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Author: Benjamin Andrew Larsen Publisher: ISBN: Category : Languages : en Pages :
Book Description
The current knowledge of flow parameters for terrestrial two-phase flow was developed through experiments that collected hundreds to thousands of data points. However, the cost associated with microgravity testing make collecting such amounts of microgravity two-phase flow data difficult. Multiple researchers have postulated the microgravity drift flux model parameters to predict void fraction, however, these methods were initially developed with no consideration given to a microgravity environment. The purpose of this thesis was to develop a process by which results from multiple microgravity experiments can be compared on a similar medium and used to develop a larger viable data set than what was previously available and to reliably calculate a value for the void fraction from the available data. Development of multiphase systems for microgravity requires accurate prediction methods. Utilizing data from multiple microgravity two-phase flow experiments, a statistically consistent slug flow database has been created. The data from 13 different microgravity two-phase flow experiments was vetted using a combination of parametric and non-parametric statistical tests to develop a valid model for the drift flux parameters that meet the axioms of a linear model. The result was a statistically consistent microgravity slug flow data base consisting of 220 data points from 8 different experiments and the associated values for the concentration parameter, Co, and drift velocity, u[subscript]gj. A key component for this model was redefining the assumptions in the drift flux model to accurately represent microgravity conditions in calculating the drift flux parameters. The resultant drift flux parameters are a distribution parameter, Co = 1.336 ± 0.013 and a drift velocity, u[subscript]gj = -0.126 ± 0.020. The electronic version of this dissertation is accessible from http://hdl.handle.net/1969.1/152740
Author: Benjamin Andrew Larsen Publisher: ISBN: Category : Languages : en Pages :
Book Description
The current knowledge of flow parameters for terrestrial two-phase flow was developed through experiments that collected hundreds to thousands of data points. However, the cost associated with microgravity testing make collecting such amounts of microgravity two-phase flow data difficult. Multiple researchers have postulated the microgravity drift flux model parameters to predict void fraction, however, these methods were initially developed with no consideration given to a microgravity environment. The purpose of this thesis was to develop a process by which results from multiple microgravity experiments can be compared on a similar medium and used to develop a larger viable data set than what was previously available and to reliably calculate a value for the void fraction from the available data. Development of multiphase systems for microgravity requires accurate prediction methods. Utilizing data from multiple microgravity two-phase flow experiments, a statistically consistent slug flow database has been created. The data from 13 different microgravity two-phase flow experiments was vetted using a combination of parametric and non-parametric statistical tests to develop a valid model for the drift flux parameters that meet the axioms of a linear model. The result was a statistically consistent microgravity slug flow data base consisting of 220 data points from 8 different experiments and the associated values for the concentration parameter, Co, and drift velocity, u[subscript]gj. A key component for this model was redefining the assumptions in the drift flux model to accurately represent microgravity conditions in calculating the drift flux parameters. The resultant drift flux parameters are a distribution parameter, Co = 1.336 ± 0.013 and a drift velocity, u[subscript]gj = -0.126 ± 0.020. The electronic version of this dissertation is accessible from http://hdl.handle.net/1969.1/152740
Author: Luca Valota Publisher: ISBN: Category : Languages : en Pages :
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: Adam Michael Shephard Publisher: ISBN: Category : Languages : en Pages :
Book Description
Flow regime transitions and the modeling thereof underlie the design of microgravity two-phase systems. Through the use of the zero-g laboratory, microgravity two-phase flows can be studied. Because microgravity two-phase flows exhibit essentially no accelerations (i.e. no buoyancy or gravitational forces), the effects of acceleration on two-phase flow can be decoupled from the effects of other fluid phenomenon. Two-phase systems on earth are understood mostly through empiricisms. Through microgravity two-phase research, a fundamental understanding of two-phase systems can be obtained and applied to both terrestrial systems in space applications. Physically based bubbly-bubbly/slug and bubbly/slug-slug flow regime transition models are introduced in this study. The physical nature of the models demonstrates a new understanding of the governing relationships between coalescence, turbulence, void fraction, boundary layer affects, and the inlet bubble size distribution. Significantly, the new models are dimensionless in addition to being physically derived. New and previous models are evaluated against zero-g data sets. Previous models are not accurate enough for design use. The new models proposed in this study are far more detailed than existing models and are within the precision necessary for most design purposes. Because of the limited data available, further experimental validation is necessary to formally vet the model. Zero-g data set qualification and flight experiment design have not been standardized and as a result, much of the data in the literature can be shown not to represent microgravity conditions. In this study, a set of zero-g quality criteria are developed and used to qualify the data sets available in the literature. The zero-g quality criteria include limitations on buoyancy forces relative to surface tension and inertial forces as well as requirements on acceleration monitoring and flow development length and time. The resulting evaluation of the data sets available in the literature unveils several experiment design shortfalls, which have resulted in data sets being misrepresented as zero-g data sets. The quality standards developed in this study should continue to be improved upon and used in the design of future zero-g fluid experiments. The use of one-g single-phase models in approximating zero-g two-phase experimental data was successfully performed in this study. Specifically the models for pressure drop, friction factor, wall shear, and velocity profile are demonstrated. It is recognized that the mixing apparatus will affect the flow regime transitions, specifically the distribution of bubble sizes that exit the mixing apparatus. Unfortunately, little-to-no information regarding the mixing apparatus used in past experiments can be found in the literature. This will be an area for further developmental research. In summary, the approach to understanding and modeling two-phase phenomenon demonstrated in this study provides tools to future researchers and engineers. Special attention to data qualification and experiment standardization provides a different prospective and interpretation of the currently available data. The physically based and dimensionless modeling demonstrated in this study can be extended to other studies in the field as well as providing a basis for the application of heat transfer modeling to microgravity two-phase systems, specifically boiling and condensation.
Author: Santiago Arias Calderon Publisher: ISBN: Category : Languages : en Pages : 164
Book Description
Promising technological applications of two-phase flows in space have captured the increasing interest of the space sector, provoking a strong demand for more fundamental knowledge. Great efforts have been made in recent decades to study the behavior of two-phase flows in low-gravity environments, which is expected to be different than the behavior observed in the presence of gravitational forces. Nevertheless, many phenomena are still poorly understood. The development of any of these new technologies demands a better knowledge of two-phase flows. In this manuscript we address questions regarding the generation of gas-liquid flows and their behavior in conditions relevant for a microgravity environment. In particular, we focus on an air-water mixture formed in a capillary T-junction. To this end, an experimental setup has been designed to accurately control both gas and liquid flow rates. We performed a quantitative characterization on ground of the T-junction, whose operation is robust to changes in gravity level. Its main performance is the generation of bubbles at a regular frequency with small size dispersion. We obtained two working regimes of the T-junction and identified the crossover region between them. Bubble, slug, churn and annular flow regimes have been observed during the experiments and a flow pattern map has been plotted. We present an experimental study on the bubble-slug transition in microgravity-related conditions. In addition, we address questions regarding the existence of a critical void fraction in order for the bubble-slug transition to occur. The gas-liquid flow has been characterized by measuring the bubble generation frequency as well as the bubble and liquid slug sizes. Since bubble dynamics is also expected to be different in the absence of buoyancy, the bubble velocity has also been studied. The mean void fraction appears as one relevant parameter that allows for the prediction of frequency, bubble velocity, and lengths. We propose curves obtained empirically for the behavior of generation frequency, the bubble velocity and the lengths. The dependence of the frequency on the Strouhal dimensionless number has been analyzed. A numerical study of the formation of mini-bubbles in a 2D T-junction by means of the fluid dynamics numerical code JADIM is also presented. Simulations were carried out for different flow conditions, giving rise to results on the bubble generation frequency, bubble velocity, void fraction and characteristic lengths. Numerical results have been then compared with experimental data.
Author: National Aeronautics and Space Administration (NASA) Publisher: Createspace Independent Publishing Platform ISBN: 9781722817558 Category : Languages : en Pages : 44
Book Description
The ability to predict gas-liquid flow patterns is crucial to the design and operation of two-phase flow systems in the microgravity environment. Flow pattern maps have been developed in this study which show the occurrence of flow patterns as a function of gas and liquid superficial velocities as well as tube diameter, liquid viscosity and surface tension. The results have demonstrated that the location of the bubble-slug transition is affected by the tube diameter for air-water systems and by surface tension, suggesting that turbulence-induced bubble fluctuations and coalescence mechanisms play a role in this transition. The location of the slug-annular transition on the flow pattern maps is largely unaffected by tube diameter, liquid viscosity or surface tension in the ranges tested. Void fraction-based transition criteria were developed which separate the flow patterns on the flow pattern maps with reasonable accuracy. Weber number transition criteria also show promise but further work is needed to improve these models. For annular gas-liquid flows of air-water and air- 50 percent glycerine under reduced gravity conditions, the pressure gradient agrees fairly well with a version of the Lockhart-Martinelli correlation but the measured film thickness deviates from published correlations at lower Reynolds numbers. Nusselt numbers, based on a film thickness obtained from standard normal-gravity correlations, follow the relation, Nu = A Re(sup n) Pr(exp l/3), but more experimental data in a reduced gravity environment are needed to increase the confidence in the estimated constants, A and n. In the slug flow regime, experimental pressure gradient does not correlate well with either the Lockhart-Martinelli or a homogeneous formulation, but does correlate nicely with a formulation based on a two-phase Reynolds number. Comparison with ground-based correlations implies that the heat transfer coefficients are lower at reduced gravity than at normal gravity under the same ...
Author: National Aeronautics and Space Adm Nasa Publisher: Independently Published ISBN: 9781729233887 Category : Science Languages : en Pages : 44
Book Description
An attempt is made to predict gas-liquid two-phase flow regime in a pipe in a microgravity environment through scaling analysis based on dominant physical mechanisms. Simple inlet geometry is adopted in the analysis to see the effect of inlet configuration on flow regime transitions. Comparison of the prediction with the existing experimental data shows good agreement, though more work is required to better define some physical parameters. The analysis clarifies much of the physics involved in this problem and can be applied to other configurations. Lee, Jinho and Platt, Jonathan A. Glenn Research Center RTOP 694-03-0A
Author: Benjamin Andrew Larsen
Author: Benjamin Andrew Larsen
Author: Jonathan David Braisted
Author: Luca Valota
Author: Adam Michael Shephard
Author: Santiago Arias Calderon
Author: Jinho Lee
Author: National Aeronautics and Space Administration (NASA)
Author: Jinho Lee
Author: National Aeronautics and Space Adm Nasa
Author: William Scott Bousman