derivation of a set of differential equations based on the thermal-fluid theory. The effects of gas leakage, heat exchange between gas and injected oil, etc. are all considered in the derivation. The derived system of equations is them solved using a Runge-Kutta method in which the rotational angle of the male rotor is selected to be the independent variable. Through the feedback of experimental data, the analytic model can further be used for the performance analysis of a certain type of screw compressor. In the present study, both the air and R22 compressors are considered, and the effects of different design parameters such as oil injected position, oil temperature, oil flow rate, tip speed, slide valve position, and economizer on the performance of the compressors are investigated. Output variables such as specific power, compression efficiency, volumetric efficiency, and discharge temperature are obtained. Some of the results are compared with the experimental data again. Good agreements between the simulation results and the experimentally measured data are found. It indicates that the theoretical model can be used by the manufacturers in the development of an optimally performed screw compressor.

Twin-screw pumps are positive displacement machines. Two meshing screws connected by timing gears convey the fluid trapped in the screw chambers axially from suction to discharge and force it out against the back pressure. Because of the screw geometry, the circumferential pressure field around the screws is not balanced, resulting in net dynamic and static pressures applied on the rotors. The research work presented here aims at building and verifying a model to predict both: (1) the exciting lateral hydrodynamic forces produced by the unbalanced pressure field, and (2) the rotor response due to those forces. The model rests on the screw pump hydraulic models for predicting the pressure in the screw chambers as a function of the discharge pressure. These models are extended to predict the steady state dynamic pressure field as a function of the rotational angle of the rotor. The dynamic force resulting from the dynamic pressure field is calculated and applied to the rotor as a set of super-synchronous periodic forces. The structural model of the screw, although nonsymmetrical, was found to be accurately represented by an axisymmetric equivalent structure. The rotor response to the dynamic super-synchronous forces is calculated to predict the pump rotordynamic behavior. The work in this dissertation presents: (1) the axisymmetric structural model of the rotors (2) the proposed dynamic pressure model, (3) the screw pump rotor response, (4) the experimental validation of the dynamic pressure model and rotor response. The topic of twin-screw pump rotordynamics is absent from the literature. The original contribution of the work presented in this dissertation to the field of rotordynamics includes: (1) demonstrating the adequacy of an axisymmetric model for modeling the screw section, (2) developing a model for predicting the dynamic pressure field around the screws, (3) characterization of the dynamic forces (synchronous and its harmonics) applied at the screw pump rotors, (4) predicting the dynamic response of twin-screw pump rotors due to hydrodynamic forces, (5) measuring the axial dynamic pressure in two circumferential planes around the screws to verify pressure predictions, (6) measuring the dynamic response of twin-screw pump rotor.

碩士
國立中正大學
機械工程所
95
Interference and abnormal wear are most common failures for the twin screw compressor. These failures are often caused by thermal expansion, hydrodynamic effects, and assembly errors. Reasonable clearance between meshing rotors is required to avoid such interference and abnormal wear. A feasible rotor profile modification is proposed in this thesis to provide reasonable clearance between rotors considering assembly errors. A numerical method is developed to calculate the interference due to assembly error. Based on these interference values, the rotor surfaces can thus be modified in accordance to several correction methods. Finally, the gap between two rotors under the given conditions can ensure be positive values by the repeat interference. Therefore, the design procedure and inclusive methods in this thesis are useful and general for the clearance distribution of rotors of twin-screw compressors.

碩士
國立屏東科技大學
機械工程系所
101
Noise emission from twin screw compressors is of concern in industry. The establishment of noise and vibration measurement and evaluation procedures is important and beneficial to increase the efficiency of development as well as quality control. To build up a standard operation procedure for measurement and evaluation on noise and vibration is the main theme of this work. This thesis first describes the idea for noise and vibration measurement and develops the receiver test and path test for detail experimental implementation. The receiver test aims to discuss the noise of compressor in different operating conditions as well as the correlation analysis between noise and vibration of compressors. Experimental approaches in the receiver test are accordingly planned. The noise characteristics for different types of twin screw compressors are then presented. The procedure for the path test is also established and conducted to evaluate and diagnosis the possible noise sources. The sound power level of a twin screw compressor is finally determined by referring to ISO standards to build up the measurement and analysis procedures. This work lays out the noise and vibration measurement as well evaluation procedure in particular for the twin screw compressor and leads to provide an objective way to conduct the noise diagnosis for machineries.

碩士
國立中正大學
機械工程所
96
The design parameters of rotor tooth profile and compressor structure are very important for the twin-screw compressor design to improve the compressor efficiency. This thesis use L36(211×312) and L50(2×511) Taguchi’s orthogonal arrays with SCCAD to analyze the contribution of these parameters upon the volumetric efficiency and the isentropic efficiency of the twin-screw compressor. Thus determine the best parameter combination. The analysis of Taguchi’s methods shows that, when the structure parameters are chosen, tooth profile parameters will affect the efficiency and the leakage path of the compressor. The smaller Blow-hole area and the shorter length of contact line, the more efficient the compressor will be. However, the analysis of Taguchi’s methods also shows that, the structure parameters of compressor have more influence to volumetric efficiency and isentropic efficiency. Therefore, for the best compressor efficiency, the level of structure parameters should be determined before the parameters of tooth profile are determined.

碩士
國立臺灣大學
機械工程學系研究所
86
The influences of design parameters on two-stage air twin screw compressor performances are theoretically investigated. A mathematical model considering the effect of real gas, gas leakage, and heat exchange between gas and injected oil, etc. is developed. The system of equations is solved using a Runge - Kutta integration algorithm with rotating angle of the male rotor as the independent variable. The model is corrected by experimental data and has better prediction ability later. The model is utiliz ed to analyze the performance of a two - stage air twin screw compressor. The design parameters considered to improve performance in the thesis include buil d-in volume ratio,intermediate pressure,intermediate temperature, oil flowrate , oil inlet temperature,and angular velocity of male rotor. Optimized designed parameters and operating conditions are presented. The numerical results show good agreements with experimental data provided by the manufacturer or ob tained from relevant literature. From the results of this study, the effect of design parameters can be realized. Besides, it may beused as a reference for manufacturers in designing or improving similar machines.

博士
國立中正大學
機械工程所
95
The rotor profiles of a twin screw compressor have a great influence on the compressor performance. This dissertation proposes novel design methods of rotor and cutter profiles for the twin screw compressor. The research subjects are: 1. Based on the gearing envelope theory, three different rotor profile design methods are derived mathematically, including: the popular generation method starting with one known rotor profile, the rack generation method and the meshing line generation method. 2. A design method for the rotor profile of a twin screw compressor starting from an arbitrary cubic-spline sealing line is presented. Based on the adjusted sealing line, the length of the contact line can be instinctively modified to obtain a better compressor performance. 3. A novel method, named the “NRGM” (Normal-Rack Generation Method), is proposed to generate rotor profiles by using a rack defined in the normal plane. The advantages of this method include: (a) higher modifiable flexibility of rotor tooth profiles and (b) the rack cutter or hob has a constant normal circular pitch and can also be used in the varied tooth combination or varied helix angles of twin screw rotors. 4. A numerical method, named the radial-ray shooting (RRS), is presented to approximate the envelope of the generating locus instead of the analytic envelope theory. The grinding wheel profile and the rotor profiles of the cutting simulation can be obtained by the RRS method with acceptable profile accuracy.

碩士
國立屏東科技大學
機械工程系所
100
The male and female rotors inside the twin-screw compressor are the core components of the refrigeration and air conditioning systems. The tooth design of male and female rotors, geometric design of the compressor main body and the internal flow channel, and the leak path inside the compression chamber all have a significant impact on the compressor performance. However, the geometry of rotor and compression chamber is very complex, and the current geometric computation software is limited to built-in rotor tooth profiles; otherwise, complicated numerical methods need to be adopted for the computation of geometrical characteristics of the compressor which often fail to find convergence solutions. For the optimal design of compressor, it is often necessary to make adjustments manually and results in many limitations in research and development. Therefore, in this study we will explore methods that quickly calculate the complex shape area using the image binarization to compute the geometric characteristics of male and female rotor structures in the twin-screw compressor. The numerical computation software Mathematica is adopted for programming and development. The discrete measurement points of female rotor tooth shapes are processed with special point data processing methods. According to the gear envelope theory, the mutually enveloped data points of male and female tooth shapes and the corresponding engagement angles are derived to improve the freedom of use of the developed program. This study applies the image binarization method to calculate the complex geometric characteristics of the rotor, including the static rotor tooth space and case wall, area and volume of all leak paths, length of dynamic leak path, and changes of area, area of tooth space and volume according to the changes of angles. Numerical examples show that the calculation error between calculation results of geometric characteristics of this study and the twin-screw compressor design software SCCAD is within 5%. The calculation results of geometric characteristics in this study can be further used as a reference for the thermodynamic performance simulation and stress analysis calculation of twin-screw compressor.

碩士
國立臺灣大學
機械工程學系
85
Screw compressors have been developed and manufactured in Taiwan in recent years. The theoretical study of screw compressor, however, is rarely found in the academic field. Therefore, some problems related to twin screw compressors are theoretically studied in the present thesis. Special attention is paid to the following topics. First, a mathematical model for the calculation of compression force and contact force of the rotors is developed. Secondly, a method for the calculation of bearing loads is proposed . A probabilistic method for the prediction of bearing life is presented as well. Thirdly, a way to estimate the deflection of the shaft is shown. Finally, formulas for the determination of some critical running speeds of the compressor are derived in consideration of various vibration modes. Numerical examples are performed based on the real geometry of marketed compressor products. Some interesting concluding remarks found in the present thesis are therefore beneficially to the improvement of the current products as well as to the future development of a new product.

碩士
國立中央大學
機械工程研究所
97
In the screw compressor factory, with the development of inspection equipment and technology, from the inspecting data analysis and Statistical Process Control (SPC) analysis, both of that can be reach and get the results by the existing software. However, the drawback is that the analysis functional constant, manual and complicated setting procedure and independent of the analysis results, it is inefficient for overall analysis process. Therefore, in this research developed a quality control and inspection system, which construction in the rotor inspection software – RotorInspector which was developed in my lab. With a focus on automating analysis of inspecting data and Statistical Process Control(SPC) analysis. And get the purpose of process integration and automation of analysis procedures. And consideration of the actual needs for quality control personnel to achieve customization of system development. In this system use database Access as the basis, which through the Visual C + + programming to transmit data by network. On this basis, we can build the inspection database automatically, and integrate the overall inspecting process. By a detailed planning to the process of inspection, that can be achieve the automated analysis procedure.

碩士
國立中正大學
機械系
88
The design of tooth profiles of twin-screw compressor plays an important role to avoid the problem of leakage. In the process of design of the tooth profile, it is known that the line of action (i.e., the summation of instant contact points in the fixed coordinate system) causes great effects on the performance of the screw compressor. It is very important to have shorter length of line of action, the closing and continuous line of action and the shorter distance between the end of line of action and the housing cusp for designing good performance rotors. Therefore, the significance of line of action is apparently. This study proposes a mathematical model for the tooth profiles of twin-screw compressor by using the given line of action. This mathematical model can be applied to any kind of line of action. The relative curvature, sliding velocity, contact ratio, limitation of undercutting and the mating tooth profiles are derived directly from the line of action. Utilizing the mathematical model, it can directly design the line of action that satisfies the requirement of lower leakage and then derive the new profiles which needs for the rotor of twin-screw compressor.

碩士
逢甲大學
機械與電腦輔助工程學系
103
The main content of this thesis is to analyze axial force and strength of the synchronous gears for driving a non-oil twin screws air compressor. The air pressure applied on the screw rotors has been estimated. This distributed pressure forces are employed to calculate the axial thrust of the screw rotors by using dynamic analysis software ADAMS. The object is to design a pair of helical synchronous gears to drive the screw rotors and generate opposite axial thrust force to balance the axial thrust from screw rotors. Helical gears of modulus 1.5 with 24 degrees helix angle and modulus 1.75 with 20 degrees helix angle are compared in this paper. Finally the strength of the helical gears are analyzed by finite element analysis software ABAQUS. The results show that bending fatigue failure at root fillet of gear teeth and surface fatigue failure caused by cyclic Hertz contact stress are two factors most likely to govern the design.

碩士
國立中央大學
機械工程學系
106
Nowadays, the estimation of twin screw compressor performance can be done quickly by using Computation Fluid Dynamics (CFD). A method of 3-D geometry simplification for CFD simulation of a twin-screw compressor has been proposed. In this method, the new suggested simplified model was developed based on theoretical approach, i.e. generating of rotor profile and sealing line for the axial suction and discharge port, while the radial suction port based on three-dimensional (3D) rotor curve. This research used an oil-injected 5/6 screw refrigeration compressor model RE-260 made by Hanbell Co. in Taiwan. This type of compressor has five and six lobes with patented profile of male and female rotor, respectively. The development of CFD model used three types of software, namely Wolfram Mathematica, AutoCAD, and SolidWorks. This model then was exported to ANSYS Mesh for the purpose of the static grid generation. In order to couple the set of generated grids from rotor domain and stator domain, CFD solver can be used to carry on this jobs. A ready to use simulation setup has been provided by TwinMesh. Finally, the results of ANSYS CFX simulation have been discussed to determine the geometric suitability between the new suggested simplified model and the manufacturing model.

碩士
國立中正大學
機械系
93
The leakage of rotors could be observed from the sealing line. The leakage is an important factor that influences the efficiency. Conventionally, the development of a twin screw rotor with high efficiency is started from designing a tooth profile. It is logical to observe the sealing line of the rotor to judge that the leakage is decreased or not. If the leakage is not decreased, modify the tooth profile till you obtain a good sealing line. Therefore, we try to develop a design process starts from the shape of the sealing line. Several segmented cubic splines are used to describe the sealing line. We develop a sealing line with little leakage and then use the sealing line to derive the equations of tooth profile. Control points on the sealing line are used as design variables. We can move the control points to change the shape of the sealing line and then derive the corresponding tooth profile of screw rotors. Using software to calculate the volumetric efficiency, isentropic indicated efficiency and average torque on male and female rotors. The tooth profiles are optimized by the isentropic indicated efficiency with the constraints of the transmitted torque, the minimum curvature of the tooth profile, etc. The design variables include the shape of the sealing line, tip radius, addendum, the ratio between rotor length and the outer diameter, and the wrap angle. A numerical example is presented to show the validation of the purposed design process.

碩士
國立中央大學
機械工程學系
104
A Study of the Correlation between Geometric and Dynamic Properties of Twin Screw Compressor Rotors under Circulating Pressure Load. High performance and low noise are characteristics of twin screw compressors, and they are often used in many industries that require energy saving and high efficiency energy systems. Establishing a model that can successfully predict the dynamic responses of twin screw compressors under circulating pressure loads can improve the system’s rotational properties, and easily change various working components such as rotor screws, bearing components, gaining preliminary understanding of changes in rotational speed, rotation frequency, tooth load, and vibration signal in female rotors., substantial design parameters for the industry can then be provided. Therefore, this study proposes a new method to establish a multibody dynamics model for rotor screws and bearing systems. Variations in axial force, radial force and moment of force of circulating pressure on rotor screws within the compressor’s working chamber are investigated, Hertz contact stiffness of varying rotor contact on radius of curvature is also examined. Multibody dynamic responses of rotor screws and bearing systems within the oil-injected twin screw compressor are then examined through theory and examination. This study then uses the established multibody dynamics model to examine the internal working chamber’s nine dynamic properties, including excessive compression, vibration, half load, rotor axial deviation, and heat and pressure effects. These property changes are organized and concluded to inspect the effects on the female rotor’s rotational frequency output, tooth load, vibration signal frequency spectrum. The conclusions are provided as substantial suggestions for manufacturers to preliminarily investigate compressor noise source, and improving the dynamic properties of compressors.

碩士
國立中正大學
機械系
90
The efficiency of the twin-screw compressor depends mainly on the leakage. Smaller leakage leads to higher efficiency. The conventional design process for the tooth profile of the twin-screw rotor is started from a pre-determined rotor addendum curve. According to the addendum curve, the conjugate dedendum are derive. Then, the length of the sealing line, the size of blow hole and volume efficiency are calculated. However, the conventional design process is very difficult to improve the tooth profile design because the performance of twin-screw rotor can not be observed directly on the addendum curve. In this thesis, a design process of the tooth profile of rotor is proposed to lower the leakage and improve the volume efficiency. Since the leakage can be observed directly form the sealing line (instantaneous contact line between rotors, i.e. line of action ), we propose a design procedure started from the line of action. The line of action can be composed from arc, involute curve, straight line, cycloidal curve, or cubic spline. The tooth profile and the conditions of undercut are derived based on the shape of the line of action. Differential geometry and theory of gearing are utilized to guarantee the smooth tooth profile and the smooth running between rotors. Numerical examples are presented to explore the design guide lines. Three improved rotor tooth profiles are proposed to show the capability of the proposed design procedures. According to the numerical examples, the proposed tooth profile have higher volume efficiency, shorter sealing line and smaller blow hole than SRM tooth profile which is the major commercial products available on the market.

碩士
國立屏東科技大學
機械工程系所
99
The twin-screw compressor has been widely used in the air-conditioning and aerodynamic fields. It comprises a pair of mating rotors within the casing, and the space trapped within them is reduced progressively to complete the compression cycle as the rotors rotate. Therefore, profile design and machining quality of the rotor may greatly affect the compressor performance. Although most rotors are manufactured by the disk-type form tools with index feed nowadays. There still exists a more economical manufacture method to be worthily considered by using the worm-type tools in rapid and large-batch production of the medium- or small-size rotors. But, there are few references mentioned about the rotor generating grinding, and almost stressed on the worm hob design. Therefore, a general mathematical model based on the rotor machining with the worm-type grinding wheel grinding worm is established in this thesis. Further, the influence of the feed parameters on the machined rotor surface is also analyzed. First, the normal-rack generation method (NRGM) is applied in this study to generate the grinding worm to machine the screw rotor. The advantage of this method is that the rotors with different helix angles can be grinded by the same grinding tool and the normal pressure angle of the machined rotor profile can be changeless. Then, a general mathematical model and coordinate systems are established to simulate the rotor machining with the grinding worm. Each instant contact point between the worm grinding worm and the machined rotor can be obtained by using the two-parameter enveloping method. Finally, the normal errors between the machined and nominal rotor surfaces with different machine settings are considered in order to offer as the research basis of the rotor grinding on the multi-axis CNC gear grinding machine in the future.

碩士
國立中央大學
機械工程學系
106
Twin-screw compressor is a fluid machinery with high efficiency, high stability and low noise used in refrigeration, air conditioning, food manufacturing and other industries. However, improving performance and reducing vibration is still an important issue for the development of compressor manufacturing industry. This thesis proposes a set of theoretical numerical analysis method to calculate gas-induced force and torque on rotors, operating power of motor and force on the bearings under different working conditions and rotor tooth types based on discrete points of rotor tooth and the pressure curve in working chamber that is calculated by thermodynamics and fluid dynamics quickly. The results calculated by theoretical numerical analysis method are then compared and verified by CFD (computational fluid dynamics) model. Importing cyclic gas-induced force and torque on rotors into MBD (multi-body dynamics) model considering Hertz contact stiffness of rotors and gas-induced load on rotors to analyze the contact force between rotors, force on bearings and acceleration of bearings under time and frequency domain for different working conditions (100%, 75%, 50% and 25% loading conditions), and investigating the characteristic of dynamic response of Twin-screw compressor and make reasonable suggestion to improve the vibration behavior of compressor.

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.