Browsing by Subject "screen"
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Item Development of a screening method for drought tolerance in cotton seedlings(Texas A&M University, 2007-04-25) Longenberger, Polly SuzanneThe key to an efficient screening method is the ability to screen large amounts of plant material in the shortest time possible. Unfortunately, due to the complexity of drought tolerance, a quick and effective screen for this trait has yet to be established. The research reported herein was designed to evaluate a screening method for drought tolerance in cotton (Gossypium hirsutum L.) seedlings. Twenty-one converted race stocks (CRS) and two cultivars were evaluated for seedling drought tolerance on an individual plant basis. CRS are day-sensitive primitive lines derived from various wild race stocks that were converted to day neutrality for use in temperate region plant improvement programs (McCarty et al., 1993). Genotypes were evaluated October - November 2004 and February - March 2005 under greenhouse conditions at the Norman E. Borlaug Center for Southern Crop Improvement, College Station, TX. Seedlings were subjected to three sequential cycles of drought at 15 days after planting (DAP). Drought cycles consisted of withholding water until the moisture content of "indicator" cone-tainers, containing Deltapine 491 (DP 491), had an average volumetric water content of 0.07. Plants were then watered to field capacity and percent survival was recorded after 48 hours. Genotypes differed in their percent survival following three consecutive drought cycles. Drought cycles 2 and 3 did not contribute to the separation of genotypes. DP 491 was the most tolerant genotype evaluated. None of the CRS were more or less tolerant than Acala 1517-99. CRS M-9044-0165 was the most stable genotype across the two experiments.Item Experimental and numerical studies of aerosol penetration through screens(2009-05-15) Han, Tae WonThis research reports the results of experimental and numerical studies performed to characterize aerosol deposition on four different types of commercially available screens (electroformed-wire, woven-wire, welded-wire, and perforated-sheet) over a wide range of Stokes numbers (Stk ~ 0.08 to 20) and Reynolds numbers (ReC ~ 0.5 to 575). The objective of the present research was to use the results of the study to develop models and data that will allow users to predict aerosol deposition on screens. Three-dimensional Computational Fluid Dynamics (CFD) simulations using Fluent (version 6.1.22), as a tool, were undertaken and thus validating the numerical technique and then the result has been compared with the experimental data. For each type of screen, results showed that beginning at critical value of Stokes number where efficiency increased gradually to its maximum value that was almost asymptotic to the areal solidity. It is shown that data obtained from experimental and numerical studies for one particular type of screen would collapse to a single curve if the collection efficiency is expressed in terms of non-dimensional parameters. Correlations characterizing the aerosol deposition process on different types of screens were developed based on the above methodology. The utility of the developed procedure was demonstrated by considering an arbitrary test case, for a particular condition and reconstructing the efficiency curve for the test case. Further, results of the current study were compared with earlier researchers? models (Landahl and Hermann, 1949; Davies, 1952; Suneja and Lee, 1974; Schweers et al., 1994) developed for aerosol deposition on fibrous filters and discussed. These results suggest that the aerosol collection characteristic on different models is different and depends on the nature of the manufacturing process for a typical model (wire or fiber). Finally, the pressure coefficient (Cp) for flow across the screen can be expressed as a function of the Reynolds number (ReC,f) and the fraction of open area (fOA). Correlations expressing the actual relationships were evolved. Additionally, a model was developed to relate pressure coefficient in terms of correction factor (OAfg) and Reynolds number.Item Experimental Measurement of a Model Pipeline Dredge Entrance Loss Coefficient and Modification of a Spreadsheet for Estimating Model Dredge Performance(2014-04-17) Girani, JosephCutter suction dredges are used in a multitude of scenarios, as they are mobile and efficient. One such situation includes dredge sites where debris could be present. In a location with the possibility of debris impeding the cutter suction dredge centrifugal pump, often a screen is placed over the suction line entrance. Although this prevents the inflow of large debris, it increases the entrance loss of the system. The objective of the study is to determine the minor loss coefficient of the Center for Dredging Studies? model cutter suction dredge. Testing was completed over the spectrum of specific gravities (SG) and flow rates achievable in the laboratory. The results show that the minor loss coefficient of the screen is a function of specific gravity and velocity, and varies between approximately 1.4 and 2.4 for the model laboratory dredge. Above the critical velocity the loss coefficient increases nearly linearly with specific gravity, if velocity is held constant. Similarly, if specific gravity is held constant the losses increase linearly with velocity. Additionally, as specific gravity is increased, the screen losses become a weaker function of velocity. Higher losses were observed at large specific gravities, as the flow rate decreased below the critical flow rate of the system. The production losses associated with the screen for the model cutter suction dredge were calculated using the pump characteristic curves. They showed variations between 2.4% and 3.4%, presenting larger production losses at higher pump speeds. An additional aspect of the study concerned comparing the experimental data with that of a widely accepted theoretical method. A previously existing spreadsheet from the Center for Dredging Studies (CDS) was modified to accommodate the minor loss values of the screen, along with the characteristics of the model laboratory dredge and intake losses. The spreadsheet outputs the predicted head loss of the system according to the flow rate and specific gravity, which was compared to the experimental head loss of the study. The theoretical methods matched the experimental results more closely at higher flow rates, achieving approximately 5.7% (no screen) and 6.9% (screen) average error for the suction line at a flow rate of 25.2 L/sec (400 GPM) and 9.4% in the discharge line at a flow rate of 18.9 L/sec (300 GPM). The modified spreadsheet allows the user to input whether or not the screen is present and predict pump performance at a specified specific gravity for a range of flow rates.