Submitted in fulfillment of the requirements for the degree of Master of Engineering in Chemical Engineering, Durban University of Technology. Durban. South Africa, 2015. / Several areas in the world such as the United States of America, Sri Lanka, China, Argentina, Canada, Tanzania, Kenya, South Africa and many others have a problem of high fluoride content in drinking water. Generally fluoride levels above 1.5 ppm in water may result in dental and skeletal fluorosis in humans depending on quantity consumed (Fan et al., 2003; Meenakshi, 2004). Remote rural areas where there are no water treatment facilities are more vulnerable to this problem. Adsorbents such as activated alumina and FR-10 resin seem to have a potential for successful application in rural areas. These methods however require pre-treatment if the feed has high turbidity. A membrane based system called woven fabric microfiltration gravity filter (WFMFGF) developed by Durban University of Technology proved to be suitable for turbidity removal. The main objective of this research was to develop a small water treatment system for fluoride removal. The small water treatment system developed in this study consists of WFMFGF for pre-treatment and an adsorption column. The WFMFGF is made up of a 40 L container packed with 15 immersed flat sheet membrane elements. The operation of the WFMFGF is in batch mode, driven by varying static head. The static head variation results in flow rate variation through the system. This in turn result in variation of contact time, velocity as well as pressure drop in the fluoride removal unit. Specific objectives of the study were: (1) to establish the maximum and minimum flow rates through the WFMFGF system, the total run time before cleaning is required and the best cleaning method for this particular membrane system. (2) to evaluate and compare the performance of activated alumina and FR-10 resin on varying contact time, velocity and pressure drop on the fluoride removal unit. The adsorbents were also compared on adsorption capacity, cost and ease of operation. The minimum and maximum flow rates through the WFMFGF were found to be 5 l/hr and 100 l/hr respectively. It was found that the system can be run for more than a month before requiring cleaning. The suitable cleaning method was found to be soaking the membranes in 0.0225 percent sodium hypochlorite solution overnight and brushing them using a plastic brush. The comparison of the performance of FR-10 resin to activated alumina found that the adsorbents gave equal performance based on the given criteria. FR-10 resin had higher adsorption capacity, gave good quality treated water even with shorter contact time and operated at wider velocity range. Activated alumina on the other hand had an advantage of lower costs, lower pressure drop and ease of use. According to Pontius (1990), the performance of activated alumina can be improved by intermittent operation. Point of use (POU) systems are generally operated intermittently. This improves the fluoride removal efficiency of activated alumina giving it more advantage over FR-10 resin. Based on this activated alumina was selected as the best adsorbent for the system. After the adsorbent was selected, the adsorption column was designed. The column operation regime was 3.5 minutes minimum contact time and 1.17 to 7.8 m/hr velocity range. The activated alumina adsorption capacity was 1.53mg/g. The column had an inside diameter of 70 mm. It was packed with activated alumina to a bed height of 400 mm. The column inlet and outlet pipes were made of PVC with a standard pipe size of 20 mm outside diameter. A valve at the column inlet pipe allowed water to flow through the system.

I industrin finns det många pumpar som inte kör i de optimala driftfall som de är skapade för. Detta bidrar till stora och onödiga kostnader för fabriker och industrier. Det finns olika reglermetoder för att få pumpen att köra så optimalt som möjligt, det vanligaste är att avända sig av en reglerventil som stryper bort flödet. Ett annat sätt är att investera i en frekvensomriktare. En frekvensomriktare kan reglera varvtalet på pumpen och göra så driften blir så optimal som möjligt för det driftfall som körs. Blir driften så optimal som möjligt kommer kostnaden att reduceras. För att lätt kunna beräkna om det är lönsamt att investera i en frekvensomriktare behövs ett standardiserat beräkningsprogram. Detta arbete har gjorts för ÅF Pöyry i Karlstad i samverkan med BillerudKorsnäs AB, Gruvön. Datainsamling har skett på BillerudKorsnäs AB på en MC-pump (423P008) denna sitter på SK 2, som även kallas barrlinjen, där man behandlar barrträd. Resultatet är ett standardiserat beräkningsprogram för att kunna beräkna både MC-pumpar och centrifugalpumpar i pappersmassaindustrin. Detta beräkningsprogram kan bland annat beräkna den totala tryckhöjden för respektive pump för att sedan kunna beräkna payoff-tiden, alltså om det är lönsamt att investera i en frekvensomriktare. Vid beräkning med hjälp av beräkningsprogrammet på MC-pump 423P008 visas det att ca 120 000 SEK/år är de kostnader som ”stryps” bort med den nuvarande reglermetoden, detta är också den besparingspotetnial som kan göras vid investering av en frekvensomriktare och detta är endast för en pump på ett bruk. Slutsatsen man kan dra med hjälp av beräkningsprogrammet är att det finns stora kostnader att spara i industrin genom att optimera drifterna hos de pumpar som finns. / In the industry, there are many pumps that do not running in the optimal operating conditions that they are created for. This contributes to large, unnecessary costs for industries. There are some different “control methods” to make the pump run as optimally as possible. One way is to invest in a frequency converter. A frequency converter can regulate the speed (rpm) of the pump and make the operation as optimal as possible for the running case. If the operation becomes as optimal as possible, money will be saved. In order to easily calculate whether it is profitable to invest in a frequency converter, a standardized calculation program is needed. This work has been made for ÅF Pöyry in Karlstad in a collaboration with BillerudKorsnäs AB, Gruvön. Data collection has taken place at BillerudKorsnäs AB on an MC-pump (423P008), which is stationary at SK 2, which is also called the coniferous-line, where you process conifers. The result is a standardized calculation program for calculating both MC-pumps and centrifugal pumps in the pulp industry. This calculation program can calculate the total pump head for each pump in order to then calculate the payoff time, i.e. whether it is profitable to invest in a frequency converter, or not. When using the calculation program for the MC-pump named 423P008, it is shown that about SEK 120,000 SEK / year are the costs that are "throttled" away with the current “control method”. This is data for just one pump out at BillerudKorsnäs. The conclusion is that with the help of the calculation program you can see there are large costs to save in the industry by optimizing the runs of the pumps that are available. / Nej

Escoamentos bifásicos estão presentes em diversos processos naturais e industriais, como na indústria de petróleo. Podem apresentar-se em diferentes configurações topológicas, ou, padrões de escoamento, entre eles o escoamento estratificado ondulado e o estratificado com mistura na interface. Os escoamentos bifásicos estratificados óleo-água têm sido utilizados como uma forma conveniente de evitar a formação de emulsões de água em óleo em oleodutos e possuem uma ocorrência comum em poços de petróleo direcionais. Quando a onda interfacial ultrapassa determinado limite geométrico e cinemático, surge o fenômeno do entranhamento de gotas, representado por misturas entre as fases junto à interface que promovem um aumento na queda de pressão. Modelos têm sido apresentados pela literatura na tentativa de descrever o fenômeno do entranhamento de gotas. Neste trabalho é apresentada uma nova proposta de modelagem matemática unidimensional para o entranhamento de gotas com o objetivo de melhorar a previsão dos parâmetros envolvidos, em especial, da fração volumétrica de óleo e da queda de pressão bifásica. Também foi utilizada simulação numérica computacional, CFD (Computational Fluid Dynamics), com o uso de software comercial para obtenção dos valores dos parâmetros do escoamento estratificado ondulado óleo-água (fração volumétrica de óleo, queda de pressão, amplitude e comprimento da onda interfacial). Os resultados da modelagem fenomenológica para entranhamento e os de CFD foram comparados com bancos de dados experimentais. Os resultados em CFD mostram concordância com os resultados experimentais, tanto na análise qualitativa das propriedades geométricas das ondas interfaciais, quanto na comparação direta com os dados para fração volumétrica e queda de pressão. Os resultados numéricos da modelagem fenomenológica para fatores de entranhamento apresentam boa concordância com dados da literatura. / Two-phase flows are present in many natural and industrial processes, such as in the oil industry. They may be found arranged in several flow patterns, including the wavy stratified flow and the stratified with mixing at the interface. The stratified oil-water flow has been used as a convenient way to avoid the formation of emulsions of water in oil and have a common occurrence in directional oil wells. When the interfacial wave exceeds a certain geometric and kinematic limit the phenomenon of drop entrainment arises at the interface, causing an increase of pressure drop. Models have been presented in the literature in an attempt to describe the phenomenon of drop entrainment. In this work, we present a new method for the one-dimensional mathematical modeling of entrainment in order to improve the prediction of oil volume fraction and pressure drop. It was also used a commercial computational fluid dynamics tool (CFD) to obtain the values of flow parameters of wavy stratified oil-water flow, such as oil volume fraction, pressure drop, amplitude and length of the interfacial waves. The results of the phenomenological modeling for entrainment and CFD were compared with experimental databases. The CFD results are in agreement with the experimental results in both the qualitative analysis of the geometric properties of the interfacial waves and in direct comparison with oil-volumetric-fraction and pressure-drop data. The numerical results of the phenomenological model for entrainment factors are in agreement with data from the literature.

A presente tese trata da análise experimental do efeito da geometria da seção transversal do canal e do desempenho de refrigerantes de reduzido GWP (Global Warming Potential) durante a ebulição convectiva em canais de reduzidas dimensões. A tese inclui ainda um estudo extenso e crítico da literatura sobre métodos de previsão da perda de pressão e do coeficiente de transferência de calor, e sobre estudos experimentais em canais não-circulares e de refrigerantes com reduzido GWP na ebulição convectiva em canais de dimensões reduzidas. Resultados para o coeficiente de transferência de calor e perda de pressão durante a ebulição convectiva foram obtidos para canais com geometrias de seção circular, quadrada e triangular para o refrigerante R134a. Nos testes utilizou-se canais com perímetros internos similares obtidos a partir da conformação de um tubo com diâmetro interno igual a 1,1 mm. No caso do canal circular, dados foram também levantados para os HFOs R1234ze(E) e R1234yf e o hidrocarboneto R600a, fluidos com reduzido GWP. Ensaios foram executados para amplas faixas de fluxos de calor e velocidades mássicas, temperaturas de saturação de 31 e 41°C e títulos de vapor entre 0 e 0,95. Aspectos relacionados aos efeitos da geometria e do fluido refrigerante foram minuciosamente investigados através da análise paramétrica dos resultados. Com base na comparação do banco de dados coletado com os métodos de previsão disponíveis na literatura, constatou-se que estes proporcionam previsões satisfatórias apenas para condições experimentais especificas. Portanto, novos métodos de previsão da perda de pressão e do coeficiente de transferência de calor foram desenvolvidos com base nos dados levantados no presente estudo. Os métodos propostos preveem satisfatoriamente o banco de dados do presente estudo e resultados independentes disponíveis na literatura. Adicionalmente, com base nos resultados levantados, verificou-se que dissipadores de calor baseados em multi-microcanais com canais de seção triangular apresentam desempenho superior comparados a dissipadores com canais quadrados e circulares. / The present thesis concerns an experimental study on the effects of cross-sectional geometry and low GWP refrigerants on the thermal-hydraulic performance for convective boiling inside micro-scale channels. Experimental results for heat transfer coefficient and pressure drop gradient during convective boiling were obtained for circular, square and triangular channels for the fluid R134a. The evaluated channels present the same external perimeter and equivalent diameters of 1.1, 0.977 and 0.835 mm, respectively. In the case of the circular geometry, experimental results were also acquired for the HFOs R1234ze(E) and R1234yf and the hydrocarbon R600a (isobutane), which are fluids with low GWP and null ODP. Experiments were performed for a wide range of heat fluxes and mass velocities, saturation temperatures of 31 and 41°C and vapor qualities up to 0.95. The experimental data were carefully analyzed and discussed based on a parametrical analysis focusing on the effect of the cross-sectional geometry and the working fluid. Subsequently, the experimental data were compared against the most quoted predictive methods from literature. In general, it was verified that none of the predictive methods were able to accurately capture the experimental trends of the overall database. So, new predictive methods for the pressure drop and heat transfer coefficient were developed based on the broad database obtained in the present study. The proposed methods provided satisfactory results not only for the experimental database used for its development, but also for independent databases collected in the literature. Additionally, based on the data obtained in the present study and a performance analysis taken into account pressure drop, heat transfer coefficient and the channel packing factor, triangular cross sectional geometry is recommended for heat sinks.

QC 20120530

L’objectif de ce travail consiste en l'étude expérimentale et la modélisation du comportement thermo-hydraulique d'un fluide frigoporteur diphasique (FFD) particulier : le coulis de paraffine, en écoulement dans un canal rectangulaire simulant un échangeur à plaques. Les coulis de paraffine sont constitués de particules millimétriques de paraffine, stabilisées dans une matrice poreuse el mises en suspension dans de l'eau. Les particules de paraffines sont composées de 75% en masse de Norpar®15 et de 25% de polymère tri-block qui sert à gélifier la paraffine. Les résultats expérimentaux issus de bilans sur les veines d'essai de l'installation développée el mise en place au Centre de Thermique de Lyon (CETHIL), mettent en évidence une intensification importante du coefficient d'échange thermique, due a la présence des particules dans le fluide porteur. Pour un écoulement laminaire du coulis de paraffine dans le canal de refroidissement, une multiplication moyenne par 1 ,25 à 1 ,5 du coefficient d'échange global par rapport au fluide monophasique a été enregistrée pour des fractions massiques en particules de 6 à 12 %. Par régression linéaire des résultats expérimentaux, des corrélations pour le calcul des nombres de Nusselt local et moyen sont proposées. Une approche théorique basée sur le modèle de mélanges (Mixture Mode!) a été élaborée pour étudier le comportement hydraulique et thermique du fluide frigoporteur diphasique FFD pendant son refroidissement en écoulement laminaire dans un canal rectangulaire. L'évolution des valeurs expérimentales et théoriques pour la température moyenne du fluide et le coemcien1 d'échange thermique paroi - fluide montrent qu'ils sont en bon accord. Le modèle peut être considéré comme satisfaisant car les écarts entre résultats théoriques et expérimentaux n'excèdent jamais 14 %. / This work concerns the experimental investigation and modelling of the thermo hydraulic behaviour of a new Iwo-phase secondary refrigerant, the paraffin slurry, flowing through a rectangular channel of a heat plate exchanger type. The paraffin slurries are made of millimetric bullets of paraffin, stabilized in an organic porous polymeric matrix, in suspension in water serving as a carrying fluid. The paraffin particles used contain 75% of paraffin called NORPAR®15 and 25% of a tri-block polymer of styrene with High Molecular Weight (HMW). The experimental results generated by the heat balances on the test sections of the experimental setup built in the Thermal Center of Lyon (CETHIL), highlight an important increase of the heat transfer coefficient, due to the particles presence in the carrying fluid. For a laminar flow of the paraffin slurry in the cold channel, an average multiplication by 1 .25 to 1.5 of the global heat transfer coefficient compared to the single-phase fluid was recorded for particles mass fractions of 6 to 12%. By regression of the experimental results, correlations for the local and average Nusselt number calculation for the laminar flows are proposed. The particularity of the presented correlations is their validity in the case of a pure fluid as we\l as for a two-phase fluid containing so\id particles. A model for the hydraulic and thermal behaviours studies of a Iwo-phase secondary refrigerant fluid during its cooling in laminar flow through a rectangular channel was developed it is based on the mixture model and to king the slip velocity into account. The evolution of the experimental and theoretical values for the fluid average temperature, the heat flow which crosses the walls and the heat transfer coefficient between the wall and fluid shows good agreement and the model is satisfactory since the variations never exceed 14%.

A presente tese trata da análise experimental do efeito da geometria da seção transversal do canal e do desempenho de refrigerantes de reduzido GWP (Global Warming Potential) durante a ebulição convectiva em canais de reduzidas dimensões. A tese inclui ainda um estudo extenso e crítico da literatura sobre métodos de previsão da perda de pressão e do coeficiente de transferência de calor, e sobre estudos experimentais em canais não-circulares e de refrigerantes com reduzido GWP na ebulição convectiva em canais de dimensões reduzidas. Resultados para o coeficiente de transferência de calor e perda de pressão durante a ebulição convectiva foram obtidos para canais com geometrias de seção circular, quadrada e triangular para o refrigerante R134a. Nos testes utilizou-se canais com perímetros internos similares obtidos a partir da conformação de um tubo com diâmetro interno igual a 1,1 mm. No caso do canal circular, dados foram também levantados para os HFOs R1234ze(E) e R1234yf e o hidrocarboneto R600a, fluidos com reduzido GWP. Ensaios foram executados para amplas faixas de fluxos de calor e velocidades mássicas, temperaturas de saturação de 31 e 41°C e títulos de vapor entre 0 e 0,95. Aspectos relacionados aos efeitos da geometria e do fluido refrigerante foram minuciosamente investigados através da análise paramétrica dos resultados. Com base na comparação do banco de dados coletado com os métodos de previsão disponíveis na literatura, constatou-se que estes proporcionam previsões satisfatórias apenas para condições experimentais especificas. Portanto, novos métodos de previsão da perda de pressão e do coeficiente de transferência de calor foram desenvolvidos com base nos dados levantados no presente estudo. Os métodos propostos preveem satisfatoriamente o banco de dados do presente estudo e resultados independentes disponíveis na literatura. Adicionalmente, com base nos resultados levantados, verificou-se que dissipadores de calor baseados em multi-microcanais com canais de seção triangular apresentam desempenho superior comparados a dissipadores com canais quadrados e circulares. / The present thesis concerns an experimental study on the effects of cross-sectional geometry and low GWP refrigerants on the thermal-hydraulic performance for convective boiling inside micro-scale channels. Experimental results for heat transfer coefficient and pressure drop gradient during convective boiling were obtained for circular, square and triangular channels for the fluid R134a. The evaluated channels present the same external perimeter and equivalent diameters of 1.1, 0.977 and 0.835 mm, respectively. In the case of the circular geometry, experimental results were also acquired for the HFOs R1234ze(E) and R1234yf and the hydrocarbon R600a (isobutane), which are fluids with low GWP and null ODP. Experiments were performed for a wide range of heat fluxes and mass velocities, saturation temperatures of 31 and 41°C and vapor qualities up to 0.95. The experimental data were carefully analyzed and discussed based on a parametrical analysis focusing on the effect of the cross-sectional geometry and the working fluid. Subsequently, the experimental data were compared against the most quoted predictive methods from literature. In general, it was verified that none of the predictive methods were able to accurately capture the experimental trends of the overall database. So, new predictive methods for the pressure drop and heat transfer coefficient were developed based on the broad database obtained in the present study. The proposed methods provided satisfactory results not only for the experimental database used for its development, but also for independent databases collected in the literature. Additionally, based on the data obtained in the present study and a performance analysis taken into account pressure drop, heat transfer coefficient and the channel packing factor, triangular cross sectional geometry is recommended for heat sinks.

Escoamentos bifásicos estão presentes em diversos processos naturais e industriais, como na indústria de petróleo. Podem apresentar-se em diferentes configurações topológicas, ou, padrões de escoamento, entre eles o escoamento estratificado ondulado e o estratificado com mistura na interface. Os escoamentos bifásicos estratificados óleo-água têm sido utilizados como uma forma conveniente de evitar a formação de emulsões de água em óleo em oleodutos e possuem uma ocorrência comum em poços de petróleo direcionais. Quando a onda interfacial ultrapassa determinado limite geométrico e cinemático, surge o fenômeno do entranhamento de gotas, representado por misturas entre as fases junto à interface que promovem um aumento na queda de pressão. Modelos têm sido apresentados pela literatura na tentativa de descrever o fenômeno do entranhamento de gotas. Neste trabalho é apresentada uma nova proposta de modelagem matemática unidimensional para o entranhamento de gotas com o objetivo de melhorar a previsão dos parâmetros envolvidos, em especial, da fração volumétrica de óleo e da queda de pressão bifásica. Também foi utilizada simulação numérica computacional, CFD (Computational Fluid Dynamics), com o uso de software comercial para obtenção dos valores dos parâmetros do escoamento estratificado ondulado óleo-água (fração volumétrica de óleo, queda de pressão, amplitude e comprimento da onda interfacial). Os resultados da modelagem fenomenológica para entranhamento e os de CFD foram comparados com bancos de dados experimentais. Os resultados em CFD mostram concordância com os resultados experimentais, tanto na análise qualitativa das propriedades geométricas das ondas interfaciais, quanto na comparação direta com os dados para fração volumétrica e queda de pressão. Os resultados numéricos da modelagem fenomenológica para fatores de entranhamento apresentam boa concordância com dados da literatura. / Two-phase flows are present in many natural and industrial processes, such as in the oil industry. They may be found arranged in several flow patterns, including the wavy stratified flow and the stratified with mixing at the interface. The stratified oil-water flow has been used as a convenient way to avoid the formation of emulsions of water in oil and have a common occurrence in directional oil wells. When the interfacial wave exceeds a certain geometric and kinematic limit the phenomenon of drop entrainment arises at the interface, causing an increase of pressure drop. Models have been presented in the literature in an attempt to describe the phenomenon of drop entrainment. In this work, we present a new method for the one-dimensional mathematical modeling of entrainment in order to improve the prediction of oil volume fraction and pressure drop. It was also used a commercial computational fluid dynamics tool (CFD) to obtain the values of flow parameters of wavy stratified oil-water flow, such as oil volume fraction, pressure drop, amplitude and length of the interfacial waves. The results of the phenomenological modeling for entrainment and CFD were compared with experimental databases. The CFD results are in agreement with the experimental results in both the qualitative analysis of the geometric properties of the interfacial waves and in direct comparison with oil-volumetric-fraction and pressure-drop data. The numerical results of the phenomenological model for entrainment factors are in agreement with data from the literature.

Ce travail de recherche examine aux échelles globale et locale les caractéristiques thermo-hydrauliques au sein des échangeurs à plaques ondulées pour les écoulements monophasiques et en mode condensation. Il comprend deux parties :La première partie concerne l'analyse des structures d'écoulement en mode monophasique à partir d'un outil de simulations numériques, et dont les résultats sont validés à partir d'une campagne expérimentale. L'exploitation des résultats de simulations, à partir d'observables judicieusement sélectionnées, a permis de quantifier les grandes classes d'écoulement en fonction des paramètres géométriques et fluidiques de l'échangeur. Ce nouvel éclairement sur les structures d'écoulement a conduit à la proposition d'un modèle général original sur les lois de friction au sein de ces échangeurs de géométrie d'écoulement complexe.La deuxième partie concerne l'étude de la condensation de la vapeur avec et sans surchauffe en entrée de l'échangeur. Ainsi, un dispositif expérimental permettant le contrôle précis des conditions aux limites a été développé, et une métrologie spécifique, basée sur la thermographie infrarouge a également été mis au point, afin de remonter à certaines grandeurs locales le long du condenseur (titre de vapeur, coefficient d'échange thermique...). On observe ainsi une très forte variabilité des coefficients d'échanges thermiques et de la densité de flux de chaleur le long du condenseur, et la surchauffe de la vapeur tend à intensifier les transferts thermiques. Ce complément de mesures remet en question certaines hypothèses de la littérature quant à l'élaboration de corrélations sur les transferts de chaleur dans les condenseurs. / This research work examines at the global and local scales the thermo-hydraulic characteristics of plate heat exchangers with corrugated chevron plates, for single-phase and condensation flows. The study is divided into two parts:The first part concerns the analysis of flow structures of single-phase flows using numerical simulations, which are validated using the results of the experimental campaign. The analysis of the simulations results, from a flow characteristic observable that has been carefully chosen, has allowed quantifying the main flow categories as a function of the heat exchanger geometric parameters and the flow characteristics. This new information on the flow structures has led to the proposal of an original generalized model of the friction law inside this type of heat exchanger with complex geometry.The second part concerns the study of condensation with and without vapor superheating at the inlet of the heat exchanger. Thus, a specific experimental setup allowing precise control of the boundary conditions has been developed. Otherwise a specific metrology, based on infrared thermography, has been set to the point in order to determine the variation of certain local quantities along the condenser (vapor mass fraction, heat transfer coefficient...). Thus, we observe a high and wide variability of the heat transfer coefficients and the heat flux density along the condenser, and the superheating of the vapor tends to increase the heat transfers. These additional measures question certain assumptions of the literature regarding the development of heat transfer correlations in plate heat condensers.

La réduction de charge de fluides frigorigènes dans les systèmes de production de froid est un enjeu important s'inscrivant dans les politiques environnementales sur la contribution de ces fluides à l'effet de serre. Une des voies menant à la réduction de charge est l'augmentation de la compacité des échangeurs de chaleur, conduisant inévitablement à la conception d'évaporateurs plus complexes. Néanmoins, si de nombreuses études ont été publiées sur l'analyse thermo-hydraulique de l'ébullition convective de frigorigènes dans les tubes horizontaux, très peu ont été menées sur des écoulements diphasiques dans des géométries non conventionnelles. Cette thèse vise à étudier les caractéristiques des écoulements diphasiques avec changement de phase des frigorigènes de troisième (HFC) et de quatrième génération tels que le HFO-1234yf dans des singularités (coudes de retour, contractions). Ainsi, un banc d'essais expérimental a été spécifiquement conçu et construit pour mener des expériences sur l'ebullition convective. Ce banc d'essais a permis de visualiser les régimes d'écoulement et de mesurer les chutes de pression dans les singularités. Des visualisations de régimes d'écoulement ont été réalisées pour les frigorigènes HFO-1234yf, R-134a et R-410A dans des tubes droits et dans des singularités. Les résultats ont été confrontés avec diverses méthodes de prédiction de la litérature. Les perturbations sur l'écoulement causées par ces singularités et leurs effets sur le comportement hydrodynamique des fluides frigorigènes ont également été etudiés. Une serie d'éxperience a été menée pour déterminer le longueur de perturbation en amont et en aval des singularités. Finalement, les valeurs expérimentales des chutes de pression ont été confrontées à différentes corrélations de la littérature. Des nouvelles méthodes de prédiction de la chute de pression pour des écoulements diphasiques dans des singularités sont présentées. / The refrigerant charge reduction in HVAC\R systems is an important issue because it falls within environmental policies regarding refrigerants contributions to the greenhouse effect. A way to move toward charge reduction is to increase the compactness of heat exchangers, which means more complex designs of the evaporators. Nevertheless, while a large amount of studies have has been published on the thermal and hydraulic analysis of flow boiling of refrigerants in horizontal tubes, very little attention has been given to flow boiling in geometries different from straight tubes. This PhD thesis aims at studying the flow boiling characteristics of third generation (HFC) and fourth generation fluids such as HFO-1234yf in geometries which modify the fluid dynamics and two-phase flow with respect to horizontal straight tubes. To achieve this goal, an experimental test facility was specifically designed and built to conduct refrigerant evaporation experiments. This test facility allowed to perform flow regimes visualizations and pressure drop measurements in singularities (such as sudden contractions and return bends). First, two-phase flow regimes visualizations have been carried out using HFO-1234yf, R-134a and R-410A either in straight tubes or in singularities. A qualitative analysis of the flow behavior and also several comparisons to flow pattern prediction methods from the literature were conducted. The second objective of this work was to characterize the flow disturbances caused by singularities such as sudden contractions and return bends, and to study their effects on the hydrodynamic performance (e.g. pressure drop) of refrigerants.Lastly, pressure drop databases for third and fourth generation refrigerants are presented.