High-pressure Turbulent Flow Research Articles

Experiment and simulation of hydrogen oxidation in a high-pressure turbulent flow reactor

Hydrogen oxidation has a complex dependence on pressure. Despite the well-known, reverse S-shape explosion limits, variation of hydrogen oxidation reactivity with pressure has rarely been investigated in a quantitative manner, particularly in the peninsula between the second and third ignition branches when the overall reactivity is low. This work investigates hydrogen oxidation in a turbulent flow reactor at 10 to 48 bar with an inlet temperature of 950 K and an equivalence ratio of 0.03–0.05, which complements our recent study at 1–8 bar in the same reactor (Lu et al. Proc. Combust. Inst. 2021, 243–250). The elevated pressures show a weak promoting effect, in contrast to the strong inhibiting effect at lower pressures in crossing the second ignition branch. Analyzing the hydrogen consumption rates across the pressure range revealed that the reactivity remains at a low level and is barely affected by pressure between 2 and 20 bar, suggesting the existence of a broad low-reactivity valley on the temperature–pressure plane which could be potentially important for practical applications.The measured species-time concentrations, combined with ignition delays selected from the literature, are used to develop a new hydrogen oxidation model focusing on hydrogen autoignition behavior. A comprehensive review of elementary reactions incorporating the latest updates for the rate coefficients is conducted to determine the prior uncertainties. A global optimization method incorporating random sampling and high-dimensional model representation is used to identify the most sensitive reactions and to constrain their uncertainty with the selected experimental targets. An optimized model is then obtained which shows excellent agreement with hydrogen autoignition experiments.

Modelling and Analysis ofDynamic Stability of Glass Reinforced Plastic Pipes Subjected to Fluid Flow

In the past, almost every industry worldwide patronizediron and its alloys for every major industrial design, construction and other forms of work. However, with the advent of the Glass Reinforced Plastic (GRP)as accepted in the United Kingdom or the Fibre Reinforced Plastic as accepted in the United States, which was discovered in the nineteen thirty’s (1930’s), the Glass Reinforced Plastic (GRP) has become very versatile as it has become a household name in most industries globally .It has attained this height through the significant properties it possesses, which include its ability to transform into moulds of difficult and delicate shapes and sizes which iron and its alloy may not find easy to submit to. It brings a host of otherbenefits in the form of long term performance and reliability, ease of installation and the ability to withstand corrosion and tuberculation. A service life of more than thrice that of the ductile iron pipes to mention but a few. Ductile Iron pipes are used in most petrochemical industries where pipeline plays a very important role in transporting crude oil and gas. As the service duration increases, the pipe lines are affected by corrosion mechanism which can lead to fatal accident. Corrosion can occur atboth the internal and external surface of the pipelines. In general, corrosion would cause metal loss which leads to reduction in pipeline thickness and consequently reduce its strength. Itbecomes necessary that the stability of the Glass Reinforced Plastic (GRP) pipes are carefully investigated especially in the event of high pressure turbulent flows. This is the thrust of this work. In the light of the above, ductileiron pipes and Glass Reinforced Plastics (GRP) pipes of the same thicknesses were investigated, some special characteristics such as the bursting pressures were calculated using Peter Barlow’s formula. The ANSYS software was also used for modelanalysisand compare the stress profile under dynamic condition for both pipes. Also the cost of production of pipes, classification and the difficulties encountered during their installation processes wereexamined. The result indicated an overwhelming encouragement to use Glass Reinforced Plastic (GRP) pipes as substitutes to the traditional ductile iron and its alloys in view of the fact that Glass Reinforced Plastic (GRP) pipes withstand corrosion and tuberculation while saving the huge cost that would have been used forpigging

The influence of the chemical composition representation according to the number of species during mixing in high-pressure turbulent flows

Mixing of several species in high-pressure (high-$p$) turbulent flows is investigated to understand the influence of the number of species on the flow characteristics. Direct numerical simulations are conducted in the temporal mixing layer configuration at approximately the same value of the momentum ratio for all realizations. The simulations are performed with mixtures of two, three, five and seven species to address various compositions at fixed number of species, at three values of initial vorticity-thickness-based Reynolds number, $Re_{0}$, and two values of the free-stream pressure, $p_{0}$, which is supercritical for each species except water. The major species are C7H16, O2 and N2, and the minor species are CO, CO2, H2 and H2O. The extensive database thus obtained allows the study of the influence not only of $Re_{0}$ and $p_{0}$, but also of the initial density ratio and of the initial density difference between streams, $\unicode[STIX]{x0394}\unicode[STIX]{x1D70C}$. The results show that the layer growth is practically insensitive to all of the above parameters; however, global vortical aspects increase with $Re_{0},p_{0}$ and the number of species; nevertheless, at the same $Re_{0},p_{0}$ and density ratio, vorticity aspects are not influenced by the number of species. Species mixing produces strong density gradients which increase with $p_{0}$ and otherwise scale with $\unicode[STIX]{x0394}\unicode[STIX]{x1D70C}$ but, when scaled by $\unicode[STIX]{x0394}\unicode[STIX]{x1D70C}$, are not affected by the number of species. Generalized Korteweg-type equations are developed for a multi-species mixture, and a priori estimates based on the largest density gradient show that the Korteweg stresses, which account for the influence of the density gradient, have negligible contribution in the momentum equation. The species-specific effective Schmidt number, $Sc_{\unicode[STIX]{x1D6FC},\mathit{eff}}$, is computed and it is found that negative values occur for all minor species – particularly for H2 – thus indicating uphill diffusion, while the major species experience only regular diffusion. The probability density function (p.d.f.) of $Sc_{\unicode[STIX]{x1D6FC},\mathit{eff}}$ shows strong variation with $p_{0}$ but weak dependence on the number of species; however, the p.d.f. substantially varies with the identity of the species. In contrast, the p.d.f. of the effective Prandtl number indicates dependence on both $p_{0}$ and the number of species. Similar to $Sc_{\unicode[STIX]{x1D6FC},\mathit{eff}}$, the species-specific effective Lewis-number p.d.f. depends on the species, and for all species the mean is smaller than unity, thus invalidating one of the most popular assumptions in combustion modelling. Simplifying the mixture composition by reducing the number of minor species does not affect the crucial species–temperature relationship of the major species that, for accuracy, must be retained in combustion simulations, but this relationship is affected for the minor species and in regions of uphill diffusion, indicating that the reduction is nonlinear in nature.

Side-jet effects in high-pressure turbulent flows: Direct Numerical Simulation of nitrogen injected into carbon dioxide

Direct Numerical Simulation realizations were generated of a round jet under high-pressure (high-p) turbulent conditions. In the simulations, a jet of nitrogen was injected into a chamber filled with carbon dioxide for three different jet-to-chamber density ratio, s, and three different chamber pressures, pch,0. The results show that for s = 0.5 and 0.35 side jets form whereas no side jets are observed for s = 1; thus providing, for the first time, evidence of side jet formation in high-p flows. Due to these side jets, mixing of the jet fluid and chamber fluid is promoted; although the species experience regular diffusional mixing, it is shown that due to turbulent conditions there can be effective uphill thermal conduction. Analysis of the vortical features of the side jets elucidated the process through which the enhanced mixing occurs: fluid from the jet is effectively pumped in the radial direction though the combined action of dilatation/compression and vortex stretching/shrinking. The value of s is shown to control radial and circumferential mixing versus axial mixing which occurs through jet penetration in the flow. Examination of dynamic and thermodynamic quantities indicates that side jets also promote flow unsteadiness. The pressure in the chamber is demonstrated to have negligible effect on the side jets.

Pressure Dependence of Butyl Nitrate Formation in the Reaction of Butylperoxy Radicals with Nitrogen Oxide

The yield of 1- and 2-butyl nitrates in the gas-phase reactions of NO with n-C4H9O2 and sec-C4H9O2, obtained from the reaction of F atoms with n-butane in the presence of O2, was determined over the pressure range of 100-600 Torr at 298 K using a high-pressure turbulent flow reactor coupled with a chemical ionization quadrupole mass spectrometer. The yield of butyl nitrates was found to increase linearly with pressure from about 3% at 100 Torr to about 8% at 600 Torr. The results obtained are compared with the available data concerning nitrate formation from NO reaction with other small alkylperoxy radicals. These results are also discussed through the topology of the lowest potential energy surface mainly obtained from DFT(B3LYP/aug-cc-pVDZ) calculations of the RO2 + NO reaction paths. The formation of alkyl nitrates, due essentially to collision processes, is analyzed through a model that points out the pertinent physical parameters of this system.

Analysis of High Pressure Transients in Water Hydraulic Pipeline Using Matlab/Simulink

Based on the continuity equation and the motion equation of fluid dynamics, a mathematical model of high pressure transients in water hydraulic pipeline is presented. In the model, the friction item is consist of steady friction item and dynamic friction item, using the Darcy-Weisbach equation to solve steady viscous friction item and using four exponential terms instead of weighting function to solve dynamic friction item. By finite difference method accompanied with Matlab/Simulink, an example of high pressure turbulent flow in water hydraulic pipeline is configured so as to simulate the dynamic characteristics of pressure transients. The comparison between the observed result and the simulation result shows the mathematical model of high pressure transients in water hydraulic pipeline with turbulent flow is reasonable.

Pressure Dependence of Iso-Propyl Nitrate Formation in the i-C3H7O2 + NO Reaction

Abstract The branching ratio β = k1b/k1a for the formation of iso-propyl nitrate, i-C3H7ONO2, in the gas-phase reaction of i-C3H7O2 with NO, i-C3H7O2 + NO → i-C3H7O + NO2 (1a), i-C3H7O2 + NO → i-C3H7ONO2 (1b), was determined over the pressure range 55–500 Torr at 298 K using a high-pressure turbulent flow reactor coupled with a chemical ionization quadrupole mass-spectrometer. The β coefficient was found to increase linearly with pressure from about 0.6% at 55 Torr to about 3% at 500 Torr. The atmospheric implication of the results obtained is briefly discussed.

Water Vapor Effect on the HNO3 Yield in the HO2 + NO Reaction: Experimental and Theoretical Evidence

The influence of water vapor on the production of nitric acid in the gas-phase HO(2) + NO reaction was determined at 298 K and 200 Torr using a high-pressure turbulent flow reactor coupled with a chemical ionization mass spectrometer. The yield of HNO(3) was found to increase linearly with the increase of water concentration reaching an enhancement factor of about 8 at [H(2)O] = 4 x 10(17) molecules cm(-3) ( approximately 50% relative humidity). A rate constant value k(1bw) = 6 x 10(-13) cm(3) molecule(-1) s(-1) was derived for the reaction involving the HO(2)xH(2)O complex: HO(2)xH(2)O + NO --> HNO(3) (1bw), assuming that the water enhancement is due to this reaction. k(1bw) is approximately 40 times higher than the rate constant of the reaction HO(2) + NO --> HNO(3) (1b), at the same temperature and pressure. The experimental findings are corroborated by density functional theory (DFT) calculations performed on the H(2)O/HO(2)/NO system. The significance of this result for atmospheric chemistry and chemical amplifier instruments is briefly discussed. An appendix containing a detailed consideration of the possible contribution from the surface reactions in our previous studies of the title reaction and in the present one is included.

HNO3 Forming Channel of the HO2 + NO Reaction as a Function of Pressure and Temperature in the Ranges of 72−600 Torr and 223−323 K

A high-pressure turbulent flow reactor coupled with a chemical ionization mass-spectrometer was used to determine the branching ratio of the HO(2) + NO reaction: HO(2) + NO --> OH + NO(2) (1a), HO(2) + NO --> HNO(3) (1b). The branching ratio, beta = k(1b)/k(1a), was derived from the measurements of "chemically amplified" concentrations of the NO(2) and HNO(3) products in the presence of O(2) and CO. The pressure and temperature dependence of beta was determined in the pressure range of 72-600 Torr of N(2) carrier gas between 323 and 223 K. At each pressure, the branching ratio was found to increase with the decrease of temperature, the increase becoming less pronounced with the increase of pressure. In the 298-223 K range, the data could be fitted by the expression: beta(T,P) = (530 +/- 10)/T(K) + (6.4 +/- 1.3) x 10(-4)P(Torr) - (1.73 +/- 0.07), giving beta approximately 0.5% near the Earth's surface (298 K, 760 Torr) and 0.8% in the tropopause region (220 K, 200 Torr). The atmospheric implication of these results is briefly discussed.

Formation of Nitric Acid in the Gas-Phase HO2 + NO Reaction: Effects of Temperature and Water Vapor

A high-pressure turbulent flow reactor coupled with a chemical ionization mass spectrometer was used to investigate the minor channel (1b) producing nitric acid, HNO3, in the HO2 + NO reaction for which only one channel (1a) is known so far: HO2 + NO --> OH + NO2 (1a), HO2 + NO --> HNO3 (1b). The reaction has been investigated in the temperature range 223-298 K at a pressure of 200 Torr of N2 carrier gas. The influence of water vapor has been studied at 298 K. The branching ratio, k1b/k1a, was found to increase from (0.18(+0.04/-0.06))% at 298 K to (0.87(+0.05/-0.08))% at 223 K, corresponding to k1b = (1.6 +/- 0.5) x 10(-14) and (10.4 +/- 1.7) x 10(-14) cm3 molecule(-1) s(-1), respectively at 298 and 223 K. The data could be fitted by the Arrhenius expression k1b = 6.4 x 10(-17) exp((1644 +/- 76)/T) cm3 molecule(-1) s(-1) at T = 223-298 K. The yield of HNO3 was found to increase in the presence of water vapor (by 90% at about 3 Torr of H2O). Implications of the obtained results for atmospheric radicals chemistry and chemical amplifiers used to measure peroxy radicals are discussed. The results show in particular that reaction 1b can be a significant loss process for the HO(x) (OH, HO2) radicals in the upper troposphere.

Branching Fractions for H2O Forming Channels of the Reaction of OH Radicals with Acetaldehyde

Branching fractions for two hydrogen abstraction channels of the OH + CH3CHO reaction producing H2O + CH3CO (a) and H2O + CH2CHO (b) were determined using chemical ionization mass spectrometry. Reaction took place in a high-pressure turbulent flow reactor at 200 Torr of carrier gas N2. The branching fraction for the abstraction from the methyl group, (5.1+2.4/-1.7) %, was determined at room temperature by direct detection of the vinoxy radicals (CH2CHO) using proton-transfer ionization. The total H2O yield of (97.7 ± 4.7) % was obtained at T = 298 and 248 K by comparison with OH + C6H12 reaction, confirming that in this temperature range reaction proceeds by H-atom abstraction. Secondary reactions of the acetyl and vinoxy radicals in the presence of O2 and NO2 were studied by monitoring the stable products CH2O, (HCO)2, and CH3OH using proton-transfer ionization. It was found that formaldehyde is the major coproduct of OH in the CH3CO + O2 reaction.

Gas-Phase Reactions of OH Radicals with Dimethyl Sulfoxide and Methane Sulfinic Acid Using Turbulent Flow Reactor and Chemical Ionization Mass Spectrometry

Reactions of OH radicals with dimethyl sulfoxide (CH3)2SO (DMSO) (reaction 1) and methane sulfinic acid CH3S(O)OH (MSIA) (reaction 2) have been studied at 298 K and 200 and 400 Torr of N2 using a newly constructed high-pressure turbulent flow reactor coupled to an ion molecule reaction mass spectrometer. The experimental setup is discussed in detail. The reactions of OH with DMSO and MSIA were found to proceed with predominant formation of MSIA and SO2, respectively. The yields of MSIA in reaction 1 and of SO2 in reaction 2 were estimated to be 0.9 ± 0.2. The reaction rate constants k1 = (9 ± 2) × 10-11 cm3 molecule-1 s-1 and k2 = (9 ± 3) × 10-11 cm3 molecule-1 s-1 were obtained. These results indicate that the OH-addition route of the gas-phase atmospheric oxidation of dimethyl sulfide, CH3SCH3 (DMS), which produces DMSO as a primary intermediate, would result in high yields of SO2, which is a precursor of H2SO4. The results then suggest that the other major end product of DMS oxidation, methane sulfonic...