Computed NOx emission characteristics of opposed-jet syngas diffusion flames

This paper reported a numerical study on the NO_x emission characteristics of opposed-jet syngas diffusion flames. A narrowband radiation model was coupled to the OPPDIF program, which used detailed chemical kinetics and thermal and transport properties to enable the study of 1-D counterflow syngas diffusion flames with flame radiation. The effects of syngas composition, pressure and dilution gases on the NO_x emission of H₂/CO synthetic mixture flames were examined. The analyses of detailed flame structures, chemical kinetics, and nitrogen reaction pathways indicate NO_x are formed through Zeldovich (or thermal), NNH and N₂O routes both in the hydrogen-lean and hydrogen-rich syngas flames at normal pressure. Zeldovich route is the main NO formation route. Therefore, the hydrogen-rich syngas flames produce more NO due to higher flame temperatures compared to that for hydrogen-lean syngas flames. Although NNH and N₂O routes also are the primary NO formation paths, a large amount of N₂ will be reformed from NNH and N₂O species. For hydrogen-rich syngas flames, the NO formation from NNH and N₂O routes are lesser, where NO can be dissipated through the reactions of NH + NO → N₂ + OH and NH + NO → N₂O + H more actively. At a rather low pressure (0.01 atm), NNH-intermediate route is the only formation path of NO. Increasing pressure then enhances NO formation reactions, especially through Zeldovich mechanisms. However, at higher pressures (5–10 atm), NO is then converted back to N₂ through reversed N₂O route for hydrogen-lean syngas flames, and through NNH as well for hydrogen-rich syngas flames. In addition, the dilution effects from CO₂, H₂O, and N₂ on NO emissions for H₂/CO syngas flames were studied. The hydrogen-lean syngas flames with H₂O dilution have the lowest NO production rate among them, due to a reduced reaction rate of NNH + O → NH + NO. But for hydrogen-rich syngas flames with CO₂ dilution, the flame temperatures decrease significantly, which leads to a reduction of NO formation from Zeldovich route.     

Investigation of NCN and prompt-NO formation in low-pressure C1–C4 alkane flames

Temperature, CH, NCN, and NO profiles were measured for eight low-pressure hydrocarbon flames fueled by methane, ethane, propane, and butane using laser-induced fluorescence (LIF) diagnostics. These measurements were used (1) to assess NCN and prompt-NO formation chemistry across a series of fuels of increasing number of carbons at different equivalence ratios (? = 1.07 and 1.28); (2) to examine the predictive capabilities of current C1–C4 hydrocarbon and NCN formation/consumption combustion mechanisms on properly capturing prompt-NO formation and (3) to examine the postulation that additional prompt-NO precursors (other than CH) exist for fuels larger than methane. For a given equivalence ratio, the measured peak CH concentration is fairly constant across all four fuels, while both the peak NCN and post-flame NO concentrations steadily increase. Furthermore, it is found that as the fuels increase in number of carbons, i.e., methane to butane, the correlation between the peak NCN and post-flame NO remains high, while the correlation between peak CH and peak NCN and peak CH and post-flame NO becomes increasingly lower. This is especially evident for rich flame cases. The experimental profiles are compared to numerical calculations using two comprehensive kinetic mechanisms suitable for C4 chemistry, where the CH + N₂ → NCN + H reaction is assumed as the only prompt-NO initiation reaction. For the ? = 1.28 flame cases, CH is over-predicted using both mechanisms for all four fuels and by as much as 60%, while for the ? = 1.07 cases, CH is predicted to within 15% of the experimentally-derived results, although there is some discrepancy concerning the spatial locations of the CH profiles. For both NCN and NO, there is an increasing under-prediction for the ? = 1.28 cases as the fuel increases in number of carbons, while for the ? = 1.07 cases there is a systematic under-prediction of NCN and NO with a weaker (although evident) fuel dependence. From the experimental results and the comparison to modeling predictions, it is apparent that additional work concerning CH formation and consumption kinetics is necessary to accurately capture the CH concentration profiles across a broad range of conditions. Furthermore the comparisons to the modeling predictions using only a single prompt-NO precursor, CH, indicate a reasonable plausibility that (an) additional prompt-NO precursor (s) exist and become important when considering fuels larger than methane, especially under rich flame conditions. Possible precursors in addition to CH are discussed.     

Flame structure and kinetic studies of carbon dioxide-diluted dimethyl ether flames at reduced and elevated pressures

The flame structure and kinetics of dimethyl ether (DME) flames with and without CO₂ dilution at reduced and elevated pressures were studied experimentally and computationally. The species distributions of DME oxidation in low-pressure premixed flat flames were measured by using electron-ionization molecular-beam mass spectrometry (EI-MBMS) at an equivalence ratio of 1.63 and 50 mbar. High-pressure flame speeds of lean and rich DME flames with and without CO₂ dilution were measured in a nearly-constant-pressure vessel between about 1 and 20 bar. The experimental results were compared with predictions from four kinetic models: the first was published by Zhao et al. (2008) [9], the second developed by the Lawrence Livermore National Laboratory (LLNL) (Kaiser et al., 2000) [13], and the third has been made available to us as the Aramco mechanism (Metcalfe et al., 2013) [14]; as the fourth, we have used an updated model developed in this study. Good agreement was found between measurements and predictions from all four models for all major and most typical intermediate species with and without CO₂ addition in low-pressure flat flame experiments. However, none of the models was able to reliably predict high-pressure flame speeds. Although the updated model improved the prediction of flame speeds for lean mixtures, errors remained for rich conditions at elevated pressure, likely due to uncertainty in the rates of CH₃ + H(+M) = CH₄(+M) and the branching and termination reaction pair of CH₃ + HO₂ = CH₃O + OH and CH₃ + HO₂ = CH₄ + O₂. CO₂ addition considerably decreased the flame speed. Kinetic comparisons between inert and chemically active CO₂ in DME flames showed that CO₂ addition affects rich and lean DME flame kinetics differently. For lean flames, both the inert third-body effect and the kinetic effect of CO₂ reduce H-atom production. However, for rich flames, the inert third-body effect increases H-atom production via HCO(+M) = H + CO(+M) and suppression of the kinetic effect of CO₂ by shifting the equilibrium of CO + OH = CO₂ + H.     

Negative pressure dependence of mass burning rates of H2/CO/O2/diluent flames at low flame temperatures

Experimental measurements of burning rates, analysis of the key reactions and kinetic pathways, and modeling studies were performed for H₂/CO/O₂/diluent flames spanning a wide range of conditions: equivalence ratios from 0.85 to 2.5, flame temperatures from 1500 to 1800 K, pressures from 1 to 25 atm, CO fuel fractions from 0 to 0.9, and dilution concentrations of He up to 0.8, Ar up to 0.6, and CO₂ up to 0.4. The experimental data show negative pressure dependence of burning rate at high pressure, low flame temperature conditions for all equivalence ratios and CO fractions as high as 0.5. Dilution with CO₂ was observed to strengthen the pressure and temperature dependence compared to Ar-diluted flames of the same flame temperature. Simulations were performed to extend the experimentally studied conditions to conditions typical of gas turbine combustion in Integrated Gasification Combined Cycle processes, including preheated mixtures and other diluents such as N₂ and H₂O.Substantial differences are observed between literature model predictions and the experimental data as well as among model predictions themselves – up to a factor of three at high pressures. The present findings suggest the need for several rate constant modifications of reactions in the current hydrogen models and raise questions about the sufficiency of the set of hydrogen reactions in most recent hydrogen models to predict high pressure flame conditions relevant to controlling NO_x emissions in gas turbine combustion. For example, the reaction O + OH + M = HO₂ + M is not included in most hydrogen models but is demonstrated here to significantly impact predictions of lean high pressure flames using rates within its uncertainty limits. Further studies are required to reduce uncertainties in third body collision efficiencies for and fall-off behavior of H + O₂(+M) = HO₂(+M) in both pure and mixed bath gases, in rate constants for HO₂ reactions with other radical species at higher temperatures, and in rate constants for reactions such as O + OH + M that become important under the present conditions in order to properly characterize the kinetics and predict global behavior of high-pressure H₂ or H₂/CO flames.     

Effects of dilution with carbon dioxide on the laminar burning velocity and flame stability of H2–CO mixtures at atmospheric condition

The objective of this investigation was to study the effect of dilution with CO₂ on the laminar burning velocity and flame stability of syngas fuel (50% H₂–50% CO by volume). Constant pressure spherically expanding flames generated in a 40 l chamber were used for determining unstretched burning velocity. Experimental and numerical studies were carried out at 0.1 MPa, 302 ± 3 K and ? = 0.6–3.0 using fuel-diluent and mixture-diluent approaches. For H₂–CO–CO₂–O₂–N₂ mixtures, the peak burning velocity shifts from ? = 2.0 for 0% CO₂ in fuel to ? = 1.6 for 30% CO₂ in fuel. For H₂–CO–O₂–CO₂ mixtures, the peak burning velocity occurred at ? = 1.0 unaffected by proportion of CO₂ in the mixture. If the mole fraction of combustibles in H₂–CO–O₂–CO₂ mixtures is less than 32%, then such mixtures are supporting unstable flames with respect to preferential diffusion. The analysis of measured unstretched laminar burning velocities of H₂–CO–O₂–CO₂ and H₂–CO–O₂–N₂ mixtures suggested that CO₂ has a stronger inhibiting effect on the laminar burning velocity than nitrogen. The enhanced dilution effect of CO₂ could be due to the active participation of CO₂ in the chemical reactions through the following intermediate reaction CO + OH ? CO₂ + H.     

Experimental and modeling study of formaldehyde combustion in flames

The increased use of alcohols in internal combustion engines has driven the attention to formaldehyde emissions. Yet the experimental database on formaldehyde flames is limited. The experimental structures of two formaldehyde flames have been investigated at low pressure (30 mbar) using a molecular beam sampling coupled with a mass spectrometer. The initial compositions are for the lean flame (? = 0.22): 18% CH₂O and 82% O₂, and for the stoichiometric one (? = 1.09): 17.7% CH₂O, 16.3% O₂ and 66.0% Ar. A kinetic model, previously elaborated, has been improved by building a complete submechanism taking into account the formation and consumption of species involved in the formaldehyde combustion. The improved mechanism contains 107 chemical species and 568 reactions in order to simulate these two formaldehyde flames accurately. The reliability of this kinetic model has also been tested in ethanol and acetaldehyde flames. This allows the extension of its validity range.     

Theoretical analysis and experimental research on transcritical CO2 two stage compression cycle with two gas coolers (TSCC + TG) and the cycle with intercooler (TSCC + IC)

As one of the natural refrigerants, CO₂ is a potential substitute for synthesized refrigerants with favorable environmental properties. In order to improve the performance of the CO₂ transcritical compression cycle, the performance of the two stage compression cycle with two gas coolers (TSCC + TG) and the two stage compression cycle with intercooler (TSCC + IC) were analyzed, respectively. Under the given calculation condition, the optimum intermediate pressure of the cycle TSCC + TG and the TSCC + IC are 7.09 MPa and 5.89 MPa, and the maximal COP are 2.77 and 3.08, respectively. Range of the given evaporating temperature and outlet temperature of gas cooler, the experimental testing shows that the performance of cycle TSCC + IC are 11.88% and 10.87% better than that of the cycle TSCC + TG, respectively. Range of the given inlet temperature and cooling water volume flow of gas cooler, the refrigeration COP (COP_c) and heat COP (COP_h) of the cycle TSCC + IC are average 10.97% and 4.39% higher than that of the cycle TSCC + TG. Range of the given inlet temperature and chilled water volume flow of evaporator, the refrigeration COP (COP_c) and heat COP (COP_h) of the cycle TSCC + IC are average 10.71% and 3.67% higher than that of the cycle TSCC + TG, respectively. The error between theoretical calculation and experimental testing is not exceeds 20%.     

Effect of radiation emission and reabsorption on flame temperature and NO formation in H2/CO/air counterflow diffusion flames

The radiation effect on flame temperature and NO emission of H₂-lean (0.2H₂ + 0.8CO) and H₂-rich (0.8H₂ + 0.2CO) syngas/air counterflow diffusion flames was numerically investigated using OPPDIF code incorporated with the optical thin model, statistical narrow band model and adiabatic condition. Firstly, the coupled effect of strain rate and radiation was studied. Disparate tendencies of NO emission with an increasing strain rate between H₂-lean and H₂-rich syngas flames were found at very small strain rate, and the effect of radiation reabsorption on NO formation can be neglected when the strain rate was greater than 100 s^?1 for both H₂-lean and H₂-rich syngas flames. Because the radiation effect is vital to flames with small strain rate, its impact on flame temperature and NO emission was investigated in detail at a strain rate of 10 s^?1. The results indicated that NO formation is more sensitive to radiation reabsorption than flame temperature, especially for the H₂-rich syngas flame. The underlying mechanism was discovered by using reaction pathway analysis. Furthermore, the radiation effect under CO₂ dilution of the syngas fuel was examined. It was demonstrated that the radiation effect on flame temperature became more prominent with the increase of CO₂ concentration for both H₂-lean and H₂-rich syngas. The radiation effect on NO emission increased first and then decreased with an increasing CO₂ content for H₂-lean syngas, whereas for H₂-rich syngas the radiation effect is monotonic.     

Inhibition of hydrogen oxidation by HBr and Br2

The high-temperature bromine chemistry was updated and the inhibition mechanisms involving HBr and Br₂ were re-examined. The thermochemistry of the bromine species was obtained using the Active Thermochemical Tables (ATcT) approach, resulting in improved data for, among others, Br, HBr, HOBr and BrO. Ab initio calculations were used to obtain rate coefficients for selected reactions of HBr and HOBr, and the hydrogen/bromine/oxygen reaction mechanism was updated. The resulting model was validated against selected experimental data from the literature and used to analyze the effect of HBr and Br₂ on laminar, premixed hydrogen flames. Our work shows that hydrogen bromide and molecular bromine act differently as inhibitors in flames. For HBr, the reaction HBr + H ? H₂ + Br (R2) is rapidly equilibrated, depleting HBr in favor of atomic Br, which is the major bromine species throughout the reaction zone. The chain-breaking steps are then H + Br + M → HBr + M (R1), Br + HO₂ → HBr + O₂ (R7), and Br + Br + M → Br₂ + M (R8). In Br₂-doped flames, the reaction Br₂ + H ? HBr + Br (R9) is far from equilibration and serves to deplete H in the reaction zone by competing with H + O₂ → O + OH. The inhibition is augmented by recombination of Br (R8). If the inlet Br₂ mole fraction exceeds about 20%, reactions (R8), (R2) are both reversed, now acting to promote chain branching and increase the flame speed. According to the present model, cycles involving HOBr are not important for generation or removal of chain carriers in these flames.     

Flame stabilization between two beds of alumina balls in a porous burner

Conditions for flame stabilization in a porous media combustor formed by two beds of different sizes of alumina balls were studied. Premixed combustion of lean methane–air mixtures were used as variables. Measurements performed included temperature profiles and chemical products compositions. Stabilized flames were observed in the range of volumetric flow rate from 7.01 l/min to 19.00 l/min at equivalence ratio of ? = 0.6 and ? = 0.7. Low pollutants emissions were found in the entire operation range.     

Ignition transition in turbulent premixed combustion

Recently, Shy and his co-workers reported a turbulent ignition transition based on measurements of minimum ignition energies (MIE) of lean premixed turbulent methane combustion in a centrally-ignited, fan-stirred cruciform burner capable of generating intense isotropic turbulence. Using the same methodology, this paper presents new complete MIE data sets for stoichiometric and rich cases at three different equivalence ratios ? = 1.0, 1.2 and 1.3, each covering a wide range of a turbulent Karlovitz number (Ka) indicating a time ratio between chemical reaction and turbulence. Thus, ignition transition in premixed turbulent combustion depending on both Ka and ? can be identified for the first time. It is found that there are two distinct modes on ignition in randomly stirred methane–air mixtures (ignition transition) separated by a critical Ka where values of Ka_c ≈ 8–26 depending on ? with the minimum Ka_c occurring near ? = 1. For Ka < Ka_c, MIE increases gradually with Ka, flame kernel formation is similar to laminar ignition remaining a torus, and 2D laser tomography images of subsequent outwardly-propagating turbulent flames show sharp fronts. For Ka > Ka_c, MIE increases abruptly with Ka, flame kernel is disrupted, and subsequent randomly-propagating turbulent flames reveal distributed-like fronts. Moreover, we introduce a reaction zone Péclet number (P_RZ) indicating the diffusivity ratio between turbulence and chemical reaction, such that the aforementioned very scattering MIE data depending on Ka and ? can be collapsed into a single curve having two drastically different increasing slopes with P_RZ which are separated by a critical P_RZ ≈ 4.5 showing ignition transition. Finally, a physical model is proposed to explain these results.     

Experimental and kinetic modeling study of methyl butanoate and methyl butanoate/methanol flames at different equivalence ratios and C/O ratios

Premixed laminar methyl butanoate/oxygen/argon and methyl butanoate/methanol/oxygen/argon flames were studied with tunable synchrotron vacuum ultraviolet (VUV) photoionization and molecular-beam sampling mass spectrometry at 30 torr (4.0 kPa). Three flames were investigated in the experiment: MB (methyl butanoate) flame F1.54 (? = 1.54, C/O = 0.479), MB flame F1.67 (? = 1.67, C/O = 0.511) and MB/methanol flame F1.67M (? = 1.67, C/O = 0.479). By measuring the signal intensities at different distances from the burner surface, the mole fraction profiles of intermediates are derived. Experimental results show that the flame front shifts downstream and peak mole fractions of intermediates increase remarkably with the increase of equivalence ratio for pure MB fuel. When methanol is added, the peak mole fractions of most intermediates including those of soot precursors decrease remarkably at the same equivalence ratio, while peaks of soot precursors vary little (only slightly decreasing) at same C/O ratio. It is concluded that the formation of soot precursors is more sensitive to C/O ratio than to equivalence ratio. Besides, more CO₂ is produced near the burner surface in MB flame than that in MB/methanol flame, and this validates an early production of CO₂ in methyl ester oxidation. In addition, a modified MB detailed mechanism is used to model flame structure, and improved agreements between the experimental and predicted results are realized. Based on the simulation results, reaction flux and sensitivity are analyzed for CO₂ and C₃H₃, respectively.     

Enhancement of capacity and cycle-life of Sn4 + δP3 (0 ≤ δ ≤ 1) anode for lithium secondary batteries

Various compositions of tin-rich, non-stoichiometric, solid solutions of Sn_4 + δP₃ are synthesized by a mechanochemical method. The materials are tested as anodes for lithium secondary batteries to enhance reversible capacity and cycleability. Investigative analyses show that the region for the solid-solution formation of Sn_4 + δP₃ is 0 ≤ δ ≤ 1. The reaction mechanism of the tin-rich solid solutions is similar to that of stoichiometric Sn₄P₃, except for the absence of a topotactic lithium insertion reaction during the first cycle. As the tin content is increased, tin-rich phosphide exhibits better cycleability and retains a higher reversible capacity, namely, about 20% more than that of stoichiometric Sn₄P₃.     

Influence of fuel fraction gradient on triple flame velocity in plain and axis-symmetrical channels

Dynamics of laminar triple flame investigated numerically for the different mixture degrees. One-step methane–air chemistry adequate to reach and lean mixture combustion was accepted. Velocity of triple flame is determined as a function of methane concentration logarithm gradients μ = d(ln Y₁)/dx (characterizing mixing degree). It is found that maximum velocity of the triple flames correspond to the value of the methane concentration logarithm gradients μ ≈ 1000 m^?1 for plain and μ ≈ 2000 m^?1 for axis-symmetrical channels. The maximum velocity of triple flame in plain and axis-symmetrical channels in the case of non-gradient incoming gas flow is about twice bigger than normal laminar flame velocity S_f ≈ 2.1S_l.     

Laminar burning speed measurement of premixed n-decane/air mixtures using spherically expanding flames at high temperatures and pressures

Normal-decane (n-C₁₀H₂₂) is regarded as a major component of possible surrogates for jet fuels and diesel fuels. The structure of spherically expanding premixed n-decane/air flames has been studied at high temperatures and pressures. The laminar burning speeds of n-decane/air mixtures have been measured for the temperatures of 350–610 K and pressures of 0.5–8 atm. The experiments were performed in lean conditions (0.7 ? ? ? 1). Laminar burning speed was measured using a thermodynamic model based on the pressure rise during the flame propagation in constant volume vessels. A cylindrical vessel equipped with a high speed CMOS camera was employed to investigate the flame structure and a spherical vessel was used for the burning speed measurements. The results are in good agreement with other experimental data available in the published literature.     

Crystallographic and electrochemical characteristics of La0.7Mg0.3Ni3.5 − x(Al0.5Mo0.5)x (x = 0–0.8) hydrogen storage alloys

The crystal structure, hydrogen storage property and electrochemical characteristics of the La_0.7Mg_0.3Ni_3.5 − x(Al_0.5Mo_0.5)_x (x = 0–0.8) alloys have been investigated systematically. It can be found that with X-ray powder diffraction and Rietveld analysis the alloys are of multiphase alloy and consisted of impurity LaNi phase and two main crystallographic phases, namely the La(La, Mg)₂Ni₉ phase and the LaNi₅ phase, and the lattice parameter and the cell volume of both the La(La, Mg)₂Ni₉ phase and the LaNi₅ phase increases with increasing Al and Mo content in the alloys. The P–C isotherms curves indicate that the hydrogen storage capacity of the alloy first increases and then decreases with increasing x, and the equilibrium pressure decreases with increasing x. The electrochemical measurements show that the maximum discharge capacity first increases from 354.2 (x = 0) to 397.6 mAh g⁻¹ (x = 0.6) and then decreases to 370.4 mAh g⁻¹ (x = 0.8). The high-rate dischargeability of the alloy electrode increases lineally from 55.7% (x = 0) to 73.8% (x = 0.8) at the discharge current density of 1200 mA g⁻¹. Moreover, the exchange current density of the alloy electrodes also increases monotonously with increasing x. The hydrogen diffusion coefficient in the alloy bulk increases with increasing Al and Mo content and thus enhances the low-temperature dischargeability of the alloy electrode.     

Measurement of OH concentration profiles by laser diagnostics and modeling in high-pressure counterflow premixed methane/air and biogas/air flames

Detailed kinetic mechanisms validated under atmospheric or low-pressure flame conditions cannot generally be directly extrapolated toward high pressure, due to the lack of experimental data or to uncertainties concerning the rate constants of elementary reactions. It is thus necessary to complete the experimental database and to extend the validation domain of combustion mechanisms at high pressure. In this work, OH concentration profiles were measured in high-pressure methane/air and biogas/air laminar premixed counterflow flames by linear laser-induced fluorescence at different equivalence ratios (0.7–1.2) and pressures (0.1–0.7 MPa). Each flame was calibrated in absolute OH concentration by a combination of laser absorption and planar laser-induced fluorescence measurements. Experimental results were compared with simulations using the OPPDIF code and three detailed kinetic mechanisms: two versions of the Gas Research Institute Mechanism, GRI-Mech 2.11 and GRI-Mech 3.0, and the recently updated GDFkin®3.0_NCN mechanisms. Results show that the flame front positions are very well predicted by modeling with the three mechanisms for lean and stoichiometric CH₄/air flames and stoichiometric CH₄/CO₂/air flames. However, discrepancies appear at a higher equivalence ratio (Φ = 1.2) for the CH₄/air flames and at a lower equivalence ratio (Φ = 0.7) for the CH₄/CO₂/air flames. OH mole fractions are quantitatively well predicted at high pressure in all cases, while systematic overestimation by modeling is observed at atmospheric pressure. A kinetic analysis of the results is also presented.     

Effect of the equivalence ratio on the concentration of CH4/NO2/O2 combustion products

A chemical kinetic model for determining the mole fractions of stable and intermediate species for CH₄/NO₂/O₂ flames is developed. The model involves 30 different species in 101 chemical elementary reactions. The mole fractions of the species are plotted as a function of the distance from the surface of the burner. The effects of the equivalence ratio on the concentrations of CO, CO₂, N₂, NH₂, OH, H₂O, NO and NO₂ for lean CH₄/NO₂/O₂ flames in the post flame zone at 50 Torr are obtained. The flames are flat, laminar, one dimensional and premixed. The calculated concentration profiles as a function of the equivalence ratio and distance from the surface of the burner are compared with the experimental data. The comparison indicates that the kinetics of the flames are reasonably described by the developed model. The mole fraction of N₂, NH₂, OH, H₂O, CO₂ and CO increase while the mole fractions of NO and NO₂ decrease by increasing the equivalence ratio for lean flames. Copyright © 1999 John Wiley & Sons, Ltd.     

Convective diffusion from strip-like micro-probes into colloidal suspensions

Full equations of convective diffusion are solved numerically for a strip-like (2D) electrodiffusion friction probe in a stream of microdisperse liquid, assuming a non-linear near-to-wall velocity profile ranging from simple shear flow (p = 1) to ideal slip (p = 0). The range of generalized Peclet number H from H = 0.01 (almost pure spatial diffusion) to H = 100 (diffusion layer with negligible longitudinal diffusion) covers all cases of possible experimental relevance. The main result is expressed as a relative deviation of actual total diffusion flux N from its diffusion-layer approximation N_DLA, Ψ = N/N_DLA ? 1.     

The first-principles investigation on the electronic structure and mechanism of LiH + NH3 → LiNH2 + H2 reaction

First-principle density functional theory calculations were used to investigate the electronic structure and mechanism of the LiH + NH₃ → LiNH₂ + H₂ reaction. Along the reaction pathway, intermediate complexes HLi…NH₃ and LiNH₂…H₂ and a transition state can be found. The N-2p electron in the highest occupied molecular orbital (HOMO) of NH₃ transfers to the Li-2s orbital in lowest unoccupied molecular orbital (LUMO) of LiH and forms the initial state HLi…NH₃. In the transition state, H1 of LiH and H2 of NH₃ turn toward each other, resulting in the formation of a H₂ bond. From the transition state to the final state, the geometric configuration changes from C_s to C_2v, and the improvement of geometric configuration symmetry results in a decrease in the energy gap between HOMO and LUMO. The LiH + NH₃ → LiNH₂ + H₂ reaction is exothermic.