Dissertations / Theses on the topic 'Swirl tube'

Diploma thesis deals with design and exploration of installation in the draft tube of the swirl turbine. Use of the draft tube is defined in the first part, with illustration of energetical gain and efficiency of draft tube. Further the suitable shape of draft tube is studied by CFD computing. Design, research and evaluation of installation in the draft tube are solved in the main part.

Orientador: Eugenio Spano Rosa
Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica
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Resumo: O presente trabalho investiga os mecanismos de separação sólido-líquido em separadores tubo-ciclônicos. O trabalho é desenvolvido a partir de testes experimentais e simulação numérica. A etapa experimental investiga a influência do aumento de viscosidade sobre a eficiência do separador. Através de uma análise dimensional, os dados experimentais são reduzidos em grupos adimensionais. Obtem-se uma correlação entre a eficiência de separação e os grupos adimensionais. Ela revela como a eficiência depende dos parâmetros geométricos e operacionais do separador. A correlação obtida possibilita dimensionar estes separadores para cenários com elevada viscosidade. As simulações numéricas são realizadas utilizando um método de volumes finitos. O processo de separação é estudado através do adimensional Stokes. São introduzidos os conceitos de superfície de captura e tempo de residência de partículas. Define -se um importante parâmetro do escoamento, o comprimento de decaimento. Propõe-se um modelo unidimensional para o separador. Realiza-se com base neste modelo uma análise comparativa entre dois separadores. Os resultados são coerentes com dados experimentais e indicam quais características geométricas melhoram a eficiência do separador
Abstract: This work investigates the solid-liquid separation mechanisms in swirl tubes through experimental and numerical analysis. In the experimental phase, it is analyzed the impact of the viscosity increase on the separation efficiency of swirl tubes. The experimental data are reduced using dimensional analysis. A functional relationship between the separation efficiency and the dimensionless groups is obtained, allowing to calculate the separation efficiency dependency on the liquid viscosity, flow rate, particle size, and other geometrical parameters of the separator. This relationship helps to design these desander devices to scenarios with high viscosity. Numerical simulations are carried out in a structured grid using a finite volume method. Separation process is studied through the Stokes number. The concepts of capture surface and residence time of particles are introduced and an important flow field parameter, the length of decay is defined. A one-dimensional model is proposed for the swirl tube. A comparative analysis between two separators is done based on the one-dimensional model. The results are in agreement with experimental data and indicate which geometrical features help to improve the separator efficiency
Mestrado
Termica e Fluidos
Mestre em Engenharia Mecânica

The aim of this master’s thesis is the optimal design of swirl turbines for small water power plant. It is described a different possibilities of turbine‘s install for locality Vrchlabí. It presents a design of turbines and draft tubes. For the installation of turbines is computed theoretical production of annual electric energy. Furthermore it describes a design of supply channel and intake structure.

This master’s thesis deals with the draft tube and its optimization for various operating conditions. The research investigates the theoretical description and function of the draft tube and explains known methods of suppressing pressure pulsation so far. In the computational part, the author proposes a new method and designs optimal geometry of adjustable installations (ribs) for the draft tube. Finally, the comparison with the default geometry without ribs is performed.

This thesis deals with the design of water turbine enabling optimal utilization of hydro-energetic potential of given location (barrage on Úpa river) chosen by ČEZ a.s. company. Moreover, the option of multi-unit layout is discussed. Because of the low-head profile of given location, the technology of swirl turbine in siphon configuration was chosen. Technology of swirl turbine presents new modification of Kaplan turbine with no need of guide vane. Swirl turbine is characterized by its high discharge and high speed. The main part of this thesis is focused on hydraulic design of the turbine.

This master’s thesis deals with CFD simulation of spiral vortex structure in the diffuser of swirl generator. The objective of the thesis is to evaluate influence of change in diffuser opening angle on frequency and amplitude of pressure pulsation. All results are compared in charts which shows courses of frequencies and amplitudes along the diffuser. Two different turbulence models and several types of mesh were tested

The goal of this diploma thesis is to design a new shape of the draft tube, which will be easier to manufacture while maintaining good strength and hydraulic properties. First part of this thesis is devoted to the formulation of the problem, description of the swirl turbine, principle of operation, the basic variants of arrangement, also the function of the draft tube, its efficiency and other formulas. In the second part of this thesis is a CFD and strength analysis of the original design, also a new design is proposed and the possibility of optimization using ANSYS Fluent Adjoint solver.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2012.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 150-157).
Previous studies conducted at MIT showed that the power performance of an inverted pressurized water reactor (IPWR) conceptual design, i.e. the coolant and moderator are inverted such that the fuel is the continuous medium and the moderator flows through coolant channels, has potential to outperform a traditional pressurized water reactor (PWR). Similar to the traditional PWR, the IPWR design involves a tradeoff between core pressure drop and the minimum departure from nucleate boiling ratio (MDNBR). In order to increase the power density of the IPWR, Ferroni [231 examined the possibility of inserting multiple short-length twisted-tapes (MSLTTs) in the cooling channels. For a fixed coolant mass flow rate, the swirling flow produced by the MSLTTs allows the IPWR to have a higher operating heat flux while maintaining the design criteria of MDNBR as compared to either the traditional PWR or IPWR without swirl promoters. However, the addition of each twisted-tape increases the core pressure drop which limits the coolant flow rate due to pumping power limitations of existing reactor coolant pumps (RCPs). In order to better characterize the critical heat flux (CHF) enhancement caused by the addition of MSLTTs, this study performed a critical analysis of existing CHF correlations and models. Initially a phenomenological model was sought to describe the mechanisms of CHF for tubes containing MSLTTs; however, the full-length twisted-tape (FLTT) model that was selected for modification was found to have terms that could not be reconciled for the transition from fully developed swirl to decaying swirl. The existing CHF correlations for swirling flow were also found to be unsatisfactory. Therefore, the insights gained through working with the phenomenological model were used to develop a new empirical correlation to describe the departure from nucleate boiling (DNB) using existing swirling flow DNB data as well as an existing swirl decay model. In order to allow for more flexibility in the placement of the MSLThs, an existing FLTT pressure drop correlation was modified to account for the form pressure drop at the entrance to each twisted-tape insert as well as the friction pressure drop in the decaying swirl region downstream from the exit of each MSLTT. A sensitivity analysis of the new pressure drop correlation was also performed to determine if the complete methodology could be simplified. Design insights were presented that help to narrow the design space for the IPWR. These steps should be followed in order to find the maximum power density possible by the IPWR design. Finally, the existing swirl flow CHF data and correlations are presented in the appendices of this thesis.
by Tyrell Wayne Arment.
S.M.

This research comprises an experimental and theoretical study on convective boiling inside tubes containing twisted-tape inserts. The demand for more compact and efficient thermal systems, in which the heat exchangers plays an important role, has led to the development and use of various heat transfer enhancement techniques. Among them twisted-tape insert as a swirl flow device is one of the most used. Twisted-tape inserts have been used for over more than one century ago as a technique of heat transfer enhancement applied to heat exchangers. However, the heat transfer augmentation comes together with pressure drop increment, impacting the pumping power and, consequently, the system efficiency. Moreover, until now it is not clear, the operational conditions under which the heat transfer coefficient augmentation by the use of twisted-tape inserts overcomes pressure drop penalty. In the present study, initially, extensive investigations of the literature concerning convective boiling inside plain tubes with and without twisted-tape inserts were performed. This literature review covers pressure drop, heat transfer coefficient and the leading frictional pressure drop gradient and heat transfer coefficient predictive methods during convective boiling inside tubes with and without twisted-tape inserts. Then, pressure drop and heat transfer coefficient results acquired in the present study were obtained in an experimental apparatus of 12.7 and 15.9 mm ID tubes during flow boiling of R134a for twisted-tape ratios of 3, 4, 9, 14 and tubes without inserts, mass velocities ranging from 75 to 200 kg/m2 s, saturation temperatures of 5 and 15°C and heat fluxes of 5 and 10 kW/m2. The experimental results were parametrically analyzed and compared against the predictive methods from literature. An analysis of the enhancement of the heat transfer coefficient and the pressure drop penalty is presented. Heat transfer coefficient increments up to 45% keeping the same pumping power and pressure drop penalty of about 35% were obtained by using twisted-tape relative to tubes without inserts. Additionally, through comparison of the present study experimental results with the predictive methods from the literature for heat transfer coefficient during two-phase flow inside tube containing twisted-tape inserts, it was verified that non of these methods predict satisfactory well the experimental results. However, a new method was develop for predicting the heat transfer coefficient during flow boiling inside tubes containing twisted-tape inserts based on the experimental results obtained in the present study. The predictive method takes into account the physical picture of the swirl flow phenomenon by including swirl flow effects promoted by the twisted-tape inserts. The proposed method predicts satisfactorily well the data obtained in the present study, predicting 89.1% of the experimental data within an error band of ± 30% and absolute mean deviation of 15.7%.
A presente pesquisa trata-se de um estudo teórico e experimental sobre a ebulição convectiva no interior de tubos com fitas retorcidas. A crescente demanda por sistemas térmicos mais compactos e eficientes, nos quais os trocadores de calor apresentam elevada relevância, tem motivado o desenvolvimento de inúmeras técnicas de intensificação de troca de calor, sendo que a utilização de fitas retorcidas é uma das técnicas mais adotadas. Fitas retorcidas são utilizadas como técnicas de intensificação de troca de calor há mais de um século. Entretanto o incremento da transferência de calor é acompanhado do aumento da perda de pressão, que por sua vez implica em aumento da potência de bombeamento, e consequentemente afeta a eficiência global do sistema. Adicionalmente, até os dias de hoje não há consenso sobre as condições operacionais em que o ganho com o incremento do coeficiente de transferência de calor é superior à perda devido ao aumento da perda de pressão. Neste estudo, inicialmente foi realizada uma extensa revisão da literatura sobre a ebulição convectiva no interior de tubos com e sem fitas retorcidas. Esta revisão aborda aspectos relacionados à perda de pressão e ao coeficiente de transferência de calor, juntamente com os métodos de previsão destes parâmetros. Foram realizados experimentos para determinação experimental de perda de pressão e coeficiente de transferência de calor, em aparato experimental contando com tubos horizontais com diâmetros internos iguais a 12,7 e 15,9 mm, para escoamento bifásico de R134a, razões de retorcimento iguais a 3, 4, 9, 14 e tubo sem fita, velocidades mássicas entre 75 e 200 kg/m²s, temperaturas de saturação iguais a 5 e 15°C, e fluxo de calor iguais a 5 e 10 kW/m². Os resultados experimentais foram analisados e comparados com estimativas segundo métodos disponíveis na literatura. Uma análise do aumento do coeficiente de transferência de calor e da perda de pressão friccional é apresentada. Foram verificados incrementos do coeficiente de transferência de calor de até 45% para a mesma potência de bombeamento, e aumento de perda de pressão de aproximadamente 35% para tubos com fitas retorcidas em relação aos tubos sem fita. Adicionalmente, através da comparação dos resultados experimentais com os métodos de previsão para coeficiente de transferência de calor, foi verificado que nenhuma metodologia apresentava previsões satisfatórias dos resultados. Portanto um novo método para previsão do coeficiente de transferência de calor durante ebulição convectiva no interior de tubos com fitas retorcidas foi desenvolvido com base nos resultados experimentais obtidos durante o presente estudo. O método proposto é função de parâmetros geométricos e do escoamento, e também de parâmetros físicos do escoamento rotacional induzido pela fita. A metodologia desenvolvida apresenta previsões satisfatórias dos resultados experimentais, prevendo 89,1% dos resultados experimentais com erro inferior a ± 30% e erro médio absoluto igual a 15,7%.