This document will present the work done on BN under high pressure conditions, both at room temperatures and at high temperatures under laser heating conditions. These experiments are performed to identify possible phase transitions within the BN system and characterize the materials present under the given conditions using a mixture of X-ray diffraction and Raman and infrared spectroscopies are employed. A review of the background and motivations for studies of BN under extreme conditions, as well as the techniques employed, is given as an introduction. A phase transition from hexagonal boron nitride (hBN) to wurtzite boron nitride (wBN) is observed beginning at 9 GPa and room temperature, with coexistence of the two phases until 14 GPa for hydrostatic conditions and to above 20 GPa for non-hydrostatic conditions. This transition is partially reversible below 2 GPa. The formed wBN has a high concentration of defects. For recovered samples, defects couple with the 532.18 nm excitation laser producing a heating effect, observed as a Raman downshift with increasing laser power. The bulk modulus B0 and pressure derivative of the bulk modulus B0′ of hBN are estimated to be 30.6 ± 0.5 GPa and 8.7 ± 0.7, respectively. The bulk modulus of wBN is estimated to be 392 ± 5 GPa, leading to a Vickers hardness of 68 ± 1 GPa. Extra diffraction lines are observed for hBN samples loaded with N2, indicating a potential new structure arising from a reaction of N2 with hBN, but Raman spectroscopy fails to corroborate this finding. The crystallinity of the hBN samples and the choice of pressure transmitting medium are shown to have little to no effect on the estimated physical properties of hBN. Laser heating is performed on hBN with various sample assemblies. The effectiveness of different assemblies is discussed. NaCl is used as a pressure and temperature gauge local to the X-ray probe to contrast the stationary ruby pressure gauge and the non-local black body temperature measurement. A large contrast between the two temperature measurements yields doubt that the intended temperatures of around 2000 K are produced in the sample. Observation of the proposed high-pressure high-temperature transition to body-centered tetragonal BN or intercalated BN cannot be confirmed, likely due to insufficient heating. The prospects for studying Li-BN intercalation compounds under extreme conditions is discussed. An initial experiment on the system studied with X-ray diffraction is unable to confirm heating of the material nor the presence of intercalation compounds.

Cette tbese comprend une étude sur les composés AB2O6 qui ont attiré un large intérêt ces dernieres années grâce à leurs propriétés de magnétisme de basse dimensionalité. Pour mieux étudier les propriétes magnétiques et les parametres qui les influencent oous oous sommes appuyé sur une bonne connaissance de la stmcture cristalline. Tous les écbantillons ont été étudié par diffraction de rayons X (pression ambiante ou sous hautes pressions) et neutroDique (basse et/ou baute température). Nous avons également effectué d'autres caractérisations, telles que mesures de susceptibilité, de cbaleur spécifique et spectroscopie Mossbauer. Nous avons produit la série MnNb2_6 V 80 6 afio de faire varier les distances intercbaines magnétiques et donc la nature des interactions d'échanges. Ces composés sont intéressants pour préseoter une faible anisotropie et un couplage des moments magnétiques dans les chaines en zig-zag le long de l'axe c, ce qui leur confere un caractere unidimensionnel et un couplage antiferromagnétique entre les chames. Nous avons fait une comparaison avec le modele théorique de la chaine d'Heisenberg classique et obtenu des constantes d'échange intra et intercbatnes, J et J', et sa dépendance par rapport à la teneur 8. Ensuite, nous avons fait une étude des séries MnxAt-xNb206 avec A = Fe, Co et Ni. Notre but a été de vérifier comment la nature et la différence de rayons atomiques peuvent influer sur le comportement structural et magnétique de ces composés. Pour ceux qui n'ont pas présenté de mise en ordre magnétique à 1,5 K nous avons fait une étude des corrélations à courtes distances en utilisant le modele de Bertaut La mise en reuvre de synthese HP et HT nous a permis de stabiliser une phase Mn V 20 6 en symétrie orthorhombique et de mettre en jour ses propriétés physiques. Nous avons ensuite comparé avec le MnV 20 6 monoclinique et également avec le MnNb20 6 orthorhombique. Les comportements magnétiques des composés isostructuraux sont tres similaires mais dans le cas de MnNb20 6, les moments magnétiques forment des chaí'nes du type + - + - et dans la pbase Mo V 20 6 nous observons des cbalnes du type + + - -, stmct.ure inédite dans ces composés. / Esta tese compreende um estudo sobre os compostos AB2O6 que chamaram a atenção nos últimos anos graças às suas propriedades de magnetismo de baixa dimensionalidacle. Para melhor entender as propriedades magnéticas e os parâmetros que as influenciam, nos apoiamos no conhecimento da estrutura cristalina. Todas as amostras foram estudadas por difração de raios X (pressão ambiente e sob altas pressões) e de nêutrons (em baixa e em alta temperatura). Também fizemos outras caractetizações como medidas ele susceptibilidade magnética, calorespecífico e espectroscopia Mossbauer. A sé ti e MnNb2_6 V 60 6 foi produzida a fim de variar as distâncias entre as cadeias magnéticas e, com isso, a natureza das interações de troca. Estes compostos são interessantes por apresentarem baixa anisotropia, um acoplamento dos momentos magnéticos nas cadeias em zig-zag ao longo elo eixo c, conferindo-lhe o caráter unidimensional, e ainda um acoplamento antiferromagnético mais fraco entre as cadeias. É feita uma comparação com o modelo teórico de cadeia de Heisenberg clássica e são obtidas as constantes ele troca intra e intercadeias, J e J', e sua dependência em relação à ó. Em seguida, foi feito um estudo das séries MnxAt-xNb20 6 com A = Fe, Co e Ni, com o objetivo de verificar como a natureza e a diferença dos raios atômicos podem influenciar o comportamento estrutural e magnético destes compostos. Para aqueles que não apresentaram ordem magnética à l ,5 K, foi feito um estudo das conelações ele curta distância utilizando o modelo de Bertaut. Graças a síntese AP e AT conseguimos estabilizar o MnV 20 6 em simetria ortorrômbica e determinar suas propriedades físicas. Fizemos então uma comparação com o polimorfo monoclínico Mn V 206 e também com o composto ortonômbico MnNb20 6 . Os comportamentos magnéticos macroscópicos dos compostos isoestruturais são muito similares, porém no caso ela fase MnNb20 6, os momentos magnéticos formam cadeias elo tipo +- + - e na fase Mn V 20 6, as cadeias são do tipo + + - -, estrutura inédita, até então não observada nestes compostos. / This thesis comprises a study of tbe compounds of AB20 6 type that have attracted wide interest in recent years due to tbeir low-dimensional magnetism properties. To better understand tbeir magnetic properties and tbe parameters lhat influence it, we have relied on a good knowledge of lhe crystal stmcture. Ali samples were studied by X-ray diffraction (ambient pressure or under hlgh pressure) and neutron diffraction (low and/or high temperature). We also performed other cbaracterizations, such as magnetic susceptibility, specific heat and Mbssbauer spectroscopy measurements. We have produced tbe MnNb2_6 V 60 6 serie in order to vary the distances between magnetic interchains and thus the nature of lhe excbange interactions. Tbese compounds are interesting due to tbe presence of Jow anisotropy and a coupling of magnetic moments in zigzag cbains along the c-axis, whlch gives lhem a one-dimensional character, and ao antiferromagnetic coupling between cbains. We made a comparison wilh the theoretical modei of the classical Heisenberg chain and obtained the exchange constants intra- and inter-cbain, J and J', and its dependency on the content b. Then we made a study o f MnxA1_.,Nb20 6 series with A = Fe, Co and Ni. Our aim was to check how the nature and tbe difference in atomic radii can influence the stmctural and magnetic properties of tbese compounds. For those whlcb sbowed no magnetic ordering at 1.5 K we made a study of correlations at short distances using Bertaut's model. Thanks to tbe use of HP and HT synthesis we managed to stabilize MnV20 6 in orthorbombic symetry and determine its physical properties. We then performed a comparison witb the monoclinic MnV20G and with tbe 011horbombic MnNb206 compound as well. Macroscopic magnetic behaviour o f isostructural compounds are ve1y similar but in the case of MnNb20 6, the magnetic moments form + - + - type chains while the Mn V 20 6 presents cbains of + + - - type, a structure never observed before in tbis family o f compounds.

Cette tbese comprend une étude sur les composés AB2O6 qui ont attiré un large intérêt ces dernieres années grâce à leurs propriétés de magnétisme de basse dimensionalité. Pour mieux étudier les propriétes magnétiques et les parametres qui les influencent oous oous sommes appuyé sur une bonne connaissance de la stmcture cristalline. Tous les écbantillons ont été étudié par diffraction de rayons X (pression ambiante ou sous hautes pressions) et neutroDique (basse et/ou baute température). Nous avons également effectué d'autres caractérisations, telles que mesures de susceptibilité, de cbaleur spécifique et spectroscopie Mossbauer. Nous avons produit la série MnNb2_6 V 80 6 afio de faire varier les distances intercbaines magnétiques et donc la nature des interactions d'échanges. Ces composés sont intéressants pour préseoter une faible anisotropie et un couplage des moments magnétiques dans les chaines en zig-zag le long de l'axe c, ce qui leur confere un caractere unidimensionnel et un couplage antiferromagnétique entre les chames. Nous avons fait une comparaison avec le modele théorique de la chaine d'Heisenberg classique et obtenu des constantes d'échange intra et intercbatnes, J et J', et sa dépendance par rapport à la teneur 8. Ensuite, nous avons fait une étude des séries MnxAt-xNb206 avec A = Fe, Co et Ni. Notre but a été de vérifier comment la nature et la différence de rayons atomiques peuvent influer sur le comportement structural et magnétique de ces composés. Pour ceux qui n'ont pas présenté de mise en ordre magnétique à 1,5 K nous avons fait une étude des corrélations à courtes distances en utilisant le modele de Bertaut La mise en reuvre de synthese HP et HT nous a permis de stabiliser une phase Mn V 20 6 en symétrie orthorhombique et de mettre en jour ses propriétés physiques. Nous avons ensuite comparé avec le MnV 20 6 monoclinique et également avec le MnNb20 6 orthorhombique. Les comportements magnétiques des composés isostructuraux sont tres similaires mais dans le cas de MnNb20 6, les moments magnétiques forment des chaí'nes du type + - + - et dans la pbase Mo V 20 6 nous observons des cbalnes du type + + - -, stmct.ure inédite dans ces composés. / Esta tese compreende um estudo sobre os compostos AB2O6 que chamaram a atenção nos últimos anos graças às suas propriedades de magnetismo de baixa dimensionalidacle. Para melhor entender as propriedades magnéticas e os parâmetros que as influenciam, nos apoiamos no conhecimento da estrutura cristalina. Todas as amostras foram estudadas por difração de raios X (pressão ambiente e sob altas pressões) e de nêutrons (em baixa e em alta temperatura). Também fizemos outras caractetizações como medidas ele susceptibilidade magnética, calorespecífico e espectroscopia Mossbauer. A sé ti e MnNb2_6 V 60 6 foi produzida a fim de variar as distâncias entre as cadeias magnéticas e, com isso, a natureza das interações de troca. Estes compostos são interessantes por apresentarem baixa anisotropia, um acoplamento dos momentos magnéticos nas cadeias em zig-zag ao longo elo eixo c, conferindo-lhe o caráter unidimensional, e ainda um acoplamento antiferromagnético mais fraco entre as cadeias. É feita uma comparação com o modelo teórico de cadeia de Heisenberg clássica e são obtidas as constantes ele troca intra e intercadeias, J e J', e sua dependência em relação à ó. Em seguida, foi feito um estudo das séries MnxAt-xNb20 6 com A = Fe, Co e Ni, com o objetivo de verificar como a natureza e a diferença dos raios atômicos podem influenciar o comportamento estrutural e magnético destes compostos. Para aqueles que não apresentaram ordem magnética à l ,5 K, foi feito um estudo das conelações ele curta distância utilizando o modelo de Bertaut. Graças a síntese AP e AT conseguimos estabilizar o MnV 20 6 em simetria ortorrômbica e determinar suas propriedades físicas. Fizemos então uma comparação com o polimorfo monoclínico Mn V 206 e também com o composto ortonômbico MnNb20 6 . Os comportamentos magnéticos macroscópicos dos compostos isoestruturais são muito similares, porém no caso ela fase MnNb20 6, os momentos magnéticos formam cadeias elo tipo +- + - e na fase Mn V 20 6, as cadeias são do tipo + + - -, estrutura inédita, até então não observada nestes compostos. / This thesis comprises a study of tbe compounds of AB20 6 type that have attracted wide interest in recent years due to tbeir low-dimensional magnetism properties. To better understand tbeir magnetic properties and tbe parameters lhat influence it, we have relied on a good knowledge of lhe crystal stmcture. Ali samples were studied by X-ray diffraction (ambient pressure or under hlgh pressure) and neutron diffraction (low and/or high temperature). We also performed other cbaracterizations, such as magnetic susceptibility, specific heat and Mbssbauer spectroscopy measurements. We have produced tbe MnNb2_6 V 60 6 serie in order to vary the distances between magnetic interchains and thus the nature of lhe excbange interactions. Tbese compounds are interesting due to tbe presence of Jow anisotropy and a coupling of magnetic moments in zigzag cbains along the c-axis, whlch gives lhem a one-dimensional character, and ao antiferromagnetic coupling between cbains. We made a comparison wilh the theoretical modei of the classical Heisenberg chain and obtained the exchange constants intra- and inter-cbain, J and J', and its dependency on the content b. Then we made a study o f MnxA1_.,Nb20 6 series with A = Fe, Co and Ni. Our aim was to check how the nature and tbe difference in atomic radii can influence the stmctural and magnetic properties of tbese compounds. For those whlcb sbowed no magnetic ordering at 1.5 K we made a study of correlations at short distances using Bertaut's model. Thanks to tbe use of HP and HT synthesis we managed to stabilize MnV20 6 in orthorbombic symetry and determine its physical properties. We then performed a comparison witb the monoclinic MnV20G and with tbe 011horbombic MnNb206 compound as well. Macroscopic magnetic behaviour o f isostructural compounds are ve1y similar but in the case of MnNb20 6, the magnetic moments form + - + - type chains while the Mn V 20 6 presents cbains of + + - - type, a structure never observed before in tbis family o f compounds.

Cette tbese comprend une étude sur les composés AB2O6 qui ont attiré un large intérêt ces dernieres années grâce à leurs propriétés de magnétisme de basse dimensionalité. Pour mieux étudier les propriétes magnétiques et les parametres qui les influencent oous oous sommes appuyé sur une bonne connaissance de la stmcture cristalline. Tous les écbantillons ont été étudié par diffraction de rayons X (pression ambiante ou sous hautes pressions) et neutroDique (basse et/ou baute température). Nous avons également effectué d'autres caractérisations, telles que mesures de susceptibilité, de cbaleur spécifique et spectroscopie Mossbauer. Nous avons produit la série MnNb2_6 V 80 6 afio de faire varier les distances intercbaines magnétiques et donc la nature des interactions d'échanges. Ces composés sont intéressants pour préseoter une faible anisotropie et un couplage des moments magnétiques dans les chaines en zig-zag le long de l'axe c, ce qui leur confere un caractere unidimensionnel et un couplage antiferromagnétique entre les chames. Nous avons fait une comparaison avec le modele théorique de la chaine d'Heisenberg classique et obtenu des constantes d'échange intra et intercbatnes, J et J', et sa dépendance par rapport à la teneur 8. Ensuite, nous avons fait une étude des séries MnxAt-xNb206 avec A = Fe, Co et Ni. Notre but a été de vérifier comment la nature et la différence de rayons atomiques peuvent influer sur le comportement structural et magnétique de ces composés. Pour ceux qui n'ont pas présenté de mise en ordre magnétique à 1,5 K nous avons fait une étude des corrélations à courtes distances en utilisant le modele de Bertaut La mise en reuvre de synthese HP et HT nous a permis de stabiliser une phase Mn V 20 6 en symétrie orthorhombique et de mettre en jour ses propriétés physiques. Nous avons ensuite comparé avec le MnV 20 6 monoclinique et également avec le MnNb20 6 orthorhombique. Les comportements magnétiques des composés isostructuraux sont tres similaires mais dans le cas de MnNb20 6, les moments magnétiques forment des chaí'nes du type + - + - et dans la pbase Mo V 20 6 nous observons des cbalnes du type + + - -, stmct.ure inédite dans ces composés. / Esta tese compreende um estudo sobre os compostos AB2O6 que chamaram a atenção nos últimos anos graças às suas propriedades de magnetismo de baixa dimensionalidacle. Para melhor entender as propriedades magnéticas e os parâmetros que as influenciam, nos apoiamos no conhecimento da estrutura cristalina. Todas as amostras foram estudadas por difração de raios X (pressão ambiente e sob altas pressões) e de nêutrons (em baixa e em alta temperatura). Também fizemos outras caractetizações como medidas ele susceptibilidade magnética, calorespecífico e espectroscopia Mossbauer. A sé ti e MnNb2_6 V 60 6 foi produzida a fim de variar as distâncias entre as cadeias magnéticas e, com isso, a natureza das interações de troca. Estes compostos são interessantes por apresentarem baixa anisotropia, um acoplamento dos momentos magnéticos nas cadeias em zig-zag ao longo elo eixo c, conferindo-lhe o caráter unidimensional, e ainda um acoplamento antiferromagnético mais fraco entre as cadeias. É feita uma comparação com o modelo teórico de cadeia de Heisenberg clássica e são obtidas as constantes ele troca intra e intercadeias, J e J', e sua dependência em relação à ó. Em seguida, foi feito um estudo das séries MnxAt-xNb20 6 com A = Fe, Co e Ni, com o objetivo de verificar como a natureza e a diferença dos raios atômicos podem influenciar o comportamento estrutural e magnético destes compostos. Para aqueles que não apresentaram ordem magnética à l ,5 K, foi feito um estudo das conelações ele curta distância utilizando o modelo de Bertaut. Graças a síntese AP e AT conseguimos estabilizar o MnV 20 6 em simetria ortorrômbica e determinar suas propriedades físicas. Fizemos então uma comparação com o polimorfo monoclínico Mn V 206 e também com o composto ortonômbico MnNb20 6 . Os comportamentos magnéticos macroscópicos dos compostos isoestruturais são muito similares, porém no caso ela fase MnNb20 6, os momentos magnéticos formam cadeias elo tipo +- + - e na fase Mn V 20 6, as cadeias são do tipo + + - -, estrutura inédita, até então não observada nestes compostos. / This thesis comprises a study of tbe compounds of AB20 6 type that have attracted wide interest in recent years due to tbeir low-dimensional magnetism properties. To better understand tbeir magnetic properties and tbe parameters lhat influence it, we have relied on a good knowledge of lhe crystal stmcture. Ali samples were studied by X-ray diffraction (ambient pressure or under hlgh pressure) and neutron diffraction (low and/or high temperature). We also performed other cbaracterizations, such as magnetic susceptibility, specific heat and Mbssbauer spectroscopy measurements. We have produced tbe MnNb2_6 V 60 6 serie in order to vary the distances between magnetic interchains and thus the nature of lhe excbange interactions. Tbese compounds are interesting due to tbe presence of Jow anisotropy and a coupling of magnetic moments in zigzag cbains along the c-axis, whlch gives lhem a one-dimensional character, and ao antiferromagnetic coupling between cbains. We made a comparison wilh the theoretical modei of the classical Heisenberg chain and obtained the exchange constants intra- and inter-cbain, J and J', and its dependency on the content b. Then we made a study o f MnxA1_.,Nb20 6 series with A = Fe, Co and Ni. Our aim was to check how the nature and tbe difference in atomic radii can influence the stmctural and magnetic properties of tbese compounds. For those whlcb sbowed no magnetic ordering at 1.5 K we made a study of correlations at short distances using Bertaut's model. Thanks to tbe use of HP and HT synthesis we managed to stabilize MnV20 6 in orthorbombic symetry and determine its physical properties. We then performed a comparison witb the monoclinic MnV20G and with tbe 011horbombic MnNb206 compound as well. Macroscopic magnetic behaviour o f isostructural compounds are ve1y similar but in the case of MnNb20 6, the magnetic moments form + - + - type chains while the Mn V 20 6 presents cbains of + + - - type, a structure never observed before in tbis family o f compounds.

Ce travail est consacré à l'étude de la viscosité de cisaillement par simulation numérique de dynamique moléculaire classique à l'équilibre avec une attention particulière à l'influence des hautes pressions sur cette propriété. La viscosité est obtenue à partir des trajectoires générées par ces simulations et en appliquant la formule de Green-Kubo. Un large panel de systèmes a été étudié, allant de fluides atomiques purs à un liquide moléculaire, en passant par des mélanges binaires. En premier lieu, nous nous sommes focalisés sur les métaux alcalins. La conclusion majeure de cette étude est que la viscosité des alcalins a un comportement universel sur une large plage du diagramme de phases. Par ailleurs, sur cet intervalle, la relation universelle que nous avons proposée permet de prédire la valeur de la viscosité de n'importe quel élément avec une incertitude inférieure à 10%. La validité de la relation de Stokes-Einstein, reliant le coefficient d'autodiffusion à la viscosité, a également été vérifiée. Une étude systématique a ensuite été menée sur des mélanges modèles de type Lennard-Jones an de tester l'influence des paramètres d'interaction sur le comportement de la viscosité. Une estimation théorique basée sur le modèle de fluide effectif pur a été proposée. D'autre part, la relation de Stokes-Einstein a été étendue aux mélanges avec succès. Ces observations ont été confrontées aux cas de deux alliages réels : K-Cs et Li-Bi. Pour finir, une étude préliminaire a été entreprise sur l'eau en modélisant les interactions par deux potentiels : SPC/E, non polarisable, et BK3, polarisable. L'effet de l'introduction de la polarisabilité sur le calcul de la viscosité a été étudié. La validité des relations de Stokes-Einstein et de Stokes-Einstein-Debye, faisant intervenir la rotation de la molécule, a été évaluée à très haute pression / This work is devoted to the study of the shear viscosity by numerical simulation of equilibrium classical molecular dynamics with a particular attention to the influence of high pressures on this property. From trajectories generated by these simulations and using the Grenn-Kubo formula, the viscosity is obtained. A broad range of systems has been studied, covering from pure atomic fluids to a molecular liquid, as well as binary mixtures. First, we focused on alkali metals. The main outcome of this study is that the viscosity of these metals has a universal behavior over a wide range of phase diagram. Furthermore, over this interval, the universal relation that we have proposed permits the prediction of the viscosity value of any elements with an uncertainty lower than 10%. The validity of the Stokes-Einstein relation, connecting the self-diffusion coefficient and the viscosity, has also been verified. Then, a systematic study has been carried out on model mixtures of Lennard-Jones fluids to test the influence of interaction parameters on the viscosity behavior. A theoretical estimation based on the effective one-component fluid model has been proposed. Moreover, the Stokes-Einstein relation has been successfully extended to mixtures. These observations have been compared with two real alloys: K-Cs and Li-Bi. Lastly, a preliminary study on water has been undertaken by modeling the interactions with two models: SPC/E, non-polarizable and BK3, polarizable. The effect of the introduction of the polarizability on the viscosity has been studied. The validity of Stokes-Einstein and Stokes-Einstein-Debye, involving the rotation of the molecule, has been evaluated under very high pressure

Tesis por compendio / [ES] Esta tesis doctoral presenta un estudio de compresores scroll con inyección de vapor (SCVI) para bombas de calor que operan en climas fríos o para aplicaciones de calentamiento de agua a alta temperatura. Para ello, se comparó experimentalmente un SCVI con un compresor de dos etapas de pistones (TSRC) trabajando con R-407C en condiciones extremas. La comparación se realizó en términos de eficiencias del compresor, capacidad, COP y rendimientos estacionales tanto para el modo calefacción como para el modo refrigeración. Los resultados proporcionan una idea general sobre el rango de aplicación de los compresores estudiados y sobre las diferencias en los rendimientos de los compresores. Sin embargo, se identificaron varias limitaciones en la caracterización de los compresores y en el análisis del ciclo. Esto motivó a profundizar en el estudio del ciclo de compresión de dos etapas y sus componentes. El siguiente paso fue realizar un análisis teórico de los ciclos de compresión de dos etapas para aplicaciones de calefacción, en donde se identificó a la presión intermedia y a la relación de inyección como los parámetros del sistema más influyentes sobre el COP. La presión intermedia se optimizó para dos configuraciones de inyección (tanque de separación y economizador) utilizando varios refrigerantes. Basándose en los resultados de la optimización, se propuso una correlación que permite obtener la presión intermedia óptima del ciclo, considerando la influencia del subenfriamiento a la salida del condensador. Además, se analizó la influencia del diseño de los componentes del sistema sobre el COP del ciclo. Posteriormente, el estudio se profundizó a nivel de componentes. El factor más crítico en el sistema es el rendimiento del compresor. Por lo tanto, el siguiente paso fue evaluar la influencia de varios sistemas de compresión con inyección de vapor sobre el COP. Se tomaron en cuenta tres tecnologías de compresores, un SCVI, un TSRC y un compresor scroll de dos etapas (TSSC). Estas tecnologías de compresores fueron caracterizadas y modeladas para estudiar su rendimiento. Para ello, se propuso una nueva metodología para caracterizar compresores scroll con inyección de vapor. Esta metodología permite evaluar el rendimiento del compresor independientemente del mecanismo de inyección que se utiliza en el ciclo. Se identificó una correlación lineal entre la relación de inyección de refrigerante y la relación de compresión intermedia. Esta correlación se utiliza para determinar el flujo másico de inyección en función de la presión intermedia. Posteriormente, se propuso un modelo semi-empírico de compresores scroll y una metodología para extender dicho modelo para compresores scroll con inyección de vapor. Los modelos fueron ajustados y validados usando datos experimentales de cuatro compresores scroll trabajando con R-290 y un SCVI trabajando con R-407C. Finalmente, se comparó un SCVI con dos compresores de dos etapas, un TSSC y un TSRC, trabajando en condiciones extremas. Se optimizó la relación de volúmenes de los compresores de dos etapas. Los resultados muestran que, en las condiciones nominales de funcionamiento (Te=-15 °C, Tc=50 °C), la relación de volúmenes óptima del TSSC es 0.58, y del TSRC es 0.57. El TSSC consigue un COP 6% mayor que el SCVI y un COP 11.7% mayor que el TSRC. Bajo un amplio rango de condiciones de operación, el SCVI presenta una mejor eficiencia y COP para relaciones de presión inferiores a 5. Para relaciones de presión más altas, el TSSC presenta mejor rendimiento y consigue una temperatura de descarga más baja. Se concluye que el SCVI es una solución fácil de implementar, desde el punto de vista del mecanizado, y que permite extender el mapa de trabajo de los compresores de una etapa. Sin embargo, los resultados muestran que la compresión en dos etapas consigue mejorar en mayor medida el COP del ciclo y la capacidad, con una mayor redu / [CA] Aquesta tesi doctoral presenta un estudi de compressors scroll amb injecció de vapor (SCVI) per a bombes de calor que operen en climes freds o per a aplicacions d'escalfament d'aigua a alta temperatura. Per a això, es va comparar experimentalment un SCVI amb un compressor de dues etapes de pistons (TSRC) treballant amb R-407C en condicions extremes. La comparació es va realitzar en termes d'eficiències del compressor, capacitat, COP i rendiments estacionals tant per al mode calefacció com per al mode refrigeració. Els resultats proporcionen una idea general sobre el rang d'aplicació dels compressors estudiats i sobre les diferències en els rendiments dels compressors. No obstant això, es van identificar diverses limitacions en la caracterització dels compressors i en l'anàlisi del cicle. Això va motivar a aprofundir en l'estudi del cicle de compressió de dues etapes i els seus components. El següent pas va ser realitzar una anàlisi teòrica dels cicles de compressió de dues etapes per a aplicacions de calefacció, on es va identificar la pressió intermèdia i la relació d'injecció com els paràmetres del sistema més influents sobre el COP. La pressió intermèdia es va optimitzar per a dues configuracions d'injecció (tanc de separació i economitzador) utilitzant diversos refrigerants. Basant-se en els resultats de l'optimització, es va proposar una correlació que permet obtindre la pressió intermèdia òptima del cicle, considerant la influència del subrefredament a l'eixida del condensador. A més, es va analitzar la influència del disseny dels components del sistema sobre el COP del cicle. Posteriorment, l'estudi es va aprofundir a nivell de components. El factor més crític en el sistema és el rendiment del compressor. Per tant, el següent pas va ser avaluar la influència de diversos sistemes de compressió amb injecció de vapor sobre el COP. Es van prendre en compte tres tecnologies de compressors, un SCVI, un TSRC i un compressor scroll de dues etapes (TSSC). Aquestes tecnologies de compressors van ser caracteritzades i modelades per a estudiar el seu rendiment. Per a això, es va proposar una nova metodologia per a caracteritzar compressors scroll amb injecció de vapor. Aquesta metodologia permet avaluar el rendiment del compressor independentment del mecanisme d'injecció que s'utilitza en el cicle. Es va identificar una correlació lineal entre la relació d'injecció de refrigerant i la relació de compressió intermèdia. Aquesta correlació s'utilitza per a determinar el flux màssic d'injecció en funció de la pressió intermèdia. Posteriorment, es va proposar un model semi-empíric de compressors scroll i una metodologia per a estendre aquest model per a compressors scroll amb injecció de vapor. Els models van ser ajustats i validats utilitzant dades experimentals de quatre compressors scroll treballant amb R-290 i un SCVI treballant amb R-407C. Finalment, es va comparar un SCVI amb dos compressors de dues etapes, un TSSC i un TSRC, treballant en condicions extremes. Es va optimitzar la relació de volums dels compressors de dues etapes. Els resultats mostren que, en les condicions nominals de funcionament (Te=-15 °C, Tc=50 °C), la relació de volums òptima del TSSC és 0.58, i del TSRC és 0.57. El TSSC aconsegueix un COP 6% major que el SCVI i un COP 11.7% major que el TSRC. Sota un ampli rang de condicions d'operació, el SCVI presenta una millor eficiència i COP per a relacions de pressió inferiors a 5. Per a relacions de pressió més altes, el TSSC presenta millor rendiment i aconsegueix una temperatura de descàrrega més baixa. Es conclou que el SCVI és una solució fàcil d'implementar, des del punt de vista del mecanitzat, i que permet estendre el mapa de treball dels compressors d'una etapa. No obstant això, els resultats mostren que la compressió en dues etapes aconsegueix millorar en major mesura el COP del cicle i la capacitat, amb una major reducció de la / [EN] This Ph.D. thesis presents a study of scroll compressors with vapor-injection (SCVI) for heat pumps operating in cold climates or in high-temperature water heating applications. To do so, firstly, an SCVI was experimentally compared with a two-stage reciprocating compressor (TSRC) working with R-407C under extreme conditions. The comparison was made in terms of compressor efficiencies, capacity, COP, and seasonal COP, both for heating and cooling modes. The results give a general idea about the application range of the studied compressors and the differences in the compressors' performance. Nevertheless, several restrictions in the compressors' characterization and the cycle analysis were identified. This motivated us to deepen in the study of the two-stage compression cycle and its components. The next step was performing a theoretical analysis of two-stage compression cycles for heating applications, where the intermediate pressure and the injection ratio were identified as the most influential system parameters on the COP. The intermediate pressure was optimized for two vapor-injection configurations (flash tank and economizer) using several refrigerants. Based on the optimization results, a correlation was proposed that allows obtaining the optimal intermediate pressure of the cycle, considering the influence of the subcooling at the condenser outlet. In addition, a theoretical analysis of the influence of the design of the system components on the COP of the cycle was performed. Once the thermodynamic analysis of the two-stage cycle was carried out, the study was deepened at the component level. The most critical factor in the system is the compressor performance. Hence, the next step was evaluating the influence of several compression systems with vapor-injection on the COP. Three compressor technologies were taken into account, an SCVI, a TSRC and a two-stage scroll compressor (TSSC). These compressor technologies were characterized and modeled in order to study their performance. To do so, a new methodology to characterize SCVI was proposed. This methodology allows evaluating the compressor performance independently of the injection mechanism used in the cycle. A linear correlation was identified between the refrigerant injection ratio and the intermediate compression ratio. This correlation is used to determine the injection mass flow as a function of the intermediate pressure. Then, a semi-empirical model of scroll compressors and a methodology to extend the model for scroll compressors with vapor-injection was proposed. The models were adjusted and validated using experimental data from four scroll compressors working with R-290 and an SCVI compressor working with R-407C. Finally, an SCVI was compared with two two-stage compressors, a TSSC, and a TSRC, working in extreme conditions. The displacement ratio of the two-stage compressors was optimized. Results show that, at the nominal operating conditions (Te=-15 °C, Tc=50 °C), the optimal displacement ratio of the TSSC is 0.58, and of the TSRC is 0.57. The TSSC achieves 6% larger COP than the SCVI and 11.7% larger COP than the TSRC. Under a wide range of operating conditions, the SCVI presents a better efficiency and COP for pressure ratios below 5. For higher-pressure ratios, the TSSC presents better performance and achieves lower discharge temperature. It is concluded that the SCVI is an easy solution to implement from the point of view of machining, which allows extending the working map of the single-stage compressors. However, the results show that the two-stage compression technology gets further improve the COP of the cycle and the capacity, with a greater reduction of the discharge temperature operating under extreme conditions. / I thank the financial support provided by the Secretaría de Educación Superior, Ciencia, Tecnología e Innovación (SENESCYT) of Ecuador, through the international scholarship program for postgraduate studies “Convocatoria Abierta 2013 Segunda Fase, Grant No 2015-AR37665”. / Tello Oquendo, FM. (2019). Study of scroll compressors with vapor-injection for heat pumps operating in cold climates or in high-temperature water heating applications [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/120473 / Compendio