Browsing by Subject "microgravity"
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Item Analytical and Experimental Study of Annular Two-Phase Flow Friction Pressure Drop Under Microgravity(2011-02-22) Nguyen, Ngoc ThanhTwo-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%.Item Diet, Disease State, and the Space Environment Modify the Intestinal Microbiota and Mucosal Environment via Microbiota-directed Alterations in Colonocyte Signalling(2013-11-25) Ritchie, Lauren EMicrobial dysbiosis and toll-like receptor (TLR) signaling play a role in colonic injury and inflammation. Ulcerative colitis and radiation are known to alter microbiota, and diets containing polyphenols impact bacterial populations. We hypothesized that diet can mitigate dextran sodium sulfate (DSS) colitis (sorghum bran diets containing polyphenols) and space environment-induced alterations (normal iron content) in colonic microbiota and TLR signaling. To test this we utilized two experimental paradigms; DSS-induced colitis (3% DSS, 48-hr, 3 exposures, 2 wk separation), and three models to emulate the space environment: 1) fractionated low linear energy transfer (LET) ? radiation (RAD) (3 Gy) and high Fe diet (IRON) (650 mg/kg), 2) high LET Si particle exposure (50 cGy) and 1/6 G hind limb unloading (HLU), and 3) 13 d spaceflight. Bran diets upregulated proliferation, and repair protein (TFF3 and TGF?) and short chain fatty acid (SCFA) transporter (Slc16a1 and Slc5a8) expression post-DSS. Diet significantly affected 24-hr fecal butyrate production, with Cellulose and Black bran having numerically higher concentrations. Two predominant phyla were identified, Firmicutes and Bacteroidetes, and this ratio was higher in Cellulose DSS. Post DSS#3 the proportion of Bacteroidales, Clostridiales, and Lactobacillales was reduced compared to post DSS#2 for all diets. Black bran non-DSS rats had the highest richness and diversity. Colonic injury negatively correlated with the proportion of Firmicutes, Actinobacteria, and Lactobacillales, and positively correlated with Unknown and Unclassified groups. Bran diets reduced the severity of epithelial injury, maintained fecal butyrate, and prevented microbial dysbiosis and depletion during DSS-induced colitis. IRON+RAD decreased SCFA concentrations. Low and high LET radiation, HLU, IRON and spaceflight increased Bacteroidetes and decreased Firmicutes. HLU and spaceflight increased Clostridiales and decreased Lactobacillales. RAD and IRON+RAD animals had increased Lactobacillales and significantly lower Clostridiales compared to CON and IRON. TLR9 and IL-6 were downregulated by RAD. TLR4, TFF3 and TGF? differentially changed with IRON and spaceflight. Microgravity independently affected the microbiota, regardless of radiation energy or dose. Each environmental insult differentially altered the microbiota and mucosal gene expression, with distinct diet, microgravity, and radiation effects observed. Bran diets mitigated deleterious effects of colitis, maintained barrier integrity, and prevented microbiota dysbiosis.Item Microgravity flow pattern identification using void fraction signals(Texas A&M University, 2005-08-29) Valota, LucaKnowledge 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.Item Microgravity Flow Regime Transition Modeling(2010-07-14) Shephard, Adam M.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.Item The Effects of Multiple Unloading Exposures on Bone Properties in the Femur of Adult Male Rats(2012-07-16) Morgan, Derrick ScottNASA goals include long-term International Space Station (ISS) missions and the ambitious objective of eventually sending astronauts to Mars. Unfortunately, exposure to unloading due to microgravity during spaceflight has been shown to cause detrimental health effects on bone. Therefore, NASA is seeking a ground-based animal model to study the long-term effects of unloading on bone in order to better insure the health and mission capability of astronauts. The hindlimb unloaded (HU) rat model was used to study the effects of multiple unloading exposures and aging on bone properties. Six month old, adult, male Sprague-Dawley rats were separated into the following groups: baseline (BL, sacrificed when received at 6 months age), aging cage control (AC, normal weight-bearing cage activity), 1HU7 (unloaded for 1 month starting at 7 months of age and allowed to recover for 3 months), 1HU10 (normal cage activity until 10 months of age, unloaded for 1 month, recovered for 2 months), and 2HU10 (unloaded for 1 month at 7 months of age, allowed to recover for 2 months, unloaded again for 1 month at 10 months of age, followed by 2 months of recovery). Every 28 days a subset of animals (n=15) were euthanized and both femurs were excised. A peripheral quantitative computed tomography (pQCT) scanner was used to collect densitometric and geometric properties at the right and left femoral neck and at the left femoral midshaft. Mechanical testing (axial and lateral compression of the femoral neck and 3pt bending of the midshaft) was performed at each location and strength indices based on pQCT parameters were calculated. Femoral neck properties decreased due to HU but recovered with respect to increase over HU, BL, and AC by the end of the recovery periods. Femoral midshaft properties were relatively unaffected, but did show slight decreases for older animals at month 10, which recovered during the two month recovery period. Femoral neck geometry exhibited increased endocortical resorption and periosteal apposition of the cortical shell which suggests that trabecular bone plays an important role in how the total bone is affected by HU. Densitometric properties were affected less by HU with respect to BL than were mechanical strength values. Results suggest that femoral neck is more affected by unloading than midshaft, particularly for multiple exposures of unloading. Also, aging does not appear to be a critical factor for bone loss due to HU for either femoral neck or midshaft.