› › Analytical And Experimental Study Of Annular Two Phase Flow Friction Pressure Drop Under Microgravity

Analytical and Experimental Study of Annular Two-phase Flow Friction Pressure Drop Under Microgravity

Author : Ngoc Thanh Nguyen

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Page : pages

File Size : 33,71 MB

Release : 2011

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Two-phase liquid-gas flow has a wide variety of applications in space, including active thermal control systems, high-power communications satellites, heat pumps and space nuclear reactors. Two-phase systems have many potential advantages over current single-phase systems due to reductions in system size, weight and power consumption. The mechanisms of pressure drop, heat transfer coefficients, void fractions, and flow regimes must be well understood under microgravity conditions in order to design reliable two-phase systems. The main objective of this present research is to develop a new mathematical model that can accurately predict the annular two-phase friction pressure drop to optimize the design of two-phase systems. The two-phase flow tests were conducted aboard the NASA KC-135 aircraft by the Interphase Transport Phenomena (ITP) group from Texas A & M University. The two-phase flow pressure drops were measured across a single transparent test section 12.7 mm ID and 1.63 m long in annular regimes under microgravity conditions during two flight campaigns. Different from previous work, this was the first time both the void fraction and the film thickness were measured under microgravity conditions. The empirical correlations for the interfacial friction factor and void fraction were developed from 57 experimental data using a linear least squares regression technique. The annular two-phase friction pressure drop can be predicted by the new mathematical model requiring only knowledge of the length and diameter of the tube, liquid and vapor mass flow rates, and properties of the working fluid. In addition, the new mathematical model was validated using Foster-Miller & ITP data collected over twelve flights aboard the KC-135 with working fluid R-12 (77 data points), Sundstrand data collected aboard the KC-135 with working fluid R-114 (43 data points) and Zhao and Rezkallah data aboard the KC-135 with working fluid water and air (43 data points). Compared with the LockhartMartinelli model, Wheeler model, Chen model and homogeneous model, the new mathematical model is the optimal model for predicting the two-phase friction pressure drop in annular regimes. The majority of the data falls within +-20% of the proposed correlation and the average error is 12%.



Experimental and Analytical Study of Two-Phase Flow in Zero Gravity

Author : Davood Abdollahian

Publisher :

Page : 147 pages

File Size : 29,21 MB

Release : 1988

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ISBN :

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More effective and efficient thermal transport techniques will be needed for heat rejection from equipment on satellites. Circulating two-phase fluid loops have been suggested and laboratory tested for possible application in the above areas. In comparison to a single-phase loop, the two-phase system operates at considerably smaller flow rates and maintains a tighter temperature control with higher heat transfer coefficients. However, the two-phase fluid flow regimes, pressure gradients and heat transfer coefficients must be evaluated for application in the weightless environment of an orbiting satellite. This projecting studies two-phase flow behavior under zero gravity conditions. The overall objectives of this study were to generate a data base for two-phase pressure drop and the void-quality relationship under simulated zero gravity conditions and to develop analytical models to predict these parameters for bubbly and annular flow. The simulation of zero gravity two-phase flow was achieved by using two immiscible liquids with equal densities to eliminate the buoyancy component. Although this approach does not eliminate the gravity effects, it provides a representation for void distribution in the absence of gravity. The modeling effort is limited to developing relations for the two-phase friction multiplier and void-quality relation under bubbly and annular flow conditions. The bubbly flow model is based on the assumption of local homogeneous conditions between the phases but allows for void distribution in the radial direction. Separated flow conservation equations are used, and single-phase turbulent flow eddy diffusivity relations are employed.







Masters Theses in the Pure and Applied Sciences

Author : Wade H. Shafer

Publisher : Springer Science & Business Media

Page : 391 pages

File Size : 42,47 MB

Release : 2012-12-06

Category : Science

ISBN : 1461524539

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Masters Theses in the Pure and Applied Sciences was first conceived, published, and disseminated by the Center for Information and Numerical Data Analysis and Synthesis (CINDAS)* at Purdue University in 1957, starting its coverage of theses with the academic year 1955. Beginning with Volume 13, the printing and dis semination phases of the activity were transferred to University Microfilms/Xerox of Ann Arbor, Michigan, with the though that such an arrangement would be more beneficial to the academic and general scientific and technical community. After five years of this joint undertaking we had concluded that it was in the interest of all concerned if the printing and distribution of the volumes were handled by an international publishing house to assure improved service and broader dissemi nation. Hence, starting with Volume 18, Masters Theses in the Pure and Applied Sciences has been disseminated on a worldwide basis by Plenum Publishing Corporation of New York, and in the same year the coverage was broadened to include Canadian universities. All back issues can also be ordered from Plenum. We have reported in Volume 37 (thesis year 1992) a total of 12,549 thesis titles from 25 Canadian and 153 United States universities. We are sure that this broader base for these titles reported will greatly enhance the value of this impor tant annual reference work. While Volume 37 reports theses submitted in 1992, on occasion, certain uni versities do report theses submitted in previous years but not reported at the time.



An Analysis of Two-phase Flows in Conditions Relevant to Microgravity

Author : Santiago Arias Calderon

Publisher :

Page : 164 pages

File Size : 22,76 MB

Release : 2013

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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.





Experimental Study on Two-phase Flow Regimes and Frictional Pressure Drop in Mini- and Micro-channels

Author : Korhan Kaan Pehlivan

Publisher :

Page : 0 pages

File Size : 20,10 MB

Release : 2003

Category : Friction

ISBN :

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Book Description

The new experimental test facility was designed in order to generate an experimental database for pressure drop and flow regime maps in mini- and micro-channels. The test facility was equipped with state-of-the-art flow meters and differential pressure transducers. Once the test facility was built, three different circular test sections, with diameters of 3 mm, 1 mm, and 800?m, were used to study the two-phase frictional pressure drop and flow regime transition regions. Most of the experiments for each test section were executed at high local superficial gas velocities (U GS> 10 m/s). The experimental pressure drop data was compared with the homogenous model, the Friedel (1979) model, and the Chisholm (1967) model. The homogenous model showed the most similarities with the data acquired during the course of this experiment, with an average error of 1.2%, 15.6%, and 24.1% for the 3 mm, 1 mm, and 0.8 mm test sections, respectively. However, it was also observed that the standard deviation of the errors increased as the channel diameter decreased. The Friedel (1979) model over-predicted the pressure drop for every test section, while the Chisholm (1967) model mostly underpredicted the pressure drop data. The flow regimes were observed for high gas superficial velocities (U GS e"10 m/s). There were three flow regimes and two transition regions observed in the 3 mm test section, which were in fairly good agreement with the experimental data obtained by Damianides (1987). There were two flow regimes and one transition region observed in both the 1 mm and the 0.8 mm test sections. Finally, the transition region from the annular to the dispersed flow regime in the 0.8 mm test section occurred when the superficial water velocity was approximately 0.9 m/s, which coincides with the results obtained in the 1 mm test tube. A 3CCD analog camera was used for the visualization of images in the present study. (Abstract shortened by UMI.).



Physics of Fluids in Microgravity

Author : Rodolfo Monti

Publisher : CRC Press

Page : 630 pages

File Size : 32,26 MB

Release : 2002-01-10

Category : Science

ISBN : 9780415275811

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Book Description

In a microgravity experiment, the conditions prevalent in fluid phases can be substantially different from those on the ground and can be exploited to improve different processes. Fluid physics research in microgravity is important for the advancement of all microgravity scients: life, material, and engineering. Space flight provides a unique laboratory that allows scientists to improve their understanding of the behaviour of fluids in low gravity, allowing the investigation of phenomena and processes normally masked by the effects of gravity and thus difficult to study on Earth. Physics of Fluids in Microgravity provides a clear view of recent research and progress in the different fields of fluid research in space. The topics presented include bubles and drops dynamics, Maragoni flows, diffustion and thermodiffusion, solidfication,a nd crystal growth. The results obtained so far are, in some cases, to be confirmed by extensive research activities on the International Space station, where basic and applied microgravity experimentation will take place in the years to come.