Chemical kinetics and self-ignition in a model supersonic hydrogen-air combustor

Self-ignition tests of a model scramjet combustor were conducted by using parallel sonic injection of gaseous hydrogen from the base of a blade-like strut into a supersonic vitiated airstream. The range of stagnation pressure and temperature studied varied from 1.0 to 4.5 MPa and from 1300 to 2200 K, respectively. Experimental results show that the self-ignition limit, in terms of either global or local quantities of pressure and temperature, exhibits a nonmonotonic behavior resembling the classical homogeneous explosion limit of the hydrogen-oxygen system. Specifically, for a given temperature, increasing pressure from a low value can render a nonignitable mixture to first become ignitable, then nonignitable again, This correspondence shows that, despite the globally supersonic nonpremixed configuration studied herein, ignition is strongly influenced by the intricate chemical reaction mechanism and thereby exhibits the homogeneous explosion character. Consequently, self-ignition criteria based on a global reaction rate approximating the complex chemistry are inadequate. An auxiliary computational study on counterflow ignition was also conducted to systematically investigate the contamination effects of vitiated air. Results indicate that the net contamination effects for the present experimental data are expected to be substantially smaller than contributions from the individual contamination species because of the counterbalancing influences of the H2O-inhibition and NO-promotion reactions in effecting ignition.

The induction plasma chemical reactor: Part II. Kinetic model

A kinetic model has been developed for the prediction of the concentration gelds in an rf plasma reactor. A sample calculation for a SiCl4/H2 system is then performed. The model considers the mixing processes along with the kinetics of seven reactions involving the decomposition of these reactants. The results obtained are compared to those assuming chemical equilibrium. The predictions indicate that an equilibrium assumption will result in lower predicted temperature fields in the reactor. Furthermore, for the chemical system considered here, while differences exist between the concentration fields obtained by the two models, the differences are not substantial.

A quantitative HPLC method for determining lactide content using hydrolytic kinetics

A new method for quantitative analysis of lactide has been developed by applying chemical kinetics to a HPLC system. The most important advance is its practical approach to the quantification of analytes that are unstable in the HPLC mobile phase. In HPLC analysis, anhydrous mobile phases cannot separate lactide from impurities, and only mixtures of water and organic solvent can achieve effective separation. By selecting conditions for testing and studying the kinetics of lactide hydrolysis, extensive experiments revealed that lactide degradation can be treated as a pseudo-first-order reaction under the given HPLC conditions, and lactide content or purity can be quantitatively determined. This method is practical for measuring the purity of the intermediate lactide in polylactic acid (PLA) production and the lactide content in PLA.

A New Ignition Criterion Based Upon a Critical Thermal Energy Density

It has long been known that various ignition criteria of energetic materials have been limited in applicability to small regions. In order to explore the physical nature of ignition, we calculated how much thermal energy per unit mass of energetic materials was absorbed under different external stimuli. Hence, data of several typical sensitivity tests were analyzed by order of magnitude estimation. Then a new concept on critical thermal energy density was formulated. Meanwhile, the chemical nature of ignition was probed into by chemical kinetics.

化学反应与饱和模型对化学氧碘激光性能的影响

将速率方程(RE)模型与化学动力学模型相结合,讨论了增益饱和模型与化学反应系统对COIL性能的影响.流动为预混的一维模型,考虑了10种成分和21个化学反应,分析计算了未分解碘分子,激发态氧产率,水含量以及温度等因素对COIL性能的影响.计算结果表明,碘流量过多,混合和反应过程中消耗大量能量;碘流量过低,导致粒子数反转和增益过低,对于能量的提取不利.

Combined Effects of Hot Curing Conditions and Reaction Heat on Rubber Vulcanization Efficiency and Vulcanizate Uniformity

A mathematical model of the chemical kinetics of silicone rubber Vulcanization is developed, with the thermal effects being computed using the increment method, and the hot Vulcanization process estimated with the finite element method. The results show that the reaction heat of rubber vulcanization is important for energy saving, and that a proper curing medium temperature is important when considering both vulcanization efficiency and vulcanizate uniformity. The results also indicate that increases in the forced convective heat transfer coefficient have no significant effect above a certain level. The validity of the numerical model is indirectly proven by comparison with existing data.

水-岩土反应的力学与环境效应研究

The research on mechanical effects of water-rock and soil interaction on deformation and failure of rocks and soils involves three aspects of mechanics, physics and chemistry. It is the cross between geochemistry and rock mechanics and soil mechanics. To sum up, the mechanical effects of water-rock and soil interaction is related to many complex processes. Research in this respect has been being an important forward field and has broad prospects. In connection with the mechanism of the effects of the chemical action of water-rock on deformation and failure of rocks and soils, the research significance, the present state, the developments in this research domain are summarized. Author prospects the future of this research. The research of the subject should be possessed of important position in studying engineering geology and will lead directly to a new understand on geological hazard and control research. In order to investigation the macroscopic mechanics effects of chemical kinetics of water-rock interaction on the deformation and failure, calcic rock, red sandstone and grey granite reacting chemically with different aqueous solution at atmospheric temperature and atmospheric pressure are uniaxially compressed. The quantitative results concerning the changes of uniaxially compressive strength and elastic modulus under different conditions are obtained. It is found that the mechanical effects of water on rock is closely related to the chemical action of water-rock or the chemical damage in rock, and the intensity of chemical damage is direct ratio to the intensity of chemical action in water-rock system. It is also found that the hydrochemical action on rock is time-dependent through the test. The mechanism of permeation and hydrochemical action resulting in failure of loaded rock mass or propagation of fractures in rocks would be a key question in rock fracture mechanics. In this paper, the fracture mechanical effects of chemical action of water-rock and their time- and chemical environment-dependent behavior in grey granite, green granite, grey sandstone and red sandstone are analyzed by testing K_(IC) and COD of rock under different conditions. It is found that: ①the fracture mechanical effect of chemical action of water-rock is outstanding and time-dependent, and high differences exist in the influence of different aqueous solution, different rocks, different immersion ways and different velocity of cycle flow on the fracture mechanical effects in rock. ②the mechanical effects of water-rock interaction on propagation of fractures is consistent with the mechanical effects on the peak strength of rock. ③the intensity of the mechanical fracture effects increases as the intensity of chemical action of water-rock increases. ④iron and calcium ion bearing mineral or cement in rock are some key ion or chemical composition, and especially iron ion-bearing mineral resulting in chemical action of water-rock to be provided with both positive and negative mechanical effects on rock. Through the above two tests, we suggest that primary factors influencing chemical damage in rock consist of the chemical property of rock and aqueous solution, the structure or homogeneity of rocks, the flow velocity of aqueous solution passing through rock, and cause of formation or evolution of rock. The paper explores the mechanism on the mechanical effects of water-rock interaction on rock by using the theory of chemistry and rock fracture mechanics with chemical damage proposed by author, the modeling method and the energy point of view. In this paper, the concept of absorbed suction between soil grains caused by capillary response is given and expounded, and the relation and basic distinction among this absorbed suction, surface tension and capillary pressure of the soil are analyzed and established. The law of absorbed suction change and the primary factors affecting it are approached. We hold that the structure suction are changeable along with the change of the saturation state in unsaturated soils. In view of this, the concept of intrinsic structure suction and variable structure suction are given and expounded, and this paper points out: What we should study is variable structure suction when studying the effective stress. By IIIy κHH's theory of structure strength of soils, the computer method for variable structure suction is analyzed, the measure method for variable structure suction is discussed, and it reach the conclusions: ①Besides saturation state, variable structure suction is affected by grain composition and packing patter of grains. ②The internal relations are present between structure parameter N in computing structure suction and structure parameter D in computing absorbed suction. We think that some problems exit in available principle of effective stress and shear strength theory for unsaturated soil. Based on the variable structure suction and absorbed suction, the classification of saturation in soil and a principle of narrow sense effective stress are proposed for unsaturated soils. Based on generalized suction, the generalized effective stress formula and a principle of generalized effective stress are proposed for unsaturated soils. The experience parameter χ in Bishop's effective stress formula is defined, and the principal factors influencing effective stress or χ. The primary factor affecting the effective stress in unsaturated soils, and the principle classifying unsaturated soils and its mechanics methods analyzing unsaturated soils are discussed, and this paper points out: The theory on studying unsaturated soil mechanics should adopt the micromechanics method, then raise it to macromechanics and to applying. Researching the mechanical effects of chemical action of water-soil on soil is of great importance to geoenvironmental hazard control. The texture of soil and the fabric of soil mass are set forth. The tests on physical and mechanical property are performed to investigate the mechanism of the positive and negative mechanical effects of different chemical property of aqueous solution. The test results make clear that the plastic limit, liquid limit and plasticity index are changed, and there exists both positive and negative effects on specimens in this test. Based on analyzing the mechanism of the mechanical effects of water-soil interaction on soil, author thinks that hydrochemical actions being provided with mechanical effects on soil comprise three kinds of dissolution, sedimentation or crystallization. The significance of these tests lie in which it is recognized for us that we may improve, adjust and control the quality of soils, and may achieve the goal geological hazard control and prevention.The present and the significance of the research on environmental effects of water-rock and soil interaction. Various living example on geoenvironmental hazard in this field are enumerated. Following above thinking, we have approached such ideals that: ①changing the intensity and distribution of source and sink in groundwater flow system can be used to control the water-rock and soil interaction. ②the chemical action of water-rock and soil can be used to ameliorate the physical and mechanical property of rocks and soils. Lastly, the research thinking and the research methods on mechanical effects and environmental effects of water-rock and soil interaction are put forward and detailed.

塔里木盆地塔中地区寒武-奥陶系烃源岩古地温及成烃演化史研究

The present maturity of Cambrian and Ordovician source rocks in Tazhong area, Tarim basin, is studied using several organic petrology methods and conodont CAI method. The highest palaeotemperature that the Cambrian-Ordovician undergone is revealed by Laser Roman Microprobe (LRM) analysis and by simulating experiment of the kerogen chemical kinetics. In according to all above study, the thermal history of Cambrian and Ordovician is reconstructed based on numerical simulating approaches. The characteristics of secondary hydrocarbon generating are studied by inclusions analysis. The reflectances of the samples in the drills located in Tazhong area show that the maturities of Cambrian source rocks are in the stages of condense oil-dry gas, and that of Ordovician source rocks range from peak of oil generating to wet gas stage. The palaeotemperature data of Cambrian-Orovician source rocks from well Tacan 1, based on LRM analysis, are in coincidence with that from other methods. Also are the palaeotemperature data of Cambrian-Orovician source rocks in well Tacan 1 based on the simulating experiments of kerogen pyrolysis, similar to the homogenization temperatures of inclusions in the source rocks. Aaccording to the vitrinite inflectance data of the TZ12 well and Tacan 1 well, the paleotemperature gradients are analysized and reconstructed. These data show that the paleotemperature gradient in Tazhong area was the highest during Cambrian-Ordovician period, it was up to 3.5°C/100m. Following, the temperature gradient descended gradually and it reached to the lowest at present (2.2°C/100m). The histories of maturation and hydrocarbon generation of Cambrian and Ordovician source rocks in Tazhong area are researched systematically and quantitatively, the results show that periods of oil generation from Cambrian and Ordovician source rocks lasted for a long time from Ordovician to Carbonferious periods because the central Cambrian stratum in the north slope of Tazhong area is buried differently in depth. The top of the Cambrian entered into the peak of oil generation in middle-late Ordovician, and most area of the north slope of Tazhong area entered into the peak of oil generation in Carbonferious period, and on the uplift belt some of source rocks entered into the peak of oil generation in Permian period. In early Devonian, the central of the Lower Ordovician source rocks near the Manjiaer depression reached the peak of oil generation and near the top of the Tazhong uplift did not reached the peak of oil generation until early Cretaceous. The middle-upper Ordovician entered into the peak of oil generation in early-middle Jurassic. The time of the middle-upper Ordovician in the top of the uplift belt entering into the peak of oil generation was delayed, because the source rock was buried shallowly, and it did not reached the peak of oil generation until middle Cretaceous. Middle-upper Ordovician in the top of the north slope has been in the peak of oil generation now, it is consistent with the maturity (1.0-1.2%Ro) of the source rocks. The characteristics of the inclusions formed by kerogens are different from that by crystal-enclosed organic matters(OM) during secondary hydrocarbon generation of Cambrian and Ordovician source rocks. The secondary hydrocarbon generation mainly occurred in Mesozoic-Cenozoic period, in an area of about 9000km2 in the north slope. The intensity of the secondary hydrocarbon generation of Cambrian and Ordovician is up to 21kg/torg and 36kg/torg) respectively. Using the staged gas chromatography, the high-over maturated carbonate source rocks are analysized to release the adsorbed OM, inclusions OM and crystal-enclosed OM, respectively, and to evaluate their relative contributions to secondary hydrocarbon generation. The three periods of oil and gas migration and petroleum pools formation in Tazhong area are determined according to organic inclusions and solid bitumen.

A collision model for DNA separation by capillary electrophoresis in dilute polymer solution

A theoretical description. based on chemical kinetics and electrochemistry, is given of DNA separation in dilute polymer solution by capillary electrophoresis. A self-consistent model was developed leading to predictions of the DNA electrophoretic velocity as a function of the experimental conditions - polymer concentration, temperature, and electric field strength. The effect of selected experimental variables is discussed. The phenomena discussed are illustrated for the example of 100 bp DNA ladder separation in dilute HPMC solution by capillary electrophoresis. This model is the first single model that can fully explain the dependence of DNA electrophoretic velocity on electrophoretic conditions.

Semi-gas kinetics model for performance modeling of flowing chemical oxygen-iodine lasers (COIL)

A semi-gas kinetics (SGK) model for performance analyses of flowing chemical oxygen-iodine laser (COIL) is presented. In this model, the oxygen-iodine reaction gas flow is treated as a continuous medium, and the effect of thermal motions of particles of different laser energy levels on the performances of the COIL is included and the velocity distribution function equations are solved by using the double-parameter perturbational method. For a premixed flow, effects of different chemical reaction systems, different gain saturation models and temperature, pressure, yield of excited oxygen, iodine concentration and frequency-shift on the performances of the COIL are computed, and the calculated output power agrees well with the experimental data. The results indicate that the power extraction of the SGK model considering 21 reactions is close to those when only the reversible pumping reaction is considered, while different gain saturation models and adjustable parameters greatly affect the output power, the optimal threshold gain range, and the length of power extraction.

Kinetics and transport model for the chemical vapor epitaxy of GexSi1-x

A numerical model that combines mass transport and surface kinetics was applied, for the first time, to the chemical vapor epitaxy of GexSi1-x. The temperature, velocity and concentration fields were calculated from the conservation equations for energy, momentum and species coupled with the boundary conditions on the growth surface which were determined by surface kinetics. The deposition rates of Si and Ge were assumed to be limited, respectively, by surface kinetics and mass transport. A theoretical relation between the initial conditions and the Ge composition in the solid was established. The calculated growth rate as well as the Ge composition in the solid and its dependence on growth temperature agree well with experimental data.

Kinetics of the oxidation of MCRR by potassium permanganate

The occurrence of the microcystins in the water bodies, especially in drinking water resources, has received considerable attentions. In situ chemical oxidation is a promising cost-effective treatment method to remove MC from water body. This research investigated the reaction kinetics of the oxidation of MCRR by permanganate. Experimental results indicate that the reaction is second order overall and first order with respect to both permanganate and MCRR, and has an activation energy of 18.9 kJ/mol. The second-order rate constant ranges from 0.154 to 0.225 l/mg/min at temperature from 15 to 30 degrees C. The MCRR degradation rates can be accelerated through increasing reaction temperature and oxidant concentration. The reaction under acid conditions was slightly faster than under alkaline conditions. The half-life of the reaction was less than 1 min, and more than 99.5% of MCRR was degraded within 10 min. (c) 2005 Elsevier Ltd. All rights reserved.

Kinetically controlled InN nucleation on GaN templates by metalorganic chemical vapour deposition

This paper presents a study on the nucleation and initial growth kinetics of InN on GaN, especially their dependence on metalorganic chemical vapour deposition conditions. It is found that the density and size of separated InN nano-scale islands can be adjusted and well controlled by changing the V/III ratio and growth temperature. InN nuclei density increases for several orders of magnitude with decreasing growth temperature between 525 and 375 degrees C. At lower growth temperatures, InN thin films take the form of small and closely packed islands with diameters less than 100 nm, whereas at elevated temperatures the InN islands grow larger and become well separated, approaching an equilibrium hexagonal shape due to enhanced surface diffusion of adatoms. The temperature dependence of InN island density gives two activation energies of InN nucleation behaviour, which is attributed to two different kinetic processes related to In adatom surface diffusion and desorption, respectively.