Statistical Comparison of Two-phase Flow, Void Fraction Fluctuations in a Microgravity Environment PDF Download

Author: Jae Ho Chang
Publisher:
ISBN:
Category :
Languages : en
Pages : 188

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Author: Luca Valota
Publisher:
ISBN:
Category :
Languages : en
Pages :

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Book Description
Knowledge of the two-phase flow state is fundamental for two-phase flow system design and operation. In traditional two-phase flow studies, the flow regime refers to the physical location of the gas and liquid in a conduit. Flow configuration is important for engineering correlations of heat and mass transfer, pressure drop, and wall shear. However, it is somewhat subjective since it is mostly defined by experimental observation, resulting in an approximate and equivocal definition. Thus, there is need for a better, objective flow regime identification. The void fraction is a key parameter in monitoring the operating state of a two-phase system and several tools have been developed in order to measure it. The purpose of this study is to use the void fraction and other parameters of the system to achieve a model for flow pattern identification. Recently, an experimental program using the Foster-Miller two-phase flow test bed and Creare Inc. capacitance void fraction sensors was conducted in the microgravity environment of the NASA KC-135 aircraft. Several data types were taken for each phase, such as flow rate, superficial velocity, density and transient void fraction at 100Hz. Several analytical approaches were pursued, including a statistical approach of the fluctuation of the void fraction, Martinelli analysis, and Drift Flux analysis, in order to reach a model for flow pattern identification in microgravity conditions. Several parameters were found to be good flow pattern identifiers such as the statistical moments variance and skewness, Signal -to- noise ratio (SNR), Half Height Value (HHV) and Linear Area Difference (LAD). Moreover, relevant conclusions were achieved using the Martinelli parameter and the Drift Flux model in microgravity conditions. These results were compared with the basic literature.

Author: Mohamed S. El-Genk
Publisher: American Institute of Physics
ISBN:
Category : Science
Languages : en
Pages : 1512

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3rd Symposium on Space Colonization. 2nd Symposium on New Frontiers and Future Concepts, Albuquerque, New Mexico, 13-17 February 2005

Author: Carlos Moreno Tavira
Publisher:
ISBN:
Category :
Languages : en
Pages :

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Book Description
Two-phase flows have gained importance over the last years due to their multiple and useful applications in space systems. For example, two-phase flows are used in fuel cells micro-channel networks, in the fluid management of Environmental Control and Life Support Systems (ECLSS) or in thermal management systems. However, many problems regarding two-phase flows in microgravity conditions are still open, so further research is needed. In this study, numerical simulations of gas-liquid two-phase flow are performed in a T-junction capillary. Bubbles are formed as a consequence of the interaction between air and water. The geometry used is the same as in [1, 2, 3] in order to make reliable comparisons with the results extracted from the laboratory experiments performed in the mentioned literature. OpenFOAM is used as the main software for the simulations, and ParaView and MATLAB are used to post-process the data. InterFoam is selected as the solver since it uses an incompressible, immiscible and isothermal Volume of Fluid (VOF) method. Some validations were made before setting up the definitive cases of the simulations. These validations were related to the adequate capillary length in order to obtain fully-developed flows, to the appropriate mesh quality to get good results and maintain an acceptable computational complexity, to the optimal contact angle value to get close to reality bubble behavior in terms of adherence to the walls, and to the right location of the sampling surfaces responsible for extracting the data. An analysis of the fluid velocity profiles along both of the capillaries of the T-junction was also made. Bubbles are analyzed in terms of their generating frequency, volume, length and velocity. Bubble volume dispersion is quantified using the polydispersity index. A pressure probe is used to measure the gauge pressure at the very center of the T-junction. Visual comparisons are made between simulation bubbles and experimental bubbles. In the end, the results of the simulations qualitatively fitted the experimental data, validating Computational Fluid Dynamics (CFD) as an alternative and correct tool to perform two-phase flow studies under microgravity conditions.

Author: G. Klidonas
Publisher:
ISBN:
Category : Two-phase flow
Languages : en
Pages : 404

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Author:
Publisher:
ISBN:
Category : Mechanics, Applied
Languages : en
Pages : 400

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Author: Satish Kandlikar
Publisher: Elsevier
ISBN: 9780080445274
Category : Science
Languages : en
Pages : 492

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&Quot;This book explores flow through passages with hydraulic diameters from about 1 [mu]m to 3 mm, covering the range of minichannels and microchannels. Design equations along with solved examples and practice problems are also included to serve the needs of practicing engineers and students in a graduate course."--BOOK JACKET.

Author: Jinho Lee
Publisher:
ISBN:
Category :
Languages : en
Pages :

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Author:
Publisher:
ISBN:
Category : Direct energy conversion
Languages : en
Pages : 592

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Author:
Publisher:
ISBN:
Category : Aeronautics
Languages : en
Pages : 1502

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Book Description
Lists citations with abstracts for aerospace related reports obtained from world wide sources and announces documents that have recently been entered into the NASA Scientific and Technical Information Database.