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Sample records for hydration kinetics modeling

  1. Experimental and modeling investigation on structure H hydrate formation kinetics

    International Nuclear Information System (INIS)

    Mazraeno, M. Seyfi; Varaminian, F.; Vafaie sefti, M.

    2013-01-01

    Highlights: • Applying affinity model for the formation kinetics of sH hydrate and two stage kinetics. • Performing the experiments of hydrate formation of sH with MCP. • A unique path for the SH hydrate formation. - Abstract: In this work, the kinetics of crystal H hydrate and two stage kinetics formation is modeled by using the chemical affinity model for the first time. The basic idea is that there is a unique path for each experiment by which the crystallization process decays the affinity. The experiments were performed at constant temperatures of 274.15, 275.15, 275.65, 276.15 and 277.15 K. The initial pressure of each experiment is up to 25 bar above equilibrium pressure of sI. Methylcyclohexane (MCH), methylcyclopentane (MCP) and tert-butyl methyl ether (TBME) are used as sH former and methane is used as a help gas. The parameters of the affinity model (A r and t k ) are determined and the results show that the parameter of (A r )/(RT) has not a constant value when temperature changes in each group of experiments. The results indicate that this model can predict experimental data very well at several conditions

  2. Kinetic Hydration Heat Modeling for High-Performance Concrete Containing Limestone Powder

    Directory of Open Access Journals (Sweden)

    Xiao-Yong Wang

    2017-01-01

    Full Text Available Limestone powder is increasingly used in producing high-performance concrete in the modern concrete industry. Limestone powder blended concrete has many advantages, such as increasing the early-age strength, reducing the setting time, improving the workability, and reducing the heat of hydration. This study presents a kinetic model for modeling the hydration heat of limestone blended concrete. First, an improved hydration model is proposed which considers the dilution effect and nucleation effect due to limestone powder addition. A degree of hydration is calculated using this improved hydration model. Second, hydration heat is calculated using the degree of hydration. The effects of water to binder ratio and limestone replacement ratio on hydration heat are clarified. Third, the temperature history and temperature distribution of hardening limestone blended concrete are calculated by combining hydration model with finite element method. The analysis results generally agree with experimental results of high-performance concrete with various mixing proportions.

  3. Hydration kinetics modeling of Portland cement considering the effects of curing temperature and applied pressure

    International Nuclear Information System (INIS)

    Lin Feng; Meyer, Christian

    2009-01-01

    A hydration kinetics model for Portland cement is formulated based on thermodynamics of multiphase porous media. The mechanism of cement hydration is discussed based on literature review. The model is then developed considering the effects of chemical composition and fineness of cement, water-cement ratio, curing temperature and applied pressure. The ultimate degree of hydration of Portland cement is also analyzed and a corresponding formula is established. The model is calibrated against the experimental data for eight different Portland cements. Simple relations between the model parameters and cement composition are obtained and used to predict hydration kinetics. The model is used to reproduce experimental results on hydration kinetics, adiabatic temperature rise, and chemical shrinkage of different cement pastes. The comparisons between the model reproductions and the different experimental results demonstrate the applicability of the proposed model, especially for cement hydration at elevated temperature and high pressure.

  4. The temperature hydration kinetics

    Directory of Open Access Journals (Sweden)

    Mircea Oroian

    2017-07-01

    Full Text Available The aim of this study is to evaluate the hydration kinetics of lentil seeds (Lens culinaris in water at different temperatures (25, 32.5, 40, 55, 70 and 80 °C for assessing the adequacy of models for describing the absorption phenomena during soaking. The diffusion coefficient values were calculated using Fick’s model for spherical and hemispherical geometries and the values were in the range of 10−6 m2/s. The experimental data were fitted to Peleg, Sigmoidal, Weibull and Exponential models. The models adequacy was determined using regression coefficients (R2, root mean square error (RMSE and reduced chi-square (χ2. The Peleg model is the suitable one for predicting the experimental data. Temperature had a positive and significant effect on the water absorption capacities and absorption was an endothermic process.

  5. A rigorous mechanistic model for predicting gas hydrate formation kinetics: The case of CO2 recovery and sequestration

    International Nuclear Information System (INIS)

    ZareNezhad, Bahman; Mottahedin, Mona

    2012-01-01

    Highlights: ► A mechanistic model for predicting gas hydrate formation kinetics is presented. ► A secondary nucleation rate model is proposed for the first time. ► Crystal–crystal collisions and crystal–impeller collisions are distinguished. ► Simultaneous determination of nucleation and growth kinetics are established. ► Important for design of gas hydrate based energy storage and CO 2 recovery systems. - Abstract: A rigorous mechanistic model for predicting gas hydrate formation crystallization kinetics is presented and the special case of CO 2 gas hydrate formation regarding CO 2 recovery and sequestration processes has been investigated by using the proposed model. A physical model for prediction of secondary nucleation rate is proposed for the first time and the formation rates of secondary nuclei by crystal–crystal collisions and crystal–impeller collisions are formulated. The objective functions for simultaneous determination of nucleation and growth kinetics are presented and a theoretical framework for predicting the dynamic behavior of gas hydrate formation is presented. Predicted time variations of CO 2 content, total number and surface area of produced hydrate crystals are in good agreement with the available experimental data. The proposed approach can have considerable application for design of gas hydrate converters regarding energy storage and CO 2 recovery processes.

  6. A unified approach for description of gas hydrate formation kinetics in the presence of kinetic promoters in gas hydrate converters

    International Nuclear Information System (INIS)

    ZareNezhad, Bahman; Varaminian, Farshad

    2013-01-01

    Highlights: • A unified kinetic model for description of promoted and non-promoted gas hydrate formation processes is presented. • Effects of impeller speed, promoter concentration and different kinetic promoters are investigated. • A unique region of gas hydrate formation is identified regarding gas hydrate formation processes. • The proposed model is useful for understanding the behavior of gas hydrate formation processes and design of GTH converters. - Abstract: The kinetic promoters have found wide applications in enhancing the rate of energy conversion and storage via gas hydrate formation processes. Effects of different kinetic promoters such as anionic surfactants sodium dodecyl sulfate (SDS), dodecylbenzene sulfonic acid (DBSA), and sodium dodecyl benzene sulfonate (SDBS); cationic surfactants, Cetyl trimethyl ammonium bromide (CTAB), dodecyl trimethyl ammonium bromide (DTAB) and non-ionic surfactants, alkylpolyglucoside (APG), dodecyl polysaccharide glycoside (DPG), TritonX-100 (TX100) on methane (CH 4 ), ethane (C 2 H 6 ) and propane (C 3 H 8 ) gas hydrate formation processes are investigated in this work. A macroscopic kinetic model based on the time variations of reaction chemical potential is also presented for global description of gas hydrate formation processes. Experimental gas hydrate formation data are employed to validate the proposed kinetic model. Effects of promoter’s concentrations and agitation intensities on the gas consumption profiles are also investigated. A universal correlation and a unified kinetic map have been proposed for macroscopic description of gas hydrate formation kinetics in the presence or absence of kinetic promoters. According to the presented unified kinetic map, a unique region of gas hydrate formation is identified for the first time. For negligible amounts of kinetic promoters, the presented region disappears and approaches to a unique path at high agitation intensities. The presented unified approach is

  7. Mathematical model of the methane replacement by carbon dioxide in the gas hydrate reservoir taking into account the diffusion kinetics

    Science.gov (United States)

    Musakaev, N. G.; Khasanov, M. K.; Rafikova, G. R.

    2018-03-01

    The problem of the replacement of methane in its hydrate by carbon dioxide in a porous medium is considered. The gas-exchange kinetics scheme is proposed in which the intensity of the process is limited by the diffusion of CO2 through the hydrate layer formed between the gas mixture flow and the CH4 hydrate. Dynamics of the main parameters of the process is numerically investigated. The main characteristic stages of the process are determined.

  8. Calcium Aluminate Cement Hydration Model

    Directory of Open Access Journals (Sweden)

    Matusinović, T.

    2011-01-01

    Full Text Available Calcium aluminate cement (AC is a very versatile special cement used for specific applications. As the hydration of AC is highly temperature dependent, yielding structurally different hydration products that continuously alter material properties, a good knowledge of thermal properties at early stages of hydration is essential. The kinetics of AC hydration is a complex process and the use of single mechanisms models cannot describe the rate of hydration during the whole stage.This paper examines the influence of temperature (ϑ=5–20 °C and water-to-cement mass ratio (mH /mAC = 0.4; 0.5 and 1.0 on hydration of commercial iron-rich AC ISTRA 40 (producer: Istra Cement, Pula, Croatia, which is a part of CALUCEM group, Figs 1–3. The flow rate of heat generation of cement pastes as a result of the hydration reactions was measured with differential microcalorimeter. Chemically bonded water in the hydrated cement samples was determined by thermo-gravimetry.Far less heat is liberated when cement and water come in contact for the first time, Fig. 1, than in the case for portland cement (PC. Higher water-to-cement ratio increases the heat evolved at later ages (Fig. 3 due to higher quantity of water available for hydration. A significant effect of the water-to-cement ratio on the hydration rate and hydration degree showed the importance of water as being the limiting reactant that slows down the reaction early. A simplified stoichiometric model of early age AC hydration (eq. (8 based on reaction schemes of principal minerals, nominally CA, C12A7 and C4AF (Table 1, was employed. Hydration kinetics after the induction period (ϑ < 20 °C had been successfully described (Fig. 4 and Table 2 by a proposed model (eq. (23 which simultaneously comprised three main mechanisms: nucleation and growth, interaction at phase boundary, and mass transfer. In the proposed kinetic model the nucleation and growth is proportional to the amount of reacted minerals (eq

  9. Modelling of hydration kinetics of brown and grey African yam bean ...

    African Journals Online (AJOL)

    The Peleg constant (K1) decreased from 6.66 x 10-2 to 1.5 x 10-2 h %-1 for the grey AYB, and from 4.89 x 10-2 to 1.21 x 10-2 h %-1 for the brown AYB seeds as the hydration temperature increased from 30 to 60oC, suggesting a corresponding increase in the initial water absorption rate. The temperature dependence of K1 ...

  10. Mechanism and kinetics of hydrated electron diffusion

    International Nuclear Information System (INIS)

    Tay, Kafui A.; Coudert, Francois-Xavier; Boutin, Anne

    2008-01-01

    Molecular dynamics simulations are used to study the mechanism and kinetics of hydrated electron diffusion. The electron center of mass is found to exhibit Brownian-type behavior with a diffusion coefficient considerably greater than that of the solvent. As previously postulated by both experimental and theoretical works, the instantaneous response of the electron to the librational motions of surrounding water molecules constitutes the principal mode of motion. The diffusive mechanism can be understood within the traditional framework of transfer diffusion processes, where the diffusive step is akin to the exchange of an extramolecular electron between neighboring water molecules. This is a second-order process with a computed rate constant of 5.0 ps -1 at 298 K. In agreement with experiment the electron diffusion exhibits Arrhenius behavior over the temperature range of 298-400 K. We compute an activation energy of 8.9 kJ mol -1 . Through analysis of Arrhenius plots and the application of a simple random walk model it is demonstrated that the computed rate constant for exchange of an excess electron is indeed the phenomenological rate constant associated with the diffusive process

  11. Modeling the kinetics of hydrates formation using phase field method under similar conditions of petroleum pipelines; Modelagem da cinetica de formacao de hidratos utilizando o Modelo do Campo de Fase em condicoes similares a dutos de petroleo

    Energy Technology Data Exchange (ETDEWEB)

    Oliveira, Mabelle Biancardi; Castro, Jose Adilson de; Silva, Alexandre Jose da [Universidade Federal Fluminense (UFF), Volta Redonda, RJ (Brazil). Programa de Pos-Graduacao em Engenharia Metalurgica], e-mails: mabelle@metal.eeimvr.uff.br; adilson@metal.eeimvr.uff.br; ajs@metal.eeimvr.uff.br

    2008-10-15

    Natural hydrates are crystalline compounds that are ice-like formed under oil extraction transportation and processing. This paper deals with the kinetics of hydrate formation by using the phase field approach coupled with the transport equation of energy. The kinetic parameters of the hydrate formation were obtained by adjusting the proposed model to experimental results in similar conditions of oil extraction. The effect of thermal and nucleation conditions were investigated while the rate of formation and morphology were obtained by numerical computation. Model results of kinetics growth and morphology presented good agreement with the experimental ones. Simulation results indicated that super-cooling and pressure were decisive parameters for hydrates growth, morphology and interface thickness. (author)

  12. THERMODYNAMIC MODEL OF GAS HYDRATES

    OpenAIRE

    Недоступ, В. И.; Недоступ, О. В.

    2015-01-01

    The interest to gas hydrates grows last years. Therefore working out of reliable settlement-theoretical methods of definition of their properties is necessary. The thermodynamic model of gas hydrates in which the central place occupies a behaviour of guest molecule in cell is described. The equations of interaction of molecule hydrate formative gas with cell are received, and also an enthalpy and energy of output of molecule from a cell are determined. The equation for calculation of thermody...

  13. The combined effect of thermodynamic promoters tetrahydrofuran and cyclopentane on the kinetics of flue gas hydrate formation

    DEFF Research Database (Denmark)

    Daraboina, Nagu; von Solms, Nicolas

    2015-01-01

    ) hydrate formation using a rocking cell apparatus. Hydrate formation and decomposition kinetics were investigated by constant cooling (hydrate nucleation temperature) and isothermal (hydrate nucleation time) methods. Improved (synergistic) hydrate formation kinetics (hydrate nucleation and growth) were...... of these two promoters is favorable both thermodynamically and kinetically for hydrate formation from flue gas....

  14. Kinetics of the reactions of hydrated electrons with metal complexes

    International Nuclear Information System (INIS)

    Korsse, J.

    1983-01-01

    The reactivity of the hydrated electron towards metal complexes is considered. Experiments are described involving metal EDTA and similar complexes. The metal ions studied are mainly Ni 2+ , Co 2+ and Cu 2+ . Rates of the reactions of the complexes with e - (aq) were measured using the pulse radiolysis technique. It is shown that the reactions of e - (aq) with the copper complexes display unusually small kinetic salt effects. The results suggest long-range electron transfer by tunneling. A tunneling model is presented and the experimental results are discussed in terms of this model. Results of approximate molecular orbital calculations of some redox potentials are given, for EDTA chelates as well as for series of hexacyano and hexaquo complexes. Finally, equilibrium constants for the formation of ternary complexes are reported. (Auth./G.J.P.)

  15. Synergistic kinetic inhibition of natural gas hydrate formation

    DEFF Research Database (Denmark)

    Daraboina, Nagu; Malmos, Christine; von Solms, Nicolas

    2013-01-01

    Rocking cells were used to investigate the natural gas hydrate formation and decomposition in the presence of kinetic inhibitor, Luvicap. In addition, the influence of poly ethylene oxide (PEO) and NaCl on the performance of Luvicap was investigated using temperature ramping and isothermal...

  16. Hydration modeling of calcium sulphates

    NARCIS (Netherlands)

    de Korte, A.C.J.; Brouwers, H.J.H.; Al-Mattarneh, Hashem; Mustapha, Kamal N.; Nuruddin, Muhd Fadhil

    2008-01-01

    The CEMHYD3D model has been extended at the University of Twente in the last ten years [1,2]. At present the cement hydration model is extended for the use of gypsum. Although gypsum was present in the model already, the model was not suitable for high contents of gypsum and did not include the

  17. Hydrate-CASM for modeling Methane Hydrate-Bearing Sediments

    Science.gov (United States)

    De La Fuente Ruiz, M.; Vaunat, J.; Marin Moreno, H.

    2017-12-01

    A clear understanding of the geomechanical behavior of methane hydrate-bearing sediments (MHBS) is crucial to assess the stability of the seafloor and submarine infrastructures to human and natural loading changes. Here we present the Hydrate-CASM, a new elastoplastic constitutive model to predict the geomechanical behavior of MHBS. Our model employs the critical state model CASM (Clay and Sand Model) because of its flexibility in describing the shape of the yield surface and its proven ability to predict the mechanical behavior of sands, the most commercially viable hydrate reservoirs. The model considers MHBS as a deformable elastoplastic continuum, and hydrate-related changes in the stress-strain behavior are predicted by a densification mechanism. The densification attributes the mechanical contribution of hydrate to; a reduction of the available void ratio; a decrease of the swelling line slope; and an increase of the volumetric yield stress. It is described by experimentally derived physical parameters except from the swelling slope coefficient that requires empirical calibration. The Hydrate-CASM is validated against published triaxial laboratory tests performed at different confinement stresses, hydrate saturations, and hydrate morphologies. During the validation, we focused on capturing the mechanical behavior of the host sediment and consider perturbations of the sediment's mechanical properties that could result from the sample preparation. Our model successfully captures the experimentally observed influence of hydrate saturation in the magnitude and trend of the stiffness, shear strength, and dilatancy of MHBS. Hence, we propose that hydrate-related densification changes might be a major factor controlling the geomechanical response of MHBS.

  18. Multicomponent modelling of Portland cement hydration reactions

    NARCIS (Netherlands)

    Ukrainczyk, N.; Koenders, E.A.B.; Van Breugel, K.

    2012-01-01

    The prospect of cement and concrete technologies depends on more in depth understanding of cement hydration reactions. Hydration reaction models simulate the development of the microstructures that can finally be used to estimate the cement based material properties that influence performance and

  19. Flash crystallization kinetics of methane (sI) hydrate in a thermoelectrically-cooled microreactor.

    Science.gov (United States)

    Chen, Weiqi; Pinho, Bruno; Hartman, Ryan L

    2017-09-12

    The crystallization kinetics of methane (sI) hydrate were investigated in a thermoelectrically-cooled microreactor with in situ Raman spectroscopy. Step-wise and precise control of the temperature allowed acquisition of reproducible data within minutes, while the nucleation of methane hydrates can take up to 24 h in traditional batch reactors. The propagation rates of methane hydrate (from 3.1-196.3 μm s -1 ) at the gas-liquid interface were measured for different Reynolds' numbers (0.7-68.9), pressures (30.0-80.9 bar), and sub-cooling temperatures (1.0-4.0 K). The precise measurement of the propagation rates and their subsequent analyses revealed a transition from mixed heat-transfer-crystallization-rate-limited to mixed heat-transfer-mass-transfer-crystallization-rate-limited kinetics. A theoretical model, based on heat transfer, mass transfer, and intrinsic crystallization kinetics, was derived for the first time to understand the non-linear relationship between the propagation rate and sub-cooling temperature. The molecular diffusivity of methane within a stagnant film (ahead of the propagation front) was discovered to follow Stokes-Einstein, while calculated Hatta (0.50-0.68), Lewis (128-207), and beta (0.79-116) numbers also confirmed that the diffusive flux influences crystal growth. Understanding methane hydrate crystal growth is important to the atmospheric, oceanic, and planetary sciences and to energy production, storage, and transportation. Our discoveries could someday advance the science of other multiphase, high-pressure, and sub-cooled crystallizations.

  20. Influence of surfactants on gas-hydrate formation' kinetics in water-oil emulsion

    Science.gov (United States)

    Zemenkov, Yu D.; Shirshova, A. V.; Arinstein, E. A.; Shuvaev, A. N.

    2018-05-01

    The kinetics of gas hydrate formation of propane in a water-oil emulsion is experimentally studied when three types of surfactants (SAA (surface acting agent)) - anionic type emulsifiers - are added to the aqueous phase. It is shown that all three types of surfactants decelerate the growth of the gas-hydrate in the emulsion and can be considered as anti-agglutinating and kinetic low-dose inhibitors. The most effective inhibitor of hydrate formation in water-oil emulsion of SV-102 surfactant was revealed. For comparison, experimental studies of gas-hydrate formation under the same conditions for bulk water have been carried out. It is shown that in bulk water, all the surfactants investigated act as promoters (accelerators) of hydrate formation. A qualitative explanation of the action mechanisms of emulsifiers in the process of gas-hydrate formation in water-oil emulsion is given.

  1. Investigation of Methane Hydrate Formation in a Recirculating Flow Loop: Modeling of the Kinetics and Tests of Efficiency of Chemical Additives on Hydrate Inhibition Étude de la formation de l'hydrate de méthane dans une conduite de recirculation : modélisation de la cinétique et tests d'efficacité d'additifs chimiques inhibiteurs d'hydrates de gaz

    Directory of Open Access Journals (Sweden)

    Peytavy J. L.

    2006-12-01

    Full Text Available Gas hydrates can be formed when light gases, such as the components of natural gas, come into contact with water under particular conditions of temperature and pressure. These solid compounds give rise to problems in natural gas and oil industry because they can plug pipelines and process equipment. To prevent hydrate formation methanol and glycols are commonly and extensively used as inhibitors. Today, the thermodynamic equilibria of hydrate formation are well known, but the kinetics of gas hydrate formation and growth has to be studied in order to find means of controlling these processes and to explore the mechanisms for hydrate formation that follows non equilibrium laws. The present work deals with the kinetics of methane hydrate formation studied in a laboratory loop where the liquid blend saturated with methane is circulated up to a pressure of 75 bar. Pressure is maintained at a constant value during experimental runs by means of methane gas make-up. First the effects of pressure (35-75 bar, liquid velocity (0. 5-3 m/s, liquid cooling temperature ramp (2-15°C/h, and liquid hydrocarbon amount (0-96%, on hydrate formation kinetics are investigated. Then a new method is proposed to predict firstly the thermodynamic conditions (pressure and temperature at the maximum values of the growth rate of methane hydrate and secondly the methane hydrate growth rate. A good agreement is found between calculated and experimental data. Finally the evaluation of the efficiency of some kinetic additives and some surfactants developed to avoid either nucleation or crystal growth and agglomeration of methane hydrates is tested based on the proposed experimental procedure. Les hydrates de gaz des composés légers du gaz naturel se forment lorsque ceux-ci entrent en contact avec l'eau dans certaines conditions de température et de pression. Ces composés solides sont nuisibles pour les industries gazière et pétrolière car des bouchons solides peuvent

  2. Role of Polycarboxylate-ether superplasticizers on cement hydration kinetics and microstructural development

    Directory of Open Access Journals (Sweden)

    Valentini L.

    2018-01-01

    Full Text Available Polycarboxylate-ether (PCE superplasticizers are a fundamental constituent of modern cementbased materials due to their impact on the rheology of the fresh mix and mechanical performance of the hardened material. The effect of PCEs on cement hydration kinetics has been known since their introduction in the early 1980s. However, detailed knowledge of the role played by PCE macromolecules on the basic mechanisms of cement hydration (dissolution, diffusion, precipitation is still lacking. A better understanding of how such mechanisms are influenced by the addition of PCE is no doubt beneficial to the design of novel superplasticizing admixtures. Here, I report on some recent findings about the role of PCE superplasticizers on cement hydration kinetics and microstructural development. The interaction between PCE and C3S pastes was investigated by an ad-hoc kinetic model based on a combination of generalized forms of the Avrami and BNG (Boundary Nucleation and Growth models. The model is used to fit the rate of C-S-H precipitation measured by in-situ X-ray powder diffraction combined with mass balance calculations. The results show that a switch from heterogeneous to homogeneous C-S-H nucleation occurs in the presence of PCEs and that the C-S-H growth rate decreases proportionally to the amount of PCE used. The predicted switch to homogeneous nucleation is in agreement with experimental results obtained by XRD-enhanced micro-tomography imaging, showing that, in the presence of PCE, C-S-H preferentially forms in the pore space rather than at the surface of clinker particles.

  3. Kinetic studies of methane-ethane mixed gas hydrates by neutron diffraction and Raman spectroscopy.

    Science.gov (United States)

    Murshed, M Mangir; Kuhs, Werner F

    2009-04-16

    In situ formations of CH(4)-C(2)H(6) mixed gas hydrates were made using high flux neutron diffraction at 270 K and 5 MPa. For this purpose, a feed gas composition of CH(4) and C(2)H(6) (95 mol% CH(4)) was employed. The rates of transformation of spherical grains of deuterated ice Ih into hydrates were measured by time-resolved neutron powder diffraction on D20 at ILL, Grenoble. Phase fractions of the crystalline constituents were obtained from Rietveld refinements. A concomitant formation of structure type I (sI) and structure type II (sII) hydrates were observed soon after the gas pressure was applied. The initial fast formation of sII hydrate reached its maximum volume and started declining very slowly. The formation of sI hydrate followed a sigmoid growth kinetics that slowed down due to diffusion limitation. This observation has been interpreted in terms of a kinetically favored nucleation of the sII hydrate along with a slow transformation into sI. Both powder diffraction and Raman spectroscopic results suggest that a C(2)H(6)-rich sII hydrate was formed at the early part of the clathration, which slowly decreased to approximately 3% after a reaction of 158 days as confirmed by synchrotron XRD. The final persistence of a small portion of sII hydrate points to a miscibility gap between CH(4)-rich sI and C(2)H(6)-rich sII hydrates.

  4. Investigation of Kinetic Hydrate Inhibition Using a High Pressure Micro Differential Scanning Calorimeter

    DEFF Research Database (Denmark)

    Daraboina, Nagu; Malmos, Christine; von Solms, Nicolas

    2013-01-01

    of hydrate growth. Additionally, hydrate formed in the presence of inhibitor decomposed at higher temperatures compared to pure water, indicating that while hydrate formation is initially inhibited; once hydrates form, they are more stable in the presence of inhibitor. Overall, this method proved a viable......Methane hydrate formation and decomposition were investigated in the presence of the kinetic inhibitor (Luvicap EG) and synergist (polyethylene oxide; PEO) using a high pressure micro-differential scanning calorimeter (HP-μDSC) with both temperature ramping and isothermal temperature programs....... These investigations were performed using small samples in four different capillary tubes in the calorimeter cell. When the isothermal method was employed, it was found that Luvicap EG significantly delays the hydrate nucleation time as compared to water. The results obtained from the ramping method demonstrated...

  5. Experimental and theoretical investigations on the carbon dioxide gas hydrate formation kinetics at the onset of turbidity regarding CO2 capture and sequestration processes

    International Nuclear Information System (INIS)

    ZareNezhad, Bahman; Mottahedin, Mona; Varaminian, Farshad

    2013-01-01

    The carbon dioxide gas hydrate formation kinetics at the onset of turbidity is experimentally and theoretically investigated. It is shown that the time-dependent heterogeneous nucleation and growth kinetics are simultaneously governing the hydrate formation process at the onset of turbidity. A new approach is also presented for determination of gas hydrate-liquid interfacial tension. The CO 2 hydrate-liquid interfacial tension according to the suggested heterogeneous nucleation mechanism is found to be about 12.7 mJ/m 2 . The overall average absolute deviation between predicted and measured CO 2 molar consumption is about 0.61%, indicating the excellent accuracy of the proposed model for studying the hydrate-based CO 2 capture and sequestration processes over wide ranges of pressures and temperatures

  6. An innovative approach to enhance methane hydrate formation kinetics with leucine for energy storage application

    International Nuclear Information System (INIS)

    Veluswamy, Hari Prakash; Kumar, Asheesh; Kumar, Rajnish; Linga, Praveen

    2017-01-01

    Highlights: • Innovative combinatorial hybrid approach to reduce nucleation stochasticity and enhance hydrate growth. • Methane hydrate growth curves are similar in UTR and STR configurations in presence of leucine. • Amalgamation of stirred (STR) and unstirred (UTR) configuration is demonstrated. • Reliable method for scale up and commercial production of Solidified Natural Gas (SNG). - Abstract: Natural gas storage in clathrate hydrates or solidified natural gas (SNG) offers the safest, cleanest and the most compact mode of storage aided by the relative ease in natural gas (NG) recovery with minimal cost compared to known conventional methods of NG storage. The stochastic nature of hydrate nucleation and the slow kinetics of hydrate growth are major challenges that needs to be addressed on the SNG production side. A deterministic and fast nucleation coupled with rapid crystallization kinetics would empower this beneficial technology for commercial application. We propose a hybrid combinatorial approach of methane hydrate formation utilizing the beneficial aspect of environmentally benign amino acid (leucine) as a kinetic promoter by combining stirred and unstirred reactor operation. This hybrid approach is simple, can easily be implemented and scaled-up to develop an economical SNG technology for efficient storage of natural gas on a large scale. Added benefits include the minimal energy requirement during hydrate growth resulting in overall cost reduction for SNG technology.

  7. First Study of Poly(3-Methylene-2-Pyrrolidone) as a Kinetic Hydrate Inhibitor

    DEFF Research Database (Denmark)

    Abrahamsen, Eirin; Heyns, Ingrid Marié; von Solms, Nicolas

    2017-01-01

    Formation of gas hydrates is a problem in the petroleum industry where the gas hydrates can cause blockage of the flowlines. Kinetic hydrate inhibitors (KHIs) are water-soluble polymers, sometimes used in combination synergistically or with non-polymeric synergists, that are used to prevent gas h...... are preferable in KHI polymers as long as they are water-soluble at hydrate-forming temperatures.......Formation of gas hydrates is a problem in the petroleum industry where the gas hydrates can cause blockage of the flowlines. Kinetic hydrate inhibitors (KHIs) are water-soluble polymers, sometimes used in combination synergistically or with non-polymeric synergists, that are used to prevent gas...... hydrate blockages. They have been used in the field successfully since 1995. In this paper, we present the first KHI results for the polymer, poly(3-methylene-2-pyrrolidone) (P(3M2P)), which is structurally similar to poly(N-vinylpyrrolidone) (PVP), one of the first KHIs to be discovered. 3M2P polymers...

  8. Experimental validation of kinetic inhibitor strength on natural gas hydrate nucleation

    DEFF Research Database (Denmark)

    Daraboina, Nagu; Pachitsas, Stylianos; von Solms, Nicolas

    2015-01-01

    The kinetics of natural gas hydrate formation in the presence of dissolved salts (NaCl) and crude oil ( a middle east crude with density 851.5 kg/m3 were investigated by using a standard rocking cell (RC-5) apparatus. The hydrate nucleation temperature was reduced in the presence of NaCl and oil...... management in oil and gas facilities. (C) 2014 Elsevier Ltd. All rights reserved....

  9. A new approach to model mixed hydrates

    Czech Academy of Sciences Publication Activity Database

    Hielscher, S.; Vinš, Václav; Jäger, A.; Hrubý, Jan; Breitkopf, C.; Span, R.

    2018-01-01

    Roč. 459, March (2018), s. 170-185 ISSN 0378-3812 R&D Projects: GA ČR(CZ) GA17-08218S Institutional support: RVO:61388998 Keywords : gas hydrate * mixture * modeling Subject RIV: BJ - Thermodynamics Impact factor: 2.473, year: 2016 https://www.sciencedirect.com/science/article/pii/S0378381217304983

  10. Modelling a deep water oil/gas spill under conditions of gas hydrate formation and decomposition

    International Nuclear Information System (INIS)

    Zheng, L.; Yapa, P.D.

    2000-01-01

    A model for the behavior of oil and gas spills at deepwater locations was presented. Such spills are subjected to pressures and temperatures that can convert gases to gas hydrates which are lighter than water. Knowing the state of gases as they rise with the plume is important in predicting the fate of an oil or gas plume released in deepwater. The objective of this paper was to develop a comprehensive jet/plume model which includes computational modules that simulate the gas hydrate formation/decomposition of gas bubbles. This newly developed model is based on the kinetics of hydrate formation and decomposition coupled with mass and heat transfer phenomena. The numerical model was successfully tested using results of experimental data from the Gulf of Mexico. Hydrate formation and decomposition are integrated with an earlier model by Yapa and Zheng for underwater oil or gas jets and plumes. The effects of hydrate on the behavior of an oil or gas plume was simulated to demonstrate the models capabilities. The model results indicate that in addition to thermodynamics, the kinetics of hydrate formation/decomposition should be considered when studying the behavior of oil and gas spills. It was shown that plume behavior changes significantly depending on whether or not the local conditions force the gases to form hydrates. 25 refs., 4 tabs., 12 figs

  11. Hydration dynamics near a model protein surface

    International Nuclear Information System (INIS)

    Russo, Daniela; Hura, Greg; Head-Gordon, Teresa

    2003-01-01

    The evolution of water dynamics from dilute to very high concentration solutions of a prototypical hydrophobic amino acid with its polar backbone, N-acetyl-leucine-methylamide (NALMA), is studied by quasi-elastic neutron scattering and molecular dynamics simulation for both the completely deuterated and completely hydrogenated leucine monomer. We observe several unexpected features in the dynamics of these biological solutions under ambient conditions. The NALMA dynamics shows evidence of de Gennes narrowing, an indication of coherent long timescale structural relaxation dynamics. The translational water dynamics are analyzed in a first approximation with a jump diffusion model. At the highest solute concentrations, the hydration water dynamics is significantly suppressed and characterized by a long residential time and a slow diffusion coefficient. The analysis of the more dilute concentration solutions takes into account the results of the 2.0M solution as a model of the first hydration shell. Subtracting the first hydration layer based on the 2.0M spectra, the translational diffusion dynamics is still suppressed, although the rotational relaxation time and residential time are converged to bulk-water values. Molecular dynamics analysis shows spatially heterogeneous dynamics at high concentration that becomes homogeneous at more dilute concentrations. We discuss the hydration dynamics results of this model protein system in the context of glassy systems, protein function, and protein-protein interfaces

  12. Modeling the methane hydrate formation in an aqueous film submitted to steady cooling

    Energy Technology Data Exchange (ETDEWEB)

    Avendano-Gomez, J.R. [ESIQIE, Laboratorio de Ingenieria Quimica Ambiental, Mexico (Mexico). Inst. Politecnico Nacional; Garcia-Sanchez, F. [Laboratorio de Termodinamica, Mexico (Mexico). Inst. Mexicano del Petroleo; Gurrola, D.V. [UPIBI, Laboratorio de Diseno de Plantas, Mexico (Mexico). Inst. Politecnico Nacional

    2008-07-01

    Gas hydrates, or clathrate hydrates, are ice-like compounds that results from the kinetic process of crystallization of an aqueous solution supersaturated with a dissolved gas. This paper presented a model that took into account two factors involved in the hydrate crystallization, notably the stochastic nature of crystallization that causes sub-cooling and the heat resulting from the exothermic enthalpy of hydrate formation. The purpose of this study was to model the thermal evolution inside a hydrate forming system which was submitted to an imposed steady cooling. The study system was a cylindrical thin film of aqueous solution at 19 Mpa. The study involved using methane as the hydrate forming molecule. It was assumed that methane was homogeneously dissolved in the aqueous phase. Ethane hydrate was formed through a kinetic process of nucleation and crystallization. In order to predict the onset time of nucleation, the induction time needed to be considered. This paper discussed the probability of nucleation as well as the estimation of the rate of nucleation. It also presented the mathematical model and boundary conditions. These included assumptions and derivation of the model; boundary conditions; initial conditions; and numerical solution of the model equation. It was concluded that the heat source must be considered when investigating crystallization effects. 34 refs., 2 tabs., 2 figs.

  13. A numerical study of natural hydrate formation kinetics in petroleum pipelines by the phase field method: influence of the model parameters; Estudo da cinetica de formacao de hidratos em dutos de petroleo pelo metodo do campo de fase: influencia dos parametros do modelo

    Energy Technology Data Exchange (ETDEWEB)

    Oliveira, Mabelle Biancardi; Castro, Jose Adilson de; Silva, Alexandre Jose da; Ferreira, Alexandre Furtado [Universidade Federal Fluminense (UFF), Volta Redonda, RJ (Brazil). Pos-Graduacao em Engenharia Metalurgica], e-mail: mabelle@metal.eeimvr.uff.br, e-mail: adilson@metal.eeimvr.uff.br, e-mail: ajs@metal.eeimvr.uff.br, e-mail: furtado@metal.eeimvr.uff.br

    2006-07-01

    The objective of this work is to study the influence of the parameters of the phase field model field on the formation of natural hydrates. It was investigated parameters such as superficial tension, effect of the super-cooling, homogeneous and heterogeneous nucleation. The influence of these parameters was analyzed according to morphology of the interface and the rate of formation. The mathematical model to describe the evolution of the natural hydrates formation is based on the simultaneous solution of the phase and energy equations. The finite volume numerical method was used to discretize the governing differential equations. Results of the simulation indicated that the reduction of the superficial tension leads to the increase of the surface rugosity, interface thickness and instability of the interface resulting in a decrease of the rate growth. In order to investigate the nucleation effect of the natural hydrates, two conditions had been simulated a) the random distribution of nuclei: where the evolution of formed hydrates suffered coalescence and the kinetic decreased due to impingement of hydrates regions and b) Nucleation in the pipeline wall, where rough interfaces were observed. (author)

  14. Modelling porewater chemistry in hydrated Portland cement

    International Nuclear Information System (INIS)

    Berner, U.R.

    1987-01-01

    Extensive employment of concrete is foreseen in radioactive waste repositories. A prerequisite for modelling the interactions between concrete and formation waters is characterization of the concrete system. Available experimental data from high pressure squeezing of cement pore-water indicate that, besides the high pH due to alkali hydroxide dissolution, cement composition itself influences the solubility determining solid phases. A model which simulates the hydration of Portland cement assuming complete hydration of the main clinker minerals is presented. The model also includes parameters describing the reactions between the cement and blending agents. Comparison with measured pore-water data generally gives a consistent picture and, as expected, the model gives correct predictions for pure Portland cements. For blended cements, the required additional parameters can, to some extent, be derived from pore-water analysis. 14 references, 1 figure, 4 tables

  15. STEREOCHEMICAL ASPECTS OF HYDRATION OF CARBOHYDRATES IN AQUEOUS-SOLUTIONS .2. KINETIC MEDIUM EFFECTS

    NARCIS (Netherlands)

    GALEMA, SA; BLANDAMER, MJ; ENGBERTS, JBFN

    1992-01-01

    Rate constants for the hydrolysis of 1-benzoyl-3-phenyl-1,2,4-triazole in aqueous solutions of carbohydrates have been measured as a function of molality and nature of added mono- and disaccharides. The kinetic medium effects induced by the carbohydrates originate from hydration sphere overlap

  16. Reservoir Models for Gas Hydrate Numerical Simulation

    Science.gov (United States)

    Boswell, R.

    2016-12-01

    Scientific and industrial drilling programs have now providing detailed information on gas hydrate systems that will increasingly be the subject of field experiments. The need to carefully plan these programs requires reliable prediction of reservoir response to hydrate dissociation. Currently, a major emphasis in gas hydrate modeling is the integration of thermodynamic/hydrologic phenomena with geomechanical response for both reservoir and bounding strata. However, also critical to the ultimate success of these efforts is the appropriate development of input geologic models, including several emerging issues, including (1) reservoir heterogeneity, (2) understanding of the initial petrophysical characteristics of the system (reservoirs and seals), the dynamic evolution of those characteristics during active dissociation, and the interdependency of petrophysical parameters and (3) the nature of reservoir boundaries. Heterogeneity is ubiquitous aspect of every natural reservoir, and appropriate characterization is vital. However, heterogeneity is not random. Vertical variation can be evaluated with core and well log data; however, core data often are challenged by incomplete recovery. Well logs also provide interpretation challenges, particularly where reservoirs are thinly-bedded due to limitation in vertical resolution. This imprecision will extend to any petrophysical measurements that are derived from evaluation of log data. Extrapolation of log data laterally is also complex, and should be supported by geologic mapping. Key petrophysical parameters include porosity, permeability and it many aspects, and water saturation. Field data collected to date suggest that the degree of hydrate saturation is strongly controlled by/dependant upon reservoir quality and that the ratio of free to bound water in the remaining pore space is likely also controlled by reservoir quality. Further, those parameters will also evolve during dissociation, and not necessary in a simple

  17. Point kinetics modeling

    International Nuclear Information System (INIS)

    Kimpland, R.H.

    1996-01-01

    A normalized form of the point kinetics equations, a prompt jump approximation, and the Nordheim-Fuchs model are used to model nuclear systems. Reactivity feedback mechanisms considered include volumetric expansion, thermal neutron temperature effect, Doppler effect and void formation. A sample problem of an excursion occurring in a plutonium solution accidentally formed in a glovebox is presented

  18. Hydration kinetics of cement composites with varying water-cement ratio using terahertz spectroscopy

    Science.gov (United States)

    Ray, Shaumik; Dash, Jyotirmayee; Devi, Nirmala; Sasmal, Saptarshi; Pesala, Bala

    2015-03-01

    Cement is mixed with water in an optimum ratio to form concrete with desirable mechanical strength and durability. The ability to track the consumption of major cement constituents, viz., Tri- and Dicalcium Silicates (C3S, C2S) reacting with water along with the formation of key hydration products, viz., Calcium-Silicate-Hydrate (C-S-H) which gives the overall strength to the concrete and Calcium Hydroxide (Ca(OH)2), a hydration product which reduces the strength and durability, using an efficient technique is highly desirable. Optimizing the amount of water to be mixed with cement is one of the main parameters which determine the strength of concrete. In this work, THz spectroscopy has been employed to track the variation in hydration kinetics for concrete samples with different water-cement ratios, viz., 0.3, 0.4, 0.5 and 0.6. Results show that for the sample with water-cement ratio of 0.3, significant amount of the C3S and C2S remain unreacted even after the initial hydration period of 28 days while for the cement with water-cement ratio of 0.6, most of the constituents get consumed during this stage. Analysis of the formation of Ca(OH)2 has been done which shows that the concrete sample with water-cement ratio of 0.6 produces the highest amount of Ca(OH)2 due to higher consumption of C3S/C2S in presence of excess water which is not desirable. Samples with water-cement ratio of 0.4 and 0.5 show more controlled reaction during the hydration which can imply formation of an optimized level of desired hydration products resulting in a more mechanically strong and durable concrete.

  19. Oxidative desulfurization: kinetic modelling.

    Science.gov (United States)

    Dhir, S; Uppaluri, R; Purkait, M K

    2009-01-30

    Increasing environmental legislations coupled with enhanced production of petroleum products demand, the deployment of novel technologies to remove organic sulfur efficiently. This work represents the kinetic modeling of ODS using H(2)O(2) over tungsten-containing layered double hydroxide (LDH) using the experimental data provided by Hulea et al. [V. Hulea, A.L. Maciuca, F. Fajula, E. Dumitriu, Catalytic oxidation of thiophenes and thioethers with hydrogen peroxide in the presence of W-containing layered double hydroxides, Appl. Catal. A: Gen. 313 (2) (2006) 200-207]. The kinetic modeling approach in this work initially targets the scope of the generation of a superstructure of micro-kinetic reaction schemes and models assuming Langmuir-Hinshelwood (LH) and Eley-Rideal (ER) mechanisms. Subsequently, the screening and selection of above models is initially based on profile-based elimination of incompetent schemes followed by non-linear regression search performed using the Levenberg-Marquardt algorithm (LMA) for the chosen models. The above analysis inferred that Eley-Rideal mechanism describes the kinetic behavior of ODS process using tungsten-containing LDH, with adsorption of reactant and intermediate product only taking place on the catalyst surface. Finally, an economic index is presented that scopes the economic aspects of the novel catalytic technology with the parameters obtained during regression analysis to conclude that the cost factor for the catalyst is 0.0062-0.04759 US $ per barrel.

  20. Oxidative desulfurization: Kinetic modelling

    International Nuclear Information System (INIS)

    Dhir, S.; Uppaluri, R.; Purkait, M.K.

    2009-01-01

    Increasing environmental legislations coupled with enhanced production of petroleum products demand, the deployment of novel technologies to remove organic sulfur efficiently. This work represents the kinetic modeling of ODS using H 2 O 2 over tungsten-containing layered double hydroxide (LDH) using the experimental data provided by Hulea et al. [V. Hulea, A.L. Maciuca, F. Fajula, E. Dumitriu, Catalytic oxidation of thiophenes and thioethers with hydrogen peroxide in the presence of W-containing layered double hydroxides, Appl. Catal. A: Gen. 313 (2) (2006) 200-207]. The kinetic modeling approach in this work initially targets the scope of the generation of a superstructure of micro-kinetic reaction schemes and models assuming Langmuir-Hinshelwood (LH) and Eley-Rideal (ER) mechanisms. Subsequently, the screening and selection of above models is initially based on profile-based elimination of incompetent schemes followed by non-linear regression search performed using the Levenberg-Marquardt algorithm (LMA) for the chosen models. The above analysis inferred that Eley-Rideal mechanism describes the kinetic behavior of ODS process using tungsten-containing LDH, with adsorption of reactant and intermediate product only taking place on the catalyst surface. Finally, an economic index is presented that scopes the economic aspects of the novel catalytic technology with the parameters obtained during regression analysis to conclude that the cost factor for the catalyst is 0.0062-0.04759 US $ per barrel

  1. Modeling chemical kinetics graphically

    NARCIS (Netherlands)

    Heck, A.

    2012-01-01

    In literature on chemistry education it has often been suggested that students, at high school level and beyond, can benefit in their studies of chemical kinetics from computer supported activities. Use of system dynamics modeling software is one of the suggested quantitative approaches that could

  2. Kinetics and efficiency of the hydrated electron-induced dehalogenation by the sulfite/UV process.

    Science.gov (United States)

    Li, Xuchun; Fang, Jingyun; Liu, Guifang; Zhang, Shujuan; Pan, Bingcai; Ma, Jun

    2014-10-01

    Hydrated electron (e(aq)(-)), which is listed among the most reactive reducing species, has great potential for removal and detoxification of recalcitrant contaminants. Here we provided quantitative insight into the availability and conversion of e(aq)(-) in a newly developed sulfite/UV process. Using monochloroacetic acid as a simple e(aq)(-)-probe, the e(aq)(-)-induced dehalogenation kinetics in synthetic and surface water was well predicted by the developed models. The models interpreted the complex roles of pH and S(IV), and also revealed the positive effects of UV intensity and temperature quantitatively. Impacts of humic acid, ferrous ion, carbonate/bicarbonate, and surface water matrix were also examined. Despite the retardation of dehalogenation by electron scavengers, the process was effective even in surface water. Efficiency of the process was discussed, and the optimization approaches were proposed. This study is believed to better understand the e(aq)(-)-induced dehalogenation by the sulfite/UV process in a quantitative manner, which is very important for its potential application in water treatment. Copyright © 2014 Elsevier Ltd. All rights reserved.

  3. Modeling dissociation behaviour of methane hydrate in porous soil media

    Energy Technology Data Exchange (ETDEWEB)

    Jayasinghe, A.G.; Grozic, J.L.H. [Calgary Univ., AB (Canada). Dept. of Civil Engineering

    2008-07-01

    Gas hydrates, or clathrates, exist in the form of crystalline solid structures of hydrogen bonded water molecules where the lattice cages are occupied by guest gas molecules. Methane gas hydrates are the most common. As such, hydrate bearing sediments are considered to be a potential future energy resource. Gas hydrates also function as a source or sink for atmospheric methane, which may influence global warming. The authors emphasized that an understanding of the behaviour of soils containing gas hydrates is necessary in order to develop ways of recovering the vast gas resources that exist in the form of hydrates, particularly since hydrates are also suspected to be a potential factor in the initiation and propagation of submarine slope failures. Gas hydrate dissociation occurs when water and gas are released, resulting in an increase in pore fluid pressure, thereby causing significant reductions in effective stress leading to sediment failure. Dissociation may occur as a result of pressure reductions or increases in temperature. This study focused on the strength and deformation behaviour of hydrate bearing soils associated with temperature induced dissociation. Modeling the dissociation behavior of hydrates in porous soil media involves an understanding of the geomechanics of hydrate dissociation. This paper addressed the issue of coupling the hydrate dissociation problem with the soil deformation problem. A mathematical framework was constructed in which the thermally stimulated hydrate dissociation process in porous soil media under undrained conditions was considered with conduction heat transfer. It was concluded that a knowledge of geomechanical response of hydrate bearing sediments will enable better estimates of benefits and risks associated with the recovery process, thereby ensuring safe and economical exploration. 20 refs., 1 fig., 1 appendix.

  4. Modeling of Hydration, Compressive Strength, and Carbonation of Portland-Limestone Cement (PLC Concrete

    Directory of Open Access Journals (Sweden)

    Xiao-Yong Wang

    2017-01-01

    Full Text Available Limestone is widely used in the construction industry to produce Portland limestone cement (PLC concrete. Systematic evaluations of hydration kinetics, compressive strength development, and carbonation resistance are crucial for the rational use of limestone. This study presents a hydration-based model for evaluating the influences of limestone on the strength and carbonation of concrete. First, the hydration model analyzes the dilution effect and the nucleation effect of limestone during the hydration of cement. The degree of cement hydration is calculated by considering concrete mixing proportions, binder properties, and curing conditions. Second, by using the gel–space ratio, the compressive strength of PLC concrete is evaluated. The interactions among water-to-binder ratio, limestone replacement ratio, and strength development are highlighted. Third, the carbonate material contents and porosity are calculated from the hydration model and are used as input parameters for the carbonation model. By considering concrete microstructures and environmental conditions, the carbon dioxide diffusivity and carbonation depth of PLC concrete are evaluated. The proposed model has been determined to be valid for concrete with various water-to-binder ratios, limestone contents, and curing periods.

  5. Hydration kinetics of some durum and bread wheat varieties grown in south-eastern region of turkey

    International Nuclear Information System (INIS)

    Yildirm, A.

    2017-01-01

    Hydration kinetics of wheat varieties grown in South-Eastern Region of Turkey, covering a temperature range from 25 to 50 degree C was examined. Peleg's model together with Arrhenius relationship were successfully used to evaluate water uptake of some Durum (Local names; Zenit and BurgosBurgos) and Bread (Local names; Dariyel and Karatopak) wheat varieties during soaking at a temperature range of 25-50 degree C. Model was found to be suitable for describing the soaking behaviour of wheat kernels with a coefficient of determination (R2) and Root mean square error (RMSE) greater than 0.9805, and less than 0.051, respectively. The Peleg rate and capacity constants, K1 and K2, were affected by temperature and wheat varieties. Activation energy values of Zenit, BurgosBurgos, Dariyel and Karatopak wheats were found as 39.94, 38.03, 36.25 and 29.54 kJ mol-1, respectively. Zenit wheat was the least hydrated while Karatopak was the most hydrated one due to kernel size and protein content. General equations to describe the water uptake of wheat varieties as a function of soaking time, temperature and initial moisture content were developed. These derived equations can be used for wheat operations such as tempering, mixing, knedding etc. (author)

  6. LLNL Chemical Kinetics Modeling Group

    Energy Technology Data Exchange (ETDEWEB)

    Pitz, W J; Westbrook, C K; Mehl, M; Herbinet, O; Curran, H J; Silke, E J

    2008-09-24

    The LLNL chemical kinetics modeling group has been responsible for much progress in the development of chemical kinetic models for practical fuels. The group began its work in the early 1970s, developing chemical kinetic models for methane, ethane, ethanol and halogenated inhibitors. Most recently, it has been developing chemical kinetic models for large n-alkanes, cycloalkanes, hexenes, and large methyl esters. These component models are needed to represent gasoline, diesel, jet, and oil-sand-derived fuels.

  7. Hydration of Portoguese cements, measurement and modelling of chemical shrinkage

    DEFF Research Database (Denmark)

    Maia, Lino; Geiker, Mette Rica; Figueiras, Joaquim A.

    2008-01-01

    form of the dispersion model. The development of hydration varied between the investigated cements; based on the measured data the degree of hydration after 24 h hydration at 20 C varied between 40 and 50%. This should be taken into account when comparing properties of concrete made from the different......Development of cement hydration was studied by measuring the chemical shrinkage of pastes. Five types of Portuguese Portland cement were used in cement pastes with . Chemical shrinkage was measured by gravimetry and dilatometry. In gravimeters results were recorded automatically during at least...

  8. Quantum kinetic Ising models

    International Nuclear Information System (INIS)

    Augusiak, R; Cucchietti, F M; Lewenstein, M; Haake, F

    2010-01-01

    In this paper, we introduce a quantum generalization of classical kinetic Ising models (KIM), described by a certain class of quantum many-body master equations. Similarly to KIMs with detailed balance that are equivalent to certain Hamiltonian systems, our models reduce to a set of Hamiltonian systems determining the dynamics of the elements of the many-body density matrix. The ground states of these Hamiltonians are well described by the matrix product, or pair entangled projected states. We discuss critical properties of such Hamiltonians, as well as entanglement properties of their low-energy states.

  9. Kinetic study of the hydration of propylene oxide in the presence of heterogeneous catalyst

    Directory of Open Access Journals (Sweden)

    Akyalcin Sema

    2017-01-01

    Full Text Available The kinetics of the hydration of propylene oxide was studied using a pressurized batch reactor for both uncatalyzed and heterogeneously catalyzed reactions. Lewatit MonoPlus M500/HCO3 - was used as heterogeneous catalyst, which showed better performance than Dowex Marathon A/HCO3 -. The effects of the parameters, namely internal and external diffusion resistances, temperature, catalyst loading and mole ratios of reactants, on the reaction rate were studied. The uncatalyzed and heterogeneously catalyzed reactions were proven to follow a series-parallel irreversible homogeneous mechanism. The temperature dependencies of the rate constants appearing in the rate expressions were determined.

  10. Broken rice kernels and the kinetics of rice hydration and texture during cooking.

    Science.gov (United States)

    Saleh, Mohammed; Meullenet, Jean-Francois

    2013-05-01

    During rice milling and processing, broken kernels are inevitably present, although to date it has been unclear as to how the presence of broken kernels affects rice hydration and cooked rice texture. Therefore, this work intended to study the effect of broken kernels in a rice sample on rice hydration and texture during cooking. Two medium-grain and two long-grain rice cultivars were harvested, dried and milled, and the broken kernels were separated from unbroken kernels. Broken rice kernels were subsequently combined with unbroken rice kernels forming treatments of 0, 40, 150, 350 or 1000 g kg(-1) broken kernels ratio. Rice samples were then cooked and the moisture content of the cooked rice, the moisture uptake rate, and rice hardness and stickiness were measured. As the amount of broken rice kernels increased, rice sample texture became increasingly softer (P hardness was negatively correlated to the percentage of broken kernels in rice samples. Differences in the proportions of broken rice in a milled rice sample play a major role in determining the texture properties of cooked rice. Variations in the moisture migration kinetics between broken and unbroken kernels caused faster hydration of the cores of broken rice kernels, with greater starch leach-out during cooking affecting the texture of the cooked rice. The texture of cooked rice can be controlled, to some extent, by varying the proportion of broken kernels in milled rice. © 2012 Society of Chemical Industry.

  11. Inhibition of hydrate formation by kinetic inhibitors. Literature study; Inhibierung von Erdgashydraten durch kinetische Inhibitoren. Literaturstudie

    Energy Technology Data Exchange (ETDEWEB)

    Eberhardt, E.; Meyn, V.; Rahimian, I. [Institut fuer Erdoel- und Erdgasforschung, Clausthal-Zellerfeld (Germany)

    2000-04-01

    The aim of this study was to represent the state-of-the art of the inhibition of gas hydrates. Corresponding to recent publications the kinetic inhibition was considered in particular. Special inhibitors were validated using a set of criteria derived from different experimental test methods. Best results were obtained by the application of terpolymer VC-713 especially in relation to nucleation and crystal growth, followed by PVCap (polyvinylcaprolactame) and THI (threshold hydrate inhibitor), the chemical structure of which is derived from the antifreeze glycopeptids of antarcitc winter flounder. (orig.) [German] Die vorliegende Literaturstudie gibt den derzeitigen Stand der Kenntnis zur Inhibierung von Gashydraten wieder. Entsprechend der neueren Literatur wird insbesondere auf die kinetische Inhibierung eingegangen. Zur Beurteilung der verschiedenen Inhibitoren werden Bewertungskriterien zur Validierung der mit unterschiedlichen Untersuchungsmethoden erzielten experimentellen Ergebnisse angegeben. Anhand dieser Vorgehensweise zeigte sich, dass mit dem Terpolymer VC-713 die besten Ergebnisse, insbesondere im Hinblick auf Keimbildung und Wachstum, erzielt werden konnten. Sehr gute Ergebnisse wurden auch mit dem Polyvinylcaprolactam (PVCap) und den aus den Antigefrierpeptiden der antarktischen Winterflunder abgeleiteten Threshold Hydrate Inhibitoren (THI) erhalten. (orig.)

  12. In situ NMR studies of hydrogen storage kinetics and molecular diffusion in clathrate hydrate at elevated hydrogen pressures

    Energy Technology Data Exchange (ETDEWEB)

    Okuchi, T. [Okayama Univ., Misasa, Tottori (Japan); Moudrakovski, I.L.; Ripmeester, J.A. [National Research Council of Canada, Ottawa, ON (Canada). Steacie Inst. for Molecular Sciences

    2008-07-01

    The challenge of storing high-density hydrogen into compact host media was investigated. The conventional storage scheme where an aqueous solution is frozen with hydrogen gas is too slow for practical use in a hydrogen-based society. Therefore, the authors developed a faster method whereby hydrogen was stored into gas hydrates. The hydrogen gas was directly charged into hydrogen-free, crystalline hydrate powders with partly empty lattices. The storage kinetics and hydrogen diffusion into the hydrate was observed in situ by nuclear magnetic resonance (NMR) in a pressurized tube cell. At pressures up to 20 MPa, the storage was complete within 80 minutes, as observed by growth of stored-hydrogen peak into the hydrate. Hydrogen diffusion within the crystalline hydrate media is the rate-determining step of current storage scheme. Therefore, the authors measured the diffusion coefficient of hydrogen molecules using the pulsed field gradient NMR method. The results show that the stored hydrogen is very mobile at temperatures down to 250 K. As such, the powdered hydrate media should work well even in cold environments. Compared with more prevailing hydrogen storage media such as metal hydrides, clathrate hydrates have the advantage of being free from hydrogen embrittlement, more chemically durable, more environmentally sound, and economically affordable. It was concluded that the powdered clathrate hydrate is suitable as a hydrogen storage media. 22 refs., 4 figs.

  13. Gas hydrate nucleation

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    1997-12-31

    The overall aim of the project was to gain more knowledge about the kinetics of gas hydrate formation especially the early growth phase. Knowledge of kinetics of gas hydrate formation is important and measurements of gas hydrate particle size and concentration can contribute to improve this knowledge. An experimental setup for carrying out experimental studies of the nucleation and growth of gas hydrates has been constructed and tested. Multi wavelength extinction (MWE) was the experimental technique selected for obtaining particle diameter and concentration. The principle behind MWE is described as well as turbidity spectrum analysis that in an initial stage of the project was considered as an alternative experimental technique. Details of the experimental setup and its operation are outlined. The measuring cell consists of a 1 litre horizontal tube sustaining pressures up to 200 bar. Laser light for particle size determination can be applied through sapphire windows. A description of the various auxiliary equipment and of another gas hydrate cell used in the study are given. A computer program for simulation and analysis of gas hydrate experiments is based on the gas hydrate kinetics model proposed by Skovborg and Rasmussen (1993). Initial measurements showed that knowledge of the refractive index of gas hydrates was important in order to use MWE. An experimental determination of the refractive index of methane and natural gas hydrate is described. The test experiments performed with MWE on collectives of gas hydrate particles and experiments with ethane, methane and natural gas hydrate are discussed. Gas hydrate particles initially seem to grow mainly in size and at latter stages in number. (EG) EFP-94; 41 refs.

  14. Gas hydrate nucleation

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    1998-12-31

    The overall aim of the project was to gain more knowledge about the kinetics of gas hydrate formation especially the early growth phase. Knowledge of kinetics of gas hydrate formation is important and measurements of gas hydrate particle size and concentration can contribute to improve this knowledge. An experimental setup for carrying out experimental studies of the nucleation and growth of gas hydrates has been constructed and tested. Multi wavelength extinction (MWE) was the experimental technique selected for obtaining particle diameter and concentration. The principle behind MWE is described as well as turbidity spectrum analysis that in an initial stage of the project was considered as an alternative experimental technique. Details of the experimental setup and its operation are outlined. The measuring cell consists of a 1 litre horizontal tube sustaining pressures up to 200 bar. Laser light for particle size determination can be applied through sapphire windows. A description of the various auxiliary equipment and of another gas hydrate cell used in the study are given. A computer program for simulation and analysis of gas hydrate experiments is based on the gas hydrate kinetics model proposed by Skovborg and Rasmussen (1993). Initial measurements showed that knowledge of the refractive index of gas hydrates was important in order to use MWE. An experimental determination of the refractive index of methane and natural gas hydrate is described. The test experiments performed with MWE on collectives of gas hydrate particles and experiments with ethane, methane and natural gas hydrate are discussed. Gas hydrate particles initially seem to grow mainly in size and at latter stages in number. (EG) EFP-94; 41 refs.

  15. Ab initio modelling of methane hydrate thermophysical properties.

    Science.gov (United States)

    Jendi, Z M; Servio, P; Rey, A D

    2016-04-21

    The key thermophysical properties of methane hydrate were determined using ab initio modelling. Using density functional theory, the second-order elastic constants, heat capacity, compressibility, and thermal expansion coefficient were calculated. A wide and relevant range of pressure-temperature conditions were considered, and the structures were assessed for stability using the mean square displacement and radial distribution functions. Methane hydrate was found to be elastically isotropic with a linear dependence of the bulk modulus on pressure. Equally significant, multi-body interactions were found to be important in hydrates, and water-water interactions appear to strongly influence compressibility like in ice Ih. While the heat capacity of hydrate was found to be higher than that of ice, the thermal expansion coefficient was significantly lower, most likely due to the lower rigidity of hydrates. The mean square displacement gave important insight into stability, heat capacity, and elastic moduli, and the radial distribution functions further confirmed stability. The presented results provide a much needed atomistic thermoelastic characterization of methane hydrates and are essential input for the large-scale applications of hydrate detection and production.

  16. Kinetic of formation for single carbon dioxide and mixed carbon dioxide and tetrahydrofuran hydrates in water and sodium chloride aqueous solution

    NARCIS (Netherlands)

    Sabil, K.M.; Duarte, A.R.C.; Zevenbergen, J.F.; Ahmad, M.M.; Yusup, S.; Omar, A.A.; Peters, C.J.

    2010-01-01

    A laboratory-scale reactor system is built and operated to measure the kinetic of formation for single and mixed carbon dioxide-tetrahydrofuran hydrates. The T-cycle method, which is used to collect the kinetic data, is briefly discussed. For single carbon dioxide hydrate, the induction time

  17. Study of the mechanism of a kinetic inhibitor on the crystallization of methane hydrate; Etude du mecanisme d'action d'un inhibiteur cinetique sur la cristallisation de l'hydrate de methane

    Energy Technology Data Exchange (ETDEWEB)

    Pic, J.St.

    2000-01-14

    In the offshore exploitation of liquid fuels, problems of line plugging often occur, especially due to gas hydrates crystallization. At the present time, operators resort to antifreeze additives, which efficiency is defeated either by harder operating conditions or by a more severe environmental legislation. So research recently shifted towards a new class of 'low dosage inhibitors'. In order to understand the influence of such additives, we designed a high pressure reactor, fitted with a liquid injection device and an in situ turbidimetric sensor. Access to both the particle size distribution of the suspension during the first stages of crystallization, and the total gas consumption, allows us to characterize the kinetics of methane hydration formation. First, we developed an original experimental procedure, which generates an initial 'breeding' of the solution, and thus improves the mastering of nucleation. The induction time then becomes one of the relevant parameters to investigate the performance of inhibitors. Afterwards, we performed a first series of experiments which allowed us to determine the influence of the operating conditions (pressure and stirring) on the evolution of the particle size distribution, in the absence of additives. Then, we pointed out the inhibiting effect of a model kinetic inhibitor, polyvinylpyrrolidone. When dissolved in the solution before crystallization occurs, it increases the induction delay, decreases the gas consumption rate and also slows down the birth of new particles for several hours. On the contrary, when injected in the medium during crystallization, this polymer no more affects the reaction kinetics. At last, we raise the bases for a modelling, taking into account the elementary crystallization processes of nucleation, growth and particles agglomeration. A parametric study has been confronted to the experimental data. It enables us to suggest hypotheses regarding the effect of gas hydrates kinetic

  18. Modeling the influence of limestone addition on cement hydration

    Directory of Open Access Journals (Sweden)

    Ashraf Ragab Mohamed

    2015-03-01

    Full Text Available This paper addresses the influence of using Portland limestone cement “PLC” on cement hydration by characterization of its microstructure development. The European Standard EN 197-1:2011 and Egyptian specification ESS 4756-1/2009 permit the cement to contain up to 20% ground limestone. The computational tools assist in better understanding the influence of limestone additions on cement hydration and microstructure development to facilitate the acceptance of these more economical and ecological materials. μic model has been developed to enable the modeling of microstructural evolution of cementitious materials. In this research μic model is used to simulate both the influence of limestone as fine filler, providing additional surfaces for the nucleation and growth of hydration products. Limestone powder also reacts relatively slow with hydrating cement to form monocarboaluminate (AFmc phase, similar to the mono-sulfoaluminate (AFm phase formed in ordinary Portland cement. The model results reveal that limestone cement has accelerated cement hydration rate, previous experimental results and computer model “cemhyd3d” are used to validate this model.

  19. A Circuit Model of Real Time Human Body Hydration.

    Science.gov (United States)

    Asogwa, Clement Ogugua; Teshome, Assefa K; Collins, Stephen F; Lai, Daniel T H

    2016-06-01

    Changes in human body hydration leading to excess fluid losses or overload affects the body fluid's ability to provide the necessary support for healthy living. We propose a time-dependent circuit model of real-time human body hydration, which models the human body tissue as a signal transmission medium. The circuit model predicts the attenuation of a propagating electrical signal. Hydration rates are modeled by a time constant τ, which characterizes the individual specific metabolic function of the body part measured. We define a surrogate human body anthropometric parameter θ by the muscle-fat ratio and comparing it with the body mass index (BMI), we find theoretically, the rate of hydration varying from 1.73 dB/min, for high θ and low τ to 0.05 dB/min for low θ and high τ. We compare these theoretical values with empirical measurements and show that real-time changes in human body hydration can be observed by measuring signal attenuation. We took empirical measurements using a vector network analyzer and obtained different hydration rates for various BMI, ranging from 0.6 dB/min for 22.7 [Formula: see text] down to 0.04 dB/min for 41.2 [Formula: see text]. We conclude that the galvanic coupling circuit model can predict changes in the volume of the body fluid, which are essential in diagnosing and monitoring treatment of body fluid disorder. Individuals with high BMI would have higher time-dependent biological characteristic, lower metabolic rate, and lower rate of hydration.

  20. Modelling the incongruent dissolution of hydrated cement minerals

    International Nuclear Information System (INIS)

    Berner, U.R.

    1988-01-01

    Hydrated calciumsilicates are the main constituents of hydrated portland cements. Their chemistry will strongly influence the longterm behaviour of a concrete system envisioned in use in radioactive waste repositories. Experimental data show that hydrated calciumsilicates dissolve incongruently, depending on the calcium/silicon ratio of the solid. A model that simulates the incongruent dissolution behaviour of these hydrated calciumsilicates is presented. In the model the hydrated calciumcilicates are represented as a mixture of two congruently soluble components. The dissolution of the particular components is described using the concept of variable activities in the solid state. Each component's activity in the solid state is obtained from a large body of solubility data by applying the Gibbs-Duhem equation for nonideal mixtures. Using this approach a simplified set of equations, which describe the solubility of the components as a function of the calcium/silicon ratio of the solid, is derived. As an application, the degradation of a standard portland cement in pure water and in a carbonate-rich groundwater is modelled. (orig.)

  1. Kinetics of CO2 and methane hydrate formation : an experimental analysis in the bulk phase

    NARCIS (Netherlands)

    He, Y.; Rudolph, E.S.J.; Zitha, P.L.J.; Golombok, M.

    2011-01-01

    Gas resources captured in the form of gas hydrates are by an order of magnitude larger than the resources available from conventional resources. In order to keep the CO2CO2 footprint in the world as small as possible, the idea is to produce methane hydrates and sequestrate CO2CO2 into hydrates in

  2. Experimental study and thermodynamic modeling of CO2 gas hydrate formation in presence of zinc oxide nanoparticles

    International Nuclear Information System (INIS)

    Mohammadi, Mohsen; Haghtalab, Ali; Fakhroueian, Zahra

    2016-01-01

    Highlights: • Nanofluids enhance heat and mass transfer and affect on kinetic and thermodynamics. • The ZnO nanoparticles in liquid affect on kinetics and P-T curve of CO 2 hydrate. • ZnO nanoparticles enhance the growth rate and gas storage in CO 2 hydrate. • A thermodynamic modeling of CO 2 hydrate proposed in the presence of nanoparticles. • Water activity in ZnO + nanofluid was affected by enhancement of the CO 2 solubility. - Abstract: The effect of synthesized zinc oxide (ZnO) nanoparticles was investigated on the kinetic and thermodynamic equilibrium conditions of CO 2 hydrate formation. The amount of the gas consumption was measured and compared for the four sample fluids: pure water, aqueous solution of sodium dodecyl sulfate (SDS), water-based ZnO-nanofluid and water-based ZnO-nanofluid in the presence of SDS (0.001 mass fraction). The time of hydrate growth decreased and the amount of the storage gas enhanced in the presence of nanoparticles. Moreover, the nanoparticles size effect besides the CO 2 solubility enhancement in ZnO-nanofluid led to the reduction of water activity, so that the equilibrium curve of hydrate formation was shifted to higher pressures. A new correlation for Henry’s law constant was obtained using CO 2 -solubility data in ZnO-nanofluid. Finally using this correlation, the water activity was calculated through the Chen–Guo approach to propose a thermodynamic method for prediction of the equilibrium hydrate formation conditions in the presence of the nanoparticles.

  3. Effective-Medium Models for Marine Gas Hydrates, Mallik Revisited

    Science.gov (United States)

    Terry, D. A.; Knapp, C. C.; Knapp, J. H.

    2011-12-01

    Hertz-Mindlin type effective-medium dry-rock elastic models have been commonly used for more than three decades in rock physics analysis, and recently have been applied to assessment of marine gas hydrate resources. Comparisons of several effective-medium models with derivative well-log data from the Mackenzie River Valley, Northwest Territories, Canada (i.e. Mallik 2L-38 and 5L-38) were made several years ago as part of a marine gas hydrate joint industry project in the Gulf of Mexico. The matrix/grain supporting model (one of the five models compared) was clearly a better representation of the Mallik data than the other four models (2 cemented sand models; a pore-filling model; and an inclusion model). Even though the matrix/grain supporting model was clearly better, reservations were noted that the compressional velocity of the model was higher than the compressional velocity measured via the sonic logs, and that the shear velocities showed an even greater discrepancy. Over more than thirty years, variations of Hertz-Mindlin type effective medium models have evolved for unconsolidated sediments and here, we briefly review their development. In the past few years, the perfectly smooth grain version of the Hertz-Mindlin type effective-medium model has been favored over the infinitely rough grain version compared in the Gulf of Mexico study. We revisit the data from the Mallik wells to review assertions that effective-medium models with perfectly smooth grains are a better predictor than models with infinitely rough grains. We briefly review three Hertz-Mindlin type effective-medium models, and standardize nomenclature and notation. To calibrate the extended effective-medium model in gas hydrates, we use a well accepted framework for unconsolidated sediments through Hashin-Shtrikman bounds. We implement the previously discussed effective-medium models for saturated sediments with gas hydrates and compute theoretical curves of seismic velocities versus gas hydrate

  4. Crystallization Kinetics within a Generic Modelling Framework

    DEFF Research Database (Denmark)

    Meisler, Kresten Troelstrup; von Solms, Nicolas; Gernaey, Krist

    2013-01-01

    An existing generic modelling framework has been expanded with tools for kinetic model analysis. The analysis of kinetics is carried out within the framework where kinetic constitutive models are collected, analysed and utilized for the simulation of crystallization operations. A modelling...... procedure is proposed to gain the information of crystallization operation kinetic model analysis and utilize this for faster evaluation of crystallization operations....

  5. Testing antifreeze protein from the longhorn beetle Rhagium mordax as a kinetic gas hydrate inhibitor using a high-pressure micro differential scanning calorimeter

    DEFF Research Database (Denmark)

    Daraboina, Nagu; Perfeldt, Christine Malmos; von Solms, Nicolas

    2015-01-01

    Low dosage kinetic hydrate inhibitors are employed as alternatives to expensive thermodynamic inhibitors to manage the risk of hydrate formation inside oil and gas pipelines. These chemicals need to be tested at appropriate conditions in the laboratory before deployment in the field. A high press...

  6. A coupled THMC model of a heating and hydration laboratory experiment in unsaturated compacted FEBEX bentonite

    Energy Technology Data Exchange (ETDEWEB)

    Zheng, L.; Samper, J.; Montenegro, L.; Fernandez, A.M.

    2010-05-01

    Unsaturated compacted bentonite is foreseen by several countries as a backfill and sealing material in high-level radioactive waste repositories. The strong interplays between thermal (T), hydrodynamic (H), mechanical (M) and chemical (C) processes during the hydration stage of a repository call for fully coupled THMC models. Validation of such THMC models is prevented by the lack of comprehensive THMC experiments and the difficulties of experimental methods to measure accurately the chemical composition of bentonite porewater. We present here a non-isothermal multiphase flow and multicomponent reactive solute transport model for a deformable medium of a heating and hydration experiment performed on a sample of compacted FEBEX bentonite. Besides standard solute transport and geochemical processes, the model accounts for solute cross diffusion and thermal and chemical osmosis. Bentonite swelling is solved with a state-surface approach. The THM model is calibrated with transient temperature, water content and porosity data measured at the end of the experiment. The reactive transport model is calibrated with porewater chemical data derived from aqueous extract data. Model results confirm that thermal osmosis is relevant for the hydration of FEBEX bentonite while chemical osmosis can be safely neglected. Dilution and evaporation are the main processes controlling the concentration of conservative species. Dissolved cations are mostly affected by calcite dissolution-precipitation and cation exchange reactions. Dissolved sulphate is controlled by gypsum/anhydrite dissolution-precipitation. pH is mostly buffered by protonation/deprotonation via surface complexation. Computed concentrations agree well with inferred aqueous extract data at all sections except near the hydration boundary where cation data are affected by a sampling artifact. The fit of Cl{sup -} data is excellent except for the data near the heater. The largest deviations of the model from inferred aqueous

  7. The impact of permafrost-associated microorganisms on hydrate formation kinetics

    Science.gov (United States)

    Luzi-Helbing, Manja; Liebner, Susanne; Spangenberg, Erik; Wagner, Dirk; Schicks, Judith M.

    2016-04-01

    The relationship between gas hydrates, microorganisms and the surrounding sediment is extremely complex: On the one hand, microorganisms producing methane provide the prerequisite for gas hydrate formation. As it is known most of the gas incorporated into natural gas hydrates originates from biogenic sources. On the other hand, as a result of microbial activity gas hydrates are surrounded by a great variety of organic compounds which are not incorporated into the hydrate structure but may influence the formation or degradation process. For gas hydrate samples from marine environments such as the Gulf of Mexico a direct association between microbes and gas hydrates was shown by Lanoil et al. 2001. It is further assumed that microorganisms living within the gas hydrate stability zone produce biosurfactants which were found to enhance the hydrate formation process significantly and act as nucleation centres (Roger et al. 2007). Another source of organic compounds is sediment organic matter (SOM) originating from plant material or animal remains which may also enhance hydrate growth. So far, the studies regarding this relationship were focused on a marine environment. The scope of this work is to extend the investigations to microbes originating from permafrost areas. To understand the influence of microbial activity in a permafrost environment on the methane hydrate formation process and the stability conditions of the resulting hydrate phase we will perform laboratory studies. Thereby, we mimic gas hydrate formation in the presence and absence of methanogenic archaea (e.g. Methanosarcina soligelidi) and other psychrophilic bacteria isolated from permafrost environments of the Arctic and Antarctic to investigate their impact on hydrate induction time and formation rates. Our results may contribute to understand and predict the occurrences and behaviour of potential gas hydrates within or adjacent to the permafrost. Lanoil BD, Sassen R, La Duc MT, Sweet ST, Nealson KH

  8. Wet-gas transport in the Mediterranean Sea. Selection of a combined kinetic hydrate/corrosion inhibitor system

    Energy Technology Data Exchange (ETDEWEB)

    Zettlitzer, M. [RWE Dea AG, Wietze (Germany); Rozengard, N.; Koeckritz, V. [Technical Univ. Freiberg (Germany); Malt, E. [RWE Dea AG (Egypt)

    2007-09-13

    Raw gas will be collected on a platform in the centre of the field. Due to volume and weight constraints, condensing fluids will not be separated from the gas on the platform so that the raw gas will be transported in three-phase mode (gas, water, and condensate) via a 33 km long pipeline to a gas treatment plant. Under the calculated pipeline pressure of about 100 barg, hydrate formation is - according to the outcome of thermodynamic simulations - to be expected at temperatures of 19 C and below while the pipeline may cool down to about 15 C in winter conditions. Due to logistical, environmental and economic reasons, RWE Dea decided to inhibit hydrate formation with kinetic hydrate inhibitors (KHI). As the gas also contains carbon dioxide, certain corrosivity was forecasted and addition of a corrosion inhibitor turned out to be necessary. Laboratory tests were carried out to confirm the feasibility of the concept and to define the required dosage of KHI. Service companies were contacted and several kinetic hydrate and corrosion inhibitors were screened. Experiments with the different chemicals were performed at the University of Freiberg in a high-pressure cell at the pipeline pressure of 100 barg. Hydrate formation was detected by continuous pressure registration during temperature changes and by observation through a glass window. In order to preselect the chemicals, first tests were performed with pure methane. These tests also served for calibration of the equipment with literature data and especially as an indication for the minimum chemical concentration required. A second test series was performed with synthetic gas in a composition close to that of the field gas under consideration in order to verify the results obtained with methane. Finally, the optimum kinetic hydrate inhibitor was identified as well as the required dosage concentration. Compatibility of KHI and corrosion inhibitor was experimentally proven. A further set of kinetic inhibitor tests with

  9. Chemical kinetics and combustion modeling

    Energy Technology Data Exchange (ETDEWEB)

    Miller, J.A. [Sandia National Laboratories, Livermore, CA (United States)

    1993-12-01

    The goal of this program is to gain qualitative insight into how pollutants are formed in combustion systems and to develop quantitative mathematical models to predict their formation rates. The approach is an integrated one, combining low-pressure flame experiments, chemical kinetics modeling, theory, and kinetics experiments to gain as clear a picture as possible of the process in question. These efforts are focused on problems involved with the nitrogen chemistry of combustion systems and on the formation of soot and PAH in flames.

  10. A polyether glycol derived from cashew nutshell as a kinetic inhibitor for methane hydrate formation

    Energy Technology Data Exchange (ETDEWEB)

    Ferreira, Jorge Cesar; Esteves, Pierre M., E-mail: pesteves@iq.ufrj.br [Instituto de Quimica, Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ (Brazil); Teixeira, Adriana [Centro de Pesquisa e Desenvolvimento Leopoldo Americo Miguez de Mello, PETROBRAS, Rio de Janeiro, RJ (Brazil)

    2012-07-01

    The polyether glycol derived from cashew nutshell liquid inhibited the formation of methane hydrate. The polymer proved to be more efficient than the polyvinyl pyrrolidone-poly(N-vinyl) caprolactam (PVP-PVCap) co-polymer under tested conditions (CH{sub 4}, 1470 psi and 4 degree C), being the latter one of the best commercially available hydrate inhibitors. (author)

  11. Carbon dioxide storage in marine sediments - dissolution, transport and hydrate formation kinetics from high-pressure experiments

    Science.gov (United States)

    Bigalke, N. K.; Savy, J. P.; Pansegrau, M.; Aloisi, G.; Kossel, E.; Haeckel, M.

    2009-12-01

    By satisfying thermodynamic framework conditions for CO2 hydrate formation, pressures and temperatures of the deep marine environment are unique assets for sequestering CO2 in clathrates below the seabed. However, feasibility and safety of this storage option require an accurate knowledge of the rate constants governing the speed of physicochemical reactions following the injection of the liquefied gas into the sediments. High-pressure experiments designed to simulate the deep marine environment open the possibility to obtain the required parameters for a wide range of oceanic conditions. In an effort to constrain mass transfer coefficients and transport rates of CO2 in(to) the pore water of marine sediments first experiments were targeted at quantifying the rate of CO2 uptake by de-ionized water and seawater across a two-phase interface. The nature of the interface was controlled by selecting p and T to conditions within and outside the hydrate stability field (HSF) while considering both liquid and gaseous CO2. Concentration increase and hydrate growth were monitored by Raman spectroscopy. The experiments revealed anomalously fast transport rates of dissolved CO2 at conditions both inside and outside the HSF. While future experiments will further elucidate kinetics of CO2 transport and hydrate formation, these first results could have major significance to safety-related issues in the discussion of carbon storage in the marine environment.

  12. Effect of conditioners upon the thermodynamics and kinetics of methane hydrate formation. A preliminary structure-properties relationship study

    Energy Technology Data Exchange (ETDEWEB)

    Di Profio, Pietro; Arca, Simone; Germani, Raimondo; Savelli, Gianfranco

    2005-07-01

    The synthesis and stability of gas hydrates was found to be heavily affected by the presence of small quantities of additives, or conditioners, particularly surfactants. In a recent work, we showed that the enhancement of hydrate formation, both from previously described and newly synthesized surfactants, is probably due to surfactant monomers, rather than micelles, and that the features of hydrate induction time should not be used as a measure of critical micelle concentration. In the present paper, we discuss the results of a structure-properties relationship study in which a preliminary attempt to relate the structural features of several amphiphilic additives to some kinetic and thermodynamic parameters of methane hydrate formation - e.g., induction times, rate of formation, occupancy, etc. - is conducted. According to the present study, it is found that, for a particular conditioner, a reduction of induction time does not correlate to an increase of the formation rate and occupancy, and vice versa. This may be related to the nature of chemical moieties forming a particular amphiphile (e.g., the hydrophobic tail, head group, counterion, etc.). The understanding of the mechanisms by which those moieties play their differential role may be the key tool to the design and synthesis of tailored conditioners. (Author)

  13. Modeling the isochronal crystallization kinetics

    International Nuclear Information System (INIS)

    Sahay, S.S.; Krishnan, Karthik

    2004-01-01

    The classical Johnson-Mehl-Avrami-Kolmogorov (JMAK) model, originally formulated for the isothermal condition, is often used in conjunction with additivity principle for modeling the non-isothermal crystallization kinetics. This approach at times results in significant differences between the model prediction and experimental data. In this article, a modification to this approach has been imposed via an additional functional relationship between the activation energy and heating rate. The methodology has been validated with experimental isochronal crystallization kinetic data in Se 71 Te 20 Sb 9 glass and Ge 20 Te 80 systems. It has been shown that the functional relationship between heating rate and activation energy, ascribed to the reduction in apparent activation energy due to increasing non-isothermality, provides better phenomenological description and therefore improves the prediction capability of the JMAK model under isochronal condition

  14. The hydration of slag, part 1: reaction models for blended cement

    NARCIS (Netherlands)

    Chen, Wei; Brouwers, Jos

    2007-01-01

    Reaction models are proposed to quantify the hydration products and to determine the composition of C–S–H from alkali-activated slags (AAS). Products of the slag hydration are first summarized from observations in literature. The main hydration products include C–S–H, hydrotalcite, hydrogarnet, AFm

  15. The hydration of slag, part 1: reaction models for alkali-activated slag

    NARCIS (Netherlands)

    Chen, Wei; Brouwers, H.J.H.

    2007-01-01

    Reaction models are proposed to quantify the hydration products and to determine the composition of C–S–H from alkali-activated slags (AAS). Products of the slag hydration are first summarized from observations in literature. The main hydration products include C–S–H, hydrotalcite, hydrogarnet, AFm

  16. Kinetics of the reaction of hydrated lime with SO{sub 2} at low temperatures: effects of the presence of CO{sub 2}, O{sub 2}, and NOx

    Energy Technology Data Exchange (ETDEWEB)

    Liu, C.F.; Shih, S.M. [National Taiwan University, Taipei (Taiwan). Dept. of Chemical Engineering

    2008-12-15

    The effects of the presence Of CO{sub 2}, O{sub 2}, and NOx in the flue gas on the kinetics of the sulfation of hydrated lime at low temperatures were studied using a differential fixed-bed reactor. When O{sub 2} and NOx were not present together the reaction kinetics was about the same as that under gas mixtures containing SO{sub 2}, H{sub 2}O, and N2 only. When both O{sub 2} and NOx were present, sulfation of hydrated lime was greatly enhanced, forming a large amount of calcium sulfate in addition to calcium sulfite. Sulfation of hydrated lime was well described by the surface coverage model, despite the gas-phase conditions being different. Relative humidity is the major factor affecting the reaction, and its effect was more marked when both O{sub 2} and NOx were present. The kinetic model equations obtained in this work can be used to describe the sulfation of hydrated lime in the low-temperature dry and semidry flue gas desulfurization processes with or without an upstream NOx removal unit.

  17. SOLVENT EFFECTS ON THE HYDRATION OF CYCLOHEXENE CATALYZED BY A STRONG ACID ION-EXCHANGE RESIN .2. EFFECT OF SULFOLANE ON THE REACTION-KINETICS

    NARCIS (Netherlands)

    PANNEMAN, HJ; BEENACKERS, AACM

    The kinetics of the' hydration of cyclohexene, catalyzed by a strong acid ion-exchange resin, have been studied in a packed bed reactor at temperatures between 353 and 413 K and a pressure of 20 bar. The kinetic rate constants were measured as a function of temperature and solvent composition (0-90

  18. A kinetic model for hydrodesulfurisation

    Energy Technology Data Exchange (ETDEWEB)

    Sau, M.; Narasimhan, C.S.L.; Verma, R.P. [Indian Oil Corporation Limited, Research and Development Centre, Faridabad (India)

    1997-07-01

    Due to stringent environmental considerations and related insistence on low sulfur fuels, hydrodesulfurisation has emerged as an important component of any refining scheme globally. The process is used ranging from Naphta/Kerosine hydrotreating to heavy oil hydrotreating. Processes such as Deep gas oil desulfurisation aiming at reduction of sulfur levels to less than 500 ppm have emerged as major players in the scenario. Hydrodesulfurisation (HDS) involves parallel desulfurisation of different organo-sulfur compounds present in the complex petroleum mixtures. In order to design, monitor, optimise and control the HDS reactor, it is necessary to have a detailed, yet simple model which follows the reaction chemistry accurately. In the present paper, a kinetic model is presented for HDS using continuum theory of lumping. The sulfur distribution in the reaction mixture is treated as continuum and parallel reaction networks are devised for kinetic modelling using continuum theory of lumping approach. The model based on the above approach follows the HDS chemistry reasonably well and hence the model parameters are almost feed invariant. Methods are also devised to incorporate heat and pressure effects into the model. The model has been validated based on commercial kero-HDS data. It is found that the model predictions agree with the experimental/commercial data. 17 refs.

  19. Kinetic modelling of enzymatic starch hydrolysis

    NARCIS (Netherlands)

    Bednarska, K.A.

    2015-01-01

    Kinetic modelling of enzymatic starch hydrolysis – a summary

    K.A. Bednarska

    The dissertation entitled ‘Kinetic modelling of enzymatic starch hydrolysis’ describes the enzymatic hydrolysis and kinetic modelling of liquefaction and saccharification of wheat starch.

  20. Role of excipients in hydrate formation kinetics of theophylline in wet masses studied by near-infrared spectroscopy

    DEFF Research Database (Denmark)

    Jørgensen, Anna C; Airaksinen, Sari; Karjalainen, Milja

    2004-01-01

    . Anhydrous theophylline was chosen as the hydrate-forming model drug compound and two excipients, silicified microcrystalline cellulose (SMCC) and alpha-lactose monohydrate, with different water absorbing properties, were used in formulation. An early stage of wet massing was studied with anhydrous...... theophylline and its 1:1 (w/w) mixtures with alpha-lactose monohydrate and SMCC with 0.1g/g of purified water. The changes in the state of water were monitored using near-infrared spectroscopy, and the conversion of the crystal structure was verified using X-ray powder diffraction (XRPD). SMCC decreased...... the hydrate formation rate by absorbing water, but did not inhibit it. The results suggest that alpha-lactose monohydrate slightly increased the hydrate formation rate in comparison with a mass comprising only anhydrous theophylline....

  1. A constitutive mechanical model for gas hydrate bearing sediments incorporating inelastic mechanisms

    KAUST Repository

    Sánchez, Marcelo

    2016-11-30

    Gas hydrate bearing sediments (HBS) are natural soils formed in permafrost and sub-marine settings where the temperature and pressure conditions are such that gas hydrates are stable. If these conditions shift from the hydrate stability zone, hydrates dissociate and move from the solid to the gas phase. Hydrate dissociation is accompanied by significant changes in sediment structure and strongly affects its mechanical behavior (e.g., sediment stiffenss, strength and dilatancy). The mechanical behavior of HBS is very complex and its modeling poses great challenges. This paper presents a new geomechanical model for hydrate bearing sediments. The model incorporates the concept of partition stress, plus a number of inelastic mechanisms proposed to capture the complex behavior of this type of soil. This constitutive model is especially well suited to simulate the behavior of HBS upon dissociation. The model was applied and validated against experimental data from triaxial and oedometric tests conducted on manufactured and natural specimens involving different hydrate saturation, hydrate morphology, and confinement conditions. Particular attention was paid to model the HBS behavior during hydrate dissociation under loading. The model performance was highly satisfactory in all the cases studied. It managed to properly capture the main features of HBS mechanical behavior and it also assisted to interpret the behavior of this type of sediment under different loading and hydrate conditions.

  2. Influence of polymeric excipient properties on crystal hydrate formation kinetics of caffeine in aqueous slurries.

    Science.gov (United States)

    Gift, Alan D; Southard, Leslie A; Riesberg, Amanda L

    2012-05-01

    The influence of polymeric excipients on the hydrate transformation of caffeine (CAF) was studied. Anhydrous CAF was added to aqueous solutions containing different additives and the transformation to the hydrate form was monitored using in-line Raman spectroscopy. Various properties of two known inhibitors of CAF hydrate formation, polyacrylic acid (PAA) and polyvinyl alcohol (PVA), were investigated. For inhibition by PAA, a pH dependence was observed: at low pH, the inhibition was greatest, whereas no inhibitory effects were observed at pH above 6.5. For PVA, grades with high percent hydrolysis were the most effective at inhibiting the transformation. In addition, PVA with higher molecular weight showed slightly more inhibition than the shorter chain PVA polymers. A variety of other hydroxyl containing compounds were examined but none inhibited the CAF anhydrate-to-hydrate transformation. The observed inhibitory effects of PAA and PVA are attributed to the large number of closely spaced hydrogen bond donating groups of the polymer molecule, which can interact with the CAF hydrate crystal. Copyright © 2012 Wiley Periodicals, Inc.

  3. Modelling the effect of hydration on skin conductivity.

    Science.gov (United States)

    Davies, L; Chappell, P; Melvin, T

    2017-08-01

    Electrical signals are recorded from and sent into the body via the skin in a number of applications. In practice, skin is often hydrated with liquids having different conductivities so a model was produced in order to determine the relationship between skin impedance and conductivity. A model representing the skin was subjected to a variety of electrical signals. The parts of the model representing the stratum corneum were given different conductivities to represent different levels of hydration. The overall impedance and conductivity of the cells did not vary at frequencies below 40 kHz. Above 40 kHz, levels of increased conductivity caused the overall impedance to decrease. The variation in impedance with conductivity between 5 and 50 mSm -1 can be modelled quadratically while variation in impedance with conductivity between 5 and 5000 mSm -1 can be modelled with a double exponential decay. © 2016 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

  4. Dynamic morphology of gas hydrate on a methane bubble in water: Observations and new insights for hydrate film models

    Science.gov (United States)

    Warzinski, Robert P.; Lynn, Ronald; Haljasmaa, Igor; Leifer, Ira; Shaffer, Frank; Anderson, Brian J.; Levine, Jonathan S.

    2014-10-01

    Predicting the fate of subsea hydrocarbon gases escaping into seawater is complicated by potential formation of hydrate on rising bubbles that can enhance their survival in the water column, allowing gas to reach shallower depths and the atmosphere. The precise nature and influence of hydrate coatings on bubble hydrodynamics and dissolution is largely unknown. Here we present high-definition, experimental observations of complex surficial mechanisms governing methane bubble hydrate formation and dissociation during transit of a simulated oceanic water column that reveal a temporal progression of deep-sea controlling mechanisms. Synergistic feedbacks between bubble hydrodynamics, hydrate morphology, and coverage characteristics were discovered. Morphological changes on the bubble surface appear analogous to macroscale, sea ice processes, presenting new mechanistic insights. An inverse linear relationship between hydrate coverage and bubble dissolution rate is indicated. Understanding and incorporating these phenomena into bubble and bubble plume models will be necessary to accurately predict global greenhouse gas budgets for warming ocean scenarios and hydrocarbon transport from anthropogenic or natural deep-sea eruptions.

  5. Kinetic effects of sulfur oxidation on catalytic nitrile hydration: nitrile hydratase insights from bioinspired ruthenium(II) complexes.

    Science.gov (United States)

    Kumar, Davinder; Nguyen, Tho N; Grapperhaus, Craig A

    2014-12-01

    Kinetic investigations inspired by the metalloenzyme nitrile hydratase were performed on a series of ruthenium(II) complexes to determine the effect of sulfur oxidation on catalytic nitrile hydration. The rate of benzonitrile hydration was quantified as a function of catalyst, nitrile, and water concentrations. Precatalysts L(n)RuPPh3 (n = 1-3; L(1) = 4,7-bis(2'-methyl-2'-mercapto-propyl)-1-thia-4,7-diazacyclononane; L(2) = 4-(2'-methyl-2'-sulfinatopropyl)-7-(2'-methyl-2'-mercapto-propyl)-1-thia-4,7-diazacyclononane; L(3) = 4-(2'-methyl-2'-sulfinatopropyl)-7-(2'-methyl-2'-sulfenato-propyl)-1-thia-4,7-diazacyclononane) were activated by substitution of triphenylphosphine with substrate in hot dimethylformamide solution. Rate measurements are consistent with a dynamic equilibrium between inactive aqua (L(n)Ru-OH2) and active nitrile (L(n)Ru-NCR) derivatives with K = 21 ± 1, 9 ± 0.9, and 23 ± 3 for L(1) to L(3), respectively. Subsequent hydration of the L(n)Ru-NCR intermediate yields the amide product with measured hydration rate constants (k's) of 0.37 ± 0.01, 0.82 ± 0.07, and 1.59 ± 0.12 M(-1) h(-1) for L(1) to L(3), respectively. Temperature dependent studies reveal that sulfur oxidation lowers the enthalpic barrier by 27 kJ/mol, but increases the entropic barrier by 65 J/(mol K). Density functional theory (DFT) calculations (B3LYP/LanL2DZ (Ru); 6-31G(d) (all other atoms)) support a nitrile bound catalytic cycle with lowering of the reaction barrier as a consequence of sulfur oxidation through enhanced nitrile binding and attack of the water nucleophile through a highly organized transition state.

  6. Modelling of tetrahydrofuran promoted gas hydrate systems for carbon dioxide capture processes

    DEFF Research Database (Denmark)

    Herslund, Peter Jørgensen; Thomsen, Kaj; Abildskov, Jens

    2014-01-01

    A thermodynamic study of a novel gas hydrate based CO2 capture process is presented.•Model predicts this process unsuitable for CO2 capture from power station flue gases. A thermodynamic modelling study of both fluid phase behaviour and hydrate phase behaviour is presented for the quaternary system...... of water, tetrahydrofuran, carbon dioxide and nitrogen. The applied model incorporates the Cubic-Plus-Association (CPA) equation of state for the fluid phase description and the van der Waals-Platteeuw hydrate model for the solid (hydrate) phase. Six binary pairs are studied for their fluid phase behaviour...... accurate descriptions of both fluid- and hydrate phase equilibria in the studied system and its subsystems. The developed model is applied to simulate two simplified, gas hydrate-based processes for post-combustion carbon dioxide capture from power station flue gases. The first process, an unpromoted...

  7. Ab initio thermodynamic model for magnesium carbonates and hydrates.

    Science.gov (United States)

    Chaka, Anne M; Felmy, Andrew R

    2014-09-04

    An ab initio thermodynamic framework for predicting properties of hydrated magnesium carbonate minerals has been developed using density-functional theory linked to macroscopic thermodynamics through the experimental chemical potentials for MgO, water, and CO2. Including semiempirical dispersion via the Grimme method and small corrections to the generalized gradient approximation of Perdew, Burke, and Ernzerhof for the heat of formation yields a model with quantitative agreement for the benchmark minerals brucite, magnesite, nesquehonite, and hydromagnesite. The model shows how small differences in experimental conditions determine whether nesquehonite, hydromagnesite, or magnesite is the result of laboratory synthesis from carbonation of brucite, and what transformations are expected to occur on geological time scales. Because of the reliance on parameter-free first-principles methods, the model is reliably extensible to experimental conditions not readily accessible to experiment and to any mineral composition for which the structure is known or can be hypothesized, including structures containing defects, substitutions, or transitional structures during solid state transformations induced by temperature changes or processes such as water, CO2, or O2 diffusion. Demonstrated applications of the ab initio thermodynamic framework include an independent means to evaluate differences in thermodynamic data for lansfordite, predicting the properties of Mg analogues of Ca-based hydrated carbonates monohydrocalcite and ikaite, which have not been observed in nature, and an estimation of the thermodynamics of barringtonite from the stoichiometry and a single experimental observation.

  8. Model of spur processes in aqueous radiation chemistry including spur overlap and a novel initial hydrated electron distribution

    International Nuclear Information System (INIS)

    Short, D.R.

    1980-01-01

    Results are presented from computer calculations based upon an improved diffusion-kinetic model of the spur which includes a novel initial distribution for the hydrated electron and an approximate mathematical treatment of the overlap of spurs in three dimensions. Experimental data for the decay of the hydrated electron and hydroxyl radical before one in electron-pulse-irradated, solute-free and air-free water are fit wihtin experimental uncertainty by adjustment of the initial spatial distributions of spur intermediates and the average energy deposited in the spur. Using the same values of these parameters, the hydrated electron decay is computed for times from 1 ps 10 μs after the radiatio pulse. The results of such calcuations for various conditions of pulse dose and concentrations of scavengers of individual primary chemical species in the spur are compared with corresponding experimental data obtained predominantly from water and aqueous solutions irradiated with 10 to 15 MeV electron pulses. Very good agreement between calculated and experimental hydrated electron decay in pure water is observed for the entire time range studied when a pulse dose of approximately 7900 rads is modeled, but the calcuated and experimental curves are observed to deviate for times greater than 10 ns nanoseconds when low pulse doses and low scavenger concentrations are considered. It is shown that this deviation is experimental and calculated hydrated electron decay cannot be explained by assuming the presence of a hydrated electron scavenging impurity nor by employing a distribution of nearest neighbor interspur distances to refine the overlap approximation

  9. Influence of supplementary cementitious materials on water transport kinetics and mechanical properties of hydrated lime and cement mortars

    Directory of Open Access Journals (Sweden)

    Ince, C.

    2015-06-01

    Full Text Available The purpose of this paper is an investigation of the possible role of supplementary cementitious materials (SCMs on water transport kinetics and mechanical properties of hydrated lime (CL90 and Portland cement (PC mortars. The properties of hydrated lime are significantly different from those of cement and therefore modifying fresh and hardened properties of these mortars are vital for mortar/substrate optimisation in masonry construction. The parameters investigated in this paper often are the main barriers to the use of hydrated lime in construction practice. The results show that transfer sorptivity and time to dewater freshly-mixed hydrated lime mortars can be modified when binder is partially replaced with SCMs. Compressive strength of CL90 mortars is increased systematically with the increased replacement levels of SCMs and the results are supported with the microstructural images. The ability to modify the water transport kinetics and mechanical properties allows compatibility between the mortar and the substrate unit in masonry construction.El objetivo de este artículo es investigar el papel de los materiales cementantes suplementarios (SCMs en la cinética de transporte del agua y en las propiedades mecánicas de los morteros de cal hidratada (CL90 y cemento Portland. Las propiedades de la cal hidratada son significativamente diferentes a las del cemento y por lo tanto el control de las propiedades de los morteros frescos y endurecidos es fundamental en la optimización mortero/substrato en albañilería. Los parámetros estudiados en este trabajo son a menudo las principales barreras para el uso de la cal hidratada en la práctica de la construcción. Los resultados indican que la absortividad y el tiempo necesario para deshidratar morteros de cal hidratada recién mezclados pueden ser controlados cuando el conglomerante es parcialmente remplazado por SCMs. La resistencia a compresión de los morteros CL90 aumenta sistem

  10. Kinetics model for lutate dosimetry

    International Nuclear Information System (INIS)

    Lima, M.F.; Mesquita, C.H.

    2013-01-01

    The use of compartmental analysis to predict the behavior of drugs in the organism is considered the better option among numerous methods employed in pharmacodynamics. A six compartments model was developed to determinate the kinetic constants of 177Lu-DOTATATO biodistribution using data from one published study with 67 patients treated by PRRT (Peptide receptor radionuclide therapy) and followed by CT during 68,25 hours. The compartmental analysis was made using the software AnaComp®. The influence of the time pos-injection over the dose assessment was studied taking into account the renal excretion management by aminoacid coinfusion, whose direct effects persist in the first day. The biodistribution curve was split in five sectors: 0-0.25h; 0-3.25h; 3.25-24.25h; 24.25-68.25h and 3.25-68.25h. After the examination of that influence, the study was concentrated in separate the biodistribution curve in two phases. Phase 1: governed by uptake from the blood, considering the time pos-injection until 3.25h and phase 2: governed by renal excretion, considering the time pos-injection from 3.25h to 68.25h. The model considered the organs and tissues superposition in the CT image acquisition by sampling parameters as the contribution of the the activity concentration in blood and relation between the sizes of the whole body and measured organs. The kinetic constants obtained from each phase (1 and 2) were used in dose assessment to patients in 26 organs and tissues described by MIRD. Dosimetry results were in agreement with the available results from literature, restrict to whole body, kidneys, bone marrow, spleen and liver. The advantage of the proposed model is the compartmental method quickness and power to estimate dose in organs and tissues, including tumor that, in the most part, were not discriminate by voxels of phantoms built using CT images. (author)

  11. Kinetics model for lutate dosimetry

    Energy Technology Data Exchange (ETDEWEB)

    Lima, M.F.; Mesquita, C.H., E-mail: mflima@ipen.br, E-mail: chmesqui@ipen.br [Instituto de Pesquisas Energeticas (IPEN/CNEN-SP), Sao Paulo, SP (Brazil)

    2013-11-01

    The use of compartmental analysis to predict the behavior of drugs in the organism is considered the better option among numerous methods employed in pharmacodynamics. A six compartments model was developed to determinate the kinetic constants of 177Lu-DOTATATO biodistribution using data from one published study with 67 patients treated by PRRT (Peptide receptor radionuclide therapy) and followed by CT during 68,25 hours. The compartmental analysis was made using the software AnaComp Registered-Sign . The influence of the time pos-injection over the dose assessment was studied taking into account the renal excretion management by aminoacid coinfusion, whose direct effects persist in the first day. The biodistribution curve was split in five sectors: 0-0.25h; 0-3.25h; 3.25-24.25h; 24.25-68.25h and 3.25-68.25h. After the examination of that influence, the study was concentrated in separate the biodistribution curve in two phases. Phase 1: governed by uptake from the blood, considering the time pos-injection until 3.25h and phase 2: governed by renal excretion, considering the time pos-injection from 3.25h to 68.25h. The model considered the organs and tissues superposition in the CT image acquisition by sampling parameters as the contribution of the the activity concentration in blood and relation between the sizes of the whole body and measured organs. The kinetic constants obtained from each phase (1 and 2) were used in dose assessment to patients in 26 organs and tissues described by MIRD. Dosimetry results were in agreement with the available results from literature, restrict to whole body, kidneys, bone marrow, spleen and liver. The advantage of the proposed model is the compartmental method quickness and power to estimate dose in organs and tissues, including tumor that, in the most part, were not discriminate by voxels of phantoms built using CT images. (author)

  12. Discrete element modeling of calcium-silicate-hydrate

    International Nuclear Information System (INIS)

    Chandler, Mei Qiang; Peters, John F; Pelessone, Daniele

    2013-01-01

    The discrete element method (DEM) was used to model calcium-silicate-hydrate (C-S-H) at the nanoscale. The C-S-H nanoparticles were modeled as spherical particles with diameters of approximately 5 nm. Interparticle forces included traditional mechanical contact forces, van der Waals forces and ionic correlation forces due to negatively charged C-S-H nanoparticles and ion species in the nanopores. Previous work by the authors demonstrated the DEM method was feasible in studying the properties of the C-S-H nanostructures. In this work, the simulations were performed to look into the effects of nanoparticle packing, nanoparticle morphology, interparticle forces and nanoparticle properties on the deformation mechanisms and mechanical properties of the C-S-H matrix. This work will provide insights into possible ways to improve the properties of the C-S-H matrix. (paper)

  13. Thermal properties of methane hydrate by experiment and modeling and impacts upon technology

    Energy Technology Data Exchange (ETDEWEB)

    Warzinski, R.P.; Gamwo, I.K.; Rosenbaum, E.J. [United States Dept. of Energy, Pittsburgh, PA (United States). National Energy Technology Laboratory; Myshakin, E.M. [NETL Support Contractor, South Park, PA (United States); Jiang, H.; Jordan, K.D. [Pittsburgh Univ., Pittsburgh, PA (United States). Dept. of Chemistry; English, N.J. [Dublin University College, Dublin (Ireland). Conway Inst. of Biomolecular and Biomedical Research, Centre for Synthesis and Chemical Biology; Shaw, D.W. [Geneva College, Beaver Falls, PA (United States). Dept. of Engineering

    2008-07-01

    The current hydrate research at the National Energy Technology Laboratory (NETL) involves both experimental and theoretical work on developing models and methods for predicting the behaviour of gas hydrates in their natural environment under production of climate change scenarios. The modeling efforts include both fundamental and reservoir scale simulations and economic modeling. The thermal properties of methane hydrate are important for hydrate production, seafloor stability and climate change scenarios. A new experimental technique and advanced molecular dynamics simulation (MDS) have determined the thermal properties of pure methane hydrate under conditions similar to naturally occurring hydrate-bearing sediments. The thermal conductivity and thermal diffusivity values of low-porosity methane hydrate formed in the laboratory were measured using an innovative single-sided, Transient Plane Source (TPS) technique. The results were in good agreement with results from an equilibrium MDS method using in-plane polarization of the water molecules. MDS was also performed using a non-equilibrium model with a fully polarizable force field for water. The Tough+Hydrate reservoir simulator was also used to evaluate the impact of thermal conductivity on gas production from a hydrate-bearing reservoir. 42 refs., 1 tab., 5 figs.

  14. Crystallization Kinetics within a Generic Modeling Framework

    DEFF Research Database (Denmark)

    Meisler, Kresten Troelstrup; von Solms, Nicolas; Gernaey, Krist V.

    2014-01-01

    of employing a well-structured model library for storage, use/reuse, and analysis of the kinetic models are highlighted. Examples illustrating the application of the modeling framework for kinetic model discrimination related to simulation of specific crystallization scenarios and for kinetic model parameter......A new and extended version of a generic modeling framework for analysis and design of crystallization operations is presented. The new features of this framework are described, with focus on development, implementation, identification, and analysis of crystallization kinetic models. Issues related...... to the modeling of various kinetic phenomena like nucleation, growth, agglomeration, and breakage are discussed in terms of model forms, model parameters, their availability and/or estimation, and their selection and application for specific crystallization operational scenarios under study. The advantages...

  15. The hydration of slag, part 2: reaction models for blended cement

    NARCIS (Netherlands)

    Chen, Wei; Brouwers, H.J.H.

    2007-01-01

    The hydration of slag-blended cement is studied by considering the interaction between the hydrations of slag and Portland cement clinker. Three reaction models for the slag-blended cement are developed based on stoichiometric calculations. These models correlate the compositions of the unhydrated

  16. Phase equilibrium modeling of gas hydrate systems for CO2 capture

    DEFF Research Database (Denmark)

    Herslund, Peter Jørgensen; Thomsen, Kaj; Abildskov, Jens

    2012-01-01

    to form from vapor phases with initial mole fractions of CO2 at or above 0.15.The two models are validated against mixed hydrate equilibrium data found in literature. Both dissociation pressures and hydrate compositions are considered in the validation process.With the fitted parameters, Model I predicts...

  17. Kinetics of methane-ethane gas replacement in clathrate-hydrates studied by time-resolved neutron diffraction and Raman spectroscopy.

    Science.gov (United States)

    Murshed, M Mangir; Schmidt, Burkhard C; Kuhs, Werner F

    2010-01-14

    The kinetics of CH(4)-C(2)H(6) replacement in gas hydrates has been studied by in situ neutron diffraction and Raman spectroscopy. Deuterated ethane structure type I (C(2)H(6) sI) hydrates were transformed in a closed volume into methane-ethane mixed structure type II (CH(4)-C(2)H(6) sII) hydrates at 5 MPa and various temperatures in the vicinity of 0 degrees C while followed by time-resolved neutron powder diffraction on D20 at ILL, Grenoble. The role of available surface area of the sI starting material on the formation kinetics of sII hydrates was studied. Ex situ Raman spectroscopic investigations were carried out to crosscheck the gas composition and the distribution of the gas species over the cages as a function of structure type and compared to the in situ neutron results. Raman micromapping on single hydrate grains showed compositional and structural gradients between the surface and core of the transformed hydrates. Moreover, the observed methane-ethane ratio is very far from the one expected for a formation from a constantly equilibrated gas phase. The results also prove that gas replacement in CH(4)-C(2)H(6) hydrates is a regrowth process involving the nucleation of new crystallites commencing at the surface of the parent C(2)H(6) sI hydrate with a progressively shrinking core of unreacted material. The time-resolved neutron diffraction results clearly indicate an increasing diffusion limitation of the exchange process. This diffusion limitation leads to a progressive slowing down of the exchange reaction and is likely to be responsible for the incomplete exchange of the gases.

  18. Modeling composting kinetics: A review of approaches

    NARCIS (Netherlands)

    Hamelers, H.V.M.

    2004-01-01

    Composting kinetics modeling is necessary to design and operate composting facilities that comply with strict market demands and tight environmental legislation. Current composting kinetics modeling can be characterized as inductive, i.e. the data are the starting point of the modeling process and

  19. Hydrate Phase Assemblages in Blends of Ye'elimite and Gypsum with Alite and Belite

    DEFF Research Database (Denmark)

    Pedersen, Malene Thostrup; Skibsted, Jørgen

    2016-01-01

    Calcium sulpho-aluminate (CSA) cements all contain ye’elimite, either as the main phase or in intermediate amounts, while they differ in their content of accessory phases. Belite is the main phase in most CSA cements, however, alite - CSA cements have been produced. The hydrate phases formed during...... and hydration kinetics. The improved understanding of the hydrate phase assemblages as well as the hydration kinetics for the model systems will form the fundamental basis for further optimizations of blended systems including ye’elimite with the aim of maximizing the reaction degree of the main clinker phases...... hydration of CSA cements depend on the type of CSA cement and the amount of gypsum added. The hydration reactions of the main phases are by themselves well documented, whereas the simultaneous hydration of CSA cement components is not fully understood in terms of hydration products and kinetics. To further...

  20. Advanced Gas Hydrate Reservoir Modeling Using Rock Physics

    Energy Technology Data Exchange (ETDEWEB)

    McConnell, Daniel

    2017-12-30

    Prospecting for high saturation gas hydrate deposits can be greatly aided with improved approaches to seismic interpretation and especially if sets of seismic attributes can be shown as diagnostic or direct hydrocarbon indicators for high saturation gas hydrates in sands that would be of most interest for gas hydrate production.

    A large 3D seismic data set in the deep water Eastern Gulf of Mexico was screened for gas hydrates using a set of techniques and seismic signatures that were developed and proven in the Central deepwater Gulf of Mexico in the DOE Gulf of Mexico Joint Industry Project JIP Leg II in 2009 and recently confirmed with coring in 2017.

    A large gas hydrate deposit is interpreted in the data where gas has migrated from one of the few deep seated faults plumbing the Jurassic hydrocarbon source into the gas hydrate stability zone. The gas hydrate deposit lies within a flat-lying within Pliocene Mississippi Fan channel that was deposited outboard in a deep abyssal environment. The uniform architecture of the channel aided the evaluation of a set of seismic attributes that relate to attenuation and thin-bed energy that could be diagnostic of gas hydrates. Frequency attributes derived from spectral decomposition also proved to be direct hydrocarbon indicators by pseudo-thickness that could be only be reconciled by substituting gas hydrate in the pore space. The study emphasizes that gas hydrate exploration and reservoir characterization benefits from a seismic thin bed approach.

  1. Calibration and validation of a numerical model against experimental data of methane hydrate formation and dissociation in a sandy porous medium

    Science.gov (United States)

    Yin, Z.; Moridis, G. J.; Chong, Z. R.; Linga, P.

    2017-12-01

    Methane hydrates (MH) are known to trap enormous amounts of CH4 in oceanic and permafrost-associated deposits, and are being considered as a potential future energy source. Several powerful numerical simulators were developed to describe the behavior of natural hydrate-bearing sediments (HBS). The complexity and strong nonlinearities in HBS do not allow analytical solutions for code validation. The only reliable method to develop confidence in these models is through comparisons to laboratory and/or field experiments. The objective of this study is to reproduce numerically the results from earlier experiments of MH formation and depressurization (and the corresponding fluid production) in 1.0L reactor involving unconsolidated sand, thus validating and calibrating the TOUGH+Hydrate v1.5 simulator. We faithfully describe the reactor geometry and the experimental process that involves both hydrate formation and dissociation. We demonstrate that the laboratory experiments can only be captured by a kinetic hydration model. There is an excellent agreement between observations and predictions (a) of the cumulative gas depletion (during formation) and production (during dissociation) and (b) of pressure over time. The temperature agreement is less satisfactory, and the deviations are attributed to the fixed locations of the limited number of sensors that cannot fully capture the hydrate heterogeneity. We also predict the spatial distributions over time of the various phase (gas, aqueous and hydrate) saturations. Thus, hydrates form preferentially along the outer boundary of the sand core, and the hydrate front moves inward leaving a significant portion of the sand at the center hydrate-free. During depressurization, dissociation advances again inward from the reactor boundary to the center of the reactor. As expected, methane gas accumulates initially at the locations of most intense dissociation, and then gradually migrates to the upper section of the reactor because of

  2. Skin Erythema, Pigmentation and Hydration Kinetics after Ultraviolet Radiation-induced Photodamage in Southern Chinese Women.

    Science.gov (United States)

    Wan, Miaojian; Hu, Rong; Xie, Xiaoyuan; Gong, Zijian; Yi, Jinling; Chen, Haiyan; Xie, Lin; Guan, Xiaomin; Guan, Lei; Lai, Wei

    2017-10-01

    Although there have been some studies about changes of skin erythema and pigmentation following ultraviolet radiation in other races, the relevant data in Chinese have never been achieved. Thus, we evaluated the long-time course of skin erythema, pigmentation and hydration changes after different doses of solar-simulated ultraviolet (SSUV) irradiation in 26 Chinese women for 168 days. The erythema index increased abruptly and peaked during 3 days of SSUV exposure, then slowly returned to the baseline level starting at day 7 and completely recovered during 168-day course of this study only in one minimal erythema doses (MED) SSUV irradiation. The melanin index started to slowly increase at day 3 of SSUV exposure, peaking at day 14 and gradually returned to the baseline level thereafter, but did not return to the baseline level during 168-day course in all doses. Skin hydration slowly declined at day 3 of exposure, hitting the lowest point at day 7, then slowly recovered starting at day 14 and completely returned to the baseline level at day 28 only in 1.5MED. These results will serve as baseline data on Chinese skin and provide useful references for the treatment of serious skin photodamage in Chinese. © 2017 The American Society of Photobiology.

  3. Interaction of Simple Ions with Water: Theoretical Models for the Study of Ion Hydration

    Science.gov (United States)

    Gancheff, Jorge S.; Kremer, Carlos; Ventura, Oscar N.

    2009-01-01

    A computational experiment aimed to create and systematically analyze models of simple cation hydrates is presented. The changes in the structure (bond distances and angles) and the electronic density distribution of the solvent and the thermodynamic parameters of the hydration process are calculated and compared with the experimental data. The…

  4. Development of hydrate risk quantification in oil and gas production

    Science.gov (United States)

    Chaudhari, Piyush N.

    order to reduce the parametric study that may require a long duration of time using The Colorado School of Mines Hydrate Kinetic Model (CSMHyK). The evolution of the hydrate plugging risk along flowline-riser systems is modeled for steady state and transient operations considering the effect of several critical parameters such as oil-hydrate slip, duration of shut-in, and water droplet size on a subsea tieback system. This research presents a novel platform for quantification of the hydrate plugging risk, which in-turn will play an important role in improving and optimizing current hydrate management strategies. The predictive strength of the hydrate risk quantification and hydrate prediction models will have a significant impact on flow assurance engineering and design with respect to building safe and efficient hydrate management techniques for future deep-water developments.

  5. Chemical Kinetic Modeling of 2-Methylhexane Combustion

    KAUST Repository

    Mohamed, Samah Y.

    2015-03-30

    Accurate chemical kinetic combustion models of lightly branched alkanes (e.g., 2-methylalkanes) are important for investigating the combustion behavior of diesel, gasoline, and aviation fuels. Improving the fidelity of existing kinetic models is a necessity, as new experiments and advanced theories show inaccuracy in certain portions of the models. This study focuses on updating thermodynamic data and kinetic model for a gasoline surrogate fuel, 2-methylhexane, with recently published group values and rate rules. These update provides a better agreement with rapid compression machine measurements of ignition delay time, while also strengthening the fundamental basis of the model.

  6. [Effect of IV hydration with sodium bicarbonate on high-dose methotrexate disposition kinetics].

    Science.gov (United States)

    Tsuda, N; Goto, M; Konishi, H; Yamashina, H

    1984-04-01

    Following two-compartment kinetic analysis, the effect of loading of transfusion with sodium bicarbonate on methotrexate disposition was investigated in 13 cases with malignant tumor, being treated with high-dose methotrexate. The mean values of total body clearance, when administered at doses 50 mg and 100 mg per kg body weight, were 0.369 and 0.402 (l/h) per kg, respectively. No significant relationship was observed between alpha value and total amount of transfusion, of urine or dosage of sodium bicarbonate. The other kinetic parameters on elimination, beta value, K10 and total body clearance, did not also correlate with those values described above. These results suggest that the elimination profile of methotrexate show linear kinetics, and that massive administration of transfusion with sodium bicarbonate be not necessary if pH value of urine exceeds 7.0.

  7. Inhibition of natural gas hydrates by means of kinetic inhibitors; Inhibierung von Erdgashydraten mit kinetischen Inhibitoren

    Energy Technology Data Exchange (ETDEWEB)

    Eberhardt, E.; Froemmel, J.; Hase, A. [Inst. fuer Erdoel- und Erdgasforschung, Clausthal-Zellerfeld (Germany)

    1997-12-31

    The use of kinetic inhibitors saves considerable costs as compared with thermodynamic inhibition. The effectivity of kinetic inhibitors can be examined by means of screening tests using an agitated autoclave. This contribution describes the experimental set-up and measuring methods used for this purpose and discusses the results obtained. (MSK) [Deutsch] Der Einsatz von kinetischen Inhibitoren fuehrt im Vergleich zur thermodynamischen Inhibition zu einer erheblichen Kostenreduzierung. Die Effektivitaet wird anhand von Screening-Versuchen in einem Ruehrautoklaven geprueft.Im Folgenden werden die Versuchsapparatur und die Messmethodik beschrieben. Ebenso werden die Ergebnisse diskutiert.

  8. A mathematical model for iodine kinetics

    International Nuclear Information System (INIS)

    Silva, E.A.T. da.

    1976-01-01

    A mathematical model for the iodine kinetics in thyroid is presented followed by its analytical solution. An eletroanalogical model is also developed for a simplified stage and another is proposed for the main case [pt

  9. Chemical Kinetic Modeling of 2-Methylhexane Combustion

    KAUST Repository

    Mohamed, Samah Y.; Sarathy, Mani

    2015-01-01

    necessity, as new experiments and advanced theories show inaccuracy in certain portions of the models. This study focuses on updating thermodynamic data and kinetic model for a gasoline surrogate fuel, 2-methylhexane, with recently published group values

  10. Analysis of vaginal microbicide film hydration kinetics by quantitative imaging refractometry.

    Directory of Open Access Journals (Sweden)

    Matthew Rinehart

    Full Text Available We have developed a quantitative imaging refractometry technique, based on holographic phase microscopy, as a tool for investigating microscopic structural changes in water-soluble polymeric materials. Here we apply the approach to analyze the structural degradation of vaginal topical microbicide films due to water uptake. We implemented transmission imaging of 1-mm diameter film samples loaded into a flow chamber with a 1.5×2 mm field of view. After water was flooded into the chamber, interference images were captured and analyzed to obtain high resolution maps of the local refractive index and subsequently the volume fraction and mass density of film material at each spatial location. Here, we compare the hydration dynamics of a panel of films with varying thicknesses and polymer compositions, demonstrating that quantitative imaging refractometry can be an effective tool for evaluating and characterizing the performance of candidate microbicide film designs for anti-HIV drug delivery.

  11. Analysis of vaginal microbicide film hydration kinetics by quantitative imaging refractometry.

    Science.gov (United States)

    Rinehart, Matthew; Grab, Sheila; Rohan, Lisa; Katz, David; Wax, Adam

    2014-01-01

    We have developed a quantitative imaging refractometry technique, based on holographic phase microscopy, as a tool for investigating microscopic structural changes in water-soluble polymeric materials. Here we apply the approach to analyze the structural degradation of vaginal topical microbicide films due to water uptake. We implemented transmission imaging of 1-mm diameter film samples loaded into a flow chamber with a 1.5×2 mm field of view. After water was flooded into the chamber, interference images were captured and analyzed to obtain high resolution maps of the local refractive index and subsequently the volume fraction and mass density of film material at each spatial location. Here, we compare the hydration dynamics of a panel of films with varying thicknesses and polymer compositions, demonstrating that quantitative imaging refractometry can be an effective tool for evaluating and characterizing the performance of candidate microbicide film designs for anti-HIV drug delivery.

  12. Measuring and modelling of the combined thermodynamic promoting effect of tetrahydrofuran and cyclopentane on carbon dioxide hydrates

    DEFF Research Database (Denmark)

    Herslund, Peter Jørgensen; Daraboina, Nagu; Thomsen, Kaj

    2014-01-01

    This work documents both experimental data, and by thermodynamic modelling, the synergistic effect occurring in promoted carbon dioxide hydrate systems at the simultaneous presence of tetrahydrofuran and cyclopentane.Cyclopentane has previously been considered a reference among gas hydrate promot...

  13. Kinetic equations for the collisional plasma model

    International Nuclear Information System (INIS)

    Rij, W.I. Van; Meier, H.K.; Beasley, C.O. Jr.; McCune, J.E.

    1977-01-01

    Using the Collisional Plasma Model (CPM) representation, expressions are derived for the Vlasov operator, both in its general form and in the drift-kinetic approximation following the recursive derivation by Hazeltine. The expressions for the operators give easily calculated couplings between neighbouring components of the CPM representation. Expressions for various macroscopic observables in the drift-kinetics approximation are also given. (author)

  14. Modelling of cyclopentane promoted gas hydrate systems for carbon dioxide capture processes

    DEFF Research Database (Denmark)

    Herslund, Peter Jørgensen; Thomsen, Kaj; Abildskov, Jens

    2014-01-01

    A thermodynamic model based on the Cubic-Plus-Association equation of state and the van der Waals-Platteeuw hydrate model is applied to perform a thermodynamic evaluation of gas hydrate forming systems relevant for post-combustion carbon dioxide capture.A modelling study of both fluid phase...... behaviour and hydrate phase behaviour is presented. Cycloalkanes ranging from cyclopropane to cyclohexane, represents a challenge for CPA, both in the description of the pure component densities and for liquid-liquid equilibrium (LLE) in the binary systems with water. It is concluded that an insufficient...

  15. Coupled numerical modeling of gas hydrates bearing sediments from laboratory to field-scale conditions

    Science.gov (United States)

    Sanchez, M. J.; Santamarina, C.; Gai, X., Sr.; Teymouri, M., Sr.

    2017-12-01

    Stability and behavior of Hydrate Bearing Sediments (HBS) are characterized by the metastable character of the gas hydrate structure which strongly depends on thermo-hydro-chemo-mechanical (THCM) actions. Hydrate formation, dissociation and methane production from hydrate bearing sediments are coupled THCM processes that involve, amongst other, exothermic formation and endothermic dissociation of hydrate and ice phases, mixed fluid flow and large changes in fluid pressure. The analysis of available data from past field and laboratory experiments, and the optimization of future field production studies require a formal and robust numerical framework able to capture the very complex behavior of this type of soil. A comprehensive fully coupled THCM formulation has been developed and implemented into a finite element code to tackle problems involving gas hydrates sediments. Special attention is paid to the geomechanical behavior of HBS, and particularly to their response upon hydrate dissociation under loading. The numerical framework has been validated against recent experiments conducted under controlled conditions in the laboratory that challenge the proposed approach and highlight the complex interaction among THCM processes in HBS. The performance of the models in these case studies is highly satisfactory. Finally, the numerical code is applied to analyze the behavior of gas hydrate soils under field-scale conditions exploring different features of material behavior under possible reservoir conditions.

  16. Gas Hydrate Petroleum System Modeling in western Nankai Trough Area

    Science.gov (United States)

    Tanaka, M.; Aung, T. T.; Fujii, T.; Wada, N.; Komatsu, Y.

    2017-12-01

    Since 2003, we have been conducting Gas Hydrate (GH) petroleum system models covering the eastern Nankai Trough, Japan, and results of resource potential from regional model shows good match with the value depicted from seismic and log data. In this year, we have applied this method to explore GH potential in study area. In our study area, GH prospects have been identified with aid of bottom simulating reflector (BSR) and presence of high velocity anomalies above the BSR interpreted based on 3D migration seismic and high density velocity cubes. In order to understand the pathway of biogenic methane from source to GH prospects 1D-2D-3D GH petroleum system models are built and investigated. This study comprises lower Miocene to Pleistocene, deep to shallow marine sedimentary successions of Pliocene and Pleistocene layers overlain the basement. The BSR were interpreted in Pliocene and Pleistocene layers. Based on 6 interpreted sequence boundaries from 3D migration seismic and velocity data, construction of a depth 3D framework model is made and distributed by a conceptual submarine fan depositional facies model derived from seismic facies analysis and referring existing geological report. 1D models are created to analyze lithology sensitivity to temperature and vitrinite data from an exploratory well drilled in the vicinity of study area. The PSM parameters are applied in 2D and 3D modeling and simulation. Existing report of the explanatory well reveals that thermogenic origin are considered to exist. For this reason, simulation scenarios including source formations for both biogenic and thermogenic reaction models are also investigated. Simulation results reveal lower boundary of GH saturation zone at pseudo wells has been simulated with sensitivity of a few tens of meters in comparing with interpreted BSR. From sensitivity analysis, simulated temperature was controlled by different peak generation temperature models and geochemical parameters. Progressive folding

  17. A Numerical Model for the Thermomechanical Conditions During Hydration of Early-age Concrete

    DEFF Research Database (Denmark)

    Hattel, Jesper; Thorborg, Jesper

    2003-01-01

    In the present study, a macroscopic numerical model for the thermomechanical conditions during hydration of early-age concrete is presented. The formulation is based on a semi-coupled, incremental thermomechanical model where the heat production from the hydration process is expressed in terms...... of the maturity and the thermal activation is expressed by the Arrhenius principle. The material properties are assumed to depend on the hydration process via the maturity. The discretization of the governing equations is accomplished by a control volume formulation involving a time-splitting scheme for the heat...

  18. Seismic modeling of multidimensional heterogeneity scales of Mallik gas hydrate reservoirs, Northwest Territories of Canada

    Science.gov (United States)

    Huang, Jun-Wei; Bellefleur, Gilles; Milkereit, Bernd

    2009-07-01

    In hydrate-bearing sediments, the velocity and attenuation of compressional and shear waves depend primarily on the spatial distribution of hydrates in the pore space of the subsurface lithologies. Recent characterizations of gas hydrate accumulations based on seismic velocity and attenuation generally assume homogeneous sedimentary layers and neglect effects from large- and small-scale heterogeneities of hydrate-bearing sediments. We present an algorithm, based on stochastic medium theory, to construct heterogeneous multivariable models that mimic heterogeneities of hydrate-bearing sediments at the level of detail provided by borehole logging data. Using this algorithm, we model some key petrophysical properties of gas hydrates within heterogeneous sediments near the Mallik well site, Northwest Territories, Canada. The modeled density, and P and S wave velocities used in combination with a modified Biot-Gassmann theory provide a first-order estimate of the in situ volume of gas hydrate near the Mallik 5L-38 borehole. Our results suggest a range of 528 to 768 × 106 m3/km2 of natural gas trapped within hydrates, nearly an order of magnitude lower than earlier estimates which did not include effects of small-scale heterogeneities. Further, the petrophysical models are combined with a 3-D finite difference modeling algorithm to study seismic attenuation due to scattering and leaky mode propagation. Simulations of a near-offset vertical seismic profile and cross-borehole numerical surveys demonstrate that attenuation of seismic energy may not be directly related to the intrinsic attenuation of hydrate-bearing sediments but, instead, may be largely attributed to scattering from small-scale heterogeneities and highly attenuate leaky mode propagation of seismic waves through larger-scale heterogeneities in sediments.

  19. Carbon dioxide gas hydrates accumulation in freezing and frozen sediments

    Energy Technology Data Exchange (ETDEWEB)

    Chuvilin, E.; Guryeva, O. [Moscow State Univ., Moscow (Russian Federation). Dept. of Geology

    2008-07-01

    Carbon dioxide (CO{sub 2}) hydrates and methane hydrates can be formed, and exist under natural conditions. The permafrost area has been considered as an environment for the potential disposal of CO{sub 2}. The favorable factors for preserving CO{sub 2} in liquid and gas hydrate states in frozen sediments and under permafrost horizons are great thickness of frozen sediments; low permeability in comparison with thawed sediments; and favourable conditions for hydrates formation. Therefore, research on the formation and existence conditions of CO{sub 2} gas hydrates in permafrost and under permafrost sediments are of great importance for estimation of CO{sub 2} disposal conditions in permafrost, and for working out specific sequestration schemes. This paper presented the results of an experimental study on the process of carbon dioxide (CO{sub 2}) gas hydrates formation in the porous media of sediments under positive and negative temperatures. Sediment samples of various compositions including those selected in the permafrost area were used. The research was conducted in a special pressure chamber, which allowed to monitor pressure and temperature. The study used the monitoring results in order to make quantitative estimation of the kinetics of CO{sub 2} hydrates accumulation in the model sediments. Results were presented in terms of kinetics of CO{sub 2} hydrates accumulation in the porous media at positive and negative temperatures; kinetics of CO{sub 2} hydrates accumulation in various porous media; gas hydrate-former influence on kinetics of hydrates accumulation in frozen sediments; and influence of freezing on CO{sub 2} hydrates accumulation in porous media. It was concluded that hydrate accumulation took an active place in porous media not only under positive, but also under high negative temperatures, when the water was mainly in the form of ice in porous media. 27 refs., 3 tabs., 5 figs.

  20. 3D pore-type digital rock modeling of natural gas hydrate for permafrost and numerical simulation of electrical properties

    Science.gov (United States)

    Dong, Huaimin; Sun, Jianmeng; Lin, Zhenzhou; Fang, Hui; Li, Yafen; Cui, Likai; Yan, Weichao

    2018-02-01

    Natural gas hydrate is being considered as an alternative energy source for sustainable development and has become a focus of research throughout the world. In this paper, based on CT scanning images of hydrate reservoir rocks, combined with the microscopic distribution of hydrate, a diffusion limited aggregation (DLA) model was used to construct 3D hydrate digital rocks of different distribution types, and the finite-element method was used to simulate their electrical characteristics in order to study the influence of different hydrate distribution types, hydrate saturation and formation of water salinity on electrical properties. The results show that the hydrate digital rocks constructed using the DLA model can be used to characterize the microscopic distribution of different types of hydrates. Under the same conditions, the resistivity of the adhesive hydrate digital rock is higher than the cemented and scattered type digital rocks, and the resistivity of the scattered hydrate digital rock is the smallest among the three types. Besides, the difference in the resistivity of the different types of hydrate digital rocks increases with an increase in hydrate saturation, especially when the saturation is larger than 55%, and the rate of increase of each of the hydrate types is quite different. Similarly, the resistivity of the three hydrate types decreases with an increase in the formation of water salinity. The single distribution hydrate digital rock constructed, combined with the law of microscopic distribution and influence of saturation on the electrical properties, can effectively improve the accuracy of logging identification of hydrate reservoirs and is of great significance for the estimation of hydrate reserves.

  1. Kinetic Model of Growth of Arthropoda Populations

    Science.gov (United States)

    Ershov, Yu. A.; Kuznetsov, M. A.

    2018-05-01

    Kinetic equations were derived for calculating the growth of crustacean populations ( Crustacea) based on the biological growth model suggested earlier using shrimp ( Caridea) populations as an example. The development cycle of successive stages for populations can be represented in the form of quasi-chemical equations. The kinetic equations that describe the development cycle of crustaceans allow quantitative prediction of the development of populations depending on conditions. In contrast to extrapolation-simulation models, in the developed kinetic model of biological growth the kinetic parameters are the experimental characteristics of population growth. Verification and parametric identification of the developed model on the basis of the experimental data showed agreement with experiment within the error of the measurement technique.

  2. Effect Of Ether Derivative Cellulose Polymers On Hydration, Erosion And Release Kinetics Of Diclofenac Sodium Matrix Tablets

    Directory of Open Access Journals (Sweden)

    Muhammad Akhlaq*1,2, Gul Majid Khan1 , Abdul Wahab1, Waqas Rabbani1, Abid Hussain1, Asif Nawaz1, & Alam Zeb1

    2011-09-01

    Full Text Available Objectives: The work aims to investigate the effect ofhydrophilic and hydrophobic polymers swelling and erosionon the release behaviour of DCL-Na from controlled matrixtablets prepared by direct compression and wet-granulationtechniques.Materials and Methods: Powder preformulation studies wereconducted. Tablets were prepared by direct compressiontechnique and their physicochemical properties wereevaluated. Drug-polymer interaction was analyzed by FTIRspectroscopy. The in-vitro drug release study was conductedusing phosphte buffer pH 7.4 as dissolution medium anddifferent kinetic parameters were applied.Results and Discussion: F-1 and F-5 containing ethycelluloseprepared by direct compression and wet granulationtechniques released 94 % and 84 % drug after 24hrs, while F-2and F-6 containing hydroxypropylmethylcellulose polymerprepared by direct compression and wet granulation released98.46 % and 91.25 % drug after within 24 hrs respectively.Ethylcellulose and hydroxypropylmethylcellulose based matrixtablets showed the best anomalous drug release behaviour,with the release exponents “ n ” ranging from 0.685 to 0.809.Conclusion: It has been concluded that ethylcellulose etherderivative polymer is used to prepare oral controlled releasematrix tablet of diclofenac sodium. Fickian drug diffusion,polymer hydration and erosion mechanisms occurredsimultaneously and were considered as the main drug releasecontrolling factors.

  3. Kinetics of the main phase transition of hydrated lecithin monitored by real-time x-ray diffraction

    International Nuclear Information System (INIS)

    Caffrey, M.; Bilderback, D.H.

    1984-01-01

    A method is described for observing and recording in real-time x-ray diffraction from an unoriented hydrated membrane lipid, dipalmitoylphosphatidylcholine (DPPC), through its thermotropic gel/liquid crystal phase transition. Synchrotron radiation from the Cornell High Energy Synchrotron Source (Ithaca, New York) was used as an x-ray source of extremely high brilliance and the dynamic display of the diffraction image was effected using a three-stage image intensifier tube coupled to an external fluorescent screen. The image on the output phosphor was sufficiently intense to be recorded cinematographically and to be displayed on a television monitor using a vidicon camera at 30 frames x s -1 . These measurements set an upper limit of 2 s on the DPPC gel → liquid crystal phase transition and indicate that the transition is a two-state process. The real-time method couples the power of x-ray diffraction as a structural probe with the ability to follow kinetics of structural changes. The method does not require an exogenous probe, is relatively nonperturbing, and can be used with membranes in a variety of physical states and with unstable samples. The method has the additional advantage over its static measurement counterpart in that it is more likely to detect transiently stable intermediates if present

  4. Hydrogen storage and carbon dioxide sequestration in TBAF semi-clathrate hydrates: Kinetics and evolution of hydrate-phase composition by in situ raman spectroscopy - Abstract -

    NARCIS (Netherlands)

    Torres Trueba, A.; Radoviæ, I.R.; Zevenbergen, J.F.; Kroon, M.C.; Peters, C.J.

    2012-01-01

    Carbon dioxide (CO2) represents almost one third of the emissions from the combustion of fossil fuels additionally, CO2 has been identified as the mayor contributor of global warming. Hydrogen (H2), on the other hand, due to its properties is considered a promising energy carrier. Clathrate hydrates

  5. Atomistic modeling of structure II gas hydrate mechanics: Compressibility and equations of state

    Directory of Open Access Journals (Sweden)

    Thomas M. Vlasic

    2016-08-01

    Full Text Available This work uses density functional theory (DFT to investigate the poorly characterized structure II gas hydrates, for various guests (empty, propane, butane, ethane-methane, propane-methane, at the atomistic scale to determine key structure and mechanical properties such as equilibrium lattice volume and bulk modulus. Several equations of state (EOS for solids (Murnaghan, Birch-Murnaghan, Vinet, Liu were fitted to energy-volume curves resulting from structure optimization simulations. These EOS, which can be used to characterize the compressional behaviour of gas hydrates, were evaluated in terms of their robustness. The three-parameter Vinet EOS was found to perform just as well if not better than the four-parameter Liu EOS, over the pressure range in this study. As expected, the Murnaghan EOS proved to be the least robust. Furthermore, the equilibrium lattice volumes were found to increase with guest size, with double-guest hydrates showing a larger increase than single-guest hydrates, which has significant implications for the widely used van der Waals and Platteeuw thermodynamic model for gas hydrates. Also, hydrogen bonds prove to be the most likely factor contributing to the resistance of gas hydrates to compression; bulk modulus was found to increase linearly with hydrogen bond density, resulting in a relationship that could be used predictively to determine the bulk modulus of various structure II gas hydrates. Taken together, these results fill a long existing gap in the material chemical physics of these important clathrates.

  6. Atomistic modeling of structure II gas hydrate mechanics: Compressibility and equations of state

    Energy Technology Data Exchange (ETDEWEB)

    Vlasic, Thomas M.; Servio, Phillip; Rey, Alejandro D., E-mail: alejandro.rey@mcgill.ca [Department of Chemical Engineering, McGill University, Montreal H3A 0C5 (Canada)

    2016-08-15

    This work uses density functional theory (DFT) to investigate the poorly characterized structure II gas hydrates, for various guests (empty, propane, butane, ethane-methane, propane-methane), at the atomistic scale to determine key structure and mechanical properties such as equilibrium lattice volume and bulk modulus. Several equations of state (EOS) for solids (Murnaghan, Birch-Murnaghan, Vinet, Liu) were fitted to energy-volume curves resulting from structure optimization simulations. These EOS, which can be used to characterize the compressional behaviour of gas hydrates, were evaluated in terms of their robustness. The three-parameter Vinet EOS was found to perform just as well if not better than the four-parameter Liu EOS, over the pressure range in this study. As expected, the Murnaghan EOS proved to be the least robust. Furthermore, the equilibrium lattice volumes were found to increase with guest size, with double-guest hydrates showing a larger increase than single-guest hydrates, which has significant implications for the widely used van der Waals and Platteeuw thermodynamic model for gas hydrates. Also, hydrogen bonds prove to be the most likely factor contributing to the resistance of gas hydrates to compression; bulk modulus was found to increase linearly with hydrogen bond density, resulting in a relationship that could be used predictively to determine the bulk modulus of various structure II gas hydrates. Taken together, these results fill a long existing gap in the material chemical physics of these important clathrates.

  7. Hydration and Proton Conductivity of Ionomers: The Model Case of Sulfonated Aromatic Polymers

    Energy Technology Data Exchange (ETDEWEB)

    Knauth, Philippe, E-mail: philippe.knauth@univ-amu.fr [Madirel (UMR 7246), CNRS, Aix Marseille Université, Marseille (France); Di Vona, Maria Luisa [Dipartimento di Scienze e Tecnologie Chimiche, Università di Roma Tor Vergata, Roma (Italy)

    2014-11-06

    The hydration of proton-conducting ionomers is described in terms of a simplified model, where only osmotic and elastic contributions to the Gibbs free energy of hydration are considered. Although only two physically meaningful parameters are used – the deformation parameter, inversely proportional to the elastic modulus of the ionomer, and the free volume parameter – simulated hydration isotherms are in good agreement with the experiment. The proton mobility u inside the electrolyte solution of the ionomer is calculated from the proton conductivity determined at various hydration numbers. Its variation with the proton concentration c reveals the percolation threshold of hydrated nanometric channels and the tortuosity of the membrane. Above the percolation threshold, a power law u ~ c{sup −3} is observed, in agreement with the “universal” law for 3-dimensional percolation. The proton conductivity σ shows at 100°C a maximum of 0.2 S/cm at a hydration number ~90. The σ = f(c) plot allows to predict, which hydration conditions are necessary for a desired area specific resistance.

  8. Atomistic modeling of structure II gas hydrate mechanics: Compressibility and equations of state

    Science.gov (United States)

    Vlasic, Thomas M.; Servio, Phillip; Rey, Alejandro D.

    2016-08-01

    This work uses density functional theory (DFT) to investigate the poorly characterized structure II gas hydrates, for various guests (empty, propane, butane, ethane-methane, propane-methane), at the atomistic scale to determine key structure and mechanical properties such as equilibrium lattice volume and bulk modulus. Several equations of state (EOS) for solids (Murnaghan, Birch-Murnaghan, Vinet, Liu) were fitted to energy-volume curves resulting from structure optimization simulations. These EOS, which can be used to characterize the compressional behaviour of gas hydrates, were evaluated in terms of their robustness. The three-parameter Vinet EOS was found to perform just as well if not better than the four-parameter Liu EOS, over the pressure range in this study. As expected, the Murnaghan EOS proved to be the least robust. Furthermore, the equilibrium lattice volumes were found to increase with guest size, with double-guest hydrates showing a larger increase than single-guest hydrates, which has significant implications for the widely used van der Waals and Platteeuw thermodynamic model for gas hydrates. Also, hydrogen bonds prove to be the most likely factor contributing to the resistance of gas hydrates to compression; bulk modulus was found to increase linearly with hydrogen bond density, resulting in a relationship that could be used predictively to determine the bulk modulus of various structure II gas hydrates. Taken together, these results fill a long existing gap in the material chemical physics of these important clathrates.

  9. Hydration and proton conductivity of ionomers: the model case of Sulfonated Aromatic Polymers

    Directory of Open Access Journals (Sweden)

    Philippe eKnauth

    2014-11-01

    Full Text Available The hydration of proton-conducting ionomers is described in terms of a simplified model, where only osmotic and elastic contributions to the Gibbs free energy of hydration are considered. Although only two physically meaningful parameters are used - the deformation parameter, inversely proportional to the elastic modulus of the ionomer, and the free volume parameter – simulated hydration isotherms are in good agreement with the experiment. The proton mobility u inside the electrolyte solution of the ionomer is calculated from the proton conductivity determined at various hydration numbers. Its variation with the proton concentration c reveals the percolation threshold of hydrated nanometric channels and the tortuosity of the membrane. Above the percolation threshold, a power law u ~ c-3 is observed, in agreement with the universal law for 3-dimensional percolation. The proton conductivity  shows at 100°C a maximum of 0.2 S/cm at a hydration number ~90. The  = f(c plot allows to predict which hydration conditions are necessary for a desired area specific resistance.

  10. Modeling of Hydrate Formation Mode in Raw Natural Gas Air Coolers

    Science.gov (United States)

    Scherbinin, S. V.; Prakhova, M. Yu; Krasnov, A. N.; Khoroshavina, E. A.

    2018-05-01

    Air cooling units (ACU) are used at all the gas fields for cooling natural gas after compressing. When using ACUs on raw (wet) gas in a low temperature condition, there is a danger of hydrate plug formation in the heat exchanging tubes of the ACU. To predict possible hydrate formation, a mathematical model of the air cooler thermal behavior used in the control system shall adequately calculate not only gas temperature at the cooler's outlet, but also a dew point value, a temperature at which condensation, as well as the gas hydrate formation point, onsets. This paper proposes a mathematical model allowing one to determine the pressure in the air cooler which makes hydrate formation for a given gas composition possible.

  11. Modelling the effects of waste components on cement hydration

    NARCIS (Netherlands)

    van Eijk, R.J.; Brouwers, Jos

    2000-01-01

    Ordinary Portland Cement (OPC) is often used for the Solidification/Stabilization (S/S) of waste containing heavy metals and salts. These waste componenents will precipitate in the form of insoluble compounds onto unreacted cement clinker grains preventing further hydration. In this study the long

  12. Embedded Cluster Models for Reactivity of the Hydrated Electron

    Czech Academy of Sciences Publication Activity Database

    Uhlig, Frank; Jungwirth, Pavel

    2013-01-01

    Roč. 227, č. 11 (2013), s. 1583-1593 ISSN 0942-9352 R&D Projects: GA ČR GBP208/12/G016 Institutional support: RVO:61388963 Keywords : hydrated electron * clusters * reactivity * ab initio molecular dynamics Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 1.178, year: 2013

  13. Alcohol cosurfactants in hydrate antiagglomeration.

    Science.gov (United States)

    York, J Dalton; Firoozabadi, Abbas

    2008-08-28

    Because of availability, as well as economical and environmental considerations, natural gas is projected to be the premium fuel of the 21st century. Natural gas production involves risk of the shut down of onshore and offshore operations because of blockage from hydrates formed from coproduced water and hydrate-forming species in natural gas. Industry practice has been usage of thermodynamic inhibitors such as alcohols often in significant amounts, which have undesirable environmental and safety impacts. Thermodynamic inhibitors affect bulk-phase properties and inhibit hydrate formation. An alternative is changing surface properties through usage of polymers and surfactants, effective at 0.5 to 3 weight % of coproduced water. One group of low dosage hydrate inhibitors (LDHI) are kinetic inhibitors, which affect nucleation rate and growth. A second group of LDHI are antiagglomerants, which prevent agglomeration of small hydrate crystallites. Despite great potential, work on hydrate antiagglomeration is very limited. This work centers on the effect of small amounts of alcohol cosurfactant in mixtures of two vastly different antiagglomerants. We use a model oil, water, and tetrahydrofuran as a hydrate-forming species. Results show that alcohol cosurfactants may help with antiagglomeration when traditional antiagglomerants alone are ineffective. Specifically, as low as 0.5 wt. % methanol cosurfactant used in this study is shown to be effective in antiagglomeration. Without the cosurfactant there will be agglomeration independent of the AA concentration. To our knowledge, this is the first report of alcohol cosurfactants in hydrate antiagglomerants. It is also shown that a rhamnolipid biosurfactant is effective down to only 0.5 wt. % in such mixtures, yet a quaternary ammonium chloride salt, i. e., quat, results in hydrate slurries down to 0.01 wt. %. However, biochemical surfactants are less toxic and biodegradable, and thus their use may prove beneficial even if at

  14. Modeling the degradation kinetics of ascorbic acid.

    Science.gov (United States)

    Peleg, Micha; Normand, Mark D; Dixon, William R; Goulette, Timothy R

    2018-06-13

    Most published reports on ascorbic acid (AA) degradation during food storage and heat preservation suggest that it follows first-order kinetics. Deviations from this pattern include Weibullian decay, and exponential drop approaching finite nonzero retention. Almost invariably, the degradation rate constant's temperature-dependence followed the Arrhenius equation, and hence the simpler exponential model too. A formula and freely downloadable interactive Wolfram Demonstration to convert the Arrhenius model's energy of activation, E a , to the exponential model's c parameter, or vice versa, are provided. The AA's isothermal and non-isothermal degradation can be simulated with freely downloadable interactive Wolfram Demonstrations in which the model's parameters can be entered and modified by moving sliders on the screen. Where the degradation is known a priori to follow first or other fixed order kinetics, one can use the endpoints method, and in principle the successive points method too, to estimate the reaction's kinetic parameters from considerably fewer AA concentration determinations than in the traditional manner. Freeware to do the calculations by either method has been recently made available on the Internet. Once obtained in this way, the kinetic parameters can be used to reconstruct the entire degradation curves and predict those at different temperature profiles, isothermal or dynamic. Comparison of the predicted concentration ratios with experimental ones offers a way to validate or refute the kinetic model and the assumptions on which it is based.

  15. Thermodynamic and Process Modelling of Gas Hydrate Systems in CO2 Capture Processes

    DEFF Research Database (Denmark)

    Herslund, Peter Jørgensen

    A novel gas separation technique based on gas hydrate formation (solid precipitation) is investigated by means of thermodynamic modeling and experimental investigations. This process has previously been proposed for application in post-combustion carbon dioxide capture from power station flue gases...... formation may be performed at pressures of approximately 20 MPa and temperatures below 280 K. Thermodynamic promoters are needed, to reduce the pressure requirement of the process, thereby making it competitive to existing capture technologies. A literature study is presented focusing mainly...... on thermodynamic gas hydrate promotion by hydrate formers stabilising the classical gas clathrate hydrate structures (sI, sII and sH) at low to moderate pressures. Much literature is available on this subject. Both experimental and theoretical studies presented in the literature have pointed out cyclopentane...

  16. Modeling Nanomechanical Behavior of Calcium-Silicate-Hydrate

    Science.gov (United States)

    2012-08-01

    coefficient is effective in making the C-S-H matrix stronger. However, increasing packing density also makes the material response more brittle ...16102-16107 Pellenq, R.J. –M and Van Damme, Henri., 2004, Why Does Concrete set?: The nature of Cohesion Forces in hardened Cement-Based...Hydrated Nanocomposites: Concrete, Bone , and Shale. J. Am. Ceram. Soc., 90(9): 2677-2692. Wu, Jianzhong. and John M. Prausnitz. 2002. Generalizations for

  17. Thermodynamic and kinetic modelling: creep resistant materials

    DEFF Research Database (Denmark)

    Hald, John; Korcakova, L.; Danielsen, Hilmar Kjartansson

    2008-01-01

    The use of thermodynamic and kinetic modelling of microstructure evolution in materials exposed to high temperatures in power plants is demonstrated with two examples. Precipitate stability in martensitic 9–12%Cr steels is modelled including equilibrium phase stability, growth of Laves phase part...

  18. Kinetics model of bainitic transformation with stress

    Science.gov (United States)

    Zhou, Mingxing; Xu, Guang; Hu, Haijiang; Yuan, Qing; Tian, Junyu

    2018-01-01

    Thermal simulations were conducted on a Gleeble 3800 simulator. The main purpose is to investigate the effects of stress on the kinetics of bainitic transformation in a Fe-C-Mn-Si advanced high strength bainitic steel. Previous studies on modeling the kinetics of stress affected bainitic transformation only considered the stress below the yield strength of prior austenite. In the present study, the stress above the yield strength of prior austenite is taken into account. A new kinetics model of bainitic transformation dependent on the stress (including the stresses below and above the yield strength of prior austenite) and the transformation temperature is proposed. The new model presents a good agreement with experimental results. In addition, it is found that the acceleration degree of stress on bainitic transformation increases with the stress whether its magnitude is below or above the yield strength of austenite, but the increasing rate gradually slows down when the stress is above the yield strength of austenite.

  19. Chemical Kinetic Models for Advanced Engine Combustion

    Energy Technology Data Exchange (ETDEWEB)

    Pitz, William J. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Mehl, Marco [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Westbrook, Charles K. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

    2014-10-22

    The objectives for this project are as follows: Develop detailed chemical kinetic models for fuel components used in surrogate fuels for compression ignition (CI), homogeneous charge compression ignition (HCCI) and reactivity-controlled compression-ignition (RCCI) engines; and Combine component models into surrogate fuel models to represent real transportation fuels. Use them to model low-temperature combustion strategies in HCCI, RCCI, and CI engines that lead to low emissions and high efficiency.

  20. Transient Electromagnetic Modelling and Imaging of Thin Resistive Structures: Applications for Gas Hydrate Assessment

    Science.gov (United States)

    Swidinsky, Andrei

    Gas hydrates are a solid, ice-like mixture of water and low molecular weight hydrocarbons. They are found under the permafrost and to a far greater extent under the ocean, usually at water depths greater than 300m. Hydrates are a potential energy resource, a possible factor in climate change, and a geohazard. For these reasons, it is critical that gas hydrate deposits are quantitatively assessed so that their concentrations, locations and distributions may be established. Due to their ice-like nature, hydrates are electrically insulating. Consequently, a method which remotely detects changes in seafloor electrical conductivity, such as marine controlled source electromagnetics (CSEM), is a useful geophysical tool for marine gas hydrate exploration. Hydrates are geometrically complex structures. Advanced electromagnetic modelling and imaging techniques are crucial for proper survey design and data interpretation. I develop a method to model thin resistive structures in conductive host media which may be useful in building approximate geological models of gas hydrate deposits using arrangements of multiple, bent sheets. I also investigate the possibility of interpreting diffusive electromagnetic data using seismic imaging techniques. To be processed in this way, such data must first be transformed into its non-diffusive, seismic-like counterpart. I examine such a transform from both an analytical and a numerical point of view, focusing on methods to overcome inherent numerical instabilities. This is the first step to applying seismic processing techniques to CSEM data to rapidly and efficiently image resistive gas hydrate structures. The University of Toronto marine electromagnetics group has deployed a permanent marine CSEM array offshore Vancouver Island, in the framework of the NEPTUNE Canada cabled observatory, for the purposes of monitoring gas hydrate deposits. In this thesis I also propose and examine a new CSEM survey technique for gas hydrate which would

  1. Seismic Modeling Of Reservoir Heterogeneity Scales: An Application To Gas Hydrate Reservoirs

    Science.gov (United States)

    Huang, J.; Bellefleur, G.; Milkereit, B.

    2008-12-01

    Natural gas hydrates, a type of inclusion compound or clathrate, are composed of gas molecules trapped within a cage of water molecules. The occurrence of gas hydrates in permafrost regions has been confirmed by core samples recovered from the Mallik gas hydrate research wells located within Mackenzie Delta in Northwest Territories of Canada. Strong vertical variations of compressional and shear sonic velocities and weak surface seismic expressions of gas hydrates indicate that lithological heterogeneities control the distribution of hydrates. Seismic scattering studies predict that typical scales and strong physical contrasts due to gas hydrate concentration will generate strong forward scattering, leaving only weak energy captured by surface receivers. In order to understand the distribution of hydrates and the seismic scattering effects, an algorithm was developed to construct heterogeneous petrophysical reservoir models. The algorithm was based on well logs showing power law features and Gaussian or Non-Gaussian probability density distribution, and was designed to honor the whole statistical features of well logs such as the characteristic scales and the correlation among rock parameters. Multi-dimensional and multi-variable heterogeneous models representing the same statistical properties were constructed and applied to the heterogeneity analysis of gas hydrate reservoirs. The petrophysical models provide the platform to estimate rock physics properties as well as to study the impact of seismic scattering, wave mode conversion, and their integration on wave behavior in heterogeneous reservoirs. Using the Biot-Gassmann theory, the statistical parameters obtained from Mallik 5L-38, and the correlation length estimated from acoustic impedance inversion, gas hydrate volume fraction in Mallik area was estimated to be 1.8%, approximately 2x108 m3 natural gas stored in a hydrate bearing interval within 0.25 km2 lateral extension and between 889 m and 1115 m depth

  2. A New Critical State Model for Geomechanical Behavior of Methane Hydrate-Bearing Sands

    Science.gov (United States)

    Lin, J. S.; Xing, P.; Rutqvist, J.; Seol, Y.; Choi, J. H.

    2014-12-01

    Methane hydrate bearing sands behave like sands once the hydrate has dissociated, but could exhibit a substantial increase in the shear strength, stiffness and dilatancy as the degree of hydrate saturation increases. A new critical state model was developed that incorporates the spatially mobilized plane (SMP) concept, which has been proven effective in modeling mechanical behavior of sands. While this new model was built on the basic constructs of the critical state model, important enhancements were introduced. The model adopted the t-stress concept, which defined the normal and shear stress on the SMP, in describing the plastic behavior of the soil. In this connection the versatile Matsuoka-Nakai yield criterion was also employed, which defined the general three dimensional yield behavior. The resulting constitutive law was associated in the t-stress space, but became non-associated in the conventional p-q stress space as it should be for sands. The model also introduced a generalized degree of hydrate saturation concept that was modified from the pioneering work of the Cambridge group. The model gives stress change when the sands are subjected to straining, and/or to hydrate saturation changes. The performance of the model has been found satisfactory using data from laboratory triaxial tests on reconstituted samples and core samples taken from Nankai Trough, Japan. The model has been implemented into FLAC3D. A coupling example with the multiphase flow code, TOUGH+, is presented which simulates the mechanical behavior of a sample when the surrounding temperature has been raised, and the hydrate undergoes state change and no longer resides in the stability zone.

  3. Modelling of oceanic gas hydrate instability and methane release in response to climate change

    International Nuclear Information System (INIS)

    Reagan, M.T.; Moridis, G.J.

    2008-01-01

    Methane releases from oceanic hydrates are thought to have played a significant role in climatic changes that have occurred in the past. In this study, gas hydrate accumulations subjected to temperature changes were modelled in order to assess their potential for future methane releases into the ocean. Recent ocean and atmospheric chemistry studies were used to model 2 climate scenarios. Two types of hydrate accumulations were used to represent dispersed, low-saturation deposits. The 1-D multiphase thermodynamic-hydrological model considered the properties of benthic sediments; ocean depth; sea floor temperature; the saturation and distribution of the hydrates; and the effect of benthic biogeochemical activity. Results of the simulations showed that shallow deposits undergo rapid dissociation and are capable of producing methane fluxes of 2 to 13 mol m 3 per year over a period of decades. The fluxes exceed the ability of the anaerobic sea floor environment to sequester or consume the methane. A large proportion of the methane released in the scenarios emerged in the gas phase. Arctic hydrates may pose a threat to regional and global ecological systems. It was concluded that results of the study will be coupled with global climate models in order to assess the impact of the methane releases in relation to global climatic change. 39 refs., 5 figs

  4. Kinetic modeling of reactions in Foods

    NARCIS (Netherlands)

    Boekel, van M.A.J.S.

    2008-01-01

    The level of quality that food maintains as it travels down the production-to-consumption path is largely determined by the chemical, biochemical, physical, and microbiological changes that take place during its processing and storage. Kinetic Modeling of Reactions in Foods demonstrates how to

  5. A MODEL FOR POSTRADIATION STEM CELL KINETICS,

    Science.gov (United States)

    In polycythemic rats observed for 17 days postradiation (300 R, 250 KVP X-rays) it was noted that stem cell release diminished to 8 percent of the...correlate these findings with a kinetic model of erythropoiesis. It was suggested that the initial depression in stem cell release might be due to cellular

  6. Modeling of Oceanic Gas Hydrate Instability and Methane Release in Response to Climate Change

    Energy Technology Data Exchange (ETDEWEB)

    Reagan, Matthew; Reagan, Matthew T.; Moridis, George J.

    2008-04-15

    Paleooceanographic evidence has been used to postulate that methane from oceanic hydrates may have had a significant role in regulating global climate, implicating global oceanic deposits of methane gas hydrate as the main culprit in instances of rapid climate change that have occurred in the past. However, the behavior of contemporary oceanic methane hydrate deposits subjected to rapid temperature changes, like those predicted under future climate change scenarios, is poorly understood. To determine the fate of the carbon stored in these hydrates, we performed simulations of oceanic gas hydrate accumulations subjected to temperature changes at the seafloor and assessed the potential for methane release into the ocean. Our modeling analysis considered the properties of benthic sediments, the saturation and distribution of the hydrates, the ocean depth, the initial seafloor temperature, and for the first time, estimated the effect of benthic biogeochemical activity. The results show that shallow deposits--such as those found in arctic regions or in the Gulf of Mexico--can undergo rapid dissociation and produce significant methane fluxes of 2 to 13 mol/yr/m{sup 2} over a period of decades, and release up to 1,100 mol of methane per m{sup 2} of seafloor in a century. These fluxes may exceed the ability of the seafloor environment (via anaerobic oxidation of methane) to consume the released methane or sequester the carbon. These results will provide a source term to regional or global climate models in order to assess the coupling of gas hydrate deposits to changes in the global climate.

  7. A new model of equilibrium subsurface hydration on Mars

    Science.gov (United States)

    Hecht, M. H.

    2011-12-01

    One of the surprises of the Odyssey mission was the discovery by the Gamma Ray Spectrometer (GRS) suite of large concentrations of water-equivalent hydrogen (WEH) in the shallow subsurface at low latitudes, consistent with 5-7% regolith water content by weight (Mitrofanov et al. Science 297, p. 78, 2002; Feldman et al. Science 297, p. 75, 2002). Water at low latitudes on Mars is generally believed to be sequestered in the form of hydrated minerals. Numerous attempts have been made to relate the global map of WEH to specific mineralogy. For example Feldman et al. (Geophys. Res. Lett., 31, L16702, 2004) associated an estimated 10% sulfate content of the soil with epsomite (51% water), hexahydrite (46% water) and kieserite (13% water). In such studies, stability maps have been created by assuming equilibration of the subsurface water vapor density with a global mean annual column mass vapor density. Here it is argued that this value significantly understates the subsurface humidity. Results from the Phoenix mission are used to suggest that the midday vapor pressure measured just above the surface is a better proxy for the saturation vapor pressure of subsurface hydrous minerals. The measured frostpoint at the Phoenix site was found to be equal to the surface temperature by night and the modeled temperature at the top of the ice table by day (Zent et al. J. Geophys. Res., 115, E00E14, 2010). It was proposed by Hecht (41st LPSC abstract #1533, 2010) that this phenomenon results from water vapor trapping at the coldest nearby surface. At night, the surface is colder than the surface of the ice table; by day it is warmer. Thus, at night, the subsurface is bounded by a fully saturated layer of cold water frost or adsorbed water at the surface, not by the dry boundary layer itself. This argument is not strongly dependent on the particular saturation vapor pressure (SVP) of ice or other subsurface material, only on the thickness of the dry layer. Specifically, the diurnal

  8. Physical properties and rock physics models of sediment containing natural and laboratory-formed methane gas hydrate

    Science.gov (United States)

    Winters, W.J.; Pecher, I.A.; Waite, W.F.; Mason, D.H.

    2004-01-01

    This paper presents results of shear strength and acoustic velocity (p-wave) measurements performed on: (1) samples containing natural gas hydrate from the Mallik 2L-38 well, Mackenzie Delta, Northwest Territories; (2) reconstituted Ottawa sand samples containing methane gas hydrate formed in the laboratory; and (3) ice-bearing sands. These measurements show that hydrate increases shear strength and p-wave velocity in natural and reconstituted samples. The proportion of this increase depends on (1) the amount and distribution of hydrate present, (2) differences, in sediment properties, and (3) differences in test conditions. Stress-strain curves from the Mallik samples suggest that natural gas hydrate does not cement sediment grains. However, stress-strain curves from the Ottawa sand (containing laboratory-formed gas hydrate) do imply cementation is present. Acoustically, rock physics modeling shows that gas hydrate does not cement grains of natural Mackenzie Delta sediment. Natural gas hydrates are best modeled as part of the sediment frame. This finding is in contrast with direct observations and results of Ottawa sand containing laboratory-formed hydrate, which was found to cement grains (Waite et al. 2004). It therefore appears that the microscopic distribution of gas hydrates in sediment, and hence the effect of gas hydrate on sediment physical properties, differs between natural deposits and laboratory-formed samples. This difference may possibly be caused by the location of water molecules that are available to form hydrate. Models that use laboratory-derived properties to predict behavior of natural gas hydrate must account for these differences.

  9. Effect of temperature on hydration kinetics and polymerization of tricalcium silicate in stirred suspensions of CaO-saturated solutions

    International Nuclear Information System (INIS)

    Grant, Steven A.; Boitnott, Ginger E.; Korhonen, Charles J.; Sletten, Ronald S.

    2006-01-01

    Tricalcium silicate was hydrated at 274, 278, 283, 298, and 313 K in stirred suspensions of saturated CaO solutions under a nitrogen-gas atmosphere until the end of deceleratory period. The suspension conductivities and energy flows were measured continuously. The individual reaction rates for tricalcium silicate dissolution, calcium silicate hydrate precipitation, and calcium hydroxide precipitation were calculated from these measurements. The results suggest that the proportion of tricalcium silicate dissolved was determined by the rate of tricalcium silicate dissolution and the time to very rapid calcium hydroxide precipitation. The time to very rapid calcium hydroxide precipitation was more sensitive to changes in temperature than was the rate of tricalcium silicate dissolution, so that the proportion of tricalcium silicate hydration dissolved by the deceleratory period increased with decreasing temperature. The average chain length of the calcium silicate hydrate ascertained by magic-angle spinning nuclear magnetic resonance spectroscopy increased with increasing temperature

  10. Kinetic mechanism for modeling of electrochemical reactions.

    Science.gov (United States)

    Cervenka, Petr; Hrdlička, Jiří; Přibyl, Michal; Snita, Dalimil

    2012-04-01

    We propose a kinetic mechanism of electrochemical interactions. We assume fast formation and recombination of electron donors D- and acceptors A+ on electrode surfaces. These mediators are continuously formed in the electrode matter by thermal fluctuations. The mediators D- and A+, chemically equivalent to the electrode metal, enter electrochemical interactions on the electrode surfaces. Electrochemical dynamics and current-voltage characteristics of a selected electrochemical system are studied. Our results are in good qualitative agreement with those given by the classical Butler-Volmer kinetics. The proposed model can be used to study fast electrochemical processes in microsystems and nanosystems that are often out of the thermal equilibrium. Moreover, the kinetic mechanism operates only with the surface concentrations of chemical reactants and local electric potentials, which facilitates the study of electrochemical systems with indefinable bulk.

  11. Kinetics model development of cocoa bean fermentation

    Science.gov (United States)

    Kresnowati, M. T. A. P.; Gunawan, Agus Yodi; Muliyadini, Winny

    2015-12-01

    Although Indonesia is one of the biggest cocoa beans producers in the world, Indonesian cocoa beans are oftenly of low quality and thereby frequently priced low in the world market. In order to improve the quality, adequate post-harvest cocoa processing techniques are required. Fermentation is the vital stage in series of cocoa beans post harvest processing which could improve the quality of cocoa beans, in particular taste, aroma, and colours. During the fermentation process, combination of microbes grow producing metabolites that serve as the precursors for cocoa beans flavour. Microbial composition and thereby their activities will affect the fermentation performance and influence the properties of cocoa beans. The correlation could be reviewed using a kinetic model that includes unstructured microbial growth, substrate utilization and metabolic product formation. The developed kinetic model could be further used to design cocoa bean fermentation process to meet the expected quality. Further the development of kinetic model of cocoa bean fermentation also serve as a good case study of mixed culture solid state fermentation, that has rarely been studied. This paper presents the development of a kinetic model for solid-state cocoa beans fermentation using an empirical approach. Series of lab scale cocoa bean fermentations, either natural fermentations without starter addition or fermentations with mixed yeast and lactic acid bacteria starter addition, were used for model parameters estimation. The results showed that cocoa beans fermentation can be modelled mathematically and the best model included substrate utilization, microbial growth, metabolites production and its transport. Although the developed model still can not explain the dynamics in microbial population, this model can sufficiently explained the observed changes in sugar concentration as well as metabolic products in the cocoa bean pulp.

  12. Modeling inhomogeneous DNA replication kinetics.

    Directory of Open Access Journals (Sweden)

    Michel G Gauthier

    Full Text Available In eukaryotic organisms, DNA replication is initiated at a series of chromosomal locations called origins, where replication forks are assembled proceeding bidirectionally to replicate the genome. The distribution and firing rate of these origins, in conjunction with the velocity at which forks progress, dictate the program of the replication process. Previous attempts at modeling DNA replication in eukaryotes have focused on cases where the firing rate and the velocity of replication forks are homogeneous, or uniform, across the genome. However, it is now known that there are large variations in origin activity along the genome and variations in fork velocities can also take place. Here, we generalize previous approaches to modeling replication, to allow for arbitrary spatial variation of initiation rates and fork velocities. We derive rate equations for left- and right-moving forks and for replication probability over time that can be solved numerically to obtain the mean-field replication program. This method accurately reproduces the results of DNA replication simulation. We also successfully adapted our approach to the inverse problem of fitting measurements of DNA replication performed on single DNA molecules. Since such measurements are performed on specified portion of the genome, the examined DNA molecules may be replicated by forks that originate either within the studied molecule or outside of it. This problem was solved by using an effective flux of incoming replication forks at the model boundaries to represent the origin activity outside the studied region. Using this approach, we show that reliable inferences can be made about the replication of specific portions of the genome even if the amount of data that can be obtained from single-molecule experiments is generally limited.

  13. Prediction of hydroxyl concentrations in cement pore water using a numerical cement hydration model

    NARCIS (Netherlands)

    Eijk, van R.J.; Brouwers, H.J.H.

    2000-01-01

    In this paper, a 3D numerical cement hydration model is used for predicting alkali and hydroxyl concentrations in cement pore water. First, this numerical model is calibrated for Dutch cement employing both chemical shrinkage and calorimetric experiments. Secondly, the strength development of some

  14. Fractional order creep model for dam concrete considering degree of hydration

    Science.gov (United States)

    Huang, Yaoying; Xiao, Lei; Bao, Tengfei; Liu, Yu

    2018-05-01

    Concrete is a material that is an intermediate between an ideal solid and an ideal fluid. The creep of concrete is related not only to the loading age and duration, but also to its temperature and temperature history. Fractional order calculus is a powerful tool for solving physical mechanics modeling problems. Using a software element based on the generalized Kelvin model, a fractional order creep model of concrete considering the loading age and duration is established. Then, the hydration rate of cement is considered in terms of the degree of hydration, and the fractional order creep model of concrete considering the degree of hydration is established. Moreover, uniaxial tensile creep tests of dam concrete under different curing temperatures were conducted, and the results were combined with the creep test data and complex optimization method to optimize the parameters of a new creep model. The results show that the fractional tensile creep model based on hydration degree can better describe the tensile creep properties of concrete, and this model involves fewer parameters than the 8-parameter model.

  15. Free Radical Chemistry of Disinfection Byproducts 1: Kinetics of Hydrated Electron and Hydroxyl Radical Reactions with Halonitromethanes in Water

    International Nuclear Information System (INIS)

    B. J. Mincher; R. V. Fox; S. P. Mezyk; T. Helgeson; S. K. Cole; W. J. Cooper; P. R. Gardinali

    2006-01-01

    Halonitromethanes are disinfection-byproducts formed during ozonation and chlorine/chloramine treatment of waters that contain bromide ion and natural organic matter. In this study, the chemical kinetics of the free-radical-induced degradations of a series of halonitromethanes were determined. Absolute rate constants for hydroxyl radical, OH, and hydrated electron, e aq - , reaction with both chlorinated and brominated halonitromethanes were measured using the techniques of electron pulse radiolysis and transient absorption spectroscopy. The bimolecular rate constants obtained, k (M -1 s -1 ), for e aq - /OH, respectively, were the following: chloronitromethane (3.01 ± 0.40) x 10 10 /(1.94 ± 0.32) x 10 8 ; dichloronitromethane (3.21 ± 0.17) x 10 10 /(5.12 ± 0.77) x 10 8 ; bromonitromethane (3.13 ± 0.06) x 10 10 /(8.36 ± 0.57) x 107; dibromonitromethane (3.07 ± 0.40) x 10 10 /(4.75 ± 0.98) x 10 8 ; tribromonitromethane (2.29 ± 0.39) x 10 10 /(3.25 ± 0.67) x 10 8 ; bromochloronitromethane (2.93 ± 0.47) x 10 10 /(4.2 ± 1.1) x 10 8 ; bromodichloronitromethane (2.68 ± 0.13) x 10 10 /(1.02 ± 0.15) x 10 8 ; and dibromochloronitromethane (2.95 ± 0.43) x 10 10 /(1.80 ± 0.31) x 10 8 at room temperature and pH ∼7. Comparison data were also obtained for hydroxyl radical reaction with bromoform (1.50 ± 0.05) x 10 8 , bromodichloromethane (7.11 ± 0.26) x 10 7 , and chlorodibromomethane (8.31 ± 0.25) x 10 7 M -1 s -1 , respectively. These rate constants are compared to recently obtained data for trichloronitromethane and bromonitromethane, as well as to other established literature data for analogous compounds

  16. A stochastic model of enzyme kinetics

    Science.gov (United States)

    Stefanini, Marianne; Newman, Timothy; McKane, Alan

    2003-10-01

    Enzyme kinetics is generally modeled by deterministic rate equations, and in the simplest case leads to the well-known Michaelis-Menten equation. It is plausible that stochastic effects will play an important role at low enzyme concentrations. We have addressed this by constructing a simple stochastic model which can be exactly solved in the steady-state. Throughout a wide range of parameter values Michaelis-Menten dynamics is replaced by a new and simple theoretical result.

  17. Compartmental modeling and tracer kinetics

    CERN Document Server

    Anderson, David H

    1983-01-01

    This monograph is concerned with mathematical aspects of compartmental an­ alysis. In particular, linear models are closely analyzed since they are fully justifiable as an investigative tool in tracer experiments. The objective of the monograph is to bring the reader up to date on some of the current mathematical prob­ lems of interest in compartmental analysis. This is accomplished by reviewing mathematical developments in the literature, especially over the last 10-15 years, and by presenting some new thoughts and directions for future mathematical research. These notes started as a series of lectures that I gave while visiting with the Division of Applied ~1athematics, Brown University, 1979, and have developed in­ to this collection of articles aimed at the reader with a beginning graduate level background in mathematics. The text can be used as a self-paced reading course. With this in mind, exercises have been appropriately placed throughout the notes. As an aid in reading the material, the e~d of a ...

  18. Feasibility Study on a Microwave-Based Sensor for Measuring Hydration Level Using Human Skin Models.

    Science.gov (United States)

    Brendtke, Rico; Wiehl, Michael; Groeber, Florian; Schwarz, Thomas; Walles, Heike; Hansmann, Jan

    2016-01-01

    Tissue dehydration results in three major types of exsiccosis--hyper-, hypo-, or isonatraemia. All three types entail alterations of salt concentrations leading to impaired biochemical processes, and can finally cause severe morbidity. The aim of our study was to demonstrate the feasibility of a microwave-based sensor technology for the non-invasive measurement of the hydration status. Electromagnetic waves at high frequencies interact with molecules, especially water. Hence, if a sample contains free water molecules, this can be detected in a reflected microwave signal. To develop the sensor system, human three-dimensional skin equivalents were instituted as a standardized test platform mimicking reproducible exsiccosis scenarios. Therefore, skin equivalents with a specific hydration and density of matrix components were generated and microwave measurements were performed. Hydration-specific spectra allowed deriving the hydration state of the skin models. A further advantage of the skin equivalents was the characterization of the impact of distinct skin components on the measured signals to investigate mechanisms of signal generation. The results demonstrate the feasibility of a non-invasive microwave-based hydration sensor technology. The sensor bears potential to be integrated in a wearable medical device for personal health monitoring.

  19. Feasibility Study on a Microwave-Based Sensor for Measuring Hydration Level Using Human Skin Models.

    Directory of Open Access Journals (Sweden)

    Rico Brendtke

    Full Text Available Tissue dehydration results in three major types of exsiccosis--hyper-, hypo-, or isonatraemia. All three types entail alterations of salt concentrations leading to impaired biochemical processes, and can finally cause severe morbidity. The aim of our study was to demonstrate the feasibility of a microwave-based sensor technology for the non-invasive measurement of the hydration status. Electromagnetic waves at high frequencies interact with molecules, especially water. Hence, if a sample contains free water molecules, this can be detected in a reflected microwave signal. To develop the sensor system, human three-dimensional skin equivalents were instituted as a standardized test platform mimicking reproducible exsiccosis scenarios. Therefore, skin equivalents with a specific hydration and density of matrix components were generated and microwave measurements were performed. Hydration-specific spectra allowed deriving the hydration state of the skin models. A further advantage of the skin equivalents was the characterization of the impact of distinct skin components on the measured signals to investigate mechanisms of signal generation. The results demonstrate the feasibility of a non-invasive microwave-based hydration sensor technology. The sensor bears potential to be integrated in a wearable medical device for personal health monitoring.

  20. MODELING STYRENE HYDROGENATION KINETICS USING PALLADIUM CATALYSTS

    Directory of Open Access Journals (Sweden)

    G. T. Justino

    Full Text Available Abstract The high octane number of pyrolysis gasoline (PYGAS explains its insertion in the gasoline pool. However, its use is troublesome due to the presence of gum-forming chemicals which, in turn, can be removed via hydrogenation. The use of Langmuir-Hinshelwood kinetic models was evaluated for hydrogenation of styrene, a typical gum monomer, using Pd/9%Nb2O5-Al2O3 as catalyst. Kinetic models accounting for hydrogen dissociative and non-dissociative adsorption were considered. The availability of one or two kinds of catalytic sites was analyzed. Experiments were carried out in a semi-batch reactor at constant temperature and pressure in the absence of transport limitations. The conditions used in each experiment varied between 16 - 56 bar and 60 - 100 ºC for pressure and temperature, respectively. The kinetic models were evaluated using MATLAB and EMSO software. Models using adsorption of hydrogen and organic molecules on the same type of site fitted the data best.

  1. A kinetic model for chemical neurotransmission

    Science.gov (United States)

    Ramirez-Santiago, Guillermo; Martinez-Valencia, Alejandro; Fernandez de Miguel, Francisco

    Recent experimental observations in presynaptic terminals at the neuromuscular junction indicate that there are stereotyped patterns of cooperativeness in the fusion of adjacent vesicles. That is, a vesicle in hemifusion process appears on the side of a fused vesicle and which is followed by another vesicle in a priming state while the next one is in a docking state. In this talk we present a kinetic model for this morphological pattern in which each vesicle state previous to the exocytosis is represented by a kinetic state. This chain states kinetic model can be analyzed by means of a Master equation whose solution is simulated with the stochastic Gillespie algorithm. With this approach we have reproduced the responses to the basal release in the absence of stimulation evoked by the electrical activity and the phenomena of facilitation and depression of neuromuscular synapses. This model offers new perspectives to understand the underlying phenomena in chemical neurotransmission based on molecular interactions that result in the cooperativity between vesicles during neurotransmitter release. DGAPA Grants IN118410 and IN200914 and Conacyt Grant 130031.

  2. A dynamic model to explain hydration behaviour along the lanthanide series

    International Nuclear Information System (INIS)

    Duvail, M.; Spezia, R.; Vitorge, P.

    2008-01-01

    An understanding of the hydration structure of heavy atoms, such as transition metals, lanthanides and actinides, in aqueous solution is of fundamental importance in order to address their solvation properties and chemical reactivity. Herein we present a systematic molecular dynamics study of Ln 3+ hydration in bulk water that can be used as reference for experimental and theoretical research in this and related fields. Our study of hydration structure and dynamics along the entire Ln 3+ series provides a dynamic picture of the CN behavioural change from light (CN=9 predominating) to heavy (CN=8 predominating) lanthanides consistent with the exchange mechanism proposed by Helm, Merbach and co-workers. This scenario is summarized in this work. The hydrated light lanthanides are stable TTP structures containing two kinds of water molecules: six molecules forming the trigonal prism and three in the centre triangle. Towards the middle of the series both ionic radii and polarizabilities decrease, such that first-shell water-water repulsion increases and water-cation attraction decreases. This mainly applies for molecules of the centre triangle of the nine-fold structure. Thus, one of these molecules stay in the second hydration sphere of the lanthanide for longer average times, as one progresses along the lanthanide series. The interchange between predominantly CN=9 and CN=8 is found between Tb and Dy. Therefore, we propose a model that determines the properties governing the change in the first-shell coordination number across the series, confirming the basic hypothesis proposed by Helm and Merbach. We show that it is not a sudden change in behaviour, but rather that it results from a statistical predominance of one first hydration shell structure containing nine water molecules over one containing eight. This is observed progressively across the series. (O.M.)

  3. Modeling the hydration process of bean grains coated with carnauba wax

    Directory of Open Access Journals (Sweden)

    Aline Almeida da Paixão

    2017-08-01

    Full Text Available Edible waxes are widely used to maintain foodstuff until they are consumed. However, some products may be subjected to industrial procedures, such as hydration, prior to their consumption. Hydration of a material is a complex process, which aims to reconstitute the original characteristics of a product when in contact with a liquid phase. An important agricultural product that requires this procedure is beans. Thus, the purpose of this work is to study the hydration process of beans (cultivar BRSMG Majestoso in different temperatures and concentrations of carnauba wax, which is applied on the product surface. Beans with initial moisture content of 0.2015, 0.1972 and 0.1745 (d.b. corresponding to treatments 0 (witness, 1 (wax diluted in water in the ratio 1:1, and 2 (carnauba wax, without dilution were used. Later, these samples were imbibed in distilled water at temperatures of 20, 30 and 40 ºC, for 15 h. The temperature and the carnauba wax influenced the water absorption rate. The Peleg model described satisfactory experimental data and the Mitscherlich model presented biased residual distribution. The constants C1 and C2 of the Peleg model exhibited opposite behaviors with increasing temperatures in the hydration process.

  4. Cinética de hidratação de ligantes à base de alumina hidratável ou aluminato de cálcio Kinetics of hydration of binders based on hydratable alumina or calcium aluminate cement

    Directory of Open Access Journals (Sweden)

    I. R. Oliveira

    2007-03-01

    hydration depends on the knowledge of the variables that determine the kinetics of the involved reactions. In this context, the objective of this work was to evaluate the influence of the sources of the hydraulic binder, the temperature and the presence of matrix or inorganic additives on the hydration process, carried out through temperature measurements and oscillatory rheological tests, as a function of the time.

  5. Modeling hydrate formation conditions in the presence of electrolytes and polar inhibitor solutions

    International Nuclear Information System (INIS)

    Osfouri, Shahriar; Azin, Reza; Gholami, Reza; Izadpanah, Amir Abbas

    2015-01-01

    Highlights: • A new predictive model is proposed for prediction of hydrate formation pressures. • A new local composition model was used to evaluate water activity in the presence of electrolyte. • MEG, DEG and TEG were used to test ability of the proposed model in the presence of polar inhibitors. • Cage occupancies by methane for the small cage were higher than carbon dioxide for gas mixtures. • The proposed model gives better match with experimental data in mixed electrolyte solutions. - Abstract: In this paper, a new predictive model is proposed for prediction of gas hydrate formation conditions in the presence of single and mixed electrolytes and solutions containing both electrolyte and a polar inhibitor such as monoethylene glycol (MEG), diethylene glycol (DEG) and triethylene glycol (TEG). The proposed model is based on the γ–φ approach, which uses modified Patel–Teja equation of state (VPT EOS) for characterizing the vapor phase, the solid solution theory by van der Waals and Platteeuw for modeling the hydrate phase, the non-electrolyte NRTL-NRF local composition model and Pitzer–Debye–Huckel equation as short-range and long-range contributions to calculate water activity in single electrolyte solutions. Also, the Margules equation was used to determine the activity of water in solutions containing polar inhibitor (glycols). The model predictions are in acceptable agreement with experimental data. For single electrolyte solutions, the model predictions are similar to available models, while for mixtures of electrolytes and mixtures of electrolytes and inhibitors, the proposed model gives significantly better predictions. In addition, the absolute average deviation of hydrate formation pressures (AADP) for 144 experimental data in solutions containing single electrolyte is 5.86% and for 190 experimental data in mixed electrolytes solutions is 5.23%. Furthermore, the proposed model has an AADP of 14.13%, 5.82% and 5.28% in solutions

  6. Kinetic modeling in PET imaging of hypoxia

    Science.gov (United States)

    Li, Fan; Joergensen, Jesper T; Hansen, Anders E; Kjaer, Andreas

    2014-01-01

    Tumor hypoxia is associated with increased therapeutic resistance leading to poor treatment outcome. Therefore the ability to detect and quantify intratumoral oxygenation could play an important role in future individual personalized treatment strategies. Positron Emission Tomography (PET) can be used for non-invasive mapping of tissue oxygenation in vivo and several hypoxia specific PET tracers have been developed. Evaluation of PET data in the clinic is commonly based on visual assessment together with semiquantitative measurements e.g. standard uptake value (SUV). However, dynamic PET contains additional valuable information on the temporal changes in tracer distribution. Kinetic modeling can be used to extract relevant pharmacokinetic parameters of tracer behavior in vivo that reflects relevant physiological processes. In this paper, we review the potential contribution of kinetic analysis for PET imaging of hypoxia. PMID:25250200

  7. MATHEMATICAL MODELING OF ORANGE SEED DRYING KINETICS

    Directory of Open Access Journals (Sweden)

    Daniele Penteado Rosa

    2015-06-01

    Full Text Available Drying of orange seeds representing waste products from juice processing was studied in the temperatures of 40, 50, 60 and 70 °C and drying velocities of 0.6, 1.0 and 1.4 m/s. Experimental drying kinetics of orange seeds were obtained using a convective air forced dryer. Three thin-layer models: Page model, Lewis model, and the Henderson-Pabis model and the diffusive model were used to predict the drying curves. The Henderson-Pabis and the diffusive models show the best fitting performance and statistical evaluations. Moreover, the temperature dependence on the effective diffusivity followed an Arrhenius relationship, and the activation energies ranging from 16.174 to 16.842 kJ/mol

  8. Kinetic electron model for plasma thruster plumes

    Science.gov (United States)

    Merino, Mario; Mauriño, Javier; Ahedo, Eduardo

    2018-03-01

    A paraxial model of an unmagnetized, collisionless plasma plume expanding into vacuum is presented. Electrons are treated kinetically, relying on the adiabatic invariance of their radial action integral for the integration of Vlasov's equation, whereas ions are treated as a cold species. The quasi-2D plasma density, self-consistent electric potential, and electron pressure, temperature, and heat fluxes are analyzed. In particular, the model yields the collisionless cooling of electrons, which differs from the Boltzmann relation and the simple polytropic laws usually employed in fluid and hybrid PIC/fluid plume codes.

  9. Kinetics of conformational changes of fibronectin adsorbed onto model surfaces.

    Science.gov (United States)

    Baujard-Lamotte, L; Noinville, S; Goubard, F; Marque, P; Pauthe, E

    2008-05-01

    Fibronectin (FN), a large glycoprotein found in body fluids and in the extracellular matrix, plays a key role in numerous cellular behaviours. We investigate FN adsorption onto hydrophilic bare silica and hydrophobic polystyrene (PS) surfaces using Fourier transform infrared spectroscopy-attenuated total reflection (FTIR-ATR) in aqueous medium. Adsorption kinetics using different bulk concentrations of FN were followed for 2h and the surface density of adsorbed FN and its time-dependent conformational changes were determined. When adsorption occurs onto the hydrophilic surface, FN molecules keep their native conformation independent of the adsorption conditions, but the amount of adsorbed FN increases with time and the bulk concentration. Although the protein surface density is the same on the hydrophobic PS surface, this has a strong impact on the average conformation of the adsorbed FN layer. Indeed, interfacial hydration changes induced by adsorption onto the hydrophobic surface lead to a decrease in unhydrated beta-sheet content and cause an increase in hydrated beta-strand and hydrated random domain content of adsorbed FN. This conformational change is mainly dependent on the bulk concentration. Indeed, at low bulk concentrations, the secondary structures of adsorbed FN molecules undergo strong unfolding, allowing an extended and hydrated conformation of the protein. At high bulk concentrations, the molecular packing reduces the unfolding of the stereoregular structures of the FN molecules, preventing stronger spreading of the protein.

  10. Kinetics of the reaction of iron blast furnace slag/hydrated lime sorbents with SO{sub 2} at low temperatures: effects of the presence of CO{sub 2}, O{sub 2}, and NOx

    Energy Technology Data Exchange (ETDEWEB)

    Liu, C.F.; Shih, S.M. [Industrial Technological Research Institute, Hsinchu (Taiwan)

    2009-09-15

    The effects of the presence of CO{sub 2}, O{sub 2}, and NOx in the flue gas on the kinetics of the sulfation of blast furnace slag/hydrated lime sorbents at low temperatures were studied using a differential fixed-bed reactor. When O{sub 2} and NOx were not present simultaneously, the reaction kinetics was about the same as that under the gas mixtures containing SO{sub 2}, H{sub 2}O, and N{sub 2} only, being affected mainly by the relative humidity. The sulfation of sorbents can be described by the surface coverage model and the model equations derived for the latter case. When both O{sub 2} and NOx, were present, the sulfation of sorbents was greatly enhanced, forming a great amount of sulfate in addition to sulfite. The surface coverage model is still valid in this case, but the model equations obtained show a more marked effect of relative humidity and negligible effects of SO{sub 2} concentration and temperature on the reaction. The effect of sorbent composition on the reaction kinetics was entirely represented by the effects of the initial specific surface area (S{sub g0}) and the Ca molar content (M{sup -1}) of sorbent. The initial conversion rate of sorbent increased linearly with increasing S{sub g0}, and the ultimate conversion increased linearly with increasing S{sub g0}M{sup -1}. The model equations obtained in this work are applicable to describe the kinetics of the sulfation of the sorbents in the low-temperature dry and semidry fine gas desulfurization processes either with an upstream NOx, removal unit or without.111

  11. Chemical kinetics and modeling of planetary atmospheres

    Science.gov (United States)

    Yung, Yuk L.

    1990-01-01

    A unified overview is presented for chemical kinetics and chemical modeling in planetary atmospheres. The recent major advances in the understanding of the chemistry of the terrestrial atmosphere make the study of planets more interesting and relevant. A deeper understanding suggests that the important chemical cycles have a universal character that connects the different planets and ultimately link together the origin and evolution of the solar system. The completeness (or incompleteness) of the data base for chemical kinetics in planetary atmospheres will always be judged by comparison with that for the terrestrial atmosphere. In the latter case, the chemistry of H, O, N, and Cl species is well understood. S chemistry is poorly understood. In the atmospheres of Jovian planets and Titan, the C-H chemistry of simple species (containing 2 or less C atoms) is fairly well understood. The chemistry of higher hydrocarbons and the C-N, P-N chemistry is much less understood. In the atmosphere of Venus, the dominant chemistry is that of chlorine and sulfur, and very little is known about C1-S coupled chemistry. A new frontier for chemical kinetics both in the Earth and planetary atmospheres is the study of heterogeneous reactions. The formation of the ozone hole on Earth, the ubiquitous photochemical haze on Venus and in the Jovian planets and Titan all testify to the importance of heterogeneous reactions. It remains a challenge to connect the gas phase chemistry to the production of aerosols.

  12. Kinetic modelling of the Maillard reaction between proteins and sugars

    NARCIS (Netherlands)

    Brands, C.M.J.

    2002-01-01

    Keywords: Maillard reaction, sugar isomerisation, kinetics, multiresponse modelling, brown colour formation, lysine damage, mutagenicity, casein, monosaccharides, disaccharides, aldoses, ketoses

    The aim of this thesis was to determine the kinetics of the Maillard reaction between

  13. Clustering mechanism of oxocarboxylic acids involving hydration reaction: Implications for the atmospheric models

    Science.gov (United States)

    Liu, Ling; Kupiainen-Määttä, Oona; Zhang, Haijie; Li, Hao; Zhong, Jie; Kurtén, Theo; Vehkamäki, Hanna; Zhang, Shaowen; Zhang, Yunhong; Ge, Maofa; Zhang, Xiuhui; Li, Zesheng

    2018-06-01

    The formation of atmospheric aerosol particles from condensable gases is a dominant source of particulate matter in the boundary layer, but the mechanism is still ambiguous. During the clustering process, precursors with different reactivities can induce various chemical reactions in addition to the formation of hydrogen bonds. However, the clustering mechanism involving chemical reactions is rarely considered in most of the nucleation process models. Oxocarboxylic acids are common compositions of secondary organic aerosol, but the role of oxocarboxylic acids in secondary organic aerosol formation is still not fully understood. In this paper, glyoxylic acid, the simplest and the most abundant atmospheric oxocarboxylic acid, has been selected as a representative example of oxocarboxylic acids in order to study the clustering mechanism involving hydration reactions using density functional theory combined with the Atmospheric Clusters Dynamic Code. The hydration reaction of glyoxylic acid can occur either in the gas phase or during the clustering process. Under atmospheric conditions, the total conversion ratio of glyoxylic acid to its hydration reaction product (2,2-dihydroxyacetic acid) in both gas phase and clusters can be up to 85%, and the product can further participate in the clustering process. The differences in cluster structures and properties induced by the hydration reaction lead to significant differences in cluster formation rates and pathways at relatively low temperatures.

  14. Hydration of Portland cement with additions of calcium sulfoaluminates

    International Nuclear Information System (INIS)

    Le Saoût, Gwenn; Lothenbach, Barbara; Hori, Akihiro; Higuchi, Takayuki; Winnefeld, Frank

    2013-01-01

    The effect of mineral additions based on calcium aluminates on the hydration mechanism of ordinary Portland cement (OPC) was investigated using isothermal calorimetry, thermal analysis, X-ray diffraction, scanning electron microscopy, solid state nuclear magnetic resonance and pore solution analysis. Results show that the addition of a calcium sulfoaluminate cement (CSA) to the OPC does not affect the hydration mechanism of alite but controls the aluminate dissolution. In the second blend investigated, a rapid setting cement, the amorphous calcium aluminate reacts very fast to ettringite. The release of aluminum ions strongly retards the hydration of alite but the C–S–H has a similar composition as in OPC with no additional Al to Si substitution. As in CSA–OPC, the aluminate hydration is controlled by the availability of sulfates. The coupling of thermodynamic modeling with the kinetic equations predicts the amount of hydrates and pore solution compositions as a function of time and validates the model in these systems.

  15. Thermodynamically consistent model calibration in chemical kinetics

    Directory of Open Access Journals (Sweden)

    Goutsias John

    2011-05-01

    Full Text Available Abstract Background The dynamics of biochemical reaction systems are constrained by the fundamental laws of thermodynamics, which impose well-defined relationships among the reaction rate constants characterizing these systems. Constructing biochemical reaction systems from experimental observations often leads to parameter values that do not satisfy the necessary thermodynamic constraints. This can result in models that are not physically realizable and may lead to inaccurate, or even erroneous, descriptions of cellular function. Results We introduce a thermodynamically consistent model calibration (TCMC method that can be effectively used to provide thermodynamically feasible values for the parameters of an open biochemical reaction system. The proposed method formulates the model calibration problem as a constrained optimization problem that takes thermodynamic constraints (and, if desired, additional non-thermodynamic constraints into account. By calculating thermodynamically feasible values for the kinetic parameters of a well-known model of the EGF/ERK signaling cascade, we demonstrate the qualitative and quantitative significance of imposing thermodynamic constraints on these parameters and the effectiveness of our method for accomplishing this important task. MATLAB software, using the Systems Biology Toolbox 2.1, can be accessed from http://www.cis.jhu.edu/~goutsias/CSS lab/software.html. An SBML file containing the thermodynamically feasible EGF/ERK signaling cascade model can be found in the BioModels database. Conclusions TCMC is a simple and flexible method for obtaining physically plausible values for the kinetic parameters of open biochemical reaction systems. It can be effectively used to recalculate a thermodynamically consistent set of parameter values for existing thermodynamically infeasible biochemical reaction models of cellular function as well as to estimate thermodynamically feasible values for the parameters of new

  16. Modeling in applied sciences a kinetic theory approach

    CERN Document Server

    Pulvirenti, Mario

    2000-01-01

    Modeling complex biological, chemical, and physical systems, in the context of spatially heterogeneous mediums, is a challenging task for scientists and engineers using traditional methods of analysis Modeling in Applied Sciences is a comprehensive survey of modeling large systems using kinetic equations, and in particular the Boltzmann equation and its generalizations An interdisciplinary group of leading authorities carefully develop the foundations of kinetic models and discuss the connections and interactions between model theories, qualitative and computational analysis and real-world applications This book provides a thoroughly accessible and lucid overview of the different aspects, models, computations, and methodology for the kinetic-theory modeling process Topics and Features * Integrated modeling perspective utilized in all chapters * Fluid dynamics of reacting gases * Self-contained introduction to kinetic models * Becker–Doring equations * Nonlinear kinetic models with chemical reactions * Kinet...

  17. Acceleration transforms and statistical kinetic models

    International Nuclear Information System (INIS)

    LuValle, M.J.; Welsher, T.L.; Svoboda, K.

    1988-01-01

    For a restricted class of problems a mathematical model of microscopic degradation processes, statistical kinetics, is developed and linked through acceleration transforms to the information which can be obtained from a system in which the only observable sign of degradation is sudden and catastrophic failure. The acceleration transforms were developed in accelerated life testing applications as a tool for extrapolating from the observable results of an accelerated life test to the dynamics of the underlying degradation processes. A particular concern of a physicist attempting to interpreted the results of an analysis based on acceleration transforms is determining the physical species involved in the degradation process. These species may be (a) relatively abundant or (b) relatively rare. The main results of this paper are a theorem showing that for an important subclass of statistical kinetic models, acceleration transforms cannot be used to distinguish between cases a and b, and an example showing that in some cases falling outside the restrictions of the theorem, cases a and b can be distinguished by their acceleration transforms

  18. THCM Coupled Model for Hydrate-Bearing Sediments: Data Analysis and Design of New Field Experiments (Marine and Permafrost Settings)

    Energy Technology Data Exchange (ETDEWEB)

    Sanchez, Marcelo J. [Texas A & M Univ., College Station, TX (United States); Santamarina, J. Carlos [King Abdullah Univ. of Science and Technology (Saudi Arabia)

    2017-02-14

    Gas hydrates are solid compounds made of water molecules clustered around low molecular weight gas molecules such as methane, hydrogen, and carbon dioxide. Methane hydrates form under pressure (P) and temperature (T) conditions that are common in sub-permafrost layers and in deep marine sediments. Stability conditions constrain the occurrence of gas hydrates to submarine sediments and permafrost regions. The amount of technically recoverable methane trapped in gas hydrate may exceed 104tcf. Gas hydrates are a potential energy resource, can contribute to climate change, and can cause large-scale seafloor instabilities. In addition, hydrate formation can be used for CO2 sequestration (also through CO2-CH4 replacement), and efficient geological storage seals. The experimental study of hydrate bearing sediments has been hindered by the very low solubility of methane in water (lab testing), and inherent sampling difficulties associated with depressurization and thermal changes during core extraction. This situation has prompted more decisive developments in numerical modeling in order to advance the current understanding of hydrate bearing sediments, and to investigate/optimize production strategies and implications. The goals of this research has been to addresses the complex thermo-hydro-chemo-mechanical THCM coupled phenomena in hydrate-bearing sediments, using a truly coupled numerical model that incorporates sound and proven constitutive relations, satisfies fundamental conservation principles. Analytical solutions aimed at verifying the proposed code have been proposed as well. These tools will allow to better analyze available data and to further enhance the current understanding of hydrate bearing sediments in view of future field experiments and the development of production technology.

  19. In vivo human corneal hydration control dynamics: A new model

    NARCIS (Netherlands)

    Odenthal, M.T.P.; Nieuwendaal, C.P.; Venema, H.W.; Oosting, J.; Kok, J.H.C.; Kijlstra, A.

    1999-01-01

    PURPOSE. To introduce a new model describing human in vivo corneal deswelling after hypoxic contact lens wear, based on a damped harmonic oscillator, which can describe an overshoot in corneal deswelling, to compare this new model with the currently used exponential model, and also to test whether a

  20. In vivo human corneal hydration control dynamics: a new model

    NARCIS (Netherlands)

    Odenthal, M. T.; Nieuwendaal, C. P.; Venema, H. W.; Oosting, J.; Kok, J. H. C.; Kijlstra, A.

    1999-01-01

    PURPOSE: To introduce a new model describing human in vivo corneal deswelling after hypoxic contact lens wear, based on a damped harmonic oscillator, which can describe an overshoot in corneal deswelling, to compare this new model with the currently used exponential model, and also to test whether a

  1. Modeling of Cation Binding in Hydrated 2:1 Clay Minerals - Final Report

    International Nuclear Information System (INIS)

    Smith, David E.

    2000-01-01

    Hydrated 2:1 clay minerals are high surface area, layered silicates that play a unique role in determining the fate of radionuclides in the environment. This project consisted of developing and implementing computer simulation methods for molecular characterization of the swelling and ion exchange properties of Hydrated 2:1 clay minerals, and the subsequent analysis and theoretical modeling with a view toward improving contaminant transport modeling as well as soil remediation and radionuclide containment strategies. Project results included the (a) development of simulation methods to treat clays under environmentally relevant conditions of variable water vapor pressure; (b) calculation of clay swelling thermodynamics as a function of interlayer ion size and charge (calculated quantities include immersion energies, free energies, and entropies of swelling); and (c) calculation of ion exchange free energies, including contributions from changing interlayer water contents and layer spacing

  2. MODELLING OF KINETICS OF FLUORINE ADSORPTION ONTO MODIFIED DIATOMITE

    Directory of Open Access Journals (Sweden)

    VEACESLAV ZELENTSOV

    2017-03-01

    Full Text Available The paper presents kinetics modelling of adsorption of fluorine onto modified diatomite, its fundamental characteristics and mathematical derivations. Three models of defluoridation kinetics were used to fit the experimental results on adsorption fluorine onto diatomite: the pseudo-first order model Lagergren, the pseudo-second order model G. McKay and H.S. Ho and intraparticle diffusion model of W.J. Weber and J.C. Morris. Kinetics studies revealed that the adsorption of fluorine followed second-order rate model, complimented by intraparticle diffusion kinetics. The adsorption mechanism of fluorine involved three stages – external surface adsorption, intraparticle diffusion and the stage of equilibrium.

  3. Holographic kinetic k-essence model

    Energy Technology Data Exchange (ETDEWEB)

    Cruz, Norman [Departamento de Fisica, Facultad de Ciencia, Universidad de Santiago de Chile, Casilla 307, Santiago (Chile)], E-mail: ncruz@lauca.usach.cl; Gonzalez-Diaz, Pedro F.; Rozas-Fernandez, Alberto [Colina de los Chopos, Instituto de Fisica Fundamental, Consejo Superior de Investigaciones Cientificas, Serrano 121, 28006 Madrid (Spain)], E-mail: a.rozas@cfmac.csic.es; Sanchez, Guillermo [Departamento de Matematica y Ciencia de la Computacion, Facultad de Ciencia, Universidad de Santiago de Chile, Casilla 307, Santiago (Chile)], E-mail: gsanchez@usach.cl

    2009-08-31

    We consider a connection between the holographic dark energy density and the kinetic k-essence energy density in a flat FRW universe. With the choice c{>=}1, the holographic dark energy can be described by a kinetic k-essence scalar field in a certain way. In this Letter we show this kinetic k-essential description of the holographic dark energy with c{>=}1 and reconstruct the kinetic k-essence function F(X)

  4. Kinetic depletion model for pellet ablation

    International Nuclear Information System (INIS)

    Kuteev, Boris V.

    2001-11-01

    A kinetic model for depletion effect, which determines pellet ablation when the pellet passes a rational magnetic surface, is formulated. The model predicts a moderate decrease of the ablation rate compared with the earlier considered monoenergy versions [1, 2]. For typical T-10 conditions the ablation rate reduces by a reactor of 2.5 when the 1-mm pellet penetrates through the plasma center. A substantial deceleration of pellets -about 15% per centimeter of low shire rational q region; is predicted. Penetration for Low Field Side and High Field Side injections is considered taking into account modification of the electron distribution function by toroidal magnetic field. It is shown that Shafranov shift and toroidal effects yield the penetration length for HFS injection higher by a factor of 1.5. This fact should be taken into account when plasma-shielding effects on penetration are considered. (author)

  5. Replacement of CH4 in the hydrate by use of liquid CO2

    International Nuclear Information System (INIS)

    Ota, Masaki; Morohashi, Kenji; Abe, Yuki; Watanabe, Masaru; Smith, Richard Lee Jr.; Inomata, Hiroshi

    2005-01-01

    The dynamics of CH 4 replacement in the CH 4 hydrate with saturated liquid CO 2 at 273.2 K was measured with a high pressure optical cell. The results showed that CH 4 in the hydrate gradually moved to the liquid CO 2 phase while CO 2 in the liquid phase penetrated into the hydrate from the quantitative analysis. The decomposing process of the CH 4 hydrate during the replacement was analyzed with in situ Raman spectroscopy, which allowed us to distinguish the cage structure of the CH 4 hydrate and discuss the microscopic view of the replacement in the hydrate. It was found that the decomposition of the medium cage (M-cage) in the CH 4 hydrate proceeded faster than that of the small cage (S-cage). The observed rate difference could be related to the stability of the S-cage in the CH 4 hydrate or the re-formation tendency of CH 4 and water molecules in the S-cage after decomposing the hydrate structure, whereas the guest molecule exchange of CH 4 with CO 2 could occur in the M-cage. Based on the experimental data, we developed a kinetic model for calculation of the CH 4 remaining in the hydrate considering the decomposition rate difference between the M-cage and S-cage in the CH 4 hydrate. The results indicate that the driving force could be the fugacity difference between the fluid phase and the hydrate phase for the replacement process

  6. Kinetic model of excess activated sludge thermohydrolysis.

    Science.gov (United States)

    Imbierowicz, Mirosław; Chacuk, Andrzej

    2012-11-01

    Thermal hydrolysis of excess activated sludge suspensions was carried at temperatures ranging from 423 K to 523 K and under pressure 0.2-4.0 MPa. Changes of total organic carbon (TOC) concentration in a solid and liquid phase were measured during these studies. At the temperature 423 K, after 2 h of the process, TOC concentration in the reaction mixture decreased by 15-18% of the initial value. At 473 K total organic carbon removal from activated sludge suspension increased to 30%. It was also found that the solubilisation of particulate organic matter strongly depended on the process temperature. At 423 K the transfer of TOC from solid particles into liquid phase after 1 h of the process reached 25% of the initial value, however, at the temperature of 523 K the conversion degree of 'solid' TOC attained 50% just after 15 min of the process. In the article a lumped kinetic model of the process of activated sludge thermohydrolysis has been proposed. It was assumed that during heating of the activated sludge suspension to a temperature in the range of 423-523 K two parallel reactions occurred. One, connected with thermal destruction of activated sludge particles, caused solubilisation of organic carbon and an increase of dissolved organic carbon concentration in the liquid phase (hydrolysate). The parallel reaction led to a new kind of unsolvable solid phase, which was further decomposed into gaseous products (CO(2)). The collected experimental data were used to identify unknown parameters of the model, i.e. activation energies and pre-exponential factors of elementary reactions. The mathematical model of activated sludge thermohydrolysis appropriately describes the kinetics of reactions occurring in the studied system. Copyright © 2012 Elsevier Ltd. All rights reserved.

  7. A multivariable model for predicting the frictional behaviour and hydration of the human skin.

    Science.gov (United States)

    Veijgen, N K; van der Heide, E; Masen, M A

    2013-08-01

    The frictional characteristics of skin-object interactions are important when handling objects, in the assessment of perception and comfort of products and materials and in the origins and prevention of skin injuries. In this study, based on statistical methods, a quantitative model is developed that describes the friction behaviour of human skin as a function of the subject characteristics, contact conditions, the properties of the counter material as well as environmental conditions. Although the frictional behaviour of human skin is a multivariable problem, in literature the variables that are associated with skin friction have been studied using univariable methods. In this work, multivariable models for the static and dynamic coefficients of friction as well as for the hydration of the skin are presented. A total of 634 skin-friction measurements were performed using a recently developed tribometer. Using a statistical analysis, previously defined potential influential variables were linked to the static and dynamic coefficient of friction and to the hydration of the skin, resulting in three predictive quantitative models that descibe the friction behaviour and the hydration of human skin respectively. Increased dynamic coefficients of friction were obtained from older subjects, on the index finger, with materials with a higher surface energy at higher room temperatures, whereas lower dynamic coefficients of friction were obtained at lower skin temperatures, on the temple with rougher contact materials. The static coefficient of friction increased with higher skin hydration, increasing age, on the index finger, with materials with a higher surface energy and at higher ambient temperatures. The hydration of the skin was associated with the skin temperature, anatomical location, presence of hair on the skin and the relative air humidity. Predictive models have been derived for the static and dynamic coefficient of friction using a multivariable approach. These

  8. A New Approach to Modeling Densities and Equilibria of Ice and Gas Hydrate Phases

    Science.gov (United States)

    Zyvoloski, G.; Lucia, A.; Lewis, K. C.

    2011-12-01

    The Gibbs-Helmholtz Constrained (GHC) equation is a new cubic equation of state that was recently derived by Lucia (2010) and Lucia et al. (2011) by constraining the energy parameter in the Soave form of the Redlich-Kwong equation to satisfy the Gibbs-Helmholtz equation. The key attributes of the GHC equation are: 1) It is a multi-scale equation because it uses the internal energy of departure, UD, as a natural bridge between the molecular and bulk phase length scales. 2) It does not require acentric factors, volume translation, regression of parameters to experimental data, binary (kij) interaction parameters, or other forms of empirical correlations. 3) It is a predictive equation of state because it uses a database of values of UD determined from NTP Monte Carlo simulations. 4) It can readily account for differences in molecular size and shape. 5) It has been successfully applied to non-electrolyte mixtures as well as weak and strong aqueous electrolyte mixtures over wide ranges of temperature, pressure and composition to predict liquid density and phase equilibrium with up to four phases. 6) It has been extensively validated with experimental data. 7) The AAD% error between predicted and experimental liquid density is 1% while the AAD% error in phase equilibrium predictions is 2.5%. 8) It has been used successfully within the subsurface flow simulation program FEHM. In this work we describe recent extensions of the multi-scale predictive GHC equation to modeling the phase densities and equilibrium behavior of hexagonal ice and gas hydrates. In particular, we show that radial distribution functions, which can be determined by NTP Monte Carlo simulations, can be used to establish correct standard state fugacities of 1h ice and gas hydrates. From this, it is straightforward to determine both the phase density of ice or gas hydrates as well as any equilibrium involving ice and/or hydrate phases. A number of numerical results for mixtures of N2, O2, CH4, CO2, water

  9. Thermal oxidative degradation kinetics of agricultural residues using distributed activation energy model and global kinetic model.

    Science.gov (United States)

    Ren, Xiu'e; Chen, Jianbiao; Li, Gang; Wang, Yanhong; Lang, Xuemei; Fan, Shuanshi

    2018-08-01

    The study concerned the thermal oxidative degradation kinetics of agricultural residues, peanut shell (PS) and sunflower shell (SS). The thermal behaviors were evaluated via thermogravimetric analysis and the kinetic parameters were determined by using distributed activation energy model (DAEM) and global kinetic model (GKM). Results showed that thermal oxidative decomposition of two samples processed in three zones; the ignition, burnout, and comprehensive combustibility between two agricultural residues were of great difference; and the combustion performance could be improved by boosting heating rate. The activation energy ranges calculated by the DAEM for the thermal oxidative degradation of PS and SS were 88.94-145.30 kJ mol -1 and 94.86-169.18 kJ mol -1 , respectively. The activation energy obtained by the GKM for the oxidative decomposition of hemicellulose and cellulose was obviously lower than that for the lignin oxidation at identical heating rate. To some degree, the determined kinetic parameters could acceptably simulate experimental data. Copyright © 2018 Elsevier Ltd. All rights reserved.

  10. A discontinuous Galerkin method on kinetic flocking models

    OpenAIRE

    Tan, Changhui

    2014-01-01

    We study kinetic representations of flocking models. They arise from agent-based models for self-organized dynamics, such as Cucker-Smale and Motsch-Tadmor models. We prove flocking behavior for the kinetic descriptions of flocking systems, which indicates a concentration in velocity variable in infinite time. We propose a discontinuous Galerkin method to treat the asymptotic $\\delta$-singularity, and construct high order positive preserving scheme to solve kinetic flocking systems.

  11. Hydration kinetics of cements by Time-Domain Nuclear Magnetic Resonance: Application to Portland-cement-derived endodontic pastes

    International Nuclear Information System (INIS)

    Bortolotti, Villiam; Fantazzini, Paola; Mongiorgi, Romano; Sauro, Salvatore; Zanna, Silvano

    2012-01-01

    Time-Domain Nuclear Magnetic Resonance (TD-NMR) of 1 H nuclei is used to monitor the maturation up to 30 days of three different endodontic cement pastes. The “Solid–liquid” separation of the NMR signals and quasi-continuous distributions of relaxation times allow one to follow the formation of chemical compounds and the build-up of the nano- and subnano-structured C–S–H gel. 1 H populations, distinguished by their different mobilities, can be identified and assigned to water confined within the pores of the C–S–H gel, to crystallization water and Portlandite, and to hydroxyl groups. Changes of the TD-NMR parameters during hydration are in agreement with the expected effects of the different additives, which, as it is known, can substantially modify the rate of reactions and the properties of cementitious pastes. Endodontic cements are suitable systems to check the ability of this non-destructive technique to give insight into the complex hydration process of real cement pastes.

  12. Medical chilling device designed for hypothermic hydration graft storage system: Design, thermohydrodynamic modeling, and preliminary testing

    Energy Technology Data Exchange (ETDEWEB)

    Seo, Jung Hwan [Hongik University, Seoul (Korea, Republic of)

    2015-02-15

    Hypothermic hydration graft storage is essential to reduce the metabolic demand of cells in vitro. The alleviated metabolic demands reduce the emergence rate of anaerobic metabolism generating adenosine triphosphate (ATP) energy that creates free radicals. The cessive free radicals can damage cells and tissues due to their highly oxidative power with molecules. Current cooling systems such as a conventional air cooling system and an ice pack system are inappropriate for chilling cell tissues in vitro because of inconvenience in use and inconsistent temperature sustainability caused by large size and progressive melting, respectively. Here, we develop a medical chilling device (MCD) for hypothermic hydration graft storage based on thermo-hydrodynamic modeling and thermal electric cooling technology. Our analysis of obtained hydrodynamic thermal behavior of the MCD revealed that the hypothermic condition of 4 .deg. C was continuously maintained, which increased the survival rates of cells in vitro test by reduced free radicals. The validated performance of the MCD promises future development of an optimal hypothermic hydration graft storage system designed for clinical use.

  13. Mathematical Model and Simulation of Gas Hydrate Reservoir Decomposition by Depressurization Modèle mathématique et simulation de dépressurisation et de décompression d’un réservoir d’hydrates de méthane

    Directory of Open Access Journals (Sweden)

    Zhao J.

    2012-05-01

    Full Text Available The numerical model for the depressurization of methane hydrates in a confined reservoir is presented based on mass conservation in porous media, incorporating multiphase flow theory and kinetics of gas hydrate dissociation. The universal implicit difference method is adopted, and the corresponding computer program is developed. During the production of the hydrate reservoir, distribution and the physical changes are analyzed and the gas hydrate dissociation and gas production law are studied from the computation. A numerical simulation shows that the reservoir pressure is descending slowly, which benefits the stabilization of the reservoir and inevitably decreases the efficiency in the production of gas hydrates in the depressurizing process. The gas production rate is controlled by the well pressure. The results are presented to show how this model may be used to estimate a lower downhole pressure of the well for hydrate recovery and how these results depend on reservoir and hydrate properties. Le modèle numérique présenté ici simule la dépressurisation d’hydrates de méthane dans un réservoir confiné; il se base sur le principe de conservation de la masse en milieu poreux, en intégrant la théorie de l’écoulement polyphasique et la cinétique de dissociation des hydrates de méthane. La méthode implicite et universelle des différences finies est utilisée et le programme informatique qui s’y rapporte est développé. Lors de l’exploitation du réservoir d’hydrates de méthane, la répartition et les changements physiques sont analysés et les lois sur la dissociation des hydrates de méthane et la production de gaz sont étudiées à partir des calculs. Une simulation numérique montre que la pression dans le réservoir diminue lentement, ce qui permet au réservoir de se stabiliser et diminue inévitablement le rendement de l’exploitation d’hydrates de méthane lors du processus de dépressurisation. Le rythme de

  14. Quantitative study of Portland cement hydration by X-Ray diffraction/Rietveld analysis and geochemical modeling

    Science.gov (United States)

    Coutelot, F.; Seaman, J. C.; Simner, S.

    2017-12-01

    In this study the hydration of Portland cements containing blast-furnace slag and type V fly ash were investigated during cement curing using X-ray diffraction, with geochemical modeling used to calculate the total volume of hydrates. The goal was to evaluate the relationship between the starting component levels and the hydrate assemblages that develop during the curing process. Blast furnace-slag levels of 60, 45 and 30 wt.% were studied in blends containing fly ash and Portland cement. Geochemical modelling described the dissolution of the clinker, and predicted quantitatively the amount of hydrates. In all cases the experiments showed the presence of C-S-H, portlandite and ettringite. The quantities of ettringite, portlandite and the amorphous phases as determined by XRD agreed well with the calculated amounts of these phases after different periods of time. These findings show that changes in the bulk composition of hydrating cements can be described by geochemical models. Such a comparison between experimental and modelled data helps to understand in more detail the active processes occurring during cement hydration.

  15. Thermoluminescence of zircon: a kinetic model

    CERN Document Server

    Turkin, A A; Vainshtein, D I; Hartog, H W D

    2003-01-01

    The mineral zircon, ZrSiO sub 4 , belongs to a class of promising materials for geochronometry by means of thermoluminescence (TL) dating. The development of a reliable and reproducible method for TL dating with zircon requires detailed knowledge of the processes taking place during exposure to ionizing radiation, long-term storage, annealing at moderate temperatures and heating at a constant rate (TL measurements). To understand these processes one needs a kinetic model of TL. This paper is devoted to the construction of such a model. The goal is to study the qualitative behaviour of the system and to determine the parameters and processes controlling TL phenomena of zircon. The model considers the following processes: (i) Filling of electron and hole traps at the excitation stage as a function of the dose rate and the dose for both (low dose rate) natural and (high dose rate) laboratory irradiation. (ii) Time dependence of TL fading in samples irradiated under laboratory conditions. (iii) Short time anneali...

  16. Reflected kinetics model for nuclear space reactor kinetics and control scoping calculations

    Energy Technology Data Exchange (ETDEWEB)

    Washington, K.E.

    1986-05-01

    The objective of this research is to develop a model that offers an alternative to the point kinetics (PK) modelling approach in the analysis of space reactor kinetics and control studies. Modelling effort will focus on the explicit treatment of control drums as reactivity input devices so that the transition to automatic control can be smoothly done. The proposed model is developed for the specific integration of automatic control and the solution of the servo mechanism problem. The integration of the kinetics model with an automatic controller will provide a useful tool for performing space reactor scoping studies for different designs and configurations. Such a tool should prove to be invaluable in the design phase of a space nuclear system from the point of view of kinetics and control limitations.

  17. Reflected kinetics model for nuclear space reactor kinetics and control scoping calculations

    International Nuclear Information System (INIS)

    Washington, K.E.

    1986-05-01

    The objective of this research is to develop a model that offers an alternative to the point kinetics (PK) modelling approach in the analysis of space reactor kinetics and control studies. Modelling effort will focus on the explicit treatment of control drums as reactivity input devices so that the transition to automatic control can be smoothly done. The proposed model is developed for the specific integration of automatic control and the solution of the servo mechanism problem. The integration of the kinetics model with an automatic controller will provide a useful tool for performing space reactor scoping studies for different designs and configurations. Such a tool should prove to be invaluable in the design phase of a space nuclear system from the point of view of kinetics and control limitations

  18. Mechanistic study and modeling of radionuclides retention by the hydrated calcium silicates (HCS) of cements

    International Nuclear Information System (INIS)

    Pointeau, I.

    2000-09-01

    This work attempts to investigate the modelling of radioisotopes (Cs + , Pb 2+ , Eu 3+ ) immobilization in cement matrix, in the frame of the design of engineered barrier of a deep radwaste repository. The model development concept consists of three major steps: - surface chemistry modelling of the calcium silicate hydrate CSH, used to simulate hydrated cement behaviour; - solid analysis of the batch sorption experiments: identification of the uptake mechanism; - both previous steps are used, with isotherm data, in the modelling of the radioisotopes immobilization in the CSH matrix. Final results: (all modelling are available for all the range of studied Ca/Si ratios and have been validated with predictive calculations). - A thermodynamic modelling of the CSH surface chemistry has been developed. The labile calcium and proton sorption constants on silanol sites (>SiOH) have been extracted. - Cs + is sorbed on two sites. The silanol site (weak site) has a high site density (10 sites.nm -2 ), which accounts for the CSH unsaturation in high [CS + ]. A strong site is also identified. - Pb 2+ immobilization in CSH matrix is modelled with surface equilibria and solubility equilibrium. - Eu 3+ fixation has been investigated with solid analysis: Site-Selective anti Time-Resolved Luminescence Spectroscopy, XPS and SEM-EDS. Eu 3+ thus does not precipitate in CSH water but is sorbed on the CSH surface (high hydroxylated environment). Europium is also (minority site) inserted in the CSH framework. (author)

  19. Supercritical kinetic analysis in simplified system of fuel debris using integral kinetic model

    International Nuclear Information System (INIS)

    Tuya, Delgersaikhan; Obara, Toru

    2016-01-01

    Highlights: • Kinetic analysis in simplified weakly coupled fuel debris system was performed. • The integral kinetic model was used to simulate criticality accidents. • The fission power and released energy during simulated accident were obtained. • Coupling between debris regions and its effect on the fission power was obtained. - Abstract: Preliminary prompt supercritical kinetic analyses in a simplified coupled system of fuel debris designed to roughly resemble a melted core of a nuclear reactor were performed using an integral kinetic model. The integral kinetic model, which can describe region- and time-dependent fission rate in a coupled system of arbitrary geometry, was used because the fuel debris system is weakly coupled in terms of neutronics. The results revealed some important characteristics of coupled systems, such as the coupling between debris regions and the effect of the coupling on the fission rate and released energy in each debris region during the simulated criticality accident. In brief, this study showed that the integral kinetic model can be applied to supercritical kinetic analysis in fuel debris systems and also that it can be a useful tool for investigating the effect of the coupling on consequences of a supercritical accident.

  20. Geological modeling for methane hydrate reservoir characterization in the eastern Nankai Trough, offshore Japan

    Science.gov (United States)

    Tamaki, M.; Komatsu, Y.; Suzuki, K.; Takayama, T.; Fujii, T.

    2012-12-01

    The eastern Nankai trough, which is located offshore of central Japan, is considered as an attractive potential resource field of methane hydrates. Japan Oil, Gas and Metals National Corporation is planning to conduct a production test in early 2013 at the AT1 site in the north slope of Daini-Atsumi Knoll in the eastern Nankai Trough. The depositional environment of methane hydrate-bearing sediments around the production test site is a deep submarine-fan turbidite system, and it is considered that the reservoir properties should show lateral as well as vertical heterogeneity. Since the variations in the reservoir heterogeneity have an impact on the methane hydrate dissociation and gas production performance, precise geological models describing reservoir heterogeneity would be required for the evaluation of reservoir potentials. In preparation for the production test, 3 wells; two monitoring boreholes (AT1-MC and AT1-MT1) and a coring well (AT1-C), were newly acquired in 2012. In addition to a geotechnical hole drilling survey in 2011 (AT1-GT), totally log data from 2 wells and core data from 2 wells were obtained around the production test site. In this study, we conducted well correlations between AT1 and A1 wells drilled in 2003 and then, 3D geological models were updated including AT1 well data in order to refine hydrate reservoir characterization around the production test site. The results of the well correlations show that turbidite sand layers are characterized by good lateral continuity, and give significant information for the distribution morphology of sand-rich channel fills. We also reviewed previously conducted 3D geological models which consist of facies distributions and petrophysical properties distributions constructed from integration of 3D seismic data and a well data (A1 site) adopting a geostatistical approach. In order to test the practical validity of the previously generated models, cross-validation was conducted using AT1 well data. The

  1. Fully implicit kinetic modelling of collisional plasmas

    International Nuclear Information System (INIS)

    Mousseau, V.A.

    1996-05-01

    This dissertation describes a numerical technique, Matrix-Free Newton Krylov, for solving a simplified Vlasov-Fokker-Planck equation. This method is both deterministic and fully implicit, and may not have been a viable option before current developments in numerical methods. Results are presented that indicate the efficiency of the Matrix-Free Newton Krylov method for these fully-coupled, nonlinear integro-differential equations. The use and requirement for advanced differencing is also shown. To this end, implementations of Chang-Cooper differencing and flux limited Quadratic Upstream Interpolation for Convective Kinematics (QUICK) are presented. Results are given for a fully kinetic ion-electron problem with a self consistent electric field calculated from the ion and electron distribution functions. This numerical method, including advanced differencing, provides accurate solutions, which quickly converge on workstation class machines. It is demonstrated that efficient steady-state solutions can be achieved to the non-linear integro-differential equation, obtaining quadratic convergence, without incurring the large memory requirements of an integral operator. Model problems are presented which simulate plasma impinging on a plate with both high and low neutral particle recycling typical of a divertor in a Tokamak device. These model problems demonstrate the performance of the new solution method

  2. Kinetic modeling of cell metabolism for microbial production.

    Science.gov (United States)

    Costa, Rafael S; Hartmann, Andras; Vinga, Susana

    2016-02-10

    Kinetic models of cellular metabolism are important tools for the rational design of metabolic engineering strategies and to explain properties of complex biological systems. The recent developments in high-throughput experimental data are leading to new computational approaches for building kinetic models of metabolism. Herein, we briefly survey the available databases, standards and software tools that can be applied for kinetic models of metabolism. In addition, we give an overview about recently developed ordinary differential equations (ODE)-based kinetic models of metabolism and some of the main applications of such models are illustrated in guiding metabolic engineering design. Finally, we review the kinetic modeling approaches of large-scale networks that are emerging, discussing their main advantages, challenges and limitations. Copyright © 2015 Elsevier B.V. All rights reserved.

  3. Kinetic modeling in pre-clinical positron emission tomography

    Energy Technology Data Exchange (ETDEWEB)

    Kuntner, Claudia [AIT Austrian Institute of Technology GmbH, Seibersdorf (Austria). Biomedical Systems, Health and Environment Dept.

    2014-07-01

    Pre-clinical positron emission tomography (PET) has evolved in the last few years from pure visualization of radiotracer uptake and distribution towards quantification of the physiological parameters. For reliable and reproducible quantification the kinetic modeling methods used to obtain relevant parameters of radiotracer tissue interaction are important. Here we present different kinetic modeling techniques with a focus on compartmental models including plasma input models and reference tissue input models. The experimental challenges of deriving the plasma input function in rodents and the effect of anesthesia are discussed. Finally, in vivo application of kinetic modeling in various areas of pre-clinical research is presented and compared to human data.

  4. Kinetic models of cell growth, substrate utilization and bio ...

    African Journals Online (AJOL)

    Bio-decolorization kinetic studies of distillery effluent in a batch culture were conducted using Aspergillus fumigatus. A simple model was proposed using the Logistic Equation for the growth, Leudeking-Piret kinetics for bio-decolorization, and also for substrate utilization. The proposed models appeared to provide a suitable ...

  5. Hydration kinetics for the alite, belite, and calcium aluminate phase in Portland cements from 27Al and 29Si MAS NMR spectroscopy

    DEFF Research Database (Denmark)

    Skibsted, Jørgen; Jensen, Ole Mejlhede; Jakobsen, Hans Jørgen

    1997-01-01

    29Si magic-angle spinning (MAS) NMR spectroscopy is shown to be a valuable tool for obtaining the quantities of alite and belite in hydrated Portland cements. The hydration (1-180 days) of a white Portland cement with 10 wt.% silica fume added is investigated and the degrees of hydration for alite...

  6. A constitutive mechanical model for gas hydrate bearing sediments incorporating inelastic mechanisms

    KAUST Repository

    Sá nchez, Marcelo; Gai, Xuerui; Santamarina, Carlos

    2016-01-01

    , hydrates dissociate and move from the solid to the gas phase. Hydrate dissociation is accompanied by significant changes in sediment structure and strongly affects its mechanical behavior (e.g., sediment stiffenss, strength and dilatancy). The mechanical

  7. Influence of limestone on the hydration of Portland cements

    International Nuclear Information System (INIS)

    Lothenbach, Barbara; Le Saout, Gwenn; Gallucci, Emmanuel; Scrivener, Karen

    2008-01-01

    The influence of the presence of limestone on the hydration of Portland cement was investigated. Blending of Portland cement with limestone was found to influence the hydrate assemblage of the hydrated cement. Thermodynamic calculations as well as experimental observations indicated that in the presence of limestone, monocarbonate instead of monosulfate was stable. Thermodynamic modelling showed that the stabilisation of monocarbonate in the presence of limestone indirectly stabilised ettringite leading to a corresponding increase of the total volume of the hydrate phase and a decrease of porosity. The measured difference in porosity between the 'limestone-free' cement, which contained less than 0.3% CO 2 , and a cement containing 4% limestone, however, was much smaller than calculated. Coupling of thermodynamic modelling with a set of kinetic equations which described the dissolution of the clinker, predicted quantitatively the amount of hydrates. The quantities of ettringite, portlandite and amorphous phase as determined by TGA and XRD agreed well with the calculated amounts of these phases after different periods of time. The findings in this paper show that changes in the bulk composition of hydrating cements can be followed by coupled thermodynamic models. Comparison between experimental and modelled data helps to understand in more detail the dominating processes during cement hydration

  8. Topological modeling of methane hydrate crystallization from low to high water cut emulsion systems

    OpenAIRE

    Melchuna , Aline; Cameirão , Ana; Herri , Jean-Michel; Glénat , Philippe

    2016-01-01

    International audience; Hydrate formation and remediation in oil flowlines facilities represent a major concern for oil industry in respect of capital and operational costs. It is necessary to have a better understanding on the hydrate formation process to be more efficient in hydrate prevention, especially in respect to additive dosage. This work is a contribution to enhance the knowledge of hydrate formation at high water cuts, by introducing new techniques of analysis in the Archimede flow...

  9. Performance of neutron kinetics models for ADS transient analyses

    International Nuclear Information System (INIS)

    Rineiski, A.; Maschek, W.; Rimpault, G.

    2002-01-01

    Within the framework of the SIMMER code development, neutron kinetics models for simulating transients and hypothetical accidents in advanced reactor systems, in particular in Accelerator Driven Systems (ADSs), have been developed at FZK/IKET in cooperation with CE Cadarache. SIMMER is a fluid-dynamics/thermal-hydraulics code, coupled with a structure model and a space-, time- and energy-dependent neutronics module for analyzing transients and accidents. The advanced kinetics models have also been implemented into KIN3D, a module of the VARIANT/TGV code (stand-alone neutron kinetics) for broadening application and for testing and benchmarking. In the paper, a short review of the SIMMER and KIN3D neutron kinetics models is given. Some typical transients related to ADS perturbations are analyzed. The general models of SIMMER and KIN3D are compared with more simple techniques developed in the context of this work to get a better understanding of the specifics of transients in subcritical systems and to estimate the performance of different kinetics options. These comparisons may also help in elaborating new kinetics models and extending existing computation tools for ADS transient analyses. The traditional point-kinetics model may give rather inaccurate transient reaction rate distributions in an ADS even if the material configuration does not change significantly. This inaccuracy is not related to the problem of choosing a 'right' weighting function: the point-kinetics model with any weighting function cannot take into account pronounced flux shape variations related to possible significant changes in the criticality level or to fast beam trips. To improve the accuracy of the point-kinetics option for slow transients, we have introduced a correction factor technique. The related analyses give a better understanding of 'long-timescale' kinetics phenomena in the subcritical domain and help to evaluate the performance of the quasi-static scheme in a particular case. One

  10. Bayesian inference of chemical kinetic models from proposed reactions

    KAUST Repository

    Galagali, Nikhil; Marzouk, Youssef M.

    2015-01-01

    © 2014 Elsevier Ltd. Bayesian inference provides a natural framework for combining experimental data with prior knowledge to develop chemical kinetic models and quantify the associated uncertainties, not only in parameter values but also in model

  11. Dissociation behavior of pellet shaped mixed gas hydrate samples that contain propane as a guest

    International Nuclear Information System (INIS)

    Kawamura, Taro; Sakamoto, Yasuhide; Ohtake, Michika; Yamamoto, Yoshitaka; Komai, Takeshi; Haneda, Hironori; Yoon, Ji-Ho; Ohga, Kotaro

    2006-01-01

    The dissociation kinetics of mixed gas hydrates that contain propane as a guest molecule have been investigated. The mixed gas hydrates used in this work were artificially prepared using the binary gas mixture of methane-propane and the ternary gas mixture of methane-ethane-propane. The crystal structures and the guest compositions of the mixed hydrates were clearly identified by using Raman spectroscopy and gas chromatography. The dissociation rates of the gas hydrates observed under several isothermal and isobaric conditions were discussed with an analytical model. The isobaric conditions were achieved by pressurizing with mixed gases using buffer cylinders, which had similar compositions to those of the initial gases used for synthesizing each hydrate sample. Interestingly, the calculated result agreed well with the experimentally observed results only when the composition of the vapor phase was assumed to be identical with that of the hydrate phase instead of the bulk (equilibrium) gas composition

  12. On the applicability of one- and many-electron quantum chemistry models for hydrated electron clusters

    Science.gov (United States)

    Turi, László

    2016-04-01

    We evaluate the applicability of a hierarchy of quantum models in characterizing the binding energy of excess electrons to water clusters. In particular, we calculate the vertical detachment energy of an excess electron from water cluster anions with methods that include one-electron pseudopotential calculations, density functional theory (DFT) based calculations, and ab initio quantum chemistry using MP2 and eom-EA-CCSD levels of theory. The examined clusters range from the smallest cluster size (n = 2) up to nearly nanosize clusters with n = 1000 molecules. The examined cluster configurations are extracted from mixed quantum-classical molecular dynamics trajectories of cluster anions with n = 1000 water molecules using two different one-electron pseudopotenial models. We find that while MP2 calculations with large diffuse basis set provide a reasonable description for the hydrated electron system, DFT methods should be used with precaution and only after careful benchmarking. Strictly tested one-electron psudopotentials can still be considered as reasonable alternatives to DFT methods, especially in large systems. The results of quantum chemistry calculations performed on configurations, that represent possible excess electron binding motifs in the clusters, appear to be consistent with the results using a cavity structure preferring one-electron pseudopotential for the hydrated electron, while they are in sharp disagreement with the structural predictions of a non-cavity model.

  13. On the applicability of one- and many-electron quantum chemistry models for hydrated electron clusters

    Energy Technology Data Exchange (ETDEWEB)

    Turi, László, E-mail: turi@chem.elte.hu [Department of Physical Chemistry, Eötvös Loránd University, P.O. Box 32, H-1518 Budapest 112 (Hungary)

    2016-04-21

    We evaluate the applicability of a hierarchy of quantum models in characterizing the binding energy of excess electrons to water clusters. In particular, we calculate the vertical detachment energy of an excess electron from water cluster anions with methods that include one-electron pseudopotential calculations, density functional theory (DFT) based calculations, and ab initio quantum chemistry using MP2 and eom-EA-CCSD levels of theory. The examined clusters range from the smallest cluster size (n = 2) up to nearly nanosize clusters with n = 1000 molecules. The examined cluster configurations are extracted from mixed quantum-classical molecular dynamics trajectories of cluster anions with n = 1000 water molecules using two different one-electron pseudopotenial models. We find that while MP2 calculations with large diffuse basis set provide a reasonable description for the hydrated electron system, DFT methods should be used with precaution and only after careful benchmarking. Strictly tested one-electron psudopotentials can still be considered as reasonable alternatives to DFT methods, especially in large systems. The results of quantum chemistry calculations performed on configurations, that represent possible excess electron binding motifs in the clusters, appear to be consistent with the results using a cavity structure preferring one-electron pseudopotential for the hydrated electron, while they are in sharp disagreement with the structural predictions of a non-cavity model.

  14. A kinetic model for the penicillin biosynthetic pathway in

    DEFF Research Database (Denmark)

    Nielsen, Jens; Jørgensen, Henrik

    1996-01-01

    A kinetic model for the first two steps in the penicillin biosynthetic pathway, i.e. the ACV synthetase (ACVS) and the isopenicillin N synthetase (IPNS) is proposed. The model is based on Michaelis-Menten type kinetics with non-competitive inhibition of the ACVS by ACV, and competitive inhibition...... of the IPNS by glutathione. The model predicted flux through the pathway corresponds well with the measured rate of penicillin biosynthesis. From the kinetic model the elasticity coefficients and the flux control coefficients are calculated throughout a fed-batch cultivation, and it is found...

  15. Kinetics and hybrid kinetic-fluid models for nonequilibrium gas and plasmas

    International Nuclear Information System (INIS)

    Crouseilles, N.

    2004-12-01

    For a few decades, the application of the physics of plasmas has appeared in different fields like laser-matter interaction, astrophysics or thermonuclear fusion. In this thesis, we are interested in the modeling and the numerical study of nonequilibrium gas and plasmas. To describe such systems, two ways are usually used: the fluid description and the kinetic description. When we study a nonequilibrium system, fluid models are not sufficient and a kinetic description have to be used. However, solving a kinetic model requires the discretization of a large number of variables, which is quite expensive from a numerical point of view. The aim of this work is to propose a hybrid kinetic-fluid model thanks to a domain decomposition method in the velocity space. The derivation of the hybrid model is done in two different contexts: the rarefied gas context and the more complicated plasmas context. The derivation partly relies on Levermore's entropy minimization approach. The so-obtained model is then discretized and validated on various numerical test cases. In a second stage, a numerical study of a fully kinetic model is presented. A collisional plasma constituted of electrons and ions is considered through the Vlasov-Poisson-Fokker-Planck-Landau equation. Then, a numerical scheme which preserves total mass and total energy is presented. This discretization permits in particular a numerical study of the Landau damping. (author)

  16. Transformation of meta-stable calcium silicate hydrates to tobermorite: reaction kinetics and molecular structure from XRD and NMR spectroscopy

    Science.gov (United States)

    2009-01-01

    Understanding the integrity of well-bore systems that are lined with Portland-based cements is critical to the successful storage of sequestered CO2 in gas and oil reservoirs. As a first step, we investigate reaction rates and mechanistic pathways for cement mineral growth in the absence of CO2 by coupling water chemistry with XRD and NMR spectroscopic data. We find that semi-crystalline calcium (alumino-)silicate hydrate (Al-CSH) forms as a precursor solid to the cement mineral tobermorite. Rate constants for tobermorite growth were found to be k = 0.6 (± 0.1) × 10-5 s-1 for a solution:solid of 10:1 and 1.6 (± 0.8) × 10-4 s-1 for a solution:solid of 5:1 (batch mode; T = 150°C). This data indicates that reaction rates for tobermorite growth are faster when the solution volume is reduced by half, suggesting that rates are dependent on solution saturation and that the Gibbs free energy is the reaction driver. However, calculated solution saturation indexes for Al-CSH and tobermorite differ by less than one log unit, which is within the measured uncertainty. Based on this data, we consider both heterogeneous nucleation as the thermodynamic driver and internal restructuring as possible mechanistic pathways for growth. We also use NMR spectroscopy to characterize the site symmetry and bonding environment of Al and Si in a reacted tobermorite sample. We find two [4]Al coordination structures at δiso = 59.9 ppm and 66.3 ppm with quadrupolar product parameters (PQ) of 0.21 MHz and 0.10 MHz (± 0.08) from 27Al 3Q-MAS NMR and speculate on the Al occupancy of framework sites by probing the protonation environment of Al metal centers using 27Al{1H}CP-MAS NMR. PMID:19144195

  17. A balance principle approach for modeling phase transformation kinetics

    International Nuclear Information System (INIS)

    Lusk, M.; Krauss, G.; Jou, H.J.

    1995-01-01

    A balance principle is offered to model volume fraction kinetics of phase transformation kinetics at a continuum level. This microbalance provides a differential equation for transformation kinetics which is coupled to the differential equations governing the mechanical and thermal aspects of the process. Application here is restricted to diffusive transformations for the sake of clarity, although the principle is discussed for martensitic phase transitions as well. Avrami-type kinetics are shown to result from a special class of energy functions. An illustrative example using a 0.5% C Chromium steel demonstrates how TTT and CCT curves can be generated using a particularly simple effective energy function. (orig.)

  18. Kinetic models in spin chemistry. 1. The hyperfine interaction

    DEFF Research Database (Denmark)

    Mojaza, M.; Pedersen, J. B.

    2012-01-01

    Kinetic models for quantum systems are quite popular due to their simplicity, although they are difficult to justify. We show that the transformation from quantum to kinetic description can be done exactly for the hyperfine interaction of one nuclei with arbitrary spin; more spins are described w...... induced enhancement of the reaction yield. (C) 2012 Elsevier B.V. All rights reserved....

  19. Experimental techniques for cement hydration studies

    Directory of Open Access Journals (Sweden)

    Andreas Luttge

    2011-10-01

    Full Text Available Cement hydration kinetics is a complex problem of dissolution, nucleation and growth that is still not well understood, particularly in a quantitative way. While cement systems are unique in certain aspects they are also comparable to natural mineral systems. Therefore, geochemistry and particularly the study of mineral dissolution and growth may be able to provide insight and methods that can be utilized in cement hydration research. Here, we review mainly what is not known or what is currently used and applied in a problematic way. Examples are the typical Avrami approach, the application of Transition State Theory (TST to overall reaction kinetics and the problem of reactive surface area. Finally, we suggest an integrated approach that combines vertical scanning interferometry (VSI with other sophisticated analytical techniques such as atomic force microscopy (AFM and theoretical model calculations based on a stochastic treatment.

  20. Prediction of Water Binding to Protein Hydration Sites with a Discrete, Semiexplicit Solvent Model.

    Science.gov (United States)

    Setny, Piotr

    2015-12-08

    Buried water molecules are ubiquitous in protein structures and are found at the interface of most protein-ligand complexes. Determining their distribution and thermodynamic effect is a challenging yet important task, of great of practical value for the modeling of biomolecular structures and their interactions. In this study, we present a novel method aimed at the prediction of buried water molecules in protein structures and estimation of their binding free energies. It is based on a semiexplicit, discrete solvation model, which we previously introduced in the context of small molecule hydration. The method is applicable to all macromolecular structures described by a standard all-atom force field, and predicts complete solvent distribution within a single run with modest computational cost. We demonstrate that it indicates positions of buried hydration sites, including those filled by more than one water molecule, and accurately differentiates them from sterically accessible to water but void regions. The obtained estimates of water binding free energies are in fair agreement with reference results determined with the double decoupling method.

  1. One-dimensional reactor kinetics model for RETRAN

    International Nuclear Information System (INIS)

    Gose, G.C.; Peterson, C.E.; Ellis, N.L.; McClure, J.A.

    1981-01-01

    This paper describes a one-dimensional spatial neutron kinetics model that was developed for the RETRAN code. The RETRAN -01 code has a point kinetics model to describe the reactor core behavior during thermal-hydraulic transients. A one-dimensional neutronics model has been developed for RETRAN-02. The ability to account for flux shape changes will permit an improved representation of the thermal and hydraulic feedback effects for many operational transients. 19 refs

  2. Lumping procedure for a kinetic model of catalytic naphtha reforming

    Directory of Open Access Journals (Sweden)

    H. M. Arani

    2009-12-01

    Full Text Available A lumping procedure is developed for obtaining kinetic and thermodynamic parameters of catalytic naphtha reforming. All kinetic and deactivation parameters are estimated from industrial data and thermodynamic parameters are calculated from derived mathematical expressions. The proposed model contains 17 lumps that include the C6 to C8+ hydrocarbon range and 15 reaction pathways. Hougen-Watson Langmuir-Hinshelwood type reaction rate expressions are used for kinetic simulation of catalytic reactions. The kinetic parameters are benchmarked with several sets of plant data and estimated by the SQP optimization method. After calculation of deactivation and kinetic parameters, plant data are compared with model predictions and only minor deviations between experimental and calculated data are generally observed.

  3. Thermodynamic modelling of the effect of temperature on the hydration and porosity of Portland cement

    International Nuclear Information System (INIS)

    Lothenbach, Barbara; Matschei, Thomas; Moeschner, Goeril; Glasser, Fred P.

    2008-01-01

    The composition of the phase assemblage and the pore solution of Portland cements hydrated between 0 and 60 deg. C were modelled as a function of time and temperature. The results of thermodynamic modelling showed a good agreement with the experimental data gained at 5, 20, and 50 deg. C. At 5 and at 20 deg. C, a similar phase assemblage was calculated to be present, while at approximately 50 deg. C, thermodynamic calculations predicted the conversion of ettringite and monocarbonate to monosulphate. Modelling showed that in Portland cements which have an Al 2 O 3 /SO 3 ratio of > 1.3 (bulk weight), above 50 deg. C monosulphate and monocarbonate are present. In Portland cements which contain less Al (Al 2 O 3 /SO 3 < 1.3), above 50 deg. C monosulphate and small amounts of ettringite are expected to persist. A good correlation between calculated porosity and measured compressive strength was observed

  4. COMPARATIVE ANALYSIS OF SOME EXISTING KINETIC MODELS ...

    African Journals Online (AJOL)

    The biosorption of three heavy metal ions namely; Zn2+, Cu2+ and Mn2+ using five microorganisms namely; Bacillus circulans, Pseudomonas aeruginosa, Staphylococcus xylosus, Streptomyces rimosus and Yeast (Saccharomyces sp.) were studied. In this paper, the effectiveness of six existing and two proposed kinetic ...

  5. Interactions between hydrated cement paste and organic acids: Thermodynamic data and speciation modeling

    Energy Technology Data Exchange (ETDEWEB)

    De Windt, Laurent, E-mail: laurent.dewindt@mines-paristech.fr [MINES ParisTech, PSL Research University, Centre de Géosciences, 35 Rue St-Honoré, 77305 Fontainebleau Cedex (France); Bertron, Alexandra; Larreur-Cayol, Steeves; Escadeillas, Gilles [University of Toulouse, UPS/INSA/LMDC, 135 Av. de Rangueil, 31077 Toulouse Cedex 04 (France)

    2015-03-15

    Interactions of short-chain organic acids with hydrated cement phases affect structure durability in the agro-food and nuclear waste industries but can also be used to modify cement properties. Most previous studies have been experimental, performed at fixed concentrations and pH, without quantitatively discriminating among polyacidity effects, or complexation and salt precipitation processes. This paper addresses such issues by thermodynamic equilibrium calculations for acetic, citric, oxalic, succinic acids and a simplified hydrated CEM-I. The thermodynamic constants collected from the literature allow the speciation to be modeled over a wide range of pH and concentrations. Citric and oxalic had a stronger chelating effect than acetic acid, while succinic acid was intermediate. Similarly, Ca-citrate and Ca-oxalate salts were more insoluble than Ca-acetate and Ca-succinate salts. Regarding aluminium complexation, hydroxyls, sulfates, and acid competition was highlighted. The exploration of acid mixtures showed the preponderant effect of oxalate and citrate over acetate and succinate.

  6. Experimental measurement of phase equilibrium for gas hydrates of refrigerants, and thermodynamic modeling by SRK, VPT and CPA EOSs

    International Nuclear Information System (INIS)

    Karamoddin, Maryam; Varaminian, Farshad

    2013-01-01

    Highlights: • Three-phase equilibrium data, (VL W H), were measured for HCFC22 and HFC134a hydrates. • The pressures were evaluated by simple EoSs (modified mixing rule) and CPA EOS. • The Kihara potential parameters were obtained by optimizing scheme for refrigerants. -- Abstract: In this study, three-phase equilibrium conditions of hydrate-liquid–vapor, (VL W H), were experimentally determined for chlorodifluoromethane and 1,1,1,2-tetrafluoroethane gas hydrates at temperatures ranging from (278 to 290) K and (280 to 285) K respectively, at pressures ranging from (0.2 to 0.8) MPa. Then the different models were presented for estimating of the hydrate dissociation conditions of chlorodifluoromethane, 1,1,1,2-tetrafluoroethane and 1,1-difluoroethane refrigerants. The cubic simple equations of state (SRK and VPT) and the cubic plus association equation of state (CPA) were employed for modeling the vapor and liquid phases, also van der Waals–Platteeuw statistical model was used for the solid hydrate phase. In this paper, the binary interaction parameters of classic and modified mixing rules were optimized by using two-phase equilibrium data (VL W H). The Kihara potential parameters in each refrigerant were estimated using obtained experimental equilibrium data (VL W H) and based on the optimization scheme by the Nelder Mead optimization method. The agreement between the experimental and the predicted pressure is acceptable by using these models. The average deviation of models for chlorodifluoromethane, 1,1,1,2-tetrafluoroethane, and 1,1-difluoroethane hydrates is about 3%, 4.3%, and 3.6%, respectively

  7. A critical look at the kinetic models of thermoluminescence-II. Non-first order kinetics

    International Nuclear Information System (INIS)

    Sunta, C M; Ayta, W E F; Chubaci, J F D; Watanabe, S

    2005-01-01

    Non-first order (FO) kinetics models are of three types; second order (SO), general order (GO) and mixed order (MO). It is shown that all three of these have constraints in their energy level schemes and their applicable parameter values. In nature such restrictions are not expected to exist. The thermoluminescence (TL) glow peaks produced by these models shift their position and change their shape as the trap occupancies change. Such characteristics are very unlike those found in samples of real materials. In these models, in general, retrapping predominates over recombination. It is shown that the quasi-equilibrium (QE) assumption implied in the derivation of the TL equation of these models is quite valid, thus disproving earlier workers' conclusion that QE cannot be held under retrapping dominant conditions. However notwithstanding their validity, they suffer from the shortcomings as stated above and have certain lacunae. For example, the kinetic order (KO) parameter and the pre-exponential factor which are assumed to be the constant parameters of the GO kinetics expression turn out to be variables when this expression is applied to plausible physical models. Further, in glow peak characterization using the GO expression, the quality of fit is found to deteriorate when the best fitted value of KO parameter is different from 1 and 2. This means that the found value of the basic parameter, namely the activation energy, becomes subject to error. In the MO kinetics model, the value of the KO parameter α would change with dose, and thus in this model also, as in the GO model, no single value of KO can be assigned to a given glow peak. The paper discusses TL of real materials having characteristics typically like those of FO kinetics. Theoretically too, a plausible physical model of TL emission produces glow peaks which have characteristics of FO kinetics under a wide variety of parametric combinations. In the background of the above findings, it is suggested that

  8. comparative analysis of some existing kinetic models with proposed

    African Journals Online (AJOL)

    IGNATIUS NWIDI

    two statistical parameters namely; linear regression coefficient of correlation (R2) and ... Keynotes: Heavy metals, Biosorption, Kinetics Models, Comparative analysis, Average Relative Error. 1. ... If the flow rate is low, a simple manual batch.

  9. Improved Kinetic Models for High-Speed Combustion Simulation

    National Research Council Canada - National Science Library

    Montgomery, C. J; Tang, Q; Sarofim, A. F; Bockelie, M. J; Gritton, J. K; Bozzelli, J. W; Gouldin, F. C; Fisher, E. M; Chakravarthy, S

    2008-01-01

    Report developed under an STTR contract. The overall goal of this STTR project has been to improve the realism of chemical kinetics in computational fluid dynamics modeling of hydrocarbon-fueled scramjet combustors...

  10. Physical characterization and kinetic modelling of matrix tablets of ...

    African Journals Online (AJOL)

    release mechanisms were characterized by kinetic modeling. Analytical ... findings demonstrate that both the desired physical characteristics and drug release profiles were obtained ..... on the compression, mechanical, and release properties.

  11. Study of growth kinetic and modeling of ethanol production by ...

    African Journals Online (AJOL)

    ... coefficient (0.96299). Based on Leudking-Piret model, it could be concluded that ethanol batch fermentation is a non-growth associated process. Key words: Kinetic parameters, simulation, cell growth, ethanol, Saccharomyces cerevisiae.

  12. Analysis of a kinetic multi-segment foot model part II: kinetics and clinical implications.

    Science.gov (United States)

    Bruening, Dustin A; Cooney, Kevin M; Buczek, Frank L

    2012-04-01

    Kinematic multi-segment foot models have seen increased use in clinical and research settings, but the addition of kinetics has been limited and hampered by measurement limitations and modeling assumptions. In this second of two companion papers, we complete the presentation and analysis of a three segment kinetic foot model by incorporating kinetic parameters and calculating joint moments and powers. The model was tested on 17 pediatric subjects (ages 7-18 years) during normal gait. Ground reaction forces were measured using two adjacent force platforms, requiring targeted walking and the creation of two sub-models to analyze ankle, midtarsal, and 1st metatarsophalangeal joints. Targeted walking resulted in only minimal kinematic and kinetic differences compared with walking at self selected speeds. Joint moments and powers were calculated and ensemble averages are presented as a normative database for comparison purposes. Ankle joint powers are shown to be overestimated when using a traditional single-segment foot model, as substantial angular velocities are attributed to the mid-tarsal joint. Power transfer is apparent between the 1st metatarsophalangeal and mid-tarsal joints in terminal stance/pre-swing. While the measurement approach presented here is limited to clinical populations with only minimal impairments, some elements of the model can also be incorporated into routine clinical gait analysis. Copyright © 2011 Elsevier B.V. All rights reserved.

  13. Kinetic model for the radical degradation of tri-halonitromethane disinfection byproducts in water

    International Nuclear Information System (INIS)

    Mezyk, Stephen P.; Mincher, Bruce J.; Cooper, William J.; Kirkham Cole, S.; Fox, Robert V.; Gardinali, Piero R.

    2012-01-01

    The halonitromethanes (HNMs) are byproducts of the ozonation and chlorine/chloramine treatment of drinking waters. Although typically occurring at low concentrations HNMs have high cytotoxicity and mutagenicity, and may therefore represent a significant human health hazard. In this study, we have investigated the radical based mineralization of fully-halogenated HNMs in water using the congeners bromodichloronitromethane and chlorodibromonitromethane. We have combined absolute reaction rate constants for their reactions with the hydroxyl radical and the hydrated electron as measured by electron pulse radiolysis and analytical measurements of stable product concentrations obtained by 60 Co steady-state radiolysis with a kinetic computer model that includes water radiolysis reactions and halide/nitrogen oxide radical chemistry to fully elucidate the reaction pathways of these HNMs. These results are compared to our previous similar study of the fully chlorinated HNM chloropicrin. The full optimized computer model, suitable for predicting the behavior of this class of compounds in irradiated drinking water, is provided. - Highlights: ► Radical-based mineralization of aqueous halonitromethane disinfection byproducts. ► Constructed kinetic computer model for tri-halogenated halonitromethane removal. ► Model predicted that superoxide reaction is unimportant for halonitromethanes. ► Measured superoxide reaction with chloropicrin was negligibly slow, 4 M −1 s −1 . ► Determined that superoxide reaction with nitrate also insignificant at ∼10 4 M −1 s −1 .

  14. Molecular Dynamics Simulations of Kinetic Models for Chiral Dominance in Soft Condensed Matter

    DEFF Research Database (Denmark)

    Toxvaerd, Søren

    2001-01-01

    Molecular dynamics simulation, models for isomerization kinetics, origin of biomolecular chirality......Molecular dynamics simulation, models for isomerization kinetics, origin of biomolecular chirality...

  15. Modeling of tri-chloro-fluoro-methane hydrate formation in a w/o emulsion submitted to steady cooling

    Energy Technology Data Exchange (ETDEWEB)

    Avendano-Gomez, Juan Ramon; Limas-Ballesteros, Roberto [Laboratorio de Investigacion en Ingenieria Quimica Ambiental, SEPI-ESIQIE, Instituto Politecnico Nacional, Unidad Profesional Adolfo Lopez Mateos, Zacatenco, Edificio 8, 3. piso 07738, Mexico DF (Mexico); Garcia-Sanchez, Fernando [Laboratorio de Termodinamica, Programa de Ingenieria Molecular, Instituto Mexicano del Petroleo, Eje Central Lazaro Cardenas 152, 07730 Mexico DF (Mexico)

    2006-05-15

    The aim of this work is to study the modeling of the thermal evolution inside an hydrate forming system which is submitted to an imposed steady cooling. The study system is a w/o emulsion where the formulation considers the CCl{sub 3}F as the hydrate forming molecule dissolved in the oil phase. The hydrate formation occurs in the aqueous phase of the emulsion, i.e. in the dispersed phase. The model equation is based on the resolution of the continuity equation in terms of a heat balance for the dispersed phase. The crystallization of the CCl{sub 3}F hydrate occurs at supercooling conditions (T{sub c}model equation subjected to boundary conditions allow to depict the evolution of temperature in the dispersed phase. The most singular point in the temperature-time curve is the onset time of hydrate crystallization. Three time intervals characterize the evolution of temperature during the steady cooling of the w/o emulsion: (1) steady cooling, (2) hydrate formation with a release of heat, (3) a last interval of steady cooling. (author)

  16. Data Requirements and Modeling for Gas Hydrate-Related Mixtures and a Comparison of Two Association Models

    DEFF Research Database (Denmark)

    Liang, Xiaodong; Aloupis, Georgios; Kontogeorgis, Georgios M.

    2017-01-01

    the performance of the CPA and sPC-SAFT EOS for modeling the fluid-phase equilibria of gas hydrate-related systems and will try to explore how the models can help in suggesting experimental measurements. These systems contain water, hydrocarbon (alkane or aromatic), and either methanol or monoethylene glycol...... parameter sets have been chosen for the sPC-SAFT EOS for a fair comparison. The comparisons are made for pure fluid properties, vapor liquid-equilibria, and liquid liquid equilibria of binary and ternary mixtures as well as vapor liquid liquid equilibria of quaternary mixtures. The results show, from...

  17. Body composition and hydration factors in infants and young children using multicompartment models

    International Nuclear Information System (INIS)

    Villegas-Valle, Rosa Consuelo; Valencia, Mauro E; Sotelo-Cruz, Norberto; Antunez-Roman, Lesley Evelyn; Lopez-Jimenez, Cesar A; Monreal-Barraza, Brianda I; Robles-Valenzuela, Edna L; Hurtado-Valenzuela, Jaime Gabriel

    2014-01-01

    Full text: Background. Until recently deuterium (2H2O) analysis has been performed almost exclusively by isotope ratio mass spectrometry (IRMS). The IAEA has promoted the FTIR methodology to measure deuterium (2H2O) enrichment, but there is limited information in infants and small children, which have different hydration status than adults. Due to the limited information available, the optimum deuterium dose amount to be administered to children in these studies has also been controversial. The aim of this investigation were to measure body composition and determine the hydration factors in infants and young children using multi-compartment models generating algorithms for prediction of body composition. Subjects and Methods. Seventy-eight male and female infants and young children (ages 3-24 months), from the urban and agricultural zones of Hermosillo, Sonora, Mexico participated. We measured weight, length and circumferences to evaluate nutritional status using the WHO Growth Reference 2006. We also measured total body water (TBW) by deuterium oxide dilution, bone mineral content (BMC) through a DXA scan and body density was estimated through published algorithms. Bioimpedance analysis (BIA) was also measured to explore the prediction of body composition using this technique. Results. In general, children from the urban area had better nutritional indicators than children from the agricultural area. Eleven (16.1%) children had some type of malnutrition (any nutritional index below -2 Z cutoff point) and 2 were overweight. Optimal amount of deuterium for dosing in this age range was 0.53 to 0.83 mg/kg body weight, which has implications for future studies of body composition in infants and young children. DXA overestimated body fat percentage compared to other 2, 3 and 4 compartment models (p 0.05). Resistance or impedance indexes (Height2/R or Z) were not important predictors of FFM or TBW (increase in R2 = 0.004). Prediction of FFM was then performed by using

  18. HyFlux - Part I: Regional Modeling of Methane Flux From Near-Seafloor Gas Hydrate Deposits on Continental Margins

    Science.gov (United States)

    MacDonald, I. R.; Asper, V.; Garcia, O. P.; Kastner, M.; Leifer, I.; Naehr, T.; Solomon, E.; Yvon-Lewis, S.; Zimmer, B.

    2008-12-01

    HyFlux - Part I: Regional modeling of methane flux from near-seafloor gas hydrate deposits on continental margins MacDonald, I.R., Asper, V., Garcia, O., Kastner, M., Leifer, I., Naehr, T.H., Solomon, E., Yvon-Lewis, S., and Zimmer, B. The Dept. of Energy National Energy Technology Laboratory (DOE/NETL) has recently awarded a project entitled HyFlux: "Remote sensing and sea-truth measurements of methane flux to the atmosphere." The project will address this problem with a combined effort of satellite remote sensing and data collection at proven sites in the Gulf of Mexico where gas hydrate releases gas to the water column. Submarine gas hydrate is a large pool of greenhouse gas that may interact with the atmosphere over geologic time to affect climate cycles. In the near term, the magnitude of methane reaching the atmosphere from gas hydrate on continental margins is poorly known because 1) gas hydrate is exposed to metastable oceanic conditions in shallow, dispersed deposits that are poorly imaged by standard geophysical techniques and 2) the consumption of methane in marine sediments and in the water column is subject to uncertainty. The northern GOM is a prolific hydrocarbon province where rapid migration of oil, gases, and brines from deep subsurface petroleum reservoirs occurs through faults generated by salt tectonics. Focused expulsion of hydrocarbons is manifested at the seafloor by gas vents, gas hydrates, oil seeps, chemosynthetic biological communities, and mud volcanoes. Where hydrocarbon seeps occur in depths below the hydrate stability zone (~500m), rapid flux of gas will feed shallow deposits of gas hydrate that potentially interact with water column temperature changes; oil released from seeps forms sea-surface features that can be detected in remote-sensing images. The regional phase of the project will quantify verifiable sources of methane (and oil) the Gulf of Mexico continental margin and selected margins (e.g. Pakistan Margin, South China Sea

  19. About one discrete model of splitting by the physical processes of a piezoconductive medium with gas hydrate inclusions

    Science.gov (United States)

    Poveshchenko, Yu A.; Podryga, V. O.; Rahimly, P. I.; Sharova, Yu S.

    2018-01-01

    The thermodynamically equilibrium model for splitting by the physical processes of a two-component three-phase filtration fluid dynamics with gas hydrate inclusions is considered in the paper, for which a family of two-layer completely conservative difference schemes of the support operators method with time weights profiled in space is constructed. On the irregular grids of the theory of the support-operators method applied to the specifics of the processes of transfer of saturations and internal energies of water and gas in a medium with gas hydrate inclusions, methods of directwind approximation of these processes are considered. These approximations preserve the continual properties of divergence-gradient operations in their difference form and are related to the velocity field providing saturations transfer and internal energies of fluids. Fluid dynamics with gas hydrate inclusions are also calculated on the basis of the proposed approach, in particular, in areas of severe pressure depression in the collector space.

  20. Modelling of the Kinetics of Sulfure Compounds in Desulfurisation Processes Based on Industry Data of Plant

    Directory of Open Access Journals (Sweden)

    Krivtcova Nadezhda

    2016-01-01

    Full Text Available Modelling of sulfur compounds kinetics was performed, including kinetics of benzothiophene and dibenzothiophene homologues. Modelling is based on experimental data obtained from monitoring of industrial hydrotreating set. Obtained results include kinetic parameters of reactions.

  1. Modelling of the Kinetics of Sulfure Compounds in Desulfurisation Processes Based on Industry Data of Plant

    OpenAIRE

    Krivtsova, Nadezhda Igorevna; Tataurshikov, A.; Kotkova, Elena

    2016-01-01

    Modelling of sulfur compounds kinetics was performed, including kinetics of benzothiophene and dibenzothiophene homologues. Modelling is based on experimental data obtained from monitoring of industrial hydrotreating set. Obtained results include kinetic parameters of reactions.

  2. Kinetics of ethylcyclohexane pyrolysis and oxidation: An experimental and detailed kinetic modeling study

    KAUST Repository

    Wang, Zhandong; Zhao, Long; Wang, Yu; Bian, Huiting; Zhang, Lidong; Zhang, Feng; Li, Yuyang; Sarathy, Mani; Qi, Fei

    2015-01-01

    species were evaluated, and good agreement was observed between the PIMS and GC data sets. Furthermore, a fuel-rich burner-stabilized laminar premixed ECH/O2/Ar flame at 30Torr was studied using synchrotron VUV PIMS. A detailed kinetic model for ECH high

  3. Modified effective medium model for gas hydrate bearing,clay-dominated sediments in the Krishna-Godavari Basin

    Digital Repository Service at National Institute of Oceanography (India)

    Sriram, G.; Dewangan, P.; Ramprasad, T.

    .D., 1990. Nonlinear elasticity and pressure-dependent wave speeds in granular media. Proc. R. Soc. London. Ser. A Math. Phys. Sci. 430, 105–131. Guerin, G., Goldberg, D., 2005. Modeling of acoustic wave dissipation in gas hydrate-bearing sediments...

  4. Dehydration kinetics of a natural montmorillonite

    International Nuclear Information System (INIS)

    Andreotti, G.; Loria, A.; Mazzega, E.; Valeri, S.

    1978-01-01

    The dehydration mass loss of samples of montmorillonite (a layered hydrated silicate) was measured in an environment at constant temperature and at constant undersatured water vapour content. The hydration curves were analyzed by assuming the model of thermally activated, monoenergetic and first-order process compatible with the experimental results. Two dehydration kinetics with activation energies (0.21+-0.02) eV and (0.34+-0.02) eV were found that can be related to the existence of two kinds of water (structured and nonstructured) in the hydrated silicate interlayers. The possibility of an icelike structure of a fraction of the adsorbed molecules is briefly discussed. The experimental results show, furthermore, that in the investigated hydration range (up to about 10% in mass) the fraction of structured water has a maximum when the hydration is about 6%. (author)

  5. Gas hydrates

    Digital Repository Service at National Institute of Oceanography (India)

    Ramprasad, T.

    , not all of them are white like snow. Some hydrates from the deep Gulf of Mexico are richly colored in shades of yellow, orange, or even red. The ice-like masses are beautiful, and contrast with the dull gray of deep sea muds. Hydrates from the Blake... volcanoes and associated gas hydrates: Marine Geology, v. 167, p. 29-42. Milkov, A.V. and R. Sassen, 2001a, Estimate of gas hydrate resource, northwestern Gulf of Mexico continental slope: Marine Geology, v. 179, pp. 71-83. Milkov, A.V., Sassen, R...

  6. TOUGH+Hydrate v1.0 User's Manual: A Code for the Simulation of System Behavior in Hydrate-Bearing Geologic Media

    Energy Technology Data Exchange (ETDEWEB)

    Moridis, George; Moridis, George J.; Kowalsky, Michael B.; Pruess, Karsten

    2008-03-01

    TOUGH+HYDRATE v1.0 is a new code for the simulation of the behavior of hydrate-bearing geologic systems. By solving the coupled equations of mass and heat balance, TOUGH+HYDRATE can model the non-isothermal gas release, phase behavior and flow of fluids and heat under conditions typical of common natural CH{sub 4}-hydrate deposits (i.e., in the permafrost and in deep ocean sediments) in complex geological media at any scale (from laboratory to reservoir) at which Darcy's law is valid. TOUGH+HYDRATE v1.0 includes both an equilibrium and a kinetic model of hydrate formation and dissociation. The model accounts for heat and up to four mass components, i.e., water, CH{sub 4}, hydrate, and water-soluble inhibitors such as salts or alcohols. These are partitioned among four possible phases (gas phase, liquid phase, ice phase and hydrate phase). Hydrate dissociation or formation, phase changes and the corresponding thermal effects are fully described, as are the effects of inhibitors. The model can describe all possible hydrate dissociation mechanisms, i.e., depressurization, thermal stimulation, salting-out effects and inhibitor-induced effects. TOUGH+HYDRATE is the first member of TOUGH+, the successor to the TOUGH2 [Pruess et al., 1991] family of codes for multi-component, multiphase fluid and heat flow developed at the Lawrence Berkeley National Laboratory. It is written in standard FORTRAN 95, and can be run on any computational platform (workstation, PC, Macintosh) for which such compilers are available.

  7. Detailed Chemical Kinetic Modeling of Hydrazine Decomposition

    Science.gov (United States)

    Meagher, Nancy E.; Bates, Kami R.

    2000-01-01

    The purpose of this research project is to develop and validate a detailed chemical kinetic mechanism for gas-phase hydrazine decomposition. Hydrazine is used extensively in aerospace propulsion, and although liquid hydrazine is not considered detonable, many fuel handling systems create multiphase mixtures of fuels and fuel vapors during their operation. Therefore, a thorough knowledge of the decomposition chemistry of hydrazine under a variety of conditions can be of value in assessing potential operational hazards in hydrazine fuel systems. To gain such knowledge, a reasonable starting point is the development and validation of a detailed chemical kinetic mechanism for gas-phase hydrazine decomposition. A reasonably complete mechanism was published in 1996, however, many of the elementary steps included had outdated rate expressions and a thorough investigation of the behavior of the mechanism under a variety of conditions was not presented. The current work has included substantial revision of the previously published mechanism, along with a more extensive examination of the decomposition behavior of hydrazine. An attempt to validate the mechanism against the limited experimental data available has been made and was moderately successful. Further computational and experimental research into the chemistry of this fuel needs to be completed.

  8. Phase equilibria and thermodynamic modeling of ethane and propane hydrates in porous silica gels.

    Science.gov (United States)

    Seo, Yongwon; Lee, Seungmin; Cha, Inuk; Lee, Ju Dong; Lee, Huen

    2009-04-23

    In the present study, we examined the active role of porous silica gels when used as natural gas storage and transportation media. We adopted the dispersed water in silica gel pores to substantially enhance active surface for contacting and encaging gas molecules. We measured the three-phase hydrate (H)-water-rich liquid (L(W))-vapor (V) equilibria of C(2)H(6) and C(3)H(8) hydrates in 6.0, 15.0, 30.0, and 100.0 nm silica gel pores to investigate the effect of geometrical constraints on gas hydrate phase equilibria. At specified temperatures, the hydrate stability region is shifted to a higher pressure region depending on pore size when compared with those of bulk hydrates. Through application of the Gibbs-Thomson relationship to the experimental data, we determined the values for the C(2)H(6) hydrate-water and C(3)H(8) hydrate-water interfacial tensions to be 39 +/- 2 and 45 +/- 1 mJ/m(2), respectively. By using these values, the calculation values were in good agreement with the experimental ones. The overall results given in this study could also be quite useful in various fields, such as exploitation of natural gas hydrate in marine sediments and sequestration of carbon dioxide into the deep ocean.

  9. Modelling membrane hydration and water balance of a pem fuel cell

    DEFF Research Database (Denmark)

    Liso, Vincenzo; Nielsen, Mads Pagh

    2015-01-01

    Polymer electrolyte membrane (PEM) fuel cells requires an appropriate hydration in order to ensure high efficiency and long durability. As water is essential for promoting proton conductivity in the membrane, it is important to control membrane water hydration to avoid flooding. In this study we...

  10. A new mathematical model for coal flotation kinetics

    OpenAIRE

    Guerrero-Pérez, Juan Sebastián; Barraza-Burgos, Juan Manuel

    2017-01-01

    Abstract This study describes the development and formulation of a novel mathematical model for coal flotation kinetic. The flotation rate was considered as a function of chemical, operating and petrographic parameters for a global flotation order n. The equation for flotation rate was obtained by dimensional analysis using the Rayleigh method. It shows the dependency of flotation kinetic on operating parameters, such as air velocity and particle size; chemical parameters, such as reagents do...

  11. Modelling opinion formation by means of kinetic equations

    OpenAIRE

    Boudin , Laurent; Salvarani , Francesco

    2010-01-01

    In this chapter, we review some mechanisms of opinion dynamics that can be modelled by kinetic equations. Beside the sociological phenomenon of compromise, naturally linked to collisional operators of Boltzmann kind, many other aspects, already mentioned in the sociophysical literature or no, can enter in this framework. While describing some contributions appeared in the literature, we enlighten some mathematical tools of kinetic theory that can be useful in the context of sociophysics.

  12. Kinetics of ethylcyclohexane pyrolysis and oxidation: An experimental and detailed kinetic modeling study

    KAUST Repository

    Wang, Zhandong

    2015-07-01

    Ethylcyclohexane (ECH) is a model compound for cycloalkanes with long alkyl side-chains. A preliminary investigation on ECH (Wang et al., Proc. Combust. Inst., 35, 2015, 367-375) revealed that an accurate ECH kinetic model with detailed fuel consumption mechanism and aromatic growth pathways, as well as additional ECH pyrolysis and oxidation data with detailed species concentration covering a wide pressure and temperature range are required to understand the ECH combustion kinetics. In this work, the flow reactor pyrolysis of ECH at various pressures (30, 150 and 760Torr) was studied using synchrotron vacuum ultraviolet (VUV) photoionization mass spectrometry (PIMS) and gas chromatography (GC). The mole fraction profiles of numerous major and minor species were evaluated, and good agreement was observed between the PIMS and GC data sets. Furthermore, a fuel-rich burner-stabilized laminar premixed ECH/O2/Ar flame at 30Torr was studied using synchrotron VUV PIMS. A detailed kinetic model for ECH high temperature pyrolysis and oxidation was developed and validated against the pyrolysis and flame data performed in this work. Further validation of the kinetic model is presented against literature data including species concentrations in jet-stirred reactor oxidation, ignition delay times in a shock tube, and laminar flame speeds at various pressures and equivalence ratios. The model well predicts the consumption of ECH, the growth of aromatics, and the global combustion properties. Reaction flux and sensitivity analysis were utilized to elucidate chemical kinetic features of ECH combustion under various reaction conditions. © 2015 The Combustion Institute.

  13. Chemical kinetic modeling of H{sub 2} applications

    Energy Technology Data Exchange (ETDEWEB)

    Marinov, N.M.; Westbrook, C.K.; Cloutman, L.D. [Lawrence Livermore National Lab., CA (United States)] [and others

    1995-09-01

    Work being carried out at LLNL has concentrated on studies of the role of chemical kinetics in a variety of problems related to hydrogen combustion in practical combustion systems, with an emphasis on vehicle propulsion. Use of hydrogen offers significant advantages over fossil fuels, and computer modeling provides advantages when used in concert with experimental studies. Many numerical {open_quotes}experiments{close_quotes} can be carried out quickly and efficiently, reducing the cost and time of system development, and many new and speculative concepts can be screened to identify those with sufficient promise to pursue experimentally. This project uses chemical kinetic and fluid dynamic computational modeling to examine the combustion characteristics of systems burning hydrogen, either as the only fuel or mixed with natural gas. Oxidation kinetics are combined with pollutant formation kinetics, including formation of oxides of nitrogen but also including air toxics in natural gas combustion. We have refined many of the elementary kinetic reaction steps in the detailed reaction mechanism for hydrogen oxidation. To extend the model to pressures characteristic of internal combustion engines, it was necessary to apply theoretical pressure falloff formalisms for several key steps in the reaction mechanism. We have continued development of simplified reaction mechanisms for hydrogen oxidation, we have implemented those mechanisms into multidimensional computational fluid dynamics models, and we have used models of chemistry and fluid dynamics to address selected application problems. At the present time, we are using computed high pressure flame, and auto-ignition data to further refine the simplified kinetics models that are then to be used in multidimensional fluid mechanics models. Detailed kinetics studies have investigated hydrogen flames and ignition of hydrogen behind shock waves, intended to refine the detailed reactions mechanisms.

  14. RELAP5 kinetics model development for the Advanced Test Reactor

    International Nuclear Information System (INIS)

    Judd, J.L.; Terry, W.K.

    1990-01-01

    A point-kinetics model of the Advanced Test Reactor has been developed for the RELAP5 code. Reactivity feedback parameters were calculated by a three-dimensional analysis with the PDQ neutron diffusion code. Analyses of several hypothetical reactivity insertion events by the new model and two earlier models are discussed. 3 refs., 10 figs., 6 tabs

  15. A tool model for predicting atmospheric kinetics with sensitivity analysis

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    A package( a tool model) for program of predicting atmospheric chemical kinetics with sensitivity analysis is presented. The new direct method of calculating the first order sensitivity coefficients using sparse matrix technology to chemical kinetics is included in the tool model, it is only necessary to triangularize the matrix related to the Jacobian matrix of the model equation. The Gear type procedure is used to integrate amodel equation and its coupled auxiliary sensitivity coefficient equations. The FORTRAN subroutines of the model equation, the sensitivity coefficient equations, and their Jacobian analytical expressions are generated automatically from a chemical mechanism. The kinetic representation for the model equation and its sensitivity coefficient equations, and their Jacobian matrix is presented. Various FORTRAN subroutines in packages, such as SLODE, modified MA28, Gear package, with which the program runs in conjunction are recommended.The photo-oxidation of dimethyl disulfide is used for illustration.

  16. A consistent and verifiable macroscopic model for the dissolution of liquid CO2 in water under hydrate forming conditions

    International Nuclear Information System (INIS)

    Radhakrishnan, R.; Demurov, A.; Trout, B.L.; Herzog, H.

    2003-01-01

    Direct injection of liquid CO 2 into the ocean has been proposed as one method to reduce the emission levels of CO 2 into the atmosphere. When liquid CO 2 is injected (normally as droplets) at ocean depths >500 m, a solid interfacial region between the CO 2 and the water is observed to form. This region consists of hydrate clathrates and hinders the rate of dissolution of CO 2 . It is, therefore, expected to have a significant impact on the injection of liquid CO 2 into the ocean. Up until now, no consistent and predictive model for the shrinking of droplets of CO 2 under hydrate forming conditions has been proposed. This is because all models proposed to date have had too many unknowns. By computing rates of the physical and chemical processes in hydrates via molecular dynamics simulations, we have been able to determine independently some of these unknowns. We then propose the most reasonable model and use it to make independent predictions of the rates of mass transfer and thickness of the hydrate region. These predictions are compared to measurements, and implications to the rates of shrinkage of CO 2 droplets under varying flow conditions are discussed. (author)

  17. Reactor kinetics revisited: a coefficient based model (CBM)

    International Nuclear Information System (INIS)

    Ratemi, W.M.

    2011-01-01

    In this paper, a nuclear reactor kinetics model based on Guelph expansion coefficients calculation ( Coefficients Based Model, CBM), for n groups of delayed neutrons is developed. The accompanying characteristic equation is a polynomial form of the Inhour equation with the same coefficients of the CBM- kinetics model. Those coefficients depend on Universal abc- values which are dependent on the type of the fuel fueling a nuclear reactor. Furthermore, such coefficients are linearly dependent on the inserted reactivity. In this paper, the Universal abc- values have been presented symbolically, for the first time, as well as with their numerical values for U-235 fueled reactors for one, two, three, and six groups of delayed neutrons. Simulation studies for constant and variable reactivity insertions are made for the CBM kinetics model, and a comparison of results, with numerical solutions of classical kinetics models for one, two, three, and six groups of delayed neutrons are presented. The results show good agreements, especially for single step insertion of reactivity, with the advantage of the CBM- solution of not encountering the stiffness problem accompanying the numerical solutions of the classical kinetics model. (author)

  18. Kinetics of the Formation and Dissociation of Gas Hydrates from CO2-CH4 Mixtures

    Directory of Open Access Journals (Sweden)

    Devinder Mahajan

    2012-07-01

    Full Text Available Sequestration of carbon dioxide (CO2 in the form of its hydrates in natural methane (CH4 hydrate reservoirs, via CO2/CH4 exchange, is an attractive pathway that also yields valuable CH4 gas as product. In this paper, we describe a macroscale experiment to form CO2 and CH4-CO2 hydrates, under seafloor-mimic conditions, in a vessel fitted with glass windows that provides visualization of hydrates throughout formation and dissociation processes. Time resolved pressure and temperature data as well as images of hydrates are presented. Quantitative gas conversions with pure CO2, calculated from gas chromatographic measurements yielded values that range from 23 – 59% that correspond to the extent of formed hydrates. In CH4-rich CH4-CO2 mixed gas systems, CH4 hydrates were found to form preferentially.

  19. Kinetic computer modeling of microwave surface-wave plasma production

    International Nuclear Information System (INIS)

    Ganachev, Ivan P.

    2004-01-01

    Kinetic computer plasma modeling occupies an intermediate position between the time consuming rigorous particle dynamic simulation and the fast but rather rough cold- or warm-plasma fluid models. The present paper reviews the kinetic modeling of microwave surface-wave discharges with accent on recent kinetic self-consistent models, where the external input parameters are reduced to the necessary minimum (frequency and intensity of the applied microwave field and pressure and geometry of the discharge vessel). The presentation is limited to low pressures, so that Boltzmann equation is solved in non-local approximation and collisional electron heating is neglected. The numerical results reproduce correctly the bi-Maxwellian electron energy distribution functions observed experimentally. (author)

  20. Hydration of krypton and consideration of clathrate models of hydrophobic effects from the perspective of quasi-chemical theory.

    Science.gov (United States)

    Ashbaugh, Henry S; Asthagiri, D; Pratt, Lawrence R; Rempe, Susan B

    2003-09-01

    Ab initio molecular dynamics (AIMD) results on a krypton-water liquid solution are presented and compared to recent XAFS results for the radial hydration structure for a Kr atom in liquid water solution. Though these AIMD calculations have important limitations of scale, the comparisons with the liquid solution results are satisfactory and significantly different from the radial distributions extracted from the data on the solid Kr/H(2)O clathrate hydrate phase. The calculations also produce the coordination number distribution that can be examined for metastable coordination structures suggesting possibilities for clathrate-like organization; none are seen in these results. Clathrate pictures of hydrophobic hydration are discussed, as is the quasi-chemical theory that should provide a basis for clathrate pictures. Outer shell contributions are discussed and estimated; they are positive and larger than the positive experimental hydration free energy of Kr(aq), implying that inner shell contributions must be negative and of comparable size. Clathrate-like inner shell hydration structures on a Kr atom solute are obtained for some, but not all, of the coordination number cases observed in the simulation. The structures found have a delicate stability. Inner shell coordination structures extracted from the simulation of the liquid, and then subjected to quantum chemical optimization, always decomposed. Interactions with the outer shell material are decisive in stabilizing coordination structures observed in liquid solution and in clathrate phases. The primitive quasi-chemical estimate that uses a dielectric model for the influence of the outer shell material on the inner shell equilibria gives a contribution to hydration free energy that is positive and larger than the experimental hydration free energy. The 'what are we to tell students' question about hydrophobic hydration, often answered with structural clathrate pictures, is then considered; we propose an

  1. RETRAN-02 one-dimensional kinetics model: a review

    International Nuclear Information System (INIS)

    Gose, G.C.; McClure, J.A.

    1986-01-01

    RETRAN-02 is a modular code system that has been designed for one-dimensional, transient thermal-hydraulics analysis. In RETRAN-02, core power behavior may be treated using a one-dimensional reactor kinetics model. This model allows the user to investigate the interaction of time- and space-dependent effects in the reactor core on overall system behavior for specific LWR operational transients. The purpose of this paper is to review the recent analysis and development activities related to the one dimensional kinetics model in RETRAN-02

  2. Vibrational kinetics in CO electric discharge lasers - Modeling and experiments

    Science.gov (United States)

    Stanton, A. C.; Hanson, R. K.; Mitchner, M.

    1980-01-01

    A model of CO laser vibrational kinetics is developed, and predicted vibrational distributions are compared with measurements. The experimental distributions were obtained at various flow locations in a transverse CW discharge in supersonic (M = 3) flow. Good qualitative agreement is obtained in the comparisons, including the prediction of a total inversion at low discharge current densities. The major area of discrepancy is an observed loss in vibrational energy downstream of the discharge which is not predicted by the model. This discrepancy may be due to three-dimensional effects in the experiment which are not included in the model. Possible kinetic effects which may contribute to vibrational energy loss are also examined.

  3. A two-point kinetic model for the PROTEUS reactor

    International Nuclear Information System (INIS)

    Dam, H. van.

    1995-03-01

    A two-point reactor kinetic model for the PROTEUS-reactor is developed and the results are described in terms of frequency dependent reactivity transfer functions for the core and the reflector. It is shown that at higher frequencies space-dependent effects occur which imply failure of the one-point kinetic model. In the modulus of the transfer functions these effects become apparent above a radian frequency of about 100 s -1 , whereas for the phase behaviour the deviation from a point model already starts at a radian frequency of 10 s -1 . (orig.)

  4. Modeling Kinetics of Distortion in Porous Bi-layered Structures

    DEFF Research Database (Denmark)

    Tadesse Molla, Tesfaye; Frandsen, Henrik Lund; Bjørk, Rasmus

    2013-01-01

    because of different sintering rates of the materials resulting in undesired distortions of the component. An analytical model based on the continuum theory of sintering has been developed to describe the kinetics of densification and distortion in the sintering processes. A new approach is used...... to extract the material parameters controlling shape distortion through optimizing the model to experimental data of free shrinkage strains. The significant influence of weight of the sample (gravity) on the kinetics of distortion is taken in to consideration. The modeling predictions indicate good agreement...

  5. A multi water bag model of drift kinetic electron plasma

    International Nuclear Information System (INIS)

    Morel, P.; Dreydemy Ghiro, F.; Berionni, V.; Gurcan, O.D.; Coulette, D.; Besse, N.

    2014-01-01

    A Multi Water Bag model is proposed for describing drift kinetic plasmas in a magnetized cylindrical geometry, relevant for various experimental devices, solar wind modeling... The Multi Water Bag (MWB) model is adapted to the description of a plasma with kinetic electrons as well as an arbitrary number of kinetic ions. This allows to describe the kinetic dynamics of the electrons, making possible the study of electron temperature gradient (ETG) modes, in addition to the effects of non adiabatic electrons on the ion temperature gradient (ITG) modes, that are of prime importance in the magnetized plasmas micro-turbulence [X. Garbet, Y. Idomura, L. Villard, T.H. Watanabe, Nucl. Fusion 50, 043002 (2010); J.A. Krommes, Ann. Rev. Fluid Mech. 44, 175 (2012)]. The MWB model is shown to link kinetic and fluid descriptions, depending on the number of bags considered. Linear stability of the ETG modes is presented and compared to the existing results regarding cylindrical ITG modes [P. Morel, E. Gravier, N. Besse, R. Klein, A. Ghizzo, P. Bertrand, W. Garbet, Ph. Ghendrih, V. Grandgirard, Y. Sarazin, Phys. Plasmas 14, 112109 (2007)]. (authors)

  6. Computer-Aided Construction of Chemical Kinetic Models

    Energy Technology Data Exchange (ETDEWEB)

    Green, William H. [Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)

    2014-12-31

    The combustion chemistry of even simple fuels can be extremely complex, involving hundreds or thousands of kinetically significant species. The most reasonable way to deal with this complexity is to use a computer not only to numerically solve the kinetic model, but also to construct the kinetic model in the first place. Because these large models contain so many numerical parameters (e.g. rate coefficients, thermochemistry) one never has sufficient data to uniquely determine them all experimentally. Instead one must work in “predictive” mode, using theoretical rather than experimental values for many of the numbers in the model, and as appropriate refining the most sensitive numbers through experiments. Predictive chemical kinetics is exactly what is needed for computer-aided design of combustion systems based on proposed alternative fuels, particularly for early assessment of the value and viability of proposed new fuels before those fuels are commercially available. This project was aimed at making accurate predictive chemical kinetics practical; this is a challenging goal which requires a range of science advances. The project spanned a wide range from quantum chemical calculations on individual molecules and elementary-step reactions, through the development of improved rate/thermo calculation procedures, the creation of algorithms and software for constructing and solving kinetic simulations, the invention of methods for model-reduction while maintaining error control, and finally comparisons with experiment. Many of the parameters in the models were derived from quantum chemistry calculations, and the models were compared with experimental data measured in our lab or in collaboration with others.

  7. Ab initio and kinetic modeling studies of formic acid oxidation

    DEFF Research Database (Denmark)

    Marshall, Paul; Glarborg, Peter

    2015-01-01

    A detailed chemical kinetic model for oxidation of formic acid (HOCHO) in flames has been developed, based on theoretical work and data from literature. Ab initio calculations were used to obtain rate coefficients for reactions of HOCHO with H, O, and HO2. Modeling predictions with the mechanism...

  8. Modeling the kinetics of volatilization from glass melts

    NARCIS (Netherlands)

    Beerkens, R.G.C.

    2001-01-01

    A model description for the evaporation kinetics from glass melts in direct contact with static atmospheres or flowing gas phases is presented. The derived models and equations are based on the solution of the second Ficks' diffusion law and quasi-steady-state mass transfer relations, taking into

  9. A mathematical model of combustion kinetics of municipal solid ...

    African Journals Online (AJOL)

    Municipal Solid Waste has become a serious environmental problem troubling many cities. In this paper, a mathematical model of combustion kinetics of municipal solid waste with focus on plastic waste was studied. An analytical solution is obtained for the model. From the numerical simulation, it is observed that the ...

  10. Simplified kinetic models of methanol oxidation on silver

    DEFF Research Database (Denmark)

    Andreasen, A.; Lynggaard, H.; Stegelmann, C.

    2005-01-01

    Recently the authors developed a microkinetic model of methanol oxidation on silver [A. Andreasen, H. Lynggaard, C. Stegelmann, P. Stoltze, Surf. Sci. 544 (2003) 5-23]. The model successfully explains both surface science experiments and kinetic experiments at industrial conditions applying...

  11. Kinetic modelling for zinc (II) ions biosorption onto Luffa cylindrica

    International Nuclear Information System (INIS)

    Oboh, I.; Aluyor, E.; Audu, T.

    2015-01-01

    The biosorption of Zinc (II) ions onto a biomaterial - Luffa cylindrica has been studied. This biomaterial was characterized by elemental analysis, surface area, pore size distribution, scanning electron microscopy, and the biomaterial before and after sorption, was characterized by Fourier Transform Infra Red (FTIR) spectrometer. The kinetic nonlinear models fitted were Pseudo-first order, Pseudo-second order and Intra-particle diffusion. A comparison of non-linear regression method in selecting the kinetic model was made. Four error functions, namely coefficient of determination (R 2 ), hybrid fractional error function (HYBRID), average relative error (ARE), and sum of the errors squared (ERRSQ), were used to predict the parameters of the kinetic models. The strength of this study is that a biomaterial with wide distribution particularly in the tropical world and which occurs as waste material could be put into effective utilization as a biosorbent to address a crucial environmental problem

  12. Sum rule limitations of kinetic particle-production models

    International Nuclear Information System (INIS)

    Knoll, J.; CEA Centre d'Etudes Nucleaires de Grenoble, 38; Guet, C.

    1988-04-01

    Photoproduction and absorption sum rules generalized to systems at finite temperature provide a stringent check on the validity of kinetic models for the production of hard photons in intermediate energy nuclear collisions. We inspect such models for the case of nuclear matter at finite temperature employed in a kinetic regime which copes those encountered in energetic nuclear collisions, and find photon production rates which significantly exceed the limits imposed by the sum rule even under favourable concession. This suggests that coherence effects are quite important and the production of photons cannot be considered as an incoherent addition of individual NNγ production processes. The deficiencies of present kinetic models may also apply for the production of probes such as the pion which do not couple perturbatively to the nuclear currents. (orig.)

  13. A kinetic approach to magnetospheric modeling

    International Nuclear Information System (INIS)

    Whipple, E.C. Jr.

    1979-01-01

    The earth's magnetosphere is caused by the interaction between the flowing solar wind and the earth's magnetic dipole, with the distorted magnetic field in the outer parts of the magnetosphere due to the current systems resulting from this interaction. It is surprising that even the conceptually simple problem of the collisionless interaction of a flowing plasma with a dipole magnetic field has not been solved. A kinetic approach is essential if one is to take into account the dispersion of particles with different energies and pitch angles and the fact that particles on different trajectories have different histories and may come from different sources. Solving the interaction problem involves finding the various types of possible trajectories, populating them with particles appropriately, and then treating the electric and magnetic fields self-consistently with the resulting particle densities and currents. This approach is illustrated by formulating a procedure for solving the collisionless interaction problem on open field lines in the case of a slowly flowing magnetized plasma interacting with a magnetic dipole

  14. A kinetic approach to magnetospheric modeling

    Science.gov (United States)

    Whipple, E. C., Jr.

    1979-01-01

    The earth's magnetosphere is caused by the interaction between the flowing solar wind and the earth's magnetic dipole, with the distorted magnetic field in the outer parts of the magnetosphere due to the current systems resulting from this interaction. It is surprising that even the conceptually simple problem of the collisionless interaction of a flowing plasma with a dipole magnetic field has not been solved. A kinetic approach is essential if one is to take into account the dispersion of particles with different energies and pitch angles and the fact that particles on different trajectories have different histories and may come from different sources. Solving the interaction problem involves finding the various types of possible trajectories, populating them with particles appropriately, and then treating the electric and magnetic fields self-consistently with the resulting particle densities and currents. This approach is illustrated by formulating a procedure for solving the collisionless interaction problem on open field lines in the case of a slowly flowing magnetized plasma interacting with a magnetic dipole.

  15. Methane Hydrates: Chapter 8

    Science.gov (United States)

    Boswell, Ray; Yamamoto, Koji; Lee, Sung-Rock; Collett, Timothy S.; Kumar, Pushpendra; Dallimore, Scott

    2008-01-01

    Gas hydrate is a solid, naturally occurring substance consisting predominantly of methane gas and water. Recent scientific drilling programs in Japan, Canada, the United States, Korea and India have demonstrated that gas hydrate occurs broadly and in a variety of forms in shallow sediments of the outer continental shelves and in Arctic regions. Field, laboratory and numerical modelling studies conducted to date indicate that gas can be extracted from gas hydrates with existing production technologies, particularly for those deposits in which the gas hydrate exists as pore-filling grains at high saturation in sand-rich reservoirs. A series of regional resource assessments indicate that substantial volumes of gas hydrate likely exist in sand-rich deposits. Recent field programs in Japan, Canada and in the United States have demonstrated the technical viability of methane extraction from gas-hydrate-bearing sand reservoirs and have investigated a range of potential production scenarios. At present, basic reservoir depressurisation shows the greatest promise and can be conducted using primarily standard industry equipment and procedures. Depressurisation is expected to be the foundation of future production systems; additional processes, such as thermal stimulation, mechanical stimulation and chemical injection, will likely also be integrated as dictated by local geological and other conditions. An innovative carbon dioxide and methane swapping technology is also being studied as a method to produce gas from select gas hydrate deposits. In addition, substantial additional volumes of gas hydrate have been found in dense arrays of grain-displacing veins and nodules in fine-grained, clay-dominated sediments; however, to date, no field tests, and very limited numerical modelling, have been conducted with regard to the production potential of such accumulations. Work remains to further refine: (1) the marine resource volumes within potential accumulations that can be

  16. Kinetic models for irreversible processes on a lattice

    International Nuclear Information System (INIS)

    Wolf, N.O.

    1979-04-01

    The development and application of kinetic lattice models are considered. For the most part, the discussions are restricted to lattices in one-dimension. In Chapter 1, a brief overview of kinetic lattice model formalisms and an extensive literature survey are presented. A review of the kinetic models for non-cooperative lattice events is presented in Chapter 2. The development of cooperative lattice models and solution of the resulting kinetic equations for an infinite and a semi-infinite lattice are thoroughly discussed in Chapters 3 and 4. The cooperative models are then applied to the problem of theoretically dtermining the sticking coefficient for molecular chemisorption in Chapter 5. In Chapter 6, other possible applications of these models and several model generalizations are considered. Finally, in Chapter 7, an experimental study directed toward elucidating the mechanistic factors influencing the chemisorption of methane on single crystal tungsten is reported. In this it differs from the rest of the thesis which deals with the statistical distributions resulting from a given mechanism

  17. Kinetic models for irreversible processes on a lattice

    Energy Technology Data Exchange (ETDEWEB)

    Wolf, N.O.

    1979-04-01

    The development and application of kinetic lattice models are considered. For the most part, the discussions are restricted to lattices in one-dimension. In Chapter 1, a brief overview of kinetic lattice model formalisms and an extensive literature survey are presented. A review of the kinetic models for non-cooperative lattice events is presented in Chapter 2. The development of cooperative lattice models and solution of the resulting kinetic equations for an infinite and a semi-infinite lattice are thoroughly discussed in Chapters 3 and 4. The cooperative models are then applied to the problem of theoretically dtermining the sticking coefficient for molecular chemisorption in Chapter 5. In Chapter 6, other possible applications of these models and several model generalizations are considered. Finally, in Chapter 7, an experimental study directed toward elucidating the mechanistic factors influencing the chemisorption of methane on single crystal tungsten is reported. In this it differs from the rest of the thesis which deals with the statistical distributions resulting from a given mechanism.

  18. Transperitoneal transport of creatinine. A comparison of kinetic models

    DEFF Research Database (Denmark)

    Fugleberg, S; Graff, J; Joffe, P

    1994-01-01

    Six kinetic models of transperitoneal creatinine transport were formulated and validated on the basis of experimental results obtained from 23 non-diabetic patients undergoing peritoneal dialysis. The models were designed to elucidate the presence or absence of diffusive, non-lymphatic convective...... including all three forms of transport is superior to other models. We conclude that the best model of transperitoneal creatinine transport includes diffusion, non-lymphatic convective transport and lymphatic convective transport....

  19. Computer models for kinetic equations of magnetically confined plasmas

    International Nuclear Information System (INIS)

    Killeen, J.; Kerbel, G.D.; McCoy, M.G.; Mirin, A.A.; Horowitz, E.J.; Shumaker, D.E.

    1987-01-01

    This paper presents four working computer models developed by the computational physics group of the National Magnetic Fusion Energy Computer Center. All of the models employ a kinetic description of plasma species. Three of the models are collisional, i.e., they include the solution of the Fokker-Planck equation in velocity space. The fourth model is collisionless and treats the plasma ions by a fully three-dimensional particle-in-cell method

  20. Possible gas hydrates on the Bjarmeland Platform; seismic expression and stability modelling

    OpenAIRE

    Løvaas, John Sverre

    2016-01-01

    Seismic evidence of shallow gas anomalies are prominent at Ververis Dome structure and Hoop Fault Complex in Bjarmeland Platform. Ubiquitous high amplitude anomalies at the same depth as these shallow gas anomalies infer a possible relation to gas hydrates. A wide range of fluid flow structures within the two study areas have previously been discovered and reported, and may possibly feed the base of the gas hydrate stability zone (BGHSZ) with upward migrating thermogenic gas. This thesis f...

  1. Gyrofluid Modeling of Turbulent, Kinetic Physics

    Science.gov (United States)

    Despain, Kate Marie

    2011-12-01

    Gyrofluid models to describe plasma turbulence combine the advantages of fluid models, such as lower dimensionality and well-developed intuition, with those of gyrokinetics models, such as finite Larmor radius (FLR) effects. This allows gyrofluid models to be more tractable computationally while still capturing much of the physics related to the FLR of the particles. We present a gyrofluid model derived to capture the behavior of slow solar wind turbulence and describe the computer code developed to implement the model. In addition, we describe the modifications we made to a gyrofluid model and code that simulate plasma turbulence in tokamak geometries. Specifically, we describe a nonlinear phase mixing phenomenon, part of the E x B term, that was previously missing from the model. An inherently FLR effect, it plays an important role in predicting turbulent heat flux and diffusivity levels for the plasma. We demonstrate this importance by comparing results from the updated code to studies done previously by gyrofluid and gyrokinetic codes. We further explain what would be necessary to couple the updated gyrofluid code, gryffin, to a turbulent transport code, thus allowing gryffin to play a role in predicting profiles for fusion devices such as ITER and to explore novel fusion configurations. Such a coupling would require the use of Graphical Processing Units (GPUs) to make the modeling process fast enough to be viable. Consequently, we also describe our experience with GPU computing and demonstrate that we are poised to complete a gryffin port to this innovative architecture.

  2. Modeling the Removal of Xenon from Lithium Hydrate with Aspen HYSYS

    Science.gov (United States)

    Efthimion, Phillip; Gentile, Charles

    2011-10-01

    The Laser Inertial Fusion Engine (LIFE) project mission is to provide a long-term, carbon-free source of sustainable energy, in the form of electricity. A conceptual xenon removal system has been modeled with the aid of Aspen HYSYS, a chemical process simulator. Aspen HYSYS provides excellent capability to model chemical flow processes, which generates outputs which includes specific variables such as temperature, pressure, and molar flow. The system is designed to strip out hydrogen isotopes deuterium and tritium. The base design bubbles plasma exhaust laden with x filled with liquid helium. The system separates the xenon from the hydrogen, deuterium, and tritium with a lithium hydrate and a lithium bubbler. After the removal of the hydrogen and its isotopes, the xenon is then purified by way of the process of cryogenic distillation. The pure hydrogen, deuterium, and tritium are then sent to the isotope separation system (ISS). The removal of xenon is an integral part of the laser inertial fusion engine and Aspen HYSYS is an excellent tool to calculate how to create pure xenon.

  3. Kinetic k-essence ghost dark energy model

    International Nuclear Information System (INIS)

    Rozas-Fernández, Alberto

    2012-01-01

    A ghost dark energy model has been recently put forward to explain the current accelerated expansion of the Universe. In this model, the energy density of ghost dark energy, which comes from the Veneziano ghost of QCD, is proportional to the Hubble parameter, ρ D =αH. Here α is a constant of order Λ QCD 3 where Λ QCD ∼100 MeV is the QCD mass scale. We consider a connection between ghost dark energy with/without interaction between the components of the dark sector and the kinetic k-essence field. It is shown that the cosmological evolution of the ghost dark energy dominated Universe can be completely described a kinetic k-essence scalar field. We reconstruct the kinetic k-essence function F(X) in a flat Friedmann-Robertson-Walker Universe according to the evolution of ghost dark energy density.

  4. TOUGH+HYDRATE v1.2 User's Manual: A Code for the Simulation of System Behavior in Hydrate-Bearing Geologic Media

    Energy Technology Data Exchange (ETDEWEB)

    Moridis, George J. [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Kowalsky, Michael B. [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Pruess, Karsten [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)

    2012-08-01

    TOUGH+HYDRATE v1.2 is a code for the simulation of the behavior of hydratebearing geologic systems, and represents the second update of the code since its first release [Moridis et al., 2008]. By solving the coupled equations of mass and heat balance, TOUGH+HYDRATE can model the non-isothermal gas release, phase behavior and flow of fluids and heat under conditions typical of common natural CH4-hydrate deposits (i.e., in the permafrost and in deep ocean sediments) in complex geological media at any scale (from laboratory to reservoir) at which Darcy’s law is valid. TOUGH+HYDRATE v1.2 includes both an equilibrium and a kinetic model of hydrate formation and dissociation. The model accounts for heat and up to four mass components, i.e., water, CH4, hydrate, and water-soluble inhibitors such as salts or alcohols. These are partitioned among four possible phases (gas phase, liquid phase, ice phase and hydrate phase). Hydrate dissociation or formation, phase changes and the corresponding thermal effects are fully described, as are the effects of inhibitors. The model can describe all possible hydrate dissociation mechanisms, i.e., depressurization, thermal stimulation, salting-out effects and inhibitor-induced effects. TOUGH+HYDRATE is a member of TOUGH+, the successor to the TOUGH2 [Pruess et al., 1991] family of codes for multi-component, multiphase fluid and heat flow developed at the Lawrence Berkeley National Laboratory. It is written in standard FORTRAN 95/2003, and can be run on any computational platform (workstation, PC, Macintosh) for which such compilers are available.

  5. Bayesian inference of chemical kinetic models from proposed reactions

    KAUST Repository

    Galagali, Nikhil

    2015-02-01

    © 2014 Elsevier Ltd. Bayesian inference provides a natural framework for combining experimental data with prior knowledge to develop chemical kinetic models and quantify the associated uncertainties, not only in parameter values but also in model structure. Most existing applications of Bayesian model selection methods to chemical kinetics have been limited to comparisons among a small set of models, however. The significant computational cost of evaluating posterior model probabilities renders traditional Bayesian methods infeasible when the model space becomes large. We present a new framework for tractable Bayesian model inference and uncertainty quantification using a large number of systematically generated model hypotheses. The approach involves imposing point-mass mixture priors over rate constants and exploring the resulting posterior distribution using an adaptive Markov chain Monte Carlo method. The posterior samples are used to identify plausible models, to quantify rate constant uncertainties, and to extract key diagnostic information about model structure-such as the reactions and operating pathways most strongly supported by the data. We provide numerical demonstrations of the proposed framework by inferring kinetic models for catalytic steam and dry reforming of methane using available experimental data.

  6. Continuum-Kinetic Models and Numerical Methods for Multiphase Applications

    Science.gov (United States)

    Nault, Isaac Michael

    This thesis presents a continuum-kinetic approach for modeling general problems in multiphase solid mechanics. In this context, a continuum model refers to any model, typically on the macro-scale, in which continuous state variables are used to capture the most important physics: conservation of mass, momentum, and energy. A kinetic model refers to any model, typically on the meso-scale, which captures the statistical motion and evolution of microscopic entitites. Multiphase phenomena usually involve non-negligible micro or meso-scopic effects at the interfaces between phases. The approach developed in the thesis attempts to combine the computational performance benefits of a continuum model with the physical accuracy of a kinetic model when applied to a multiphase problem. The approach is applied to modeling a single particle impact in Cold Spray, an engineering process that intimately involves the interaction of crystal grains with high-magnitude elastic waves. Such a situation could be classified a multiphase application due to the discrete nature of grains on the spatial scale of the problem. For this application, a hyper elasto-plastic model is solved by a finite volume method with approximate Riemann solver. The results of this model are compared for two types of plastic closure: a phenomenological macro-scale constitutive law, and a physics-based meso-scale Crystal Plasticity model.

  7. Modeling uptake kinetics of cadmium by field-grown lettuce

    Energy Technology Data Exchange (ETDEWEB)

    Chen Weiping [Department of Environmental Sciences, University of California, 900 University Avenue, Riverside, CA 92521 (United States)], E-mail: chenweip@yahoo.com.cn; Li Lianqing [Institute of Resources, Ecosystem and Environment of Agriculture, Nanjing Agricultural University, Nanjing 210095 (China); Chang, Andrew C.; Wu Laosheng [Department of Environmental Sciences, University of California, 900 University Avenue, Riverside, CA 92521 (United States); Kwon, Soon-Ik [Agricultural Environmental and Ecology Division, National Institute of Agricultural Science and Technology, Suwon 441-707 (Korea, Republic of); Bottoms, Rick [Desert Research and Extension Center, 1004 East Holton Road, El Centro, CA 92243 (United States)

    2008-03-15

    Cadmium uptake by field grown Romaine lettuce treated with P-fertilizers of different Cd levels was investigated over an entire growing season. Results indicated that the rate of Cd uptake at a given time of the season can be satisfactorily described by the Michaelis-Menten kinetics, that is, plant uptake increases as the Cd concentration in soil solution increases, and it gradually approaches a saturation level. However, the rate constant of the Michaelis-Menten kinetics changes over the growing season. Under a given soil Cd level, the cadmium content in plant tissue decreases exponentially with time. To account for the dynamic nature of Cd uptake, a kinetic model integrating the time factor was developed to simulate Cd plant uptake over the growing season: C{sub Plant} = C{sub Solution} . PUF{sub max} . exp[-b . t], where C{sub Plant} and C{sub Solution} refer to the Cd content in plant tissue and soil solution, respectively, PUF{sub max} and b are kinetic constants. - A kinetic model was developed to evaluate the uptake of Cd under field conditions.

  8. Modeling uptake kinetics of cadmium by field-grown lettuce

    International Nuclear Information System (INIS)

    Chen Weiping; Li Lianqing; Chang, Andrew C.; Wu Laosheng; Kwon, Soon-Ik; Bottoms, Rick

    2008-01-01

    Cadmium uptake by field grown Romaine lettuce treated with P-fertilizers of different Cd levels was investigated over an entire growing season. Results indicated that the rate of Cd uptake at a given time of the season can be satisfactorily described by the Michaelis-Menten kinetics, that is, plant uptake increases as the Cd concentration in soil solution increases, and it gradually approaches a saturation level. However, the rate constant of the Michaelis-Menten kinetics changes over the growing season. Under a given soil Cd level, the cadmium content in plant tissue decreases exponentially with time. To account for the dynamic nature of Cd uptake, a kinetic model integrating the time factor was developed to simulate Cd plant uptake over the growing season: C Plant = C Solution . PUF max . exp[-b . t], where C Plant and C Solution refer to the Cd content in plant tissue and soil solution, respectively, PUF max and b are kinetic constants. - A kinetic model was developed to evaluate the uptake of Cd under field conditions

  9. Equilibrium and kinetic models for colloid release under transient solution chemistry conditions.

    Science.gov (United States)

    Bradford, Scott A; Torkzaban, Saeed; Leij, Feike; Simunek, Jiri

    2015-10-01

    We present continuum models to describe colloid release in the subsurface during transient physicochemical conditions. Our modeling approach relates the amount of colloid release to changes in the fraction of the solid surface area that contributes to retention. Equilibrium, kinetic, equilibrium and kinetic, and two-site kinetic models were developed to describe various rates of colloid release. These models were subsequently applied to experimental colloid release datasets to investigate the influence of variations in ionic strength (IS), pH, cation exchange, colloid size, and water velocity on release. Various combinations of equilibrium and/or kinetic release models were needed to describe the experimental data depending on the transient conditions and colloid type. Release of Escherichia coli D21g was promoted by a decrease in solution IS and an increase in pH, similar to expected trends for a reduction in the secondary minimum and nanoscale chemical heterogeneity. The retention and release of 20nm carboxyl modified latex nanoparticles (NPs) were demonstrated to be more sensitive to the presence of Ca(2+) than D21g. Specifically, retention of NPs was greater than D21g in the presence of 2mM CaCl2 solution, and release of NPs only occurred after exchange of Ca(2+) by Na(+) and then a reduction in the solution IS. These findings highlight the limitations of conventional interaction energy calculations to describe colloid retention and release, and point to the need to consider other interactions (e.g., Born, steric, and/or hydration forces) and/or nanoscale heterogeneity. Temporal changes in the water velocity did not have a large influence on the release of D21g for the examined conditions. This insensitivity was likely due to factors that reduce the applied hydrodynamic torque and/or increase the resisting adhesive torque; e.g., macroscopic roughness and grain-grain contacts. Our analysis and models improve our understanding and ability to describe the amounts

  10. Kinetics of steel slag leaching: Batch tests and modeling

    International Nuclear Information System (INIS)

    De Windt, Laurent; Chaurand, Perrine; Rose, Jerome

    2011-01-01

    Reusing steel slag as an aggregate for road construction requires to characterize the leaching kinetics and metal releases. In this study, basic oxygen furnace (BOF) steel slag were subjected to batch leaching tests at liquid to solid ratios (L/S) of 10 and 100 over 30 days; the leachate chemistry being regularly sampled in time. A geochemical model of the steel slag is developed and validated from experimental data, particularly the evolution with leaching of mineralogical composition of the slag and trace element speciation. Kinetics is necessary for modeling the primary phase leaching, whereas a simple thermodynamic equilibrium approach can be used for secondary phase precipitation. The proposed model simulates the kinetically-controlled dissolution (hydrolysis) of primary phases, the precipitation of secondary phases (C-S-H, hydroxide and spinel), the pH and redox conditions, and the progressive release of major elements as well as the metals Cr and V. Modeling indicates that the dilution effect of the L/S ratio is often coupled to solubility-controlled processes, which are sensitive to both the pH and the redox potential. A sensitivity analysis of kinetic uncertainties on the modeling of element releases is performed.

  11. Modeling intrinsic kinetics in immobilized photocatalytic microreactors

    NARCIS (Netherlands)

    Visan, Aura; Rafieian Boroujeni, Damon; Ogieglo, Wojciech; Lammertink, Rob G.H.

    2014-01-01

    The article presents a simple model for immobilized photocatalytic microreactors following a first order reaction rate with either light independency or light dependency described by photon absorption carrier generation semiconductor physics. Experimental data obtained for various residence times,

  12. Kinetic and thermodynamic modelling of TBP synthesis processes

    International Nuclear Information System (INIS)

    Azzouz, A.; Attou, M.

    1989-02-01

    The present paper deals with kinetic and thermodynamic modellisation of tributylphosphate (TBP) synthesis processes. Its aim consists in a purely comparative study of two different synthesis ways i.e. direct and indirect estirification of butanol. The methodology involves two steps. The first step consists in approximating curves which describe the process evolution and their dependence on the main parameters. The results gave a kinetic model of the process rate yielding in TBP. Further, on the basis of thermodynamic data concerning the various involved compounds a theoretical model was achieved. The calculations were carried out in Basic language and an interpolation mathematical method was applied to approximate the kinetic curves. The thermodynamic calculations were achieved on the basis of GIBBS' free energy using a VAX type computer and a VT240 terminal. The calculations accuracy was reasonable and within the norms. For each process, the confrontation of both models leads to an appreciable accord. In the two processes, the thermodynamic models were similar although the kinetic equations present different reaction orders. Hence the reaction orders were determined by a mathematical method which conists in searching the minimal difference between an empiric relation and a kinetic model with fixed order. This corresponds in fact in testing the model proposed at various reaction order around the suspected value. The main idea which results from such a work is that this kind of processes is well fitting with the model without taking into account the side chain reactions. The process behaviour is like that of a single reaction having a quasi linear dependence of the rate yielding and the reaction time for both processes

  13. Exploring the chemical kinetics of partially oxidized intermediates by combining experiments, theory, and kinetic modeling.

    Science.gov (United States)

    Hoyermann, Karlheinz; Mauß, Fabian; Olzmann, Matthias; Welz, Oliver; Zeuch, Thomas

    2017-07-19

    Partially oxidized intermediates play a central role in combustion and atmospheric chemistry. In this perspective, we focus on the chemical kinetics of alkoxy radicals, peroxy radicals, and Criegee intermediates, which are key species in both combustion and atmospheric environments. These reactive intermediates feature a broad spectrum of chemical diversity. Their reactivity is central to our understanding of how volatile organic compounds are degraded in the atmosphere and converted into secondary organic aerosol. Moreover, they sensitively determine ignition timing in internal combustion engines. The intention of this perspective article is to provide the reader with information about the general mechanisms of reactions initiated by addition of atomic and molecular oxygen to alkyl radicals and ozone to alkenes. We will focus on critical branching points in the subsequent reaction mechanisms and discuss them from a consistent point of view. As a first example of our integrated approach, we will show how experiment, theory, and kinetic modeling have been successfully combined in the first infrared detection of Criegee intermediates during the gas phase ozonolysis. As a second example, we will examine the ignition timing of n-heptane/air mixtures at low and intermediate temperatures. Here, we present a reduced, fuel size independent kinetic model of the complex chemistry initiated by peroxy radicals that has been successfully applied to simulate standard n-heptane combustion experiments.

  14. Numerical modeling of the simulated gas hydrate production test at Mallik 2L-38 in the pilot scale pressure reservoir LARS - Applying the "foamy oil" model

    Science.gov (United States)

    Abendroth, Sven; Thaler, Jan; Klump, Jens; Schicks, Judith; Uddin, Mafiz

    2014-05-01

    In the context of the German joint project SUGAR (Submarine Gas Hydrate Reservoirs: exploration, extraction and transport) we conducted a series of experiments in the LArge Reservoir Simulator (LARS) at the German Research Centre of Geosciences Potsdam. These experiments allow us to investigate the formation and dissociation of hydrates at large scale laboratory conditions. We performed an experiment similar to the field-test conditions of the production test in the Mallik gas hydrate field (Mallik 2L-38) in the Beaufort Mackenzie Delta of the Canadian Arctic. The aim of this experiment was to study the transport behavior of fluids in gas hydrate reservoirs during depressurization (see also Heeschen et al. and Priegnitz et al., this volume). The experimental results from LARS are used to provide details about processes inside the pressure vessel, to validate the models through history matching, and to feed back into the design of future experiments. In experiments in LARS the amount of methane produced from gas hydrates was much lower than expected. Previously published models predict a methane production rate higher than the one observed in experiments and field studies (Uddin et al. 2010; Wright et al. 2011). The authors of the aforementioned studies point out that the current modeling approach overestimates the gas production rate when modeling gas production by depressurization. They suggest that trapping of gas bubbles inside the porous medium is responsible for the reduced gas production rate. They point out that this behavior of multi-phase flow is not well explained by a "residual oil" model, but rather resembles a "foamy oil" model. Our study applies Uddin's (2010) "foamy oil" model and combines it with history matches of our experiments in LARS. Our results indicate a better agreement between experimental and model results when using the "foamy oil" model instead of conventional models of gas flow in water. References Uddin M., Wright J.F. and Coombe D

  15. Chloral Hydrate

    Science.gov (United States)

    ... if you are allergic to chloral hydrate, aspirin, tartrazine (a yellow dye in some processed foods and ... in, tightly closed, and out of reach of children. Store it at room temperature, away from excess ...

  16. Kinetic modelling and thermodynamic studies on purification of ...

    African Journals Online (AJOL)

    Adsorbent capacities have been determined by mathematical fitting of equilibrium data using the most common isotherms: Freundlich isotherm and Langmuir isotherm. Several kinetic models have been applied to the process. Thermodynamic parameters: △So, △Ho, △Go and Ea (kJ/mol) have been determined.

  17. Development of simple kinetic models and parameter estimation for ...

    African Journals Online (AJOL)

    In order to describe and predict the growth and expression of recombinant proteins by using a genetically modified Pichia pastoris, we developed a number of unstructured models based on growth kinetic equation, fed-batch mass balance and the assumptions of constant cell and protein yields. The growth of P. pastoris on ...

  18. Modelling of thermal degradation kinetics of ascorbic acid in ...

    African Journals Online (AJOL)

    Ascorbic acid (vitamin C) loss in thermally treated pawpaw and potato was modelled mathematically. Isothermal experiments in the temperature range of 50 -80 oC for the drying of pawpaw and 60 -100 oC for the blanch-drying of potato were utilized to determine the kinetics of ascorbic acid loss in both fruit and vegetable.

  19. Formulation, construction and analysis of kinetic models of metabolism: A review of modelling frameworks

    DEFF Research Database (Denmark)

    Saa, Pedro A.; Nielsen, Lars K.

    2017-01-01

    Kinetic models are critical to predict the dynamic behaviour of metabolic networks. Mechanistic kinetic models for large networks remain uncommon due to the difficulty of fitting their parameters. Recent modelling frameworks promise new ways to overcome this obstacle while retaining predictive ca...

  20. Prediction of hydrate formation temperature by both statistical models and artificial neural network approaches

    International Nuclear Information System (INIS)

    Zahedi, Gholamreza; Karami, Zohre; Yaghoobi, Hamed

    2009-01-01

    In this study, various estimation methods have been reviewed for hydrate formation temperature (HFT) and two procedures have been presented. In the first method, two general correlations have been proposed for HFT. One of the correlations has 11 parameters, and the second one has 18 parameters. In order to obtain constants in proposed equations, 203 experimental data points have been collected from literatures. The Engineering Equation Solver (EES) and Statistical Package for the Social Sciences (SPSS) soft wares have been employed for statistical analysis of the data. Accuracy of the obtained correlations also has been declared by comparison with experimental data and some recent common used correlations. In the second method, HFT is estimated by artificial neural network (ANN) approach. In this case, various architectures have been checked using 70% of experimental data for training of ANN. Among the various architectures multi layer perceptron (MLP) network with trainlm training algorithm was found as the best architecture. Comparing the obtained ANN model results with 30% of unseen data confirms ANN excellent estimation performance. It was found that ANN is more accurate than traditional methods and even our two proposed correlations for HFT estimation.

  1. Chemical kinetics and combustion modelling with CFX 4

    Energy Technology Data Exchange (ETDEWEB)

    Stopford, P [AEA Technology, Computational Fluid Dynamics Services Harwell, Oxfordshire (United Kingdom)

    1998-12-31

    The presentation describes some recent developments in combustion and kinetics models used in the CFX software of AEA Technology. Three topics are highlighted: the development of coupled solvers in a traditional `SIMPLE`-based CFD code, the use of detailed chemical kinetics mechanism via `look-up` tables and the application of CFD to large-scale multi-burner combustion plant. The aim is identify those physical approximations and numerical methods that are likely to be most useful in the future and those areas where further developments are required. (author) 6 refs.

  2. Chemical kinetics and combustion modelling with CFX 4

    Energy Technology Data Exchange (ETDEWEB)

    Stopford, P. [AEA Technology, Computational Fluid Dynamics Services Harwell, Oxfordshire (United Kingdom)

    1997-12-31

    The presentation describes some recent developments in combustion and kinetics models used in the CFX software of AEA Technology. Three topics are highlighted: the development of coupled solvers in a traditional `SIMPLE`-based CFD code, the use of detailed chemical kinetics mechanism via `look-up` tables and the application of CFD to large-scale multi-burner combustion plant. The aim is identify those physical approximations and numerical methods that are likely to be most useful in the future and those areas where further developments are required. (author) 6 refs.

  3. A flexible multipurpose model for normal and transient cell kinetics

    International Nuclear Information System (INIS)

    Toivonen, Harri.

    1979-07-01

    The internal hypothetical compartments within the different phases of the cell cycle have been adopted as the basis of models dealing with various specific problems in cell kinetics. This approach was found to be of more general validity, extending from expanding cell populations to complex maturation processes. The differential equations describing the system were solved with an effective, commercially available library subroutine. Special attention was devoted to analysis of transient and feedback kinetics of cell populations encountered in diverse environmental and exposure conditions, for instance in cases of wounding and radiation damage. (author)

  4. Kinetics and modeling of anaerobic digestion process

    DEFF Research Database (Denmark)

    Gavala, Hariklia N.; Angelidaki, Irini; Ahring, Birgitte Kiær

    2003-01-01

    Anaerobic digestion modeling started in the early 1970s when the need for design and efficient operation of anaerobic systems became evident. At that time not only was the knowledge about the complex process of anaerobic digestion inadequate but also there were computational limitations. Thus...

  5. Laplace transform in tracer kinetic modeling

    Energy Technology Data Exchange (ETDEWEB)

    Hauser, Eliete B., E-mail: eliete@pucrs.br [Instituto do Cerebro (InsCer/FAMAT/PUC-RS), Porto Alegre, RS, (Brazil). Faculdade de Matematica

    2013-07-01

    The main objective this paper is to quantify the pharmacokinetic processes: absorption, distribution and elimination of radiopharmaceutical(tracer), using Laplace transform method. When the drug is administered intravenously absorption is complete and is available in the bloodstream to be distributed throughout the whole body in all tissues and fluids, and to be eliminated. Mathematical modeling seeks to describe the processes of distribution and elimination through compartments, where distinct pools of tracer (spatial location or chemical state) are assigned to different compartments. A compartment model is described by a system of differential equations, where each equation represents the sum of all the transfer rates to and from a specific compartment. In this work a two-tissue irreversible compartment model is used for description of tracer, [{sup 18}F]2-fluor-2deoxy-D-glucose. In order to determine the parameters of the model, it is necessary to have information about the tracer delivery in the form of an input function representing the time-course of tracer concentration in arterial blood or plasma. We estimate the arterial input function in two stages and apply the Levenberg-Marquardt Method to solve nonlinear regressions. The transport of FDG across de arterial blood is very fast in the first ten minutes and then decreases slowly. We use de Heaviside function to represent this situation and this is the main contribution of this study. We apply the Laplace transform and the analytical solution for two-tissue irreversible compartment model is obtained. The only approach is to determinate de arterial input function. (author)

  6. Phase equilibria with hydrate formation in H2O + CO2 mixtures modeled with reference equations of state

    Czech Academy of Sciences Publication Activity Database

    Jäger, A.; Vinš, Václav; Gernert, J.; Span, R.; Hrubý, Jan

    2013-01-01

    Roč. 338, Januar (2013), s. 100-113 ISSN 0378-3812 R&D Projects: GA ČR(CZ) GPP101/11/P046; GA ČR(CZ) GAP101/11/1593 Institutional support: RVO:61388998 Keywords : carbon dioxide * gas hydrate * modeling Subject RIV: BJ - Thermodynamics Impact factor: 2.241, year: 2013 http://www.sciencedirect.com/science/article/pii/S0378381212005158

  7. Ensemble Kinetic Modeling of Metabolic Networks from Dynamic Metabolic Profiles

    Directory of Open Access Journals (Sweden)

    Gengjie Jia

    2012-11-01

    Full Text Available Kinetic modeling of metabolic pathways has important applications in metabolic engineering, but significant challenges still remain. The difficulties faced vary from finding best-fit parameters in a highly multidimensional search space to incomplete parameter identifiability. To meet some of these challenges, an ensemble modeling method is developed for characterizing a subset of kinetic parameters that give statistically equivalent goodness-of-fit to time series concentration data. The method is based on the incremental identification approach, where the parameter estimation is done in a step-wise manner. Numerical efficacy is achieved by reducing the dimensionality of parameter space and using efficient random parameter exploration algorithms. The shift toward using model ensembles, instead of the traditional “best-fit” models, is necessary to directly account for model uncertainty during the application of such models. The performance of the ensemble modeling approach has been demonstrated in the modeling of a generic branched pathway and the trehalose pathway in Saccharomyces cerevisiae using generalized mass action (GMA kinetics.

  8. Gyrofluid turbulence models with kinetic effects

    International Nuclear Information System (INIS)

    Dorland, W.; Hammett, G.W.

    1992-12-01

    Nonlinear gyrofluid equations are derived by taking moments of the nonlinear, electrostatic gyrokinetic equation. The principal model presented includes evolution equations for the guiding center n, u parallel, T parallel, and T perpendicular along with an equation expressing the quasineutrality constraint. Additional evolution equations for higher moments are derived which may be used if greater accuracy is desired. The moment hierarchy is closed with a Landau-damping model which is equivalent to a multi-pole approximation to the plasma dispersion function, extended to include finite Larmor radius effects. In particular, new dissipative, nonlinear terms are found which model the perpendicular phase-mixing of the distribution function along contours of constant electrostatic potential. These ''FLR phase-mixing'' terms introduce a hyperviscosity-like damping ∝ k perpendicular 2 |Φ rvec k rvec k x rvec k'| which should provide a physics-based damping mechanism at high k perpendicular ρ which is potentially as important as the usual polarization drift nonlinearity. The moments are taken in guiding center space to pick up the correct nonlinear FLR terms and the gyroaveraging of the shear. The equations are solved with a nonlinear, three dimensional initial value code. Linear results are presented, showing excellent agreement with linear gyrokinetic theory

  9. A Kinetic Model Describing Injury-Burden in Team Sports.

    Science.gov (United States)

    Fuller, Colin W

    2017-12-01

    Injuries in team sports are normally characterised by the incidence, severity, and location and type of injuries sustained: these measures, however, do not provide an insight into the variable injury-burden experienced during a season. Injury burden varies according to the team's match and training loads, the rate at which injuries are sustained and the time taken for these injuries to resolve. At the present time, this time-based variation of injury burden has not been modelled. To develop a kinetic model describing the time-based injury burden experienced by teams in elite team sports and to demonstrate the model's utility. Rates of injury were quantified using a large eight-season database of rugby injuries (5253) and exposure (60,085 player-match-hours) in English professional rugby. Rates of recovery from injury were quantified using time-to-recovery analysis of the injuries. The kinetic model proposed for predicting a team's time-based injury burden is based on a composite rate equation developed from the incidence of injury, a first-order rate of recovery from injury and the team's playing load. The utility of the model was demonstrated by examining common scenarios encountered in elite rugby. The kinetic model developed describes and predicts the variable injury-burden arising from match play during a season of rugby union based on the incidence of match injuries, the rate of recovery from injury and the playing load. The model is equally applicable to other team sports and other scenarios.

  10. Developments in kinetic modelling of chalcocite particle oxidation

    Energy Technology Data Exchange (ETDEWEB)

    Jaervi, J; Ahokainen, T; Jokilaakso, A [Helsinki Univ. of Technology, Otaniemi (Finland). Lab. of Materials Processing and Powder Metallurgy

    1998-12-31

    A mathematical model for simulating chalcocite particle oxidation is presented. Combustion of pure chalcocite with oxygen is coded as a kinetic module which can be connected as a separate part of commercial CFD-package, PHOENICS. Heat transfer, fluid flow and combustion phenomena can be simulated using CFD-calculation together with the kinetic model. Interaction between gas phase and particles are taken into account by source terms. The aim of the kinetic model is to calculate the particle temperature, contents of species inside the particle, oxygen consumption and formation of sulphur dioxide. Four oxidation reactions are considered and the shrinking core model is used to describe the rate of the oxidation reactions. The model is verified by simulating the particle oxidation reactions in a laboratory scale laminar-flow furnace under different conditions and the model predicts the effects of charges correctly. In the future, the model validation will be done after experimental studies in the laminar flow-furnace. (author) 18 refs.

  11. Developments in kinetic modelling of chalcocite particle oxidation

    Energy Technology Data Exchange (ETDEWEB)

    Jaervi, J.; Ahokainen, T.; Jokilaakso, A. [Helsinki Univ. of Technology, Otaniemi (Finland). Lab. of Materials Processing and Powder Metallurgy

    1997-12-31

    A mathematical model for simulating chalcocite particle oxidation is presented. Combustion of pure chalcocite with oxygen is coded as a kinetic module which can be connected as a separate part of commercial CFD-package, PHOENICS. Heat transfer, fluid flow and combustion phenomena can be simulated using CFD-calculation together with the kinetic model. Interaction between gas phase and particles are taken into account by source terms. The aim of the kinetic model is to calculate the particle temperature, contents of species inside the particle, oxygen consumption and formation of sulphur dioxide. Four oxidation reactions are considered and the shrinking core model is used to describe the rate of the oxidation reactions. The model is verified by simulating the particle oxidation reactions in a laboratory scale laminar-flow furnace under different conditions and the model predicts the effects of charges correctly. In the future, the model validation will be done after experimental studies in the laminar flow-furnace. (author) 18 refs.

  12. One-dimensional reactor kinetics model for RETRAN

    International Nuclear Information System (INIS)

    Gose, G.C.; Peterson, C.E.; Ellis, N.L.; McClure, J.A.

    1981-01-01

    Previous versions of RETRAN have had only a point kinetics model to describe the reactor core behavior during thermal-hydraulic transients. The principal assumption in deriving the point kinetics model is that the neutron flux may be separated into a time-dependent amplitude funtion and a time-independent shape function. Certain types of transients cannot be correctly analyzed under this assumption, since proper definitions for core average quantities such as reactivity or lifetime include the inner product of the adjoint flux with the perturbed flux. A one-dimensional neutronics model has been included in a preliminary version of RETRAN-02. The ability to account for flux shape changes will permit an improved representation of the thermal and hydraulic feedback effects. This paper describes the neutronics model and discusses some of the analyses

  13. Kinetic modeling of Nernst effect in magnetized hohlraums

    OpenAIRE

    Joglekar, A. S.; Ridgers, Christopher Paul; Kingham, R J; Thomas, A. G. R.

    2016-01-01

    We present nanosecond time-scale Vlasov-Fokker-Planck-Maxwell modeling of magnetized plasma transport and dynamics in a hohlraum with an applied external magnetic field, under conditions similar to recent experiments. Self-consistent modeling of the kinetic electron momentum equation allows for a complete treatment of the heat flow equation and Ohm's law, including Nernst advection of magnetic fields. In addition to showing the prevalence of nonlocal behavior, we demonstrate that effects such...

  14. A kinetic-MHD model for low frequency phenomena

    International Nuclear Information System (INIS)

    Cheng, C.Z.

    1991-07-01

    A hybrid kinetic-MHD model for describing low-frequency phenomena in high beta anisotropic plasmas that consist of two components: a low energy core component and an energetic component with low density. The kinetic-MHD model treats the low energy core component by magnetohydrodynamic (MHD) description, the energetic component by kinetic approach such as the gyrokinetic equation, and the coupling between the dynamics of these two components through plasma pressure in the momentum equation. The kinetic-MHD model optimizes both the physics contents and the theoretical efforts in studying low frequency MHD waves and transport phenomena in general magnetic field geometries, and can be easily modified to include the core plasma kinetic effects if necessary. It is applicable to any magnetized collisionless plasma system where the parallel electric field effects are negligibly small. In the linearized limit two coupled eigenmode equations for describing the coupling between the transverse Alfven type and the compressional Alfven type waves are derived. The eigenmode equations are identical to those derived from the full gyrokinetic equation in the low frequency limit and were previously analyzed both analytically nd numerically to obtain the eigenmode structure of the drift mirror instability which explains successfully the multi-satellite observation of antisymmetric field-aligned structure of the compressional magnetic field of Pc 5 waves in the magnetospheric ring current plasma. Finally, a quadratic form is derived to demonstrate the stability of the low-frequency transverse and compressional Alfven type instabilities in terms of the pressure anisotropy parameter τ and the magnetic field curvature-pressure gradient parameter. A procedure for determining the stability of a marginally stable MHD wave due to wave-particle resonances is also presented

  15. Kinetic modeling of Nernst effect in magnetized hohlraums.

    Science.gov (United States)

    Joglekar, A S; Ridgers, C P; Kingham, R J; Thomas, A G R

    2016-04-01

    We present nanosecond time-scale Vlasov-Fokker-Planck-Maxwell modeling of magnetized plasma transport and dynamics in a hohlraum with an applied external magnetic field, under conditions similar to recent experiments. Self-consistent modeling of the kinetic electron momentum equation allows for a complete treatment of the heat flow equation and Ohm's law, including Nernst advection of magnetic fields. In addition to showing the prevalence of nonlocal behavior, we demonstrate that effects such as anomalous heat flow are induced by inverse bremsstrahlung heating. We show magnetic field amplification up to a factor of 3 from Nernst compression into the hohlraum wall. The magnetic field is also expelled towards the hohlraum axis due to Nernst advection faster than frozen-in flux would suggest. Nonlocality contributes to the heat flow towards the hohlraum axis and results in an augmented Nernst advection mechanism that is included self-consistently through kinetic modeling.

  16. Kinetic models for historical processes of fast invasion and aggression

    Science.gov (United States)

    Aristov, Vladimir V.; Ilyin, Oleg V.

    2015-04-01

    In the last few decades many investigations have been devoted to theoretical models in new areas concerning description of different biological, sociological, and historical processes. In the present paper we suggest a model of the Nazi Germany invasion of Poland, France, and the USSR based on kinetic theory. We simulate this process with the Cauchy boundary problem for two-element kinetic equations. The solution of the problem is given in the form of a traveling wave. The propagation velocity of a front line depends on the quotient between initial forces concentrations. Moreover it is obtained that the general solution of the model can be expressed in terms of quadratures and elementary functions. Finally it is shown that the front-line velocities agree with the historical data.

  17. Reproducing Phenomenology of Peroxidation Kinetics via Model Optimization

    Science.gov (United States)

    Ruslanov, Anatole D.; Bashylau, Anton V.

    2010-06-01

    We studied mathematical modeling of lipid peroxidation using a biochemical model system of iron (II)-ascorbate-dependent lipid peroxidation of rat hepatocyte mitochondrial fractions. We found that antioxidants extracted from plants demonstrate a high intensity of peroxidation inhibition. We simplified the system of differential equations that describes the kinetics of the mathematical model to a first order equation, which can be solved analytically. Moreover, we endeavor to algorithmically and heuristically recreate the processes and construct an environment that closely resembles the corresponding natural system. Our results demonstrate that it is possible to theoretically predict both the kinetics of oxidation and the intensity of inhibition without resorting to analytical and biochemical research, which is important for cost-effective discovery and development of medical agents with antioxidant action from the medicinal plants.

  18. Chemistry resolved kinetic flow modeling of TATB based explosives

    Science.gov (United States)

    Vitello, Peter; Fried, Laurence E.; William, Howard; Levesque, George; Souers, P. Clark

    2012-03-01

    Detonation waves in insensitive, TATB-based explosives are believed to have multiple time scale regimes. The initial burn rate of such explosives has a sub-microsecond time scale. However, significant late-time slow release in energy is believed to occur due to diffusion limited growth of carbon. In the intermediate time scale concentrations of product species likely change from being in equilibrium to being kinetic rate controlled. We use the thermo-chemical code CHEETAH linked to an ALE hydrodynamics code to model detonations. We term our model chemistry resolved kinetic flow, since CHEETAH tracks the time dependent concentrations of individual species in the detonation wave and calculates EOS values based on the concentrations. We present here two variants of our new rate model and comparison with hot, ambient, and cold experimental data for PBX 9502.

  19. Activation-energy for the reaction h+oh--]eaq- - kinetic determination of the enthalpy and entropy of solvation of the hydrated electron

    DEFF Research Database (Denmark)

    Hickle, B.; Sehested, Knud

    1985-01-01

    The reaction between atomic hydrogen and hydroxide ion in aqueous solutions H + OH- - eaq- + H20 has been studied by pulse radiolysis. The rate constant was measured at pH 11.7 and 12 by following the growth of the hydrated electron absorption at 600 nm. The activation energy of the reaction has...

  20. Comparisons of hydrodynamic beam models with kinetic treatments

    International Nuclear Information System (INIS)

    Boyd, J.K.; Mark, J.W.; Sharp, W.M.; Yu, S.S.

    1983-01-01

    Hydrodynamic models have been derived by Mark and Yu and by others to describe energetic self-pinched beams, such as those used in ion-beam fusion. The closure of the Mark-Yu model is obtained with adiabatic assumptions mathematically analogous to those of Chew, Goldberger, and Low for MHD. The other models treated here use an ideal gas closure and a closure by Newcomb based on an expansion in V/sub th//V/sub z/. Features of these hydrodynamic beam models are compared with a kinetic treatment

  1. Focuss algorithm application in kinetic compartment modeling for PET tracer

    International Nuclear Information System (INIS)

    Huang Xinrui; Bao Shanglian

    2004-01-01

    Molecular imaging is in the process of becoming. Its application mostly depends on the molecular discovery process of imaging probes and drugs, from the mouse to the patient, from research to clinical practice. Positron emission tomography (PET) can non-invasively monitor . pharmacokinetic and functional processes of drugs in intact organisms at tracer concentrations by kinetic modeling. It has been known that for all biological systems, linear or nonlinear, if the system is injected by a tracer in a steady state, the distribution of the tracer follows the kinetics of a linear compartmental system, which has sums of exponential solutions. Based on the general compartmental description of the tracer's fate in vivo, we presented a novel kinetic modeling approach for the quantification of in vivo tracer studies with dynamic positron emission tomography (PET), which can determine a parsimonious model consisting with the measured data. This kinetic modeling technique allows for estimation of parametric images from a voxel based analysis and requires no a priori decision about the tracer's fate in vivo, instead determining the most appropriate model from the information contained within the kinetic data. Choosing a set of exponential functions, convolved with the plasma input function, as basis functions, the time activity curve of a region or a pixel can be written as a linear combination of the basis functions with corresponding coefficients. The number of non-zero coefficients returned corresponds to the model order which is related to the number of tissue compartments. The system macro parameters are simply determined using the focal underdetermined system solver (FOCUSS) algorithm. The FOCUSS algorithm is a nonparametric algorithm for finding localized energy solutions from limited data and is a recursive linear estimation procedure. FOCUSS algorithm usually converges very fast, so demands a few iterations. The effectiveness is verified by simulation and clinical

  2. Stepwise kinetic equilibrium models of quantitative polymerase chain reaction

    Directory of Open Access Journals (Sweden)

    Cobbs Gary

    2012-08-01

    Full Text Available Abstract Background Numerous models for use in interpreting quantitative PCR (qPCR data are present in recent literature. The most commonly used models assume the amplification in qPCR is exponential and fit an exponential model with a constant rate of increase to a select part of the curve. Kinetic theory may be used to model the annealing phase and does not assume constant efficiency of amplification. Mechanistic models describing the annealing phase with kinetic theory offer the most potential for accurate interpretation of qPCR data. Even so, they have not been thoroughly investigated and are rarely used for interpretation of qPCR data. New results for kinetic modeling of qPCR are presented. Results Two models are presented in which the efficiency of amplification is based on equilibrium solutions for the annealing phase of the qPCR process. Model 1 assumes annealing of complementary targets strands and annealing of target and primers are both reversible reactions and reach a dynamic equilibrium. Model 2 assumes all annealing reactions are nonreversible and equilibrium is static. Both models include the effect of primer concentration during the annealing phase. Analytic formulae are given for the equilibrium values of all single and double stranded molecules at the end of the annealing step. The equilibrium values are then used in a stepwise method to describe the whole qPCR process. Rate constants of kinetic models are the same for solutions that are identical except for possibly having different initial target concentrations. Analysis of qPCR curves from such solutions are thus analyzed by simultaneous non-linear curve fitting with the same rate constant values applying to all curves and each curve having a unique value for initial target concentration. The models were fit to two data sets for which the true initial target concentrations are known. Both models give better fit to observed qPCR data than other kinetic models present in the

  3. Stepwise kinetic equilibrium models of quantitative polymerase chain reaction.

    Science.gov (United States)

    Cobbs, Gary

    2012-08-16

    Numerous models for use in interpreting quantitative PCR (qPCR) data are present in recent literature. The most commonly used models assume the amplification in qPCR is exponential and fit an exponential model with a constant rate of increase to a select part of the curve. Kinetic theory may be used to model the annealing phase and does not assume constant efficiency of amplification. Mechanistic models describing the annealing phase with kinetic theory offer the most potential for accurate interpretation of qPCR data. Even so, they have not been thoroughly investigated and are rarely used for interpretation of qPCR data. New results for kinetic modeling of qPCR are presented. Two models are presented in which the efficiency of amplification is based on equilibrium solutions for the annealing phase of the qPCR process. Model 1 assumes annealing of complementary targets strands and annealing of target and primers are both reversible reactions and reach a dynamic equilibrium. Model 2 assumes all annealing reactions are nonreversible and equilibrium is static. Both models include the effect of primer concentration during the annealing phase. Analytic formulae are given for the equilibrium values of all single and double stranded molecules at the end of the annealing step. The equilibrium values are then used in a stepwise method to describe the whole qPCR process. Rate constants of kinetic models are the same for solutions that are identical except for possibly having different initial target concentrations. Analysis of qPCR curves from such solutions are thus analyzed by simultaneous non-linear curve fitting with the same rate constant values applying to all curves and each curve having a unique value for initial target concentration. The models were fit to two data sets for which the true initial target concentrations are known. Both models give better fit to observed qPCR data than other kinetic models present in the literature. They also give better estimates of

  4. Influence of fluorosurfactants on hydrate formation rates

    Energy Technology Data Exchange (ETDEWEB)

    Kim, C.U.; Jeong, K.E.; Chae, H.J.; Jeong, S.Y. [Korea Reasearch Inst. of Chemical Technology, Alternative Chemicals/Fuel Research Center, Yuseong-Gu, Daejon (Korea, Republic of)

    2008-07-01

    Gas hydrates, or clathrates, are ice-like solids that forms when natural gas is in contact with liquid water or ice under high pressure and low temperature. There is significant interest in studying the storage and transportation of gas in the form of hydrates. However, a critical problem impacting the industrial application of gas hydrates for storage and transportation of natural gas is the slow formation rate of natural gas hydrate. Researchers have previously reported on the promotion effect of some additives on gas hydrate formation and hydrate gas content. Fluorosurfactants are significantly superior to nonfluorinated surfactants in wetting action, as well as stability in harsh environments, both thermal and chemical. This paper discussed an experimental investigation into the effects of fluorosurfactants with different ionic types on the formation of methane hydrate. The surfactants used were FSN-100 of DuPont Zonyl as non-ionic surfactant and FC-143 of DuPont as anionic surfactant. The paper discussed the experimental apparatus for methane hydrate formation. It also discussed hydrate formation kinetics and the series of hydrate formation experiments that were conducted in the presence of fluorosurfactants. Last, the paper explored the results of the study. It was concluded that anionic fluorosurfactant of FC-143 had a better promoting effect on methane hydrate formation compared with nonionic surfactant of FSN-100. 8 refs., 2 tabs., 2 figs.

  5. Tracer kinetic modelling of receptor data with mathematical metabolite correction

    International Nuclear Information System (INIS)

    Burger, C.; Buck, A.

    1996-01-01

    Quantitation of metabolic processes with dynamic positron emission tomography (PET) and tracer kinetic modelling relies on the time course of authentic ligand in plasma, i.e. the input curve. The determination of the latter often requires the measurement of labelled metabilites, a laborious procedure. In this study we examined the possibility of mathematical metabolite correction, which might obviate the need for actual metabolite measurements. Mathematical metabilite correction was implemented by estimating the input curve together with kinetic tissue parameters. The general feasibility of the approach was evaluated in a Monte Carlo simulation using a two tissue compartment model. The method was then applied to a series of five human carbon-11 iomazenil PET studies. The measured cerebral tissue time-activity curves were fitted with a single tissue compartment model. For mathematical metabolite correction the input curve following the peak was approximated by a sum of three decaying exponentials, the amplitudes and characteristic half-times of which were then estimated by the fitting routine. In the simulation study the parameters used to generate synthetic tissue time-activity curves (K 1 -k 4 ) were refitted with reasonable identifiability when using mathematical metabolite correciton. Absolute quantitation of distribution volumes was found to be possible provided that the metabolite and the kinetic models are adequate. If the kinetic model is oversimplified, the linearity of the correlation between true and estimated distribution volumes is still maintained, although the linear regression becomes dependent on the input curve. These simulation results were confirmed when applying mathematical metabolite correction to the 11 C iomazenil study. Estimates of the distribution volume calculated with a measured input curve were linearly related to the estimates calculated using mathematical metabolite correction with correlation coefficients >0.990. (orig./MG)

  6. Kinetic models of gene expression including non-coding RNAs

    Energy Technology Data Exchange (ETDEWEB)

    Zhdanov, Vladimir P., E-mail: zhdanov@catalysis.r

    2011-03-15

    In cells, genes are transcribed into mRNAs, and the latter are translated into proteins. Due to the feedbacks between these processes, the kinetics of gene expression may be complex even in the simplest genetic networks. The corresponding models have already been reviewed in the literature. A new avenue in this field is related to the recognition that the conventional scenario of gene expression is fully applicable only to prokaryotes whose genomes consist of tightly packed protein-coding sequences. In eukaryotic cells, in contrast, such sequences are relatively rare, and the rest of the genome includes numerous transcript units representing non-coding RNAs (ncRNAs). During the past decade, it has become clear that such RNAs play a crucial role in gene expression and accordingly influence a multitude of cellular processes both in the normal state and during diseases. The numerous biological functions of ncRNAs are based primarily on their abilities to silence genes via pairing with a target mRNA and subsequently preventing its translation or facilitating degradation of the mRNA-ncRNA complex. Many other abilities of ncRNAs have been discovered as well. Our review is focused on the available kinetic models describing the mRNA, ncRNA and protein interplay. In particular, we systematically present the simplest models without kinetic feedbacks, models containing feedbacks and predicting bistability and oscillations in simple genetic networks, and models describing the effect of ncRNAs on complex genetic networks. Mathematically, the presentation is based primarily on temporal mean-field kinetic equations. The stochastic and spatio-temporal effects are also briefly discussed.

  7. Comparison of kinetic model for biogas production from corn cob

    Science.gov (United States)

    Shitophyta, L. M.; Maryudi

    2018-04-01

    Energy demand increases every day, while the energy source especially fossil energy depletes increasingly. One of the solutions to overcome the energy depletion is to provide renewable energies such as biogas. Biogas can be generated by corn cob and food waste. In this study, biogas production was carried out by solid-state anaerobic digestion. The steps of biogas production were the preparation of feedstock, the solid-state anaerobic digestion, and the measurement of biogas volume. This study was conducted on TS content of 20%, 22%, and 24%. The aim of this research was to compare kinetic models of biogas production from corn cob and food waste as a co-digestion using the linear, exponential equation, and first-kinetic models. The result showed that the exponential equation had a better correlation than the linear equation on the ascending graph of biogas production. On the contrary, the linear equation had a better correlation than the exponential equation on the descending graph of biogas production. The correlation values on the first-kinetic model had the smallest value compared to the linear and exponential models.

  8. Modelling reveals kinetic advantages of co-transcriptional splicing.

    Directory of Open Access Journals (Sweden)

    Stuart Aitken

    2011-10-01

    Full Text Available Messenger RNA splicing is an essential and complex process for the removal of intron sequences. Whereas the composition of the splicing machinery is mostly known, the kinetics of splicing, the catalytic activity of splicing factors and the interdependency of transcription, splicing and mRNA 3' end formation are less well understood. We propose a stochastic model of splicing kinetics that explains data obtained from high-resolution kinetic analyses of transcription, splicing and 3' end formation during induction of an intron-containing reporter gene in budding yeast. Modelling reveals co-transcriptional splicing to be the most probable and most efficient splicing pathway for the reporter transcripts, due in part to a positive feedback mechanism for co-transcriptional second step splicing. Model comparison is used to assess the alternative representations of reactions. Modelling also indicates the functional coupling of transcription and splicing, because both the rate of initiation of transcription and the probability that step one of splicing occurs co-transcriptionally are reduced, when the second step of splicing is abolished in a mutant reporter.

  9. Modelling reveals kinetic advantages of co-transcriptional splicing.

    Science.gov (United States)

    Aitken, Stuart; Alexander, Ross D; Beggs, Jean D

    2011-10-01

    Messenger RNA splicing is an essential and complex process for the removal of intron sequences. Whereas the composition of the splicing machinery is mostly known, the kinetics of splicing, the catalytic activity of splicing factors and the interdependency of transcription, splicing and mRNA 3' end formation are less well understood. We propose a stochastic model of splicing kinetics that explains data obtained from high-resolution kinetic analyses of transcription, splicing and 3' end formation during induction of an intron-containing reporter gene in budding yeast. Modelling reveals co-transcriptional splicing to be the most probable and most efficient splicing pathway for the reporter transcripts, due in part to a positive feedback mechanism for co-transcriptional second step splicing. Model comparison is used to assess the alternative representations of reactions. Modelling also indicates the functional coupling of transcription and splicing, because both the rate of initiation of transcription and the probability that step one of splicing occurs co-transcriptionally are reduced, when the second step of splicing is abolished in a mutant reporter.

  10. Progress in Chemical Kinetic Modeling for Surrogate Fuels

    Energy Technology Data Exchange (ETDEWEB)

    Pitz, W J; Westbrook, C K; Herbinet, O; Silke, E J

    2008-06-06

    Gasoline, diesel, and other alternative transportation fuels contain hundreds to thousands of compounds. It is currently not possible to represent all these compounds in detailed chemical kinetic models. Instead, these fuels are represented by surrogate fuel models which contain a limited number of representative compounds. We have been extending the list of compounds for detailed chemical models that are available for use in fuel surrogate models. Detailed models for components with larger and more complicated fuel molecular structures are now available. These advancements are allowing a more accurate representation of practical and alternative fuels. We have developed detailed chemical kinetic models for fuels with higher molecular weight fuel molecules such as n-hexadecane (C16). Also, we can consider more complicated fuel molecular structures like cyclic alkanes and aromatics that are found in practical fuels. For alternative fuels, the capability to model large biodiesel fuels that have ester structures is becoming available. These newly addressed cyclic and ester structures in fuels profoundly affect the reaction rate of the fuel predicted by the model. Finally, these surrogate fuel models contain large numbers of species and reactions and must be reduced for use in multi-dimensional models for spark-ignition, HCCI and diesel engines.

  11. Differential Scanning Calorimetric Study and Potential Model of the Binding of the Primary Water of Hydration to K-Hyaluronate

    Science.gov (United States)

    Whitson, K. B.; Marlowe, R. L.; Lukan, A. M.; Lee, S. A.; Anthony, L.; Rupprecht, A.

    1997-11-01

    DSC was performed on samples of K-hyaluronate (KHA) through a temperature range of 25-180^oC. A transition peak was observed which is due to the desorption of the primary water of hydration. The maximum position of the peak was observed to change with different scan rates. The average energy of activation, E_A, and enthalpy for desorption of the primary water of hydration was determined to be 0.62 and 0.17 eV per water molecule, respectively. Analysis of Mossbauer data(G. Albanese et al., Hyperfine Int.,) 95, 97 (1995) allowed us to determine the effective force constant, k_eff, of the water bound to KHA to be approximately 19.4 eV/nm^2. The parameters E_A, ΔH,and k_eff allow us to construct a potential model for the primary water of hydration of KHA. Comparison of these parameters with the same parameters for HA and DNA with different counterions reveal that the energy of activation is similar, as well as the enthalpy change.

  12. Models of talik, permafrost and gas hydrate histories - Beaufort Mackenzie Basin, Canada

    Czech Academy of Sciences Publication Activity Database

    Majorowicz, J.; Osadetz, K.; Šafanda, Jan

    2015-01-01

    Roč. 8, č. 7 (2015), s. 6738-6764 ISSN 1996-1073 Institutional support: RVO:67985530 Keywords : gas hydrates * permafrost * Beaufort-Mackenzie Basin * taliks Subject RIV: DC - Siesmology, Volcanology, Earth Structure Impact factor: 2.077, year: 2015

  13. Numerical modeling of hydration process and temperature evolution in early age concrete

    NARCIS (Netherlands)

    Caggiano, A.; Pepe, M.; Koenders, E.A.B.; Martinelli, E.; Etse, G.J.

    2012-01-01

    Heat production induced by the hydration reaction and the resulting temperature evolution in the early phases of setting and hardening processes are critical phenomena, often leading to premature cracking of concrete members. However, the interest for simulating such phenomena is also related to the

  14. Impact of CO{sub 2} hydrates on ocean carbon dioxide deposition options

    Energy Technology Data Exchange (ETDEWEB)

    Lund, P C

    1995-04-01

    The objective of the research project described in this report was to contribute to the research on greenhouse gases and the global environment. The focus is on the concept of storing large amounts of CO{sub 2} in the ocean. The project was divided into three subtasks: (1) a comprehensive study of the thermodynamic, physical and chemical properties of the seawater/CO{sub 2}/hydrate system, (2) establishment of a micro-scale kinetic model for CO{sub 2} hydrate formation and stability, based on (1), and (3) establishment of macro-scale models for various ocean deposition options based on (2). A database of selected thermodynamic functions has been set up. A large database of oceanic data has also been made; for any given coordinates at sea a computer program provides the temperature, salinity and oxygen profiles from the sea surface to the sea floor. The kinetic model predicts the formation and pseudo-stability of a very thin hydrate film which acts as an inhibitor for diffusion of CO{sub 2} into the sea water. The model predicts that the hydrate film reduces the overall flux from a liquid CO{sub 2} source with about 90%. Thermodynamically, pure CO{sub 2} in contact with water might form hydrates at depths below about 400 m, which would indicate that hydrate formation could play a role for all ocean CO{sub 2} deposition options. However, this study shows that other mechanisms significantly reduce the role of hydrate formation. It is finally concluded that although more modelling and experimental work is required within this field of research, the hydrate film may play an important role for all options except from shallow water injection. 86 refs., 32 figs., 16 tabs.

  15. Mechanisms and kinetics models for ultrasonic waste activated sludge disintegration.

    Science.gov (United States)

    Wang, Fen; Wang, Yong; Ji, Min

    2005-08-31

    Ultrasonic energy can be applied as pre-treatment to disintegrate sludge flocs and disrupt bacterial cells' walls, and the hydrolysis can be improved, so that the rate of sludge digestion and methane production is improved. In this paper, by adding NaHCO3 to mask the oxidizing effect of OH, the mechanisms of disintegration are investigated. In addition, kinetics models for ultrasonic sludge disintegration are established by applying multi-variable linear regression method. It has been found that hydro-mechanical shear forces predominantly responsible for the disintegration, and the contribution of oxidizing effect of OH increases with the amount of the ultrasonic density and ultrasonic intensity. It has also been inferred from the kinetics model which dependent variable is SCOD+ that both sludge pH and sludge concentration significantly affect the disintegration.

  16. A kinetic model for the first stage of pygas upgrading

    Directory of Open Access Journals (Sweden)

    J. L. de Medeiros

    2007-03-01

    Full Text Available Pyrolysis gasoline - PYGAS - is an intermediate boiling product of naphtha steam cracking with a high octane number and high aromatic/unsaturated contents. Due to stabilization concerns, PYGAS must be hydrotreated in two stages. The first stage uses a mild trickle-bed conversion for removing extremely reactive species (styrene, dienes and olefins prior to the more severe second stage where sulfured and remaining olefins are hydrogenated in gas phase. This work addresses the reaction network and two-phase kinetic model for the first stage of PYGAS upgrading. Nonlinear estimation was used for model tuning with kinetic data obtained in bench-scale trickle-bed hydrogenation with a commercial Pd/Al2O3 catalyst. On-line sampling experiments were designed to study the influence of variables - temperature and spatial velocity - on the conversion of styrene, dienes and olefins.

  17. Polar Coordinate Lattice Boltzmann Kinetic Modeling of Detonation Phenomena

    International Nuclear Information System (INIS)

    Lin Chuan-Dong; Li Ying-Jun; Xu Ai-Guo; Zhang Guang-Cai

    2014-01-01

    A novel polar coordinate lattice Boltzmann kinetic model for detonation phenomena is presented and applied to investigate typical implosion and explosion processes. In this model, the change of discrete distribution function due to local chemical reaction is dynamically coupled into the modified lattice Boltzmann equation which could recover the Navier—Stokes equations, including contribution of chemical reaction, via the Chapman—Enskog expansion. For the numerical investigations, the main focuses are the nonequilibrium behaviors in these processes. The system at the disc center is always in its thermodynamic equilibrium in the highly symmetric case. The internal kinetic energies in different degrees of freedom around the detonation front do not coincide. The dependence of the reaction rate on the pressure, influences of the shock strength and reaction rate on the departure amplitude of the system from its local thermodynamic equilibrium are probed. (electromagnetism, optics, acoustics, heat transfer, classical mechanics, and fluid dynamics)

  18. Kinetics approach to modeling of polymer additive degradation in lubricants

    Institute of Scientific and Technical Information of China (English)

    llyaI.KUDISH; RubenG.AIRAPETYAN; Michael; J.; COVITCH

    2001-01-01

    A kinetics problem for a degrading polymer additive dissolved in a base stock is studied.The polymer degradation may be caused by the combination of such lubricant flow parameters aspressure, elongational strain rate, and temperature as well as lubricant viscosity and the polymercharacteristics (dissociation energy, bead radius, bond length, etc.). A fundamental approach tothe problem of modeling mechanically induced polymer degradation is proposed. The polymerdegradation is modeled on the basis of a kinetic equation for the density of the statistical distribu-tion of polymer molecules as a function of their molecular weight. The integrodifferential kineticequation for polymer degradation is solved numerically. The effects of pressure, elongational strainrate, temperature, and lubricant viscosity on the process of lubricant degradation are considered.The increase of pressure promotes fast degradation while the increase of temperature delaysdegradation. A comparison of a numerically calculated molecular weight distribution with an ex-perimental one obtained in bench tests showed that they are in excellent agreement with eachother.

  19. Kinetic modelling of radiochemical ageing of ethylene-propylene copolymers

    International Nuclear Information System (INIS)

    Colin, Xavier; Richaud, Emmanuel; Verdu, Jacques; Monchy-Leroy, Carole

    2010-01-01

    A non-empirical kinetic model has been built for describing the general trends of radiooxidation kinetics of ethylene-propylene copolymers (EPR) at low γ dose rate and low temperature. It is derived from a radical chain oxidation mechanism composed of 30 elementary reactions: 19 relative to oxidation of methylene and methyne units plus 11 relative to their eventual cooxidation. The validity of this model has been already checked successfully elsewhere for one homopolymer: polyethylene (PE) (; ). In the present study, it is now checked for polypropylene (PP) and a series of three EPR differing essentially by their mole fraction of ethylene (37%, 73% and 86%) and their crystallinity degree (0%, 5% and 26%). Predicted values of radiation-chemical yields are in good agreement with experimental ones published in the last half past century.

  20. Kinetic modeling and exploratory numerical simulation of chloroplastic starch degradation

    Directory of Open Access Journals (Sweden)

    Nag Ambarish

    2011-06-01

    Full Text Available Abstract Background Higher plants and algae are able to fix atmospheric carbon dioxide through photosynthesis and store this fixed carbon in large quantities as starch, which can be hydrolyzed into sugars serving as feedstock for fermentation to biofuels and precursors. Rational engineering of carbon flow in plant cells requires a greater understanding of how starch breakdown fluxes respond to variations in enzyme concentrations, kinetic parameters, and metabolite concentrations. We have therefore developed and simulated a detailed kinetic ordinary differential equation model of the degradation pathways for starch synthesized in plants and green algae, which to our knowledge is the most complete such model reported to date. Results Simulation with 9 internal metabolites and 8 external metabolites, the concentrations of the latter fixed at reasonable biochemical values, leads to a single reference solution showing β-amylase activity to be the rate-limiting step in carbon flow from starch degradation. Additionally, the response coefficients for stromal glucose to the glucose transporter kcat and KM are substantial, whereas those for cytosolic glucose are not, consistent with a kinetic bottleneck due to transport. Response coefficient norms show stromal maltopentaose and cytosolic glucosylated arabinogalactan to be the most and least globally sensitive metabolites, respectively, and β-amylase kcat and KM for starch to be the kinetic parameters with the largest aggregate effect on metabolite concentrations as a whole. The latter kinetic parameters, together with those for glucose transport, have the greatest effect on stromal glucose, which is a precursor for biofuel synthetic pathways. Exploration of the steady-state solution space with respect to concentrations of 6 external metabolites and 8 dynamic metabolite concentrations show that stromal metabolism is strongly coupled to starch levels, and that transport between compartments serves to

  1. Uptake of selenate on hydrated and degraded cement: batch and dynamic experiments

    International Nuclear Information System (INIS)

    Rojo, I.; Rovira, I.; Marti, V.; Pablo, J. de; Duro, L.; Gaona, X.; Colas, E.; Grive, M.

    2009-01-01

    The evaluation of selenate sorption and retardation in batch and dynamic experiments on hydrated and degraded cement has been studied. Desorption studies have also been carried in order to assess the reversibility of the sorption process. Sorption data onto degraded cement have been treated assuming the formation of surface complexes, whereas sorption kinetics has been fitted by using a pseudo-first order kinetic equation. Dynamic flow experiments have also been modelled. (authors)

  2. A model for recovery kinetics of aluminum after large strain

    DEFF Research Database (Denmark)

    Yu, Tianbo; Hansen, Niels

    2012-01-01

    A model is suggested to analyze recovery kinetics of heavily deformed aluminum. The model is based on the hardness of isothermal annealed samples before recrystallization takes place, and it can be extrapolated to longer annealing times to factor out the recrystallization component of the hardness...... for conditions where recovery and recrystallization overlap. The model is applied to the isothermal recovery at temperatures between 140 and 220°C of commercial purity aluminum deformed to true strain 5.5. EBSD measurements have been carried out to detect the onset of discontinuous recrystallization. Furthermore...

  3. A Thermal Evolution Model of the Earth Including the Biosphere, Continental Growth and Mantle Hydration

    Science.gov (United States)

    Höning, D.; Spohn, T.

    2014-12-01

    By harvesting solar energy and converting it to chemical energy, photosynthetic life plays an important role in the energy budget of Earth [2]. This leads to alterations of chemical reservoirs eventually affecting the Earth's interior [4]. It further has been speculated [3] that the formation of continents may be a consequence of the evolution life. A steady state model [1] suggests that the Earth without its biosphere would evolve to a steady state with a smaller continent coverage and a dryer mantle than is observed today. We present a model including (i) parameterized thermal evolution, (ii) continental growth and destruction, and (iii) mantle water regassing and outgassing. The biosphere enhances the production rate of sediments which eventually are subducted. These sediments are assumed to (i) carry water to depth bound in stable mineral phases and (ii) have the potential to suppress shallow dewatering of the underlying sediments and crust due to their low permeability. We run a Monte Carlo simulation for various initial conditions and treat all those parameter combinations as success which result in the fraction of continental crust coverage observed for present day Earth. Finally, we simulate the evolution of an abiotic Earth using the same set of parameters but a reduced rate of continental weathering and erosion. Our results suggest that the origin and evolution of life could have stabilized the large continental surface area of the Earth and its wet mantle, leading to the relatively low mantle viscosity we observe at present. Without photosynthetic life on our planet, the Earth would be geodynamical less active due to a dryer mantle, and would have a smaller fraction of continental coverage than observed today. References[1] Höning, D., Hansen-Goos, H., Airo, A., Spohn, T., 2014. Biotic vs. abiotic Earth: A model for mantle hydration and continental coverage. Planetary and Space Science 98, 5-13. [2] Kleidon, A., 2010. Life, hierarchy, and the

  4. An experimental and kinetic modeling study of glycerol pyrolysis

    International Nuclear Information System (INIS)

    Fantozzi, F.; Frassoldati, A.; Bartocci, P.; Cinti, G.; Quagliarini, F.; Bidini, G.; Ranzi, E.M.

    2016-01-01

    Highlights: • Glycerol pyrolysis can produce about 44–48%v hydrogen at 750–800 °C. • A simplified 452 reactions kinetic model of glycerol pyrolysis has been developed. • The model has good agreement with experimental data. • Non condensable gas yields can reach 70%. - Abstract: Pyrolysis of glycerol, a by-product of the biodiesel industry, is an important potential source of hydrogen. The obtained high calorific value gas can be used either as a fuel for combined heat and power (CHP) generation or as a transportation fuel (for example hydrogen to be used in fuel cells). Optimal process conditions can improve glycerol pyrolysis by increasing gas yield and hydrogen concentration. A detailed kinetic mechanism of glycerol pyrolysis, which involves 137 species and more than 4500 reactions, was drastically simplified and reduced to a new skeletal kinetic scheme of 44 species, involved in 452 reactions. An experimental campaign with a batch pyrolysis reactor was properly designed to further validate the original and the skeletal mechanisms. The comparisons between model predictions and experimental data strongly suggest the presence of a catalytic process promoting steam reforming of methane. High pyrolysis temperatures (750–800 °C) improve process performances and non-condensable gas yields of 70%w can be achieved. Hydrogen mole fraction in pyrolysis gas is about 44–48%v. The skeletal mechanism developed can be easily used in Computational Fluid Dynamic software, reducing the simulation time.

  5. Modelling of individual subject ozone exposure response kinetics.

    Science.gov (United States)

    Schelegle, Edward S; Adams, William C; Walby, William F; Marion, M Susan

    2012-06-01

    A better understanding of individual subject ozone (O(3)) exposure response kinetics will provide insight into how to improve models used in the risk assessment of ambient ozone exposure. To develop a simple two compartment exposure-response model that describes individual subject decrements in forced expiratory volume in one second (FEV(1)) induced by the acute inhalation of O(3) lasting up to 8 h. FEV(1) measurements of 220 subjects who participated in 14 previously completed studies were fit to the model using both particle swarm and nonlinear least squares optimization techniques to identify three subject-specific coefficients producing minimum "global" and local errors, respectively. Observed and predicted decrements in FEV(1) of the 220 subjects were used for validation of the model. Further validation was provided by comparing the observed O(3)-induced FEV(1) decrements in an additional eight studies with predicted values obtained using model coefficients estimated from the 220 subjects used in cross validation. Overall the individual subject measured and modeled FEV(1) decrements were highly correlated (mean R(2) of 0.69 ± 0.24). In addition, it was shown that a matrix of individual subject model coefficients can be used to predict the mean and variance of group decrements in FEV(1). This modeling approach provides insight into individual subject O(3) exposure response kinetics and provides a potential starting point for improving the risk assessment of environmental O(3) exposure.

  6. Emergence of a Stern Layer from the Incorporation of Hydration Interactions into the Gouy-Chapman Model of the Electrical Double Layer.

    Science.gov (United States)

    Brown, Matthew A; Bossa, Guilherme Volpe; May, Sylvio

    2015-10-27

    In one of the most commonly used phenomenological descriptions of the electrical double layer, a charged solid surface and a diffuse region of mobile ions are separated from each other by a thin charge-depleted Stern layer. The Stern layer acts as a capacitor that improves the classical Gouy-Chapman model by increasing the magnitude of the surface potential and limiting the maximal counterion concentration. We show that very similar Stern-like properties of the diffuse double layer emerge naturally from adding a nonelectrostatic hydration repulsion to the electrostatic Coulomb potential. The interplay of electrostatic attraction and hydration repulsion of the counterions and the surface leads to the formation of a diffuse counterion layer that remains well separated from the surface. In addition, hydration repulsions between the ions limit and control the maximal ion concentration and widen the width of the diffuse double layer. Our mean-field model, which we express in terms of electrostatic and hydration potentials, is physically consistent and conceptually similar to the classical Gouy-Chapman model. It allows the incorporation of ion specificity, accounts for hydration properties of charged surfaces, and predicts Stern layer properties, which we analyze in terms of the effective size of the hydrated counterions.

  7. A Markov State-based Quantitative Kinetic Model of Sodium Release from the Dopamine Transporter

    Science.gov (United States)

    Razavi, Asghar M.; Khelashvili, George; Weinstein, Harel

    2017-01-01

    The dopamine transporter (DAT) belongs to the neurotransmitter:sodium symporter (NSS) family of membrane proteins that are responsible for reuptake of neurotransmitters from the synaptic cleft to terminate a neuronal signal and enable subsequent neurotransmitter release from the presynaptic neuron. The release of one sodium ion from the crystallographically determined sodium binding site Na2 had been identified as an initial step in the transport cycle which prepares the transporter for substrate translocation by stabilizing an inward-open conformation. We have constructed Markov State Models (MSMs) from extensive molecular dynamics simulations of human DAT (hDAT) to explore the mechanism of this sodium release. Our results quantify the release process triggered by hydration of the Na2 site that occurs concomitantly with a conformational transition from an outward-facing to an inward-facing state of the transporter. The kinetics of the release process are computed from the MSM, and transition path theory is used to identify the most probable sodium release pathways. An intermediate state is discovered on the sodium release pathway, and the results reveal the importance of various modes of interaction of the N-terminus of hDAT in controlling the pathways of release.

  8. Towards a universal method for calculating hydration free energies: a 3D reference interaction site model with partial molar volume correction.

    Science.gov (United States)

    Palmer, David S; Frolov, Andrey I; Ratkova, Ekaterina L; Fedorov, Maxim V

    2010-12-15

    We report a simple universal method to systematically improve the accuracy of hydration free energies calculated using an integral equation theory of molecular liquids, the 3D reference interaction site model. A strong linear correlation is observed between the difference of the experimental and (uncorrected) calculated hydration free energies and the calculated partial molar volume for a data set of 185 neutral organic molecules from different chemical classes. By using the partial molar volume as a linear empirical correction to the calculated hydration free energy, we obtain predictions of hydration free energies in excellent agreement with experiment (R = 0.94, σ = 0.99 kcal mol (- 1) for a test set of 120 organic molecules).

  9. Towards a universal method for calculating hydration free energies: a 3D reference interaction site model with partial molar volume correction

    International Nuclear Information System (INIS)

    Palmer, David S; Frolov, Andrey I; Ratkova, Ekaterina L; Fedorov, Maxim V

    2010-01-01

    We report a simple universal method to systematically improve the accuracy of hydration free energies calculated using an integral equation theory of molecular liquids, the 3D reference interaction site model. A strong linear correlation is observed between the difference of the experimental and (uncorrected) calculated hydration free energies and the calculated partial molar volume for a data set of 185 neutral organic molecules from different chemical classes. By using the partial molar volume as a linear empirical correction to the calculated hydration free energy, we obtain predictions of hydration free energies in excellent agreement with experiment (R = 0.94, σ = 0.99 kcal mol -1 for a test set of 120 organic molecules). (fast track communication)

  10. Integrated stoichiometric, thermodynamic and kinetic modelling of steady state metabolism.

    Science.gov (United States)

    Fleming, R M T; Thiele, I; Provan, G; Nasheuer, H P

    2010-06-07

    The quantitative analysis of biochemical reactions and metabolites is at frontier of biological sciences. The recent availability of high-throughput technology data sets in biology has paved the way for new modelling approaches at various levels of complexity including the metabolome of a cell or an organism. Understanding the metabolism of a single cell and multi-cell organism will provide the knowledge for the rational design of growth conditions to produce commercially valuable reagents in biotechnology. Here, we demonstrate how equations representing steady state mass conservation, energy conservation, the second law of thermodynamics, and reversible enzyme kinetics can be formulated as a single system of linear equalities and inequalities, in addition to linear equalities on exponential variables. Even though the feasible set is non-convex, the reformulation is exact and amenable to large-scale numerical analysis, a prerequisite for computationally feasible genome scale modelling. Integrating flux, concentration and kinetic variables in a unified constraint-based formulation is aimed at increasing the quantitative predictive capacity of flux balance analysis. Incorporation of experimental and theoretical bounds on thermodynamic and kinetic variables ensures that the predicted steady state fluxes are both thermodynamically and biochemically feasible. The resulting in silico predictions are tested against fluxomic data for central metabolism in Escherichia coli and compare favourably with in silico prediction by flux balance analysis. Copyright (c) 2010 Elsevier Ltd. All rights reserved.

  11. Kinetic modeling of ethylbenzene dehydrogenation over hydrotalcite catalysts

    KAUST Repository

    Atanda, Luqman

    2011-07-01

    Kinetics of ethylbenzene dehydrogenation to styrene was investigated over a series of quaternary mixed oxides of Mg3Fe0.25Me0.25Al0.5 (Me=Co, Mn and Ni) catalysts prepared by calcination of hydrotalcite-like compounds and compared with commercial catalyst. The study was carried out in the absence of steam using a riser simulator at 400, 450, 500 and 550°C for reaction times of 5, 10, 15 and 20s. Mg3Fe0.25Mn0.25Al0.5 afforded the highest ethylbenzene conversion of 19.7% at 550°C. Kinetic parameters for the dehydrogenation process were determined using the catalyst deactivation function based on reactant conversion model. The apparent activation energies for styrene production were found to decrease as follows: E1-Ni>E1-Co>E1-Mn. © 2011 Elsevier B.V.

  12. Kinetic modelling and mechanism of dye adsorption on unburned carbon

    Energy Technology Data Exchange (ETDEWEB)

    Wang, S.B.; Li, H.T. [Curtin University of Technology, Perth, WA (Australia). Dept. of Chemical Engineering

    2007-07-01

    Textile dyeing processes are among the most environmentally unfriendly industrial processes by producing coloured wastewaters. The adsorption method using unburned carbon from coal combustion residue was studied for the decolourisation of typical acidic and basic dyes. It was discovered that the unburned carbon showed high adsorption capacity at 1.97 x 10{sup -4} and 5.27 x 10{sup -4} mol/g for Basic Violet 3 and Acid Black 1, respectively. The solution pH, particle size and temperature significantly influenced the adsorption capacity. Higher solution pH favoured the adsorption of basic dye while reduced the adsorption of acid dye. The adsorption of dye increased with increasing temperature but decreased with increasing particle size. Sorption kinetic data indicated that the adsorption kinetics followed the pseudo-second-order model. The adsorption mechanism consisted of two processes, external diffusion and intraparticle diffusion, and the external diffusion was the dominating process.

  13. A neural model of border-ownership from kinetic occlusion.

    Science.gov (United States)

    Layton, Oliver W; Yazdanbakhsh, Arash

    2015-01-01

    Camouflaged animals that have very similar textures to their surroundings are difficult to detect when stationary. However, when an animal moves, humans readily see a figure at a different depth than the background. How do humans perceive a figure breaking camouflage, even though the texture of the figure and its background may be statistically identical in luminance? We present a model that demonstrates how the primate visual system performs figure-ground segregation in extreme cases of breaking camouflage based on motion alone. Border-ownership signals develop as an emergent property in model V2 units whose receptive fields are nearby kinetically defined borders that separate the figure and background. Model simulations support border-ownership as a general mechanism by which the visual system performs figure-ground segregation, despite whether figure-ground boundaries are defined by luminance or motion contrast. The gradient of motion- and luminance-related border-ownership signals explains the perceived depth ordering of the foreground and background surfaces. Our model predicts that V2 neurons, which are sensitive to kinetic edges, are selective to border-ownership (magnocellular B cells). A distinct population of model V2 neurons is selective to border-ownership in figures defined by luminance contrast (parvocellular B cells). B cells in model V2 receive feedback from neurons in V4 and MT with larger receptive fields to bias border-ownership signals toward the figure. We predict that neurons in V4 and MT sensitive to kinetically defined figures play a crucial role in determining whether the foreground surface accretes, deletes, or produces a shearing motion with respect to the background. Copyright © 2014 Elsevier Ltd. All rights reserved.

  14. The modelling of direct chemical kinetic effects in turbulent flames

    Energy Technology Data Exchange (ETDEWEB)

    Lindstet, R.P. [Imperial College of Science, Technology and Medicine, London (United Kingdom). Dept. of Mechanical Engineering

    2000-06-01

    Combustion chemistry-related effects have traditionally been of secondary importance in the design of gas turbine combustors. However, the need to deal with issues such as flame stability, relight and pollutant emissions has served to bring chemical kinetics and the coupling of finite rate chemistry with turbulent flow fields to the centre of combustor design. Indeed, improved cycle efficiency and more stringent environmental legislation, as defined by the ICAO, are current key motivators in combustor design. Furthermore, lean premixed prevaporized (LPP) combustion systems, increasingly used for power generation, often operate close to the lean blow-off limit and are prone to extinction/reignition type phenomena. Thus, current key design issues require that direct chemical kinetic effects be accounted for accurately in any simulation procedure. The transported probability density function (PDF) approach uniquely offers the potential of facilitating the accurate modelling of such effects. The present paper thus assesses the ability of this technique to model kinetically controlled phenomena, such as carbon monoxide emissions and flame blow-off, through the application of a transported PDF method closed at the joint scalar level. The closure for the velocity field is at the second moment level, and a key feature of the present work is the use of comprehensive chemical kinetic mechanisms. The latter are derived from recent work by Lindstedt and co-workers that has resulted in a compact 141 reactions and 28 species mechanism for LNG combustion. The systematically reduced form used here features 14 independent C/H/O scalars, with the remaining species incorporated via steady state approximations. Computations have been performed for hydrogen/carbon dioxide and methane flames. The former (high Reynolds number) flames permit an assessment of the modelling of flame blow-off, and the methane flame has been selected to obtain an indication of the influence of differential

  15. An enhanced Brinson model with modified kinetics for martensite transformation

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Young-Jin; Lee, Jung Ju [Korea Advanced Institute of Science and Technology, Daejeon (Korea, Republic of); Jeong, Ju-Won [Korea Aerospace Research Institute, Daejeon (Korea, Republic of); Lim, Jae Hyuk [Chonbuk National University, Jeonju (Korea, Republic of)

    2017-03-15

    We propose an enhanced Brinson model with modified kinetics for martensite transformation. Two additional material constants are considered to follow the stress-temperature diagram above austenite start temperature (As) along with treatment to keep the continuity of the martensite volume fraction and the path dependency of the phase transformation. To demonstrate the performance of the proposed model, we implement this algorithm into ABAQUS user subroutine, then conduct several numerical simulations and compare their results with SMA wire experiments as well as those of three-dimensional SMA constitutive models. From the results, it turns out that the proposed model is as accurate as the three-dimensional models and shows better accuracy over original Brinson model in terms of recovery stress.

  16. A physiologically based kinetic model for bacterial sulfide oxidation.

    Science.gov (United States)

    Klok, Johannes B M; de Graaff, Marco; van den Bosch, Pim L F; Boelee, Nadine C; Keesman, Karel J; Janssen, Albert J H

    2013-02-01

    In the biotechnological process for hydrogen sulfide removal from gas streams, a variety of oxidation products can be formed. Under natron-alkaline conditions, sulfide is oxidized by haloalkaliphilic sulfide oxidizing bacteria via flavocytochrome c oxidoreductase. From previous studies, it was concluded that the oxidation-reduction state of cytochrome c is a direct measure for the bacterial end-product formation. Given this physiological feature, incorporation of the oxidation state of cytochrome c in a mathematical model for the bacterial oxidation kinetics will yield a physiologically based model structure. This paper presents a physiologically based model, describing the dynamic formation of the various end-products in the biodesulfurization process. It consists of three elements: 1) Michaelis-Menten kinetics combined with 2) a cytochrome c driven mechanism describing 3) the rate determining enzymes of the respiratory system of haloalkaliphilic sulfide oxidizing bacteria. The proposed model is successfully validated against independent data obtained from biological respiration tests and bench scale gas-lift reactor experiments. The results demonstrate that the model is a powerful tool to describe product formation for haloalkaliphilic biomass under dynamic conditions. The model predicts a maximum S⁰ formation of about 98 mol%. A future challenge is the optimization of this bioprocess by improving the dissolved oxygen control strategy and reactor design. Copyright © 2012 Elsevier Ltd. All rights reserved.

  17. Small velocity and finite temperature variations in kinetic relaxation models

    KAUST Repository

    Markowich, Peter; Jü ngel, Ansgar; Aoki, Kazuo

    2010-01-01

    A small Knuden number analysis of a kinetic equation in the diffusive scaling is performed. The collision kernel is of BGK type with a general local Gibbs state. Assuming that the flow velocity is of the order of the Knudsen number, a Hilbert expansion yields a macroscopic model with finite temperature variations, whose complexity lies in between the hydrodynamic and the energy-transport equations. Its mathematical structure is explored and macroscopic models for specific examples of the global Gibbs state are presented. © American Institute of Mathematical Sciences.

  18. Feasibility study on a microwave-based sensor for measuring hydration level using human skin models

    OpenAIRE

    Brendtke, R.; Wiehl, M.; Groeber, F.; Schwarz, T.; Walles, H.; Hansmann, J.

    2016-01-01

    Tissue dehydration results in three major types of exsiccosis--hyper-, hypo-, or isonatraemia. All three types entail alterations of salt concentrations leading to impaired biochemical processes, and can finally cause severe morbidity. The aim of our study was to demonstrate the feasibility of a microwave-based sensor technology for the non-invasive measurement of the hydration status. Electromagnetic waves at high frequencies interact with molecules, especially water. Hence, if a sample cont...

  19. Molecular structure, dynamics and hydration studies of soybean storage proteins and model systems by nuclear magnetic resonance

    International Nuclear Information System (INIS)

    Kakalis, L.T.

    1989-01-01

    The potential of high-resolution 13 C NMR for the characterization of soybean storage proteins was explored. The spectra of a commercial soy protein isolate as well as those of alkali-denatured 7S and 11S soybean globulins were well resolved and tentatively assigned. Relaxation measurements indicated fast motion for several side chains and the protein backbone. Protein fractions (11S and 7S) were also investigated at various states of molecular association. The large size of the multisubunit soybean storage proteins affected adversely both the resolution and the sensitivity of their 13 C NMR spectra. A comparison of 17 O and 2 H NMR relaxation rates of water in solutions of lysozyme (a model system) as a function of concentration, pH and magnetic field suggested that only 17 O monitors directly the hydration of lysozyme. Analysis of 17 O NMR lysozyme hydration data in terms of a two-state, fast-exchange, anisotropic model resulted in hydration parameters which are consistent with the protein's physico-chemical properties. The same model was applied to the calculation of the amount and mobility of bound water in soy protein dispersions by means of 17 O NMR relaxation measurements as a function of protein concentration. The protein concentration dependences of 1 H transverse NMR relaxation measurements at various pH and ionic strength values were fitted by a viral expansion. The interpretation of the data was based on the effects of protein aggregation, salt binding and protein group ionization on the NMR measurements. In all cases, relaxation rates showed a linear dependence on protein activity

  20. Norepinephrine metabolism in humans. Kinetic analysis and model

    International Nuclear Information System (INIS)

    Linares, O.A.; Jacquez, J.A.; Zech, L.A.; Smith, M.J.; Sanfield, J.A.; Morrow, L.A.; Rosen, S.G.; Halter, J.B.

    1987-01-01

    The present study was undertaken to quantify more precisely and to begin to address the problem of heterogeneity of the kinetics of distribution and metabolism of norepinephrine (NE) in humans, by using compartmental analysis. Steady-state NE specific activity in arterialized plasma during [ 3 H]NE infusion and postinfusion plasma disappearance of [ 3 H]NE were measured in eight healthy subjects in the supine and upright positions. Two exponentials were clearly identified in the plasma [ 3 H]NE disappearance curves of each subject studied in the supine (r = 0.94-1.00, all P less than 0.01) and upright (r = 0.90-0.98, all P less than 0.01) positions. A two-compartment model was the minimal model necessary to simultaneously describe the kinetics of NE in the supine and upright positions. The NE input rate into the extravascular compartment 2, estimated with the minimal model, increased with upright posture (1.87 +/- 0.08 vs. 3.25 +/- 0.2 micrograms/min per m2, P less than 0.001). Upright posture was associated with a fall in the volume of distribution of NE in compartment 1 (7.5 +/- 0.6 vs. 4.7 +/- 0.3 liters, P less than 0.001), and as a result of that, there was a fall in the metabolic clearance rate of NE from compartment 1 (1.80 +/- 0.11 vs. 1.21 +/- 0.08 liters/min per m2, P less than 0.001). We conclude that a two-compartment model is the minimal model that can accurately describe the kinetics of distribution and metabolism of NE in humans

  1. Hydration water and microstructure in calcium silicate and aluminate hydrates

    International Nuclear Information System (INIS)

    Fratini, Emiliano; Ridi, Francesca; Chen, Sow-Hsin; Baglioni, Piero

    2006-01-01

    Understanding the state of the hydration water and the microstructure development in a cement paste is likely to be the key for the improvement of its ultimate strength and durability. In order to distinguish and characterize the reacted and unreacted water, the single-particle dynamics of water molecules in hydrated calcium silicates (C 3 S, C 2 S) and aluminates (C 3 A, C 4 AF) were studied by quasi-elastic neutron scattering, QENS. The time evolution of the immobile fraction represents the hydration kinetics and the mobile fraction follows a non-Debye relaxation. Less sophisticated, but more accessible and cheaper techniques, like differential scanning calorimetry, DSC, and near-infrared spectroscopy, NIR, were validated through QENS results and they allow one to easily and quantitatively follow the cement hydration kinetics and can be widely applied on a laboratory scale to understand the effect of additives (i.e., superplasticizers, cellulosic derivatives, etc) on the thermodynamics of the hydration process. DSC provides information on the free water index and on the activation energy involved in the hydration process while the NIR band at 7000 cm -1 monitors, at a molecular level, the increase of the surface-interacting water. We report as an example the effect of two classes of additives widely used in the cement industry: superplasticizers, SPs, and cellulose derivatives. SPs interact at the solid surface, leading to a consistent increment of the activation energy for the processes of nucleation and growth of the hydrated phases. In contrast, the cellulosic additives do not affect the nucleation and growth activation energy, but cause a significant increment in the water availability: in other words the hydration process is more efficient without any modification of the solid/liquid interaction, as also evidenced by the 1 H-NMR. Additional information is obtained by scanning electron microscopy (SEM), ultra small angle neutron scattering (USANS) and wide

  2. Effect of gas hydrates melting on seafloor slope stability

    Science.gov (United States)

    Sultan, N.; Cochonat, P.; Foucher, J. P.; Mienert, J.; Haflidason, H.; Sejrup, H. P.

    2003-04-01

    Quantitative studies of kinetics of gas hydrate formation and dissociation is of a particular concern to the petroleum industry for an evaluation of environmental hazards in deep offshore areas. Gas hydrate dissociation can generate excess pore pressure that considerably decreases the strength of the soil. In this paper, we present a theoretical study of the thermodynamic chemical equilibrium of gas hydrate in soil, which is based on models previously reported by Handa (1989), Sloan (1998) and Henry (1999). Our study takes into account the influence of temperature, pressure, pore water chemistry, and the pore size distribution of the sediment. This model fully accounts for the latent heat effects, as done by Chaouch and Briaud (1997) and Delisle et al. (1998). It uses a new formulation based on the enthalpy form of the law of conservation of energy. The model allows for the evaluation of the excess pore pressure generated during gas hydrate dissociation using the Soave’s (1972) equation of state. Fluid flow in response to the excess pore pressure is simulated using the finite element method. In the second part of the paper, we present and discuss an application of the model through a back-analysis of the case of the giant Storegga slide on the Norwegian margin. Two of the most important changes during and since the last deglaciation (hydrostatic pressure due to the change of the sea level and the increase of the sea water temperature) were considered in the calculation. Simulation results are presented and discussed. Chaouch, A., &Briaud, J.-L., 1997. Post melting behavior of gas hydrates in soft ocean sediments, OTC-8298, in 29th offshore technology conference proceedings, v. 1, Geology, earth sciences and environmental factors: Society of Petroleum Engineers, p. 217-224. Delisle, G.; Beiersdorf, H.; Neben, S.; Steinmann, D., 1998. The geothermal field of the North Sulawesi accretionary wedge and a model on BSR migration in unstable depositional environments. in

  3. Dehydration behaviour of hydrates

    Energy Technology Data Exchange (ETDEWEB)

    Dette, S.S.; Stelzer, T.; Jones, M.J.; Ulrich, J. [Martin-Luther-Universitaet Halle-Wittenberg, Zentrum fuer Ingenieurwissenschaften, Verfahrenstechnik/TVT, 06099 Halle (Germany)

    2010-07-15

    Immersing a crystalline solvate in a suitable anti-solvent can induce phase transformation to solvent-free solid phase. In certain cases the solvent-mediated phase transition results in the generation of hollow, tubular structures. Both the tube dimensions of sodium-2-keto-L-gulonate anhydrate (skga) and the dehydration kinetics of sodium-2-keto-L-gulonate monohydrate (skgm) can be modified by the antisolvent employed. An explanation for the variable dehydration behaviour of skgm in the antisolvents is presented here. Furthermore, other crystalline hydrates were dehydrated in dry methanol. Providing an operational window can be found, any hydrate material could possibly find use in the production of tubes (micro- or nanotubes for different applications). The experimental conditions selected (dry methanol as antisolvent, dehydration temperature at 25 C) for the dehydration did not lead to the anhydrate tube growth for all hydrates investigated. Based upon the results presented here a first hypothesis is presented to explain this effect. (copyright 2010 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  4. Simultaneous removal of sulfide, nitrate and acetate: Kinetic modeling

    International Nuclear Information System (INIS)

    Wang Aijie; Liu Chunshuang; Ren Nanqi; Han Hongjun; Lee Duujong

    2010-01-01

    Biological removal of sulfide, nitrate and chemical oxygen demand (COD) simultaneously from industrial wastewaters to elementary sulfur (S 0 ), N 2 , and CO 2 , or named the denitrifying sulfide (DSR) process, is a cost effective and environmentally friendly treatment process for high strength sulfide and nitrate laden organic wastewater. Kinetic model for the DSR process was established for the first time on the basis of Activated Sludge Model No. 1 (ASM1). The DSR experiments were conducted at influent sulfide concentrations of 200-800 mg/L, whose results calibrate the model parameters. The model correlates well with the DSR process dynamics. By introducing the switch function and the inhibition function, the competition between autotrophic and heterotrophic denitrifiers is quantitatively described and the degree of inhibition of sulfide on heterotrophic denitrifiers is realized. The model output indicates that the DSR reactor can work well at 0.5 1000 mg/L influent sulfide, however, the DSR system will break down.

  5. 3D CFD Modeling of the LMF System: Desulfurization Kinetics

    Science.gov (United States)

    Cao, Qing; Pitts, April; Zhang, Daojie; Nastac, Laurentiu; Williams, Robert

    A fully transient 3D CFD modeling approach capable of predicting the three phase (gas, slag and steel) fluid flow characteristics and behavior of the slag/steel interface in the argon gas bottom stirred ladle with two off-centered porous plugs (Ladle Metallurgical Furnace or LMF) has been recently developed. The model predicts reasonably well the fluid flow characteristics in the LMF system and the observed size of the slag eyes for both the high-stirring and low-stirring conditions. A desulfurization reaction kinetics model considering metal/slag interface characteristics is developed in conjunction with the CFD modeling approach. The model is applied in this study to determine the effects of processing time, and gas flow rate on the efficiency of desulfurization in the studied LMF system.

  6. Simulation of styrene polymerization reactors: kinetic and thermodynamic modeling

    Directory of Open Access Journals (Sweden)

    A. S. Almeida

    2008-06-01

    Full Text Available A mathematical model for the free radical polymerization of styrene is developed to predict the steady-state and dynamic behavior of a continuous process. Special emphasis is given for the kinetic and thermodynamic models, where the most sensitive parameters were estimated using data from an industrial plant. The thermodynamic model is based on a cubic equation of state and a mixing rule applied to the low-pressure vapor-liquid equilibrium of polymeric solutions, suitable for modeling the auto-refrigerated polymerization reactors, which use the vaporization rate to remove the reaction heat from the exothermic reactions. The simulation results show the high predictive capability of the proposed model when compared with plant data for conversion, average molecular weights, polydispersity, melt flow index, and thermal properties for different polymer grades.

  7. Experimental kinetic study and modeling of calcium oxide carbonation

    International Nuclear Information System (INIS)

    Rouchon, L.

    2012-01-01

    Anthropogenic carbon dioxide (CO 2 ) emissions, major contributors to the greenhouse effect, are considered as the main cause of global warming. So, decrease of CO 2 emitted by large industrial combustion sources or power plants, is an important scientific goal. One of the approaches is based on CO 2 separation and capture from flue gas, followed by sequestration in a wide range of geological formations. In this aim, CO 2 is captured by sorbents like calcium oxide (CaO) in multi-cycle process of carbonation/de-carbonation. However, it was shown that the most important limitations of such process are related to the reversibility of reaction. CaO rapidly loses activity towards CO 2 , so the maximum extent of carbonation decreases as long as the number of cycles increases. In order to well understand the processes and parameters influencing the capture capacity of CaO-based sorbents, it appears important to get details on the kinetic law governing the reaction, which have not been really studied up to now. To investigate this reaction, CaO carbonation kinetics was followed by means of thermogravimetric analysis (TGA) on divided materials. Special care was given to the validation of the usual kinetic assumptions such as steady state and rate-determining step assumptions. The aim was to obtain a model describing the reaction in order to explain the influence of intensive variables such as carbonation temperature and CO 2 partial pressure. TGA curves obtained under isothermal and isobaric conditions showed an induction period linked to the nucleation process and a strong slowing down of the reaction rate once a given fractional conversion was reached. Both phenomena were observed to depend on carbonation temperature and CO 2 partial pressure. To explain these results, the evolution of texture and microstructure of the solid during the reaction was regarded as essential. Reaction at the grain scale induces a volume increase from CaO to CaCO 3 which causes a change in the

  8. 3D Finite Element Modeling for Possible Creeping Behavior of Gas Hydrate-related Slipstream Submarine Slide, offshore Vancouver Island, Canada

    Science.gov (United States)

    LONG, S.; He, T.; Lan, K.; Spence, G.; Yelisetti, S.

    2017-12-01

    Natural gas hydrate-related submarine landslides have been identified on worldwide continental slope. Being a potential risk for marine environment and engineering projects, it has been a hot topic of hydrate research in recent decades. The study target is Slipstream submarine landslide, one of the slope failures on the frontal ridges of the Northern Cascadia accretionary margin, off Vancouver Island, Canada. The previous studies of P- & S-wave velocity structure based on OBS (Ocean Bottom Seismometer) data of SeaJade (Seafloor Earthquake Array - Japan Canada Cascadia Experiment) project indicated that there are two high concentration gas-hydrate layers within the ridge, one is at a depth of 100 mbsf (meter beneath the seafloor) with anomalous high P-wave velocities and the other is just above the prominent BSR (bottom-simulating reflector) at a depth of 265-275 mbsf. In this study we investigated the possible creeping behavior of gas hydrate layer to examine the critical instability of the ridge slope using the finite element method for self weight and additional stress (e.g., mega earthquake) conditions. The elastic and elasticoplasticity moduli of gas hydrate layer were obtained from laboratory measurements for different uniaxial pressure tests, which indicated that the sediments behave elastically for uniaxial pressures below 6 MPa, but elasticoplastically between 6-6.77 MPa. The modeled shear stress distribution indicated that the current sliding surface is more likely connected with the shallow high-velocity gas hydrate layer and sliding process related with gas hydrate starts from the toe of the slope and then progressively retreats to the place of current headwall, in a series of triangular blocks or wedges. Since the study area is in the earthquake belt, the large seismic acceleration will greatly affect the stress field and pore pressure distribution within the ridge, and the landslide is going to happen and supposedly at the shallow high-velocity gas

  9. Detailed Modelling of Kinetic Biodegradation Processes in a Laboratory Mmicrocosm

    Science.gov (United States)

    Watson, I.; Oswald, S.; Banwart, S.; Mayer, U.

    2003-04-01

    Biodegradation of organic contaminants in soil and groundwater usually takes places via different redox processes happening sequentially as well as simultaneously. We used numerical modelling of a long-term lab microcosm experiment to simulate the dynamic behaviour of fermentation and respiration in the aqueous phase in contact with the sandstone material, and to develop a conceptual model describing these processes. Aqueous speciation, surface complexation, mineral dissolution and precipitation were taken into account also. Fermentation can be the first step of the degradation process producing intermediate species, which are subsequently consumed by TEAPs. Microbial growth and substrate utilisation kinetics are coupled via a formulation that also includes aqueous speciation and other geochemical reactions including surface complexation, mineral dissolution and precipitation. Competitive exclusion between TEAPs is integral to the conceptual model of the simulation, and the results indicate that exclusion is not complete, but some overlap is found between TEAPs. The model was used to test approaches like the partial equilibrium approach that currently make use of hydrogen levels to diagnose prevalent TEAPs in groundwater. The observed pattern of hydrogen and acetate concentrations were reproduced well by the simulations, and the results show the relevance of kinetics, lag times and inhibition, and especially that intermediate products play a key role.

  10. Modeling texture kinetics during thermal processing of potato products.

    Science.gov (United States)

    Moyano, P C; Troncoso, E; Pedreschi, F

    2007-03-01

    A kinetic model based on 2 irreversible serial chemical reactions has been proposed to fit experimental data of texture changes during thermal processing of potato products. The model links dimensionless maximum force F*(MAX) with processing time. Experimental texture changes were obtained during frying of French fries and potato chips at different temperatures, while literature data for blanching/cooking of potato cubes have been considered. A satisfactory agreement between experimental and predicted values was observed, with root mean square values (RMSs) in the range of 4.7% to 16.4% for French fries and 16.7% to 29.3% for potato chips. In the case of blanching/cooking, the proposed model gave RMSs in the range of 1.2% to 17.6%, much better than the 6.2% to 44.0% obtained with the traditional 1st-order kinetics. The model is able to predict likewise the transition from softening to hardening of the tissue during frying.

  11. Modeling of subtle kinetic processes in plasma simulation

    International Nuclear Information System (INIS)

    Sydora, R.D.; Decyk, V.K.; Dawson, J.M.

    1988-01-01

    A new diagnostic method for plasma simulation models is presented which enables one to probe the subtle dielectric properties of the plasma medium. The procedure involves the removal of the background plasma response in order to isolate the effects of small perturbing influences which are externally added. We have found the technique accurately describes fundamental kinetic plasma behavior such as the shielding of individual test charges and currents. Wave emission studies and drag of test particles has been carried out in explicit particle algorithms as well as large time step implicit and gyrokinetic models. Accurate plasma behavior is produced and it is possible to investigate in detail, processes which can be compared with plasma kinetic theory. The technique of subtraction is not only limited to particle simulation models but also can be used in MHD or fluid models where resolution is difficult due to the intensity of the background response relative to the phenomena one is interested in measuring, such as a weakly grouwing instability or nonlinear mode coupling effect. (author)

  12. Kinetics and mechanism of transitions involving the lamellar, cubic, inverted hexagonal, and fluid isotropic phases of hydrated monoacylglycerides monitored by time-resolved X-ray diffraction

    International Nuclear Information System (INIS)

    Caffrey, M.

    1987-01-01

    A study of the dynamics and mechanism of the various thermotropic phase transitions undergone by the hydrated monoacylglycerides monoolein and monoelaidin, in the temperature range of 20-120 0 C and from 0 to 5 M NaCl, has been undertaken. Measurements were made by using time-resolved X-ray diffraction at the Cornell High-Energy Synchrotron Source. The lamellar chain order/disorder, lamellar/cubic (body centered, space group No.8), cubic (body centered, No.8)/cubic (primitive No.4), cubic (body centered, No.12)/cubic (primitive, No.4), cubic (primitive, No.4)/fluid isotropic, cubic (body centered, No.12)/inverted hexagonal, cubic (primitive, No.4)/inverted hexagonal, and hexagonal/fluid isotropic transitions were examined under active heating and passive cooling by using a jump in temperature to effect phase transformation. All of the transitions with the exception of the cubic (body centered, No.8)/cubic (primitive, No.4) and the cubic (body centered, No.12)/cubic (primitive, No.4) cooling transitions were found (1) to be repeatable, (2) to be reversible, and (3) to have an upper bound on the transit time (time required to complete the transition) of ≤ 3s. In addition to the time-resolved measurements, data were obtained on the stability of the various phases in the temperature range of 20-120 0 C and from 0 to 5 M NaCl. In the case of fully hydrated monoolein, high salt strongly favors the hexagonal over the cubic (body centered, No.8) phase and slightly elevates the hexagonal/fluid isotropic transition temperature. With fully hydrated monoelaidin, the hexagonal phase which is not observed in the absence of salt becomes the dominant phase at high salt concentration

  13. Mathematical Modeling of Conversion Kinetics during Vitrification of Nuclear Waste

    International Nuclear Information System (INIS)

    Pokorny, Richard; Pierce, David A.; Chun, Jae Hun; Hrma, Pavel

    2012-01-01

    The last part of the high-level waste (HLW) glass melter that has not yet been fully understood, not to mention mathematically modeled, is the cold cap. Cold cap is a layer of dry melter feed, a mixture of the HLW with glass forming and modifying additives. It floats on the pool of molten glass from which it receives the heat necessary for melting. Mathematical modeling of the cold cap solves differential equations that express the mass and energy balances for the feed-to-glass conversion within the cold cap. The feed-to-glass conversion consists of multiple chemical reactions and phase transitions. Reaction enthalpies and mass losses to gases evolved provide an important input for the cold cap modeling. In this study, we measured the kinetics of cold cap reactions using the non-isothermal thermo-gravimetric analysis (TGA) and differential scanning calorimetry (DSC). These thermoanalytical techniques show multiple overlapping peaks, necessitating the development of a deconvolution method for the determination of the kinetics of major reactions needed for cold cap modeling. Assuming that the cold cap reactions are independent, we expressed the overall rate as a sum of rates of individual reactions that we treat as Arrheniustype processes with a power-law based kinetics. Accordingly, we fitted to experimental data the following equation: dx/dT=1/Φ N Σ 1 w i A i (1-x i ) ni exp(-B i /T) (1) where x is the fraction of material reacted, T is temperature, Φ is the heating rate, wi the weight of the i th reaction (the fraction of the total mass loss caused by the i th reaction), Ai is the i th reaction pre-exponential factor, B i is the i th reaction activation energy, and n i is the i th reaction (apparent) reaction order. Because HLW melter feeds contain a large number of constituents, such as oxides, acids, hydroxides, oxyhydrates, and ionic salts, the number of cold cap reactions is very large indeed. For example, hydroxides, oxyhydrates, boric acid, and various

  14. Improved point-kinetics model for the BWR control rod drop accident

    International Nuclear Information System (INIS)

    Neogy, P.; Wakabayashi, T.; Carew, J.F.

    1985-01-01

    A simple prescription to account for spatial feedback weighting effects in RDA (rod drop accident) point-kinetics analyses has been derived and tested. The point-kinetics feedback model is linear in the core peaking factor, F/sub Q/, and in the core average void fraction and fuel temperature. Comparison with detailed spatial kinetics analyses indicates that the improved point-kinetics model provides an accurate description of the BWR RDA

  15. Bona Fide Thermodynamic Temperature in Nonequilibrium Kinetic Ising Models

    OpenAIRE

    Sastre, Francisco; Dornic, Ivan; Chaté, Hugues

    2003-01-01

    We show that a nominal temperature can be consistently and uniquely defined everywhere in the phase diagram of large classes of nonequilibrium kinetic Ising spin models. In addition, we confirm the recent proposal that, at critical points, the large-time ``fluctuation-dissipation ratio'' $X_\\infty$ is a universal amplitude ratio and find in particular $X_\\infty \\approx 0.33(2)$ and $X_\\infty = 1/2$ for the magnetization in, respectively, the two-dimensional Ising and voter universality classes.

  16. Application of Detailed Chemical Kinetics to Combustion Instability Modeling

    Science.gov (United States)

    2016-01-04

    Clearance Number 15692 Clearance Date 12/3/2015 14. ABSTRACT A comparison of a single step global reaction and the detailed GRI -Mech 1.2 for combustion...comparison of a single step global reaction and the detailed GRI -Mech 1.2 for com- bustion instability modeling in a methane-fueled longitudinal-mode...methane as the fuel. We use the GRI -Mech 1.2 kinetics mechanism for methane oxidation.11 The GRI -Mech 1.2 was chosen over 2.11 because the only

  17. Rheological study of an hydrate slurry as secondary two-phase refrigerant. Experimental results and modelling; Etude rheologique d'une suspension d'hydrates en tant que fluide frigoporteur diphasique: resultats experimentaux et modelisation

    Energy Technology Data Exchange (ETDEWEB)

    Darbouret, M.

    2005-12-15

    Secondary two-phase fluids are suspensions of solid crystals. Thanks to the melting latent heat, they present a great interest for cold transportation. Moreover, they are a mean of reducing the amount of classical refrigerant. In the refrigeration field, ice slurries are already used. The goal is now to extend this technology to other temperature ranges suitable for other applications like freezing or air-conditioning. For an air-conditioning application, a TBAB (Tetra-Butyl-Ammonium Bromide) aqueous solution is studied. Under atmospheric pressure and for positive temperatures, this solution crystallizes into ice-like compounds named 'hydrates'. First, the physical properties of the aqueous solution and its crystallisation conditions were studied. Two different types of hydrates can appear. The goal of the experimental set-up is to study the rheological behaviour of two-phase fluids. Slurries are made in brushed-surface heat exchanger and pumped into pipes where flow rates and pressure drops are measured. The rheological behaviour of TBAB hydrates slurries can be described using a Bingham fluid model. We highlight that the two rheological parameters, which are the apparent viscosity and the yield shear stress, depend on the volume fraction of crystal of course, but also on the hydrate type, and on the initial concentration of the solution. The yield shear stress is interpreted as the consequence of the Van der Waals inter-particle interaction forces. Finally, possible stratification effects are modelled with a finite difference method. The principle is to calculate particle concentration and velocity profiles following the flow of the slurry. Calculations are validated with experimental velocity profiles published by P. Reghem (2002). This model underlines the influence of the particle distribution in the pipe on pressure drops. (author)

  18. A new kinetic model for human iodine metabolism

    International Nuclear Information System (INIS)

    Ficken, V.J.; Allen, E.W.; Adams, G.D.

    1985-01-01

    A new kinetic model of iodine metabolism incorporating preferential organification of tyrosil (TYR) residues of thyroglobulin is developed and evaluated for euthyroid (n=5) and hyperthyroid (n=11) subjects. Iodine and peripheral T4 metabolims were measured with oral /sup 131/I-NaI and intravenous /sup 125/I-74 respectively. Data (obtained over 10 days) and kinetic model are analyzed using the SAAM27 program developed by Berman (1978). Compartment rate constants (mean rate per hour +- ISD) are tabulated in this paper. Thyroid and renal iodide clearance compare favorably with values reported in the literature. TYR rate constants were not unique; however, values obtained are within the range of rate constants determined from the invitro data reported by others. Intraluminal iodine as coupled TYR is predicted to be 21% for euthyroid and 59% for hyperthyroid subjects compared to analytical chemical methods of 30% and 51% respectively determined elsewhere. The authors plan to evaluate this model as a method of predicting the thyroid radiation dose from orally administered I/sup 131/

  19. Raman studies of methane-ethane hydrate metastability.

    Science.gov (United States)

    Ohno, Hiroshi; Strobel, Timothy A; Dec, Steven F; Sloan, E Dendy; Koh, Carolyn A

    2009-03-05

    The interconversion of methane-ethane hydrate from metastable to stable structures was studied using Raman spectroscopy. sI and sII hydrates were synthesized from methane-ethane gas mixtures of 65% or 93% methane in ethane and water, both with and without the kinetic hydrate inhibitor, poly(N-vinylcaprolactam). The observed faster structural conversion rate in the higher methane concentration atmosphere can be explained in terms of the differences in driving force (difference in chemical potential of water in sI and sII hydrates) and kinetics (mass transfer of gas and water rearrangement). The kinetic hydrate inhibitor increased the conversion rate at 65% methane in ethane (sI is thermodynamically stable) but retards the rate at 93% methane in ethane (sII is thermodynamically stable), implying there is a complex interaction between the polymer, water, and hydrate guests at crystal surfaces.

  20. Kinetic modeling of ethane pyrolysis at high conversion.

    Science.gov (United States)

    Xu, Chen; Al Shoaibi, Ahmed Sultan; Wang, Chenguang; Carstensen, Hans-Heinrich; Dean, Anthony M

    2011-09-29

    The primary objective of this study is to develop an improved first-principle-based mechanism that describes the molecular weight growth kinetics observed during ethane pyrolysis. A proper characterization of the kinetics of ethane pyrolysis is a prerequisite for any analysis of hydrocarbon pyrolysis and oxidation. Flow reactor experiments were performed with ~50/50 ethane/nitrogen mixtures with temperatures ranging from 550 to 850 °C at an absolute pressure of ~0.8 atm and a residence time of ~5 s. These conditions result in ethane conversions ranging from virtually no reaction to ~90%. Comparisons of predictions using our original mechanism to these data yielded very satisfactory results in terms of the temperature dependence of ethane conversion and prediction of the major products ethylene and hydrogen. However, there were discrepancies in some of the minor species concentrations that are involved in the molecular weight growth kinetics. We performed a series of CBS-QB3 analyses for the C(3)H(7), C(4)H(7), and C(4)H(9) potential energy surfaces to better characterize the radical addition reactions that lead to molecular weight growth. We also extended a published C(6)H(9) PES to include addition of vinyl to butadiene. The results were then used to calculate pressure-dependent rate constants for the multiple reaction pathways of these addition reactions. Inclusion of the unadjusted rate constants resulting from these analyses in the mechanism significantly improved the description of several of the species involved in molecular weight growth kinetics. We compare the predictions of this improved model to those obtained with a consensus model recently published as well as to ethane steam cracking data. We find that a particularly important reaction is that of vinyl addition to butadiene. Another important observation is that several radical addition reactions are partially equilibrated. Not only does this mean that reliable thermodynamic parameters are essential

  1. Dynamic Modeling of Cell-Free Biochemical Networks Using Effective Kinetic Models

    Directory of Open Access Journals (Sweden)

    Joseph A. Wayman

    2015-03-01

    Full Text Available Cell-free systems offer many advantages for the study, manipulation and modeling of metabolism compared to in vivo processes. Many of the challenges confronting genome-scale kinetic modeling can potentially be overcome in a cell-free system. For example, there is no complex transcriptional regulation to consider, transient metabolic measurements are easier to obtain, and we no longer have to consider cell growth. Thus, cell-free operation holds several significant advantages for model development, identification and validation. Theoretically, genome-scale cell-free kinetic models may be possible for industrially important organisms, such as E. coli, if a simple, tractable framework for integrating allosteric regulation with enzyme kinetics can be formulated. Toward this unmet need, we present an effective biochemical network modeling framework for building dynamic cell-free metabolic models. The key innovation of our approach is the integration of simple effective rules encoding complex allosteric regulation with traditional kinetic pathway modeling. We tested our approach by modeling the time evolution of several hypothetical cell-free metabolic networks. We found that simple effective rules, when integrated with traditional enzyme kinetic expressions, captured complex allosteric patterns such as ultrasensitivity or non-competitive inhibition in the absence of mechanistic information. Second, when integrated into network models, these rules captured classic regulatory patterns such as product-induced feedback inhibition. Lastly, we showed, at least for the network architectures considered here, that we could simultaneously estimate kinetic parameters and allosteric connectivity from synthetic data starting from an unbiased collection of possible allosteric structures using particle swarm optimization. However, when starting with an initial population that was heavily enriched with incorrect structures, our particle swarm approach could converge

  2. CO2 capture by gas hydrate crystallization: Application on the CO2-N2 mixture

    International Nuclear Information System (INIS)

    Bouchemoua, A.

    2012-01-01

    CO 2 capture and sequestration represent a major industrial and scientific challenge of this century. There are different methods of CO 2 separation and capture, such as solid adsorption, amines adsorption and cryogenic fractionation. Although these processes are well developed at industrial level, they are energy intensive. Hydrate formation method is a less energy intensive and has an interesting potential to separate carbon dioxide. Gas hydrates are Document crystalline compounds that consist of hydrogen bonded network of water molecules trapping a gas molecule. Gas hydrate formation is favored by high pressure and low temperature. This study was conducted as a part of the SECOHYA ANR Project. The objective is to study the thermodynamic and kinetic conditions of the process to capture CO 2 by gas hydrate crystallization. Firstly, we developed an experimental apparatus to carry out experiments to determine the thermodynamic and kinetic formation conditions of CO 2 -N 2 gas hydrate mixture in water as liquid phase. We showed that the operative pressure may be very important and the temperature very low. For the feasibility of the project, we used TBAB (Tetrabutylammonium Bromide) as thermodynamic additive in the liquid phase. The use of TBAB may reduce considerably the operative pressure. In the second part of this study, we presented a thermodynamic model, based on the van der Waals and Platteeuw model. This model allows the estimation of thermodynamic equilibrium conditions. Experimental equilibrium data of CO 2 -CH 4 and CO 2 -N 2 mixtures are presented and compared to theoretical results. (author)

  3. Gas Hydrate Formation Probability Distributions: The Effect of Shear and Comparisons with Nucleation Theory.

    Science.gov (United States)

    May, Eric F; Lim, Vincent W; Metaxas, Peter J; Du, Jianwei; Stanwix, Paul L; Rowland, Darren; Johns, Michael L; Haandrikman, Gert; Crosby, Daniel; Aman, Zachary M

    2018-03-13

    Gas hydrate formation is a stochastic phenomenon of considerable significance for any risk-based approach to flow assurance in the oil and gas industry. In principle, well-established results from nucleation theory offer the prospect of predictive models for hydrate formation probability in industrial production systems. In practice, however, heuristics are relied on when estimating formation risk for a given flowline subcooling or when quantifying kinetic hydrate inhibitor (KHI) performance. Here, we present statistically significant measurements of formation probability distributions for natural gas hydrate systems under shear, which are quantitatively compared with theoretical predictions. Distributions with over 100 points were generated using low-mass, Peltier-cooled pressure cells, cycled in temperature between 40 and -5 °C at up to 2 K·min -1 and analyzed with robust algorithms that automatically identify hydrate formation and initial growth rates from dynamic pressure data. The application of shear had a significant influence on the measured distributions: at 700 rpm mass-transfer limitations were minimal, as demonstrated by the kinetic growth rates observed. The formation probability distributions measured at this shear rate had mean subcoolings consistent with theoretical predictions and steel-hydrate-water contact angles of 14-26°. However, the experimental distributions were substantially wider than predicted, suggesting that phenomena acting on macroscopic length scales are responsible for much of the observed stochastic formation. Performance tests of a KHI provided new insights into how such chemicals can reduce the risk of hydrate blockage in flowlines. Our data demonstrate that the KHI not only reduces the probability of formation (by both shifting and sharpening the distribution) but also reduces hydrate growth rates by a factor of 2.

  4. [Skin hydration and hydrating products].

    Science.gov (United States)

    Duplan, H; Nocera, T

    2018-05-01

    One of the skin's principal functions is to protect the body against its environment by maintaining an effective epidermal barrier, not only against external factors, but also to prevent water loss from the body. Indeed, water homeostasis is vital for the normal physiological functioning of skin. Hydration levels affect not only visible microscopic parameters such as the suppleness and softness of skin, but also molecular parameters, enzyme activities and cellular signalling within the epidermis. The body is continually losing some of its water, but this phenomenon is limited and the optimal hydration gradient in skin is ensured via a set of sophisticated regulatory processes that rely on the functional and dynamic properties of the uppermost level of the skin consisting of the stratum corneum. The present article brings together data recently acquired in the fields of skin hydration and the characterisation of dehydrated or dry skin, whether through study of the regulatory processes involved or as a result of changes in the techniques used for in situ measurement, and thus in optimisation of management. Copyright © 2018. Published by Elsevier Masson SAS.

  5. Rotational and divergent kinetic energy in the mesoscale model ALADIN

    Directory of Open Access Journals (Sweden)

    V. Blažica

    2013-03-01

    Full Text Available Kinetic energy spectra from the mesoscale numerical weather prediction (NWP model ALADIN with horizontal resolution 4.4 km are split into divergent and rotational components which are then compared at horizontal scales below 300 km and various vertical levels. It is shown that about 50% of kinetic energy in the free troposphere in ALADIN is divergent energy. The percentage increases towards 70% near the surface and in the upper troposphere towards 100 hPa. The maximal percentage of divergent energy is found at stratospheric levels around 100 hPa and at scales below 100 km which are not represented by the global models. At all levels, the divergent energy spectra are characterised by shallower slopes than the rotational energy spectra, and the difference increases as horizontal scales become larger. A very similar vertical distribution of divergent energy is obtained by using the standard ALADIN approach for the computation of spectra based on the extension zone and by applying detrending approach commonly used in mesoscale NWP community.

  6. Kinetic Models for Topological Nearest-Neighbor Interactions

    Science.gov (United States)

    Blanchet, Adrien; Degond, Pierre

    2017-12-01

    We consider systems of agents interacting through topological interactions. These have been shown to play an important part in animal and human behavior. Precisely, the system consists of a finite number of particles characterized by their positions and velocities. At random times a randomly chosen particle, the follower, adopts the velocity of its closest neighbor, the leader. We study the limit of a system size going to infinity and, under the assumption of propagation of chaos, show that the limit kinetic equation is a non-standard spatial diffusion equation for the particle distribution function. We also study the case wherein the particles interact with their K closest neighbors and show that the corresponding kinetic equation is the same. Finally, we prove that these models can be seen as a singular limit of the smooth rank-based model previously studied in Blanchet and Degond (J Stat Phys 163:41-60, 2016). The proofs are based on a combinatorial interpretation of the rank as well as some concentration of measure arguments.

  7. Models for the transport of low energy electrons in water and the yield of hydrated electrons at early times

    International Nuclear Information System (INIS)

    Brenner, D.J.; Miller, J.H.; Ritchie, R.H.; Bichsel, H.

    1985-01-01

    An insulator model with four experimental energy bands was used to fit the optical properties of liquid water and to extend these data to non-zero momentum transfer. Inelastic mean free paths derived from this dielectric response function provided the basic information necessary to degrade high energy electrons to the subexcitation energy domain. Two approaches for the transport of subexcitation electrons were investigated. (i) Gas phase cross sections were used to degrade subexcitation electrons to thermal energy and the thermalization lengths were scaled to unit density. (ii) Thermalization lengths were estimated by age-diffusion theory with a stopping power deduced from the data on liquid water and transport cross sections derived from elastic scattering in water vapor. Theoretical ranges were compared to recent experimental results. A stochastic model was used to calculate the rapid diffusion and reaction of hydrated electrons with other radiolysis products. The sensitivity of the calculated yields to the model assumptions and comparison with experimental data are discussed

  8. Seismic reflections associated with submarine gas hydrates

    Energy Technology Data Exchange (ETDEWEB)

    Andreassen, K

    1996-12-31

    Gas hydrates are often suggested as a future energy resource. This doctoral thesis improves the understanding of the concentration and distribution of natural submarine gas hydrates. The presence of these hydrates are commonly inferred from strong bottom simulating reflection (BSR). To investigate the nature of BSR, this work uses seismic studies of hydrate-related BSRs at two different locations, one where gas hydrates are accepted to exist and interpreted to be very extensive (in the Beaufort Sea), the other with good velocity data and downhole logs available (offshore Oregon). To ascertain the presence of free gas under the BSR, prestack offset data must supplement near-vertical incidence seismic data. A tentative model for physical properties of sediments partially saturated with gas hydrate and free gas is presented. This model, together with drilling information and seismic data containing the BSR beneath the Oregon margin and the Beaufort Sea, made it possible to better understand when to apply the amplitude-versus-offset (AVO) method to constrain BSR gas hydrate and gas models. Distribution of natural gas hydrates offshore Norway and Svalbard is discussed and interpreted as reflections from the base of gas hydrate-bearing sediments, overlying sediments containing free gas. Gas hydrates inferred to exist at the Norwegian-Svalbard continental margin correlate well with Cenozoic depocenters, and the associated gas is assumed to be mainly biogenic. Parts of that margin have a high potential for natural gas hydrates of both biogenic and thermogenic origin. 235 refs., 86 figs., 4 tabs.

  9. Seismic reflections associated with submarine gas hydrates

    Energy Technology Data Exchange (ETDEWEB)

    Andreassen, K.

    1995-12-31

    Gas hydrates are often suggested as a future energy resource. This doctoral thesis improves the understanding of the concentration and distribution of natural submarine gas hydrates. The presence of these hydrates are commonly inferred from strong bottom simulating reflection (BSR). To investigate the nature of BSR, this work uses seismic studies of hydrate-related BSRs at two different locations, one where gas hydrates are accepted to exist and interpreted to be very extensive (in the Beaufort Sea), the other with good velocity data and downhole logs available (offshore Oregon). To ascertain the presence of free gas under the BSR, prestack offset data must supplement near-vertical incidence seismic data. A tentative model for physical properties of sediments partially saturated with gas hydrate and free gas is presented. This model, together with drilling information and seismic data containing the BSR beneath the Oregon margin and the Beaufort Sea, made it possible to better understand when to apply the amplitude-versus-offset (AVO) method to constrain BSR gas hydrate and gas models. Distribution of natural gas hydrates offshore Norway and Svalbard is discussed and interpreted as reflections from the base of gas hydrate-bearing sediments, overlying sediments containing free gas. Gas hydrates inferred to exist at the Norwegian-Svalbard continental margin correlate well with Cenozoic depocenters, and the associated gas is assumed to be mainly biogenic. Parts of that margin have a high potential for natural gas hydrates of both biogenic and thermogenic origin. 235 refs., 86 figs., 4 tabs.

  10. Generalized kinetic model of reduction of molecular oxidant by metal containing redox

    International Nuclear Information System (INIS)

    Kravchenko, T.A.

    1986-01-01

    Present work is devoted to kinetics of reduction of molecular oxidant by metal containing redox. Constructed generalized kinetic model of redox process in the system solid redox - reagent solution allows to perform the general theoretical approach to research and to obtain new results on kinetics and mechanism of interaction of redox with oxidants.

  11. A Global Modeling Framework for Plasma Kinetics: Development and Applications

    Science.gov (United States)

    Parsey, Guy Morland

    The modern study of plasmas, and applications thereof, has developed synchronously with com- puter capabilities since the mid-1950s. Complexities inherent to these charged-particle, many- body, systems have resulted in the development of multiple simulation methods (particle-in-cell, fluid, global modeling, etc.) in order to both explain observed phenomena and predict outcomes of plasma applications. Recognizing that different algorithms are chosen to best address specific topics of interest, this thesis centers around the development of an open-source global model frame- work for the focused study of non-equilibrium plasma kinetics. After verification and validation of the framework, it was used to study two physical phenomena: plasma-assisted combustion and the recently proposed optically-pumped rare gas metastable laser. Global models permeate chemistry and plasma science, relying on spatial averaging to focus attention on the dynamics of reaction networks. Defined by a set of species continuity and energy conservation equations, the required data and constructed systems are conceptually similar across most applications, providing a light platform for exploratory and result-search parameter scan- ning. Unfortunately, it is common practice for custom code to be developed for each application-- an enormous duplication of effort which negatively affects the quality of the software produced. Presented herein, the Python-based Kinetic Global Modeling framework (KGMf) was designed to support all modeling phases: collection and analysis of reaction data, construction of an exportable system of model ODEs, and a platform for interactive evaluation and post-processing analysis. A symbolic ODE system is constructed for interactive manipulation and generation of a Jacobian, both of which are compiled as operation-optimized C-code. Plasma-assisted combustion and ignition (PAC/PAI) embody the modernization of burning fuel by opening up new avenues of control and optimization

  12. A kinetic model for the burst phase of processive cellulases

    DEFF Research Database (Denmark)

    Præstgaard, Eigil; Olsen, Jens Elmerdahl; Murphy, Leigh

    2011-01-01

    . This approach generally accounts well for the initial time course (approximately 1 h) of the hydrolysis. We suggest that the models will be useful in attempts to rationalize the initial kinetics of processive cellulases, and demonstrate their application to some open questions, including the effect of repeated......Cellobiohydrolases (exocellulases) hydrolyze cellulose processively, i.e. by sequential cleaving of soluble sugars from one end of a cellulose strand. Their activity generally shows an initial burst, followed by a pronounced slowdown, even when substrate is abundant and product accumulation...... of the model, which can be solved analytically, shows that the burst and slowdown can be explained by the relative rates of the sequential reactions in the hydrolysis process and the occurrence of obstacles for the processive movement along the cellulose strand. More specifically, the maximum enzyme activity...

  13. Combined kinetic and transport modeling of radiofrequency current drive

    International Nuclear Information System (INIS)

    Dumont, R.; Giruzzi, G.; Barbato, E.

    2000-07-01

    A numerical model for predictive simulations of radiofrequency current drive in magnetically confined plasmas is developed. It includes the minimum requirements for a self consistent description of such regimes, i.e., a 3-D ,kinetic equation for the electron distribution function, 1-D heat and current transport equations, and resonant coupling between velocity space and configuration space dynamics, through suitable wave propagation equations. The model finds its full application in predictive studies of complex current profile control scenarios in tokamaks, aiming at the establishment of internal transport barriers by the simultaneous use of various radiofrequency current drive methods. The basic properties of this non-linear numerical system are investigated and illustrated by simulations applied to reversed magnetic shear regimes obtained by Lower Hybrid and Electron Cyclotron current drive for parameters typical of the Tore Supra tokamak. (authors)

  14. Predicting the Impact of Multiwalled Carbon Nanotubes on the Cement Hydration Products and Durability of Cementitious Matrix Using Artificial Neural Network Modeling Technique

    Directory of Open Access Journals (Sweden)

    Babak Fakhim

    2013-01-01

    Full Text Available In this study the feasibility of using the artificial neural networks modeling in predicting the effect of MWCNT on amount of cement hydration products and improving the quality of cement hydration products microstructures of cement paste was investigated. To determine the amount of cement hydration products thermogravimetric analysis was used. Two critical parameters of TGA test are PHPloss and CHloss. In order to model the TGA test results, the ANN modeling was performed on these parameters separately. In this study, 60% of data are used for model calibration and the remaining 40% are used for model verification. Based on the highest efficiency coefficient and the lowest root mean square error, the best ANN model was chosen. The results of TGA test implied that the cement hydration is enhanced in the presence of the optimum percentage (0.3 wt% of MWCNT. Moreover, since the efficiency coefficient of the modeling results of CH and PHP loss in both the calibration and verification stages was more than 0.96, it was concluded that the ANN could be used as an accurate tool for modeling the TGA results. Another finding of this study was that the ANN prediction in higher ages was more precise.

  15. Elementary Processes and Kinetic Modeling for Hydrogen and Helium Plasmas

    Directory of Open Access Journals (Sweden)

    Roberto Celiberto

    2017-05-01

    Full Text Available We report cross-sections and rate coefficients for excited states colliding with electrons, heavy particles and walls useful for the description of H 2 /He plasma kinetics under different conditions. In particular, the role of the rotational states in resonant vibrational excitations of the H 2 molecule by electron impact and the calculation of the related cross-sections are illustrated. The theoretical determination of the cross-section for the rovibrational energy exchange and dissociation of H 2 molecule, induced by He atom impact, by using the quasi-classical trajectory method is discussed. Recombination probabilities of H atoms on tungsten and graphite, relevant for the determination of the nascent vibrational distribution, are also presented. An example of a state-to-state plasma kinetic model for the description of shock waves operating in H 2 and He-H 2 mixtures is presented, emphasizing also the role of electronically-excited states in affecting the electron energy distribution function of free electrons. Finally, the thermodynamic properties and the electrical conductivity of non-ideal, high-density hydrogen plasma are finally discussed, in particular focusing on the pressure ionization phenomenon in high-pressure high-temperature plasmas.

  16. Pyrolysis Kinetic Modelling of Wheat Straw from the Pannonian Region

    Directory of Open Access Journals (Sweden)

    Ivan Pešenjanski

    2016-01-01

    Full Text Available The pyrolysis/devolatilization is a basic step of thermochemical processes and requires fundamental characterization. In this paper, the kinetic model of pyrolysis is specified as a one-step global reaction. This type of reaction is used to describe the thermal degradation of wheat straw samples by measuring rates of mass loss of solid matter at a linear increase in temperature. The mentioned experiments were carried out using a derivatograph in an open-air environment. The influence of different factors was investigated, such as particle size, humidity levels, and the heating rate in the kinetics of devolatilization. As the measured values of mass loss and temperature functions transform in Arrhenius coordinates, the results are shown in the form of saddle curves. Such characteristics cannot be approximated with one equation in the form of Arrhenius law. For use in numerical applications, transformed functions can be approximated by linear regression for three separate intervals. Analysis of measurement resulting in granulation and moisture content variations shows that these factors have no significant influence. Tests of heating rate variations confirm the significance of this impact, especially in warmer regions. The influence of this factor should be more precisely investigated as a general variable, which should be the topic of further experiments.

  17. Discrete kinetic models from funneled energy landscape simulations.

    Directory of Open Access Journals (Sweden)

    Nicholas P Schafer

    Full Text Available A general method for facilitating the interpretation of computer simulations of protein folding with minimally frustrated energy landscapes is detailed and applied to a designed ankyrin repeat protein (4ANK. In the method, groups of residues are assigned to foldons and these foldons are used to map the conformational space of the protein onto a set of discrete macrobasins. The free energies of the individual macrobasins are then calculated, informing practical kinetic analysis. Two simple assumptions about the universality of the rate for downhill transitions between macrobasins and the natural local connectivity between macrobasins lead to a scheme for predicting overall folding and unfolding rates, generating chevron plots under varying thermodynamic conditions, and inferring dominant kinetic folding pathways. To illustrate the approach, free energies of macrobasins were calculated from biased simulations of a non-additive structure-based model using two structurally motivated foldon definitions at the full and half ankyrin repeat resolutions. The calculated chevrons have features consistent with those measured in stopped flow chemical denaturation experiments. The dominant inferred folding pathway has an "inside-out", nucleation-propagation like character.

  18. Clathrate hydrate dissociation conditions of refrigerants R404A, R406A, R408A and R427A: Experimental measurements and thermodynamic modeling

    International Nuclear Information System (INIS)

    Hashemi, Hamed; Babaee, Saeedeh; Mohammadi, Amir H.; Naidoo, Paramespri; Ramjugernath, Deresh

    2015-01-01

    Highlights: • The application of refrigerant hydrates in cold storage systems is investigated. • Hydrate dissociation conditions of various refrigerants have been measured. • A correlative thermodynamic model was applied to the data. • Enthalpy of dissociation for the refrigerants studied calculated. • Experimental measurements performed over a wide range of pressures. - Abstract: Clathrate hydrate dissociation conditions were measured for four “alternative” refrigerants, viz. R404A, R406A, R408A and R427A. The experimental measurements were performed within the pressure range of (0.079 to 9.995) MPa and temperatures ranging from (272.7 to 288.7) K. An isochoric pressure-search method was used to perform the measurements. A thermodynamic model based on the van der Waals–Platteeuw (vdW–P) model was applied for the prediction of the dissociation conditions which were compared to the experimental measurements. The fluid phase was modeled using the MHV2 G E -EoS mixing rule along with the UNIFAC (original) activity model. The van der Waals–Platteeuw (vdW–P) model was used for the modeling of the hydrate phase. There was reasonable agreement between the experimental and predicted values

  19. BACCHUS 2: an in situ backfill hydration experiment for model validation

    International Nuclear Information System (INIS)

    Volckaert, G.; Bernier, F.; Alonso, E.; Gens, A.

    1995-01-01

    The BACCHUS 2 experiment is an in situ backfill hydration test performed in the HADES underground research facility situated in the plastic Boom clay layer at 220 m depth. The experiment aims at the optimization and demonstration of an installation procedure for a clay based backfill material. The instrumentation has been optimized in such a way that the results of the experiments can be used for the validation of hydro-mechanical codes such a NOSAT developed at the University of Catalunya Spain (UPC). The experimental set-up consists in a bottom flange and a central filter around which the backfill material was applied. The backfill material consist of a mixture of high density clay pellets and clay powder. The experimental set-up and its instrumentation are described in detail. The results of the hydro-mechanical characterization of the backfill material is summarized. (authors). 8 refs., 16 figs., 1 tab

  20. Evidence from mixed hydrate nucleation for a funnel model of crystallization

    Science.gov (United States)

    Hall, Kyle Wm.; Carpendale, Sheelagh; Kusalik, Peter G.

    2016-01-01

    The molecular-level details of crystallization remain unclear for many systems. Previous work has speculated on the phenomenological similarities between molecular crystallization and protein folding. Here we demonstrate that molecular crystallization can involve funnel-shaped potential energy landscapes through a detailed analysis of mixed gas hydrate nucleation, a prototypical multicomponent crystallization process. Through this, we contribute both: (i) a powerful conceptual framework for exploring and rationalizing molecular crystallization, and (ii) an explanation of phenomenological similarities between protein folding and crystallization. Such funnel-shaped potential energy landscapes may be typical of broad classes of molecular ordering processes, and can provide a new perspective for both studying and understanding these processes. PMID:27790987

  1. Predicting hydration free energies of amphetamine-type stimulants with a customized molecular model

    International Nuclear Information System (INIS)

    Li, Jipeng; Lu, Diannan; Fu, Jia; Wu, Jianzhong; Huang, Xing

    2016-01-01

    Amphetamine-type stimulants (ATS) are a group of incitation and psychedelic drugs affecting the central nervous system. Physicochemical data for these compounds are essential for understanding the stimulating mechanism, for assessing their environmental impacts, and for developing new drug detection methods. However, experimental data are scarce due to tight regulation of such illicit drugs, yet conventional methods to estimate their properties are often unreliable. Here we introduce a tailor-made multiscale procedure for predicting the hydration free energies and the solvation structures of ATS molecules by a combination of first principles calculations and the classical density functional theory. We demonstrate that the multiscale procedure performs well for a training set with similar molecular characteristics and yields good agreement with a testing set not used in the training. The theoretical predictions serve as a benchmark for the missing experimental data and, importantly, provide microscopic insights into manipulating the hydrophobicity of ATS compounds by chemical modifications. (paper)

  2. Kinetic modeling of methyl butanoate in shock tube.

    Science.gov (United States)

    Huynh, Lam K; Lin, Kuang C; Violi, Angela

    2008-12-25

    An increased necessity for energy independence and heightened concern about the effects of rising carbon dioxide levels have intensified the search for renewable fuels that could reduce our current consumption of petrol and diesel. One such fuel is biodiesel, which consists of the methyl esters of fatty acids. Methyl butanoate (MB) contains the essential chemical structure of the long-chain fatty acids and a shorter, but similar, alkyl chain. This paper reports on a detailed kinetic mechanism for MB that is assembled using theoretical approaches. Thirteen pathways that include fuel decomposition, isomerization, and propagation steps were computed using ab initio calculations [J. Org. Chem. 2008, 73, 94]. Rate constants from first principles for important reactions in CO(2) formation, namely CH(3)OCO=CH(3) + CO(2) (R1) and CH(3)OCO=CH(3)O + CO (R2) reactions, are computed at high levels of theory and implemented in the mechanism. Using the G3B3 potential energy surface together with the B3LYP/6-31G(d) gradient, Hessian and geometries, the rate constants for reactions R1 and R2 are calculated using the Rice-Ramsperger-Kassel-Marcus theory with corrections from treatments for tunneling, hindered rotation, and variational effects. The calculated rate constants of reaction R1 differ from the data present in the literature by at most 20%, while those of reaction R2 are about a factor of 4 lower than the available values. The new kinetic model derived from ab initio simulations is combined with the kinetic mechanism presented by Fisher et al. [Proc. Combust. Inst. 2000, 28, 1579] together with the addition of the newly found six-centered unimolecular elimination reaction that yields ethylene and methyl acetate, MB = C(2)H(4) + CH(3)COOCH(3). This latter pathway requires the inclusion of the CH(3)COOCH(3) decomposition model suggested by Westbrook et al. [Proc. Combust. Inst. 2008, accepted]. The newly composed kinetic mechanism for MB is used to study the CO(2) formation

  3. Molecular Simulation Models of Carbon Dioxide Intercalation in Hydrated Sodium Montmorillonite

    Energy Technology Data Exchange (ETDEWEB)

    Myshakin, Evgeniy [National Energy Technology Lab. (NETL), Pittsburgh, PA, (United States); Saidi, Wissam [Univ. of Pittsburgh, PA (United States); Romanov, Vyacheslav [National Energy Technology Lab. (NETL), Pittsburgh, PA, (United States); Cygan, Randall [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Jordan, Kenneth [National Energy Technology Lab. (NETL), Pittsburgh, PA, (United States); Univ. of Pittsburgh, PA (United States); Guthrie, George [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

    2016-11-22

    In this study, classical molecular dynamics simulations and density functional theory (DFT)-based molecular dynamics are used to elucidate the process of CO2 intercalation into hydrated Na-montmorillonite at P-T conditions relevant to geological formations suitable for CO2 storage. Of particular interest are the structural and transport properties of interlayer species after CO2 intercalation. The conducted simulations allowed the research team to quantify expansion/contraction of smectite as a function of CO2 and H2O compositions. The resulting swelling curves can be used to gauge the amount of stored CO2, compare it to the experiment, and estimate changes in geomechanical properties of the storage formation. The obtained results showed that the infrared signal of the asymmetric stretch vibration of CO2 molecule is extremely sensitive to the solvent environment. The extent of the frequency shift relative to the gas-phase value can be used to probe hydration level in the interlayer with intercalated CO2. Interaction of supercritical CO2 with brine in deep geological formations promotes an increase of hydrophobicity of clay surfaces. As a result of wettability alteration, estimated diffusion constants of CO2 and H2O increase with the increased CO2 load; this can contribute to faster migration of CO2 throughout the formation.

  4. A model of aerosol evaporation kinetics in a thermodenuder

    Directory of Open Access Journals (Sweden)

    C. D. Cappa

    2010-05-01

    Full Text Available Aerosol thermodenuders provide a measure of particle volatility. The information provided by a thermodenuder is fundamentally related to the kinetics of evaporation and condensation within the device. Here, a time-dependent, multi-component model of particle and gas-phase mass transfer in a thermodenuder is described. This model empirically accounts for the temperature profile along the length of a typical thermodenuder and distinguishes between the influence of the heating section and of the adsorbent denuder section. It is shown that "semi-volatile" aerosol is particularly sensitive to the inclusion of an adsorbent denuder in the model. As expected, the mass loss from evaporation of particles as they pass through the thermodenuder is directly related to the compound vapor pressure, although the assumptions regarding the enthalpy of vaporization are shown to also have a large influence on the overall calculated mass thermograms. The model has been validated by comparison with previously measured mass thermograms for single-component aerosols and is shown to provide reasonable semi-quantitative agreement. The model that has been developed here can be used to provide quantitative understanding of aerosol volatility measurements of single and multi-component aerosol made using thermodenuders that include adsorbent denuder sections.

  5. Simultaneous removal of sulfide, nitrate and acetate: Kinetic modeling

    Energy Technology Data Exchange (ETDEWEB)

    Wang Aijie, E-mail: waj0578@hit.edu.cn [State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology (SKLUWRE, HIT), Harbin 150090 (China); Liu Chunshuang; Ren Nanqi; Han Hongjun [State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology (SKLUWRE, HIT), Harbin 150090 (China); Lee Duujong [State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology (SKLUWRE, HIT), Harbin 150090 (China); Department of Chemical Engineering, National Taiwan University, Taipei 10617, Taiwan (China)

    2010-06-15

    Biological removal of sulfide, nitrate and chemical oxygen demand (COD) simultaneously from industrial wastewaters to elementary sulfur (S{sup 0}), N{sub 2}, and CO{sub 2}, or named the denitrifying sulfide (DSR) process, is a cost effective and environmentally friendly treatment process for high strength sulfide and nitrate laden organic wastewater. Kinetic model for the DSR process was established for the first time on the basis of Activated Sludge Model No. 1 (ASM1). The DSR experiments were conducted at influent sulfide concentrations of 200-800 mg/L, whose results calibrate the model parameters. The model correlates well with the DSR process dynamics. By introducing the switch function and the inhibition function, the competition between autotrophic and heterotrophic denitrifiers is quantitatively described and the degree of inhibition of sulfide on heterotrophic denitrifiers is realized. The model output indicates that the DSR reactor can work well at 0.5 < C/S < 3.0 with influent sulfide concentration of 400-1000 mg/L. At >1000 mg/L influent sulfide, however, the DSR system will break down.

  6. Simulation of microwave stimulation for the production of gas from methane hydrate sediment

    International Nuclear Information System (INIS)

    Zhao, Jiafei; Fan, Zhen; Wang, Bin; Dong, Hongsheng; Liu, Yu; Song, Yongchen

    2016-01-01

    Graphical abstract: Schematic diagram illustrating the process of gas production in hydrate-bearing sediment induced by microwave stimulation. Temperature gradients caused by the drop of microwave penetration depth appear in the sediment, leading to a rapid dissociation rate at the upper part of reservoir. - Highlights: • Hydrate dissociation behavior was analyzed in porous media by microwave stimulation. • Microwave stimulation provides sufficient energy conversion for hydrate dissociation. • Hydrate saturation and specific heat capacity of sediment mainly affect efficiency. • Heat conduction decreases temperature gradients promoting homogeneous dissociation. - Abstract: Natural gas hydrates dissociate via an endothermic process. One of the key requirements for any production technique is to supply the heat necessary for this dissociation. In this study, first, a microwave stimulation model for the production of gas from methane hydrate sediment is developed, which includes mass transport, energy conversion and conservation, and intrinsic kinetic reactions as the governing equations. In addition, the theoretical mixing rule of Lichtenecker and Rother is introduced for calculating the average dielectric data of the sediment containing methane hydrates, which affects the penetration of microwaves into the sediment. Next, simulations are performed for investigating gas production, as well as effects of initial water saturation, initial hydrate saturation, and sediment thermal properties induced by microwave stimulation. Moreover, the energy efficiency ratio is employed in the simulation. The simulation results show that microwave stimulation provides timely energy conversion sufficient for promoting the dissociation of hydrates, with rapid, continuous gas production. Temperature gradients caused by the decrease of the microwave penetration depth appear in the reservoir, leading to a rapid dissociation rate in the upper part of the sediment. The energy

  7. Incorporation of chemical kinetic models into process control

    International Nuclear Information System (INIS)

    Herget, C.J.; Frazer, J.W.

    1981-01-01

    An important consideration in chemical process control is to determine the precise rationing of reactant streams, particularly when a large time delay exists between the mixing of the reactants and the measurement of the product. In this paper, a method is described for incorporating chemical kinetic models into the control strategy in order to achieve optimum operating conditions. The system is first characterized by determining a reaction rate surface as a function of all input reactant concentrations over a feasible range. A nonlinear constrained optimization program is then used to determine the combination of reactants which produces the specified yield at minimum cost. This operating condition is then used to establish the nominal concentrations of the reactants. The actual operation is determined through a feedback control system employing a Smith predictor. The method is demonstrated on a laboratory bench scale enzyme reactor

  8. Energetic Mapping of Ni Catalysts by Detailed Kinetic Modeling

    DEFF Research Database (Denmark)

    Bjørgum, Erlend; Chen, De; Bakken, Mari G.

    2005-01-01

    Temperature-programmed desorption (TPD) of CO has been performed on supported and unsupported nickel catalysts. The unsupported Ni catalyst consists of a Ni(14 13 13) single crystal which has been studied under ultrahigh vacuum conditions. The desorption energy for CO at low CO surface coverage...... was found to be 119 kJ/mol, and the binding energy of C to the Ni(111) surface of the crystal was 703 kJ/mol. The supported catalysts consist of nickel supported on hydrotalcite-like compounds with three different Mg2+/Al3+ ratios. The experimental results show that for the supported Ni catalysts TPD of CO...... precursor seems to result in more steplike sites, kinks, and defects for carbon monoxide dissociation. A detailed kinetic modeling of the TPO results based on elementary reaction steps has been conducted to give an energetic map of supported Ni catalysts. Experimental results from the ideal Ni surface fit...

  9. Formulation and kinetic modeling of curcumin loaded intranasal mucoadhesive microemulsion

    Directory of Open Access Journals (Sweden)

    B Mikesh Patel

    2012-01-01

    Full Text Available It is a challenge to develop the optimum dosage form of poorly water-soluble drugs and to target them due to limited bioavailability, intra and inter subject variability. In this investigation, mucoadhesive microemulsion of curcumin was developed by water titration method taking biocompatible components for intranasal delivery and was characterized. Nasal ciliotoxicity studies were carried out using excised sheep nasal mucosa. in vitro release studies of formulations and PDS were performed. Labrafil M 1944 CS based microemulsion was transparent, stable and nasal non-ciliotoxic having particle size 12.32±0.81nm (PdI=0.223 and from kinetic modeling, the release was found to be Fickian diffusion for mucoadhesive microemulsion.

  10. Effective-field theory on the kinetic Ising model

    International Nuclear Information System (INIS)

    Shi Xiaoling; Wei Guozhu; Li Lin

    2008-01-01

    As an analytical method, the effective-field theory (EFT) is used to study the dynamical response of the kinetic Ising model in the presence of a sinusoidal oscillating field. The effective-field equations of motion of the average magnetization are given for the square lattice (Z=4) and the simple cubic lattice (Z=6), respectively. The dynamic order parameter, the hysteresis loop area and the dynamic correlation are calculated. In the field amplitude h 0 /ZJ-temperature T/ZJ plane, the phase boundary separating the dynamic ordered and the disordered phase has been drawn, and the dynamical tricritical point has been observed. We also make the compare results of EFT with that given by using the mean field theory (MFT)

  11. Testing a dissipative kinetic k-essence model

    Energy Technology Data Exchange (ETDEWEB)

    Cardenas, Victor H.; Villanueva, J.R. [Universidad de Valparaiso, Instituto de Fisica y Astronomia, Valparaiso (Chile); Centro de Astrofisica de Valparaiso, Valparaiso (Chile); Cruz, Norman [Universidad de Santiago de Chile, Departamento de Fisica, Santiago (Chile)

    2015-04-01

    In thiswork,we present a study of a purely kinetic k-essence model, characterized basically by a parameter α in presence of a bulk dissipative term, whose relationship between viscous pressure Π and energy density ρ of the background follows a polytropic type law, Π ∝ ρ{sup λ+1/2}, where λ, in principle, is a parameter without restrictions. Analytical solutions for the energy density of the k-essence field are found in two specific cases: λ = 1/2 and λ = (1 - α)/2α, and then we show that these solutions possess the same functional form as the non-viscous counterpart. Finally, both approaches are contrasted with observational data from type Ia supernova, and the most recent Hubble parameter measurements, and therefore, the best values for the parameters of the theory are found. (orig.)

  12. Mechanism of nitric acid reduction and kinetic modelling

    International Nuclear Information System (INIS)

    Sicsic, David; Balbaud-Celerier, Fanny; Tribollet, Bernard

    2014-01-01

    In France, the recycling of nuclear waste fuels involves the use of hot concentrated nitric acid. The understanding and prediction of the behaviour of the structural materials (mainly austenitic stainless steels) requires the determination and modelling of the nitric acid reduction process. Nitric acid is indirectly reduced by an autocatalytic mechanism depending on the cathodic overpotential and acid concentration. This mechanism has been widely studied. All the authors agree on its autocatalytic nature, characterized by the predominant role of the reduction products. It is also generally admitted that neither nitric acid nor the nitrate ion is the electro-active species. However, the nature of the electro-active species, the place where the catalytic species regenerates and the thermodynamic and kinetic behaviour of the reaction intermediates remain uncertain. The aim of this study was to clarify some of these uncertainties by performing an electrochemical investigation of the reduction of 4 M nitric acid at 40 C at an inert electrode (platinum or gold). An inert electrode was chosen as the working electrode in a first step to avoid its oxidation and focus the research on the reduction mechanism. This experimental work enabled us to suggest a coherent sequence of electrochemical and chemical reactions. Kinetic modelling of this sequence was then carried out for a gold rotating disk electrode. A thermodynamic study at 25 C allowed the composition of the liquid and gaseous phases of nitric acid solutions in the concentration range 0.5-22 M to be evaluated. The kinetics of the reduction of 4 M nitric acid was investigated by cyclic voltammetry and chrono-amperometry at an inert electrode at 40 C. The coupling of chrono-amperometry and FTIR spectroscopy in the gaseous phase led to the identification of the gaseous reduction products as a function of the cathodic overpotential. The results showed that the reduction process is autocatalytic for potentials between 0

  13. High fidelity kinetic modeling of magnetic reconnection in laboratory plasma

    Science.gov (United States)

    Stanier, A.; Daughton, W. S.

    2017-12-01

    Over the past decade, a great deal of progress has been made towards understanding the physics of magnetic reconnection in weakly collisional regimes of relevance to both fusion devices, and to space and astrophysical plasmas. However, there remain some outstanding unsolved problems in reconnection physics, such as the generation and influence of plasmoids (flux ropes) within reconnection layers, the development of magnetic turbulence, the role of current driven and streaming instabilities, and the influence of electron pressure anisotropy on the layer structure. Due to the importance of these questions, new laboratory reconnection experiments are being built to allow controlled and reproducible study of such questions with the simultaneous acquisition of high time resolution measurements at a large number of spatial points. These experiments include the FLARE facility at Princeton University and the T-REX experiment at the University of Wisconsin. To guide and interpret these new experiments, and to extrapolate the results to space applications, new investments in kinetic modeling tools are required. We have recently developed a cylindrical version of the VPIC Particle-In-Cell code with the capability to perform first-principles kinetic simulations that approach experimental device size with more realistic geometry and drive coils. This cylindrical version inherits much of the optimization work that has been done recently for the next generation many-cores architectures with wider vector registers, and achieves comparable conservation properties as the Cartesian code. Namely it features exact discrete charge conservation, and a so-called "energy-conserving" scheme where the energy is conserved in the limit of continuous time, i.e. without contribution from spatial discretization (Lewis, 1970). We will present initial results of modeling magnetic reconnection in the experiments mentioned above. Since the VPIC code is open source (https

  14. Orestes Kinetics Model for the Electra KrF Laser

    Science.gov (United States)

    Giuliani, J. L.; Kepple, P.; Lehmberg, R. H.; Myers, M. C.; Sethian, J. D.; Petrov, G.; Wolford, M.; Hegeler, F.

    2003-10-01

    Orestes is a first principles simulation code for the electron deposition, plasma chemistry, laser transport, and amplified spontaneous emission (ASE) in an e-beam pumped KrF laser. Orestes has been benchmarked against results from Nike at NRL and the Keio laser facility. The modeling tasks are to support ongoing oscillator experiments on the Electra laser ( 500 J), to predict performance of Electra as an amplifier, and to develop scaling relations for larger systems such as envisioned for an inertial fusion energy power plant. In Orestes the energy deposition of the primary beam electrons is assumed to be spatially uniform, but the excitation and ionization of the Ar/Kr/F2 target gas by the secondary electrons is determined from the energy distribution function as calculated by a Boltzmann code. The subsequent plasma kinetics of 23 species subject to over 100 reactions is followed with 1-D spatial resolution along the lasing axis. In addition, the vibrational relaxation among excited electronic states of the KrF molecule are included in the kinetics since lasing at 248 nm can occur from several vibrational lines of the B state. Transport of the lasing photons is solved by the method of characteristics. The time dependent ASE is calculated in 3-D using a ``local look-back'' scheme with discrete ordinates and includes specular reflection off the side walls and rear mirror. Gain narrowing is treated by multi-frequency transport of the ASE. Calculations for the gain, saturation intensity, extraction efficiency, and laser output from the Orestes model will be presented and compared with available data from Electra operated as an oscillator. Potential implications for the difference in optimal F2 concentration will be discussed along with the effects of window transmissivity at 248 nm.

  15. Mechanistic kinetic models of enzymatic cellulose hydrolysis-A review.

    Science.gov (United States)

    Jeoh, Tina; Cardona, Maria J; Karuna, Nardrapee; Mudinoor, Akshata R; Nill, Jennifer

    2017-07-01

    Bioconversion of lignocellulose forms the basis for renewable, advanced biofuels, and bioproducts. Mechanisms of hydrolysis of cellulose by cellulases have been actively studied for nearly 70 years with significant gains in understanding of the cellulolytic enzymes. Yet, a full mechanistic understanding of the hydrolysis reaction has been elusive. We present a review to highlight new insights gained since the most recent comprehensive review of cellulose hydrolysis kinetic models by Bansal et al. (2009) Biotechnol Adv 27:833-848. Recent models have taken a two-pronged approach to tackle the challenge of modeling the complex heterogeneous reaction-an enzyme-centric modeling approach centered on the molecularity of the cellulase-cellulose interactions to examine rate limiting elementary steps and a substrate-centric modeling approach aimed at capturing the limiting property of the insoluble cellulose substrate. Collectively, modeling results suggest that at the molecular-scale, how rapidly cellulases can bind productively (complexation) and release from cellulose (decomplexation) is limiting, while the overall hydrolysis rate is largely insensitive to the catalytic rate constant. The surface area of the insoluble substrate and the degrees of polymerization of the cellulose molecules in the reaction both limit initial hydrolysis rates only. Neither enzyme-centric models nor substrate-centric models can consistently capture hydrolysis time course at extended reaction times. Thus, questions of the true reaction limiting factors at extended reaction times and the role of complexation and decomplexation in rate limitation remain unresolved. Biotechnol. Bioeng. 2017;114: 1369-1385. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

  16. Detailed kinetic modeling study of n-pentanol oxidation

    KAUST Repository

    Heufer, Karl Alexander; Sarathy, Mani; Curran, Henry J.; Davis, Alexander C.; Westbrook, Charles K.; Pitz, William J.

    2012-01-01

    To help overcome the world's dependence upon fossil fuels, suitable biofuels are promising alternatives that can be used in the transportation sector. Recent research on internal combustion engines shows that short alcoholic fuels (e.g., ethanol or n-butanol) have reduced pollutant emissions and increased knock resistance compared to fossil fuels. Although higher molecular weight alcohols (e.g., n-pentanol and n-hexanol) exhibit higher reactivity that lowers their knock resistance, they are suitable for diesel engines or advanced engine concepts, such as homogeneous charge compression ignition (HCCI), where higher reactivity at lower temperatures is necessary for engine operation. The present study presents a detailed kinetic model for n-pentanol based on modeling rules previously presented for n-butanol. This approach was initially validated using quantum chemistry calculations to verify the most stable n-pentanol conformation and to obtain C-H and C-C bond dissociation energies. The proposed model has been validated against ignition delay time data, speciation data from a jet-stirred reactor, and laminar flame velocity measurements. Overall, the model shows good agreement with the experiments and permits a detailed discussion of the differences between alcohols and alkanes. © 2012 American Chemical Society.

  17. Bayesian inference for hybrid discrete-continuous stochastic kinetic models

    International Nuclear Information System (INIS)

    Sherlock, Chris; Golightly, Andrew; Gillespie, Colin S

    2014-01-01

    We consider the problem of efficiently performing simulation and inference for stochastic kinetic models. Whilst it is possible to work directly with the resulting Markov jump process (MJP), computational cost can be prohibitive for networks of realistic size and complexity. In this paper, we consider an inference scheme based on a novel hybrid simulator that classifies reactions as either ‘fast’ or ‘slow’ with fast reactions evolving as a continuous Markov process whilst the remaining slow reaction occurrences are modelled through a MJP with time-dependent hazards. A linear noise approximation (LNA) of fast reaction dynamics is employed and slow reaction events are captured by exploiting the ability to solve the stochastic differential equation driving the LNA. This simulation procedure is used as a proposal mechanism inside a particle MCMC scheme, thus allowing Bayesian inference for the model parameters. We apply the scheme to a simple application and compare the output with an existing hybrid approach and also a scheme for performing inference for the underlying discrete stochastic model. (paper)

  18. Detailed kinetic modeling study of n-pentanol oxidation

    KAUST Repository

    Heufer, Karl Alexander

    2012-10-18

    To help overcome the world\\'s dependence upon fossil fuels, suitable biofuels are promising alternatives that can be used in the transportation sector. Recent research on internal combustion engines shows that short alcoholic fuels (e.g., ethanol or n-butanol) have reduced pollutant emissions and increased knock resistance compared to fossil fuels. Although higher molecular weight alcohols (e.g., n-pentanol and n-hexanol) exhibit higher reactivity that lowers their knock resistance, they are suitable for diesel engines or advanced engine concepts, such as homogeneous charge compression ignition (HCCI), where higher reactivity at lower temperatures is necessary for engine operation. The present study presents a detailed kinetic model for n-pentanol based on modeling rules previously presented for n-butanol. This approach was initially validated using quantum chemistry calculations to verify the most stable n-pentanol conformation and to obtain C-H and C-C bond dissociation energies. The proposed model has been validated against ignition delay time data, speciation data from a jet-stirred reactor, and laminar flame velocity measurements. Overall, the model shows good agreement with the experiments and permits a detailed discussion of the differences between alcohols and alkanes. © 2012 American Chemical Society.

  19. Critical Analysis of Underground Coal Gasification Models. Part II: Kinetic and Computational Fluid Dynamics Models

    Directory of Open Access Journals (Sweden)

    Alina Żogała

    2014-01-01

    Originality/value: This paper presents state of art in the field of coal gasification modeling using kinetic and computational fluid dynamics approach. The paper also presents own comparative analysis (concerned with mathematical formulation, input data and parameters, basic assumptions, obtained results etc. of the most important models of underground coal gasification.

  20. Physical, mechanical and hydration kinetics of particleboards manufactured with woody biomass (Cupressus lusitanica, Gmelina arborea, Tectona grandis), agricultural resources, and Tetra Pak packages.

    Science.gov (United States)

    Moya, Róger; Camacho, Diego; Oporto, Gloria S; Soto, Roy F; Mata, Julio S

    2014-02-01

    Lignocellulosic wastes resulting from agricultural activities as well as Tetra Pak residues from urban centres can cause significant levels of pollution. A possible action to minimize this problem is to use them in the production of particleboards. The purpose of this study was to evaluate the physical, mechanical, and hydration properties of particleboards manufactured with the mixture of woody biomass (Cupressus lusitanica, Gmelina arborea, and Tectona grandis) and either agricultural wastes [pineapple leaves (Ananas comosus) and palm residues (Elaeis guineensis)] or Tetra Pak residues (TP). The results show that the particleboards prepared with TP and woody biomass can reduce the swelling and water absorption in up to 40% and 50% compared with particleboards without TP. Also, these particleboards had increased flexure resistance and shear stress (up to 100%) compared with those without TP. On the contrary, particleboards prepared with pineapple leaves in combination with woody biomass showed the lowest mechanical properties, particularly for tensile strength, hardness, glue-line shear, and nail and screw evaluation.

  1. Treatment of polymer surfaces in plasma Part I. Kinetic model

    International Nuclear Information System (INIS)

    Tabaliov, N A; Svirachev, D M

    2006-01-01

    The surface tension of the polymer materials depends on functional groups over its surface. As a result from the plasma treatment the kind and concentration of the functional groups can be changed. In the present work, the possible kinetic reactions are defined. They describe the interaction between the plasma and the polymer surface of polyethylene terephthalate (PET). Basing on these reactions, the systems of differential kinetic equations are suggested. The solutions are obtained analytically for the system kinetic equations at defined circumstances

  2. Modeling the Alzheimer Abeta17-42 fibril architecture: tight intermolecular sheet-sheet association and intramolecular hydrated cavities.

    Science.gov (United States)

    Zheng, Jie; Jang, Hyunbum; Ma, Buyong; Tsai, Chung-Jun; Nussinov, Ruth

    2007-11-01

    We investigate Abeta(17-42) protofibril structures in solution using molecular dynamics simulations. Recently, NMR and computations modeled the Abeta protofibril as a longitudinal stack of U-shaped molecules, creating an in-parallel beta-sheet and loop spine. Here we study the molecular architecture of the fibril formed by spine-spine association. We model in-register intermolecular beta-sheet-beta-sheet associations and study the consequences of Alzheimer's mutations (E22G, E22Q, E22K, and M35A) on the organization. We assess the structural stability and association force of Abeta oligomers with different sheet-sheet interfaces. Double-layered oligomers associating through the C-terminal-C-terminal interface are energetically more favorable than those with the N-terminal-N-terminal interface, although both interfaces exhibit high structural stability. The C-terminal-C-terminal interface is essentially stabilized by hydrophobic and van der Waals (shape complementarity via M35-M35 contacts) intermolecular interactions, whereas the N-terminal-N-terminal interface is stabilized by hydrophobic and electrostatic interactions. Hence, shape complementarity, or the "steric zipper" motif plays an important role in amyloid formation. On the other hand, the intramolecular Abeta beta-strand-loop-beta-strand U-shaped motif creates a hydrophobic cavity with a diameter of 6-7 A, allowing water molecules and ions to conduct through. The hydrated hydrophobic cavities may allow optimization of the sheet association and constitute a typical feature of fibrils, in addition to the tight sheet-sheet association. Thus, we propose that Abeta fiber architecture consists of alternating layers of tight packing and hydrated cavities running along the fibrillar axis, which might be possibly detected by high-resolution imaging.

  3. A Hydrate Database: Vital to the Technical Community

    Directory of Open Access Journals (Sweden)

    D Sloan

    2007-06-01

    Full Text Available Natural gas hydrates may contain more energy than all the combined other fossil fuels, causing hydrates to be a potentially vital aspect of both energy and climate change. This article is an overview of the motivation, history, and future of hydrate data management using a CODATA vehicle to connect international hydrate databases. The basis is an introduction to the Gas Hydrate Markup Language (GHML to connect various hydrate databases. The accompanying four articles on laboratory hydrate data by Smith et al., on field hydrate data by L?wner et al., on hydrate modeling by Wang et al., and on construction of a Chinese gas hydrate system by Xiao et al. provide details of GHML in their respective areas.

  4. In situ Low-temperature Pair Distribution Function (PDF) Analysis of CH4 and CO2 Hydrates

    Science.gov (United States)

    Cladek, B.; Everett, M.; McDonnell, M.; Tucker, M.; Keffer, D.; Rawn, C.

    2017-12-01

    Gas hydrates occur in ocean floor and sub-surface permafrost deposits and are stable at moderate to high pressures and low temperatures. They are a clathrate structure composed of hydrogen bonded water cages that accommodate a wide variety of guest molecules. CO2 and CH4 hydrates both crystallize as the cubic sI hydrate and can form a solid solution. Natural gas hydrates are interesting as a potential methane source and for CO2 sequestration. Long-range diffraction studies on gas hydrates give valuable structural information but do not provide a detailed understanding of the disordered gas molecule interactions with the host lattice. In-situ low temperature total scattering experiments combined with pair distribution function (PDF) analysis are used to investigate the gas molecule motions and guest-cage interactions. CO2 and methane hydrates exhibit different decomposition behavior, and CO2 hydrate has a smaller lattice parameter despite it being a relatively larger molecule. Total scattering studies characterizing both the short- and long-range order simultaneously help to elucidate the structural source of these phenomena. Low temperature neutron total scattering data were collected using the Nanoscale Ordered MAterials Diffractometer (NOMAD) beamline at the Spallation Neutron Source (SNS) on CO2 and CH4 hydrates synthesized with D2O. Guest molecule motion within cages and interactions between gases and cages are investigated through the hydrate stability and decomposition regions. Data were collected from 2-80 K at a pressure of 55 mbar on CO2 and CH4 hydrates, and from 80-270 K at 25 bar on CH4 hydrate. The hydrate systems were modeled with classical molecular dynamic (MD) simulations to provide an analysis of the total energy into guest-guest, guest-host and host-host contributions. Combined Reitveld and Reverse Monte Carlo (RMC) structure refinement were used to fit models of the data. This combined modeling and simulation characterizes the effects of CO2 and

  5. Model of SNARE-mediated membrane adhesion kinetics.

    Directory of Open Access Journals (Sweden)

    Jason M Warner

    Full Text Available SNARE proteins are conserved components of the core fusion machinery driving diverse membrane adhesion and fusion processes in the cell. In many cases micron-sized membranes adhere over large areas before fusion. Reconstituted in vitro assays have helped isolate SNARE mechanisms in small membrane adhesion-fusion and are emerging as powerful tools to study large membrane systems by use of giant unilamellar vesicles (GUVs. Here we model SNARE-mediated adhesion kinetics in SNARE-reconstituted GUV-GUV or GUV-supported bilayer experiments. Adhesion involves many SNAREs whose complexation pulls apposing membranes into contact. The contact region is a tightly bound rapidly expanding patch whose growth velocity v(patch increases with SNARE density Gamma(snare. We find three patch expansion regimes: slow, intermediate, fast. Typical experiments belong to the fast regime where v(patch ~ (Gamma(snare(2/3 depends on SNARE diffusivities and complexation binding constant. The model predicts growth velocities ~10 - 300 microm/s. The patch may provide a close contact region where SNAREs can trigger fusion. Extending the model to a simple description of fusion, a broad distribution of fusion times is predicted. Increasing SNARE density accelerates fusion by boosting the patch growth velocity, thereby providing more complexes to participate in fusion. This quantifies the notion of SNAREs as dual adhesion-fusion agents.

  6. Modelling and parallel calculation of a kinetic boundary layer

    International Nuclear Information System (INIS)

    Perlat, Jean Philippe

    1998-01-01

    This research thesis aims at addressing reliability and cost issues in the calculation by numeric simulation of flows in transition regime. The first step has been to reduce calculation cost and memory space for the Monte Carlo method which is known to provide performance and reliability for rarefied regimes. Vector and parallel computers allow this objective to be reached. Here, a MIMD (multiple instructions, multiple data) machine has been used which implements parallel calculation at different levels of parallelization. Parallelization procedures have been adapted, and results showed that parallelization by calculation domain decomposition was far more efficient. Due to reliability issue related to the statistic feature of Monte Carlo methods, a new deterministic model was necessary to simulate gas molecules in transition regime. New models and hyperbolic systems have therefore been studied. One is chosen which allows thermodynamic values (density, average velocity, temperature, deformation tensor, heat flow) present in Navier-Stokes equations to be determined, and the equations of evolution of thermodynamic values are described for the mono-atomic case. Numerical resolution of is reported. A kinetic scheme is developed which complies with the structure of all systems, and which naturally expresses boundary conditions. The validation of the obtained 14 moment-based model is performed on shock problems and on Couette flows [fr

  7. Modeling thermodynamic properties of propane or tetrahydrofuran mixed with carbon dioxide or methane in structure-II clathrate hydrates

    NARCIS (Netherlands)

    Fang, Bin; Ning, Fulong; Cao, Pinqiang; Peng, Li; Wu, Jianyang; Zhang, Zhun; Vlugt, T.J.H.; Kjelstrup, Signe

    2017-01-01

    A sound knowledge of thermodynamic properties of sII hydrates is of great importance to understand the stability of sII gas hydrates in petroleum pipelines and in natural settings. Here, we report direct molecular dynamics (MD) simulations of the thermal expansion coefficient, the

  8. Heterogeneous kinetic modeling of the catalytic conversion of cycloparaffins

    Science.gov (United States)

    Al-Sabawi, Mustafa N.

    catalytic conversions respectively, are reported. Using these data, heterogeneous kinetic models accounting for intracrystallite molecular transport, adsorption and thermal and catalytic cracking of both cycloparaffin reactants are established. Results show that undesirable hydrogen transfer reactions are more pronounced and selectively favoured against other reactions at lower reaction temperatures, while the desirable ring-opening and cracking reactions predominate at the higher reaction temperatures. Moreover, results of the present work show that while crystallite size may have an effect on the overall conversion in some situations, there is a definite effect on the selectivity of products obtained during the cracking of MCH and decalin and the cracking of MCH in a mixture with co-reactants such as 1,3,5-triisopropylbenzene. Keywords. cycloparaffins, naphthenes, fluid catalytic cracking, kinetic modeling, Y-zeolites, diffusion, adsorption, ring-opening, hydrogen transfer, catalyst selectivity.

  9. Satl model lesson in chemical kinetics | Nazir | African Journal of ...

    African Journals Online (AJOL)

    Studies in order to pursue kinetics and mechanism of chemical reactions are a vital component of chemical literature. SATL literature is still not available for promoting this vital aspect of chemistry teaching. A lesson pertaining to this important issue has been developed and various parameters of kinetic studies are ...

  10. Chemical kinetic model uncertainty minimization through laminar flame speed measurements

    Science.gov (United States)

    Park, Okjoo; Veloo, Peter S.; Sheen, David A.; Tao, Yujie; Egolfopoulos, Fokion N.; Wang, Hai

    2016-01-01

    Laminar flame speed measurements were carried for mixture of air with eight C3-4 hydrocarbons (propene, propane, 1,3-butadiene, 1-butene, 2-butene, iso-butene, n-butane, and iso-butane) at the room temperature and ambient pressure. Along with C1-2 hydrocarbon data reported in a recent study, the entire dataset was used to demonstrate how laminar flame speed data can be utilized to explore and minimize the uncertainties in a reaction model for foundation fuels. The USC Mech II kinetic model was chosen as a case study. The method of uncertainty minimization using polynomial chaos expansions (MUM-PCE) (D.A. Sheen and H. Wang, Combust. Flame 2011, 158, 2358–2374) was employed to constrain the model uncertainty for laminar flame speed predictions. Results demonstrate that a reaction model constrained only by the laminar flame speed values of methane/air flames notably reduces the uncertainty in the predictions of the laminar flame speeds of C3 and C4 alkanes, because the key chemical pathways of all of these flames are similar to each other. The uncertainty in model predictions for flames of unsaturated C3-4 hydrocarbons remain significant without considering fuel specific laminar flames speeds in the constraining target data set, because the secondary rate controlling reaction steps are different from those in the saturated alkanes. It is shown that the constraints provided by the laminar flame speeds of the foundation fuels could reduce notably the uncertainties in the predictions of laminar flame speeds of C4 alcohol/air mixtures. Furthermore, it is demonstrated that an accurate prediction of the laminar flame speed of a particular C4 alcohol/air mixture is better achieved through measurements for key molecular intermediates formed during the pyrolysis and oxidation of the parent fuel. PMID:27890938

  11. Modeling turbulence structure. Chemical kinetics interaction in turbulent reactive flows

    Energy Technology Data Exchange (ETDEWEB)

    Magnussen, B F [The Norwegian Univ. of Science and Technology, Trondheim (Norway)

    1998-12-31

    The challenge of the mathematical modelling is to transfer basic physical knowledge into a mathematical formulation such that this knowledge can be utilized in computational simulation of practical problems. The combustion phenomena can be subdivided into a large set of interconnected phenomena like flow, turbulence, thermodynamics, chemical kinetics, radiation, extinction, ignition etc. Combustion in one application differs from combustion in another area by the relative importance of the various phenomena. The difference in fuel, geometry and operational conditions often causes the differences. The computer offers the opportunity to treat the individual phenomena and their interactions by models with wide operational domains. The relative magnitude of the various phenomena therefore becomes the consequence of operational conditions and geometry and need not to be specified on the basis of experience for the given problem. In mathematical modelling of turbulent combustion, one of the big challenges is how to treat the interaction between the chemical reactions and the fluid flow i.e. the turbulence. Different scientists adhere to different concepts like the laminar flamelet approach, the pdf approach of the Eddy Dissipation Concept. Each of these approaches offers different opportunities and problems. All these models are based on a sound physical basis, however none of these have general validity in taking into consideration all detail of the physical chemical interaction. The merits of the models can only be judged by their ability to reproduce physical reality and consequences of operational and geometric conditions in a combustion system. The presentation demonstrates and discusses the development of a coherent combustion technology for energy conversion and safety based on the Eddy Dissipation Concept by Magnussen. (author) 30 refs.

  12. Modeling turbulence structure. Chemical kinetics interaction in turbulent reactive flows

    Energy Technology Data Exchange (ETDEWEB)

    Magnussen, B.F. [The Norwegian Univ. of Science and Technology, Trondheim (Norway)

    1997-12-31

    The challenge of the mathematical modelling is to transfer basic physical knowledge into a mathematical formulation such that this knowledge can be utilized in computational simulation of practical problems. The combustion phenomena can be subdivided into a large set of interconnected phenomena like flow, turbulence, thermodynamics, chemical kinetics, radiation, extinction, ignition etc. Combustion in one application differs from combustion in another area by the relative importance of the various phenomena. The difference in fuel, geometry and operational conditions often causes the differences. The computer offers the opportunity to treat the individual phenomena and their interactions by models with wide operational domains. The relative magnitude of the various phenomena therefore becomes the consequence of operational conditions and geometry and need not to be specified on the basis of experience for the given problem. In mathematical modelling of turbulent combustion, one of the big challenges is how to treat the interaction between the chemical reactions and the fluid flow i.e. the turbulence. Different scientists adhere to different concepts like the laminar flamelet approach, the pdf approach of the Eddy Dissipation Concept. Each of these approaches offers different opportunities and problems. All these models are based on a sound physical basis, however none of these have general validity in taking into consideration all detail of the physical chemical interaction. The merits of the models can only be judged by their ability to reproduce physical reality and consequences of operational and geometric conditions in a combustion system. The presentation demonstrates and discusses the development of a coherent combustion technology for energy conversion and safety based on the Eddy Dissipation Concept by Magnussen. (author) 30 refs.

  13. Thermodynamic model for predicting equilibrium conditions of clathrate hydrates of noble gases + light hydrocarbons: Combination of Van der Waals–Platteeuw model and sPC-SAFT EoS

    International Nuclear Information System (INIS)

    Abolala, Mostafa; Varaminian, Farshad

    2015-01-01

    Highlights: • Applying sPC-SAFT for phase equilibrium calculations. • Determining Kihara potential parameters for hydrate formers. • Successful usage of the model for systems with hydrate azeotropes. - Abstract: In this communication, equilibrium conditions of clathrate hydrates containing mixtures of noble gases (Argon, Krypton and Xenon) and light hydrocarbons (C 1 –C 3 ), which form structure I and II, are modeled. The thermodynamic model is based on the solid solution theory of Van der Waals–Platteeuw combined with the simplified Perturbed-Chain Statistical Association Fluid Theory equation of state (sPC-SAFT EoS). In dispersion term of sPC-SAFT EoS, the temperature dependent binary interaction parameters (k ij ) are adjusted; taking advantage of the well described (vapor + liquid) phase equilibria. Furthermore, the Kihara potential parameters are optimized based on the P–T data of pure hydrate former. Subsequently, these obtained parameters are used to predict the binary gas hydrate dissociation conditions. The equilibrium conditions of the binary gas hydrates predicted by this model agree well with experimental data (overall AAD P ∼ 2.17)

  14. Kinetic Modeling of a Heterogeneous Fenton Oxidative Treatment of Petroleum Refining Wastewater

    Science.gov (United States)

    Basheer Hasan, Diya'uddeen; Abdul Raman, Abdul Aziz; Wan Daud, Wan Mohd Ashri

    2014-01-01

    The mineralisation kinetics of petroleum refinery effluent (PRE) by Fenton oxidation were evaluated. Within the ambit of the experimental data generated, first-order kinetic model (FKM), generalised lumped kinetic model (GLKM), and generalized kinetic model (GKM) were tested. The obtained apparent kinetic rate constants for the initial oxidation step (k 2′), their final oxidation step (k 1′), and the direct conversion to endproducts step (k 3′) were 10.12, 3.78, and 0.24 min−1 for GKM; 0.98, 0.98, and nil min−1 for GLKM; and nil, nil, and >0.005 min−1 for FKM. The findings showed that GKM is superior in estimating the mineralization kinetics. PMID:24592152

  15. Sorption kinetics of superabsorbent polymers (SAPs) in fresh Portland cement-based pastes visualized and quantified by neutron radiography and correlated to the progress of cement hydration

    Energy Technology Data Exchange (ETDEWEB)

    Schroefl, Christof, E-mail: christof.schroefl@tu-dresden.de [Technische Universität Dresden, Fakultät Bauingenieurwesen, Institut für Baustoffe, DE-01062 Dresden (Germany); Mechtcherine, Viktor [Technische Universität Dresden, Fakultät Bauingenieurwesen, Institut für Baustoffe, DE-01062 Dresden (Germany); Vontobel, Peter; Hovind, Jan; Lehmann, Eberhard [Paul Scherrer Institut, Laboratory for Neutron Scattering and Imaging, CH-5232 Villigen/AG (Switzerland)

    2015-09-15

    Water sorption of two superabsorbent polymers in cement-based pastes has been characterized by neutron radiography. Cement pastes with W/C of 0.25 and 0.50 and one additionally containing silica fume (W/C = 0.42) were investigated. The SAPs differed in their inherent sorption kinetics in extracted cement pore solution (SAP 1: self-releasing; SAP 2: retentive). Desorption from SAP 1 started very early after paste preparation. Hence, its individual non-retentiveness governs its behavior only. SAP 2 released water into all matrices, but its kinetics were different. In the paste with the highest W/C, some moderate water release was recorded from the beginning. In the other two pastes, SAP 2 retained its stored liquid during the dormant period, i.e., up to the percolation threshold. Intense desorption then set in and continued throughout the acceleration period. These findings explain the pronouncedly higher efficiency of SAP 2 as internal curing admixture as compared to SAP 1.

  16. Sorption kinetics of superabsorbent polymers (SAPs) in fresh Portland cement-based pastes visualized and quantified by neutron radiography and correlated to the progress of cement hydration

    International Nuclear Information System (INIS)

    Schroefl, Christof; Mechtcherine, Viktor; Vontobel, Peter; Hovind, Jan; Lehmann, Eberhard

    2015-01-01

    Water sorption of two superabsorbent polymers in cement-based pastes has been characterized by neutron radiography. Cement pastes with W/C of 0.25 and 0.50 and one additionally containing silica fume (W/C = 0.42) were investigated. The SAPs differed in their inherent sorption kinetics in extracted cement pore solution (SAP 1: self-releasing; SAP 2: retentive). Desorption from SAP 1 started very early after paste preparation. Hence, its individual non-retentiveness governs its behavior only. SAP 2 released water into all matrices, but its kinetics were different. In the paste with the highest W/C, some moderate water release was recorded from the beginning. In the other two pastes, SAP 2 retained its stored liquid during the dormant period, i.e., up to the percolation threshold. Intense desorption then set in and continued throughout the acceleration period. These findings explain the pronouncedly higher efficiency of SAP 2 as internal curing admixture as compared to SAP 1

  17. Electron kinetics modeling in a weakly ionized gas

    International Nuclear Information System (INIS)

    Boeuf, Jean-Pierre

    1985-01-01

    This work presents some features of electron kinetics in a weakly ionized gas. After a summary of the basis and recent developments of the kinetic theory, and a review of the most efficient numerical techniques for solving the Boltzmann equation, several aspects of electron motion in gases are analysed. Relaxation phenomena toward equilibrium under a uniform electric field, and the question of the existence of the hydrodynamic regime are first studied. The coupling between electron kinetics and chemical kinetics due to second kind collisions in Nitrogen is then analysed; a quantitative description of the evolution of the energy balance, accounting for electron-molecule as well as molecule-molecule energy transfer is also given. Finally, electron kinetics in space charge distorted, highly non uniform electric fields (glow discharges, streamers propagation) is investigated with microscopic numerical methods based on Boltzmann and Poisson equations. (author) [fr

  18. Water sorption kinetics of damaged beans: GAB model

    Directory of Open Access Journals (Sweden)

    Fernanda M. Baptestini

    Full Text Available ABSTRACT The objective of this study was to model the water sorption kinetics of damaged beans. Grains with initial moisture content of 53.85%, dry basis (d.b., were used. One portion of the grains was used to obtain desorption isotherms, while the other was subjected to drying until the moisture content of 5.26% (d.b., so that it was subjected to the adsorption. For the induction of damage, a Stein Breakage Tester was used. To obtain the equilibrium moisture content, grains were placed in a climatic chamber at 20, 30, 40 and 50 ± 1 °C combined with relative humidity of 30, 40, 50, 70 and 90 ± 3%. The GAB model fitted well to the equilibrium moisture experimental data of damaged grains and control. With increasing temperature, the monolayer moisture contents decreased in adsorption and desorption processes, ranging from 9.84 to 5.10% d.b. The lower moisture content in the monolayer in damaged grains indicates that lower moisture content is necessary to ensure their conservation.

  19. A Kinetics Model for KrF Laser Amplifiers

    Science.gov (United States)

    Giuliani, J. L.; Kepple, P.; Lehmberg, R.; Obenschain, S. P.; Petrov, G.

    1999-11-01

    A computer kinetics code has been developed to model the temporal and spatial behavior of an e-beam pumped KrF laser amplifier. The deposition of the primary beam electrons is assumed to be spatially uniform and the energy distribution function of the nascent electron population is calculated to be near Maxwellian below 10 eV. For an initial Kr/Ar/F2 composition, the code calculates the densities of 24 species subject to over 100 reactions with 1-D spatial resolution (typically 16 zones) along the longitudinal lasing axis. Enthalpy accounting for each process is performed to partition the energy into internal, thermal, and radiative components. The electron as well as the heavy particle temperatures are followed for energy conservation and excitation rates. Transport of the lasing photons is performed along the axis on a dense subgrid using the method of characteristics. Amplified spontaneous emission is calculated using a discrete ordinates approach and includes contributions to the local intensity from the whole amplifier volume. Specular reflection off side walls and the rear mirror are included. Results of the model will be compared with data from the NRL NIKE laser and other published results.

  20. Challenges for the kinetic unified dark matter model

    International Nuclear Information System (INIS)

    Giannakis, Dimitrios; Hu, Wayne

    2005-01-01

    Given that the dark matter and dark energy in the Universe affect cosmological observables only gravitationally, their phenomenology may be described by a single stress-energy tensor. True unification however requires a theory that reproduces the successful phenomenology of ΛCDM and that requirement places specific constraints on the stress structure of the matter. We show that a recently proposed unification through an offset quadratic kinetic term for a scalar field is exactly equivalent to a fluid with a closed-form barotropic equation of state plus cosmological constant. The finite pressure at high densities introduces a cutoff in the linear power spectrum, which may alleviate the dark matter substructure problem; we provide a convenient fitting function for such studies. Given that sufficient power must remain to reionize the Universe, the equation of state today is nonrelativistic with p∝ρ 2 and a Jeans scale in the parsec regime for all relevant densities. Structure may then be evolved into the nonlinear regime with standard hydrodynamic techniques. In fact, the model is equivalent to the well-studied collisional dark matter with negligible mean free path. If recent observations of the triaxiality of dark matter halos and ram pressure stripping in galaxy clusters are confirmed, this model will be ruled out

  1. Mesoscopic kinetic Monte Carlo modeling of organic photovoltaic device characteristics

    Science.gov (United States)

    Kimber, Robin G. E.; Wright, Edward N.; O'Kane, Simon E. J.; Walker, Alison B.; Blakesley, James C.

    2012-12-01

    Measured mobility and current-voltage characteristics of single layer and photovoltaic (PV) devices composed of poly{9,9-dioctylfluorene-co-bis[N,N'-(4-butylphenyl)]bis(N,N'-phenyl-1,4-phenylene)diamine} (PFB) and poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT) have been reproduced by a mesoscopic model employing the kinetic Monte Carlo (KMC) approach. Our aim is to show how to avoid the uncertainties common in electrical transport models arising from the need to fit a large number of parameters when little information is available, for example, a single current-voltage curve. Here, simulation parameters are derived from a series of measurements using a self-consistent “building-blocks” approach, starting from data on the simplest systems. We found that site energies show disorder and that correlations in the site energies and a distribution of deep traps must be included in order to reproduce measured charge mobility-field curves at low charge densities in bulk PFB and F8BT. The parameter set from the mobility-field curves reproduces the unipolar current in single layers of PFB and F8BT and allows us to deduce charge injection barriers. Finally, by combining these disorder descriptions and injection barriers with an optical model, the external quantum efficiency and current densities of blend and bilayer organic PV devices can be successfully reproduced across a voltage range encompassing reverse and forward bias, with the recombination rate the only parameter to be fitted, found to be 1×107 s-1. These findings demonstrate an approach that removes some of the arbitrariness present in transport models of organic devices, which validates the KMC as an accurate description of organic optoelectronic systems, and provides information on the microscopic origins of the device behavior.

  2. Natural gas hydrates. Experimental techniques and their applications

    Energy Technology Data Exchange (ETDEWEB)

    Ye, Yuguang; Liu, Changling (eds.) [Qingdao Institute of Marine Geology (China). Gas Hydrate Laboratory

    2013-07-01

    Focuses on gas hydrate experiment in laboratory. Intends to provide practical significant parameters for gas hydrate exploration and exploitation in the oceanic and permafrost environments. Consists of different themes that present up-to-date information on hydrate experiments. ''Natural Gas Hydrates: Experimental Techniques and Their Applications'' attempts to broadly integrate the most recent knowledge in the fields of hydrate experimental techniques in the laboratory. The book examines various experimental techniques in order to provide useful parameters for gas hydrate exploration and exploitation. It provides experimental techniques for gas hydrates, including the detection techniques, the thermo-physical properties, permeability and mechanical properties, geochemical abnormalities, stability and dissociation kinetics, exploitation conditions, as well as modern measurement technologies etc.

  3. Disposition of smoked cannabis with high [Delta]9-tetrahydrocannabinol content: A kinetic model.

    NARCIS (Netherlands)

    Hunault, C.C.; van Eijkeren, J.C.; Mensinga, T.T.; de Vries, I.; Leenders, M.E.C.; Meulenbelt, J.

    2010-01-01

    Introduction No model exists to describe the disposition and kinetics of inhaled cannabis containing a high THC dose. We aimed to develop a kinetic model providing estimates of the THC serum concentrations after smoking cannabis cigarettes containing high THC doses (up to 69 mg THC).Methods

  4. A kinetic model for the glucose/glycine Maillard reaction pathways

    NARCIS (Netherlands)

    Martins, S.I.F.S.; Boekel, van M.A.J.S.

    2005-01-01

    A comprehensive kinetic model for the glucose/glycine Maillard reaction is proposed based on an approach called multiresponse kinetic modelling. Special attention was paid to reactants, intermediates and end products: -fructose, N-(1-deoxy--fructos-1-yl)-glycine (DFG), 1-deoxy-2,3-hexodiulose and

  5. Thermochemical Kinetics of H2O and HNO3 on crystalline Nitric Acid Hydrates (alpha-, beta-NAT, NAD) in the range 175-200 K

    Science.gov (United States)

    Rossi, Michel J.; Iannarelli, Riccardo

    2015-04-01

    The growth of NAT (Nitric Acid Trihydrate, HNO3x3H2O) and NAD (Nitric Acid Dihydrate, HNO3x2H2O) on an ice substrate, the evaporative lifetime of NAT and NAD as well as the interconversion of alpha- and beta-NAT competing with evaporation and growth under UT/LS conditions depends on the interfacial kinetics of H2O and HNO3 vapor on the condensed phase. Despite the existence of some literature results we have embarked on a systematic investigation of the kinetics using a multidiagnostic experimental approach enabled by the simultaneous observation of both the gas (residual gas mass spectrometry) as well as the condensed phase (FTIR absorption in transmission). We report on thermochemically consistent mass accommodation coefficients alpha and absolute evaporation rates Rev/molecule s-1cm-3 as a function of temperature which yields the corresponding vapor pressures of both H2O and HNO3 in equilibrium with the crystalline phases, hence the term thermochemical kinetics. These results have been obtained using a stirred flow reactor (SFR) using a macroscopic pure ice film of 1 micron or so thickness as a starting substrate mimicking atmospheric ice particles and are reported in a phase diagram specifically addressing UT (Upper Troposphere)/LS (Lower Stratosphere) conditions as far as temperature and partial pressures are concerned. The experiments have been performed either at steady-state flow conditions or in transient supersaturation using a pulsed solenoid valve in order to generate gas pulses whose decay were subsequently monitored in real time. Special attention has been given to the effect of the stainless-steel vessel walls in that Langmuir adsorption isotherms for H2O and HNO3 have been used to correct for wall-adsorption of both probe gases. Typically, the accommodation coefficients of H2O and HNO3 are similar throughout the temperature range whereas the rates of evaporation Rev of H2O are significantly larger than for HNO3 thus leading to the difference in

  6. Growth of hydrated gel layers in nuclear waste glasses

    International Nuclear Information System (INIS)

    Sullivan, T.M.; Machiels, A.J.

    1984-01-01

    The hydration kinetics of waste glasses in contact with an aqueous solution has been studied by using three different approaches. Emphasis has been placed on modeling processes in the transition zone defined as the region in which the nature of the glass changes from the original dry glass to an open hydrated structure. The first model relies on concentration-dependent diffusion coefficients to obtain a transition zone in which the ions mobility is extremely low compared to that in the gel layer. In the second model, the transition zone and hydrated layer are treated as distinct phases and it is assumed that ion exchange at their common boundary is the rate-controlling process. The third model treats the transition zone as a thin film of constant thickness and low diffusivity. In the absence of appreciable network dissolution, all three models indicate that growth of the gel layer becomes eventually proportional to the square root of time; however, as long as processes in the transition zone are rate controlling, growth is linearly proportional to time

  7. Dsc cure kinetics of an unsaturated polyester resin using empirical kinetic model

    International Nuclear Information System (INIS)

    Abdullah, I.

    2015-01-01

    In this paper, the kinetics of curing of unsaturated polyester resin initiated with benzoyl peroxide was studied. In case of unsaturated polyester (UP) resin, isothermal test alone could not predict correctly the curing time of UP resin. Therefore, isothermal kinetic analysis through isoconventional adjustment was used to correctly predict the curing time and temperature of UP resin. Isothermal kinetic analysis through isoconversional adjustment indicated that 97% of UP resin cures in 33 min at 120 degree C. Curing of UP resin through microwaves was also studied and found that 67% of UP resin cures in 1 min at 120 degree C. The crosslinking reaction of UP resin is so fast at 120 degree C that it becomes impossible to predict correctly the curing time of UP resin using isothermal test and the burial of C=C bonds in microgels makes it impossible to be fully cured by microwaves at 120 degree C. The rheological behaviour of unsaturated polyester resin was also studied to observe the change in viscosity with respect to time and temperature. (author)

  8. FY1995 molecular control technology for mining of methane-gas-hydrate; 1995 nendo methane hydrate no bunshi seigyo mining

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    1997-03-01

    The objectives of the investigation are as follows: 1) developing a method to control formation/dissociation of methane-gas-hydrate, 2) developing a technology to displace methane gas by CO{sub 2} in methane-gas-hydrate deposit, 3) developing a technology to produce methane gas from the deposit efficiently. The final purpose of the project is to create new mining industry that solves both the problems of energy and global environment. 1) Clustering of water molecules is found to play the key role in the methane gas hydrate formation. 2) Equilibrium properties and kinetics of gas hydrates formation and dissociation in bulk-scale gas-hydrate are clarified in the practical environmental conditions. 3) Particle size of hydrate deposit influences the formation and dissociation of bulk-scale gas-hydrate crystal. 4) Mass transfer between gas and liquid phase in turbulent bubbly flow is a function of bubble diameter. The mass transfer depends on interfacial dynamics. (NEDO)

  9. A kinetic model for runaway electrons in the ionosphere

    Directory of Open Access Journals (Sweden)

    G. Garcia

    2006-09-01

    Full Text Available Electrodynamic models and measurements with satellites and incoherent scatter radars predict large field aligned current densities on one side of the auroral arcs. Different authors and different kinds of studies (experimental or modeling agree that the current density can reach up to hundreds of µA/m2. This large current density could be the cause of many phenomena such as tall red rays or triggering of unstable ion acoustic waves. In the present paper, we consider the issue of electrons moving through an ionospheric gas of positive ions and neutrals under the influence of a static electric field. We develop a kinetic model of collisions including electrons/electrons, electrons/ions and electrons/neutrals collisions. We use a Fokker-Planck approach to describe binary collisions between charged particles with a long-range interaction. We present the essential elements of this collision operator: the Langevin equation for electrons/ions and electrons/electrons collisions and the Monte-Carlo and null collision methods for electrons/neutrals collisions. A computational example is given illustrating the approach to equilibrium and the impact of the different terms (electrons/electrons and electrons/ions collisions on the one hand and electrons/neutrals collisions on the other hand. Then, a parallel electric field is applied in a new sample run. In this run, the electrons move in the z direction parallel to the electric field. The first results show that all the electron distribution functions are non-Maxwellian. Furthermore, runaway electrons can carry a significant part of the total current density, up to 20% of the total current density.

  10. A kinetic model for runaway electrons in the ionosphere

    Directory of Open Access Journals (Sweden)

    G. Garcia

    2006-09-01

    Full Text Available Electrodynamic models and measurements with satellites and incoherent scatter radars predict large field aligned current densities on one side of the auroral arcs. Different authors and different kinds of studies (experimental or modeling agree that the current density can reach up to hundreds of µA/m2. This large current density could be the cause of many phenomena such as tall red rays or triggering of unstable ion acoustic waves. In the present paper, we consider the issue of electrons moving through an ionospheric gas of positive ions and neutrals under the influence of a static electric field. We develop a kinetic model of collisions including electrons/electrons, electrons/ions and electrons/neutrals collisions. We use a Fokker-Planck approach to describe binary collisions between charged particles with a long-range interaction. We present the essential elements of this collision operator: the Langevin equation for electrons/ions and electrons/electrons collisions and the Monte-Carlo and null collision methods for electrons/neutrals collisions. A computational example is given illustrating the approach to equilibrium and the impact of the different terms (electrons/electrons and electrons/ions collisions on the one hand and electrons/neutrals collisions on the other hand. Then, a parallel electric field is applied in a new sample run. In this run, the electrons move in the z direction parallel to the electric field. The first results show that all the electron distribution functions are non-Maxwellian. Furthermore, runaway electrons can carry a significant part of the total current density, up to 20% of the total current density.

  11. Mechanistic study and modeling of radionuclides retention by the hydrated calcium silicates (HCS) of cements; Etude mecanistique et modelisation de la retention de radionucleides par les silicates de calcium hydrates (CSH) des ciments

    Energy Technology Data Exchange (ETDEWEB)

    Pointeau, I

    2000-09-01

    This work attempts to investigate the modelling of radioisotopes (Cs{sup +}, Pb{sup 2+}, Eu{sup 3+}) immobilization in cement matrix, in the frame of the design of engineered barrier of a deep radwaste repository. The model development concept consists of three major steps: - surface chemistry modelling of the calcium silicate hydrate CSH, used to simulate hydrated cement behaviour; - solid analysis of the batch sorption experiments: identification of the uptake mechanism; - both previous steps are used, with isotherm data, in the modelling of the radioisotopes immobilization in the CSH matrix. Final results: (all modelling are available for all the range of studied Ca/Si ratios and have been validated with predictive calculations). - A thermodynamic modelling of the CSH surface chemistry has been developed. The labile calcium and proton sorption constants on silanol sites (>SiOH) have been extracted. - Cs{sup +} is sorbed on two sites. The silanol site (weak site) has a high site density (10 sites.nm{sup -2}), which accounts for the CSH unsaturation in high [CS{sup +}]. A strong site is also identified. - Pb{sup 2+} immobilization in CSH matrix is modelled with surface equilibria and solubility equilibrium. - Eu{sup 3+} fixation has been investigated with solid analysis: Site-Selective anti Time-Resolved Luminescence Spectroscopy, XPS and SEM-EDS. Eu{sup 3+} thus does not precipitate in CSH water but is sorbed on the CSH surface (high hydroxylated environment). Europium is also (minority site) inserted in the CSH framework. (author)

  12. Comparison of kinetic and fluid neutral models for attached and detached state

    International Nuclear Information System (INIS)

    Furubayashi, M.; Hoshino, K.; Toma, M.; Hatayama, A.; Coster, D.; Schneider, R.; Bonnin, X.; Kawashima, H.; Asakura, N.; Suzuki, Y.

    2009-01-01

    Neutral behavior has an important role in the transport simulations of the edge plasma. Most of the edge plasma transport codes treat neutral particles by a simple fluid model or a kinetic model. The fluid model allows faster calculations. However, the applicability of the fluid model is limited. In this study, simulation results of JT-60U from kinetic neutral model and fluid neutral model are compared under the attached and detached state, using the 2D edge plasma code package, SOLPS5.0. In the SOL region, no significant differences are observed in the upstream plasma profiles between kinetic and fluid neutral models. However, in the divertor region, large differences are observed in plasma and neutral profiles. Therefore, further optimization of the fluid neutral model should be performed. Otherwise kinetic neutral model should be used to analyze the divertor region.

  13. Kinetic transport model for the ELMO Bumpy Torus

    International Nuclear Information System (INIS)

    Jaeger, E.F.; Hedrick, C.L.; Tolliver, J.S.

    1978-05-01

    A bounce-averaged drift kinetic equation is solved for the toroidal plasma in the ELMO Bumpy Torus (EBT). The distribution function is assumed isotropic in pitch angle and calculated as a function of radius and speed using finite differences on a two-dimensional grid. A Fokker-Planck representation of the collision operator includes Coulomb, microwave, ionizing, and charge-exchange collisions. Ion and electron fluxes, computed as integrals of the distribution function, are of comparable magnitude for ambipolar potentials which are approximately self-consistent. Initial results assume an unperturbed distribution function which is Maxwellian; however, this is not a necessary assumption in the model. Careful accounting of loss regions where electric and magnetic poloidal drifts cancel (super banana particle orbits) leads to ion loss rates which are in some cases two orders of magnitude greater than electron rates. In these cases, radially inward pointing self-consistent electric fields occur with potentials on the order of a few times the ion temperature. These negative field results are in approximate agreement with experiment and appear to be stable to the electric field runaway encountered in positive field cases

  14. Kinetic model of the bichromatic dark trap for atoms

    Science.gov (United States)

    Krasnov, I. V.

    2017-08-01

    A kinetic model of atom confinement in a bichromatic dark trap (BDT) is developed with the goal of describing its dissipative properties. The operating principle of the deep BDT is based on using the combination of multiple bichromatic cosine-Gaussian optical beams (CGBs) for creating high-potential barriers, which is described in our previous work (Krasnov 2016 Laser Phys. 26 105501). In the indicated work, particle motion in the BDT is described in terms of classical trajectories. In the present study, particle motion is analyzed by means of the Wigner function (phase-space distribution function (DF)), which allows one to properly take into account the quantum fluctuations of optical forces. Besides, we consider an improved scheme of the BDT, where CGBs create, apart from plane potential barriers, a narrow cooling layer. We find an asymptotic solution of the Fokker-Planck equation for the DF and show that the DF of particles deeply trapped in a BDT with a cooling layer is the Tsallis distribution with the effective temperature, which can be considerably lower than in a BDT without a cooling layer. Moreover, it can be adjusted by slightly changing the CGBs’ radii. We also study the effect of particle escape from the trap due to the scattering of resonant photons and show that the particle lifetime in a BDT can exceed several tens of hours when it is limited by photon scattering.

  15. KINETIC MODELS STUDY OF HYDRODESULPHURIZATION VACUUM DISTILLATE REACTION

    Directory of Open Access Journals (Sweden)

    AbdulMunem A. Karim

    2013-05-01

    Full Text Available    This study deals with  kinetics of hydrodesulphurization (HDS reaction of vacuum gas oil (611-833 K which was distillated from Kirkuk crude oil and which was obtained by blending the fractions, light vacuum gas oil (611 - 650 K, medium vacuum gas oil (650-690 K, heavy vacuum gas oil (690-727 K and very heavy vacuum gas oil (727-833 K.   The vacuum gas oil was hydrotreated on a commercial cobalt-molybdenum alumina catalyst presulfied at specified conditions in a laboratory trickle bed reactor. The reaction temperature range (583-643 K,liquid hourly space velocity range (1.5-3.75 h-1 and hydrogen pressure was kept constant at 3.5 MPa with hydrogen to oil ratio about 250 lt/lt.           The conversion results for desulphurization reaction appeared to obey the second order reaction. According to this model, the rate constants for desulphurization reaction were determined. Finally, the apparent activation energy (Ea, enthalpy of activation ( H* and entropy ( S* were calculated based on the values of rate constant (k2 and were equal 80.3792 KJ/mole, 75.2974 KJ/mole and 197.493 J/mole, respectively.

  16. MIDAS/PK code development using point kinetics model

    International Nuclear Information System (INIS)

    Song, Y. M.; Park, S. H.

    1999-01-01

    In this study, a MIDAS/PK code has been developed for analyzing the ATWS (Anticipated Transients Without Scram) which can be one of severe accident initiating events. The MIDAS is an integrated computer code based on the MELCOR code to develop a severe accident risk reduction strategy by Korea Atomic Energy Research Institute. In the mean time, the Chexal-Layman correlation in the current MELCOR, which was developed under a BWR condition, is appeared to be inappropriate for a PWR. So as to provide ATWS analysis capability to the MIDAS code, a point kinetics module, PKINETIC, has first been developed as a stand-alone code whose reference model was selected from the current accident analysis codes. In the next step, the MIDAS/PK code has been developed via coupling PKINETIC with the MIDAS code by inter-connecting several thermal hydraulic parameters between the two codes. Since the major concern in the ATWS analysis is the primary peak pressure during the early few minutes into the accident, the peak pressure from the PKINETIC module and the MIDAS/PK are compared with the RETRAN calculations showing a good agreement between them. The MIDAS/PK code is considered to be valuable for analyzing the plant response during ATWS deterministically, especially for the early domestic Westinghouse plants which rely on the operator procedure instead of an AMSAC (ATWS Mitigating System Actuation Circuitry) against ATWS. This capability of ATWS analysis is also important from the view point of accident management and mitigation

  17. Kinetic modeling of formic acid pulping of bagasse.

    Science.gov (United States)

    Tu, Qiliang; Fu, Shiyu; Zhan, Huaiyu; Chai, Xinsheng; Lucia, Lucian A

    2008-05-14

    Organic solvent or organosolv pulping processes are alternatives to soda or kraft pulping to delignify lignocellulosic materials for the production of paper pulp. Formic acid, a typical organosolv system, has been presently examined under atmospheric pressure to pulp bagasse fibers. It was shown that efficient bagasse pulping was achieved when the formic acid concentration was limited to 90% (v/v). A statistical kinetic model based on the experimental results for the delignification of bagasse during formic acid pulping was developed that can be described as follows: D (delignification) = 0.747 x C(formicacid) (1.688) x (1 - e(-0.05171t)), an equation that can be used to predict the lignin content in formic acid during the pulping process. The delignification of bagasse by 90% formic acid was almost completed after approximately 80 min, while extended pulping did not improve the delignification but tended to degrade the carbohydrates in bagasse, especially the hemicelluloses, which were rapidly hydrolyzed at the onset of pulping.

  18. Comparing effectiveness of rhamnolipid biosurfactant with a quaternary ammonium salt surfactant for hydrate anti-agglomeration.

    Science.gov (United States)

    York, J Dalton; Firoozabadi, Abbas

    2008-01-24

    Natural gas is projected to be the premium fuel of the 21st century because of availability, as well as economical and environmental considerations. Natural gas is coproduced with water from the subsurface forming gas hydrates. Hydrate formation may result in shutdown of onshore and offshore operations. Industry practice has been usage of alcohols--which have undesirable environmental impacts--to affect bulk-phase properties and inhibit hydrate formation. An alternative to alcohols is changing the surface properties through usage of polymers and surfactants, effective at 0.5-3 wt % of coproduced water. One group of low-dosage hydrate inhibitors (LDHI) are kinetic inhibitors, which affect nucleation rate and growth. A second group of LDHI are anti-agglomerants, which prevent agglomeration of small hydrate crystallites. Despite great potential, reported work on hydrate anti-agglomeration is very limited. In this paper, our focus is on the use of two vastly different surfactants as anti-agglomerants. We use a model oil, water, and tetrahydrofuran as a hydrate-forming species. We examine the effectiveness of a quaternary ammonium salt (i.e., quat). Visual observation measurements show that a small concentration of the quat (0.01%) can prevent agglomeration. However, a quat is not a green chemical and therefore may be undesirable. We show that a rhamnolipid biosurfactant can be effective to a concentration of 0.05 wt %. One difference between the two surfactants is the stability of the water-in-oil emulsions created. The biosurfactant forms a less stable emulsion, which makes it very desirable for hydrate application.

  19. Kinetic modelling of runaway electron avalanches in tokamak plasmas

    International Nuclear Information System (INIS)

    Nilsson, E; Peysson, Y; Saint-Laurent, F; Decker, J; Granetz, R S; Vlainic, M

    2015-01-01

    Runaway electrons can be generated in tokamak plasmas if the accelerating force from the toroidal electric field exceeds the collisional drag force owing to Coulomb collisions with the background plasma. In ITER, disruptions are expected to generate runaway electrons mainly through knock-on collisions (Hender et al 2007 Nucl. Fusion 47 S128–202), where enough momentum can be transferred from existing runaways to slow electrons to transport the latter beyond a critical momentum, setting off an avalanche of runaway electrons. Since knock-on runaways are usually scattered off with a significant perpendicular component of the momentum with respect to the local magnetic field direction, these particles are highly magnetized. Consequently, the momentum dynamics require a full 3D kinetic description, since these electrons are highly sensitive to the magnetic non-uniformity of a toroidal configuration. For this purpose, a bounce-averaged knock-on source term is derived. The generation of runaway electrons from the combined effect of Dreicer mechanism and knock-on collision process is studied with the code LUKE, a solver of the 3D linearized bounce-averaged relativistic electron Fokker–Planck equation (Decker and Peysson 2004 DKE: a fast numerical solver for the 3D drift kinetic equation Report EUR-CEA-FC-1736, Euratom-CEA), through the calculation of the response of the electron distribution function to a constant parallel electric field. The model, which has been successfully benchmarked against the standard Dreicer runaway theory now describes the runaway generation by knock-on collisions as proposed by Rosenbluth (Rosenbluth and Putvinski 1997 Nucl. Fusion 37 1355–62). This paper shows that the avalanche effect can be important even in non-disruptive scenarios. Runaway formation through knock-on collisions is found to be strongly reduced when taking place off the magnetic axis, since trapped electrons can not contribute to the runaway electron population. Finally

  20. Elimination kinetic model for organic chemicals in earthworms.

    NARCIS (Netherlands)

    Dimitrova, N.; Dimitrov, S.; Georgieva, D.; van Gestel, C.A.M.; Hankard, P.; Spurgeon, D.J.; Li, H.; Mekenyan, O.

    2010-01-01

    Mechanistic understanding of bioaccumulation in different organisms and environments should take into account the influence of organism and chemical depending factors on the uptake and elimination kinetics of chemicals. Lipophilicity, metabolism, sorption (bioavailability) and biodegradation of

  1. Modelling of the enzymatic kinetically controlled synthesis of cephalexin

    NARCIS (Netherlands)

    Schroën, C.G.P.H.; Fretz, C.B.; Bruin, de V.H.; Berendsen, W.; Moody, H.M.; Roos, E.C.; Roon, van J.L.; Kroon, P.J.; Strubel, M.; Janssen, A.E.M.; Tramper, J.

    2002-01-01

    In this study the influence of diffusion limitation on enzymatic kinetically controlled cephalexin synthesis from phenylglycine amide and 7-aminodeacetoxycephalosporinic acid (7-ADCA) was investigated systematically. It was found that if diffusion limitation occurred, both the synthesis/hydrolysis

  2. Extended symmetries of the kinetic plasma theory models

    International Nuclear Information System (INIS)

    Taranov, V.B.

    2005-01-01

    Symmetry extension of the kinetic theory of collisionless plasma containing particles with equal charge to mass ratio is considered. It is shown that this symmetry allows us to reduce the number of equations. Symmetries obtained for the integro-differential equations of the kinetic theory by the indirect algorithm are compared to those obtained by direct methods. The importance of additional conditions - positiveness and integrability of distribution functions, existence of their moments - is underlined

  3. Heterogeneous kinetics of H2O, HNO3 and HCl on HNO3 hydrates (α-NAT, β-NAT, NAD) in the range 175-200 K

    Science.gov (United States)

    Iannarelli, Riccardo; Rossi, Michel J.

    2016-09-01

    Experiments on the title compounds have been performed using a multidiagnostic stirred-flow reactor (SFR) in which the gas phase as well as the condensed phase has been simultaneously investigated under stratospheric temperatures in the range 175-200 K. Wall interactions of the title compounds have been taken into account using Langmuir adsorption isotherms in order to close the mass balance between deposited and desorbed (recovered) compounds. Thin solid films at 1 µm typical thickness have been used as a proxy for atmospheric ice particles and have been deposited on a Si window of the cryostat, with the optical element being the only cold point in the deposition chamber. Fourier transform infrared (FTIR) absorption spectroscopy in transmission as well as partial and total pressure measurement using residual gas mass spectrometry (MS) and sensitive pressure gauges have been employed in order to monitor growth and evaporation processes as a function of temperature using both pulsed and continuous gas admission and monitoring under SFR conditions. Thin solid H2O ice films were used as the starting point throughout, with the initial spontaneous formation of α-NAT (nitric acid trihydrate) followed by the gradual transformation of α- to β-NAT at T > 185 K. Nitric acid dihydrate (NAD) was spontaneously formed at somewhat larger partial pressures of HNO3 deposited on pure H2O ice. In contrast to published reports, the formation of α-NAT proceeded without prior formation of an amorphous HNO3 / H2O layer and always resulted in β-NAT. For α- and β-NAT, the temperature-dependent accommodation coefficient α(H2O) and α(HNO3), the evaporation flux Jev(H2O) and Jev(HNO3) and the resulting saturation vapor pressure Peq(H2O) and Peq(HNO3) were measured and compared to binary phase diagrams of HNO3 / H2O in order to afford a thermochemical check of the kinetic parameters. The resulting kinetic and thermodynamic parameters of activation energies for evaporation (Eev) and

  4. Review of reactive kinetic models describing reductive dechlorination of chlorinated ethenes in soil and groundwater

    DEFF Research Database (Denmark)

    Chambon, Julie Claire Claudia; Bjerg, Poul Løgstrup; Scheutz, Charlotte

    2013-01-01

    Reductive dechlorination is a major degradation pathway of chlorinated ethenes in anaerobic subsurface environments, and reactive kinetic models describing the degradation process are needed in fate and transport models of these contaminants. However, reductive dechlorination is a complex biologi...

  5. Decarboxylation of Δ 9-tetrahydrocannabinol: Kinetics and molecular modeling

    Science.gov (United States)

    Perrotin-Brunel, Helene; Buijs, Wim; van Spronsen, Jaap; van Roosmalen, Maaike J. E.; Peters, Cor J.; Verpoorte, Rob; Witkamp, Geert-Jan

    2011-02-01

    Efficient tetrahydrocannabinol (Δ 9-THC) production from cannabis is important for its medical application and as basis for the development of production routes of other drugs from plants. This work presents one of the steps of Δ 9-THC production from cannabis plant material, the decarboxylation reaction, transforming the Δ 9-THC-acid naturally present in the plant into the psychoactive Δ 9-THC. Results of experiments showed pseudo-first order reaction kinetics, with an activation barrier of 85 kJ mol -1 and a pre-exponential factor of 3.7 × 10 8 s -1. Using molecular modeling, two options were identified for an acid catalyzed β-keto acid type mechanism for the decarboxylation of Δ 9-THC-acid. Each of these mechanisms might play a role, depending on the actual process conditions. Formic acid proved to be a good model for a catalyst of such a reaction. Also, the computational idea of catalysis by water to catalysis by an acid, put forward by Li and Brill, and Churchev and Belbruno was extended, and a new direct keto-enol route was found. A direct keto-enol mechanism catalyzed by formic acid seems to be the best explanation for the observed activation barrier and the pre-exponential factor of the decarboxylation of Δ 9-THC-acid. Evidence for this was found by performing an extraction experiment with Cannabis Flos. It revealed the presence of short chain carboxylic acids supporting this hypothesis. The presented approach is important for the development of a sustainable production of Δ 9-THC from the plant.

  6. Exploration of the Singlet O2 Oxidation of 8-Oxoguanine by Guided-Ion Beam Scattering and Density Functional Theory: Changes of Reaction Intermediates, Energetics, and Kinetics upon Protonation/Deprotonation and Hydration.

    Science.gov (United States)

    Sun, Yan; Lu, Wenchao; Liu, Jianbo

    2017-02-09

    8-Oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodGuo) is one of the most common DNA lesions resulting from reactive oxygen species and ionizing radiation, and is involved in mutagenesis, carcinogenesis, and cell death. Notably, 8-oxodGuo is more reactive toward singlet (a 1 Δ g ) O 2 than the undamaged guanosine, and the lesions arising from the secondary oxidation of 8-oxodGuo are more mutagenic. Herein the 1 O 2 oxidation of free base 8-oxoguanine (8-oxoG) was investigated at different initial conditions including protonated [8-oxoG + H] + , deprotonated [8-oxoG - H] - , and their monohydrates. Experiment was carried out on a guided-ion beam scattering tandem mass spectrometer. Measurements include the effects of collision energy (E col ) on reaction cross sections over a center-of-mass E col range from 0.1 to 0.5 eV. The aim of this study is to quantitatively probe the sensitivity of the early stage of 8-oxoG oxidation to ionization and hydration. Density functional theory and Rice-Ramsperger-Kassel-Marcus calculations were performed to identify the intermediates and the products along reaction pathways and locate accessible reaction potential energy surfaces, and to rationalize reaction outcomes from energetic and kinetic points of view. No product was observed for the reaction of [8-oxoG + H] + ·W 0,1 (W = H 2 O) because insurmountable barriers block the addition of 1 O 2 to reactant ions. Neither was [8-oxoG - H] - reactive with 1 O 2 , in this case due to the rapid decay of transient intermediates to starting reactants. However, the nonreactivity of [8-oxoG - H] - was inverted by hydration; as a result, 4,5-dioxetane of [8-oxoG - H] - was captured as the main oxidation product. Reaction cross section for [8-oxoG - H] - ·W + 1 O 2 decreases with increasing E col and becomes negligible above 0.3 eV, indicating that the reaction is exothermic and has no barriers above reactants. The contrasting oxidation behaviors of [8-oxoG + H] + ·W 0,1 and [8-oxoG - H] - ·W 0

  7. Study and discretization of kinetic models and fluid models at low Mach number

    International Nuclear Information System (INIS)

    Dellacherie, Stephane

    2011-01-01

    This thesis summarizes our work between 1995 and 2010. It concerns the analysis and the discretization of Fokker-Planck or semi-classical Boltzmann kinetic models and of Euler or Navier-Stokes fluid models at low Mach number. The studied Fokker-Planck equation models the collisions between ions and electrons in a hot plasma, and is here applied to the inertial confinement fusion. The studied semi-classical Boltzmann equations are of two types. The first one models the thermonuclear reaction between a deuterium ion and a tritium ion producing an α particle and a neutron particle, and is also in our case used to describe inertial confinement fusion. The second one (known as the Wang-Chang and Uhlenbeck equations) models the transitions between electronic quantified energy levels of uranium and iron atoms in the AVLIS isotopic separation process. The basic properties of these two Boltzmann equations are studied, and, for the Wang-Chang and Uhlenbeck equations, a kinetic-fluid coupling algorithm is proposed. This kinetic-fluid coupling algorithm incited us to study the relaxation concept for gas and immiscible fluids mixtures, and to underline connections with classical kinetic theory. Then, a diphasic low Mach number model without acoustic waves is proposed to model the deformation of the interface between two immiscible fluids induced by high heat transfers at low Mach number. In order to increase the accuracy of the results without increasing computational cost, an AMR algorithm is studied on a simplified interface deformation model. These low Mach number studies also incited us to analyse on cartesian meshes the inaccuracy at low Mach number of Godunov schemes. Finally, the LBM algorithm applied to the heat equation is justified

  8. Large scale structures in the kinetic gravity braiding model that can be unbraided

    International Nuclear Information System (INIS)

    Kimura, Rampei; Yamamoto, Kazuhiro

    2011-01-01

    We study cosmological consequences of a kinetic gravity braiding model, which is proposed as an alternative to the dark energy model. The kinetic braiding model we study is characterized by a parameter n, which corresponds to the original galileon cosmological model for n = 1. We find that the background expansion of the universe of the kinetic braiding model is the same as the Dvali-Turner's model, which reduces to that of the standard cold dark matter model with a cosmological constant (ΛCDM model) for n equal to infinity. We also find that the evolution of the linear cosmological perturbation in the kinetic braiding model reduces to that of the ΛCDM model for n = ∞. Then, we focus our study on the growth history of the linear density perturbation as well as the spherical collapse in the nonlinear regime of the density perturbations, which might be important in order to distinguish between the kinetic braiding model and the ΛCDM model when n is finite. The theoretical prediction for the large scale structure is confronted with the multipole power spectrum of the luminous red galaxy sample of the Sloan Digital Sky survey. We also discuss future prospects of constraining the kinetic braiding model using a future redshift survey like the WFMOS/SuMIRe PFS survey as well as the cluster redshift distribution in the South Pole Telescope survey

  9. Analysis of a kinetic multi-segment foot model. Part I: Model repeatability and kinematic validity.

    Science.gov (United States)

    Bruening, Dustin A; Cooney, Kevin M; Buczek, Frank L

    2012-04-01

    Kinematic multi-segment foot models are still evolving, but have seen increased use in clinical and research settings. The addition of kinetics may increase knowledge of foot and ankle function as well as influence multi-segment foot model evolution; however, previous kinetic models are too complex for clinical use. In this study we present a three-segment kinetic foot model and thorough evaluation of model performance during normal gait. In this first of two companion papers, model reference frames and joint centers are analyzed for repeatability, joint translations are measured, segment rigidity characterized, and sample joint angles presented. Within-tester and between-tester repeatability were first assessed using 10 healthy pediatric participants, while kinematic parameters were subsequently measured on 17 additional healthy pediatric participants. Repeatability errors were generally low for all sagittal plane measures as well as transverse plane Hindfoot and Forefoot segments (median<3°), while the least repeatable orientations were the Hindfoot coronal plane and Hallux transverse plane. Joint translations were generally less than 2mm in any one direction, while segment rigidity analysis suggested rigid body behavior for the Shank and Hindfoot, with the Forefoot violating the rigid body assumptions in terminal stance/pre-swing. Joint excursions were consistent with previously published studies. Copyright © 2012 Elsevier B.V. All rights reserved.

  10. Application of the independent molecule model to elucidate the dynamics of structure I methane hydrate: a third report.

    Science.gov (United States)

    Yoshioki, Shuzo

    2009-01-01

    Two new model systems of methane hydrate, larger than the previous systems, are constructed. One consists of 63 small and large cages with a small cage at the centre. The other has 65 small and large cages with a large cage at the centre. Three different H-bonding network patterns between water are formed, and three random orientations of methane in each cage are chosen. Using the surface water fixed method, we obtained the energy minimum conformations, fitted to the X-ray crystallographic structure. With normal mode analysis, we calculated frequencies of 2915.1 cm(-1) for a small cage, and 2911.0 cm(-1) for a large cage. These frequencies are a little nearer to the Raman spectra than were previous model systems. Treating three force constants of anharmonic potential energy and the strength of H-bonding between methane and water as four parameters, we obtained frequencies of 2913.6 cm(-1) for a small cage, a little lower than the Raman, and 2906.6 cm(-1) for a large cage, a little higher than the Raman. The calculations thus almost reach the Raman spectra.

  11. Modelling of elementary kinetics of H2 and CO oxidation on ceria pattern cells

    International Nuclear Information System (INIS)

    Patel, HC; Tabish, AN; Aravind, PV

    2015-01-01

    Elementary kinetic mechanisms of fuel oxidation on ceria have not been dealt with in detail in literature. An elementary kinetic model is developed considering charge transfer and adsorption steps for electrochemical H 2 and CO oxidation on ceria. The reaction chemistry is solved by fitting previously obtained impedance spectra for H 2 and CO oxidation on ceria. The rate determining step is found to be the charge transfer rather than the adsorption for both H 2 and CO. A method is presented to extend the kinetics obtained from pattern anodes to macroscopic simulations in which the activation overvoltage can be calculated on the basis of elementary kinetics.

  12. A detailed chemical kinetic model for pyrolysis of the lignin model compound chroman

    Directory of Open Access Journals (Sweden)

    James Bland

    2013-12-01

    Full Text Available The pyrolysis of woody biomass, including the lignin component, is emerging as a potential technology for the production of renewable fuels and commodity chemicals. Here we describe the construction and implementation of an elementary chemical kinetic model for pyrolysis of the lignin model compound chroman and its reaction intermediate ortho-quinone methide (o-QM. The model is developed using both experimental and theoretical data, and represents a hybrid approach to kinetic modeling that has the potential to provide molecular level insight into reaction pathways and intermediates while accurately describing reaction rates and product formation. The kinetic model developed here can replicate all known aspects of chroman pyrolysis, and provides new information on elementary reaction steps. Chroman pyrolysis is found to proceed via an initial retro-Diels–Alder reaction to form o-QM + ethene (C2H4, followed by dissociation of o-QM to the C6H6 isomers benzene and fulvene (+ CO. At temperatures of around 1000–1200 K and above fulvene rapidly isomerizes to benzene, where an activation energy of around 270 kJ mol-1 is required to reproduce experimental observations. A new G3SX level energy surface for the isomerization of fulvene to benzene supports this result. Our modeling also suggests that thermal decomposition of fulvene may be important at around 950 K and above. This study demonstrates that theoretical protocols can provide a significant contribution to the development of kinetic models for biomass pyrolysis by elucidating reaction mechanisms, intermediates, and products, and also by supplying realistic rate coefficients and thermochemical properties.

  13. Modeling of hydrogen production methods: Single particle model and kinetics assessment

    Energy Technology Data Exchange (ETDEWEB)

    Miller, R.S.; Bellan, J. [California Institute of Technology, Pasadena, CA (United States)

    1996-10-01

    The investigation carried out by the Jet Propulsion Laboratory (JPL) is devoted to the modeling of biomass pyrolysis reactors producing an oil vapor (tar) which is a precursor to hydrogen. This is an informal collaboration with NREL whereby JPL uses the experimentally-generated NREL data both as initial and boundary conditions for the calculations, and as a benchmark for model validation. The goal of this investigation is to find drivers of biomass fast-pyrolysis in the low temperature regime. The rationale is that experimental observations produce sparse discrete conditions for model validation, and that numerical simulations produced with a validated model are an economic way to find control parameters and an optimal operation regime, thereby circumventing costly changes in hardware and tests. During this first year of the investigation, a detailed mathematical model has been formulated for the temporal and spatial accurate modeling of solid-fluid reactions in biomass particles. These are porous particles for which volumetric reaction rate data is known a priori and both the porosity and the permeability of the particle are large enough to allow for continuous gas phase flow. The methodology has been applied to the pyrolysis of spherically symmetric biomass particles by considering previously published kinetics schemes for both cellulose and wood. The results show that models which neglect the thermal and species boundary layers exterior to the particle will generally over predict both the pyrolysis rates and experimentally obtainable tar yields. An evaluation of the simulation results through comparisons with experimental data indicates that while the cellulose kinetics is reasonably accurate, the wood pyrolysis kinetics is not accurate; particularly at high reactor temperatures. Current effort in collaboration with NREL is aimed at finding accurate wood kinetics.

  14. Dynamic Model of Basic Oxygen Steelmaking Process Based on Multizone Reaction Kinetics: Modeling of Decarburization

    Science.gov (United States)

    Rout, Bapin Kumar; Brooks, Geoffrey; Akbar Rhamdhani, M.; Li, Zushu; Schrama, Frank N. H.; Overbosch, Aart

    2018-03-01

    In a previous study by the authors (Rout et al. in Metall Mater Trans B 49:537-557, 2018), a dynamic model for the BOF, employing the concept of multizone kinetics was developed. In the current study, the kinetics of decarburization reaction is investigated. The jet impact and slag-metal emulsion zones were identified to be primary zones for carbon oxidation. The dynamic parameters in the rate equation of decarburization such as residence time of metal drops in the emulsion, interfacial area evolution, initial size, and the effects of surface-active oxides have been included in the kinetic rate equation of the metal droplet. A modified mass-transfer coefficient based on the ideal Langmuir adsorption equilibrium has been proposed to take into account the surface blockage effects of SiO2 and P2O5 in slag on the decarburization kinetics of a metal droplet in the emulsion. Further, a size distribution function has been included in the rate equation to evaluate the effect of droplet size on reaction kinetics. The mathematical simulation indicates that decarburization of the droplet in the emulsion is a strong function of the initial size and residence time. A modified droplet generation rate proposed previously by the authors has been used to estimate the total decarburization rate by slag-metal emulsion. The model's prediction shows that about 76 pct of total carbon is removed by reactions in the emulsion, and the remaining is removed by reactions at the jet impact zone. The predicted bath carbon by the model has been found to be in good agreement with the industrially measured data.

  15. Dynamic Model of Basic Oxygen Steelmaking Process Based on Multizone Reaction Kinetics: Modeling of Decarburization

    Science.gov (United States)

    Rout, Bapin Kumar; Brooks, Geoffrey; Akbar Rhamdhani, M.; Li, Zushu; Schrama, Frank N. H.; Overbosch, Aart

    2018-06-01

    In a previous study by the authors (Rout et al. in Metall Mater Trans B 49:537-557, 2018), a dynamic model for the BOF, employing the concept of multizone kinetics was developed. In the current study, the kinetics of decarburization reaction is investigated. The jet impact and slag-metal emulsion zones were identified to be primary zones for carbon oxidation. The dynamic parameters in the rate equation of decarburization such as residence time of metal drops in the emulsion, interfacial area evolution, initial size, and the effects of surface-active oxides have been included in the kinetic rate equation of the metal droplet. A modified mass-transfer coefficient based on the ideal Langmuir adsorption equilibrium has been proposed to take into account the surface blockage effects of SiO2 and P2O5 in slag on the decarburization kinetics of a metal droplet in the emulsion. Further, a size distribution function has been included in the rate equation to evaluate the effect of droplet size on reaction kinetics. The mathematical simulation indicates that decarburization of the droplet in the emulsion is a strong function of the initial size and residence time. A modified droplet generation rate proposed previously by the authors has been used to estimate the total decarburization rate by slag-metal emulsion. The model's prediction shows that about 76 pct of total carbon is removed by reactions in the emulsion, and the remaining is removed by reactions at the jet impact zone. The predicted bath carbon by the model has been found to be in good agreement with the industrially measured data.

  16. Modelling fungal solid-state fermentation: The role of inactivation kinetics

    NARCIS (Netherlands)

    Smits, J.P.; Sonsbeek, H.M. van; Knol, W.; Tramper, J.; Geelhoed, W.; Peeters, M.; Rinzema, A.

    1999-01-01

    The theoretical mathematical models described in this paper are used to evaluate the effects of fungal biomass inactivation kinetics on a non- isothermal tray solid-state fermentation (SSF). The inactivation kinetics, derived from previously reported experiments done under isothermal conditions and

  17. Kinetic model for an up-flow anaerobic packed bed bioreactor: Dairy ...

    African Journals Online (AJOL)

    Kinetic studies of anaerobic digestion process of cheese whey were conducted in a pilot-scale up-flow anaerobic packed bed bioreactor (UAPB). An influent COD concentration of 59419 mg/l was utilized at steady state condition. Logistic and Monod kinetic models were employed to describe microbial activities of cheese ...

  18. Application of Uncertainty and Sensitivity Analysis to a Kinetic Model for Enzymatic Biodiesel Production

    DEFF Research Database (Denmark)

    Price, Jason Anthony; Nordblad, Mathias; Woodley, John

    2014-01-01

    This paper demonstrates the added benefits of using uncertainty and sensitivity analysis in the kinetics of enzymatic biodiesel production. For this study, a kinetic model by Fedosov and co-workers is used. For the uncertainty analysis the Monte Carlo procedure was used to statistically quantify...

  19. A calculation of internal kinetic energy and polarizability of compressed argon from the statistical atom model

    NARCIS (Netherlands)

    Seldam, C.A. ten; Groot, S.R. de

    1952-01-01

    From Jensen's and Gombás' modification of the statistical Thomas-Fermi atom model, a theory for compressed atoms is developed by changing the boundary conditions. Internal kinetic energy and polarizability of argon are calculated as functions of pressure. At 1000 atm. an internal kinetic energy of

  20. Experimental study and thermodynamic modelling of methane clathrate hydrate dissociation conditions in silica gel porous media in the presence of methanol aqueous solution

    International Nuclear Information System (INIS)

    Hashemi, Hamed; Javanmardi, Jafar; Zarifi, Mojdeh; Eslamimanesh, Ali; Mohammadi, Amir H.

    2012-01-01

    Highlights: ► Phase equilibria of hydrates of methane in confined silica gel pores are reported. ► Dissociation data in the presences of methanol aqueous solution are also measured. ► A thermodynamic model is developed for prediction of the obtained data. ► Acceptable agreement is found between the obtained data and the predicted results. - Abstract: In this work, the phase equilibria of clathrate hydrates of methane in the presence of pure water and 0.035 mass fraction of methanol aqueous solution in confined silica gel pores with (10 and 15) nm mean diameters are measured and reported. A thermodynamic model is also developed for prediction of the obtained experimental hydrate dissociation data. The Valderrama–Patel–Teja (VPT-EoS) equation of state (EoS) accompanied with the non-density dependent (NDD) mixing rules coupled with a previously developed activity model are applied to evaluate the fugacity of the species present and the activity coefficient of water in methanol aqueous solution. Acceptable agreement between the reported data and the predicted results using the proposed model and an existing method reported in the literature demonstrates the reliability of the presented model.

  1. Kinetic parameter estimation model for anaerobic co-digestion of waste activated sludge and microalgae.

    Science.gov (United States)

    Lee, Eunyoung; Cumberbatch, Jewel; Wang, Meng; Zhang, Qiong

    2017-03-01

    Anaerobic co-digestion has a potential to improve biogas production, but limited kinetic information is available for co-digestion. This study introduced regression-based models to estimate the kinetic parameters for the co-digestion of microalgae and Waste Activated Sludge (WAS). The models were developed using the ratios of co-substrates and the kinetic parameters for the single substrate as indicators. The models were applied to the modified first-order kinetics and Monod model to determine the rate of hydrolysis and methanogenesis for the co-digestion. The results showed that the model using a hyperbola function was better for the estimation of the first-order kinetic coefficients, while the model using inverse tangent function closely estimated the Monod kinetic parameters. The models can be used for estimating kinetic parameters for not only microalgae-WAS co-digestion but also other substrates' co-digestion such as microalgae-swine manure and WAS-aquatic plants. Copyright © 2016 Elsevier Ltd. All rights reserved.

  2. Comparative evaluation of kinetic, equilibrium and semi-equilibrium models for biomass gasification

    Energy Technology Data Exchange (ETDEWEB)

    Buragohain, Buljit [Center for Energy, Indian Institute of Technology Guwahati, Guwahati – 781 039, Assam (India); Chakma, Sankar; Kumar, Peeush [Department of Chemical Engineering, Indian Institute of Technology Guwahati, Guwahati – 781 039, Assam (India); Mahanta, Pinakeswar [Center for Energy, Indian Institute of Technology Guwahati, Guwahati – 781 039, Assam (India); Department of Mechanical Engineering, Indian Institute of Technology Guwahati, Guwahati – 781 039, Assam (India); Moholkar, Vijayanand S. [Center for Energy, Indian Institute of Technology Guwahati, Guwahati – 781 039, Assam (India); Department of Chemical Engineering, Indian Institute of Technology Guwahati, Guwahati – 781 039, Assam (India)

    2013-07-01

    Modeling of biomass gasification has been an active area of research for past two decades. In the published literature, three approaches have been adopted for the modeling of this process, viz. thermodynamic equilibrium, semi-equilibrium and kinetic. In this paper, we have attempted to present a comparative assessment of these three types of models for predicting outcome of the gasification process in a circulating fluidized bed gasifier. Two model biomass, viz. rice husk and wood particles, have been chosen for analysis, with gasification medium being air. Although the trends in molar composition, net yield and LHV of the producer gas predicted by three models are in concurrence, significant quantitative difference is seen in the results. Due to rather slow kinetics of char gasification and tar oxidation, carbon conversion achieved in single pass of biomass through the gasifier, calculated using kinetic model, is quite low, which adversely affects the yield and LHV of the producer gas. Although equilibrium and semi-equilibrium models reveal relative insensitivity of producer gas characteristics towards temperature, the kinetic model shows significant effect of temperature on LHV of the gas at low air ratios. Kinetic models also reveal volume of the gasifier to be an insignificant parameter, as the net yield and LHV of the gas resulting from 6 m and 10 m riser is same. On a whole, the analysis presented in this paper indicates that thermodynamic models are useful tools for quantitative assessment of the gasification process, while kinetic models provide physically more realistic picture.

  3. On the asymptotic preserving property of the unified gas kinetic scheme for the diffusion limit of linear kinetic models

    International Nuclear Information System (INIS)

    Mieussens, Luc

    2013-01-01

    The unified gas kinetic scheme (UGKS) of K. Xu et al. (2010) [37], originally developed for multiscale gas dynamics problems, is applied in this paper to a linear kinetic model of radiative transfer theory. While such problems exhibit purely diffusive behavior in the optically thick (or small Knudsen) regime, we prove that UGKS is still asymptotic preserving (AP) in this regime, but for the free transport regime as well. Moreover, this scheme is modified to include a time implicit discretization of the limit diffusion equation, and to correctly capture the solution in case of boundary layers. Contrary to many AP schemes, this method is based on a standard finite volume approach, it does neither use any decomposition of the solution, nor staggered grids. Several numerical tests demonstrate the properties of the scheme

  4. Artificial Hydration and Nutrition

    Science.gov (United States)

    ... Crisis Situations Pets and Animals myhealthfinder Food and Nutrition Healthy Food Choices Weight Loss and Diet Plans ... Your Health Resources Healthcare Management Artificial Hydration and Nutrition Artificial Hydration and Nutrition Share Print Patients who ...

  5. Evaluation of kinetic uncertainty in numerical models of petroleum generation

    Science.gov (United States)

    Peters, K.E.; Walters, C.C.; Mankiewicz, P.J.

    2006-01-01

    Oil-prone marine petroleum source rocks contain type I or type II kerogen having Rock-Eval pyrolysis hydrogen indices greater than 600 or 300-600 mg hydrocarbon/g total organic carbon (HI, mg HC/g TOC), respectively. Samples from 29 marine source rocks worldwide that contain mainly type II kerogen (HI = 230-786 mg HC/g TOC) were subjected to open-system programmed pyrolysis to determine the activation energy distributions for petroleum generation. Assuming a burial heating rate of 1??C/m.y. for each measured activation energy distribution, the calculated average temperature for 50% fractional conversion of the kerogen in the samples to petroleum is approximately 136 ?? 7??C, but the range spans about 30??C (???121-151??C). Fifty-two outcrop samples of thermally immature Jurassic Oxford Clay Formation were collected from five locations in the United Kingdom to determine the variations of kinetic response for one source rock unit. The samples contain mainly type I or type II kerogens (HI = 230-774 mg HC/g TOC). At a heating rate of 1??C/m.y., the calculated temperatures for 50% fractional conversion of the Oxford Clay kerogens to petroleum differ by as much as 23??C (127-150??C). The data indicate that kerogen type, as defined by hydrogen index, is not systematically linked to kinetic response, and that default kinetics for the thermal decomposition of type I or type II kerogen can introduce unacceptable errors into numerical simulations. Furthermore, custom kinetics based on one or a few samples may be inadequate to account for variations in organofacies within a source rock. We propose three methods to evaluate the uncertainty contributed by kerogen kinetics to numerical simulations: (1) use the average kinetic distribution for multiple samples of source rock and the standard deviation for each activation energy in that distribution; (2) use source rock kinetics determined at several locations to describe different parts of the study area; and (3) use a weighted

  6. Point kinetics model with one-dimensional (radial) heat conduction formalism

    International Nuclear Information System (INIS)

    Jain, V.K.

    1989-01-01

    A point-kinetics model with one-dimensional (radial) heat conduction formalism has been developed. The heat conduction formalism is based on corner-mesh finite difference method. To get average temperatures in various conducting regions, a novel weighting scheme has been devised. The heat conduction model has been incorporated in the point-kinetics code MRTF-FUEL. The point-kinetics equations are solved using the method of real integrating factors. It has been shown by analysing the simulation of hypothetical loss of regulation accident in NAPP reactor that the model is superior to the conventional one in accuracy and speed of computation. (author). 3 refs., 3 tabs

  7. Generalizing a unified model of dark matter, dark energy, and inflation with a noncanonical kinetic term

    International Nuclear Information System (INIS)

    De-Santiago, Josue; Cervantes-Cota, Jorge L.

    2011-01-01

    We study a unification model for dark energy, dark matter, and inflation with a single scalar field with noncanonical kinetic term. In this model, the kinetic term of the Lagrangian accounts for the dark matter and dark energy, and at early epochs, a quadratic potential accounts for slow roll inflation. The present work is an extension to the work by Bose and Majumdar [Phys. Rev. D 79, 103517 (2009).] with a more general kinetic term that was proposed by Chimento in Phys. Rev. D 69, 123517 (2004). We demonstrate that the model is viable at the background and linear perturbation levels.

  8. AquaSAXS: a web server for computation and fitting of SAXS profiles with non-uniformally hydrated atomic models

    Science.gov (United States)

    Poitevin, Frédéric; Orland, Henri; Doniach, Sebastian; Koehl, Patrice; Delarue, Marc

    2011-01-01

    Small Angle X-ray Scattering (SAXS) techniques are becoming more and more useful for structural biologists and biochemists, thanks to better access to dedicated synchrotron beamlines, better detectors and the relative easiness of sample preparation. The ability to compute the theoretical SAXS profile of a given structural model, and to compare this profile with the measured scattering intensity, yields crucial structural informations about the macromolecule under study and/or its complexes in solution. An important contribution to the profile, besides the macromolecule itself and its solvent-excluded volume, is the excess density due to the hydration layer. AquaSAXS takes advantage of recently developed methods, such as AquaSol, that give the equilibrium solvent density map around macromolecules, to compute an accurate SAXS/WAXS profile of a given structure and to compare it to the experimental one. Here, we describe the interface architecture and capabilities of the AquaSAXS web server (http://lorentz.dynstr.pasteur.fr/aquasaxs.php). PMID:21665925

  9. Behaviour of defective CANDU fuel: fuel oxidation kinetic and thermodynamic modelling

    International Nuclear Information System (INIS)

    Higgs, J.

    2005-01-01

    The thermal performance of operating CANDU fuel under defect conditions is affected by the ingress of heavy water into the fuel element. A mechanistic model has been developed to predict the extent of fuel oxidation in defective fuel and its affect on fuel thermal performance. A thermodynamic treatment of such oxidized fuel has been performed as a basis for the boundary conditions in the kinetic model. Both the kinetic and thermodynamic models have been benchmarked against recent experimental work. (author)

  10. Physical Properties of Gas Hydrates: A Review

    Energy Technology Data Exchange (ETDEWEB)

    Gabitto, Jorge [Prairie View A& M University; Tsouris, Costas [ORNL

    2010-01-01

    Methane gas hydrates in sediments have been studied by several investigators as a possible future energy resource. Recent hydrate reserves have been estimated at approximately 1016?m3 of methane gas worldwide at standard temperature and pressure conditions. In situ dissociation of natural gas hydrate is necessary in order to commercially exploit the resource from the natural-gas-hydrate-bearing sediment. The presence of gas hydrates in sediments dramatically alters some of the normal physical properties of the sediment. These changes can be detected by field measurements and by down-hole logs. An understanding of the physical properties of hydrate-bearing sediments is necessary for interpretation of geophysical data collected in field settings, borehole, and slope stability analyses; reservoir simulation; and production models. This work reviews information available in literature related to the physical properties of sediments containing gas hydrates. A brief review of the physical properties of bulk gas hydrates is included. Detection methods, morphology, and relevant physical properties of gas-hydrate-bearing sediments are also discussed.

  11. Hydration study of ordinary portland cement in the presence of zinc ions

    Directory of Open Access Journals (Sweden)

    Monica Adriana Trezza

    2007-12-01

    Full Text Available Hydration products of Portland cement pastes, hydrated in water and in the presence of zinc ions were studied comparatively at different ages. Hydration products were studied by X ray diffractions (XRD and infrared spectroscopy (IR. Although IR is not frequently used in cement chemistry, it evidenced a new phase Ca(Zn(OH32. 2H2O formed during cement hydration in the presence of zinc. The significant retardation of early cement hydration in the presence of zinc is assessed in detail by differential calorimetry as a complement to the study carried out by IR and XRD, providing evidence that permits to evaluate the kinetic of the early hydration.

  12. Strength Estimation for Hydrate-Bearing Sediments From Direct Shear Tests of Hydrate-Bearing Sand and Silt

    Science.gov (United States)

    Liu, Zhichao; Dai, Sheng; Ning, Fulong; Peng, Li; Wei, Houzhen; Wei, Changfu

    2018-01-01

    Safe and economic methane gas production, as well as the replacement of methane while sequestering carbon in natural hydrate deposits, requires enhanced geomechanical understanding of the strength and volume responses of hydrate-bearing sediments during shear. This study employs a custom-made apparatus to investigate the mechanical and volumetric behaviors of carbon dioxide hydrate-bearing sediments subjected to direct shear. The results show that both peak and residual strengths increase with increased hydrate saturation and vertical stress. Hydrate contributes mainly the cohesion and dilatancy constraint to the peak strength of hydrate-bearing sediments. The postpeak strength reduction is more evident and brittle in specimens with higher hydrate saturation and under lower stress. Significant strength reduction after shear failure is expected in silty sediments with high hydrate saturation Sh ≥ 0.65. Hydrate contribution to the residual strength is mainly by increasing cohesion at low hydrate saturation and friction at high hydrate saturation. Stress state and hydrate saturation are dominating both the stiffness and the strength of hydrate-bearing sediments; thus, a wave velocity-based peak strength prediction model is proposed and validated, which allows for precise estimation of the shear strength of hydrate-bearing sediments through acoustic logging data. This method is advantageous to geomechanical simulators, particularly when the experimental strength data of natural samples are not available.

  13. Kinetic model for hydrothermal biomass gasification; Kinetisches Modell der hydrothermalen Biomassevergasung

    Energy Technology Data Exchange (ETDEWEB)

    Kruse, A.; Keskin, M.; Faquir, M.; Dahmen, N. [Inst. fuer Technische Chemie, Forschungszentrum Karlsruhe (Germany)

    2008-07-01

    Hydrothermal biomass gasification is a promising technology to produce hydrogen from wet biomass, i.e. a water content of at least 50 %. This process allows the utilization of agricultural wastes or residuals from biochemical conversions. Since the reaction is highly kinetically controlled, it should be possible to optimimize gas yield and composition with respect to a maximum hydrogen yield. The paper describes the simulation of the process using a kinetic reaction model and experimental data from appropriate test facilities. Experiments were performed for several reactor types and a variety of model systems, like glucose, methane and hydroxy methyl furfural, that were identified as intermediate product for the hydrothermal hydrogen production. The influence of different additive 'catalysts' was tested. It was shown that the biomass composition has an important influence on the gas yield. Alkaline salts can be added to increase the yield. A fast heating and agitation of the biomass are also increasing the gas yield.

  14. Relations between the kinetic equation and the Langevin models in two-phase flow modelling

    International Nuclear Information System (INIS)

    Minier, J.P.; Pozorski, J.

    1997-05-01

    The purpose of this paper is to discuss PDF and stochastic models which are used in two-phase flow modelling. The aim of the present analysis is essentially to try to determine relations and consistency between different models. It is first recalled that different approaches actually correspond to PDF models written either in terms of the process trajectories or in terms of the PDF itself. The main difference lies in the choice of the independent variables which are retained. Two particular models are studied, the Kinetic Equation and the Langevin Equation model. The latter uses a Langevin equation to model the fluid velocities seen along particle trajectories. The Langevin model is more general since it contains an additional variable. It is shown that, in certain cases, this variable can be summed up exactly to retrieve the Kinetic Equation model as a marginal PDF. A joint fluid and solid particle PDF which includes the characteristics of both phases is proposed at the end of the paper. (author)

  15. Ordering kinetics in model systems with inhibited interfacial adsorption

    DEFF Research Database (Denmark)

    Willart, J.-F.; Mouritsen, Ole G.; Naudts, J.

    1992-01-01

    . The results are related to experimental work on ordering processes in orientational glasses. It is suggested that the experimental observation of very slow ordering kinetics in, e.g., glassy crystals of cyanoadamantane may be a consequence of low-temperature activated processes which ultimately lead...

  16. Calcite growth kinetics: Modeling the effect of solution stoichiometry

    NARCIS (Netherlands)

    Wolthers, M.; Nehrke, G.; Gustafsson, J.P.; Van Cappellen, P.

    2012-01-01

    Until recently the influence of solution stoichiometry on calcite crystal growth kinetics has attracted little attention, despite the fact that in most aqueous environments calcite precipitates from non-stoichiometric solution. In order to account for the dependence of the calcite crystal growth

  17. Unanimous Model for Describing the Fast Bioluminescence Kinetics of Ca

    NARCIS (Netherlands)

    Eremeeva, Elena V.; Bartsev, Sergey I.; Berkel, van Willem J.H.; Vysotski, Eugene S.

    2017-01-01

    Upon binding their metal ion cofactors, Ca2+-regulated photoproteins display a rapid increase of light signal, which reaches its peak within milliseconds. In the present study, we investigate bioluminescence kinetics of the entire photoprotein family. All five recombinant hydromedusan Ca2+-regulated

  18. Unravelling the Maillard reaction network by multiresponse kinetic modelling

    NARCIS (Netherlands)

    Martins, S.I.F.S.

    2003-01-01

    The Maillard reaction is an important reaction in food industry. It is responsible for the formation of colour and aroma, as well as toxic compounds as the recent discovered acrylamide. The knowledge of kinetic parameters, such as rate constants and activation energy, is necessary to predict its

  19. Dynamic Modeling of Cell-Free Biochemical Networks Using Effective Kinetic Models

    Science.gov (United States)

    2015-03-03

    based whole-cell models of E. coli [6]. Conversely , highly abstracted kinetic frameworks, such as the cybernetic framework, represented a paradigm shift...metabolic objective function has been the optimization of biomass formation [18], although other metabolic objectives have also been estimated [19...experimental data. Toward these questions, we explored five hypothetical cell-free networks. Each network shared the same enzymatic connectivity, but

  20. Velocity Structure and 3D Finite Element Modeling for Critical Instability of Gas Hydrate-related Slipstream Submarine Slide, offshore Vancouver Island, Canada

    Science.gov (United States)

    LONG, S.; He, T.; Lan, K.; Spence, G.; Yelisetti, S.

    2016-12-01

    The previous study indicated that Slipstream submarine landslide is one of a gas hydrate-related slope failures on the frontal ridges of the Northern Cascadia accretionary margin, off Vancouver Island, Canada. The OBS data collected during SeaJade project were used to derive the subseafloor Vp & Vs structures. The anomalous high Vp of about 2.0 km/s at shallow depths of 100 (± 10) mbsf closely matches the estimated depth of the glide plane. The modelled Vs above the BSR at a depth of 265-275 mbsf is about 100-150 m/s higher than a theoretical 100% water saturated background value, indicating that the hydrate acts as part of the load-bearing matrix to increase the rigidity of the sediment. Also, the Vp & Vs above BSR both indicate a consistent 40% saturation of gas hydrate. On the basis of high accurate submarine bathymetry obtained by multibeam sounding system, the submarine landform before slump is reconstructed by comparing the slump headwall geometry with surrounding ridges. Using the elastic moduli determined from Vp & Vs, the stress status was calculated by the finite element method for different conditions and confirmed that the undersea sliding process related with gas hydrate starts from the toe of the slope and then progressively retreats to the place of current headwall, in a series of triangular blocks or wedges. The shear stress are then compared with the frame shear strength of geological model, which is critical for controlling slope stability of steep frontal ridges The simulation results found that the ridge was stable under its own weight, but gas hydrate saturation decrease and pore-water pressure increase will greatly reduce shear strength of sediments and may cause a landslide. Since the study area is in the earthquake belt, the large seismic acceleration will greatly affect pore pressure distribution within the ridge. The simulation results indicated that the shallow high-velocity gas hydrate layer coincident with glide plane depth is more