Magnetic Refrigeration at Room Temperature: Design, construction and evaluation of a reciprocating demonstrator and a rotary prototype. Numerical modelling and analysis of an active magnetic regenerator system
The present work aims to bring the magnetic refrigeration technology closer to the commercial application at room temperature. The study is carried out from physical principles in order to understand and optimize the potential of the technology. An exhaustive overview of the technology is presented...
| Autores: | , , |
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| Tipo de recurso: | tesis de maestría |
| Estado: | Versión publicada |
| Fecha de publicación: | 2018 |
| País: | España |
| Institución: | Universidad de Zaragoza |
| Repositorio: | Zaguán. Repositorio Digital de la Universidad de Zaragoza |
| OAI Identifier: | oai:zaguan.unizar.es:86985 |
| Acceso en línea: | http://zaguan.unizar.es/record/86985 |
| Access Level: | acceso abierto |
| Palabra clave: | equipo de refrigeración termodinamica magnetismo simulación |
| Sumario: | The present work aims to bring the magnetic refrigeration technology closer to the commercial application at room temperature. The study is carried out from physical principles in order to understand and optimize the potential of the technology. An exhaustive overview of the technology is presented collecting the literature knowledge and some own considerations. A reciprocating demonstrator was designed and built as a first contact with the technology checking its potential. Experiments carried out with gadolinium showed promising results. Then, a rotary prototype, reaching greater magnetocaloric material (MCM) mass and operation frequencies than the demonstrator, was also designed and built in order to test potential MCMs for magnetic refrigeration, as a system in between the demonstrator and a real application machine. Experiments with the promising LaFeCoSi material family were carried out. Finally, a computer simulation model was developed to better know the dependence of magnetic refrigeration on the various parameters, and specially, to obtain a powerful tool to design efficient magnetic refrigeration systems and maximize their performance.<br />The thesis contains four chapters, as follows:<br />A detailed introduction of magnetic refrigeration at room temperature is provided in chapter 1. The development of the technology is motivated and its weaknesses are explained. Then, the origins of the technology, showing its evolution from the discovery of the magnetocaloric effect (MCE) until its room temperature application, are described. Besides, the thermodynamics of the MCE is briefly introduced supporting the fundamentals of the magnetic refrigeration. The main part of this chapter is an exhaustive overview of the technology including thermodynamic cycles, parts of the refrigerators, performance metrics, irreversibilities and a collection of the earlier prototypes at room temperature and the systems that have reached relevant results. Finally, the current research efforts of the technology are commented.<br />The design of a reciprocating magnetic refrigeration demonstrator is given in chapter 2. A complete description including the magnetic field source (C-shape permanent magnet), the active magnetic regenerator (AMR), fluid flow scheme and its corresponding measurement system, is explained in detail. The experimental setup is also given. Experimental results are carried out with the well-known benchmark MCM gadolinium, exhibiting promising results. A comprehensive study including temperature span, cooling power, coefficient of performance and thermodynamic cycles, is carried out in a broad range of operation parameters. Finally, the general trends of the performance are detailed.<br />The design of a rotary magnetic refrigeration prototype is provided in chapter 3. A full description including the magnetic field source (double Halbach cylinder magnet), the multi-layer AMR, the fluid flow scheme, the cold and hot sinks, the traction system, the room temperature control system and its corresponding measurement system is given in detail. The experimental setup is also given. Experimental results are accomplished with the promising first-order phase transition (FOPT) material family LaFeCoSi. A lower performance than expected with both AMR configurations, 30/20/10/0 and 20/15/10/5 peak temperatures (of the adiabatic temperature change upon the application of a magnetic field) of each multi-layer AMR, is reached. A comprehensive study including temperature span and cooling power is carried out in a broad range of operation parameters. Finally, the main causes of the low performance are pointed out and analysed briefly.<br />A computer simulation model of a static multi-layer AMR system with parallel plate geometry is developed in chapter 4. The model, which includes heat losses to the ambient, viscous dissipation of the fluid and friction heat of the pumping piston, is described in detail together with their governing equations, as well as, the method for discretizing them, the finite volume method. The Gauss-Seidel method is applied to solve the resulting system of linear equations. The post-processing calculations of temperatures, powers and performance metrics are also given. A numerical and an experimental validation is carried out setting the input parameters according to the rotary prototype studied in chapter 3. Reasonable predictions are reported, and then, simulation studies for improving its performance, such as magnetic field, thermal losses, spacing of the peak temperatures of the layers and spacing between the layer with the highest peak temperature and the hot source, are carried out. A comprehensive study of the performance metrics for the better AMR configuration simulated, the 20/17.5/15/12.5 AMR, is also included. Finally, some future studies to improve even more the overall performance are suggested, as well as some interesting ideas for saving computing time.<br />Besides, various appendices are included to complete information from the thesis. The appendix A, which refers to chapter 2, detail an immersion corrosion test with the LaFeCoSi family for choosing the proper heat transfer fluid, Luzar(R) diluted in distilled water. The following appendices refers exclusively to chapter 4: In appendix B, the equivalence between bidirectional and unidirectional flow schemes in static AMR systems is demonstrated by means 1D simulation models for both schemes. In appendix C, measurements of the thermal conductivity for the LaFeCoSi family are given. In appendix D, the principles for measuring (dT/dB)s, which defines the MCE of the MCM in the simulation model, are provided. Finally, in appendices E and F, the measurements of the specific heat and (dT/dB)s, as well as, their corresponding data reproduction as input parameters for the simulation model are included.<br />Additionally, various annexes are provided as digital material to bring some related information with the thesis. In annex I, the drawings of the reciprocating magnetic refrigeration demonstrator, developed in chapter 2, are given, including mechanical, regenerator housing and wiring drawings. In annex II, the drawings of the rotary magnetic refrigeration prototype, developed in chapter 3, are provided, including magnet, mechanical, regenerator housing, thermostated box, and wiring drawings. In annex III, the properties datasheet of the heat transfer fluid employed with the rotary magnetic refrigeration prototype, Luzar(R), as functions of its dilution in distilled water, is given. Finally, in annex IV, the FORTRAN 90 code of the static multi-layer AMR model, developed in chapter 4, is supplied.<br /> |
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