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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.

Characterization of Drip Emitters and Computing Distribution Uniformity in a Drip Irrigation System at Low Pressure Under Uniform Land Slopes

Dutta, Deba P. 15 January 2010 (has links)
Characteristics of emitters under low pressure are essential for designing drip irrigation systems. Low pressure data for drip emitters are not available from manufacturers. A laboratory test was conducted to evaluate the performance of five types of newly manufactured drip tapes, especially under a low pressure distribution system. The five drip products that were tested were (i) Toro Drip in PC (PCS 1810-18- 100), (ii) T-Tape (TT15-1245-0100), (iii) Mister_LS (MLD-HDT100), (iv) Mister_PS (MLD-1PC 25), and (v) Netafim (Techline CV 560 050). Drip tapes tested in this study have design discharge rates of 4.00 L/hr @ 206.84 Kpa (1.06 gph @ 30 psi), 1.02 L/hr @ 55.16 Kpa (0.27 gph @ 8 psi), 3.785 L/hr @ 172.37 Kpa (1.00 gph @ 25 psi), 3.785 L/hr @172.37 Kpa (1.00 gph @ 25 psi), and 0.984 L/hr @ 206.84 Kpa (0.26 gph @ 20psi), respectively. All of them, except T-Tape, were pressure compensating (PC) emitters; the T-Tape was non-pressure compensating (NPC). For all products, except Toro, the emitter spacing was 0.305 m (12 inches) and for Toro, it was 0.46 m (18 inches). Mister_PS (MLD-1PC 25) was the point source (PS) emitter and all others were line source emitters. Drip products were tested with 15 different operating pressures ranging from 5.97 KPa (0.87 psi) to 344.74 KPa (50.00 psi). From an evaluation of 60 emitters from each product, the Toro brand showed an average uniformity coefficient (UC) of 91.24 %, with a coefficient of variation (Cv) of 0.06, T-Tape drip products showed an average UC of 96.63 % with a Cv of 0.04, Mister_ LS showed an average UC of 93.12 % with a Cv of 0.08, Mister_PS showed an average UC of 96.33 % with a Cv of 0.04, and Netafim showed an average UC of 97.92 % with a Cv of 0.02. Flow rate vs. pressure head (Q-H) curves were also developed for each drip emitter tested. From emitter exponent values it was observed that all of the pressure compensating (PC) products behaved like NPC emitters at low pressures, although they behaved like PC emitters under normal operating pressures. From statistical analysis, it was determined that except for Netafim product, all other tested products were effective under low operating pressures as were under high operating or recommended pressures. Netafim product had no emission under low pressures. Using the measured average emission rate and developed Q-H curves, the distribution uniformities of all products except Netafim were calculated under low pressure ranges of 5.97 KPa (0.87 psi) to 23.88 KPa (3.50 psi ) for different lengths of laterals and under 0%, 1%, 2%

Extinguishment of a Low-pressure Argon Discharge by a Magnetic Field

Criswell, David Russell 01 1900 (has links)
The experiment in this study involves the extinguishment of a low-pressure argon discharge by a magnetic field.


Pluim, Jonathon Douglas 08 September 2009 (has links)
No description available.

Experimental Study and Numerical Simulation of Methane Oxygen Combustion inside a Low Pressure Rocket Motor

kaya, mine 10 August 2016 (has links)
In this thesis, combustion processes in a laboratory-scale methane based low pressure rocket motor (LPRM) is studied experimentally and numerically. Experiments are conducted to measure flame temperatures and chamber temperature and pressure. Single reaction-four species reacting flow of gaseous methane and gaseous oxygen in the combustion chamber is also simulated numerically using a commercial CFD solver based on 2-D, steady-state, viscous, turbulent and compressible flow assumptions. LPRM geometry is simplified to several configurations, i.e. Channel and Combustion Chamber with Nozzle and FWD. Flow in a Bunsen burner is simulated inside Channel geometry in order to validate the reaction model. Grid independence study is also conducted for reacting as well as non-reacting flows. Numerical model is calibrated based on experimental results. Results of the computational model are found in a good agreement with the experimental data after calibrating specific heats of the products. Parametric study is conducted in order to investigate the effects of different mass flow rates and chamber pressures on flow and combustion characteristics of a LPRM to provide insight to future studies.

The study of the interactions between a low pressure steam turbine and axial-radial diffuser

Singh, Gursharanjit January 2015 (has links)
Specific power output from a Low Pressure (LP) steam turbine can be enhanced by increasing the stage efficiency or raising its pressure ratio; both methods are interlinked and must be dealt with together. The latter is achieved by connecting to the exhaust diffuser; space and cost constraints often insist the use of an axial-radial diffuser with high levels of diffusion. The present study aims to investigate the interaction between the last-stage blade and the axial-radial diffuser, which can influence the diffuser performance and thus the total work output from the stage. This work is carried out using CFD simulations of a generic last stage low pressure (LP) turbine and axial-radial exhaust diffuser attached to it. In order to determine the validity of the computational method, the CFD predictions are first compared with data obtained from an experimental test facility. A computational study is then performed for different design configurations of the diffuser and rotor casing shapes. The study focuses on typical flow features such as effects of rotor tip leakage flows and subsequent changes in the rotor-diffuser interactions. The results suggest that the rotor casing shape and diffuser configurations influences the rotor work extraction capability and yields significant improvements in the static pressure recovery.

Hydraulics of IDEal Drip Irrigation Systems

Thompson, Evan J 01 May 2009 (has links)
The hydraulics of IDEal drip irrigation system components were analyzed under controlled laboratory conditions and the results can be applied to the design of IDEal systems. The hydraulic loss coefficient for the lateral-submain connector valves was determined based on laboratory measurements. It was found that the hydraulic loss due to friction in the lay-flat laterals can be accurately estimated with standard friction loss equations using a smaller effective diameter based on the wall thickness and inlet pressure head. The equivalent length barb loss, expressed as an equivalent length of lateral, was calculated for button emitters, as well as for micro-tubes inserted to lengths of 5 and 10 cm. It was concluded that the barb loss is essentially constant over the micro-tube insertion range of 5-10 cm. The head-discharge relationship and coefficient of manufacturer's variation of pre-punched lateral holes (without emitters), button emitters, and micro-tubes were characterized. Finally, several IDEal drip irrigation systems in the Central Rift Valley of Ethiopia were evaluated in the field. Recommendations were given for future research and improvements in the manufacturing, installation, operation, and maintenance of IDEal drip irrigation equipment.


Vinci, Samuel J. 07 June 2011 (has links)
No description available.


SINGH, NAVTEJ 27 May 2005 (has links)
No description available.

The low-pressure partial-melting behaviour of natural boron-bearing metapelites from the Mt Stafford area, Central Australia

Spicer, Esme Marelien 12 1900 (has links)
Thesis (DSc)--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: This study has examined the 3 kbar partial melting behaviour of 4 metapelites collected from the highest grade rocks occurring below the anatectic zone of the Mt Stafford area, Arunta Inlier, central Australia. In this area, metasediments are interpreted to have undergone partial melting within the andalusite stability field, possibly as a result of a lowering of the metapelite solidus by the presence of boron in the rocks. Two of the samples were two mica metapelites (MTS70 and MTS71) that both contained significant quantities of tourmaline and were thus boron enriched. The other two samples were biotite metapelites. One of these rocks contains only a trace of tourmaline (MTS8) and the other is tourmaline free (MTS7). Despite expectations that muscovite in the two mica samples would break down via a subsolidus reaction, muscovite was stable to above 750 C due to the incorporation of Ti, phengitic and possibly F components into its structure. Between 750 and 800 C, muscovite melted out completely via a coupled muscovite + biotite fluid-absent incongruent reaction. In the most mica-rich sample this reaction produced ~ 60 % melt at 800 C. In the biotite metapelites, biotite melting began at a temperature below 800 C and was accompanied by very modest melt production at this low temperature. In contrast to the two mica metapelites, the main pulse of melt production in these samples occurred at a temperature between 850 and 950 C. In both these samples biotite + melt coexistence persisted for a temperature range in excess of 150 C, and in MTS8, biotite was still in the run products at 950 C. The very refractory nature of these evolved biotite compositions is most likely a consequence of both the presence of a Ti buffering phase in the assemblage (ilmenite) and the essentially plagioclase-free nature of the starting compositions. Under the fluid-absent conditions of this study tourmaline is clearly a reactant in the partial melting process, but does not appear to shift the fluid-absent incongruent melting reactions markedly. Neither quartz, nor andalusite was completely consumed in the melting reactions, indicating the metastable persistence of andalusite to higher than the wet solidus temperatures. The assemblages do not change much with increasing temperature and mimic the field relationships. The fluid-absent melting experiments indicated that the main pulse of melting occurred between 850 and 950 °C, significantly higher than indicated by the field evidence of 600 to 675 °C, therefor disequilibrium in the experiments can not be ruled out. The presence of a fluid during partial melting at Mt Stafford provides therefor an explanation of the low temperatures at which melting occurred. / AFRIKAANSE OPSOMMING: Die 3 Mpa vloeistof-vrye gedeeltelike smelting van 4 metapeliete, gekollekteer van die hoogste graad rotse net onder die anatektiese sone van die Mt Stafford area, Arunta inlêer, sentraal Australië, is bestudeer. Die metapeliete van hierdie area word geinterpreteer dat hulle gedeeltelike smelting in die andalusiet stabiliteitsveld ondergaan het, moontlik as 'n resultaat van die verlaging van die metapeliet solidus as gevolg van die teenwoordigheid van boor. Twee van die monsters bestudeer was twee-mika metapeliete (MTS70 en MTS71) met beduidende hoeveelhede toermalyn en is dus boor-verryk. Die ander twee monsters was biotiet metapeliete, waarvan een spoorhoeveelhede toermalyn (MTS8) bevat het en die ander toermalyn vry was (MTS7). Ten spyte van verwagtinge dat muskoviet in die twee mika monsters sou afbreek via 'n subsolidus reaksie, was dit stabiel tot bo 750°C as gevolg van die vervanging van Ti, fengitiese en moontlik F komponente in die muskoviet struktuur. Tussen 750 en 800°C het muskoviet heeltemal gesmelt deur die vloeistof-vrye gekoppelde muskoviet+biotiet reaksie. In die monster met die meeste mika het hierdie reaksie ~ 60 % gesmelt by 80°C en lae hoeveelhede smelt is by hierdie lae temperature geproduseer. In kontras met die twee-mika metapeliete het die hoof puls van smeltproduksie in hierdie monsters plaasgevind tussen 850 en 950°C. In beide hierdie monsters het biotiet+smelt 150°C. Biotiet was steeds ongesmelt in MTS8 by 950°. Die hoë refraktoriese natuur van hierdie biotiet samestellings is hoogs waarskynlik 'n gevolg van die teenwoordigheid van 'n Ti-bufferende fase (ilmenite) en die afwesigheid van plagioklaas in die begin samestellings. Toermalyn is duidelik 'n reaktant in hierdie vloeistof-vrye gedeeltelike smelting studie, maar dra nie beduidend by tot die verlaging van die inkongruente smeltingsreaksies nie. Nie kwarts of andalusiet het heeltemal gesmelt oor die temperatuurreeks nie, wat aandui dat die andalusiet stabiel is by temperature hoër as die nat solidus. Die mineraalverspreidings verander nie veel met verhoging in temperatuur nie en mimiek dus die veld verwantskappe. Die vloeistof-vrye smeltings eksperimente het aangedui dat die hoofpuls van smelting tussen 850 en 950°C geskied het, wat aansienlik hoër is soos aangedui uit die veldgetuienis van 600 tot 675°C, dus is die moontlikheid van disekwilibrium gedurende die eksperimente 'n moontlikheid. Die moontlikheid dat vloeistof teenwoordig was tydens die smeltproses by Mt Stafford verskaf dus 'n oplossing vir die lae temperature wat tydens smelting bereik is.

Caracterização mecânica e metalúrgica das ligas hipoeutéticas de Al-Si utilizadas no processo de fundição da placa reforçadora de solo

Rodrigues, Marcelo Colnaghi January 2016 (has links)
O objetivo deste trabalho é realizar um estudo comparativo das propriedades mecânicas e metalúrgicas em duas peças de ligas de Al-Si produzidas por injeção sob baixa pressão. As peças estudadas referem-se às placas acessórias utilizadas para fornecer sustentação durante a entrada e saída de vaus por carros de combate do Exército Brasileiro, sendo uma nacional e a outra importada. Para a caracterização metalúrgica foram realizados ensaios metalográficos (microscopia óptica e eletrônica). Para a obtenção das propriedades mecânicas foram realizados ensaios de tração, microdureza Vickers e impacto. Quanto aos resultados metalográficos observou-se: na peça nacional, a presença de uma estrutura predominantemente eutética com silício em forma acicular e a fase Al15 (Fe, Mn)3Si2 com morfologia tipo escrita chinesa; na peça importada, foi identificado silício disperso com formato arredondado. A análise da porosidade por gases realizada no canal de alimentação indicou baixos índices para as duas peças. De outro modo, foi observada a presença de porosidades por contração na peça nacional. Nos resultados mecânicos, a peça importada apresentou valores significativamente superiores para a tensão de escoamento e máxima, energia de impacto e deformação. A partir dos resultados obtidos nos ensaios mecânicos realizaram-se simulações no software Solidworks, módulo Simulation, para a determinação da ocorrência de falha quando utilizado por dois carros de combate: o Leopard 1A5, sobre lagartas, e o URUTU, sobre roda. As simulações indicaram falha da peça nacional pelo uso do carro sobre rodas. O resultado em peso da composição química da peça nacional revelou uma liga de alumínio com 12%Si e 0,88%Fe, enquanto a peça importada apresentou 10,38%Si, 0,294%Mg e somente 0,12%Fe. Com a análise dos resultados, conclui-se que os principais fatores da baixa durabilidade da peça nacional foram, preponderantemente, a composição química e a morfologia do silício. / The objective of this research is to perform a comparative study of the mechanical and metallurgical properties in two castings of Al-Si alloys produced by injection under low pressure. The pieces studied refer to soil reinforcing plates used as accessory plates used to provide support during the entry and exit of the Brazilian Army combat vehicles, one national and other imported. For the metallurgical characterization, metallographic analysis by electron and optical microscopy were performed and. To obtain the mechanical properties tensile tests, Vickers microhardness and impact were performed. Regarding the metallographic results, it was observed: In the national piece, the presence of a predominantly eutectic structure with needle-shaped silicon and the Al15(Fe,Mn)3Si2 phase with Chinese writing morphology; In the imported part, dispersed silicon with a rounded shape was identified. The gas porosity analysis performed on the feed channel indicated low indexes for the two pieces.Otherwise, the presence of porosities by contraction in the national piece was observed. In the mechanical results, the imported part presented values significantly higher for the yield stress and maximum, impact energy and deformation. From the results obtained in the mechanical tests it was able to perform simulations on the Solidworks software, Simulation mode, to determine the failures occurrence when used by two battle cars: Leopard 1A5, on caterpillars, and URUTU, on wheels. The simulations indicated failure of the national part by the use of the car on wheels. The weight result of the chemical composition of the domestic part revealed an aluminum alloy with 12% Si and 0.88% Fe, while the imported piece revealed 10.38% Si, 0.294% Mg and only 0.12% Fe. Analyzing the results, it is concluded that the main factors of the low durability of the national piece were, predominantly, the chemical composition and the morphology of the silicon.

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