Rozprawy doktorskie na temat „Pulse Tube Refrigerator”

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2007.
"June 2007."
Includes bibliographical references (p. 41).
A first order model for the behavior of a linear orifice pulse tube refrigerator (OPTR) was developed as a design tool for construction of actual OPTRs. The model predicts cooling power as well as the pressure/volume relationships for various segments of the refrigerator with minimal computational requirements. The first portion of this document describes the development of this model and its simplifications relative to higher-order numerical models. The second portion of this document details a physical implementation of the pulse tube and compares its performance to the predicted performance of the model. It was found that the model accurately predicted qualitative behavior and trends of the orifice pulse tube refrigerator, but that the predicted temperature difference was approximately five times higher than the measured temperature difference. It is believed that the model can be improved with provisions for flow choking as well as warnings for behavior outside of the accepted operating conditions.
by Alisha R. Schor.
S.B.

A single-stage pulse tube cryocooler was designed and fabricated to provide cooling at 50 K for a high temperature superconducting (HTS) magnet, with a nominal electrical input frequency of 50 Hz and a maximum mean helium working gas pressure of 2.5 MPa. Sage software was used for the thermodynamic design of the pulse tube, with an initially predicted 30 W of cooling power at 50 K, and an input indicated power of 1800 W. Sage was found to be a useful tool for the design, and although not perfect, some correlation was established. The fabricated pulse tube was closely coupled to a metallic diaphragm pressure wave generator (PWG) with a 60 ml swept volume. The pulse tube achieved a lowest no-load temperature of 55 K and provided 46 W of cooling power at 77 K with a p-V input power of 675 W, which corresponded to 19.5% of Carnot COP. Recommendations included achieving the specified displacement from the PWG under the higher gas pressures, design and development of a more practical co-axial pulse tube and a multi-stage configuration to achieve the power at lower temperatures required by HTS.

L'4He et l'3He sont des systèmes modèles pour comprendre les propriétés quantiques de la matière fortement corrélée. C'est pour cette raison que plusieurs études ont été consacrées à la compréhension de leur dynamique. A basses températures où les effets quantiques jouent un rôle essentiel, les excitations élémentaires dans l'4He sont décrites par un mode collectif d'excitations: phonon-roton. Par contre pour un système d'3He la description est plus complexe, le spectre d'excitation a deux composantes: un mode collectif (zéro-son) et un continuum d'excitations incohérentes de type particule-trou. Les deux sont bien décrites par la théorie de Landau des liquides de Fermi qui trouve sa validité pour des petits vecteurs d'onde. Jusqu'à présent, on supposait que la dynamique dans les liquides de Fermi à vecteurs d'onde élevés était essentiellement incohérente. Cette thèse porte sur l'exploration, par diffusion inélastique de neutrons, des excitations collectives dans l'3He liquide 2D adsorbé sur un substrat de graphite. Un tel travail expérimental requiert trois ingrédients essentiels : un réfrigérateur à dilution afin de travailler à basses températures, un spectromètre temps de vol afin de mesurer le facteur de structure dynamique du système et un substrat solide (graphite exfolié ZYX) pour la préparation de films d'3He-2D par physisorption. Nos expériences sur ces films d'3He déposés en deuxième couche sur de l'4He solide adsorbé sur le graphite nous ont permis de faire les observations suivantes : à petit vecteur d'onde, le zéro-son est plus proche de la bande particule-trou que celui observé dans le cas de l'3He massif, tandis qu'à fort vecteur d'onde le mode collectif entre dans le continuum et réapparait de l'autre côté. Cette nouvelle branche, observée pour la première fois, est aujourd'hui décrite par la théorie dynamique à N-corps développée par nos collaborateurs de l'université Johannes Kepler de Linz, Autriche. Au cours de ce travail de thèse plusieurs techniques expérimentales ont été développées, en particulier, un réfrigérateur à dilution sans fluide cryogénique robuste adapté à des expériences de diffusion neutronique. Son optimisation a permis de réduire le temps de refroidissement de ce type de réfrigérateurs.

Pulse tube refrigerators (PTR) are robust, rugged cryocoolers that do not have a moving component at their cold ends. They are often employed for cryogenic cooling of high performance electronics in space applications where reliability is paramount. Miniaturizing these refrigerators has been a subject of intense research interest because of the benefits of minimal size and weight for airborne operation and because miniature coolers would be an enabling technology for other applications. Despite much effort, the extent of possible PTR miniaturization is still uncertain. To partially remedy this, an investigation of the miniaturization of pulse tube refrigerators has been undertaken using several numerical modeling techniques. In support of these models, experiments were performed to determine directional hydrodynamic parameters characteristic of stacked screens of #635 stainless steel and #325 phosphor bronze wire mesh, two fine-mesh porous materials suitable for use in the regenerator and heat exchanger components of miniature PTRs. Complete system level and pulse tube component level CFD models incorporating these parameters were then employed to quantitatively estimate the effects of several phenomena expected to impact the performance of miniature PTRs. These included the presence of preferential flow paths in an annular region near the regenerator wall and increased viscous and thermal boundary layer thicknesses relative to the pulse tube diameter. The effects of tapering or chamfering the junctions between components of dissimilar diameters were also investigated. The results of these models were subsequently applied to produce successively smaller micro-scale PTR models having total volumes as small as 0.141 cc for which sufficient net cooling was predicted to make operation at cryogenic temperatures feasible. The results of this investigation provide design criteria for miniaturized PTRs and establish the feasibility of their operation at frequencies up to 1000 Hz with dimensions roughly an order of magnitude smaller than those that have recently been demonstrated, provided that challenges related to their regenerator fillers and compressors can be addressed.

Le tube a gaz pulse est un cryogenerateur qui, par sa grande fiabilite (pas de partie mecanique fonctionnant a froid ni orifice a basse temperature), sa relative facilite de construction et son importante capacite de refrigeration, est un candidat potentiel pour, par exemple, les applications embarquees sur satellites. Le principal objectif de cette these est d'expliquer le fonctionnement d'un tube a gaz pulse (t. G. P. ) avec orifice. Un modele analytique du t. G. P. Ideal a ete developpe. Le mecanisme des flux de chaleur aux extremites du tube est explique comme le resultat du cycle d'hysteresis subi par les elements de gaz entrant et quittant le tube. Nous avons demontre que, dans les conditions normales de travail le rapport theorie/experience calcule pour la puissance extraite par le gaz a la source froide (egale a celle evacuee a la source chaude) est seulement de 1. 2 alors que ceux des modeles precedents sont compris entre 3 et 5#|#1#,#2#|. Le modele etudie est valable pour n'importe quelle variation temporelle de pression. Pour une forme de pression donnee (mesuree dans le tube, est exprimee avec un minimum de parametres independants, permettant ainsi une optimisation ulterieure du systeme. Les mesures de temperature et de vitesse le long du tube sont en bon accord avec les calculs numeriques. Avec un t. G. P. Ameliore dit hybride, nous obtenons une efficacite comparable a celle d'un cryogenerateur du commerce type gifford-mac mahon. La temperature limite de notre t. G. P. A double entree est de 32 k pour une puissance de 8w a 77k

Pulse tube cryocoolers (PTCs) are among the most attractive choices of refrigerators for applications requiring up to 1 kW of cooling in the temperature range of 4-123 K as a result of the high relative efficiency of the Stirling cycle, the reliability of linear compressors, and the lack of cryogenic moving parts resulting in long life and low vibration signature. Recently, PTCs have been successfully used in applications in the 150 K range, extending the useful range of the device beyond the traditional cryogenic regime. A carefully designed cylindrical cavity referred to as the pulse tube replaces the mechanical expander piston found in a Stirling machine. A network consisting of the pulse tube, inertance tube, and surge volume invoke out-of-phase pressure and mass flow oscillations while eliminating all moving parts in the cold region of the device, significantly improving reliability over Stirling cryocoolers. Terrestrial applications of PTCs expose a fundamental flaw. Many PTCs only function properly in a narrow range of orientations, with the cold end of the pulse tube pointed downward with respect to gravity. Unfavorable orientation of the cold head often leads to a catastrophic loss of cooling, rendering the entire cryocooler system inoperable. Previous research indicates that cooling loss is most likely attributed to secondary flow patterns in the pulse tube caused by free convection. Convective instability is initiated as a result of non-uniform density gradients within the pulse tube. The ensuing secondary flow mixes the cryogen and causes enhanced thermal transport between the warm and cold heat exchangers of the cryocooler. This study investigates the nonlinear stabilizing effect of fluid oscillation on Rayleigh-Bénard instability in a cryogenic gas subject to misalignment between gravitational body force and the primary flow direction. The results are directly applicable to the flow conditions frequently experienced in PTCs. Research has shown that the convective component can be minimized by parametrically driven fluid oscillation as a result of sinusoidal pressure excitation; however, a reliable method of predicting the influence of operating parameters has not been reported. In this dissertation, the entire PTC domain is first fully simulated in three dimensions at various angles of inclination using a hybrid method of finite volume and finite element techniques in order to incorporate conjugate heat transfer between fluid domains and their solid containment structures. The results of this method identify the pulse tube as the sole contributor to convective instability, and also illustrate the importance of pulse tube design by incorporating a comparison between two pulse tubes with constant volume but varying aspect ratio. A reduced domain that isolates the pulse tube and its adjacent components is then developed and simulated to improve computational efficiency, facilitating the model’s use for parametric study of the driving variables. A parametric computational study is then carried out and analyzed for pulse tubes with cold end temperatures ranging from 4 K to 80 K, frequencies between 25-60 Hz, mass flow - pressure phase relationships of -30◦ and +30◦, and Stokes thickness-based Reynolds numbers in the range of 43-350, where the turbulent transition occurs at 500. In order to validate the computational models reported and therefore justify their suitability to perform parametric exploration, the CFD codes are applied to a commercially developed single stage PTR design. The results of the CFD model are compared to laboratory-measured values of refrigeration power at temperatures ranging from 60 K to 120 K at inclination angles of 0◦ and 91◦. The modeled results are shown to agree with experimental values with less than 8.5% error for simulation times of approximately six days using high performance computing (HPC) resources through Georgia Tech’s Partnership for Advanced Computing (PACE) cluster resource, and 10 days on a common quad-core desktop computer. The results of the computational parametric study as well as the commercial cryocooler data sets are compiled in a common analysis of the body of data as a whole. The results are compared to the current leading pulse tube convective stability model to improve the reliability of the predictions and bracket the range of losses expected as a function of pulse tube convection number. Results can be used to bracket the normalized cooling loss as a function of the pulse tube convection number NPTC. Experimental data and simulated results indicate that a value of NPTC greater than 10 will yield a loss no greater than 10% of the net pulse tube energy flow at any angle. A value of NPTC greater than 40 is shown to yield a loss no greater than 1% of the net pulse tube energy flow at all angles investigated. The computational and experimental study completed in this dissertation addresses static angles of inclination. Recent interest in the application of PTCs to mobile terrestrial platforms such as ships, aircraft, and military vehicles introduces a separate regime wherein the angle of inclination is dynamically varying. To address this research need, the development of a single axis rotating cryogenic vacuum facility is documented. A separate effects apparatus with interchangeable pulse tube components has also been built in a modular fashion to accommodate future research needs.

Thesis (M. S.)--Mechanical Engineering, Georgia Institute of Technology, 2008.
Kirkconnell, Carl S., Committee Member ; Ghiaasiaan, S. Mostafa, Committee Chair ; Desai, Prateen V., Committee Member ; Jeter, Sheldon M., Committee Member.

Les SQUID (Superconducting QUantum Interference Device), à haute température critique, permettent la réalisation de magnétomètres directionnels à haute sensibilité, pour des fréquences allant du continu à plusieurs centaines de kHz. Les seuils de détection atteints en chambre blindée autorisent la caractérisation fine du biomagnétisme, dont celui du muscle cardiaque. L'objectif de cette thèse était de réaliser un magnétomètre portable, opérant la détection des signaux cardiaques en milieu magnétiquement non-blindé. La modélisation du signal magnétique cardiaque par un moment magnétique variable permet de montrer qu'une mesure optimale de ce champ peut être réduite à celle de sa composante normale au plan d'étude. Nous montrons également qu'une résolution de $100\,\mathrm(fT)/\sqrt(\mathrm(Hz))$ dans une bande passante de 100 Hz est nécessaire à sa caractérisation. Cependant, de nombreuses sources magnétiques contrarient toutes mesures sans blindage. Ces sources parasites, que nous avons analysées, peuvent être discriminées par leur évolution spatiale. Un sytème gradiométrique permet alors d'extraire le signal magnétique cardiaque en réalisant un filtrage spatial. Un tel dispositif, mis en oeuvre avec deux flux-gates et associé à un processeur de signal numérique (DSP), permet la mise en évidence des pics magnétiques du signal cardiaque et montre l'utilité et la souplesse du traitement numérique en temps réel pour notre application, y compris en milieu ouvert. Un magnétomètre à SQUID dc refroidi par un système cryogénique portable, du type tube à gaz pulsé, s'est révélé inadapté à la magnéto-cardiographie, le bruit lié à ce cryogénérateur pertubant trop largement les mesures dans la bande passante utile. Plusieurs systèmes gradiométriques à SQUID, refroidis par azote liquide, ont été mis en oeuvre. Le signal magnétique cardiaque a été mesuré sans blindage. Des techniques de réductions du bruit à basse fréquence du capteur permettront une meilleure caractérisation du signal cardiaque.

Thesis (Ph. D.)--Mechanical Engineering, Georgia Institute of Technology, 2008.
Jeremy P. Harvey, Committee Member ; Carl S. Kirkconnell, Committee Member ; Kurt D. Pennell, Committee Member ; S. Mostafa Ghiaasiaan, Committee Chair ; Prateen V. Desai, Committee Member ; Sheldon M. Jeter, Committee Member.

碩士
國立臺灣大學
機械工程學研究所
87
The main purpose of the research is to discuss replacing a needle valve or an orifice used in an orifice pulse tube refrigerator(OPT) with a variable resistence, and its effects to the performance of a pulse tube refrigerator.From three different types of designs(random-switch variable resistence,synchronous-switch variable resistence,and pressure-controlled-switch variable resistence) of a variable resistence pulse tube refrigerator(VRPT),we can find the optimal operating conditions for a VRPT.From analyses of the flow network theory to the system,we can compare the difference between analyses of the theory and experimental results,and test the applicability of the theory.Finally we can find the performance of a VRPT is not better than the performance of an OPT.But the facility of a variable resistence is better than a needle valve,so VRPT has the potential of practical application.

碩士
國立臺灣大學
機械工程學研究所
88
The main purpose of this study is to control the cold-end temperature of the VRPT (Variable Resistance Pulse Tube refrigerator) including fixed the cold-end temperature control and increasing the cooling speed in order to apply the VRPT to the CPU cooling in personal computers. The system identification was used in this study to find out the transfer function of the cold-end temperature and the particular input by separating the influence of many inputs of the system. The controller controlled the cold-end temperature in order to achieve a faster cooling speed was designed by an average model of the system over the operating range after considering the nonlinear of the system. The result showed that controlling the cold-end temperature of the VRPT is feasible. The PDF controller can fit the specification and have a better robustness after controlling the cold-end temperature precisely. As a result, the theory of designing the PDF controller makes the VRPT be able to applied in CPU cooling.

The performance evaluation and parametric studies of an Inertance Tube Pulse Tube Refrigerator (IPTR) are performed for different length-to-diameter ratios, with the Computational Fluid Dynamics (CFD) package FLUENT. The integrated model consists of individual models of the components, namely, the compressor, compressor cooler, regenerator, cold heat exchanger, pulse tube, warm heat exchanger, inertance tube and the reservoir. The formulation consists of the governing equations expressing the conservation of mass, momentum and energy with axi-symmetry assumption and relations for the variable thermophysical properties of the working medium and the regenerator matrix, and friction factor and heat transfer coefficients in oscillatory flows. The local thermal non-equilibrium of the gas and the matrix is taken into account for the modeling of heat exchangers and the regenerator which are treated as porous zones. In addition, the wall thickness of the components is also accounted for. Dynamic meshing is used to model the compressor zone. The heat interaction between pulse tube wall and the oscillating gas, leading to surface heat pumping, is quantified. The axial heat conduction is found to reduce the overall performance. The thermal non-equilibrium results in a higher cold heat exchanger temperature due to inefficiencies. The dynamic characteristics of pulse tube are analyzed by introducing a time constant. The study is extended to other types of PTRs, namely, the Orifice type Pulse Tube Refrigerator (OPTR), Double Inlet type Pulse Tube Refrigerator (DIPTR) and a PTR with parallel combination of inertance tube and orifice (OIPTR). The focus of the second phase of analysis is the pulse tube region. The oscillatory flow and temperature fields in an open-ended pipe driven by a time-wise sinusoidally varying pressure at one end and subjected to an ambient-to-cryogenic temperature difference across the ends, is numerically studied both with and without the inclusion of buoyancy effects. Conjugate effects arising out of the interaction of oscillatory flow with heat conduction in the pipe wall are taken into account by considering a finite thickness wall with an insulated exterior surface. Parametric studies are conducted with frequencies in the range 5-15 Hz for an end-to-end temperature difference of 200 K. As the pressure amplitude increases, the temperature difference between the wall and the fluid decreases due to mixing at the cold end. The pressure amplitude and the frequency have negligible effect on the time averaged Nusselt number. The effect of buoyancy is studied for hot side up and cold side up configurations. It is found that the time averaged Nusselt number does not change significantly with orientation or Rayleigh number. Sharp changes in Nusselt number and velocity profiles and an increase in energy transfer through solid and gas were observed when natural convection comes into play with hot end placed down. Cooldown experiments are conducted on a preliminary experimental setup. Comparison of the numerical and experimental cooldown curves disclosed a number of areas where improvement is required, primarily the leakage past the piston and the design of the heat exchangers. The setup is being improved to bring out a second and improved version for attaining the lower cold heat exchanger temperature.

碩士
國立臺灣大學
機械工程學研究所
87
The concept of using electro-magnetic valves to adjust the pressure waveform in an orifice pulse tube refrigerator (OPT) is experimentally and theoretically investigated. The objective of this thesis is to build an OPT system using a modified commercial refrigerant compressor and a pair of solenoid valves. A linear flow network model was developed for the system analysis of this refrigerator. The experiment results show that adjusting the duty cycle of input pressure may improve the cooling power of an OPT up to 20%, but the flow network model is not as accurate as expected.

碩士
國立高雄海洋科技大學
輪機工程研究所
99
The purse seiner is one of the fishing vessels with lots of capital and technology in fishery industries. In west Pacific Ocean, there are 205 American Purse Seiner vessels, of which 88 vessels belong to Taiwan ship-owners (34 vessels are registered in Taiwan others are convenience flag ships). It almost occupies approximately 43 percents. The annual catching of these 34 Taiwan vessels is about two hundred thousand tons, and this is the largest amount in Taiwan deep-sea fishery. The most influential effect of the fish price depends on its fresh condition which can be well tackled by refrigerating the captured fish in best freezing condition. Thus, the design of the freezing system is of paramount importance. A 1100-ton Purse Seiner vessel of the latest design was to achieve cooling approximately 220 tons of fresh cargo (skip jack) from 2°C to -17°C within 24 hours with the aid of brine. After that, the skip jacks are moved to the dry hold and are maintained at about -40°C. The designed cargo capacity were about 1485 cubic meters, and the Purse Seiner vessel can accommodate 935.55tons (ρ=0.63 T/m3 ) at full catching and transits cargo to another vessel one time per month. This article investigates the latest condenser in a refrigerating system of Purse Seiner vessels. Nowadays, the condenser uses pure titanium tubes to replace the traditional steel tubes. Though the titanium condenser has the heat transfer area much smaller than that of the steel-tube condenser, the two condensers possess almost equivalent heat transfer performance. In addition, the former has larger margin in condensing because of its greater overall heat transfer coefficient. Moreover, it is reported that the service life of titanium tube is about 20-30 years. Key words : purse seiner, brine, pre-cooling, full catching, transit cargo