De Bruin och Hartogensis har föreslagit en ny metod för att beräkna impulsflödet och det sensibla värmeflödet vid stabila förhållanden. Metoden bygger på att de normaliserade standardavvikelserna är approximativt konstanta för den horisontella vinden och temperaturen. Beräkningarna görs endast utifrån medelvinden och temperaturen och dess standardavvikelser. Den här metoden testas i den här studien med datamaterial från Labans kvarnar på Gotland i Östersjön och Östergarnsholm som ligger 4 km utanför Gotland. Labans kvarnar representerar flöden över land och Östergarnsholm flöden över hav. Konstanterna som De Bruin och Hartogensis använde är följande: Cu=2.5 och CT=2.3, vilket gav en mycket liten spridning i deras beräkningar av flöden. Datamaterialet de använde sig av var från Kansas, USA, över en plan grässlätt. Olika statistiska mått har här testats för att erhålla värden på konstanterna. Medel-, median- och typvärde för de normaliserade standardavvikelserna för respektive kvantitet har beräknats. För landförhållanden i den här studien fås lite högre värden på konstanterna, Cu=2.6 och CT=2.6, än vad De Bruin och Hartogensis erhöll.  Vid beräkningar av flöden över hav delas vindriktningen upp i två intervall. Vindriktningen som ligger mellan 220o - 300o representerar vindar som blåser ifrån Gotland och vindriktningar som ligger mellan 80o - 220o representerar vindar från öppet hav. För öppna havsförhållanden fås konstanter som har ett lägre värde vid beräkning av impulsflödet, Cu=2.2 , än de värde som De Bruin och Hartogensis fick. För vindar som blåser ifrån Gotland erhålls konstanten till:Cu=3.0. Konstanter för beräkning av värmeflödet är svårare att bestämma och ger inte alls lika bra resultat över hav som för impulsflödet. Bestämningar av värmeflöde är mycket mer komplicerade än för impulsflöde. Delvis på grund av att det behövs två konstanter, men det beror också på att temperaturstrukturen i det marina gränsskiktet inte följer Monin-Obukhovs similaritetsteori.Framsidans foto / De Bruin and Hartogensis have proposed a new method to determine momentum flux and sensible heat flux at stable conditions. When using this method the assumption is made that the standard deviations for the longitudinal wind component and temperature are approximately constant. Only the mean wind and the temperature and the standard deviations are necessary for the calculations. The method has been analyzed in this study with data from Labans kvarnar sited on Gotland in the Baltic Sea and Östergarnsholm which is situated 4 km outside Gotland. Labans kvarnar represents fluxes over land and Östergarnsholm represents fluxes over sea. The constants that De Bruin and Hartogensis found are the following:Cu=2.5 for wind speed and CT=2.3  for temperature, which shows very little scatter in the calculations of the fluxes. The data they used where measured in Kansas over a very flat grassland site. Different statistics measurements have been tested to receive values of the constants. In search of constants the mean value, median value and the modal value for respectively quantity have been calculated. For land conditions the values of the constants are a little bit higher, Cu=2.6 and CT=2.6, than the values De Bruin and Hartogensis received. When calculating the fluxes over ocean the wind direction is divided in to two intervals. The wind direction between 220o - 300o represents winds from Gotland and wind direction between  80o - 220o represents winds from open sea. For the open sea conditions the constants calculated for the momentum flux in this study are a little bit lower, Cu=2.2, than the value De Bruin and Hartogensis found. For winds from Gotland the constant for momentum flux was found to be: Cu=3.0. When calculating the sensible heat flux the constants are very difficult to find and do not give as good result as for the momentum flux over sea. The conditions for the sensible heat are much more complicated than it is for momentum flux. Firstly two constants are needed and secondly the temperature structure in the marine boundary layer does not follow Monin-Obukhov similarity theory.

Thermal energy storage (TES) systems play a crucial part in the success of concentrated solar power as a reliable thermal energy source. The economics and operational effectiveness of TES systems are the subjects of continuous research for improvement, in order to lower the localized cost of energy (LCOE). This study investigates the use of spherical tanks and their role in sensible heat storage in liquids. In the two tank system, typical cylindrical tanks were replaced by spherical tanks of the same volume and subjected to heat loss, stress analysis, and complete tank cost evaluation. The comparison revealed that replacing cylindrical tanks by spherical tanks in two tank molten salt storage systems could result in a 30% reduction in heat loss from the wall, with a comparable reduction in total cost. For a one tank system (or thermocline system), a parametric computational fluid dynamic (CFD) study was performed in order to obtain fluid flow parameters that govern the formation and maintenance of a thermocline in a spherical tank. The parametric study involved the following dimensionless numbers: Re (500-7500), Ar (0.5-10), Fr (0.5-3), and Ri (1-100). The results showed that within the examined range of flow characteristics, the inlet Fr number is the most influential parameter in spherical tank thermocline formation and maintenance, and the largest tank thermal efficiency in a spherical tank is achieved at Fr = 0.5. Experimental results were obtained to validate the CFD model used in the parametric study. For the flow parameters within the current model, the use of an eddy viscosity turbulence model with variable turbulence intensity delivered the best agreement with experimental results. Overall, the experimental study using a spherical one tank setup validated the results of the CFD model with acceptable accuracy.

Inorganic salts are very promising as high-temperature heat transfer fluids and thermal storage media in solar thermal power production. The dual-tank molten salt storage system, for example, has been demonstrated to be effective for continuous operation in solar power tower plants. In this particular storage regime, however, much of the thermal storage potential of the salts is ignored. Most inorganic salts are characterized by high heats of fusion, so their use as phase-change materials (PCMs) allows for substantially higher energy storage density than their use as sensible heat storage alone. For instance, use of molten sodium-potassium eutectic salt over a temperature range of 260 to 560°C (the approximate operating parameters of a proposed utility-scale storage system) allows for a volumetric energy storage density of 212 kWhth/m3, whereas the use of pure sodium nitrate (T_m = 307°C) over the same temperature range (utilizing both sensible and latent heat) yields a storage density of 347 kWhth/m3. The main downside to these media is their relatively low thermal conductivity (typically on the order of 1 W/m-K). While low conductivity is not as much an issue with heat transfer fluids, which, owing to convective heat transfer, are not as reliant on conduction as a heat transfer mode, it can become important for PCM storage strategies, in which transient charging behavior will necessarily involve heating the solid-phase material up to and through the process of melting. This investigation seeks to develop new methods of improving heat transfer in inorganic salt latent heat thermal energy storage (TES) media, such as sodium / potassium nitrates and chlorides. These methods include two basic strategies: first, inclusion of conductivity-enhancing additives, and second, incorporation of infrared absorptive additives in otherwise transparent media. Also, in the process, a group of chloride based salts for use as sensible storage media and/or heat transfer fluids has been developed, based on relevant cost and thermophysical properties data. For direct conductivity enhancement, the idea is simple: a PCM with low conductivity can be enhanced by incorporation of nanoparticulate additives at low concentration (~5 wt %). This concept has been explored extensively with lower temperature heat transfer fluids such as water, ethylene glycol, etc. (e.g., nanofluids), as well as with many lower temperature PCMs, such as paraffin wax. Extension of the concept to high temperature inorganic salt thermal storage media brings new challenges—most importantly, material compatibility. Also, maintenance of the additive distribution can be more difficult. Promising results were obtained in both these regards with nitrate salt systems. The second heat transfer enhancement strategy examined here is more novel in principle: increasing the infrared absorption of a semitransparent salt PCM (e.g., NaCl) with a suitable additive can theoretically enhance radiative heat transfer (for sufficiently high temperatures), thereby compensating for low thermal conductivity. Here again, material compatibility and maintenance of additive dispersion become the focus, but in very different ways, owing to the higher temperatures of application (>600°C) and the much lower concentration of additives required (~0.5 wt %). Promising results have been obtained in this case, as well, in terms of demonstrably greater infrared absorptance with inclusion of additives.

Direct measurements of wintertime surface heat fluxes between the ocean and atmosphere in lead and polynya environments in the Canadian Arctic are presented. Such environments can yield very large vertical temperature gradients during the winter months and are particularly dynamic micrometeorological environments. We found that sensible heat fluxes can exceed +100 W m-2 during the winter months, much larger than most regional estimates (~ 0 W m-2). In addition, large heat fluxes are shown to affect the characteristics of the near surface temperature inversion (temperature increases with height). The height, depth and strength of the characteristic wintertime inversion are shown to be influenced in cases where large surface fluxes were observed. Such findings are likely to have implications on the regional and planetary heat budget, general circulation models and larger scale weather processes, which most often omit local scale heat fluxes in their analyses and calculations. / February 2016

<p>In this study the flux attenuation due to sensor displacement has been investigated over sea using an extensive set of data from the "Ocean Horizontal Array Turbulence Study". All previous investigations of the flux attenuation have been performed over land.</p><p>A function developed for correcting fluxes in the homogenous surface layer was compared to measured flux attenuation. This investigation revealed the possibility to find new functions describing the flux attenuation when measurements are carried out over sea. From the measured flux attenuation studied here a change in the form of correction functions was required to improve the estimated flux loss. The most significant difference found in this report compared to the previous landbased study Horst (2006) is for stable conditions, where significantly less flux loss is found over sea. Two new functions describing the attenuation due to sensor displacement over sea have been constructed.</p><p>One of these expressions has a discontinuity at z/L = 0. This is supported by measured flux attenuation. A reasonable interpretation is; however, that this discontinuity is caused by two separate turbulence regimes near neutrality on the stable and unstable side respectively. The discontinuity is thus not believed to be an effect merely of stability. A second correction function which is continuous over all stabilities has therefore also been constructed. These two functions and the correction function from Horst (2006) have been compared to measured flux loss. Based on this comparison the continuous correction function is recommended for correcting scalar fluxes measured over sea. It should be noted, however, that this expression only describes the mean attenuation and has been constructed from measurements at 5 and 5.5 m above mean sea level.</p><p>The theoretical basis used in the development of the function for flux attenuation over land allows for a direct link between a spectral shape and the attenuation expression. This link has been preserved for the new expressions presented in this report. The spectral shape corresponding to the continuous correction function has been compared to measured mean cospectra and also to the cospectra from Horst (2006) corresponding to crosswind displacements.</p><p>At a height of 10 m and a sensor displacement of 0.2 m the mean flux attenuation is about 1.3-4% in the stability interval −1 < z/L < 1.5 when using the new correction functions presented in this report.</p>

In this study the flux attenuation due to sensor displacement has been investigated over sea using an extensive set of data from the "Ocean Horizontal Array Turbulence Study". All previous investigations of the flux attenuation have been performed over land. A function developed for correcting fluxes in the homogenous surface layer was compared to measured flux attenuation. This investigation revealed the possibility to find new functions describing the flux attenuation when measurements are carried out over sea. From the measured flux attenuation studied here a change in the form of correction functions was required to improve the estimated flux loss. The most significant difference found in this report compared to the previous landbased study Horst (2006) is for stable conditions, where significantly less flux loss is found over sea. Two new functions describing the attenuation due to sensor displacement over sea have been constructed. One of these expressions has a discontinuity at z/L = 0. This is supported by measured flux attenuation. A reasonable interpretation is; however, that this discontinuity is caused by two separate turbulence regimes near neutrality on the stable and unstable side respectively. The discontinuity is thus not believed to be an effect merely of stability. A second correction function which is continuous over all stabilities has therefore also been constructed. These two functions and the correction function from Horst (2006) have been compared to measured flux loss. Based on this comparison the continuous correction function is recommended for correcting scalar fluxes measured over sea. It should be noted, however, that this expression only describes the mean attenuation and has been constructed from measurements at 5 and 5.5 m above mean sea level. The theoretical basis used in the development of the function for flux attenuation over land allows for a direct link between a spectral shape and the attenuation expression. This link has been preserved for the new expressions presented in this report. The spectral shape corresponding to the continuous correction function has been compared to measured mean cospectra and also to the cospectra from Horst (2006) corresponding to crosswind displacements. At a height of 10 m and a sensor displacement of 0.2 m the mean flux attenuation is about 1.3-4% in the stability interval −1 &lt; z/L &lt; 1.5 when using the new correction functions presented in this report.

ABSTRACT HEAT REMOVAL FROM A LARGE SCALE WARM WATER STORAGE Kayserilioglu, Yavuz Selim M.S., Department of Mechanical Engineering Supervisor: Prof. Dr. R&uuml / knettin Oskay August 2004, 88 Pages A preliminary experimental study was performed in order to investigate the charging and heat removal characteristics of a sensible heat storage. Two sets of experiments were performed at two aspect ratios. Heat removal processes of these two sets were different while the charging processes were similar. In the first set of experiments, after the charging of the storage unit with relatively warm water was complete, heat removal process was started with simple heat exchangers from different elevations within the storage while the charging of the storage unit was continued. In the second set of experiments, after the charging of the storage unit was complete, heat removal from the storage unit was started without further charging of the storage unit. Charging water was fed into the storage from the top of one side and relatively colder water was drained from the bottom of the opposite side. Internal heat exchangers were used for the heat removal. Vertical temperature profile developments during the charging and heat removal periods were investigated. Thermal stratification was observed in all experiments. Heat exchangers extracted heat from different elevations in different experiments and the trend was that more heat can be extracted in upper elevations. Comparable heat can be extracted from the same elevation of lower and higher aspect ratio. Keywords: Sensible Heat Storage, Heat Removal, Thermal Stratification, Warm Water Storage

Cette étude porte sur les systèmes de stockage thermique régénératif dont le principe consiste à stocker de l’énergie sous forme de chaleur sensible dans un lit fixe. Le système est chargé et déchargé à l’aide d’un fluide caloporteur circulant à travers le lit fixe. Ce type de système est prometteur pour réduire le coût des infrastructures de stockage, par exemple dans les centrales solaires thermodynamiques. Cependant, le pilotage de ces systèmes est relativement complexe car leur fonctionnement est régi par divers phénomènes et met en jeux plusieurs modes de transfert de chaleur. Leur identification a permis de développer un modèle numérique monodimensionnel constitué d’une équation de continuité et de trois équations d’énergie : une pour le fluide caloporteur, une pour le solide du lit fixe et une pour les parois du réservoir. Les études expérimentales réalisées sur trois systèmes différents (un système huile/roches+sable, un système gaz/roches et un système gaz/céramique structuré en canaux), ainsi que des résultats issus de la littérature ont permis de valider le modèle proposé dans une large gamme de configurations. Le modèle s’avère notamment capable de traiter les fluides caloporteurs liquides ou gazeux et les lits fixes structurés en canaux ou constitués de milieux granulaires à granulométrie simple ou double. / This study deals with regenerative heat storage systems which aim to store sensible heat in a packed bed. The system is charged and discharged thanks to a heat transfer fluid which circulates through the packed bed. This kind of system is promising to reduce the cost of heat storage facilities, for example in concentrated solar power plants. However, the operation of these systems is relatively complex because their thermal behavior is governed by several phenomena and heat transfer modes. Thanks to the identification of these mechanisms, a one-dimensional numerical model consisting of one continuity equation and three energy conservation equations has been developed. There is one energy equation for the heat transfer fluid, one for the packed bed and one for the walls of the tank. The experimental studies carried out on three different systems (an oil/rock+sand system, a gas/rock system and a structured gas/ceramic system) and experimental results from the literature have enabled to validate the model in various configurations. The model is able to deal with liquid or gaseous heat transfer fluids and with structured packed beds with channels or granular packed beds with uniformly sized particles or particles of two different sizes.

Este trabalho apresenta a otimização de sistemas de acumulação sensível de energia térmica, submetidos a fontes de energia intermitentes (solar). Este tipo de sistema de acumulação é definido pelo seu material de acumulação e pelo fluido de trabalho, que realiza o transporte da energia. A metodologia empregada consiste em aplicar o modelo da capacitância global para descrever o comportamento dinâmico do material de acumulação, disposto na forma de placas planas paralelas, enquanto que o fluido de trabalho foi modelado via balanço de energia. O material de acumulação foi dividido em diversas seções menores, de modo a satisfazer a condição de validade do modelo da capacitância global, resultando em números de Biot menores ou iguais a 0,1, para cada seção. Os parâmetros identificados para a otimização foram a geometria do material de acumulação (número de placas e volume), propriedades do material de acumulação (massa específica e calor específico) e vazão do fluido de trabalho. Definiu-se a função a ser minimizada como o módulo da diferença entre a taxa de energia de saída do sistema de acumulação e a taxa de energia de saída alvo. Os resultados para duas geometrias e materiais distintos (aço AISI304 e granito), foram comparados com simulações efetuadas com o software comercial COMSOL, e os desvios encontrados ficaram na faixa de 10,16% a 8,88% para o aço e de 1,45% a 0,25% para o granito. A formulação proposta neste trabalho foi implementada no programa Engineering Equation Solver (EES), e otimizada com algoritmos genéticos. Observou-se que a massa específica e o calor específico são parâmetros que podem ser avaliados pelo seu produto (capacidade térmica volumétrica), quando a massa do material de acumulação não foi fixada. Para os casos nos quais a massa foi definida, o calor específico e a massa específica devem ser considerados parâmetros independentes, pois cada um atuou de forma diferente sobre o sistema. Observou-se que aumentando a quantidade de parâmetros de otimização, a diferença entre a taxa de energia na saída e a mesma taxa alvo diminuiu. Na simulação com dois parâmetros de otimização, a diferença relativa máxima entre estas taxas foi de 50%, enquanto que para quatro parâmetros de otimização, este valor caiu para 24%. / This work presents the optimization of sensible heat storage system, subjected to intermittent energy sources (solar). This type of storage system is defined by its storage material and the working fluid, which transports the energy. The methodology consists of using the global capacitance method to describe the dynamic behavior of the storage material, disposed in the form of parallel flat plates, while the working fluid was modeled via an energy balance. The storage material was divided into several smaller sections in order to satisfy the validity condition of the global capacitance model, resulting in Biot numbers smaller or equal than 0.1 for each section. The optimized parameters were the geometry of the storage material (number of plates and volume), the storage material properties (mass and specific heat) and flow rate of the working fluid. The minimized objective function is the difference between the output energy rate of the storage system and the target output energy rate. The results for two different geometries and materials (steel AISI304 and granite), were compared to simulations performed with the commercial software COMSOL, and the deviations were found in the range of 10.16% to 8.88% for steel and 1,45% to 0.25% for granite. The formulation proposed in this paper is implemented in the Engineering Equation Solver (EES), and optimized with genetic algorithm. It was observed that the density and specific heat are parameters that can be evaluated for its product (volumetric heat capacity) when the mass of the storage material was not defined. For the cases where the mass was defined, the specific heat and the density should be considered independent parameters, as each one act differently in the system. It was observed that increasing the number of optimized parameters, the difference between the output energy rate and the same target rate decreased. In the simulation with two optimized parameters, the maximum relative difference between these rates was 50%, while for four optimized parameters, this value dropped to 24%.

Submitted by Maria Medeiros (maria.dilva1@ufcg.edu.br) on 2018-08-30T13:43:17Z No. of bitstreams: 1 ANA PAULA NUNES DA SILVA - TESE (PPGMet) 2016.pdf: 25525790 bytes, checksum: 973f4462b19d6c6616cfec5845906a37 (MD5) / Made available in DSpace on 2018-08-30T13:43:17Z (GMT). No. of bitstreams: 1 ANA PAULA NUNES DA SILVA - TESE (PPGMet) 2016.pdf: 25525790 bytes, checksum: 973f4462b19d6c6616cfec5845906a37 (MD5) Previous issue date: 2016-05-06 / CNPq / O objetivo deste trabalho foi verificar a ocorrência de ilha de calor urbana (ICU) e sua influência no microclima na Região Metropolitana de Macapá (RMM), situada no Nordeste da Amazônia Legal, já que esta região vem apresentando um rápido processo de urbanização. Este processo de crescimento urbano provoca mudanças na cobertura e uso do solo, que podem modificar diretamente o balanço de energia em superfície gerando modificações na atmosfera que podem variar da escala local até a regional. Para verificar o crescimento urbano da RMM utilizou-se imagens do LANDSAT TM e OLI/TIRS de cinco diferentes épocas e através da classificação supervisionada MAXVER, verificou-se a expansão da classe área construída entre 1986 e 2015, classe que subentende a malha urbana. Uma análise climática com dados de precipitação e temperatura, permitiu verificar que possivelmente a variabilidade da temperatura e precipitação encontrada deve estar mais associado com eventos como El Niño do que com mudanças climáticas, entretanto, as tendências de aquecimento observadas podem estar relacionadas com o crescimento urbano. Para entender os impactos do crescimento urbano na modificação do microclima da RMM analisou-se índices de extremos climáticos de duas estações meteorológicas: uma situada no perímetro urbano e outra numa área rural da RMM. Verificou-se que as maiores mudanças térmicas ocorreram na área mais afastada da cidade, fato devido às mudanças de uso do solo na região periférica da RMM, enquanto que os índices relacionados a precipitação foram mais significativos na área urbana. Foram instalados termo-higrômetros em quatro pontos da RMM em áreas suburbanas e rurais para analisar os índices ICU, verificou-se que o índice sazonal de ICU foi maior (menor) nos meses de março a abril (outubro a dezembro), enquanto o índice horário obteve diferentes resultados de acordo com a época do ano: no mês chuvoso (seco) foi mais intenso no início da noite (do dia) com valor para a RMM atingiram valores máximos de 6°C (4,9°C). Na análise da Ilha de Calor Urbana em Superfície (ICUS) utilizaram-se cinco imagens de satélite e se verificou que em todas as imagens houve a comprovação de ICUS com núcleos nos centros da malhas urbanas das duas cidades da RMM e num distrito situado entre os dois centros urbanos analisados. Verificando os índices de conforto térmico gerados pela formação de ICU na RMM, comprovou-se que a região central da RMM apresenta os maiores valores e, que os índices de calor e de temperatura efetiva apresentaram boa relação com a percepção térmica da população de RMM, entrando o índice de conforto humano não se mostrou aplicabilidade na região em estudo. / The goal of the this Doctoral Thesis is to verify the occurrence of the Urban Heat Island (UHI) in the Macapá Metropolitan Area (RMM) Micro climate, which is placed in the Legal Amazon Northeast, due to the fact of the fast urbanization of the area. The development of the urban areas causes changes on the cover and use of the soil which could have a direct effect on the surface energy balance that may result in atmospheric modification in a local, or even regional,scale. In order to verify the RMM urban development, were used images from LANDSAT TM and OLI/TIRS of five different periods. Therefore, through the supervised classification MAXVER, it was possible to verify a expansion of the build-up area, the class of soil that covers the urban sheet, between 1986 and 2015. A climatic Analysis containing precipitation and temperature data showed that, probably, the variation of precipitation and temperature which appeared in the numbers presented are more likely to be associated with specific events, e.g. El Niño, than with the climatic changes. How ever, the growing heat trend observed during the research may be related to the urban development. In order to understand the impact of the development of the urban areas in the modification of the RMM micro climate, extreme climatic levels from two meteorologic bases were adopted: one of the those was placed within the urban perimeter; while the other was located in the RMM rural area. The data collected showed the biggest thermal changes took place further from the city, due to changes in the use of the soil in the isolated region of the RMM. About the levels related to precipitation, they were more significant in the urban areas. Term-hygrometers were installed in four different spots of the RMM, in suburban and rural areas, with the objective of analyzing the UHI levels. It was possible to verify that the season UHI levels were bigger (smaller) between March and April (October and December). The schedule levels showed different results along the year: during the rainy month (dry) it was more intense in the beginning of night (day) reaching maximum levels, in the RMM, of 6.0ºC (4.9ºC). For the analysis of the Urban Heat Island on Surface (SUHI) 5 satellite images were used and it was possible to verify in all of them the existence of ICUS with their cores located in the center of the urban sheets of the two cities that form the RMM and in a district placed between them. Trough the verification of the heat levels generated by the UHI formation in the RMM, it was possible to probe that the central area of the RMM presents the biggest values, and the IC and ITE levels are well connected to the RMM population's thermal perception. Considering the ICH it was evident the applicability of this Thesis in the area of the research.