Increase Of Initial Pressure Research Articles

Numerical Simulation on the Influences of Initial Temperature and Initial Pressure on Attenuation Characteristics and Safety Distance of Gas Explosion

Understanding a safety distance necessary to avoid the harms of a shock wave to underground personnel may have great significance to the safety of underground personnel, disaster relief efforts, and the treatment of the gas explosion in coal mines. Through a roadway model with a cross-section area of 80 × 80 mm2 and a length of 100 m, the explosive attenuation characteristics of a methane/air mixture with a fuel concentration of 9.5% and a filling ratio of 10% were simulated by using AutoReaGas software for various initial temperatures (248–328 K) and initial pressures (20–200 KPa). The results show that the safety distance increases with the increase of the initial temperature and follows the changing trend of decreasing, increasing, and decreasing again with the increase of the initial pressure. The time of flame arrival to each point away from initiation and the maximum distance of flame propagation both increase with the increase of the initial temperature, but they are almost the same for various initial pressures. Before the attenuation of the shock wave occurs, increasing the initial temperature increases the maximum temperature, but decreases the peak overpressure, the maximum density, the maximum combustion rate, and the maximum gas velocity. However, increasing the initial pressure increases the peak overpressure, the maximum density, and the maximum combustion rate. The influences of the initial temperature and the initial pressure on these parameters at the longer distance points from the ignition source are greater than those at the shorter distance points.

From Brain to Behavior: Hypertension's Modulation of Cognition and Affect

Accumulating evidence from animal models and human studies of essential hypertension suggest that brain regulation of the vasculature is impacted by the disease. Human neuroimaging findings suggest that the brain may be an early target of the disease. This observation reinforces earlier research suggesting that psychological factors may be one of the many contributory factors to the initiation of the disease. Alternatively or in addition, initial blood pressure increases may impact cognitive and/or affective function. Evidence for an impact of blood pressure on the perception and experience of affect is reviewed vis-a-vis brain imaging findings suggesting that such involvement in hypertensive individuals is likely.

Effect of water density and air pressure on partial oxidation of bitumen in supercritical water

Partial oxidation of bitumen was examined in supercritical water from 653 to 723K at a water/oil ratio from 0 to 3 and up to 5.1MPa of initial air pressure. The contents in the reactor were separated into water rich phase and oil rich phase. Most of oxygen was quickly consumed within 30min and the main gases produced were CO, CO2 and methane. The low temperature gave higher CO/(CO+CO2) ratio and suppressed coke formation. The amount of total gas tended to decrease and the ratio of CO/(CO+CO2) increased about two times by the increase in water/oil ratio from 0.5 to 3. The high water/oil ratio was preferred for selective partial oxidation to produce CO, which means that the effect of the enhancement of partial oxidation by supercritical water was probably larger than that of CO oxidation by water and water gas shift reaction. The increase in initial air pressure increased the amount of CO and CO2 and decreased the ratio of CO/(CO+CO2). The total oxidation route was enhanced under high air pressure.

Kinetics of Hydrogen Absorption in Ti-V-Cr Burn-Resistant Alloy

Abstract The hydrogen absorption kinetics of Ti40 alloy was studied in the temperature range of 550–700 °C and the pressure range of 15.88–45.88 kPa. The initial temperature of hydrogen absorption for Ti40 alloy is 515 °C. With the increase of temperature and initial hydrogen pressure, the time to reach the equilibrium condition becomes shorter, while hydrogen absorption rate and equilibrium hydrogen pressure increase. At low temperature, the process of hydrogen absorption consists of three stages: I incubation stage, II the first absorption stage and III the second absorption stage. At the same temperature, the rate constants at different stages follow the relation: kII>kI>kIII. At the same stage, the rate constants increase with the increase of temperature. The activation energy of the first and second absorption stage are 73.3 kJ/mol and 29.6 kJ/mol, respectively. The rate controlling step at the second absorption stage is the hydrogen diffusion in β-Ti.

Dual endothelin receptor blockade with tezosentan markedly attenuates hypoxia‐induced pulmonary vasoconstriction in a porcine model

Our aim was to test the hypothesis that dual endothelin receptor blockade with tezosentan attenuates hypoxia-induced pulmonary vasoconstriction. Fourteen anaesthetized, ventilated pigs, with a mean ± SEM weight of 30.5 ± 0.6 kg, were studied, in normoxia (FiO(2) 0.21) and with tezosentan (5 mg kg(-1)) infusion during (n = 7) or before (n = 7) hypoxia (FiO(2) 0.10). Compared to normoxia, hypoxia increased (P < 0.05) pulmonary vascular resistance (PVR) by 3.4 ± 0.7 WU, mean pulmonary artery pressure by 13.7 ± 1.3 mmHg, mean right atrial pressure by 1.9 ± 0.4 mmHg and decreased (P < 0.02) systemic vascular resistance (SVR) by 5.2 ± 2.1 WU. Pulmonary capillary wedge pressure (PCWP), mean aortic blood pressure, heart rate, cardiac output, stroke volume and blood-O(2)-consumption were unaltered (P = ns). Tezosentan infused during hypoxia, normalized PVR, decreased (P < 0.05) maximally mean pulmonary artery pressure by 7.5 ± 0.8 mmHg, SVR by 5.8 ± 0.7 WU, mean aortic blood pressure by 10.8 ± 3.0 mmHg and increased (P < 0.04) stroke volume by 8.5 ± 1.8 mL. Mean right atrial pressure, PCWP, heart rate, cardiac output and blood-O(2) -consumption were unaltered (P = ns). Tezosentan infused before hypoxia additionally attenuated approx. 70% of the initial mean pulmonary artery pressure increase and abolished the PVR increase, without additionally affecting the other parameters. Dual endothelin receptor blockade during hypoxia attenuates the 'sustained' acute pulmonary vasoconstrictor response by reducing the mean pulmonary artery pressure increase by approx. 62% and by normalizing PVR. Pre-treatment with tezosentan before hypoxia, additionally attenuates the initial hypoxia-induced mean pulmonary artery pressure rise by approx. 70% and abolishes the PVR increase, during stable circulatory conditions, without affecting oxygenation.

The Surface Characteristics and Friction Properties of PTFE Yarn

To discuss the surface characteristics and friction properties of PTFE yarn, the longitudinal structure and cross section were analyzed, it were investigated that the influence on friction coefficient of running speed, guide material and initial tension on ring spinning for producing PTFE film yarn. The results show that the longitudinal section of PTFE yarn was regular cylinder, the cross section was polygon, the yarn surface was very smooth, not easy to absorb dust, PTFE yarn had very good self-cleaning function. The friction coefficient of PTFE yarn was decreased at first with the increase of running speed but increased later, and the friction coefficient of PTFE yarn was reduced with the increase of initial pressure. The friction coefficient between PTFE yarn and plastic was very small, it can be said that plastic was the best guide material for ring spinning of PTFE yarn. Introduction

Measurement of laminar flame speeds and flame stability analysis of tert-butanol–air mixtures at elevated pressures

Laminar flame speeds and Markstein lengths of tert-butanol–air premixed mixtures were measured over a wide range of equivalence ratios at different initial temperatures and pressures by using the spherically propagating flame in a constant volume combustion chamber. Effects of Markstein number, flame thickness and density ratio at two sides of flame front on flame instability were analyzed combined with the schlieren photos. Results show that the unstretched flame propagation speeds and laminar flame speeds of the tert-butanol–air mixtures increase with the increase of initial temperature and decrease with the increase of initial pressure. Peak values of laminar flame speeds present at equivalence ratio of 1.1 regardless of initial pressure and temperature. Markstein length decreases with the increase of initial pressure. Flame front instability increases as equivalence ratio and initial pressure increase. Cellular structure appears at elevated pressure. The combined effect of diffusional–thermal instability and hydrodynamic instability leads to the increase of flame instability as initial pressure increases.

Additive Effects on the Burning Velocity of Ethylene–Air Mixtures

Using a simple correlation based on the cubic law of early pressure rise during a closed vessel explosion, the laminar burning velocities of the stoichiometric ethylene–air mixture diluted with several additives (Ar, N2, and CO2) (concentrations between 4 and 40 vol %) were calculated from pressure–time records, at total initial pressures between 0.2 and 1.2 bar and ambient initial temperature. These are important input properties for numerical modeling of explosion propagation in closed or vented enclosures and for safety recommendations concerning the necessary inert gas addition. The decrease of burning velocities determined by the increase of the total initial pressure and inert gas addition is examined. A computational study of free laminar premixed flames of ethylene–air in the presence of the same additives based on the use of 53 species and an extended reaction mechanism with 592 elementary reactions delivered the temperature and species profiles in the flame front, together with the flame width a...

Prediction of strain energy-based liquefaction resistance of sand–silt mixtures: An evolutionary approach

Liquefaction is a catastrophic type of ground failure, which usually occurs in loose saturated soil deposits under earthquake excitations. A new predictive model is presented in this study to estimate the amount of strain energy density, which is required for the liquefaction triggering of sand–silt mixtures. A wide-ranging database containing the results of cyclic tests on sand–silt mixtures was first gathered from previously published studies. Input variables of the model were chosen from the available understandings evolved from the previous studies on the strain energy-based liquefaction potential assessment. In order to avoid overtraining, two sets of validation data were employed and a particular monitoring was made on the behavior of the evolved models. Results of a comprehensive parametric study on the proposed model are in accord with the previously published experimental observations. Accordingly, the amount of strain energy required for liquefaction onset increases with increase in initial effective overburden pressure, relative density, and mean grain size. The effect of nonplastic fines on strain energy-based liquefaction resistance shows a more complicated behavior. Accordingly, liquefaction resistance increases with increase in fines up to about 10–15% and then starts to decline for a higher increase in fines content. Further verifications of the model were carried out using the valuable results of some downhole array data as well as centrifuge model tests. These verifications confirm that the proposed model, which was derived from laboratory data, can be successfully utilized under field conditions.

Dependence of the optic nerve sheath diameter on acutely applied subarachnoidal pressure - an experimental ultrasound study

To determine the distensibility and elastic characteristics of the optic nerve sheath for development of a basic understanding of ultrasound studies aimed to measure optic nerve sheath diameter (ONSD) for detection of acutely elevated intracranial pressure (ICP). Isolated human optic nerves preparations obtained from autopsies were submitted to predefined pressure alterations, and consecutive changes in ONSD were measured by B-scan ultrasound under defined conditions. Following submission to pressure, the diameter of the nerve sheath increased up to 140% of its baseline value. The increase (mean 1.97 mm, SD 0.52 mm) corresponded to the magnitude of pressure steps measured in the perineural subarachnoidal space (SAS). Similarly, the ONSD declined in each of the preparations within a few minutes after the optic nerve was decompressed. However, it did not reach its baseline value again when pressure loads of 45-55 mmHg or more had been applied. The elasticity of the anterior sheath of the optic nerve is sufficient for the detection of pressure changes in the SAS especially for upward pressure steps. This is basically important for the application of clinical monitoring of the sheath diameter to facilitate the identification of patients with elevated ICP non-invasively (screening). However, further implementation of this procedure in neurointensive care and emergency medicine has to consider that the sheath diameter reversibility may be impaired after episodes of prolonged intracranial hypertension and a model for hysteresis is proposed.

Effect of hydrogen pressure on growth kinetics of Nd2Fe14B phase during hydrogen-induced reverse phase transformation in Nd2Fe14B type hard magnetic alloy

The effect of initial hydrogen pressure on growth kinetics of Nd₂Fe₁₄B phase during hydrogen-induced reverse phase transformation in the industrial Nd₂Fe₁₄B hard magnetic alloy has been studied. It has been determined that, as the temperature and the initial hydrogen pressure increase, a reverse phase transformation significantly accelerates. It has been shown that the kinetics of growth of Nd₂Fe₁₄B phase is controlled by the Fe atoms diffusion and that the rate growth of new Nd₂Fe₁₄B phase increase with increase of initial hydrogen pressure. On the base of the Kolmogorov-Hillert-Smirnov kinetic models the kinetic equation for describing of influence of initial hydrogen pressure on the isothermal kinetic diagram for this transformation has been proposed.

Growth Kinetics of Nd&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;Fe&amp;lt;sub&amp;gt;14&amp;lt;/sub&amp;gt;B Phase during Hydrogen-Induced Reverse Phase Transformation in Nd&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;Fe&amp;lt;sub&amp;gt;14&amp;lt;/sub&amp;gt;B Type Nanocrystalline Magnetic Alloy

The influence of hydrogen pressure on kinetics of growth of Nd2Fe14B phase during hydrogen-induced reverse phase transformations in the industrial Nd2Fe14B hard magnetic alloy has been studied. It has been determined that, as the temperature and the initial hydrogen pressure increase, a reverse phase transformation significantly accelerates. It has been shown that the kinetics of the reverse phase transformation is controlled by the Fe atoms diffusion and that the rate growth of new Nd2Fe14B phase increase with increase of initial hydrogen pressure. On the base of the Kolmogorov kinetic theory the kinetic equation describing influence of initial hydrogen pressure on the isothermal kinetic diagram for this transformation has been obtained.

Co-liquefaction of lignite and sawdust under syngas

Individual and co-liquefaction of lignite and sawdust (CLLS) under syngas was performed in an autoclave and the effects of temperature, initial syngas pressure, reaction time and ratio of solvent to coal and biomass on the product distribution of CLLS were studied. Sawdust is easier to be liquefied than lignite and the addition of sawdust promotes the liquefaction of lignite. There is some positive synergetic effect during CLLS. In the range of the experimental conditions investigated, the oil yield of CLLS increases with the increase of temperature, reaction time (10–30 min) and the ratio of the solvent to the feedstock (0–3), but varies little with the increase of initial syngas pressure. Accordingly, the total conversion, the yield of preasphaltene and asphaltene (PA + A) and gas, changes by the difference in operation conditions of liquefaction. The gas products are mainly CO and CO 2 with a few C 1–C 4 components. The syngas can replace the pure hydrogen during CLLS. The optimized operation conditions in the present work for CLLS are as follows: syngas, temperature 360 °C, initial cold pressure 3.5 MPa, reaction time 30 min, the ratio of solvent to coal and sawdust 3:1. Water gas shift reaction occurs between CO in the syngas and H 2O from coal and sawdust moisture during the co-liquefaction, producing the active hydrogen which increases the conversion of liquefaction and decreases the hydrogen consumption.

Kinetic of formation for single carbon dioxide and mixed carbon dioxide and tetrahydrofuran hydrates in water and sodium chloride aqueous solution

A laboratory-scale reactor system is built and operated to measure the kinetic of formation for single and mixed carbon dioxide–tetrahydrofuran hydrates. The T-cycle method, which is used to collect the kinetic data, is briefly discussed. For single carbon dioxide hydrate, the induction time decreases with the increase of the initial carbon dioxide pressure up to 2.96 MPa. Beyond this pressure, the induction time is becoming relatively constant with the increase of initial carbon dioxide pressure indicating that the liquid phase is completely supersaturated with carbon dioxide. Experimental results show that the inclusion of tetrahydrofuran reduces the induction time required for hydrate formation. These observations indicate hydrate nucleation process and onset growth are more readily to occur in the presence of tetrahydrofuran. In contrast, the presence of sodium chloride prolongs the induction time due to clustering of water molecules with the ions and the salting-out effects. It is also shown that the degree of subcooling required for hydrate formation is affected by the presence of tetrahydrofuran and sodium chloride in the hydrate forming system. The presence of tetrahydrofuran in the hydrate system significantly reduces the amount of carbon dioxide uptake. The apparent rate constant, k, for those systems are reported.

Measurement of laminar burning velocities of iso-butanol-air mixtures

The laminar burning velocity of iso-butanol-air mixtures was measured under different initial pressures, initial temperatures and equivalence ratios using high-speed schlieren photography and outwardly propagation flame in a constant volume combustion bomb. Based on the analysis of stretched flame propagation speed and stretch rate, the laminar burning velocities and Markstein lengths of iso-butanol-air flames are obtained. In accordance, with photos of flame, an analysis of flame stability and the influencing factors is carried out. The results show that the laminar burning velocity is decreased with the increase of initial pressure and is increased with the increase of initial temperature. The maximum value of laminar burning velocity is presented at the equivalence ratio of 1.2. The Markstein length is decreased with the increase of equivalence ratio. For specified equivalence ratio, the Markstein length is decreased with the increase of initial temperature and initial pressure. Thus, the flame instability is increased with the increase of equivalence ratio, initial temperature and initial pressure.

Numerical simulation of temperature rise within hydrogen vehicle cylinder during refueling

Basing on the Spallart-Allmaras turbulence model and the real gas equation of state, a numerical model is proposed in this paper to study the mechanism of temperature rise within hydrogen vehicle cylinder during refueling. The model is validated by comparing calculated results with experimental data. With the validated model, the effect of mass filling rate, initial pressure within cylinder and ambient temperature on the maximum temperature rise during refueling are investigated. The study shows that the maximum temperature rise increases with the growth in mass filling rate and ambient temperature, while it descends as the initial pressure increases. Finally, an empirical formula is obtained by fitting numerical results and effective methods for temperature control is given.

Experimental study on premixed combustion of spherically propagating methanol-air-nitrogen flames

The outward propagation and development of surface instability of the spark-ignited spherical premixed flames for methanol-air-nitrogen mixtures were experimentally studied by using a constant volume combustion chamber and a high-speed schlieren photography system. The laminar burning velocities, the mass burning fluxes, and the Markstein lengths were obtained at different equivalence ratios, dilution ratios, initial temperatures, and pressures. The laminar burning velocities and the mass burning fluxes give a similar curve versus the equivalence ratios. They increase with the increase of initial temperature and decrease with the increase of dilution ratio. The laminar burning velocity decreases with elevating the initial pressure, while the mass burning flux increases with the increase of the initial pressure. Markstein length decreases slightly with the increase of initial temperature for the rich mixtures. High initial pressure corresponds to low Markstein length. Markstein length increases with the increase of dilution ratio, which is more obvious when the mixture becomes leaner. Equivalence ratio has a slight impact on the development of the diffusive-thermal cellular structure at elevated initial pressures. The initial pressure has a significant influence on the occurrence of the flame front cellular structure. At the elevated pressures, the cracks on the flame surface branch and develop into the cell structure. These cells are bounded by cracks emitting a bright light, which may indicate soot formation. For very lean mixture combustion, the buoyancy effect and cooling effect from the spark electrodes have a significant impact on the flame propagation. The hydrodynamic instability, inhibited with the increase of initial temperature around the stoichiometric equivalence ratio, is enhanced with the increase of initial pressure and suppressed by mixture dilution.

Flame instability analysis of diethyl ether-air premixed mixtures at elevated pressures

Combustion characteristics of premixed diethyl ether-air mixtures were studied at different equivalence ratios and elevated initial pressures using schlieren photography and spherically propagating flame. Laminar burning velocities, Markstein number and critical radii at onset of cellular structure were obtained. The results show that an increase in initial pressure leads to a decrease in the unstretched laminar burning velocities. Laminar burning velocities give their peak values at the equivalence ratio of 1.1. Markstein number decrease with the increase of initial pressure and equivalence ratio, indicating that the instability of flame front is increased with the increase of initial pressure and equivalence ratio. The critical radii at onset of cellular flame structure are decreased with the increase of initial pressure.

Bioenergy II: Effect of Experimental Conditions on the Slow Batch Pyrolysis of Mixtures of Plastics, Tyres and Forestry Biomass Wastes

This work aimed to study the recovery of three types of waste by the process of pyrolysis: biomass, plastics and used tyres. The effects of experimental conditions in products yield and composition were studied. The increase of reaction time increased alkane content both in gas phase from 53% to 70% v/v and in liquid fraction from 48% to 60% w/w. The rise of reaction temperature led to a decrease of liquid yield (from 82% to 73% w/w), which was followed by the increase of solids and gases. The increase of reaction temperature also allowed the increase of the alkane content in gas phase from 39% to 70% v/v. The increase of initial pressure did not lead to appreciable variations in product yields or composition. The parameter that most affected products yield and composition was plastics content on the wastes initial mixture. The enhancement of this parameter increased liquids yield from 33% to 92% w/w, at the expenses of solids and gases contents and also decreased aromatics contents from 52% to 28% w/w.

Study on Laminar Burning Characteristics of Premixed High-Octane Fuel−Air Mixtures at Elevated Pressures and Temperatures

Laminar burning characteristics of high-octane fuel−air premixed mixtures (ETBE, TBA, and ethanol) were studied in a constant-volume bomb at various equivalence ratios, initial temperatures, and initial pressures by using outwardly propagating spherical flames with a high-speed schlieren imaging system. The flame propagation speed, the laminar burning velocity, the Markstein length, the adiabatic flame temperature, the flame thickness, and the density ratio were obtained and the influence of equivalence ratio, initial temperature, and initial pressure on these parameters was analyzed. The experimental results show that both the unstretched flame propagation speed and unstretched laminar burning velocity increase with the increase of initial temperature and decrease with the increase of initial pressure. Thermal-diffusive instabilities (Markstein length) decrease at higher initial temperature and/or at lower initial pressure. Meanwhile, the unstretched flame propagation speed and the unstretched laminar bu...