Cette thèse, de nature expérimentale, rentre dans le cadre de la récupération d’énergie pour les micro-générateurs et l’autonomie des dispositifs électroniques à faible consommation. Ce travail propose les possibilités de récupérer de l’énergie thermique par effet pyroélectrique. L’éner- gie thermique à convertir est une variation temporelle de température. Nous avons proposé deux principales techniques pour produire de l’énergie électrique via une céramique pyroélectrique de type PZT. La première est centrée sur la récupération des radiations infrarouges associé à la tech- nique SSHI. Originellement, la technique SSHI a été développée dans le cas de la récupération d’énergie piézoélectrique, mais nous l’avons appliqué dans le cas de la pyroélectricité et qui nous a permis de maximiser la puissance récupérée d’un facteur de 2. La seconde technique proposée concerne la récupération des fluctuations thermiques provenant des mouvements convectifs nais- sant à l’intérieur d’un fluide dans la configuration de Rayleigh-Bénard. Nous avons mené plusieurs études pour augmenter le transfert convectif dans le but d’améliorer la réponse pyroélectrique et donc maximiser la puissance récupérée. Dans le cas des convections naturelles, le choix de fluide adéquat et l’optimisation des paramètres de contrôle de la configuration Rayleigh-Bénard consti- tuent des étapes primordiales pour aboutir à un meilleur transfert thermique par convection. Dans le cas des convections forcée, il a été étudié l’intérêt de disperser des particules de Cuivre de taille nanométrique dans un fluide porteur pour augmenter plus davantage le transfert convectif. Avec ce nanofluide, la réponse pyroélectrique a été maximisée d’un facteur de 10. / This experimental thesis focuses on the energy harvesting for micro-generators and au- tonomy of electronic devices with low consumption. This work proposes the possibilities of har- vesting thermal energy by pyroelectric effect. The thermal energy to be converted is thermal fluc- tuations. We proposed two main techniques to generate electricity by pyroelectric ceramic. The first one focuses on the harvesting of infrared radiation associated with the SSHI technique. Ori- ginally, the SSHI technique was developed in the case of the piezoelectric energy harvesting, but we applied it in the case of pyroelectricity and which allowed us to maximize the harvested power by a factor of 2. The second proposed technique concerns the harvesting of thermal fluctuations resulting from convective movements originating inside a fluid in the Rayleigh-Bernard configu- ration. We have carried out several studies to increase the convective transfer in order to improve the pyroelectricresponse and maximize the harvested power. In the case of natural convection, the choice of a suitable fluid and the optimization of the control parameters of the Rayleigh-Bernard configuration are essential steps in order to achieve better heat transfer by convection. In the case of forced convection, it has been studied the advantage of dispersing copper nanoparticles in a pure fluid to increase the convective transfer. With this nanofluid, the pyroelectric response was maximized by a factor of 10.

Diante das atuais questões ambientais, o uso eficiente da energia é uma premissa em todos os setores de atividades. Sabe-se que as edificações são grandes consumidores de energia e boa parcela desse consumo se dá em sistemas de condicionamento artificial. São três os principais fatores que atuam no balanço térmico e influenciam esse consumo: arquitetura, ocupação e clima. A arquitetura atua como intermediária nesse balanço térmico, podendo ajudar ou prejudicar as condições internas. Este trabalho estuda o desempenho térmico e energético dos edifícios de escritórios em São Paulo e Rio de Janeiro, cidades que apresentam condições extremas de calor durante o verão e até em outras estações do ano. O tipo de ocupação e a atividade realizada em edifícios de escritórios nos dias de hoje criam, por si sós, cargas térmicas elevadas que dificultam ainda mais a obtenção de conforto. Este trabalho parte do pressuposto de que existem soluções arquitetônicas de edifícios de escritórios na cidade de São Paulo capazes de garantir conforto térmico aos usuários durante parte do período de ocupação sem uso de condicionamento artificial, porém acreditar que é possível obter conforto apenas com sistemas passivos durante o ano todo nos atuais edifícios de escritórios das cidades de São Paulo e Rio de Janeiro é ilusão. Diante desse desafio, o sistema de modo misto de condicionamento ambiental une as vantagens do sistema ativo às do passivo, operando com sistemas naturais sempre que possível, reduzindo o consumo de energia e acionando o sistema ativo em situações fora das condições de conforto. Utilizar o sistema de modo misto não significa abrir as janelas de qualquer edifício no inverno. O edifício deve estar preparado para o sistema desde as etapas de projeto. Com base nesse pensamento, a pesquisa analisa o desempenho térmico e energético de três tipologias arquitetônicas operando com o sistema de modo misto em São Paulo e investiga o desempenho das mesmas tipologias sob as condições climáticas da cidade do Rio de Janeiro. As avaliações de desempenho térmico e energético das tipologias são feitas por meio de análises e comparações de resultados de simulações computacionais com o programa TAS (9.0.7 maio, 2005). / Considering current environmental issues, all sectors of activities are premised on the efficient use of energy. Its known that constructions are great energy consumers and part of this consumption is given by artificial conditioning systems. Therere three main factors in thermal balance that influences this consumption: architecture, occupation and climate. The architecture acts as intermediate in this thermal balance, being able to help or harm internal conditions. This research treats office building thermal and energy performance in São Paulo and Rio de Janeiro, cities with high temperatures not only during the summer but also in other seasons. Nowadays, offices occupation and activity are themselves great heat producers, what makes thermal comfort even more difficult to achieve. This project considers that there are office building design solutions able to produce thermal environmental conditions acceptable to a majority of occupants, without air-conditioning system, during part of the working period, in São Paulo. However, believing the possibility of achieving comfort conditions in actual office buildings, only with passive cooling strategies, during all year, in the cities of São Paulo and Rio de Janeiro, is an illusion. Facing this challenge, mixed mode system combines the best of air-conditioning and natural ventilation, operating with natural strategies whenever its possible, reducing energy consumption and using the air-conditioning system only when thermal environmental conditions are not acceptable. Mixed mode operation does not mean to open any building windows during the winter. The building must have been designed for the mixed mode system since its first projects. This research is based on this thought and thermal analysis and energy performance of three architectural design buildings operating with mixed mode system in São Paulo and investigates the performance of these building types under climate conditions of Rio de Janeiro city. The thermal and energy performance evaluations of the building types are based on the analysis and comparison of computer simulations results, with the software TAS (9.0.7 May, 2005).

<p>This project deals with the potential of membrane stratified solar ponds which consist of two water layers, where one is a salt solution here, and a separating translucent membrane. An experimental pond was set up to study the thermal behaviour of such collector systems. The input is mainly solar radiation, sometimes when the ambient temperatures are higher than the pond temperatures also heat from the environment is transferred into the pond.</p><p>The measured temperatures of the pond, the ambient temperature, the global radiation and wind speed were the basis data for thermal calculations which showed that the pond was working well as a solar collector and thermal storage system all in one. Heat was not extracted from the pond however, only the losses to the environment were studied.</p><p>It was found out that the pond temperatures were higher than the ambient temperature over the whole measurement period of 12 days, and insulation and pollution problems as well as future prospects and suggestions for further studies are discussed at the end of this paper.</p>

<p>This thesis investigates the possibility of using an unglazed flat-plate solar collector as a cooling radiator. The solar collector will be connected to the condenser of a heat pump and used as cooler during nighttime. Daytime the solar collector will be connected to the evaporator of the heat pump and used as heat source. The two widely differing fields of application make special demands on the solar collector. The task is given by the heat pump manufacturer Thermia and the main objective is to find out whether a solar collector should be used as a cooler or not. The performance of the solar collector under varying environmental conditions is investigated using COMSOL Multiphysics 3.3. Only the cooling properties are investigated here. The performance of the solar collector as a heat exchanger is estimated using the effectiveness-NTU method, and the solar collector is found to be a good heat exchanger at low wind speeds. The heat transfer coefficients of the convection and radiation are determined for varying temperature and wind speeds. The convective heat transfer coefficient is lowered by tubes above the absorber plate and for a high convective heat transfer rate the solar collector surface should be smooth. For a high radiative heat transfer rate the surface needs to have a high emissivity. The cooling rate is higher from a warm surface than from a cold and since no temperature change of the heat carrier is necessary the solar collector should be kept at a high temperature. To increase the cooling rate alterations need to be made to the solar collector that makes its heating performance deteriorate. A solar collector that can be used for cooling is not an efficient solar collector.</p>

Due to climatic change, increasing thermal loads inbuildings and rising living standards, comfort cooling inbuildings is becoming increasingly important and the demand forcomfort cooling is expanding very quickly around the world. Theincreased cooling demand results in a peak in electrical powerdemand during the hottest summer hours. This peak presents newchallenges and uncertainties to electricity utilities and theircustomers. Cool thermal storage systems have not only the potential tobecome one of the primary solutions to the electrical powerimbalance between production and demand, but also shift coolingenergy use to off-peak periods and avoid peak demand charges.It increases the possibilities of utilizing renewable energysources and waste heat for cooling generation. In addition, acool storage can actually increase the efficiency of combinedheat and power (CHP) generation provided that heat drivencooling is coupled to CHP. Then, the cool storage may avoidpeaks in the heat demand for cooling generation, and this meansthat the CHP can operate at design conditions in most oftime. Phase Change Materials (PCMs) used for cool storage hasobtained considerable attention, since they can be designed tomelt and freeze at a selected temperature and have shown apromising ability to reduce the size of storage systemscompared with a sensible heat storage system because they usethe latent heat of the storage medium for thermal energystorage. The goal of this thesis is to define suitable PCM candidatesfor comfort cooling storage. The thesis work combines differentmethods to determine the thermophysical properties oftetradecane, hexadecane and their binary mixtures, anddemonstrates the potential of using these materials as PCM forcomfort cooling storage. The phase equilibrium of the binarysystem has been studied theoretically as well asexperimentally, resulting in the derivation of the phasediagram. With knowledge of the liquid-solid phase equilibriumcharacteristics and the phase diagram, an improvedunderstanding is provided for the interrelationships involvedin the phase change of the studied materials. It has beenindicated that except for the minimum-melting point mixture,all mixtures melt and freeze within a temperature range and notat a constant temperature, which is so far often assumed in PCMstorage design. In addition, the enthalpy change during thephase transition (heat of fusion) corresponds to the phasechange temperature range; thus, the storage density obtaineddepends on how large a part of the phase change temperaturerange is valid for a given application. Differential Scanning Calorimetery (DSC) is one frequentlyused method in the development of PCMs. In this thesis, it hasbeen found that varying results are obtained depending on theDSC settings throughout the measurements. When the DSC runs ata high heating/cooling rate it will lead to erroneousinformation. Also, the correct phase transition temperaturerange cannot be obtained simply from DSC measurement. Combiningphase equilibrium considerations with DSC measurements gives areliable design method that incorporates both the heat offusion and the phase change temperature range. The potential of PCM storage for peak shaving in differentcooling systems has been demonstrated. A Computer model hasbeen developed for rapid phase equilibrium calculation. The useof phase equilibrium data in the design of a cool storagesystem is presented as a general methodology. Keywords:Comfort cooling, peak shaving, PCM, coolthermal storage system, DSC, phase change temperature range,the heat of fusion, phase equilibrium, phase diagram. Language:English

Oxygen-diluted Combustion (OdC) technology has evolved from the concept of Excess Enthalpy Combustion and is characterized by reactants of low oxygen concentration and high temperature. Recent advances in this technology have demonstrated significant energy savings, high and uniform thermal field, low pollution, and the possibility for downsizing the equipment for a range of furnace applications. Moreover, the technology has shown promise for wider applications in various processes and power industries. The objectives of this thesis are to analyze the thermodynamic aspects of this novel combustion technology and to quantify the enhancement in efficiency and heat transfer inside a furnace in order to explore the potentials for reduced thermodynamic irreversibility of a combustion process and reduced energy consumption in an industrial furnace. Therefore, theoretical and experimental investigations were carried out. The 2nd law of thermodynamics analyses of OdC systems have been carried out for cases in which the oxidizer is either oxygen (Flameless-oxy-fuel) or air (High Temperature Air Combustion, HiTAC). The analyses demonstrate the possibilities of reducing thermodynamic irreversibility of combustion by considering an oxygen-diluted combustion process that utilizes both gas- and/or heat-recirculation. Furthermore, the results showed that an oxygen-diluted combustion system that utilizes oxygen as an oxidizer, in place of air, results in higher 1st and 2nd law efficiencies. Mathematical models for heat regenerators were developed to be designing tools for maximized heat recovery. These models were verified by heat performance experiments carried out on various heat regenerators. Furthermore, experiments were performed in a semi-industrial test furnace. It was equipped with various regenerative burning systems to establish combustion and heat transfer conditions prevailing in an industrial furnace operating based on HiTAC. The tests were carried out at seven firing configurations, two conventional and five HiTAC configurations, for direct and indirect heating systems. Measurements of energy balance were performed on the test furnace at various configurations in order to obtain the 1st law efficiency. Moreover, local measurements of temperature, gas composition, and heat fluxes in the semi-industrial test furnace were performed to find out the main characteristics of HiTAC flame and the effects of these characteristics on the heating potential, i.e., useful heating in the furnace. In the case of HiTAC, these measurements showed uniformities of chemistry, temperature, temperature fluctuation, and heat fluxes profiles. The values of fluctuations in temperature were small. The high speed jets of the fuel and air penetrated deep into the furnace. The fuel gradually disappeared while intermediate species gradually appeared in relatively high concentrations and at broader regions inside the furnace. These findings indicate: a large reaction zone, low specific combustion intensity in the flame, low specific fuel energy release, and high heat release from this large flame. In addition to the thermodynamic limitations to the maximum temperature of the Oxygen-diluted Combustion, the low specific energy release of the fuel and the high heat release from the flame to its surroundings cause this uniform and relatively moderate temperature profile in a HiTAC flame, consequently suppressing thermal-NO formation. Heat flux and energy balance measurements showed that heating potential is significantly increased in the case of HiTAC compared to that in the conventional case, implying much more energy savings than the apparent heat recovery from the heat regenerators, and consequently much less pollutants emissions. Therefore, it is certain that this large HiTAC flame emits more thermal radiation to its surroundings than the conventional flame does, in spite of the moderate-uniform temperature profile of the flame. This intense heat flux was more uniform in all HiTAC configurations, including the indirect heating configuration, than that of the conventional-air combustion configuration. / QC 20101011

This project deals with the potential of membrane stratified solar ponds which consist of two water layers, where one is a salt solution here, and a separating translucent membrane. An experimental pond was set up to study the thermal behaviour of such collector systems. The input is mainly solar radiation, sometimes when the ambient temperatures are higher than the pond temperatures also heat from the environment is transferred into the pond. The measured temperatures of the pond, the ambient temperature, the global radiation and wind speed were the basis data for thermal calculations which showed that the pond was working well as a solar collector and thermal storage system all in one. Heat was not extracted from the pond however, only the losses to the environment were studied. It was found out that the pond temperatures were higher than the ambient temperature over the whole measurement period of 12 days, and insulation and pollution problems as well as future prospects and suggestions for further studies are discussed at the end of this paper.

Nowadays, lighting represents 20% of the global electricity consumption. Light can be produced using different technologies but more than 100 years after its invention, the incandescent bulb is still the most sold and one of the more used light sources. Of the total energy input in an incandescent bulb more than 90% is lost as heat while less than 10% is converted into visible light. However, there are alternative technologies which use up to 85% less energy for conventional lighting and there are even more efficient light sources for other purposes that if they replace completely all incandescent lamps over the world could reduce dramatically the global electricity consumption and greenhouse gases emissions. One may identify these alternative technologies mainly as LEDs and discharge lamps, but are they the unique alternatives? This thesis is focused on a new lighting technology whose name is LightLab and which is based on the field emission and cathodoluminescence concepts. This technology is under the research and development stage but prototypes have already achieved energy savings over 85% compared to incandescent lamps with a great color performance and with the advantage that it does not use mercury or other hazardous substances compared with discharge lamps. Thus, in the first part of the project all technologies and last improvements are studied while the second part analyses the market applications possibilities for the LightLab lamp considering the environmental perspective regulations and comparing the lamp with the other light sources. The result is that despite there are still some unknown parameters that need to be developed or improved, the lamp has a great potential for different applications fields.

<p>Due to climatic change, increasing thermal loads inbuildings and rising living standards, comfort cooling inbuildings is becoming increasingly important and the demand forcomfort cooling is expanding very quickly around the world. Theincreased cooling demand results in a peak in electrical powerdemand during the hottest summer hours. This peak presents newchallenges and uncertainties to electricity utilities and theircustomers.</p><p>Cool thermal storage systems have not only the potential tobecome one of the primary solutions to the electrical powerimbalance between production and demand, but also shift coolingenergy use to off-peak periods and avoid peak demand charges.It increases the possibilities of utilizing renewable energysources and waste heat for cooling generation. In addition, acool storage can actually increase the efficiency of combinedheat and power (CHP) generation provided that heat drivencooling is coupled to CHP. Then, the cool storage may avoidpeaks in the heat demand for cooling generation, and this meansthat the CHP can operate at design conditions in most oftime.</p><p>Phase Change Materials (PCMs) used for cool storage hasobtained considerable attention, since they can be designed tomelt and freeze at a selected temperature and have shown apromising ability to reduce the size of storage systemscompared with a sensible heat storage system because they usethe latent heat of the storage medium for thermal energystorage.</p><p>The goal of this thesis is to define suitable PCM candidatesfor comfort cooling storage. The thesis work combines differentmethods to determine the thermophysical properties oftetradecane, hexadecane and their binary mixtures, anddemonstrates the potential of using these materials as PCM forcomfort cooling storage. The phase equilibrium of the binarysystem has been studied theoretically as well asexperimentally, resulting in the derivation of the phasediagram. With knowledge of the liquid-solid phase equilibriumcharacteristics and the phase diagram, an improvedunderstanding is provided for the interrelationships involvedin the phase change of the studied materials. It has beenindicated that except for the minimum-melting point mixture,all mixtures melt and freeze within a temperature range and notat a constant temperature, which is so far often assumed in PCMstorage design. In addition, the enthalpy change during thephase transition (heat of fusion) corresponds to the phasechange temperature range; thus, the storage density obtaineddepends on how large a part of the phase change temperaturerange is valid for a given application.</p><p>Differential Scanning Calorimetery (DSC) is one frequentlyused method in the development of PCMs. In this thesis, it hasbeen found that varying results are obtained depending on theDSC settings throughout the measurements. When the DSC runs ata high heating/cooling rate it will lead to erroneousinformation. Also, the correct phase transition temperaturerange cannot be obtained simply from DSC measurement. Combiningphase equilibrium considerations with DSC measurements gives areliable design method that incorporates both the heat offusion and the phase change temperature range.</p><p>The potential of PCM storage for peak shaving in differentcooling systems has been demonstrated. A Computer model hasbeen developed for rapid phase equilibrium calculation. The useof phase equilibrium data in the design of a cool storagesystem is presented as a general methodology.</p><p><b>Keywords:</b>Comfort cooling, peak shaving, PCM, coolthermal storage system, DSC, phase change temperature range,the heat of fusion, phase equilibrium, phase diagram. Language:English</p>

<p>Oxygen-diluted Combustion (OdC) technology has evolved from the concept of Excess Enthalpy Combustion and is characterized by reactants of low oxygen concentration and high temperature. Recent advances in this technology have demonstrated significant energy savings, high and uniform thermal field, low pollution, and the possibility for downsizing the equipment for a range of furnace applications. Moreover, the technology has shown promise for wider applications in various processes and power industries.</p><p>The objectives of this thesis are to analyze the thermodynamic aspects of this novel combustion technology and to quantify the enhancement in efficiency and heat transfer inside a furnace in order to explore the potentials for reduced thermodynamic irreversibility of a combustion process and reduced energy consumption in an industrial furnace. Therefore, theoretical and experimental investigations were carried out.</p><p>The 2nd law of thermodynamics analyses of OdC systems have been carried out for cases in which the oxidizer is either oxygen (Flameless-oxy-fuel) or air (High Temperature Air Combustion, HiTAC). The analyses demonstrate the possibilities of reducing thermodynamic irreversibility of combustion by considering an oxygen-diluted combustion process that utilizes both gas- and/or heat-recirculation. Furthermore, the results showed that an oxygen-diluted combustion system that utilizes oxygen as an oxidizer, in place of air, results in higher 1st and 2nd law efficiencies.</p><p>Mathematical models for heat regenerators were developed to be designing tools for maximized heat recovery. These models were verified by heat performance experiments carried out on various heat regenerators.</p><p>Furthermore, experiments were performed in a semi-industrial test furnace. It was equipped with various regenerative burning systems to establish combustion and heat transfer conditions prevailing in an industrial furnace operating based on HiTAC. The tests were carried out at seven firing configurations, two conventional and five HiTAC configurations, for direct and indirect heating systems.</p><p>Measurements of energy balance were performed on the test furnace at various configurations in order to obtain the 1st law efficiency. Moreover, local measurements of temperature, gas composition, and heat fluxes in the semi-industrial test furnace were performed to find out the main characteristics of HiTAC flame and the effects of these characteristics on the heating potential, i.e., useful heating in the furnace. In the case of HiTAC, these measurements showed uniformities of chemistry, temperature, temperature fluctuation, and heat fluxes profiles. The values of fluctuations in temperature were small. The high speed jets of the fuel and air penetrated deep into the furnace. The fuel gradually disappeared while intermediate species gradually appeared in relatively high concentrations and at broader regions inside the furnace. These findings indicate: a large reaction zone, low specific combustion intensity in the flame, low specific fuel energy release, and high heat release from this large flame. In addition to the thermodynamic limitations to the maximum temperature of the Oxygen-diluted Combustion, the low specific energy release of the fuel and the high heat release from the flame to its surroundings cause this uniform and relatively moderate temperature profile in a HiTAC flame, consequently suppressing thermal-NO formation.</p><p>Heat flux and energy balance measurements showed that heating potential is significantly increased in the case of HiTAC compared to that in the conventional case, implying much more energy savings than the apparent heat recovery from the heat regenerators, and consequently much less pollutants emissions. Therefore, it is certain that this large HiTAC flame emits more thermal radiation to its surroundings than the conventional flame does, in spite of the moderate-uniform temperature profile of the flame. This intense heat flux was more uniform in all HiTAC configurations, including the indirect heating configuration, than that of the conventional-air combustion configuration.</p>