• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 63
  • 7
  • 6
  • 5
  • 2
  • 2
  • 1
  • 1
  • 1
  • 1
  • Tagged with
  • 111
  • 111
  • 80
  • 37
  • 25
  • 25
  • 23
  • 14
  • 13
  • 13
  • 13
  • 12
  • 12
  • 12
  • 11
  • 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.
81

Novel Synthesis Of Transition Metal And Nobel Metal Ion Substituted CeO2 And TiO2 Nanocrystallites For Hydrogen Generation And Electro-Chemical Applications

Singh, Preetam 07 1900 (has links) (PDF)
Ceria based materials have attracted a great deal of interest particularly in area of UV shielding, oxide ion conductivity, solid state electrolyte for fuel cells, automotive exhaust catalysis, water gas shift (WGS) reaction catalysis and also in thermo-chemical water splitting cycles to generate hydrogen. Therefore great deal of efforts was devoted to synthesize nanocrystalline ceria and related materials with different shape and sizes. For example, hierarchically mesostructured doped CeO2 showed potential photvoltic response for solar cell applications. Substitution of lower valent metal ions (Ca2+, Gd3+, Tb3+, Sm3+) in CeO2 enhances oxide ion conductivity for solid oxide fuel cell applications. Eventhough ZrO2 is a nonreducible oxide, CeO2-ZrO2 solid solution has attracted a lot of attention in exhaust catalysis because it exhibited high oxygen storage capacity (OSC). Noble metal ion (M = Pt4+/2+, Au3+, Rh3+, Pd2+ and Ag+) substituted CeO2 (Ce1-xMxO2-δ and Ti1-xMxO2-δ, x = 0.01-0.03) prepared by solution combustion method have shown much higher three-way catalytic property compared same amount of noble metal impregnated to CeO2. Ionically substituted Pt and Au in CeO2 also showed high WGS activity. CeO2-MOx (M= Mn, Fe, Cu, Ni) mixed oxides have shown high activity for hydrogen generation by thermal splitting of water. In chapter 1, we have discussed recent developments on various synthesis strategies of ceria based materials for specific catalytic application. In this thesis, we have explored new route to synthesize Ce1-xMxO2-δ and Ti1-xMxO2-δ (M = transition metal, noble metal) nanocrystallites. Specifically we have addressed the effect of reducible metal ion substitution on the OSC of CeO2 for auto exhaust treatment, hydrogen generation and electro-chemical applications. Controlled synthesis of CeO2 and Ce1-xMxO2-δ (M = Zr, Ti, Y, Pr and Fe) nanocrystallites by hydrothermal method is presented in Chapter 2. The method is based on complexation of metal ion by diethylenetriamine (DETA) or melamine and the simultaneous hydrolysis of metal ion complexes in hydrothermal condition. Size of the crystallites can be controlled by varying the time and temperature of the reaction. 15% Fe3+ ion substituted CeO2 (Ce0.85Fe0.15O2-δ) nanocrystallites have shown higher oxygen storage capacity than Ce0.5Zr0.5O2 at lower temperature. A brief description of material characterization techniques such as powder X-ray diffraction (XRD) and Rietveld refinement of structure, high resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS) is presented. The home-built hydrogen uptake measurement system for OSC study and temperature programmed catalytic reaction system with a quadrupole mass spectrometer and an on-line gas-chromatograph for gas analysis is also described in this chapter. In chapter 3, hydrothermal synthesis of Ce1-xCrxO2+δ (0≤x≤1/3) nanocrystallites is presented. Up to 33% Cr ion substitution in CeO2 could be achieved only by the complexation of Ce(NH4)2(NO3)6 and CrO3 with DETA and simultaneous hydrolysis of the complexes in hydrothermal condition at 200 oC. Powder XRD, XPS and TEM studies confirm that the compound crystallizes in cubic fluorite structure where Ce exist in +4 oxidation state and Cr exist in 4+ and +6 (mixed valance) oxidation states in the ratio of 2: 1. Composition x = 0.33 (Ce2/3Cr1/3O2+δ) showed higher OSC (0.33 mol of [O]) than the maximum OSC observed for CeO2-ZrO2 solid solutions. Formation and higher OSC of Ce2/3Cr1/3O2+δ is attributed to interaction of Ce4+/3+ and Cr3+/4+/6+ redox couples in fluorite structure. The material shows oxygen evolution at ~400 oC in air and hence it is a true oxygen storage material. Oxygen evolution property of Ce0.67Cr0.33O2.11 and subsequent generation of hydrogen by thermal splitting of water is presented in chapter 4. Among the ceria based oxides, Ce0.67Cr0.33O2.11 being the only compound like UO2+δ to have excess oxygen possessing fluorite structure, it releases a large proportion of its lattice oxygen (0.167 M [O]/mole of compound) by heating the material under N2 flow at relatively low temperature (465 oC) directly and almost stoichiometric amount of H2 (0.152 M/Mol of compound) is generated at much lower temperature (65 oC) by thermosplitting of water. The reversible nature of oxygen release and intake of this material is attributed to its fluorite structure and internal coupling between the Ce4+/Ce3+ and Cr4+/6+/Cr3+ redox couples. In chapter 5, we present the hydrothermal synthesis and three-way catalytic activity of Ce1-xRuxO2-δ (0≤x≤0.1) nanocrystallites. Powder XRD, Rietveld refinement, TEM and XPS reveals that the compounds crystallized in fluorite structure where Ru exist in +4 state and Ce in mixed valent (+3, +4) state. Substitution of Ru4+ ion in CeO2 activated the lattice oxygen and Ce0.9Ru0.1O2-δ can reversibly releases 0.42[O]/mol of compound, which is higher than maximum OSC of 0.22 [O]/mol of compound observed for Ce0.50Zr0.50O2. Utilization of higher OSC of Ce1-xRuxO2-δ (x = 0.05 and 0.10) is also shown by low temperature CO oxidation with these catalysts, both in presence/absence of feed oxygen. Ru4+ ion act as active centre for reducing molecules (CO, hydrocarbon ‘HC’) and oxide ion vacancy acts as an active centre for O2 and NOx in this compound. Ce1-xRuxO2-δ not only act as a high oxygen storage material but it also shows high activity towards CO, hydrocarbon ‘HC’ oxidation and NO reduction by CO at low temperature with high N2 selectivity for 3-way catalysis. Study of water gas shift reaction over Ce0.95Ru0.05O2-δ catalyst is presented in chapter 6. The catalyst showed very high WGS activity in terms of high conversion rate (20.5 μmol.g-1.s-1 at 275 oC) and low activation energy (~50.6 kcal/mol). The reason for this seems to be high adsorption propensity of CO on Ru4+ ion and easy extraction of oxygen from lattice to form CO2. This step creates oxide ion vacancy in the catalyst lattice and H2O can adsorb on lattice sites oxygen vacancy and regenerate the lattice by releasing H2. Even in presence of externally fed CO2 and H2, complete conversion of CO to CO2 was observed with 100 % H2 selectivity with Ce0.95Ru0.05O2-δcatalyst in the temperature range of 305-385 oC and no trace of methane formation was observed in this temperature range. Catalyst does not deactivate in long duration on/off WGS reaction cycle because sintering of noble metal or active sites is avoided in this catalyst as Ru4+ ion is substituted in CeO2 lattice. Due to highly acidic nature of Ru4+ ion, surface carbonated formation is prohibited. In chapter 7, synthesis of Ce1-xFexO2-δ (0≤x≤0.45) and Ce0.65Fe0.33Pd0.02O2-δnanocrystallites is presented by sonochemical method. Powder XRD, XPS and TEM studies confirm that the compounds of ~4 nm sizes is crystallized in fluorite structure where Fe is in +3, Ce is in +4 and Pd is in +2 oxidation state. Due to substitution of smaller Fe3+ ion in CeO2, lattice oxygen is activated and Ce0.67Fe0.33O1.835 reversibly releases 0.31[O] up to 600 oC which is higher or comparable to the maximum OSC observed for CeO2-ZrO2 based solid solutions. Due to internal interaction of Pd2+/0(0.89 V), Fe3+/2+ (0.77 V) with Ce4+/3+ (1.61 V) redox couples, Pd ion accelerates the electron transfer from Fe2+ to Ce4+ in Ce0.65Fe0.33Pd0.02O1.815, making it a high oxygen storage material as well as highly active catalyst for CO oxidation and WGS reaction. Activation energy for CO oxidation with O2 over Ce0.65Fe0.33Pd0.02O1.815 is found as low as 38 kJ/mol. CO conversion to CO2 is 100% H2 specific in WGS reaction with these catalysts. Conversion rate was found as high 27.2 μmol.g-1.s-1 and activation energy was found 46.4 kJ/mol for Ce0.65Fe0.33Pd0.02O1.815. Only 1-3% Pt, Pd ion can be substituted in CeO2 is by the solution combustion method. We show that even up to 10% of Pt and Pd ion can be substituted in CeO2 by sonication method. In chapter 8, we present the sonochemical synthesis redox property and methanol electro-oxidation activity of hierarchical Ce1-xMxO2-δ (M = Pt and Pd, 0≤x≤0.1) nanocrystallites. Powder XRD, TEM, SEM and XPS study confirms that hierarchical structure compound crystallize in fluorite structure. Pt exists in +4 state and Ce in mixed valent (+3, +4) state in Ce1-xPtxO2-δ and Pd exist in +2 state and Ce in mixed valent (+3, +4) state in Ce1-xPdxO2-δ. Substitution of Pt and Pd ion in CeO2 activated the lattice oxygen. Hydrogen absorption study show higher H/Pt ratio ~8.1 and H/Pd ratio ~4.2 in respective oxides. Reversible nature of higher oxygen storage capacity or higher H/P, H/Pd ratio is due to interaction of redox couples of Pt4+/2+(0.91V), Pt2+/0(1.18V), Pd2+/0(0.92V) and Ce4+/3+(1.61V). Due to participation of lattice oxygen, Ce0.95Pt0.05O1.95 and Ce0.95Pd0.05O1.90 have shown higher electro-oxidation of methanol compared to same moles of Pt in 5%Pt/C. In chapter 9, we present sonochemical synthesis of Ti1-xPtxO2 (0≤x≤0.1) nanocrystallites: a new high capacity anode material for rechargeable Li ion battery. Continuing our interest in synthesis of nanomaterials, we thought if we can extend the same sonochemical method to synthesize metal ion doped TiO2. Doping of TiO2 with a suitable metal ion where dopant redox potential couples with that of titanium (Ti4+) and act as catalyst for additional reduction of Ti4+ to Ti2+ (Ti4+ →Ti3+→Ti2+) is envisaged here to enhance lithium storage even higher than one Li/TiO2. 10 atom % Pt ion substituted TiO2, Ti0.9Pt0.1O2 nanocrystallites of ~4 nm size was synthesized by sonochemical method using diethylenetriamine (DETA) as complexing agent. Powder XRD, Rietveld refinement, TEM and XPS studies reveal that Ti0.9Pt0.1O2 nanocrystallites crystallize in anatase structure and both Ti and Pt are in 4+ oxidation state. Due to Pt4+ ion substitution in TiO2, reducibility of TiO2 was enhanced and Ti4+ was reduced up to Ti2+ state via coupling of Pt states (Pt4+/Pt2+/Pt0) with Ti states (Ti4+/Ti3+/Ti2+). Galvanostatic cycling of Ti0.9Pt0.1O2 against lithium showed very high capacity of 430 mAhg-1 or exchange of ~1.5Li/Ti0.9Pt0.1O2 which is much higher than the highest capacity of 305 mAhg-1 or insertion of ~0.9Li/TiO2 achieved for TiO2(B) nanowires. In chapter 10, we present the conclusions and critical review on the study of transition metal and noble metal ion substituted CeO2 and TiO2.
82

Supported Copper, Nickel and Copper-Nickel Nanoparticle Catalysts for Low Temperature Water-Gas-Shift Reaction

Lin, Jiann-Horng 19 April 2012 (has links)
No description available.
83

Synthesis and Evaluation of PtW Solid-Solution Nanoparticles and Bioactive Metal-Organic Frameworks / PtW固溶体ナノ粒子および生理活性金属-有機構造体の合成と評価

Kobayashi, Daiya 24 January 2022 (has links)
京都大学 / 新制・論文博士 / 博士(理学) / 乙第13460号 / 論理博第1577号 / 新制||理||1683(附属図書館) / (主査)教授 北川 宏, 教授 吉村 一良, 教授 竹腰 清乃理 / 学位規則第4条第2項該当 / Doctor of Science / Kyoto University / DGAM
84

Characterisation of proton conducting oxide materials for use in reverse water gas shift catalysis and solid oxide fuel cells

De A. L. Viana, Hermenegildo January 2007 (has links)
This study concerned the preparation, characterisation and evaluation of different proton conductors for the Reverse Water Gas Shift Reaction (RWGS) and their evaluation as electrolytes for Solid Oxide Fuel Cells (SOFC) under H₂ and O₂. Materials with both catalytic and conductive properties are of a great interest, as their use in electrocatalytical systems may be very important. Sr₃CaZr₀.₅Ta₁.₅O₈.₇₅ (SCZT), BaCe₀.₉Y₀.₁O₂.₉₅ (BCY10) and Ba₃Ca₁.₁₈Nb₁.₈₂O₈.₇₃ (BCN18), were the initial materials in this study. Thermogravimetric analysis under different atmospheres (5%H₂/Ar, Ar, 5%CO₂, etc), were performed on SCZT and BCN18; with both materials being shown to be stable under reducing and oxidising conditions. Conductivity measurements by two terminal a.c. impedance were also conducted on SCZT and BCN18 under oxidising and reducing atmospheres. As found in literature, BCN18 showed mixed conductivity; with electronic conductivity at high temperatures and pure ionic conductivity below 550ºC, This behaviour was shown in chapter 3, where the change on conduction process was observed upon different gas feeds. Its maximum conductivity values for the different atmospheres were: 8.50x10⁻⁵ S/cm (Dry 5%H₂/Ar at 200ºC), 4.24x10⁻⁴ S/cm (Wet 5%H₂/Ar at 500ºC) and 4.48x10⁻³ S/cm (Air at 900ºC). SCZT proton conducting behaviour was also measured (wet and dry 5%H₂/Ar). Exhibiting an order of magnitude higher in total conductivity upon hydration of the gas feed (σdry=1.01x10⁻⁶ and σwet=1.07x10⁻⁵ at 450ºC). The doping of barium cerate with Zr and Zn by Tao and Irvine, lead to a more stable and easily sinterable BaCe₀.₅Zr₀.₃Y₀.₁₆Zn₀.₀₄O₃ (BCZYZ). Following this work, the introduction of ZnO as a sintering aid to SCZT and BCN18 resulted in Sr₃CaZr₀.₄Ta₁.₅Zn₀.₁O₈.₇₅ (SCZTZ), and Ba₃(Ca₁.₁₈Nb₁.₇₀Zn₀.₁₂)O₈.₅₅ (BCNZ); with higher final densities (above 90% dense). As with BCN18, BCNZ also exhibited mixed conductivity; with higher total conductivity values than BCN18. A maximum of total conductivity of 1.85x10⁻³ S/cm at 900ºC for BCNZ was measured against 6.99x10⁻⁴ S/cm at 900ºC for BCN18. A change in conductivity process was observed when using air or wet 5%H₂/Ar, achieving a maximum of 3.85x10⁻⁴ S/cm at 400ºC when under wet hydrogen. All materials (as powders) have shown catalytic activity for the reverse water gas shift (RWGS) reaction, with the lowest conversion temperature onset at 400ºC for SCZT and a maximum conversion of CO₂ to CO of 42%, with circa 0.52 and 0.59 mmol/s.m² of CO produced at 900ºC by BCN18 and BCZYZ, respectively. No relation between mechanisms for the RWGS and σ for these materials were expected below 10% conversion, as no correlation was found between their activation energies. BCY10 as shown a partial decomposition when exposed to the RWGS reaction, for what BCZYZ After fuel cell testing under H₂ and O₂ both SCZTZ and BCNZ showed mixed conductivity. SCZTZ under different hydrogen partial pressures, exhibited a behaviour close to a pure proton conductor, however, when exposed to both reducing and oxidising conditions, its behaviour did not follow the theoretical values. On the other hand, BCNZ behaves as a pure ionic conductor below 500ºC; with increasing influence of the electronic conductivity on temperature increase. However, as seen for BCNZ conductivity data from 2 terminal a.c. impedance, below 650ºC wet 5%H₂ exhibited the highest conductivity values. This, in additions to the pure ionic conductive behaviour below 400ºC (from the effective ionic transport number), suggests that BCNZ becomes closer to a pure proton conductor with temperature decrease.
85

An Applied Numerical Simulation of Entrained-Flow Coal Gasification with Improved Sub-models

Lu, Xijia 06 August 2013 (has links)
The United States holds the world's largest estimated reserves of coal and is also a net exporter of it. Coal gasification provides a cleaner way to utilize coal than directly burning it. Gasification is an incomplete oxidation process that converts various carbon-based feedstocks into clean synthetic gas (syngas), which can be used to produce electricity and mechanical power with significantly reduced emissions. Syngas can also be used as feedstock for making chemicals and various materials. A Computational Fluid Dynamics (CFD) scheme has been used to simulate the gasification process for many years. However, many sub-models still need to be developed and improved. The objective of this study is to use the improved CFD modeling to understand the thermal-flow behavior and the gasification process and to provide guidance in the design of more efficient and cheaper gasifiers. Fundamental research has been conducted to improve the gasification sub-models associated with the volatile thermal cracking, water-gas-shift (WGS) reaction, radiation effect, low-rank-coal gasification, coal to synthetic-natural-gas (SNG), and ash deposition mechanisms. The improved volatile thermal cracking model includes H2S and COS contents. A new empirical WGS reaction model is developed by matching the result with experimental data. A new coal demoisturization model is developed for evaporating the inherent moisture inside the coal particles during low-rank-coal gasification. An ash deposition model has also been developed. Moreover, the effect of different radiation models on the simulated result has been investigated, and the appropriate models are recommended. Some improved model tests are performed to help modify an industrial entrained-flow gasifier. A two-stage oxygen feeding scheme and a unique water quench design are investigated. For the two-stage oxygen feeding design, both experimental data and CFD predictions verify that it is feasible to reduce the peak temperature and achieve a more uniform temperature distribution in the gasifier by controlling the injection scheme without changing the composition and production rate of the syngas. Furthermore, the CFD simulation can acceptably approximate the thermal-flow and reaction behaviors in the coal gasification process, which can then be used as a preliminary screening tool for improving existing gasifiers’ performance and designing new gasifiers.
86

Technical and Economic Performance Assessment of Pd/Alloy Membrane Reactor Technology Options in the Presence of Uncertainty

Koc, Reyyan 13 April 2012 (has links)
A comprehensive process intensification analysis was performed for the integration of the Pd-based membrane reactor technology into IGCC power plants by designing effective process control strategies as well as identifying and optimally characterizing inherently safe operational conditions to achieve the most favorable economic outcomes. Experimental results indicated that Pd-based composite membranes supported on porous stainless steel tubes, fabricated with H2 permeance values as high as ~50 m3/[m2.h.atm0.5] at 450°C were capable of extra purity H2 production (≥99.99%). Two illustrative process control and performance monitoring cases namely, process regulation and servo mechanism, were considered and quite satisfactory process control was attained by maintaining CO conversion at levels higher than 95% so that the retentate stream could become suitable for high pressure CO2 sequestration. From a process safety standpoint, process parameters and operating conditions were identified and optimized to achieve the target performance level of 98% CO conversion and 95% H2 recovery and at the same time to prevent conditions which could potentially induce hazards and thus compromise process system safety. Furthermore, the average total product cost of a water-gas shift membrane reactor module including manufacturing costs and general expenses was carefully estimated by taking into account the full cost structure and found to be 1464 $/ft2. Moreover, a comprehensive economic assessment was performed for composite Pd/Alloy membrane reactor technology options integrated into IGCC power plants in the presence of market and regulatory uncertainty (possible regulatory action on CO2 emissions) as well as technology risks with the aid of Monte-Carlo simulation techniques. Within such a context, it was demonstrated that an IGCC plant with embedded Pd-based membrane reactors and a stream of revenues coming from electricity and H2 selling (IGCC co-production mode), represented an economically attractive and advantageous option when comparatively assessed against its main competitors namely, an IGCC plant with shift reactors and double stage Selexol units as well as the more traditional supercritical pulverized coal power plant option with an Econamine unit installed for CO2 capture purposes.
87

Catalytic and Electrocatalytic Pathways in Fuel Cells

Vilekar, Saurabh A. 19 April 2010 (has links)
A fundamental understanding of the kinetics and mechanisms of the catalytic reaction steps involved in the process of converting a fuel into hydrogen rich stream suitable for a fuel cell, as well as the electro-catalytic reactions within a fuel cell, is not only conceptually appealing, but could provide a sound basis for the design and development of efficient fuel processor/fuel cell systems. With the quantum chemical calculations on kinetics of elementary catalytic reaction steps becoming rather commonplace, and with increasing information now available in terms of electronic structures, vibration spectra, and kinetic data (activation energy and pre-exponential factors), the stage is set for development of a comprehensive approach. Toward this end, we have developed a framework that can utilize this basic information to develop a comprehensive understanding of catalytic and electrocatalytic reaction networks. The approach is based on the development of Reaction Route (RR) Graphs, which not only represent the reaction pathways pictorially, but are quantitative networks consistent with the Kirchhoff's laws of flow networks, allowing a detailed quantitative analysis by exploiting the analogy with electrical circuits. The result is an unambiguous portrayal of the reaction scheme that lays bare the dominant pathways. Further, the rate-limiting steps are identified rationally with ease, based on comparison of step resistances, as are the dominant pathways via flux analysis. In fact, explicit steady-state overall reaction (OR) rate expression can also be derived in an Ohm's law form, i.e. OR rate = OR motive force/OR resistance of an equivalent electric circuit, which derives directly from the RR graph of its mechanism. This approach is utilized for a detailed analysis of the catalytic and electro-catalytic reaction systems involved in reformer/fuel cell systems. The catalytic reaction systems considered include methanol decomposition, water gas shift, ammonia decomposition, and methane steam reforming, which have been studied mechanistically and kinetically. A detailed analysis of the electro-catalytic reactions in connection to the anode and cathode of fuel cells, i.e. hydrogen electrode reaction and the oxygen reduction reaction, has also been accomplished. These reaction systems have not so far been investigated at this level of detail. The basic underlying principles of the RR graphs and the topological analysis for these reaction systems are discussed.
88

Experiments investigating momentum transfer, turbulence and air-water gas transfer in a wind wave tank

Mukto, Moniz 06 1900 (has links)
A series of laboratory experiments were conducted at three fetches of 4.8, 8.8 and 12.4 m, and at six wind speeds ranging from 4.1 to 9.6 m/s at each fetch in a wind-wave-current research facility. In addition, five surfactant-influenced experiments were conducted at concentrations ranging from 0.1 to 5.0 ppm at a wind speed of 7.9 m/s and a fetch of 4.8 m. The goals were to examine the momentum transfer and to characterize the turbulent flow structure beneath wind waves, and to investigate the relationship between wind waves and the gas transfer rate at the air-water interface. Digital particle image velocimetry (DPIV) was used to measure two-dimensional instantaneous velocity fields beneath the wind waves. The friction velocities and roughness lengths of the coupled boundary layers were used to characterize the flow regime and momentum transfer. The air-side flows were found to be aerodynamically rough and the water-side flows were found to be in transition and then become hydrodynamically smooth as wind speed increased. Airflow separation from the crests of breaking waves may be responsible for making the air-side boundary layer rougher and water-side boundary layer smoother. Momentum transfer was studied by examining the partitioning of the wind stress into the viscous tangential stress and wave-induced stress. It was found that the wave steepness was the most important wind-wave property that controls the momentum transfer in the coupled boundary layers. Two distinct layers were observed in the near-surface turbulence in the presence of a surfactant and three layers in clean water. In the surfactant-influenced experiments, the energy dissipation rate decayed as zeta^(-0.3) in the upper layer and in the lower layer energy dissipation rate decayed as zeta^(-1.0) similar to a wall-layer. For clean experiments, the energy dissipation rate could be scaled using the depth, friction velocity, wave height and phase speed as proposed by Terray et al. (1996) provided that layer based friction velocities were used. In the upper layer, the near-surface turbulence was dominated by wave-induced motions and the dissipation rates decayed as zeta^(-0.2) at all fetches. Below this in the transition layer turbulence was generated by both wave-induced motions and shear currents and the dissipation rate decayed as zeta^(-2.0) at a fetch of 4.8 m. However, at fetches of 8.8 and 12.4 m, the dissipation rate decayed at two different rates; as zeta^(-2.0) in the upper region and as zeta^(-4.0) in the lower region. In the third layer, the dissipation rate decayed as zeta^(-1.0) similar to a wall-layer at a fetch of 4.8 m. Four empirical relationships commonly used to predict the gas transfer rate were evaluated using laboratory measurements. The gas transfer rate was found to correlate most closely with the total mean square wave slope and varied linearly with this parameter. The three other parameterizations using wind speed, wind friction velocity and energy dissipation did not correlate as well. / Water Resources Engineering
89

Experiments investigating momentum transfer, turbulence and air-water gas transfer in a wind wave tank

Mukto, Moniz Unknown Date
No description available.
90

Advanced numerical and experimental transient modelling of water and gas pipeline flows incorporating distributed and local effects.

Kim, Young Il January 2008 (has links)
One of the best opportunities to reduce pipeline accidents and subsequent product loss comes from implementing better pipeline condition assessment and fault detection systems. Transient analysis model based condition assessment is the most promising technique because pressure transients propagate entire system interacting with the pipe and any devices in the system. Transient measurements embody a large amount of information about the physical characteristics of the system. The performance of this technique has its difficulties because a highly accurate transient model is required. Real systems have numerous uncertainties and flow system components that presents a major challenge in the development of precise transient analysis models. To improve transient modelling for the performance of condition assessment, this research undertakes a comprehensive investigation into the transient behaviour of distributed and various local energy loss system components in water and gas pipelines. The dynamic behaviours that have been investigated in this research are the effect of unsteady wall resistance, viscoelasticity effects of polymer pipe, and local energy loss elements including leakages, entrapped air pockets, orifices, and blockages during unsteady pipe flow conditions. The dynamic characteristics of these system components are modelled based on the conservative solution scheme using the governing equations in their conservative form. Use of the conservative form of the equations improves the sensitivity and applicability of transient analysis in both liquid and gas pipeline systems. The numerical model results are compared to laboratory experiments in water and gas pipelines to observe the interaction between transient pressure wave and system components and to verify the proposed models. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1337145 / Thesis( Ph.D.) -- University of Adelaide, School of Civil, Environmental and Mining Engineering 2008

Page generated in 0.0725 seconds