High temperature rate coefficient for the reaction of O(P) with H2 obtained by the resonance absorption of O and H atoms

The reaction of O(³P) with H₂ has been studied behind reflected shock waves in the temperature range of 1713–3532K at total pressures of about 1.4–2.0 bar by Atomic Resonance Absorption Spectroscopy using mixtures of N₂O and H₂ highly diluted in Ar. The O atoms were generated by the fast thermal decomposition of N₂O and the reaction with H₂ was followed by monitoring the time dependent O and H atom concentrations in the postshock reaction zone. For the experimental conditions chosen, the measured O and H atom concentrations were primarily sensitive to the well-known N₂O dissociation and to the studied reaction and hence its rate coefficient could be deduced. The measured rate coefficient data are fitted by the least-squares method to obtain the following three parameter expression: K₄=3.72×10⁶(T/K)^2.17exp(−4080K/T)cm³ mol⁻¹8⁻, which is in excellent agreement with the recent ab initio calculations for the rate coefficient of this reaction in the overlapping temperature range. The present result is also compared to the experimental results reported by earlier investigators.     

Shock tube measurements of high temperature rate constants for OH with cycloalkanes and methylcycloalkanes

High temperature experiments were performed with the reflected shock tube technique using multi-pass absorption spectrometric detection of OH radicals at 308 nm. The present experiments span a wide T-range, 801-1347 K, and represent the first direct measurements of the title rate constants at T>500 K for cyclopentane and cyclohexane and the only high temperature measurements for the corresponding methyl derivatives. The present work utilized 48 optical passes corresponding to a total path length ∼4.2 m. As a result of this increased path length, the high [OH] detection sensitivity permitted unambiguous analyses for measuring the title rate constants. The experimental rate constants in units, cm³ molecule⁻¹ s⁻¹, can be expressed in Arrhenius form as

     

Modified Johnson-Cook description of wide temperature and strain rate measurements made on a nickel-base superalloy

In this study, uniaxial compression experiments of a Nickel-base superalloy is conducted over a wide range of temperatures (298–1073 K) and strain rates (0.1–5200/s) to obtain further understandings of the plastic flow behaviours. The temperature and strain rate effects on the plastic flow behaviour are analysed. The flow stress decreases with increasing temperature below 673 K. Within the temperature range of about 673–873 K, the flow stress varies indistinctively, and even increases slightly with increasing temperature. As the temperature further increases, the flow stress decreases again. The flow stress of the Nickel-base superalloy displays insensitive to strain rate below 800/s and an enormous increase with increasing strain rate in excess of 800/s. Then the effects of temperature and strain rate on the microstructure are discussed. The result shows that high strain rate and high temperature may make the grain boundary of Nickel-base superalloy frail. Taking into account the anomalous temperature and strain rate dependences of flow stress, modified J–C constitutive model is developed. The model is shown to be able to accurately predict the plastic flow behaviour of Nickel-base superalloy over a wide range of temperatures and strain rates.     

Wide band cumulative absorption coefficient distribution model for overlapping absorption in H2O and CO2 mixtures

An accurate wide band cumulative absorption coefficient distribution, g(k), model for thermal radiative transfer in gaseous media containing H₂O and CO₂ is presented. Assuming that the convoluted g(k) function for gas mixture retains the same functional form as the individual gases, the model treats overlapping bands as a “single”, complex band with scaled parameters. Corresponding scaling algorithms are proposed for specific overlapping regions. Predictions of the mixture g(k) function and the band absorptance are in good agreement with the line-by-line calculation over a wide range of temperatures from 500 to 2500 K, and pressures up to 10.0 atm. The g(k) model is generally more accurate than the exponential wide band model, and provides comparable accuracy to the statistical narrow-band model in predicting the total emissivity along an isothermal and homogeneous gas column under typical combustion conditions. In addition, this approach significantly enhances the computational efficiency.     

Updated band model parameters for H2O,CO2, CH4 and CO radiation at high temperature

Statistical narrow-band (SNB) model parameters for H₂O, CO₂, CH₄ and CO, and correlated-k (CK) parameters for H₂O and CO₂ are generated from line by line calculations and recently improved spectroscopic databases in wide temperature and spectral ranges. Results from the new parameters are compared to direct line by line calculations and to results from earlier model parameters [A. Soufiani, J. Taine, High temperature gas radiative property parameters of statistical narrow-band model for H₂O, CO₂ and CO and correlated-k (ck) model for H₂O and CO₂, Int. J. Heat Mass Transfer 40 (1997) 987–991] in terms of band averaged spectral transmissivities, Planck mean absorption coefficients, and total emissivities. The comparisons show first a good agreement between updated SNB, CK and LBL results. Significant improvements on earlier parameters are observed for H₂O and CO₂, especially at very high temperatures and path lengths. Model parameters and computer programs illustrating their implementation are provided as Supplementary data.     

Diffusion coefficient of hydrogen in the Pd3Mn compound as deduced from absorption measurements at high temperature

The hydrogen absorption rate has been investigated by the gas–solid reaction method in the disordered and ordered (L1₂) Pd₃Mn compound. With the disordered material the measurements were carried out from 825 K up to 1038 K, with the ordered one from 485 K to 666 K. The H absorption data, analyzed according to the second Fick's equation, provided the H chemical diffusion coefficient D_c which exhibited an exponential temperature dependence. In the disordered state D_c was higher than in the ordered one in agreement with previous lower temperature data from Gorsky relaxation. This finding could be accounted for in terms of the different kinds of jumps between adjacent interstitial (I) octahedral sites that H is able to make in the two different states of order. In the disordered state H diffusion takes place through sequences of I₆–I₆, I₆ ↔ I₅ and I₅–I₅ jumps (sub-index indicates the number of Pd atoms in the first atomic shell of an octahedral interstitial site), while in the state of order L1₂ the involved jumps are I₆ ↔ I₄ and I₄–I₄.     

High resolution measurements of wall temperature distribution underneath a single vapour bubble under low gravity conditions

Heat transfer performance in nucleate boiling crucially depends on a circular thin film area near the foot of a vapour bubble where high heat fluxes and thus high local evaporation rates occur. The corresponding wall temperature drop close to the tiny thin film area is computed using an existing nucleate boiling model. To verify the predicted temperature distribution, an experiment is designed with a thin electrically heated wall featuring two-dimensional, high resolution temperature measurement using unencapsulated thermochromic liquid crystals. By means of temperature measurements during a parabolic flight under low-g conditions, the validity of the model used to calculate the temperature distribution in the tiny thin film area could be confirmed.     

Improved band parameters for a simplified wide band cumulative absorption coefficient distribution model for H2O and CO2

An accurate and computationally efficient approach to evaluate wide band parameters with polynomial series for use in a simplified wide band cumulative absorption coefficient distribution, g(k), model is presented. The fitting coefficients are determined by a best fit with g(k) functions generated from the latest high resolution spectroscopic database. The approach significantly improves the prediction of the g(k) function over a wide range of temperatures from 500 to 2500 K, pressures from 0.01 to 1.0 atm, and all single bands of H₂O and CO₂. The root mean square error of the predicted absorption coefficient is below 25% except the single 4.3 μm band model. The approach also provides accurate calculations for the wide band absorptance, generally with differences below 7% when compared to benchmark results.     

High rate lithium intercalation properties of V2O5/carbon/ceramic-filler composites

Composite electrodes of amorphous vanadium pentoxide/carbon/ceramic filler were prepared by mixing vanadium oxide hydrosol, acetone, carbon and ceramic fillers, and by extension on aluminum foil. High rate charge/discharge property of the composite electrode was examined, and the effect of fillers was discussed. The composite electrode had a porous structure, in which pores were 0.5–3 μm in diameter and penetrated through the composite. The composite electrode showed a large capacity of 98 mA h/g-electrode at a high current density of 17.2 mA/cm² (270 A/g-electrode). The relation between discharge capacity and current density was calculated by solving the simplified diffusion equation. The apparent diffusion coefficient of lithium ion in the composite electrode was found to be 10 times larger than that of electrode without fillers.     

Numerical study of the O2/CO2, O2/CO2/N2, and O2/N2-syngas MILD combustion: Effects of oxidant temperature,O2 mole fraction,and fuel blends

Moderate or Intense Low-oxygen Dilution (MILD) combustion of a syngas fuel under air-fuel, oxygen-enhanced, and oxy-fuel condition are numerically studied with using counterflow diffusion flame. Fuel composition, temperature of oxidant (T_ox), and oxygen mole fraction (X_O2) are selected as the main parameters. Fake species (FCO₂) with the same CO₂ physical properties is used for separation the physical and chemical effects of replacing CO₂ with N₂. According to the results, under the high preheating temperatures, the chemical effect of changing the oxidant composition from N₂ to CO₂ is the main reason of the changes in flame structure, ignition delay time (IDT) and heat release rate (HRR) while physical differences play a more prominent role in the low preheating temperature MILD combustion. In all X_O2, the physical and chemical effects of replacing CO₂ with N₂ have almost the same role on the maximum flame temperature. The results of IDT expressed that chemical discrepancies of CO₂ and N₂ play a key role on IDT enhancement by increasing CO₂ in the oxidant composition. The sensitivity analysis of CH₂O for variations of T_ox and X_O2 shows that reactions R54, R56, R58, and R101 are the main responsible of lower HRR and higher IDT by moving from air-syngas to oxy-fuel MILD combustion.     

High rate capability of the Mg-doped Li–Mn–O spinel prepared via coprecipitated precursor

Coprecipitation was applied to prepare Mg–Mn hydroxide precursor for optimal synthesis of Mg-doped Li–Mn–O spinel. The as-obtained precursor was then mixed with LiOH followed by an annealing at 850 ^oC for 15 h. The spinel prepared from coprecipitated precursor can deliver over 100 mAh g⁻¹ at a discharge rate as high as 10C (1.2 A g⁻¹) and retain 100% of the initial capacity in the 45th cycle while the spinel prepared directly from the as-purchased metal salts yields both smaller initial capacity and lower capacity retention after cycling. It was found that the crystallinity is higher and the charge transfer resistance is lower for the spinel prepared via coprecipitated precursor, which maybe resulted from the more homogeneous distribution of metal ion in such a spinel, than that in the spinel prepared from as-purchased reagents.     

High temperature kinetics of NCO

Mixtures of cyanogen and nitrous oxide diluted in argon were shock heated to measure the ratio of the rate constants for

(3)$\text{NCO}\text{+}\text{O}\text{→}\text{CO}\text{+}\text{NO}$

and

(4)$\text{NCO}\text{+}\text{M}\text{→}\text{N}\text{+}\text{CO}\text{+}\text{M}\text{.}$

The diagnostic was narrow-line absorption of NCO at 440.479 nm using a remotely located cw ring dye laser source. By varying the mole fraction of nitrous oxide in the initial mixture and conducting otherwise identical experiments, we inferred at 2240°K

$\text{k}{}_3\text{k}{}_4\text{=10}{}^{\mathrm{3.54(+0.34,\; ?0.37)}}\text{.}$

Utilizing a recent determination of k₃ and previous measurements of the ratio $\text{k}{}_3\text{k}{}_4$, we recommend over the temperature range 2150 ? T ? 2400°K

$\text{k}{}_4\text{=10}{}^{16.8}\text{T}{}^{\mathrm{?0.5}}\text{exp}\text{[?24000/T] cm}{}^3\text{/mole/s [×2.3, ×0.4].}$

An additional mixture of cyanogen, oxygen, hydrogen, and nitrous oxide diluted in argon was shock heated and NCO was monitored to infer the rate constant for

(5)$\text{NCO}\text{+}\text{H}\text{→}\text{CO}\text{+}\text{NH}$

and the ratio $\text{k}{}_6\text{k}{}_7$:

(6)$\text{C}{}_2\text{N}{}_2\text{+}\text{H}\text{→}\text{CN}\text{+}\text{HCN}\text{,}$

(7)$\text{CN}\text{+}\text{H}{}_2\text{→}\text{HCN}\text{+}\text{H}\text{.}$

We found near 1490°K

$\text{k}{}_5\text{=10}{}^{\mathrm{13.73(+0.42,?0.27)}}\text{cm}{}^3\text{/mole/s,}$

and

$\text{k}{}_6\text{k}{}_7\text{=0.81(+0.89, ?0.47).}$

These experiments also led to an estimate of the rate constant for

(8)$\text{NCO}\text{+}\text{H}{}_2\text{→}\text{HNCO}\text{+}\text{H}\text{,}$

with the result, near 1490°K,

$\text{k}{}_8\text{?10}{}^{\mathrm{12.1(+0.4,?0.7)}}\text{cm}{}^3\text{/mole/s.}$

     

Influence of fuel composition on chemiluminescence emission in premixed flames of CH4/CO2/H2/CO blends

The growing concern about pollutant emissions and depletion of fossil fuels has been a strong motivator for the development of cleaner and more efficient combustion strategies, such as the gasification of coal, biomass or waste, which have increased the interest in using a new type of fuels, mainly composed of CH₄, H₂, CO and CO₂.These new fuels, commonly called syngas, display a wide range of compositions, which affects their combustion characteristics and, in some cases, are more prone to instabilities or flashback. Since flame properties have been demonstrated to be strongly related to equivalence ratio, a precise measurement of the flame stoichiometry is a key pre-requisite for combustion optimization and prevention of unstable regimes. In particular, chemiluminescence emission from flames has been largely tested for stoichiometry monitoring for methane flames, but its use in syngas flames has been far less studied. Consequently, the main goal of this work is analyzing the effect of fuel composition on the chemiluminescence vs. equivalence ratio curves for different fuel blends, as a first approach for a wide range of syngas compositions. The experimental results revealed that the ratio OH*/CH*, which had been widely demonstrated to be the best option for methane, may not be suitable for monitoring with certain fuels, such as those with a high percent of hydrogen. Alternatively, other signals, in particular the ratio OH*/CO₂*, appear as viable stoichiometry indicators in those cases.The analysis was also completed by numerical predictions with CHEMKIN. The comparisons of calculations with different flame models and experimental data reveals differences in the chemiluminescence vs. equivalence ratio curves for the different combustion regimes, depending on the range of the equivalence ratio ranges and fuel compositions. This finding, which confirms previous observations for a much narrower range of fuels, could have important practical consequences for the application of the technique in real combustors.     

Diffusion coefficient of Li+ in solid-state rechargeable battery materials

Simple mathematical model of charge/discharge process was developed, and the method of Li⁺ diffusion coefficient determination was elaborated based on the analysis of galvanostatic curves. The model and the method also enable the theoretical capacity of the rechargeable material to be found.     

The temperature dependence of the overall heat-loss coefficient for flat-plate collectors

The temperature dependence of the overall heat-loss coefficient for flat-plate collectors has been studied by using stagnation measurements made with different configurations, viz., tilt 45 °s with single and double glazing and tilt 0 ° with single glazing. Comparisons have been made with theoretical results. The agreement between the calculated and experimental results is found to be quite good.     

Impact of Ce-Loading on Ni-catalyst supported over La2O3+ZrO2 in methane reforming with CO2

This paper investigated the effect of doping Ni supported catalysts with different ceria loading. The catalysts (5%Ni+x%Ce/La₂O₃+ZrO₂, where x = 0, 1, 2, 2.5, 3, 5) were synthesized via the wet impregnation technique and tested for methane reforming with carbon dioxide at atmospheric pressure, 700 °C and 42, 000 ml/g_cat.h gas hourly space velocity. The fresh catalysts were subjected to different characterization techniques such as X-ray diffraction, Surface area and pore analysis, H₂-temperature programmed reduction, CO₂-temperature programmed desorption and thermogravimetric analysis (TGA). A fine correlation between characterization results and catalytic activity is found. The results of the reactions indicated that 5%Ni/La₂O₃+ZrO₂ has the lowest conversion which increased with the percentage loading of CeO₂ up to 2.5 wt % and then began to decline. This suggests that 2.5 wt % loading is the optimum for CH₄ and CO₂ conversion. This particular catalyst composition has NiO species that could be reduced easily, as well as dense and wide distribution of all type of basic sites with respect to other catalyst system. The used catalysts were again subjected to TGA and RAMAN analysis where the least carbon deposition and the least deactivation factor was observed for 5%Ni+5%Ce/La₂O₃+ZrO₂ catalysts.     

Effect of recent temperature change on shallow geothermal measurements

The measured underground temperatures of four boreholes (Rapagnano, Giulianova, Imola and San Marino) drilled into clayey formations in the central regions of Italy, as part of a geothermal research program, have shown that they are affected by more or less regular disturbances. The absence of groundwater movements in these formations, the relative flatness of the topography around the holes and the shape of the disturbances have led them to be considered as the effects of some recent local climatic variations.An inverse theory approach has been used to construct the local surface thermal history. It was not possible to compare it with the temperatures observed by meteorological instruments over the areas close to the boreholes because these data are not available. The results have been compared successfully with the climatic variations over the Northern Hemisphere during the last century. Among several models of the surface forcing temperature, the most reliable one for Rapagnano is represented by a sinusoidal wave, while a parabolic decrease holds good for Giulianova.Suggestions are given for geothermal prospecting.     

Determination of thermal contact resistance from transient temperature measurements

The temperature distribution in combustion engine components is highly influenced by thermal contact resistance. For the prediction and optimisation of the thermal behaviour of modern combustion engines knowledge about the contact heat transfer is crucial.Available correlations to predict the contact resistance are simplifications of the real geometric conditions and only tested for moderate pressures up to 7 MPa. Typical combustion engine applications include contact pressures up to 250 MPa.The experimental approach presented here to derive the thermal contact resistance in terms of contact heat transfer coefficients for high temperature and high pressure conditions is based on transient infrared temperature measurements. Two bodies initially at two different temperatures are brought in contact and the surface temperature histories are recorded with a high-speed infrared camera. The contact heat flux is calculated by solving the related inverse problem. From the contact heat flux and from the measured temperature jump at the interface the contact heat transfer coefficient is calculated.The inverse method used for the calculation of the heat flux is based on the analytical solution for a semi-infinite body and a step response to a Neumann boundary condition. This method provides an algorithm that is used in a sequential manner. The use of “future” temperature data greatly improve the stability of the governing equations and reduce the sensitivity to measurement errors.