The use of nebulization is becoming increasingly frequent in treatment of acute or chronic lung diseases for delivery of topically active drugs and is also an attractive way to deliver systemic drugs. A nebulizer can be defined by the aerodynamic properties of the emitted particles which are directly related to the lung deposition and the clinical response to a nebulized drug. New guidelines elaborated by an European norm (ENFR13544-1) aim to participate to a better control on quality and efficiency of existing devices and inspired the elaboration of the studies of this thesis. The aim of these works was to evaluate the nebulization function of a new kind of modality, the intrapulmonary percussive ventilation which contrarily to classical jet nebulizers nebulizes drugs under superimposed percussion conditions. In vitro measurements were realized by cascade impaction and laser diffraction. Lung deposition was investigated by imagery techniques and pharmacokinetic study. Aerodynamic properties were different between the in vitro methods. When measured by cascade impaction, MMAD and FPF were smaller for IPV comparatively to SST. By laser diffraction, FPF remained lower but MMAD was higher with IPV than with SST. The effect of percussions was greater on MMAD than on FPF. An irregular intrapulmonary deposition and a higher whole body deposition due to a higher extrapulmonary deposition with the IPV were measured by scintigraphy. The pharmacokinetic study highlighted that the drug output and the lung dose were lower when amikacin was delivered by IPV comparatively to SST. All results of these different studies seem unfavourable to the use of intrapulmonary percussive ventilation as modality of administration for nebulized drugs without further investigations. Results presented in this thesis concerning exclusively healthy subjects, we hope that they encouraged to perform complementary analysis and observations in different conditions such as patients with lung disease.

An imaging system was developed to visualize Drop-on-Demand (DOD) inkjet drop formation and impaction on substrate over drop sizes and impaction speeds of the magnitudes encountered in applications of inkjet printing. Using a pulsed laser, a low-speed charge-coupled-device (CCD) camera, and signal generators, the imaging system based on flash photography was used to capture sharp images with a temporal resolution of 200 ns and a spatial resolution of 0.81 micron/pixel. First, the dynamics of DOD drop formation was studied experimentally. The effects of the driving signal, which controls the piezoelectric transducer that produces the pressure pulse to drive the liquid from the reservoir through the orifice, have been examined along with those of liquid properties. The main stages of DOD drop formation, including ejection and stretching of liquid, pinch-off of liquid thread from the nozzle exit, contraction of liquid thread, breakup of liquid thread into primary drop and satellites, and recombination of primary drop and satellites, are analyzed. A necessary condition for the recombination of the primary drop and satellite and the limit for liquid thread length without breakup during contraction are proposed. Second, using the visualization system coupled with a motorized stage, micron-drop impaction on a smooth substrate was investigated over a regime of We and Oh typical for inkjet printing applications. The results indicate that scaling of micron-drop impaction from millimeter-drop impaction, based on dimensionless numbers (Oh, We and cos ), is valid. The predictions of maximum spreading ratio by six existing models agree well with experimental values for high-We impaction, but not for low-We and low-contact-angle impactions; however, the model of Park et al. predicts well for high- and low-We impaction due to its inclusion of spontaneous spreading dissipation. Fingering and splashing do not occur in the micron drop impaction on either dry solid substrates or a pre-existing liquid layer. The drying time of a micron drop deposited on a substrate is less than one second and increases as the contact angle of the drop on the substrate increases.

Present day water spray based dust removal technologies do not effectively remove respirable submicron coal and silica dust particles in the underground coal mines causing Coal worker’s pneumoconiosis (CWP). The objective of this research was to study the electrostatic charges present in the airborne coal dust in order to develop efficient water spraying based dust removal technology where water drops charged using ionic compounds and surfactants would be used to capture the oppositely charged coal particles. In an experimental scrubbing column, coal particles dispersed in an air stream by a Fluidized Bed Aerosol Generator were captured by water drops sprayed by an atomizer. Characterization studies performed using an Aerodynamic Particle Sizer and Aerosol Electrometer showed that airborne coal particles have a significant amount of positive charge with an average of 140 elementary units of charge. The capture efficiencies of the water drops evaluated were found to be higher than those predicted by previously determined mathematical models. It was predicted that apart from the effects of Brownian diffusion, interception and impaction, the effect of Coulombic attraction was present and the charge of the water drops was predicted to be between - 2 x 10-6 C and -2 x 10-4 C.

Orientador: Elizete Aparecida Lomazi da Costa Pinto / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Ciencias Medicas / Made available in DSpace on 2018-08-12T22:39:31Z (GMT). No. of bitstreams: 1 Fernandes_VanessaPaciniInaba_M.pdf: 849519 bytes, checksum: f4dae55b9aff4fa63a90c060178a1915 (MD5) Previous issue date: 2009 / Resumo: Distúrbios da motilidade do trato digestório podem estar envolvidos na fisiopatologia da constipação funcional. Retarde no esvaziamento gástrico tem sido observado em associação à constipação funcional e a relação de causa e efeito entre as condições não está definida. O objetivo desse estudo foi avaliar a motilidade gástrica antes da remoção da impactação fecal e após a regularização do hábito intestinal em crianças com constipação funcional. Casuística e métodos: Crianças (N= 22; 18 meninos, 10±2,2 anos) com constipação funcional e escape fecal retentivo, início da constipação aos 6,8±1,6 anos, acompanhadas no ambulatório de gastropediatria do Hospital das Clinicas da Universidade de Campinas. Estudo prospectivo, desenvolvido no período de 2000 a 2003. Os sintomas gastrintestinais foram registrados e estudos de esvaziamento gástrico foram conduzidos antes da remoção da impactação fecal (EG1) e após a regularização do hábito intestinal (EG2). O esvaziamento gástrico foi avaliado por método cintilográfico usando volumes individualizados de água. O T ½ do esvaziamento gástrico foi obtido para todos os pacientes nos dois momentos. Resultados: Vinte e um pacientes relataram sintomas gastrintestinais ao início do estudo, mais comumente dor abdominal após a ingestão de alimentos. A maioria dos pacientes relatou melhora desses sintomas com o tratamento da constipação. Não houve diferença significativa entre as médias de T ½ do esvaziamento gástrico nos tempos EG1 (32,8 ± 24,8 minutos) e EG2 (25,8 ±10,5 minutos), realizados com intervalo de 12 ± 5 semanas, p=0,09. Houve correlação positiva entre o tempo para recuperação da constipação e EG1(R=0,61, p=0,01) e EG2 (R=0,58, p=0,01). Conclusão: Pacientes pediátricos com constipação funcional crônica grave apresentaram tempo de esvaziamento gástrico prolongado ao início do tratamento e após a regularização do hábito intestinal. O tempo para recuperação da constipação correlacionou-se positivamente com os valores de esvaziamento gástrico. Palavras-chave: constipação funcional, impactação fecal, escape fecal retentivo, esvaziamento gástrico, cintilografia / Abstract: Gastrointestinal motility disorders may be at the basis of constipation. Gastric emptying delay has been reported in constipated patients and a causality relation is still not outlined. The objective of this study was to evaluate pre- and post-treatment gastric emptying values and dyspeptic symptoms in a group of children with functional constipation and fecal retention. Methods: Twenty-two children (eighteen boys, median age 10±2.2 years) with chronic constipation, fecal retention and soiling were seen in a tertiary pediatric gastroenterology clinic. Gastric emptying (GE) T1/2 was measured by scintigraphy before fecal impaction removal (GE1) and repeated (GE2) when patients recovered regular bowel movements (12±5 weeks after GE1). Patients were followed until complete relieve of constipation (11.6 ± 5.7 months). Gastric half-emptying time of a liquid meal (water) was measured using a radionuclide technique, reference value t ½ 12 ± 3 minutes. Results: Twenty-one children reported symptoms related to food ingestion, which were completely relieved after resuming regular bowel movements. Mean GE1 was 32.8 ± 24.8 minutes and mean GE2 was 25.8 ±10.5 minutes. There was no significant difference between GE1 and GE2 (p=0,09). There was significant correlation between mean time to resume regular bowel movements and gastric emptying values GE1 (R=0,61, p=0,01) and GE2 (R=0,58, p=0,01). Conclusion: The results of the present study indicate that slow gastric emptying is a common feature among children with chronic constipation and fecal impaction, and that this correlates with a slow response to therapy. Resuming of satisfactory bowel function did not result in normalization of gastric emptying studies. Key words: functional constipation, fecal retention, soiling, gastric emptying, scintigraphy / Mestrado / Pediatria / Mestre em Saude da Criança e do Adolescente

The occurrence of plastic impaction in ruminants is a growing concern. As indiscriminate feeders, cattle may consume plastic foreign materials incorporated into their diets and it is currently estimated that 20% of cattle contain plastic foreign materials in their rumen. These materials are indigestible and accumulate for the lifetime of the animal. As these materials accumulate, they may reduce feed efficiency and production by erosion and ulceration of rumen epithelium, stunting of papillae, blockage of the reticulo-omasal orifice, and leaching of toxic heavy metals. It is necessary to reduce the incidences of plastic impaction in domestic ruminants. Using polyhydroxyalkanoate (PHA) and poly(butylene succinate-co-adipate) (PBSA) biodegradable materials for feed storage products such as bale netting could reduce the incidences and effects of polyethylene-based plastic impaction in ruminants. The objectives of these studies were to evaluate the degradability of PHA and PBSA materials in the reticulorumen via in vitro, in situ, and in vivo methods. Our hypothesis was that these materials would degrade in the rumen and that a melt-blend of PHA and PBSA may degrade faster than its individual components. An in vitro study incubated a proprietary PHA-based polymer, PBSA, and PBSA:PHA melt blend nurdles, and forage controls in rumen fluid for up to 240h in DaisyII Incubators. Mass loss was measured, and digestion kinetic parameters were estimated. Thermogravimetric and differential scanning calorimetry analyses were conducted on incubated samples. Results indicated that the first stage of degradation occurs within 24h and PHA degrades slowly. Degradation kinetics demonstrated that polymer treatments were still in the exponential degradation phase at 240h with a maximum disappearance rate of 0.0031%/h, and mass loss was less than 2% for all polymers. Melting temperature increased and onset thermal degradation temperature decreased with incubation time, indicating structural changes to the polymers starting at 24h. Further in situ degradation, however, indicated these biodegradable materials degrade at more accelerated rates in the rumen. Polyhydroxyalkanote, PBSA, PBSA:PHA blend, and low-density polyethylene (LDPE) films were incubated in the rumens of three cannulated, non-lactating Holsteins for 0, 1, 14, 30, 60, 90, 120, and 150d. In situ disappearance (ISD) and residue length were assessed after every incubation time. Polyhydroxyalkanoate achieved 100% degradation by 30d, with initiation occurring at 14d indicated by ISD and a reduction in residue length. The fractional rate of disappearance of PHA was 7.84%/d. Poly(butylene succinate-co¬-adipate) and Blend did not achieve any significant ISD, yet fragmentation of PBSA occurred at 60d and the blend at just 1d likely due to abiotic hydrolysis. Low-density polyethylene achieved no ISD and residue length did not change over incubation time. From these results, we proposed a PBSA:PHA blend is a valid alternative to polyethylene single-use agricultural plastic products based on its fragmentation within 1d of incubation. Administration of PBSA:PHA film boluses compared to LDPE films and a control further supported this dissemination. Holstein bull calves (n = 12, 62 ± 9d, 74.9 ± 8.0kg) were randomly allocated to one of three daily bolus treatments: 13.6g of PBSA:PHA in 4 gelatin capsules (Blend), 13.6g of LDPE in 4 gelatin capsules (LDPE), or 4 empty gelatin capsules (Control) for 30d. Hemograms were conducted on blood samples collected on d0 and d30. On d31, animals were sacrificed to evaluate gross rumen measurements and pathology, determine papillae length, and characterize polymer residues present in rumen contents. Feed intake, body weight, body temperature, and general health were determined throughout the study. No animals presented any symptoms related to plastic impaction and animal health was not particularly affected by treatment. Daily grain and hay intake, body weight, rectal temperature, hematological parameters, gross rumen measurements and pathology, and rumen pH and temperature were not affected by treatment. There was evidence that degradation of PBSA:PHA may release byproducts that support rumen functionality. Methylene blue reduction time of Blend calves tended to be decreased by 30% compared to LDPE calves, and caudal ventral papillae length of Blend calves were 50% longer than those of Control animals. Though studies are needed to specifically elucidate the production of byproducts due to degradation of PBSA:PHA and their correlations. Polymer accumulation and residue length differed among treatments. Calves dosed with LDPE retained 6.7% of the dosed polymer, undegraded, while Blend calves retained 0.4% of the dosed polymer. The polymer residues in Blend calves were 10% of their original size. Single-use agricultural plastics developed from PBSA:PHA may be a suitable alternative to LDPE-based products in the case of ingestion in ruminants due to no acute health inflictions, fragmentation of polymers with 1d, and improved clearance from the reticulorumen. As such, utilization of these materials may reduce the incidences of plastic impaction in ruminants in commercial operations. Further long-term feeding studies are needed to evaluate specific byproduct production of PBSA:PHA and their potential influences on rumen function and animal health and production in normal commercial conditions. / Master of Science in Life Sciences / Plastic feed-storage materials may unintentionally be incorporated into animal feeds. Net wraps and bale twines may be stuck or left on forages when they are ground and incorporated into mixed rations. As cattle are largely non-selective, they may inadvertently consume these plastic materials. Approximately 20% of cattle contain plastic foreign materials in their rumen. These materials are indigestible and accumulate for the animal's lifetime. As plastics build up in the rumen, they may reduce feed efficiency, body weight, and milk production by damaging the rumen lining, blocking the digestive tract, and leaching toxic heavy metals. Therefore, it is necessary to reduce the incidences of plastic impaction in domestic ruminants to improve their health and productivity. Using biodegradable materials that degrade by bacteria, such as polyhydroxyalkanoate (PHA) and poly(butylene succinate-co-adipate) (PBSA), for feed storage products could reduce the occurrence and effects of plastic impaction in ruminants due to the materials' potential degradation in and passage from the rumen. The objectives of these studies were to evaluate the breakdown of PHA and PBSA materials in the rumen. Our hypothesis was that these biodegradable materials would degrade in the rumen and that a blend of PHA and PBSA may degrade faster than its individual components. In our first study, PHA, PBSA, a PBSA:PHA blend, and forage controls were incubated in rumen fluid for up to 240h. Mass loss, degradation rate, and the structure of polymers were determined over incubation time. Results indicated that biodegradable polymers may begin to break down within 24h. Polymer treatments were still in the early stages of degradation at 240h with a maximum degradation rate of 0.0031%/h, and mass loss of polymers was less than 2%. However, within 24h, the structures of polymers may have altered to promote future degradation at longer incubation times. Accelerated degradation was observed when PHA, PBSA, PBSA:PHA (Blend), and polyethylene (LDPE) films were incubated in the rumens of three Holstein cows up to 150d. Mass loss and the length of the remaining polymers were assessed monthly. Polyhydroxyalkanoate began to degrade by 14d and completely degraded by 30d with a disappearance rate of 7.84%/d. The remaining polymer did not achieve any mass loss. However, PBSA and Blend residue size began to decrease by 60d and 1d, respectively. Based on Blend's structural degradation within 1d of incubation that may promote its clearance from the rumen if ingested, we proposed that the material may be an alternative to polyethylene single-use agricultural plastic products. When Blend films were fed to calves, breakdown of the material further supported our dissemination that PBSA:PHA may be a suitable alternative to LDPE in the case of animal ingestion. Holstein bull calves (n = 12, 62 ± 9d, 74.9 ± 8.0kg) were randomly allotted to one of three daily bolus treatments: 13.6g of PBSA:PHA (Blend), 13.6g of polyethylene (LDPE), or no polymer (Control) distributed over 4 gelatin capsules for 30d. Feed intake, body weight, body temperature, and general health were determined throughout the study. Blood analyses were conducted on blood samples collected before and after the experimental period. On d31, animals were sacrificed to evaluate rumen growth and health, measure rumen papillae length, and describe polymers that may reside in the rumen. No animals presented any signs related to plastic impaction and animal health was not particularly affected by treatment. Daily grain and hay intake, body weight, rectal temperature, blood parameters, and rumen growth and health were not affected by treatment. There was evidence that degradation of Blend may support rumen function. Methylene blue reduction time of Blend calves tended to be decreased by 30% compared to LDPE calves, which indicates the rumen microbiome of Blend calves may better ferment feeds. Papillae length of Blend calves were also 50% longer than those of Control animals, which would improve the absorption of nutrients. Byproduct formation from Blend degradation could explain this; however, studies are needed to specifically elucidate the production of byproducts and their relationship to rumen function. Polymer accumulation and residue length differed among treatments. Calves dosed with LDPE retained 6.7% of the dosed polymer, undegraded, while Blend calves retained 0.4% of the dosed polymer. The polymer residues in Blend calves were 10% of their original size. Single-use agricultural plastics developed from PBSA:PHA may be a suitable alternative to polyethylene-based products in the case of ingestion in ruminants due to no short-term health inflictions, the reduced polymer size within 1d, and improved clearance from the rumen. As such, utilization of these materials may reduce the incidences of plastic impaction in ruminants in commercial operations. Further long-term feeding studies are needed to evaluate specific byproduct production of PBSA:PHA and their potential influences on rumen function and animal health and production in normal commercial conditions.

Made available in DSpace on 2015-03-26T13:46:54Z (GMT). No. of bitstreams: 1 texto completo.pdf: 691613 bytes, checksum: 53e3adaea617739a5125fb5bc7242691 (MD5) Previous issue date: 2005-08-10 / Large colon (LC) impaction is the most commonly diagnosed disease causing colic in horses, however the complete ethyopathogenesis of this condition is still unknown.Changes produced by diet in the properties of ingesta not yet investigated may also be important contributing factors to impaction formation and to other gastrointestinal diseases. The aim of this study was: 1- to create a tube viscometer able to measure the viscosity of horse ingesta, 2- to assess the effects of grain intake on hydration, gas content, particulate matter content, density, viscosity, and pH of ingesta, 3- to assess the potential for impaction formation with large colon contents in an ex vivo model, 4- to testify a modification on surgical technique for right dorsal colon fistulation. Using a cross-over design, 4 horses with experimental fistulas in the right dorsal colon were alternately fed two diets: 1- exclusively free choice grass hay or 2- pelleted feed rich in hydrolazable carbohydrates plus free choice grass hay. The ingesta were dried at 80°C to determine the water content. The gas content was estimated by the difference in volume after centrifuging the ingesta sample. The amount of particulate mater was determined by flushing a 1 Kg fresh sample of ingesta in a sequence of sieves with 100 L of water and weighing the dry matter of the material retained at the sieves. Ingesta density was calculated by the formula: density = sample weight / sample volume. After measuring the force to move 1 kg of fresh ingesta within a tube viscometer and the force to penetrate a probe into the ingesta in a texture analyzer, the sample was tested for impaction formation with a funnel attached to the viscometer end, in order to increase the resistance to flow. The water content of ingesta as well as density were significantly decreased; gas content and viscosity were increased and pH and particulate matter was not altered, when grain was fed. Despite diet, impaction did not form with any of the fresh ingesta samples. After adjusting ingesta viscosity, impaction was formed in eight repetitions when only hay was fed. Only one impaction could be produced when hay and grain were fed in eight repetitions, even after adjusting ingesta viscosity. Ingesta dehydration produced by grain intake may be explained as the result of reduced water consumption or an increase in the absorption of water following the absorption of larger amounts of volatile fatty acids. Formation of foamy ingesta and the increase in gas content of ingesta is explained by an increase in microbial production of gas and substances that stabilizes the froth. The decreased density may be explained by the increased amount of gas trapped within the ingesta. The increase in viscosity may be explained by the reduced water content of ingesta. It is possible that these changes may affect the likelihood of impaction formation. Although it has been demonstrated that grain ingestion has the potential to increase the risk of colic by several mechanisms, the findings of the present study suggest that grain ingestion may actually have a protective effect for large colon impaction. / A compactação do cólon maior é a principal causa de cólica em eqüinos. No entanto, sua etiopatogenia ainda não é completamente conhecida. Alterações produzidas pela dieta em algumas propriedades da ingesta que ainda não foram estudadas podem contribuir para a formação das compactações e outras doenças gastrointestinais. Os objetivos desse estudo foram: 1- construir um viscosímetro de tubo capaz de medir a resistência viscosa da ingesta de eqüinos, 2- verificar os efeitos da ingestão de concentrado rico em grãos na hidratação, conteúdo de gás, conteúdo de partículas, densidade, viscosidade, pH e textura da ingesta, 3- verificar o potencial para formação de compactação da ingesta do cólon maior em um modelo ex vivo , 4- testar uma modificação da técnica cirúrgica pra criação de uma fístula no cólon dorsal direito . Em um delineamento tipo cross-over , quatro cavalos com fístulas experimentais no cólon dorsal direito foram alimentados alternadamente com duas dietas: 1- exclusivamente feno de gramínea e 2- feno de gramínea mais ração comercial peletizada . A ingesta foi desidratada a 80o C para determinação da hidratação. O conteúdo de gás foi estimado pela diferença no volume das amostras após centrifugação. O conteúdo de partículas foi determinado através da lavagem com 100 litros de água de 1 kg de ingesta fresca sobre uma seqüência de peneiras e pesando-se a matéria seca do material retido nas peneiras. A densidade foi calculada pela fórmula: peso da ingesta / volume da ingesta. Após a mensuração da força para mover 1 kg de ingesta em um viscosímetro de tubo e da força de penetração de uma sonda na ingesta em um texturômetro, a amostra foi testada para a formação de compactação, acoplando-se um funil redutor ao viscosímetro para aumentar a resistência ao fluxo. A hidratação e a densidade foram diminuídas, o conteúdo de gás e a viscosidade aumentadas e não houve diferença no pH e no conteúdo de partículas, quando os animais ingeriram ração à base de grãos. Independentes da dieta, não foram observadas compactações quando a ingesta fresca foi testada. No entanto, após o ajuste da viscosidade, foram formadas compactações em oito repetições quando a dieta era exclusivamente feno. Por outro lado, somente uma compactação foi observada em oito repetições quando os animais ingeriram ração à base de grãos. A desidratação da ingesta pode ser explicada pela menor ingestão ou pela absorção aumentada de água juntamente com ácidos graxos voláteis quando os animais receberam ração à base de grãos. A formação de espuma e o aumento na produção de gás na ingesta podem ser explicados pela fermentação microbiana aumentada e produção de substâncias estabilizadoras da espuma. A densidade diminuída foi devido a grande quantidade de gás incorporada à ingesta. O aumento da viscosidade pode ser explicado pela menor hidratação da ingesta. É possível que essas alterações influenciem o potencial da ingesta em formar compactações. Embora tenha sido demonstrado que o fornecimento de ração à base de grãos aumente o risco de cólica por vários mecanismos, os achados do presente trabalho sugerem um efeito protetor desse tipo de dieta contra a formação de compactação do cólon maior.

Beetle-killed trees and woody residues degenerate and may lead to wildfires and uncontrolled CO2 emission. Woody biomass is known as a neutral CO2 solid fuel since it generates the same amount of CO2 that takes from atmosphere during its growing up. Cofiring woody biomass with coal in existing coal power plants is a reasonable solution to reduce the net amount of CO2 emission and decrease the risk of wildfires. However, there are some challenges ranging from providing and handling the woody biomass to the operation of cofiring woody biomass with coal. Co-milling of the fuels and ash deposition on the heat exchanger surfaces during cofiring are among the most critical challenges. A CFD model simulated the behavior of the pulverized particles and evaluate the impact of geometry and operational changes on mill performance. In addition, we measured the ash deposit rate derived from cofiring woody biomass with coal in a pilot combustor (1500 kW) and full-scale furnace. Moreover, we developed a model to predict ash deposit rate during combustion of coal and its blend with a variety of biomass. The post-processing analysis of CFD modelling of co-milling woody biomass with coal shows that the entrained large woody biomass particles exit the pulverizer along with the fine coal particles due to their lower density than that of coal particles. Some simple geometry and operational changes can optimize mill performance by reducing the number of large biomass particles in the product stream. Therefore, it makes the particle size distribution (PSD) of the product stream of co-milling more like that of coal. The collected data set of fly ash particles and ash deposit samples shows that the ash formation and deposit rates were not impacted significantly by cofiring woody biomass with coal. The concentration of alkali metals in the ash aerosol during cofiring was slightly higher than that of coal. Cofiring in pilot scale combustor made a tri-modal PSD of ash aerosol particles; however, the distribution was bimodal in the full-scale boiler. The ash deposit rates during cofiring in 1500 kW combustor were higher (30 to 70%) at locations closer to the burner at short operation times. Our developed model of ash deposit rate investigated two types of stickiness models of fly ash particles to the surface of heat exchanger: melt fraction stickiness model (MFSM) and kinetic energy stickiness model (KESM). The developed model suggested that the MFSM, which is based on the melt fraction of ash and our novel approach to condensation of alkali vapor species, was more accurate in predicting ash deposit rate of a variety of fuel combustion of a 100-kW combustor. The model calculated four mechanisms: inertial impaction, thermophoresis, condensation, and eddy impaction.

Coal plays a significant role in meeting the world's need for energy and will continue to do so for many years to come. Economic, environmental, and public opinion are requiring coal derived energy to be cleaner and operate in a more narrow window of operating conditions. Fouling and slagging of heat transfer surfaces continues to be a challenge for maintaining boiler availability and expanding the use of available fuels and operating conditions. The work incorporates existing information in the literature on ash deposition into a User-Defined Function (UDF) for a commercial comprehensive combustion and CFD code. Results from the new submodel and CFD code is are then compared to deposition measurements in on a simulated boiler tube where particle mass deposited and ash size distribution are measured. Several model components governing various aspects of ash deposition have been incorporated into the UDF which has been implemented in a quasi-unsteady Computation Fluid Dynamics (CFD) simulation. The UDF consists of models governing ash particle impaction and sticking, thermal and physical properties of ash deposits, unsteady growth of the ash deposits, and the effects of the insulating ash layers on the combustion processes. The ash layer is allowed to transition from an accumulation of individual particles, to a sintered layer, and finally to a molten or frozen slag layer. The model attempts to predict the deposit thickness, thermal conductivity, and emittance. Measurements showed fly ash particle sizes that were much smaller than predicted under a non-fragmentation assumption. Use of a fragmentation model matched mean particle diameters well but did not match the upper tail of the particle sizes where inertial impaction takes place. Assuming 100% capture efficiency for all particles provided reasonably good agreement with measured deposition rates. The observed trend of lower deposition rates under reducing conditions was captured when the gas viscosity was calculated using the probe temperature.

No description available.

Η διδακτορική διατριβή πραγματεύεται την πειραματική διερεύνηση της αλληλεπίδρασης δέσμης εκροής νέφους σταγονιδίων νερού με το θερμικά στρωματοποιημένο,τυρβώδες ρευστο-θερμικό πεδίο που αναπτύσσεται πάνω από οριζόντια θερμαινόμενη επίπεδη επιφάνεια. Τα φαινόμενα και οι φυσικοί μηχανισμοί που διέπουν την ως άνω αλληλεπίδραση πέρα από τη σημασία τους σε σχέση με τη βασική έρευνα στο πεδίο των ρευστοθερμικών φαινομένων, παρουσιάζουν ενδιαφέρον σε πληθώρα πρακτικών προβλημάτων όπως κατά τον ψεκασμό καυσίμου σε κινητήρες εσωτερικής καύσης και καυστήρες, στη διφασική ψύξη ηλεκτρονικών, στην μετεωρολογία, στην πυρόσβεση, σε διεργασίες απόθεσης και επικάλυψης κ.α. Το ρευστο-θερμικό πεδίο αναπτύσσεται πάνω από οριζόντια θερμαινόμενη επιφάνεια μεταλλικής πλάκας μέσα σε ορθογωνική κοιλότητα με ανοικτή οροφή. Το νέφος σταγονιδίων δημιουργείται σε έναν νεφελοποιητή και εκτοξεύεται μέσα από ένα ακροφύσιο κυλινδρικού σωλήνα εσωτερικής διαμέτρου 4mm, κάθετα προς την οριζόντια επίπεδη επιφάνεια και σε σημαντική απόσταση από αυτήν (50cm), δημιουργώντας αρχικά μια διφασική δέσμη εκροής σταγονιδίων. Για την δημιουργία βάσης δεδομένων αναφοράς, σημαντικό μέρος της εργασίας αναφέρεται στην καταγραφή και μελέτη του θερμικού πεδίου ελεύθερης συναγωγής που δημιουργείται πάνω από τη θερμαινόμενη πλάκα χωρίς την παρουσία σταγονιδίων. Αντίστοιχα μελετήθηκε η ανάπτυξη της δέσμης εκροής σταγονιδίων σε ισοθερμοκρασιακές συνθήκες. Η παραμετρική μελέτη της αλληλεπίδρασης δέσμης εκροής σταγονιδίων και θερμικά στρωματοποιημένου πεδίου πραγματοποιήθηκε για δέσμες σε δύο αριθμούς Reynolds και για δύο ρυθμούς ροής θερμότητας από την πλάκα. Οι αριθμοί Reynolds που επιβάλλονται στη ροή δέσμης του νέφους (mistjet) είναι σχετικά χαμηλοί έτσι ώστε να ισχυροποιηθεί σχετικά η επίδραση του τοιχώματος και κυρίως οι ροϊκές δομές που δημιουργούνται λόγω των ανωστικών δυνάμεων κοντά στη θερμαινόμενη επιφάνεια. Η σύνθετη ροή που παράγεται λόγω της σημαντικής απόστασης μεταξύ του ακροφυσίου και της επίπεδης επιφάνειας - στόχου κατατάσσεται στην κατηγορία των δεσμών εκροής ασθενούς πρόσκρουσης. Οι παράμετροι που εξετάζονται περιλαμβάνουν μέσα και τυρβώδη χαρακτηριστικά τόσο των σταγόνων (μέγεθος και ταχύτητα), όσο και της θερμοκρασιακής κατανομής πάνω από την θερμαινόμενη πλάκα. Το θερμικό πεδίο σε συνθήκες ελεύθερης μεταφοράς και υπό την επίδραση της ροής των σταγονιδίων καταγράφτηκε με τη βοήθεια θερμοζεύγους πολύ μικρών διαστάσεων ώστε να αλλοιώνει όσο το δυνατόν λιγότερο τη ροή. Οι διαστάσεις του αισθητηρίου είναι σημαντικά μικρότερες της κλίμακας μήκους Kolmogorov και επομένως το αισθητήριο κρίθηκε ικανό για την ανάλυση όλων των σχετικών κλιμάκων της ροής. Το πεδίο νέφους σταγονιδίων μελετήθηκε με την τεχνική Ανεμομετρίας Φάσης Doppler (PhaseDopplerAnemometry - PDA) η οποία επιτρέπει την μέτρηση τόσο της ταχύτητας όσο και του μεγέθους των σταγονιδίων παρέχοντας τη δυνατότητα συσχέτισης των δύο μεγεθών για τον ενδελεχή χαρακτηρισμό της συμπεριφοράς των σταγονιδίων. Η τεχνική αυτή είναι μια από τις λίγες μη παρεμβατικές μεθόδους σημειακών μετρήσεων σε διφασικά ροϊκά πεδία η οποία δίνει πληροφορία για τη συγκέντρωση και την παροχή, με την τελευταία να αποτελεί σημαντικό εργαλείο στον υπολογισμό της εξάτμισης. Τα αποτελέσματα των μετρήσεων κατά την αλληλεπίδραση των πεδίων (θερμικού και σταγονιδίων) μελετώνται και συγκρίνονται με τις συνθήκες αναφοράς της στρωματοποιημένης ροής του θερμοκρασιακού πεδίου και της ισόθερμης ροής του πεδίου ταχυτήτων δίνοντας πληροφορία για την επίδραση του νέφους σταγονιδίων στους μηχανισμούς τυρβώδους μεταφοράς. Αναγνωρίστηκε ως κυρίαρχη δομή του πεδίου συναγωγής το κινούμενο πλούμιο συχνά μορφής μανιταριού. Η μορφή των κατανομών πυκνότητας πιθανότητας (PDF) ερμηνεύθηκε σε σχέση με το ιστορικό δημιουργίας και ανταλαγών θερμότητας των επί μέρους αερίων μαζών που διέρχοτναι από τη θέση μέτρησης. Στις κατανομές φασματικής ισχύος (PSD) του σήματος της θερμοκρασίας αναγνωρίσθηκε ιδιοσυχνότηταπου υποδεικνύει την παρουσία δομής μεγάλης κλίμακας. Αναφορικά με το πεδίο σταγονιδίων παρατηρήθηκε ότι η παρουσία της επιφάνειας – στόχου επιβραδύνει τις δέσμες πρόσπτωσης ελαττώνοντας και τις διακυμάνσεις στην περιοχή του τοιχώματος. Η θέρμανση επηρεάζει τις μέσες και κυμαινόμενες ταχύτητες σε σημαντική απόσταση από την οριζόντια πλάκα, ενώ το μέγεθος των σταγονιδίων μειώνεται κατάντη της ροής με διαφορετικές τάσεις ως προς τον Re. Αυξημένες τιμές της μέσης διαμέτρου Sauter (D32) παρατηρούνται κοντά στην επιφάνεια ειδικά για την περίπτωση ισόθερμου ψεκασμού του υψηλότερου Re. Η θέρμανση της επιφάνειας έχει σημαντική επίπτωση στον περιορισμό της αυξητικής τάσης της παροχής αέρα λόγω συμπαράσυρσης, που είναι πιο εμφανής στις περιπτώσεις χαμηλού Re. / The interaction of a water mist jet with the thermally stratified turbulent field developing over a horizontal heated flat plate, in an open top cavity, is investigated experimentally. The physical phenomena dominating this interaction, besides their importance for theoretical thermo-fluids, influence a wide spectrum of applications including fuel injection in internal combustion engines and burners, electronics cooling, meteorology, fire extinguishing, deposition and coating processes etc. Water mist, generated in a nebulizer, is sprayed through a cylindrical orifice of internal diameter 4mm, vertically, towards the horizontal surface and at considerable distance from it (50cm). In order to establish a reference case data base, a significant part of the work refers to data collection and study on the thermal convection field characteristics, in the absence of the spray mist, as well as on the isothermal mist jet development. The interaction field has been investigated for mist jets of two Reynolds numbers and at two flat plate heating rates. The mist jet Reynolds numbers were rather low in order to enhance the influence of the plate and the flow structures generated due to buoyancy. Mean and turbulent characteristics of the spray (velocity and size) and the temperature distribution were monitored. A small thermocouple, significantly smaller than the Kolmogorov length scale, was used for temperature measurements. Droplet velocities and sizes were measured with Phase Doppler Anemometry, which also provided concentration and flux measurements. Moving plumes, often in the form of mushrooms, were identified as the dominant structures in the convection field. The form of temperature probability density functions was related to the past history of formation and heat exchange of air masses crossing the measuring point. An eigenfrequency, identified in the temperature power spectra indicates the presence of a large scale structure. The presence of the target plate decelerates the mist jets reducing also turbulent fluctuations close to the surface. Heating influences the mean and fluctuating velocities at considerable distance from the plate, reducing the rate of jet mass flux growth due to entrainment, more evidently for the low Re jet. Droplet sizes decrease downstream, presenting different trends in relation to Re. Increased values of the Sauter mean diameter (D32) are observed very close to the plate surface, particularly for the high Re number, isothermal jet.