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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Numerical modeling of two-phase flashing propellant flow inside the twin-orifice system of pressurized metered dose inhalers

Shaik, Abdul Qaiyum January 2010 (has links)
Pressurized metered-dose inhalers (pMDIs) are the most widely-prescribed inhaler devices for therapeutic aerosol delivery in the treatment of lung diseases. In spite of its undoubted therapeutic and commercial success, the propellant flow mechanics and aerosol formation by the pMDIs is poorly understood. The process involves a complex transient cavitating turbulent fluid that flashes into rapidly evaporating droplets, but details remain elusive, partly due to the difficulty of performing experiments at the small length scales and short time scales. The objective of the current work is the development of a numerical model to predict the internal flow conditions (pressure, temperature, velocity, void fraction, quality, etc.) and provide deeper insight into the atomization process and fluid mechanics involved in the twin-orifice of pMDIs. The main focus is propellant metastability, which has been identified by several past authors as a key element that is missing in accounts of pMDI performance. First the flashing propellant flow through single orifice systems (both long and short capillary tubes) was investigated using three different models : homogeneous equilibrium model (HEM), delayed equilibrium model (DEM) and improved delayed equilibrium model (IDEM). Both, the pure propellants and the propellant mixtures were used as working fluid. The numerical results were compared with the experimental data. For long capillary tubes the three models gave reasonable predictions, but the present results showed that DEM predicts the mass flow rate well for pure propellants and IDEM predicts the mass flow rate well for propellant mixtures. For short capillary tubes, the present results showed that DEM predicts the mass flow rate and pressure distribution along the short tube better compared to HEM and IDEM. The geometry of the twin-orifice system of a pMDI is complex and involves several singularities (sudden enlargements and sudden contractions). Various assumptions were made to evaluate their effect on the vaporisation process and to evaluate the flow variables after the shock at the exit of the spray orifice when the flow is choked. Also, three different propellant flow regimes were explored at the inlet of the valve orifice. A specific combination of assumptions, which offers good agreement with the experimental data was selected for further computations. Numerical investigations were carried out using delayed equilibrium model (DEM) with these new assumptions to validate the two-phase metastable flow through twin-orifice systems with continuous flows of various propellants studied previously by Fletcher (1975) and Clark (1991). A new correlation was developed for the coefficient in the relaxation equation. Along with this correlation a constant coefficient was used in the relaxation equation to model the metastability. Both the coefficients showed good agreement against the Fletcher's experimental data. The comparison with the Clark s experimental data showed that the new correlation coefficient predicted the mass flow rate well in compare to that of the constant coefficient, but over predicted the expansion chamber pressure. The DEM with both the coefficients for continuous discharge flows were applied to investigate the quasi-steady flashing flow inside the metered discharge flows at various time instants. The DEM results were compared with the Clark s metered discharge experimental data and the well established homogeneous equilibrium model (HEM). The comparison between the HEM and DEM with Clark s (1991) experimental data showed that the DEM predicted the mass flow well in compare to that of HEM. Moreover, both the models underpredicted the expansion chamber pressure and temperature. The findings of the present thesis have given a better understanding of the role played by the propellant metastability inside the twin-orifice system of pMDIs. Also, these have provided detailed knowledge of thermodynamic state, void fraction and critical velocity of the propellant at the spray orifice exit, which are essential step towards the development of improved atomisation models. Improved understanding of the fluid mechanics of pMDIs will contribute to the development of next-generation pMDI devices with higher treatment efficacy, capable of delivering a wider range of therapeutic agents including novel therapies based around.
2

Análise da ocorrência do atraso de vaporização no escoamento do R-410A em tubos capilares adiabáticos. / Analysis on the delay of vaporization occurence for R-410A flow in adiabatic capillary tubes.

Carlos Augusto Simões Silva 18 December 2008 (has links)
Este trabalho apresenta os resultados de um estudo experimental sobre a ocorrência do atraso de vaporização no escoamento de misturas de fluidos refrigerantes em tubos capilares adiabáticos, com o intuito de aprimorar modelos de simulação do desempenho desse componente do ciclo de refrigeração previamente desenvolvidos. Foi realizada uma série de levantamentos experimentais para o R410A, uma mistura quase azeotrópica composta de 50% de HFC 32 e 50% de HFC 125 em base mássica, utilizando a unidade laboratorial para estudo de tubos capilares do Laboratório de Máquinas Térmicas do PMEEPUSP. Os sensores de temperatura foram posicionados adequadamente ao longo do tubo capilar, com maior concentração na região onde o atraso de vaporização tende a ocorrer, de forma a permitir uma determinação acurada do ponto onde se inicia a mudança de fase para diversas condições operacionais e geométricas. Primeiramente foram realizados estudos para caracterização de alguns parâmetros geométricos, como a medição dos diâmetros dos tubos capilares e a determinação das curvas de fator de atrito em função do n° de Reynolds para cada tubo capilar. A seguir foram realizados 27 ensaios, nos quais se obteve um total de 44 pontos experimentais, caracterizando o efeito de vários parâmetros geométricos e operacionais na diferença de pressão de saturação e no comprimento do trecho metaestável. Os dados obtidos foram correlacionados com os parâmetros experimentais no intuito de obter uma correlação para previsão da diferença de pressão de saturação no escoamento do R 410A em tubos capilares adiabáticos. A correlação obtida prevê 67% dos valores experimentais dentro da faixa de ± 26,4%, com um erro médio de 3,2%, resultado semelhante a outros trabalhos existentes na literatura. / This work presents the results of an experimental study on the occurrence of the delay of vaporization in the flow of refrigerant blends in adiabatic capillary tubes in order to improve previously developed models that simulate this component of refrigeration cycle. Experiments were carried out for R410A, a near azeotropic mixture composed of 50% of HFC 32 and 50% of HFC 125 on mass basis, using the capillary tubes laboratorial unit of the Mechanical Engineering Department of University of São Paulo. The temperature sensors was properly positioned along the capillary tubes, concentrated in the region where the delay of vaporization is expected to happen, to allow an accurate determination of the flashing point inception for a several operational conditions and geometries. Preliminary studies for characterization of some geometric parameters like capillary tubes diameters and determination of friction factor curves as function of the Reynolds number were performed. A total of 44 experimental points, collected from 27 runs, allowed the characterization of the effect of geometric and operational parameters on the underpressure of vaporization and metastable length. A correlation was developed for predicting the underpressure of vaporization as function of operational parameters and capillary tube geometry. The obtained correlation predicts 67% of experimental data within a ± 26,4% range, with an average error of 3,2%. This result is similar to other works in the literature.
3

Análise da ocorrência do atraso de vaporização no escoamento do R-410A em tubos capilares adiabáticos. / Analysis on the delay of vaporization occurence for R-410A flow in adiabatic capillary tubes.

Silva, Carlos Augusto Simões 18 December 2008 (has links)
Este trabalho apresenta os resultados de um estudo experimental sobre a ocorrência do atraso de vaporização no escoamento de misturas de fluidos refrigerantes em tubos capilares adiabáticos, com o intuito de aprimorar modelos de simulação do desempenho desse componente do ciclo de refrigeração previamente desenvolvidos. Foi realizada uma série de levantamentos experimentais para o R410A, uma mistura quase azeotrópica composta de 50% de HFC 32 e 50% de HFC 125 em base mássica, utilizando a unidade laboratorial para estudo de tubos capilares do Laboratório de Máquinas Térmicas do PMEEPUSP. Os sensores de temperatura foram posicionados adequadamente ao longo do tubo capilar, com maior concentração na região onde o atraso de vaporização tende a ocorrer, de forma a permitir uma determinação acurada do ponto onde se inicia a mudança de fase para diversas condições operacionais e geométricas. Primeiramente foram realizados estudos para caracterização de alguns parâmetros geométricos, como a medição dos diâmetros dos tubos capilares e a determinação das curvas de fator de atrito em função do n° de Reynolds para cada tubo capilar. A seguir foram realizados 27 ensaios, nos quais se obteve um total de 44 pontos experimentais, caracterizando o efeito de vários parâmetros geométricos e operacionais na diferença de pressão de saturação e no comprimento do trecho metaestável. Os dados obtidos foram correlacionados com os parâmetros experimentais no intuito de obter uma correlação para previsão da diferença de pressão de saturação no escoamento do R 410A em tubos capilares adiabáticos. A correlação obtida prevê 67% dos valores experimentais dentro da faixa de ± 26,4%, com um erro médio de 3,2%, resultado semelhante a outros trabalhos existentes na literatura. / This work presents the results of an experimental study on the occurrence of the delay of vaporization in the flow of refrigerant blends in adiabatic capillary tubes in order to improve previously developed models that simulate this component of refrigeration cycle. Experiments were carried out for R410A, a near azeotropic mixture composed of 50% of HFC 32 and 50% of HFC 125 on mass basis, using the capillary tubes laboratorial unit of the Mechanical Engineering Department of University of São Paulo. The temperature sensors was properly positioned along the capillary tubes, concentrated in the region where the delay of vaporization is expected to happen, to allow an accurate determination of the flashing point inception for a several operational conditions and geometries. Preliminary studies for characterization of some geometric parameters like capillary tubes diameters and determination of friction factor curves as function of the Reynolds number were performed. A total of 44 experimental points, collected from 27 runs, allowed the characterization of the effect of geometric and operational parameters on the underpressure of vaporization and metastable length. A correlation was developed for predicting the underpressure of vaporization as function of operational parameters and capillary tube geometry. The obtained correlation predicts 67% of experimental data within a ± 26,4% range, with an average error of 3,2%. This result is similar to other works in the literature.
4

Transport of Components and Phases in a Surfactant/Foam

Lopez Salinas, Jose 24 July 2013 (has links)
The transport of components and phases plays a fundamental role in the success of an EOR process. Because many reservoirs have harsh conditions of salinity, temperature and rock heterogeneity, which limit process options, a robust system with flexibility is required. Systematic experimental study of formulations capable to transport surfactant as foam at 94°C, formulated in sea water, is presented. It includes methodology to conduct core floods in sand packs using foaming surfactants and to develop “surfactant blend ratio- salinity ratio maps” using equilibrium phase behavior to determine favorable conditions for oil recovery in such floods. Mathematical model able to reproduce the foam strength behavior observed in sand packs with the formulations studied is presented. Visualization of oil recovery mechanism from matrix is realized using a model system of micro-channels surrounded by glass beads to mimic matrix and fractures respectively. The observations illustrate how components may distribute within the matrix, thereby releasing oil into the fractures. The use of chemicals to minimize adsorption is required when surfactant adsorption is important. The presence of anhydrite may limit the use of sodium carbonate to reduce adsorption of carbonates. A methodology is presented to estimate the amount, if any, of anhydrite present in the reservoir. The method is based on brine software analysis of produced water compositions and inductively coupled plasma (ICP) analysis of core samples. X-ray powder diffraction (XRD) was used to verify the mineralogy of the rock. X-ray photoelectron spectroscopy (XPS) was used to obtain surface composition for comparison with bulk composition of the rock. Adsorption of surfactants was measured using dynamic and static adsorption experiments. Determining the flow properties of the rock samples via tracer analysis permitted the simulation of the dynamic adsorption process using a mathematical model that considers the distribution of adsorbed materials in the three different regions of pore space. Using this method allows one to predict adsorption in a reservoir via simulation.
5

Análise do escoamento de fluidos refrigerantes alternativos ao HCFC22 em tubos capilares adiabáticos. / Analysis of HCFC 22 alternative refrigerant fluids flow through adiabatic capillary tubes.

Flávio Augusto Sanzovo Fiorelli 15 December 2000 (has links)
Este trabalho apresenta os resultados da pesquisa "Análise do Escoamento de Fluidos Refrigerantes Alternativos ao HCFC 22 em Tubos Capilares Adiabáticos", desenvolvida para obtenção do título de Doutor em Engenharia no Departamento de Engenharia Mecânica da EPUSP. Essa pesquisa foi motivada pelas resoluções do Protocolo de Montreal, que prevêem a eliminação gradativa do HCFC 22 e, conseqüentemente, impõem a necessidade da realização de estudos sobre o comportamento de fluidos alternativos ecologicamente aceitáveis nos sistemas de refrigeração e seus componentes. Até o momento, as pesquisas e as referências bibliográficas indicam a utilização de misturas zeotrópicas e quase-azeotrópicas como a melhor alternativa para substituição do HCFC 22. Desta forma, foi realizado um extenso levantamento experimental do escoamento do R-407C (uma mistura zeotrópica) e do R-410A (uma mistura quase-azeotrópica) através de tubos capilares, em uma unidade laboratorial construída para essa finalidade. Esse levantamento, realizado para condições de entrada subresfriada e saturada, caracterizou a influência destes fluidos refrigerantes e dos diversos parâmetros operacionais e geométricos no comportamento do tubo capilar em sistemas de refrigeração. Foram desenvolvidos dois modelos (fases separadas e homogêneo) para a modelagem matemática do escoamento de fluidos refrigerantes através de tubos capilares, a fim de verificar o efeito do tipo de escoamento adotado nessa modelagem. A validação dos programas de simulação desenvolvidos, tanto para os dados experimentais obtidos no presente trabalho quanto para dados de literatura, mostra que os dois modelos podem ser utilizados para essa modelagem, apresentando desvios semelhantes em relação aos dados experimentais. A fim de aprimorar os modelos, é necessária a realização de estudos mais aprofundados sobre o atraso de vaporização e a ocorrência de blocagem na saída do tubo capilar. Por fim, foi realizado um estudo numérico comparativo do desempenho do HCFC 22 e dos alternativos R-407C e R-410A, que indicou que o primeiro é adequado tanto para o "retrofit" de equipamentos existentes quanto para utilização em novos equipamentos, enquanto que o segundo deve ser utilizado apenas em novos equipamentos. / This work presents the results of the research activities on the "Analysis of HCFC 22 Alternatives Flow Through Adiabatic Capillary Tubes", developed at the Mechanical Engineering Department of Escola Politécnica da Universidade de São Paulo. Such research was motivated by the resolutions of Montreal Protocol, which imposes gradational elimination of several refrigerants, among them HCFC 22. This leads to the necessity of carrying out studies on the behaviour of ecologically acceptable refrigerants in refrigeration systems and components. So far, researches and literature indicate the usage of zeotropic and near azeotropic refrigerant mixtures as the best alternative to HCFC 22. Therefore, it was performed an extensive experimental survey on R-407C (a zeotropic mixture) and R-410A (a near azeotropic mixture) flow through capillary tubes. Such survey, which was carried out for both subcooled and two-phase inlet conditions, characterised the influence of these refrigerants, as well as the several operating and geometric parameters on the behaviour of capillary tubes used in refrigeration systems. In order to analyse the effect of different approaches for two-phase flow, it was developed two models (separated flow model and homogeneous model) for mathematical simulation of refrigerant flow through adiabatic capillary tubes. Models validation using both experimental and literature data shows that the two models are suitable for such simulation, with the same error level in relation to experimental data. It was also noticed that it is necessary to perform more comprehensive studies on the delay of vaporisation and capillary tube outlet shocking flow phenomena. Finally, it was performed a comparative study on the performance of HCFC 22, R-407C and R-410A, which indicates that R-407C is suitable both for retrofitting actual equipment and for new ones, while R-410A is suitable only for new equipment.
6

Alimenta??o artificial de f?meas de Rhipicephalus sanguineus (Acari: Ixodidae) por meio de tubos capilares. / Artificial feeding of female Rhipicephalus sanguineus (Acari: Ixodidae) through capillary tubes.

Sakai, Renata Kazuko 22 February 2010 (has links)
Submitted by Sandra Pereira (srpereira@ufrrj.br) on 2018-05-11T13:46:52Z No. of bitstreams: 1 2010 - Renata Kazuko Sakai.pdf: 1267056 bytes, checksum: 688ad78c0490ec2ff8c2c641467143d0 (MD5) / Made available in DSpace on 2018-05-11T13:46:53Z (GMT). No. of bitstreams: 1 2010 - Renata Kazuko Sakai.pdf: 1267056 bytes, checksum: 688ad78c0490ec2ff8c2c641467143d0 (MD5) Previous issue date: 2010-02-22 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior, CAPES, Brasil. / Artificial feeding of ticks can be used to study the relationship between vectors and pathogens, biological aspects, to test acaricides and to minimize the use of animals in scientific studies. The objectives of this study were artificially feeding through capillary tubes, females partially engorged of Rhipicephalus sanguineus previously fed on rabbits and dogs. In addition, the gain in weight of females and the influence of the technique in the biological aspects of non-parasitic phase of this species were also analyzed. Partially engorged females of R. sanguineus were obtained from infestation in rabbits and dogs in different intervals of initial weights and fed artificially for 24 hours to assess the best weight gains for the next stage. Female ticks with the best gains in weight were obtained on rabbits and dogs were separated into five groups of homogeneous weight, between 35 and 80mg and 21 to 50mg, respectively. The females were fixed in polystyrene tray with double-sided tape and fed artificially through capillary tubes for 6, 12, 24, 36 and 42 hours with citrated canine blood. After artificial feeding, ticks were again weighed to analyze the weight gain. Subsequently, they were fixed in Petri dishes and incubated at 27?1?C and humidity above 80%, in order to analyze the biological aspects. Control groups were obtained from natural fall of rabbits and dogs and the ticks were kept under the same conditions of temperature and humidity. For the statistical analysis, ANOVA and Tukey test were used for quantitative variables. In addition, the nonparametric Kruskal-Wallis was applied for qualitative variables, both with 5% of significance level. After 36 hours of artificial feeding there were difference statistically significant between groups, in relation to weight gain, for both females obtained from rabbits and dogs. Although the females of R. sanguineus had not been submitted to complete engorgement, the technique of artificial feeding of females derived from rabbits and dogs, no deleterious effects on the biological aspects of non-parasitic stage were observed. / A alimenta??o artificial de carrapatos pode ser utilizada para estudar a rela??o entre vetores e agentes patog?nicos, aspectos biol?gicos, para testar acaricidas e para minimizar a utiliza??o de animais em estudos cient?ficos. Os objetivos deste estudo foram alimentar artificialmente, por meio de tubos capilares, f?meas parcialmente ingurgitadas do carrapato Rhipicephalus sanguineus previamente alimentadas em coelhos e c?es. Al?m disso, foram analisados tamb?m o ganho de peso das f?meas e a influ?ncia da t?cnica nos aspectos biol?gicos da fase n?o parasit?ria desta esp?cie. F?meas parcialmente ingurgitadas de R. sanguineus foram obtidas de infesta??o em coelhos e c?es, em diferentes faixas de pesos iniciais e alimentadas artificialmente por 24 horas, para avaliar os melhores ganhos de peso para a pr?xima etapa. F?meas de carrapatos com os melhores ganhos de peso obtidas de infesta??o em coelhos e c?es, foram separadas em cinco grupos de peso homog?neo, pesando entre 35 a 80 mg e 21 a 50 mg, respectivamente. As f?meas foram fixadas em bandeja de isopor com fita adesiva dupla face e alimentadas artificialmente por meio de tubos capilares por 6, 12, 24, 36 e 42 horas, com sangue canino citratado. Ap?s alimenta??o artificial, os carrapatos foram pesados para avaliar o ganho de peso. Posteriormente, foram fixados em Placas de Petri e mantidos em estufa a 27?1?C e umidade superior a 80%, para avaliar os aspectos biol?gicos. Os grupos controles foram obtidos de queda natural de coelhos e c?es e mantidos nas mesmas condi??es de temperatura e umidade. Para an?lise estat?stica das vari?veis quantitativas foram utilizada an?lise de vari?ncia e teste de Tukey e para as vari?veis qualitativas foram utilizados o teste n?o param?trico Kruskal-Wallis, ambas com n?vel de signific?ncia de 5%. A partir de 36 horas de alimenta??o artificial foi observada diferen?a estat?stica significativa entre os grupos, em rela??o ao ganho de peso, tanto para f?meas obtidas de coelhos e de c?es. Embora as f?meas de R. sanguineus n?o tenham apresentado ingurgitamento total, a t?cnica de alimenta??o artificial de f?meas oriundas de coelhos e de c?es, n?o apresentou efeitos delet?rios sobre os aspectos biol?gicos da fase n?o parasit?ria.
7

Integrace materiálů s fázovou změnou ve stavebních konstrukcích / Integration of phase change materials in building structures

Klubal, Tomáš January 2017 (has links)
The thesis deals with the integration of phase change materials (PCMs) into building structures. The basic requirement is improved thermal stability during the summer season without using an air conditioner. This can be achieved by increasing the thermal storage capacity of the building structures. If the thermal capacity cannot be increased on the level of weight, phase change materials can be used. These materials are capable of storing latent heat and thus increasing the thermal storage capacity of the building. In the thesis the phase change materials were investigated in a thermal incubator by thermal analysis and, above all, in full-scale experiments using comparative measurements. The comparative measurements were carried out in two attic rooms at the Faculty of Civil Engineering, Brno University of Technology, where in one was used as a reference and the other for the experiment. Manufactured heat storage panels were installed in the experimental room. These panels are composed of a base plate; the capillary tubes placed on it are coated with modified plaster. The gypsum plaster is modified with micro-capsules paraffin for improving the thermal storage capacity. This system is connected to a thermal air-water pump, by which the storage panels can be additionally cooled or heated. In the experimental measurements, different operating modes were investigated and their effect on the indoor environment was evaluated. Thermal storage in PCMs dampens the temperature amplitude in the building during the summer season and, at the same time, allows the stored heat to be discharged during the night. Moreover, the time interval of withdrawing electric energy from the supply mains is much shorter than in the case of air conditioning. A conventional air conditioner must operate simultaneously with the thermal load, i.e. at the time of peak consumption of electric energy. Thanks to the set regimes, the installed system is capable of responding to external thermal condit

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