Title: Frequency analysis of precipitation amounts Author: Mgr. Zuzana Rulfová Department: Department of Atmospheric Physics Supervisor: RNDr. Jan Kyselý, Ph.D., Institute of Atmospheric Physics CAS Abstract: This thesis deals with analysing characteristics of mean and extreme precipitation in observations and regional climate models (RCMs) with respect to their convective and stratiform origin. An algorithm for subdivision of precipitation amounts into predominantly convective and stratiform using station weather data is proposed and evaluated. The time series of convective and stratiform precipitation from the Czech Republic over 1982-2010 are used for analysing basic climatological characteristics of precipitation, including extremes, and evaluating RCMs from the ENSEMBLES project. Projected changes of convective and stratiform precipitation in Central Europe (the Czech Republic) are analysed using data from RCM simulations from the EURO-CORDEX project. The last part of the thesis introduces a new statistical model for analysing precipitation extremes. This model takes advantage from knowledge of origin of precipitation extremes. In future climate we could expect more convective and stratiform precipitation amounts in all seasons except summer, when climate models project decline in amounts of stratiform...

The significant increase in energy requirements across the world, provides several opportunities for innovative methods to be developed to facilitate the storage and utilization of energy. The major energy demand is in the form of electrical energy for domestic as well as industrial sectors, a large part of which are the heating and cooling requirements. Appropriate utilization of thermal energy storage can effectively aid in reducing the electrical demand by storage and release of this thermal energy during peak hours. Thermal Energy Storage using Phase Change Materials (PCMs) is an attractive method of energy storage, with a wide variety of potential applications. Several configurations have been tested by researchers to develop energy storage devices with PCMs. The cycling of melting and solidification of PCMs results in storage and release of heat at a relatively small temperature difference. Design and deployment of these storage systems have certain challenges and considerations associated to them for instance, when used in buildings, PCMs should be non-toxic, non-corrosive, and others. In this thesis, we aim to provide models for designing Latent Thermal Energy Storage (LTES) devices with PCMs, based on their operating conditions, thermophysical properties of materials, and geometric parameters. The models are developed considering fluid dynamics and heat transfer involved in melting and solidification of PCMs. Parameters like inlet temperature and velocity, and volume of storage container are varied to determine the time taken for melting or solidification. For sizing and predicting performance of the storage devices we aim at presenting an analytical correlation, with time taken for melting as the variable defining the ‘charging/discharging time’ of storage device. Along with this, a transient model is developed to predict amount of PCM melted/solidified, along with rate of latent energy storage in defined time period intervals.

High interstitial fluid pressure (IFP) in tumours is recognized as a barrier to drug delivery resulting in reduced efficacy. High IFP impedes the normal process of convective fluid flow (CFF) from blood vessels into the interstitium. The aim of this study was to develop an in vitro model that could be used to measure CFF and to study its effects on drug delivery. The model consists of a transwell cell culture insert which supports the growth of multicell layers (MCL) on collagen coated membranes. A graduated tube is inserted into the transwell and a pressure gradient is applied across the membrane by raising the volume of medium in the tube above that of the bottom chamber. CFF is determined by measuring the weight of medium in the bottom chamber as a function of time. CFF was inversely proportional to MCL thickness and 41.1±3.6µm thick MCL has completely stopped CFF. Using a physiologically relevant hydrostatic pressure of 28mmHg, a CFF of 21µL/min was recorded using a DLD-1 MCL that was 12.21±3.2µm thick. Under these conditions, the rates of penetration of doxorubicin, imatinib and gefitinib were respectively 42, 26 and 13 folds greater than when no CFF exists. Reversing the CFF so that it opposed the drug diffusion gradient significantly impairs drug penetration. In conclusion, a novel in vitro model for assessing the impact of CFF on drug delivery has been developed. This model could be used to evaluate strategies designed to increase drug delivery to solid tumours by modifying the CFF.

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Yes / The Molecular Stress Function (MSF) constitutive model with convective constraint release mechanism has been shown to accurately fit a large range of viscometric data, and also shown to give strong vortex growth in flows of LDPE through planar and axisymmetric contractions. This work compares simulation and experimental results for 3-D flows of Lupolen 1840H LDPE through a contraction slit; 3-D effects are introduced by using a slit with a low upstream aspect ratio of 5:3. Comparisons are made with vortex opening angles obtained from streak photography, and also with stress birefringence measurements. The comparisons are made with two versions of the convective constraint release (CCR) mechanism. The simulated vortex angles for one version of the CCR mechanism are found to approach what is seen experimentally. The best-fit value for the stress optical coefficient was found to vary between CCRs and to decrease with flow rate. This is partially explained by different centreline elongational rates with the two CCRs, which in turn is related to different opening angles. A 3-D simulation is compared to the corresponding 2-D simulation. It is shown that both velocity vectors and birefringence show only small changes to around 60% of the distance to the side wall.

The different technologies of passive cooling concepts have to rely on a good thermal coupling between a building's thermal mass and indoor air. In many cases, the ceiling is the only surface remaining for a good coupling. Further research is necessary to investigate discrepancies between existing correlations. Therefore, the overall aim of the work described in this thesis is the investigation of heat transfer at a heated ceiling in an experimental chamber. Acoustic baffles obstruct the surface of the ceiling and impede heat transfer. However, there is nearly no published data about the effect of such baffles on heat transfer. Available results from simulations should be verified with an experimental investigation. Consequently, one of the primary aims of this work was to experimentally determine the influence of such acoustic baffles. A suitable experimental chamber has been built at Biberach University of Applied Sciences. The thesis describes the experimental chamber, the experimental programme as well as results from five different test series. With a value of ±0.1Wm⁻²K⁻¹ for larger temperature differences, uncertainty in resulting convective heat transfer coefficients for natural convection is comparable to that of results from an existing recent experimental work often recommended for use. Additionally, total heat transfer (by convection and radiation) results are presented. Results are given for natural, forced and mixed convection conditions at an unobstructed heated ceiling. Furthermore, results for acoustic baffles in both an unventilated and a ventilated chamber are shown. Natural convection results show a very good agreement with existing correlations. Under mixed convection conditions, convective heat transfer at an unobstructed ceiling decreases to the limiting case described by natural convection. Installation of acoustic baffles leads to a reduction in total heat transfer (convection and radiation) between 20% and 30% when compared to the case of an unobstructed ceiling.

Dans un contexte de réchauffement climatique, la région d'Afrique de l'Ouest, où les sécherresses sont dévastatrices pour les populations, montre les plus fortes incertitudes sur l'évolution des précipitations. C'est aussi la première source de poussières désertiques au monde dont la production est en augmentation par la sur-exploitation des sols. Or ces poussières désertiques, associées à des épidémies de méningite, absorbent et diffusent le flux solaire entraînant alors une modification du taux d'échauffement atmosphérique. En modifiant le bilan radiatif atmosphérique elles sont alors succeptible d'influencer de la turbulence de fine échelle aux circulations atmosphériques de grande échelle. Seulement les processus en jeu dans les interactions entre les poussières désertiques et l'atmosphère sont très variés, complexes, et constituent une grande source d'incertitude dans la prévision numérique. Afin d'appréhender ces processus, un cadre de modélisation à été développé permettant à la fois la résolution explicite de la convection, la résolution du cycle de vie des poussières et de leur impact radiatif, et la prise en compte de leurs interactions sur toute l'Afrique de l'Ouest à échelle mensuelle. Sur un cas extrême de tempête de poussières en saison sèche, la forte quantité de poussières soulevée par le front entraîne une amplification par eux de la signature de la tempête. La modélisation explicite des poussières améliore la prévisibilité de la tempête. De manière plus statistique, pendant la mise en place de la mousson, en juin, la fréquente présence de poussières participe activement à l'initiation du saut de mousson. D'une part, en affaiblissant la dépression thermique Saharienne, un des principaux moteurs de la mousson, mais aussi, d'autre part, en renforçant le déplacement vers le nord du coeur de la zone de convergence inter-tropicale et des jets. A plus fine échelle, la présence de poussières impacte la localisation et le cycle diurne des systèmes convectifs. Les poussières modifient alors la couverture nuageuse dont les impacts radiatifs sont plus forts que l'effet direct des poussières. La prise en compte des effets semi-directs des poussières sont donc essentiels pour la prévision en Afrique de l'Ouest.

Doctor of Philosophy / Department of Mechanical and Nuclear Engineering / Steven J. Eckels / The current research presents the experimental investigation of the effect of tube pitch on enhanced tube bundles’ performance. The typical application of this research is flooded refrigerant evaporators. Boosting evaporator’s performance through optimizing tube spacing reduces cost and energy consumption. R-134a with the enhanced tube Turbo BII-HP and R-123 with Turbo BII-LP were used in this study. Three tube pitches were tested P/D 1.167, P/D 1.33, and P/D 1.5. Each tube bundle includes 20 tubes (19.05 mm outer diameter and 1 m long each) constructed in four passes. The test facility’s design allows controlling three variables, heat flux, mass flux, and inlet quality. The type of analysis used is local to one location in the bundle. This was accomplished by measuring the water temperature drop in the four passes. The water-side pressure drop is included in the data analysis. A new method called the EBHT (Enthalpy Based Heat Transfer) was introduced, which uses the water-side pressure drop in performing the heat transfer analysis. The input variables ranges are: 15-55 kg/m².s for mass flux, 5-60 kW/m² for heat flux, and 10-70% for inlet quality. The effect of local heat flux, local quality, and mass flux on the local heat transfer coefficient was investigated. The comparison between the bundle performance and single tube performance was included in the results of each tube bundle. The smallest tube pitch has the lowest performance in both refrigerants, with a significantly lower performance in the case of R-134a. However, the two bigger tube pitches have very similar performance at low heat flux. Moreover, the largest tube pitch performance approaches that of the single tube at medium and high heat fluxes. For the R-123 study, the smallest tube bundle experienced quick decease in performance at high qualities, exhibiting tube enhancement dry-out at certain flow rates and high qualities. The flow pattern effect was demonstrated by the dry-out phenomena. At medium and high heat fluxes, as the tube pitch increases, the performance approaches that of the single tube. All tube bundles experience quick decrease in performance at high qualities. Evidently, P/D 1.33 is the optimum tube pitch for the studied refrigerants and enhanced tubes combinations.

L’objectif de ce travail est l’étude du comportement des matériaux minéraux de grande diffusion lors du séchage convectif : étude expérimentale et modélisation. Une première étape a été consacrée à la caractérisation (physico-chimique et comportement en température) des matières premières de deux composés argileux tunisiens (AX et AR), d’un mélange argileux par porcelaine (BC) et de deux composés innovants commercialisés par la société BIBLIONTEK : un mélange argileux (MG) et un composite argilo-cellulosique (CA). La mesure des propriétés d’équilibre thermodynamique, des propriétés de transfert et des propriétés mécaniques a été effectuée, dans un second temps, afin de comprendre le comportement hydro-thermo-mécanique de ces matériaux. Les cinétiques de séchage expérimentales ont été ensuite établies pour le mélange argileux (MG) et le composite argilo-cellulosique (CA) sous forme de monocouche d’échantillons ou en échantillon individuel, à différentes températures sèches, humidités relatives et vitesses de l’air. Ces cinétiques ont servi à valider les deux modèles développés. Le premier modèle hydro-thermo-mécanique 2D d’un produit déformable saturé d’eau lors du séchage convectif a été appliqué à un échantillon du mélange argileux (MG). Partant de la validation de ce modèle, les distributions spatio-temporelles de la teneur en eau, de la température et de la contrainte mécanique ont été simulées et interprétées en termes d’endommagement potentiel du produit. Un deuxième modèle hydro-thermique spécifique à un produit capillaro-poreux non saturé et hygroscopique a été aussi établi. Le modèle est appliqué au composite argilo-cellulosique. L’endommagement mécanique du produit, qui est conditionné par la surpression interne de la phase gazeuse, a été évalué en cours du procédé. Les résultats de ces travaux de recherche pourront être exploités à moyen termes dans l’industrie, afin de réduire le coût énergétique du séchage et de contrôler la qualité du produit fini. / The aim of this work is to study behavior of low cost mineral materials during convective drying: experiment and theoretical modeling. A first part is devoted to the physical and chemical characterization of materials. These are two Tunisian clays (AX and AR), a porcelain clay mixture (BC) and two clay mixtures (MG and CA) commercialized by the company BIBLIONTEK, one of which is a composite of clay and cellulose fibers (CA). Measurements of thermodynamic equilibrium, transfer proprieties and the mechanical proprieties were then made in order to understand the continued hydric, thermal and mechanical behavior of the materials. Experimental characterization of the drying kinetics for the MG and CA clay mixtures (MG and CA) was made on single layer samples or individual samples at different dry temperatures, relative humidities and air speeds. These kinetics were used to validate two theoretical models. The first is two dimensions of a deformable material saturated in water during convective drying was applied to the case of MG clay mixture. The spatial distributions of water content in the material, temperature and mechanical stress were simulated as a function of time and interpreted in terms of possible damage to the material. A second model, specific to a hygroscopic material contuning non saturated capillary pore, was also established. The model was applied to the clay-cellulose fibers composite material (CA). The mechanical damage to the material, conditioned by internal pressure due to the gas phase, was evaluated during the drying process. The conclusions of this research can be exploited in on industrial context in order to reduce energy costs of drying and improve final product quality.

Os sistemas convectivos da região Amazônica possuem características microfísicas peculiares, que variam de um caráter convectivo marítimo (estação chuvosa) a continental (estação de transição seca-chuvosa). Essas características modulam a eletrificação desses sistemas, porém ainda não se sabe quais são os processos dominantes que intensificam o número de descargas elétricas de uma estação para outra: efeito dos aerossóis, termodinâmico, grande-escala ou topografia? Para responder à essa pergunta, o objetivo deste trabalho foi identificar e quantificar a importância de cada um desses efeitos na eletrificação dos sistemas convectivos da Amazônia. A metodologia foi baseada em análises de dados observacionais do experimento de campo DRYTOWET e em um modelo numérico com parametrizações de transferências de cargas e descargas elétricas. A análise do ciclo anual das descargas elétricas do tipo nuvem-solo (CGs) mostrou que a atividade elétrica dos sistemas precipitantes da região sudoeste da Amazônia aumenta durante a transição da estação seca para a estação chuvosa (Agosto a Setembro), associada aos sistemas convectivos com maior desenvolvimento vertical que acontecem nesse período. Com o estabelecimento da estação chuvosa (Novembro a Março), o número de CGs diminui porém a atividade elétrica ainda se mantêm. A porcentagem desses totais de CGs que tinham polaridade positiva (+CGs) tem média de 12% durante todo o ano, aumentando drasticamente para até 25% em Setembro, durante a transição entre as estações secas e chuvosa. Esse aumento da %+CGs ocorreu simultaneamente ao aumento da poluição atmosférica provocada pela queima de biomassa das pastagens realizada pelos fazendeiros locais, que as preparam para a agricultura e pecuária durante o início das primeiras chuvas. Por outro lado, o aumento da %+CGs das tempestades também ocorreu preferencialmente sobre a área de pastagem do estado de Rondônia. Através da análise de dados de radar dos sistemas precipitantes que ocorreram durante o experimento DRYTOWET, foi constatado que as tempestades positivas (tempestades que produzem mais de 50% de +CGs em 50% de seu tempo de vida) se formaram em ambientes mais secos e com alturas do nível de convecção por levantamento (NCL, altura da base da nuvem) maiores do que as demais tempestades (tempestades negativas), durante todo o experimento mas com maiores diferenças durante o final da estação seca (Setembro-Outubro). Com altura da base da nuvem mais elevada, a espessura da camada quente (ECQ - base da nuvem até a isoterma de 0oC) diminui, aumentando assim a velocidade das correntes ascendentes através de um melhor processamento da energia potencial disponível para convecção (CAPE) devido a um menor entranhamento. O aumento da velocidade das correntes ascendentes dentro da nuvem resulta em tempestades mais profundas e mais intensas. O efeito do aumento do NCL é uma característica das regiões com vegetação de pastagem, onde a razão entre o calor sensível e latente na superfície é maior do que as áreas florestadas, aumentando a altura da camada limite planetária. As diferenças de concentração total e distribuição de tamanho dos aerossóis devido ao aumento da poluição durante a transição entre as estações seca e chuvosa não foram conclusivas quanto a um possível efeito na distribuição de hidrometeoros das tempestade positivas e negativas, uma vez que o ciclo diurno da concentração dos aerossóis acompanha o ciclo diurno da camada limite planetária, que também regula o efeito da ECQ. Simulações numéricas com um modelo 1D de nuvem, acoplado à parametrizações de transferências de cargas elétricas entre hidrometeoros e raios, mostraram que a estrutura termodinâmica da atmosfera foi a maior responsável pela eletrificação das tempestades simuladas, aumentando a velocidade das correntes ascendentes. O efeito do aumento do número de aerossóis, que inibe da fase quente da nuvem e conseqüentemente fortalece a da fase fria da nuvem fornecendo mais vapor e gotículas de nuvem para essa região, provocou a diminuição da quantidade de granizo nas tempestades simuladas e o aumento de partículas agregadas menores, como os flocos de neve e graupel, diminuindo a freqüência de raios. / Amazonian convective systems have unique microphysical characteristics, varying from a maritime convective behavior (rainy season) to a continental behavior (wet-dry transition season). These characteristics modulate the electrification of these systems, however it is still not well understood which are the dominant processes that intensify the frequency of lightning from one season to another: aerosol effect, thermodynamics, large-scale variability, landscape or topography? To answer this question, the objective of this study was to identify and quantify the importance of each one of these effects on the electrification of convective systems over the Amazon. The methodology was based on the analysis of observational data from the field experiment DRYTOWET and a numerical model with charge transfer parameterizations and lightning discharges. The cloud-to-ground (CG) lightning discharges annual cycle presented that the electrical activity of the southwestern Amazonian precipitating systems increased during the transition between the dry and wet seasons (August to September), in association with the convective systems deepening. With the establishment of the wet season (November to March), the number of CGs decreased but the electrical activity continued. The mean annual percentage of cloud-to-ground lightning of positive polarity (+CGs) was 12%, increasing drastically to 25% in September during the transition between the dry and wet seasons. This percentage of +CGs raise happened simultaneously with the increase in the atmospheric pollution due to the pasture biomass burning, held by local farmers to prepare the soil for agriculture and livestock during the begging of first rains. On the other hand, the increase in %+CGs also occurred preferentially over pasture areas of Rondonia state. Through the analysis of radar precipitating systems that occurred during the field campaign DRYTOWET, it was noted that positive thunderstorms (storms that produced more than 50% of +CGs over 50% of their life time) were initiated in drier and higher lift condensation levels (cloud base height) environments than other storms (negative thunderstorms) during all the field experiment, especially in the end of the dry season (September-October). A higher cloud base height is associated with a shallower warm cloud depth (cloud base height to the 0oC isotherm) and consequently less entrainment, increasing the updrafts due to a more efficient processing of the convective available potential energy (CAPE). This increase in updrafts inside the clouds results in deeper and stronger thunderstorms. The higher cloud base heights is a characteristic from pasture regions, where the ratio between sensible and latent heats at surface is greater than forested areas, which increases the top of the planetary boundary layer. The differences in the aerosol total concentration and size distribution, due to the increase in the atmospheric pollution during the transition between the dry and wet seasons, were inconclusive in a possible aerosol effect in the strength of positive and negative thunderstorms, once the aerosol concentration diurnal cycle follows the cycle of the planetary boundary layer, that also regulates the warm cloud depth effect. Numerical simulation of an 1D cloud model, coupled with charge transfer between the hydrometeors, showed that the thermodynamic structure was the main responsible feature for cloud electrification, increasing the updraft velocities. The pollution effect was masked in simulations, which inhibit the warm precipitation and consequently strength the the mixed and cold regions of the cloud, was responsible for an increase in the number of smaller aggregated particles, like snow flakes and graupel, decreasing the electrification and lightning frequency.