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EN
Numerical studies on detonation wave propagation in rotating detonation engine and its propulsive performance with one- and multi-step chemistries of a hydrogen-based mixture are presented. The computational codes were developed based on the three-dimensional Euler equations coupled with source terms that incorporate high-temperature chemical reactions. The governing equations were discretized using Roe scheme-based finite volume method for spatial terms and second-order Runge-Kutta method for temporal terms. One-dimensional detonation simulations with one- and multi-step chemistries of a hydrogen-air mixture were performed to verify the computational codes and chemical mechanisms. In two-dimensional simulations, detonation waves rotating in a rectangular chamber were investigated to understand its flowfield characteristics, where the detailed flowfield structure observed in the experiments was successfully captured. Three-dimensional simulations of two-waved rotating detonation engine with an annular chamber were performed to evaluate its propulsive performance in the form of thrust and specific impulse. It was shown that rotating detonation engine produced constant thrust after the flowfield in the chamber was stabilized, which is a major difference from pulse detonation engine that generates repetitive and intermittent thrust.
PL
Przedstawiono badania numeryczne propagacji fali detonacyjnej w wirującym silniku detonacyjnym oraz jego wydajności pędnej z jedno- i wielostopniową mieszanką chemiczną na bazie wodoru. Kody obliczeniowe opracowano w oparciu o trójwymiarowe równania Eulera w połączeniu z pojęciami źródłowymi, które obejmują wysokotemperaturowe reakcje chemiczne. Obowiązujące równania zostały zdyskredytowane przy użyciu metody skończonej objętości opartej na schemacie Roe'a dla terminów przestrzennych oraz metody Runge-Kutta drugiego rzędu dla terminów czasowych. W celu weryfikacji kodów obliczeniowych i mechanizmów chemicznych przeprowadzono jednowymiarowe symulacje detonacji z jedno- i wieloetapowymi chemikaliami mieszaniny wodoru i powietrza. W symulacjach dwuwymiarowych badano fale detonacyjne obracające się w komorze prostokątnej w celu zrozumienia jej charakterystyki pola przepływu, gdzie udało się uchwycić szczegółową strukturę pola przepływu zaobserwowaną w doświadczeniach. Przeprowadzono trójwymiarowe symulacje dwufalowego wirującego silnika detonacyjnego z komorą pierścieniową w celu oceny jego właściwości pędnych w postaci ciągu i impulsu właściwego. Wykazano, że wirujący silnik detonujący wytwarza stały ciąg po ustabilizowaniu się pola przepływu w komorze, co stanowi istotną różnicę w stosunku do silnika detonującego impulsowo, który wytwarza powtarzalny i przerywany ciąg.
PL
Wyznaczono przebiegi krzywych kinetycznych dla reakcji złożonych przy użyciu metody Monte Carlo. Rozważono zarówno odwracalne, jak i nieodwracalne reakcje równoległe, następcze, następczo-równoległe oraz autokatalityczne. Wykazano całkowitą zgodność wyników symulacji stochastycznych z wynikami otrzymanymi w oparciu o modele deterministyczne.
EN
Kinetic curves for multiple reactions have been determined by the means of the Monte Carlo method. Both reversible and nonreversible parallel, series, series-parallel and autocatalytic reactions have been taken under consideration. The complete consistency between results of stochastic calculations and results obtained with the use of deterministic models has been shown.
EN
The problem of simultaneous growth and competition of intermediate phases during reactive diffusion was analyzed by Gösele and Tu in 1982. In this work we reformulate old problem and propose method based on volume fixed frame of reference. It allows computing the material velocity in the reacting system in which reactions at several moving interfaces occur. All reactions lead to the lattice shift due to the difference of intrinsic diffusivities and different molar volumes. The following peculiarities are taken into account: (1) the deviation from local equilibrium at both interfaces of each moving inter-phase zone (i.e., at each side of the moving phase-boundary); (2) different mobility of the components in the interphase zone; (3) nonzero steps of molar volumes for each component from phase to phase and (5) different physicochemical properties of the interphase zones. We show the scale effect on the kinetic of the corrosion, the non-parabolic reactions, the multiphase scale growth and present the potential applications of the method.
PL
W 1982 roku Gösele i Tu analizowali problem równoczesnego wzrostu i kolejności powstawania wielofazowej zgorzeliny podczas procesu dyfuzji. W niniejszej pracy problem ten został rozwinięty i po raz pierwszy prezentujemy rozwiązanie w układzie odniesienia jakim jest sieć krystaliczna materiału. Takie podejście pozwala na wyznaczenie prędkości materiału uwzględniając wiele poruszających się granic międzyfazowych. Przesuwanie się granic faz jest wynikiem różnicy we współczynnikach dyfuzji oraz objętości molowych tworzących się faz (tlenków). W modelu wzięto pod uwagę: (1) niestechiometrię faz (po każdej stronie granicy między fazowej); (2) różne współczynniki dyfuzji składników; (3) różne objętości molowe składników oraz (4) różne właściwości fizykochemiczne granic faz. W pracy pokazany został wpływ skali na kinetykę procesu korozji, nieparaboliczność, wzrost warstw wielofazowych oraz inne możliwości aplikacyjne modelu.
EN
In this work, our goal is to study the effect of the total pressure and the charging voltage on the amplification and propagation of non-uniformities in volume for a XeCl laser. This study is executed by using a parallel resistor network model (PRN). In this model, the surface of discharge is divided ideally into a resistances network in parallel. The obtained results show clearly that the formation of the plasma non-uniformity in volume and on a large scale is in this case related mainly to the chemical kinetics of the laser medium, and the increase in the pressure and applied voltage discharge parameters consequently amplifies any non-uniformity.
5
Content available remote Badania Ludwika Brunera (1871-1913) kinetyki chemicznej
EN
In the article were discussed research works that were taken up on Polish territories by the Cracow scientist, and the first professor of Physical Chemistry - Ludwik Bruner over kinetics of homogenous and heterogenous systems. The kinetic searches of Bruner rere the crucial point in his activity. Up till now there has appeared a small number of ublications presenting the most significant achievements of the scientist. Bruner's research works over kinetics can be divided thematically into 2 main: part: -reactions velocity, photokinetics and catalysis of homogenous systems: kinetics of substitution of bromine in aromatic compounds, and addition of bromine to nonsaturated compounds, catalysis in bromination - and particularly the catalyctic action of iodine, kinetics of estrification; experiments on effect of light on the process and chemical reactions velocity -kinetics of heterogenous systems: research on the velocity of dissolution of solid bodies according to Noyes-Whitney's standard. Bruner's research works over kinetics played a significant role in the development of the scientific research on organic reactions velocity and dissolution velocity.
EN
An attempt of interpretation of the different temperature relationship of macrokinetic equation constant in the process of nitric oxide oxidation has been undertaken. It has been proved that the reaction at lower temperature proceeds according to the composite reaction mechanism. At higher temperature the mechanism of an elementary reaction prevails. The worked out quantitative relations are the completing information about correct values of rate constants.
PL
Podjęto próbę interpretacji stałej równania makrokinetycznego procesu utleniania tlenku azotu w zmiennej temperaturze. Dowiedziono, że w niższej temperaturze proces przebiega według mechanizmu reakcji złożonej. W temperaturze wyższej przeważa mechanizm reakcji elementarnej. Wyprowadzone ilościowe zależności uzupełniają informacje o poprawnych wartościach stałych szybkości reakcji elementarnych.
PL
Badano kinetykę procesu hydrolizy mocznika w roztworze wodnym w zakresie stężeń mocznika odpowiadającym ściekom przemysłowym 5-20 g/dm3, dla temperatur 343-363 K i czasu 0-4200 s. Wyznaczono równanie kinetyczne procesu, stałe szybkości reakcji hydrolizy oraz parametry równania Arrheniusa. Uzyskane równanie kinetyczne jest użyteczne przy projektowaniu technologii oczyszczania ścieków mocznikowych.
EN
Kinetics of urea hydrolysis process was examined. Range of urea concentration corresponded to industrial wastewater concentration of 5-20 g/dm3, temperature was 345-363 K and time 0-4200 s. Kinetic equation of the process, rate constants hydrolysis process and Arrhenius equation's parameters were determined. Results can be used during design of urea removal processes.
EN
Quantum mechanical ab initio calculations have been performed at various levels of theory to study kinetics of the reactions of fluorine, chlorine and bromine atoms with trifluoromethanol. Total energies were improved by using Gaussian-2 (G2) methodology. It is shown that the considered reactions proceed with formation of intermediate complexes. The mechanism of the reactions studied appears to be more complex and may consist of three elementary steps. The heights of the calculated energy barriers explain the differences of the reactivity of F, C1 and Br atoms towards CFsOH. The rate constants and their temperature dependence for the reactions CFsOH + X (fcx) and CFaO + HX (kfix) were calculated. The derived analytical expressions [chemical formulas] allow the description of the kinetics of the reactions under investigation. This is of considerable importance for the chemical modelling studies because of the lack of experimental measurements.
EN
The kinetics of oxidation of threonine by permanganate in alkaline medium at a constant ionic strength has been studied spectrophotometrically. The reaction between permanganate threonine in alkaline medium exhibits 1:2 stoichiometry (KMnC>4: threonine). The reaction shows first order dependence of rate on permanganate concentration and less than unit order dependence each in threonine and alkali concentrations. Reaction rate increases with an increase in ionic strength and a decrease in solvent polarity of the medium. Initial addition of reaction products did not affect the rate significantly. A mechanism involving the formation of an intermediate complex between oxidant and substrate has been proposed. The rate constants and the activation parameters for the slow step of the mechanism have been evaluated and discussed.
EN
The rate of gel-growth for spherical ionotropic metal alginate gel droplets has been studied. Experimental observations have shown that the relaxation time of the metal alginate ionotropic gel complexes of the droplet shapes decreased in the order Hg > Cd > Sn > Pb-alginates, whereas the velocity of sinking under gravitational acceleration decreases in the same order. The factors which affect the relaxation time and velocity of acceleration, such as the concentration and viscosity of the alginate sol, the nature and radius of the metal ion as well as the density and pH of the electrolyte solution have been examined. The activation energies indicated that the stability of these metal alginate gel complexes follows the order Hg > Cd > Pb ~ Sn alginates. A mechanism consistent with the experimental results has been discussed.
EN
Defect structure and the mobility of point defects in pure metal-deficient cobalt oxide (Co1-yO) and in Co1-yO-Cr(2)O(3) solid solutions have been studied as a function of temperature (1,223-1,573 K) and oxygen pressure (10-10(5)Pa) using microther-mograwimetric techniques. It has been shown that the predominant defects in pure and Cr-doped cobaltous oxide are singly ionized cation vacancies, and 3% at. of dopant is high enough to fix the concentration of predominant defects in such solid solutions on a constant level, being much higher than in pure Co(1-yO. The mobility of point defects in pure Co1-yO has been found to be concentration independent, strongly suggesting that in spite of rather high concentration no interactions and clustering of defects is to be expected. On the other hand, in Cr-doped cobaltous oxide, the defect structure is more complicated, although singly ionized cation vacancies seem to be still predominant defects.
PL
Dążąc do porównania metod wyznaczania reakcyjności paliw stałych metodą genewską i Nippon Steel Corporation (NSC) na podstawie wcześniejszych prac własnych i ustalonych w nich prawidłowościach, przeprowadzono doświadczalną analizę wpływu rozdrobnienia próbki na wynik ich oznaczania. Badania te dały podstawę do weryfikacji założeń kinetyki metody genewskiej w stosunku do badań opisanych w literaturze nad przebiegiem reakcji Boudouarda. Dyskusja upoważniła do stwierdzenia, że w metodzie genewskiej wyznaczamy reakcyjność pozorną mimo, że odnosimy ją tylko do zewnętrznej powierzchni właściwej a nie do reaktywnej. Praca umożliwiła stwierdzenie, że metoda NSC zminimalizowała wątpliwości dotyczące związków pomiędzy reakcyjnością wyznaczoną z analizy fazy gazowej a powirzch-nią właściwą. Wyznaczany wskaźnik CRI zmienia się z czasem reakcji wg kinetyki 0-rzędu dla szerokiej gamy koksów wysokogatunkowych.
EN
The influence of chromium and lithium on the manganese sulphidation kinetics has been studied as a function of temperature (973-1273 K) and sulphur activity (10(-1)-10(4)Pa) using a novel microthermogravimetric technique. It has been shown that the sulphidation of Mn-Cr and Mn-Li alloys, like that of pure manganese metal, follows strictly parabolic rate law being thus diffusion controlled. In agreement with the defect model of Mn(1-y)S it has been found that the sulphidation rate of Mn-Cr alloy is higher than that of pure manganese, the reaction rate is pressure independent and the activation energy of this process is lower. This implies that the concentration of cation vacancies in Mn(1-y)S-Cr(2)S(3) solid solution is fixed on the constant level by three-valent chromium ions substitutionally incorporated in the cation sublattice of this sulphide. In the case of Mn-Li alloy, on the other hand, the sulphidation rate is lower than that of pure manganese, and the activation energy is higher. These results can again be explained in terms of doping effect.
EN
The kinetics of gelation between Zn(II), Cd(II) and Pb(II) metal ion electrolytes and sodium alginate polysaccharide sol have been studied complexometrically at temperatures between 35 and 65°C. Using a large excess of alginate sol concentration, the pseudo first-order plots of exchange between Na+ counter ions of the macromolecular chains of alginate sol and the metal ions give sigmoidal curves with two distinct regions. The initial part was relatively fast and curved significantly at early times, followed by a slow decrease in the rates at longer times. The rate constants of gelation were found to show second-order overall kinetics and first-order in the concentration of both reac-tants. The kinetic parameters have been evaluated and a consistent gelation mechanism is suggested.
EN
The reaction between permanganate and choline chloride (Ch-Cl) in alkaline medium exhibits 4:1 stoichiometry (KMnO(4) choline chloride). The reaction shows first order dependence of the rate on permanganate concentration and less than a unit order dependence each in choline chloride and alkali concentration. The reaction rate decreases with an increase in ionic strength. Initial addition of reaction products did not affect the rate significantly. A mechanism involving the formation of an intermediate complex between alkaline species of permanganate and substrate has been proposed. The rate constants and activation parameters for the slow step of the mechanism have been evaluated and discussed.
EN
Irreversible adsorption of colloid particles at heterogeneous surfaces was studied experimentally. The substrate of controlled heterogeneity was produced by covering mica sheets by colloid iron oxide (hematite) particles to a desired concentration. The particles of averaged diameter of 70 nm were produced by forced hydrolysis of FeCls solutions followed by a hydrothermal ageing. The coverage of colloid hematite particles (heterogeneity degree) was determined by electron microscopy and atomic force microscopy (AFM). Adsorption kinetics of polystyrene latex (averaged diameter 0.87Mim) at heterogeneous surfaces was studied by using the direct optical microscope observations in the impinging-jet cell. It was demonstrated that the initial adsorption rate attained the limiting value pertinent to homogeneous surfaces for heterogeneity degree of a few per cent. This behaviour was quantitatively interpreted in terms of the theoretical model considering the coupling between surface and bulk transport of particles. Similarly, the experimental results obtained for higher surface coverage of latex (long adsorption times) were in a good agreement with the random sequential adsorption (RSA) model.
EN
The oxidation is first order each in [substrate] and the [oxidant]. The reaction follows an acid catalysed path, exhibiting second order dependence in [H+]. Bunnett's plot indicates that water acts as a nucleophile. Protonated form of oxidant has been postulated as the reacting oxidizing species. The rate studied at four different temperatures enabled us to calculate activation parameters. A suitable mechanism has been proposed.
EN
The kinetics and mechanism of oxidation of some primary and secondary alcohols with pyridinium dichromate (PDC) catalyzed by p-toluenesulphonic acid (TsOH) has been investigated in acetonitrile medium. The reaction exhibits first-order dependence on [PDC]. Michaelis-Menten dependence is observed on [alcohol]. TsOH enhances the rate of the reaction remarkably. Order dependence on [TsOH] is more than a first-order and less than a second-order. Pyridine retards the rate of oxidation significantly indicating the possibility of a parallel competitive reaction with TsOH. Studies indicate the formation of water even under anhydrous conditions. The kinetic results are analyzed in terms of Taft's original constants (a and Es) and the improved constants (cr* and El). Minor importance of steric effects is well justified by the low values of steric reaction constants.
EN
The title reaction has been studied by infrared tunable diode laser spec-troscopy which allows for the detection of both reactant and product molecules. The decay rate of ammonia in the presence of nitrogen dioxide was found to be second order with respect to the concentration of NO2- The simultaneous formation of water was found to occur with a relative yield of 4[H2O] = —0.5^[NH3]. The formation of aerosols containing crystalline ammonium nitrate implies that nitric acid is also a primary reaction product in the overall reaction 2NO2 + 2NHa —> N2 + H(2)O + NH(4)NOs. A reaction mechanism involving asym-N(2)O(4) reacting with NHa has been tested by detailed computer modelling which was used to account for all of the observed kinetic and mechanistic features. For the rate controlling step 2NO2 + M —> asym- N2C>4 + M (1) we have determined an apparent bimolecular rate constant of k\ — 2.30 x 10(-4) x exp(3838 =360/T)M(-1)s(-1) at a total pressure of 30 mbar.
EN
The kinetics of kojic acid reduction of hexachloroiridate (IV) in aqueous perchlorate solutions at constant ionic strength of 1.0 mol dm (-3) has been investigated spectrophotometrically. The reaction showed a first-order dependence in [IrCle]2" and a fractional-order with respect to kojic acid concentration. Kinetic evidence for the formation of an intermediate complex via free-radical mechanism is presented. The results obtained indicate that increasing the [H+] is accompanied by an appreciable acceleration of the rate of reaction at pH's< 0.4. The activation parameters have been evaluated and a tentative reaction mechanism consistent with the results is suggested.
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