Gas Initial Pressure Research Articles

Kinetic studies of ignition of coal char particle suspension in hot air

Coal ignition has been a focal point in the pursuit of improved energy efficiency and reduced emissions. This study focuses on investigating the kinetic characteristics of char ignition within a closed reactor. The combustion process is modeled using a one-step global reaction in a quiescent air environment. The results show that particle ignition time increases with equivalence ratio and particle size, while decreases with gas initial pressure and initial temperature. Particle ignition temperature is minimally affected by the particle size, slightly influenced by the gas initial pressure and initial temperature, but substantially influenced by the equivalence ratio. In the fuel-rich condition, the coal char combustion exhibits a thermal runaway stage, primarily driven by the escalating particle temperature, followed by a decaying stage, mainly influenced by the depleting oxygen mass fraction. The dominant kinetic factors affecting the heat release rate (HRR) peak are detailly investigated: the HRR peak shows an initial increase and subsequent decrease with the equivalence ratio, which is mainly controlled by the total particle number and particle temperature; Particle size affects the HRR peak through altering the total particle specific surface area, i.e., the product of the particle number and the particle diameter squared; the gas initial pressure and temperature all affect the HRR peak through directly altering the gas density. Additionally, larger retention coefficient leads to faster particle ignition and higher HRR peak. These findings provide valuable insights into the regulations of coal combustion processes, particularly in scenarios involving elevated pressure and temperature, such as coal/mine explosions.

Extraction of bioactive compounds from pomegranate peel (Punica granatum L.) with pressurized liquids assisted by ultrasound combined with an expansion gas

In this study it is proposed the introduction of an expansion gas in high pressure water to maximize the cavitation caused by the application of ultrasound to improve the extraction of phenolic compounds from pomegranate peel. Different combinations of ultrasound power (US-Pwr), expansion gas initial pressure (N2-Pi), system pressure (SP) and particle size of sample were evaluated using water as solvent. The use of US-Pwr and N2-Pi individually or combined improved the extraction process proving higher yields. SP was an important parameter affecting extraction yield, showing an inverse relation between its increase and extraction yield. Although higher yields were produced with samples with smaller particles, the combination of ultrasound and expansion gas had a positive effect on the process independently of particle size, promoting an increase of 20–26% in yield. These results suggest an enormous potential to be explored with the introduction of an expansion gas in pressurized liquids in processes assisted by ultrasound for the extraction of phenolic compounds from natural products using green solvents.

Influence of initial pressure on hydrogen/air flame acceleration during severe accident in NPP

Flame acceleration (FA) and explosion of hydrogen/air mixtures remain key issues for severe accident management in nuclear power plants. Empirical criteria were developed in the early 2000s by Dorofeev and colleagues, providing effective tools to discern possible FA or DDT (Deflagration-to-Detonation Transition) scenarios. A large experimental database, composed mainly of middle-scale experiments in obstacle-laden ducts at atmospheric pressure condition, has been used to validate these criteria. However, during a severe accident, the high release rate of steam and non-condensable gases into the containment can result in pressure increase up to 5 bar abs. In the present work, the influence of the unburnt gas initial pressure on flame propagation mechanisms was experimentally investigated. Premixed hydrogen/air mixtures with hydrogen concentration close to 11% and 15% were considered. From the literature, we know that these flames are supposed to accelerate up to Chapman-Jouguet deflagration velocity in long obstacle-laden tubes at initial atmospheric conditions. Varying the pressure in the fresh gas in the range 0.6–4 bar, no effects on the flame acceleration phase were observed. However, as the initial pressure was increased, we observed a decrease in the flame velocity close to the end of the tube. The pressure increase due to the combustion reaction was found to be proportional to the initial pressure according to adiabatic isochoric complete combustion.

An Evaluation of Kinetic Parameters and Mass Transfer Coefficient in the Biodesulfurization of Natural Gas

Biodesulfurization of natural gas in a batch culture was investigated. The microorganisms used for the removal of hydrogen sulfide were isolated from a local hot spring. The experiments were conducted with natural gas initial pressures of 1 to 1.8 atm. The kinetic parameters and mass transfer coefficients were determined. With gas pressure of 1.2 atm, maximum cell dry weight of 3.136 g.l−1 and mass transfer coefficient of 0.023 h−1 were obtained. The kinetic model was growth dependent. Andrew's equation predicted the inhibition constant; as the gas pressure increased the inhibition coefficient increased. The maximum specific growth rate (μmax) for Andrew's model was 0.176 h−1.

Thermal Analysis of Candidate Armor Materials for Use in the Magnetic Cusp Field HAPL Reactor Design

The introduction of magnetic cusp fields into the High Average Power Laser (HAPL) reactor design is to prevent target ions from interacting with the armor layer. Diverting the ions and preventing their impact on the chamber armor eases thermal design constraints considerably. The BUCKY code was used to simulate thermal loads for the candidate armor materials tungsten and silicon carbide.Parametric analysis was done to ascertain the peak temperature rise in the armor due to X-rays from the HAPL target thermonuclear ignition. Temperature values as a function of chamber armor radius were obtained using initial conditions of T0 = 600 °C and xenon buffer gas pressures of 66.7, 666.7 and 6666.1 mPa (0.5, 5 and 50 mTorr). The armor radius was decreased until thermal thresholds were met (2400 °C and 1000 °C for tungsten and silicon carbide, respectively) to determine the minimum allowable radius of the HAPL chamber.A second set of parametric simulations were performed at xenon gas initial pressures of 666.7 and 6666.1 mPa (5 and 50 mTorr) and temperature of 600°C to a time of 5 ms to observe the effect of re-radiation from the buffer gas on the surface temperature of tungsten and silicon carbide.

The effects of pressure, temperature, and concentration on the reactivity of alkanes: Experiments and modeling in a rapid compression machine

Experiments in a rapid compression machine have examined the influences of variations in pressure, temperature, and equivalence ratio on the autoignition of n-pentane. Equivalence ratios included values from 0.5 to 2.0, compressed gas initial temperatures were varied between 675 and 980 K, and compressed gas initial pressures varied from 8 to 20 bar. Numerical simulations of the same experiments were carried out using a detailed chemical kinetic reaction mechanism. The results are interpreted in terms of a lowtemperature oxidation mechanism involving addition of molecular oxygen to alkyl and hydroperoxyalkyl radicals. Idealized calculations are also reported that identify the major reaction paths at each temperature. Results indicate that in most cases, the reactive gases experience a two-stage autoignition. The first stage follows a low-temperature alkylperoxy radical isomerization pathway that is effectively quenched when the temperature reaches a level where dissociation reactions of alkylperoxy and hydroperoxyalkylperoxy radicals are more rapid than the reverse addition steps. The second stage is controlled by the onset of dissociation of hydrogen peroxide. Results also show that in some cases, the first-stage ignition takes place during the compression stroke in the rapid compression machine, making the interpretation of the experiments some-what more complex than commonly assumed. At the highest compression temperatures achieved, little or no first-stage ignition is observed.