Decrease In Initial Pressure Research Articles

Experimental and numerical study of the temperature evolution in hydrogen cylinder under fast-refueling process

Hydrogen has been considered a feasible energy carrier for fuel cell vehicles (FCVs), which offers a clean and efficient alternative for transportation. The hydrogen is filled from high-pressure stations into hydrogen storage systems (HSS) in FCVs. During the refueling of high-pressure hydrogen, it can cause a rapid increase in temperature in the HSS due to the thermal characteristics of the system leading to safety problems. For safety reasons, the tank's maximum temperature and fueling pressure are limited to less than 85 oC and 125% of the vessel design pressure, respectively. This paper presents the fast-filling process of hydrogen tanks through experiments and simulations based on Computational Fluid Dynamics (CFD). Several critical parameters, such as the initial pressure, the initial temperature of hydrogen, and the filling rate that can contribute to the temperature rise, are investigated during the fast-filling process. The temperature within the tank increase with the decrease of initial pressure and the increase of ambient temperature with less filling time. In the case of a linear pressure increase from 2 to 35 MPa within 180 s at the ambient temperature of 20 oC, the maximum temperature reached 82.97 °C. In addition, the average velocity of the inlet gas of the hydrogen cylinder increases to 202.41 m/s rapidly in the first second and then decreases to 14.3 m/s slowly for the remaining filling process. For an ambient temperature of 40 oC, the maximum temperature can reach 101.24 oC during the process except for the first 10 s when the gas temperature within the tank was consistently above 85 oC, causing significant damage to the cylinder. As a result, reasonable and effective fast-filling strategies are designed to ensure safety at high ambient temperatures.

Extensive study on the detonation cell size of biogas-oxygen mixtures

Detonation cell size is one of the most important and most widely used parameters to describe the detonation process of a given mixture. It is used in both safety analyses and the design process of experiments and engines utilizing detonative combustion. Although much research has been carried out to collect data on the detonation cell of a wide range of combustible mixtures, few studies have focused on biogas. The presented study aims to fill this gap. Several biogas compositions, initial pressures p0 and equivalence ratios Φ were tested, totaling 200 different cases. Both a decrease of initial pressure and a decrease of methane content in the biogas result in an increase in the detonation cell width. When the equivalence ratio is moved away from stoichiometric (Φ = 1) towards either lean or rich mixtures it is accompanied by an increase in detonation cell size. Additionally, ZND induction length and instability parameter χ were calculated. Induction length correlates linearly with the cell size and the χ shows that the cellular structure is expected to be very irregular. Because of that it does not suffice to report merely the average cell size. Thus, a more detailed statistical description is provided.

Экспериментальные исследования гидратообразования природного газа в пористой среде в присутствии растворов хлорида и гидрокарбоната натрия

The paper presents the results of investigation of the natural gas hydrates formation and decomposition in quartz sand in the presence of fresh water, sodium bicarbonate (0,25 and 2 mass%) and chloride (5 mass%) solutions. The selected solutions are models of stratum water of subpermafrost aquifers of the Vilyui syneclise. The study of the porous medium and salinity influence on the hydrate formation was carried out by differential thermal analysis at initial gas pressures from 4 to 7 MPa. Equilibrium conditions and kinetic parameters of the hydrate formation were determined. The kinetic parameters of the hydrate formation in porous media, depending on salinityand at each value of the initial pressure decrease in the following sequence: 0,25 mass% NaHCO3 H2O > 2 mass% NaHCO3 > 5 mass% NaCl. The stability of hydrates obtained in porous media with different salinity has been studied. It has been established that the hydrates stability in porous media decreases with an increase of the solution concentration.

Effects of Dilution and Pressure on Detonation Propagation Across an Inert Layer

In explosion accidents, inert layer(s) can be used to dampen or suppress detonation propagation. In detonation engines, the detonation may propagate in an inhomogeneous mixture with inert layer(s). Here, the detonation propagation in hydrogen/oxygen/nitrogen mixtures with a single inert layer normal to the detonation propagation direction was investigated. Six hydrogen/oxygen/nitrogen mixtures with different amounts of nitrogen dilution and at different initial pressures were considered. The emphasis was placed on assessing the effects of nitrogen dilution and pressure on detonation across an inert layer. It was found that successful detonation reinitiation occurs only when the inert layer thickness is below some critical value. The detonation reinitiation process was analyzed. The interactions of transverse waves, the reactive–inert layer interface, and instabilities jointly induced local autoignition/explosions and detonation reinitiation. Counterintuitively, it was found that a thicker inert layer is required to quench a weaker detonation (with more nitrogen dilution or with lower-energy density at lower pressure). With the increase of nitrogen dilution or the decrease of initial pressure, the induction length and cell size of the detonation became larger, which unexpectedly resulted in the larger critical inert layer thickness.

Drying Characteristics of a Combined Drying System of Low-Pressure Superheated Steam and Heat Pump

The present study aimed at investigating the use of a drying system combining the concept of low-pressure superheated steam drying and heat pump drying for fish. The effects of various drying medium pressures on the temperature field, airflow field, drying time, equipment performance as well as the power consumption of the drying process were investigated and discussed. Four comparative tests with different initial pressures were carried out according to a specified drying process by the combined drying system. The results showed that when the vacuum was high, the temperature field and airflow field in the drying chamber were more uniform. Due to the poor heat transfer performance of the drying medium at high vacuum, the drying time increased with a decrease in initial pressure. It was also found that with the decrease in drying medium pressure, the power consumption of the heat pump and the axial fans was reduced, while the power consumption of the electric heater went up. Overall, the total power consumption is directly proportional to the drying medium pressure.

The Equivalent Effect of Initial Condition Coupling on the Laminar Burning Velocity of Natural Gas Diluted by CO2

Initial temperature has a promoting effect on laminar burning velocity, while initial pressure and dilution rate have an inhibitory effect on laminar burning velocity. Equal laminar burning velocities can be obtained by initial condition coupling with different temperatures, pressures and dilution rates. This paper analysed the equivalent distribution pattern of laminar burning velocity and the variation pattern of an equal weight curve using the coupling effect of the initial pressure (0.1–0.3 MPa), initial temperature (323–423 K) and dilution rate (0–16%). The results show that, as the initial temperature increases, the initial pressure decreases and the dilution rate decreases, the rate of change in laminar burning velocity increases. The equivalent effect of initial condition coupling can obtain equal laminar burning velocity with an dilution rate increase (or decrease) of 2% and an initial temperature increase (or decrease) of 29 K. Moreover, the increase in equivalence ratio leads to the rate of change in laminar burning velocity first increasing and then decreasing, while the increases in dilution rate and initial pressure make the rate of change in laminar burning velocity gradually decrease and the increase in initial temperature makes the rate of change in laminar burning velocity gradually increase. The area of the region, where the initial temperature influence weight is larger, gradually decreases as the dilution rate increases, and the rate of decrease gradually decreases.

Effects of initial condition and fuel composition on laminar burning velocities of blast furnace gas with low heat value

Laminar burning velocities of blast furnace gas with low heat value were investigated using constant volume combustion chamber and CHEMKIN package. Experiments and numerical simulations using Li, Davis, Gri-Mech 3.0, San Diego Mech, USC Mech II, NUI Galway Mech models were conducted at initial pressures of 0.1–0.2 MPa, initial temperatures of 303–453 K, and equivalence ratios of 0.8–1.6. Fuel composition was changed considering the volume fraction variation in blast furnace gas with calorific values of 3.27–4.03 MJ/m3. The effects of initial pressure and temperature on laminar burning velocities were correlated with high-order polynomials dependent on the equivalence ratio. The thermal and transport effects were examined and sensitivity analyses were further conducted to study the chemical kinetic effect. The results show that the laminar burning velocities increase with the decrease of initial pressure and the increase of initial temperature, and the Gri-Mech 3.0 mechanism gives very good predications among the six kinetic mechanisms. In addition, the laminar burning velocities increase with the increase of H2/CO ratio and the decrease of CO2/N2 ratio under the same low heat value. The chemical kinetic effect plays a major part during the laminar flame propagation under all the operation conditions considered. Due to the high CO content and low H2 content in blast furnace gas, R99 and R45 are the main chain branching and chain termination reactions, respectively. The effects of initial condition and fuel composition on laminar burning velocities are closely related to the concentrations of H, O and OH radicals.

Effects of CH4 mixing on the laminar burning velocity and Markstein length of RP-3/air premixed flame

Experiments have been carried out in a constant volume combustion bomb to investigate the effects of initial temperature (450 and 480 K), initial pressure (0.1 and 0.3 MPa) and CH4 mixing ratio (0, 0.2, 0.4, 0.6, 0.8, 0.85, 0.9 and 0.95) on the laminar burning velocity and Markstein length of homogeneous, quiescent CH4/RP-3/air mixture over wide equivalence ratio from 0.7 to 1.4. Results show that with the increase of initial temperature from 450 to 480 K, no cellular structure in flame is observed, but obvious cellular structure is observed when initial pressure increases to 0.3 MPa at equivalence ratio of 1.2. The laminar burning velocity reaches its maximum in slightly rich mixture (ϕ = 1.1) and with the increase of initial temperature and decrease of initial pressure the peak laminar burning velocity of CH4/RP-3/air mixture increases. It is found that the laminar burning velocity of CH4/RP-3/air mixture decreases slowly when methane mixing rate increase from 0 to 0.8, but decreases rapidly from 0.8 to 0.95. Analysis results show that at equivalence ratio of 1.1, the Arrhenius factor exp-Ta/2Tad has greater effect on the laminar burning velocity of CH4/RP-3/air mixtures when the methane mixing ratio is larger than 0.8. At equivalence ratio of 0.8 (lean mixture), with the increase of CH4 mixing ratio the Le-1 decreases, which leads to the decrease of Markstein length and make the premixed flame tends to be unstable, while at equivalence ratio of 1.4 (rich mixture), with the increase of CH4 mixing ratio the Ze and δ increase, which stabilizes the premixed flame.

On the detonation behavior of methane-oxygen in a round tube filled with orifice plates

Abstract In this study, the detonation behaviors of stoichiometric methane-oxygen mixture were examined in a round tube filled with orifice plates. The blockage ratio was 0.56 and the plate spacings were 1, 1.5 and 2 times the tube diameter. Detonation velocity measurement and soot foils were adopted to study the propagation characteristics. Experimental results show that the abrupt velocity jump was only observed for the obstacle configuration with S = 2 D , where S and D are the plate spacing and the tube diameter. For a fixed plate spacing, the detonation velocity as well as the detonation limits are independent of the orifice geometry, since the effective diameters ( d e f f ) of the orifices are almost the same. The ratios of d e f f to the detonation cell size ( λ ) were found to be 0.4–0.5. For sensitive mixtures, the soot foils indicate that the detonation re-initiation occurs via hot spots formed on the wall. As the initial pressure decreases, the detonation can travel without hot spots generation. At the limits, no indication of detonation can be observed for obstacle configurations with smaller spacings in spite of the higher velocity (compared with the isobaric sound speed of the products). The propagation mechanism near the limits is left, however, for further investigation.

The importance of endothermic pyrolysis reactions in the understanding of diesel spray combustion

The significance of pyrolysis reactions in the early stages of diesel combustion has received little attention in the literature, which warrants a mechanistic investigation of the controlling chemistry along with its potential impacts on the overall combustion process in engines. Experiments were performed in a constant volume vessel to probe these pyrolytic reactions, where diesel fuel sprays were injected into air at varied pressures and temperatures chosen to represent an engine operating at various loads. The pressure inside the vessel was found to decrease immediately following the start of injection before increasing as the exothermic heat release occurs. The initial pressure decrease has been conventionally attributed to an evaporative cooling effect of the diesel spray, but the objective of this paper is to test the hypothesis that endothermic pyrolysis reactions can make a significant contribution to the observed pressure decrease.The addition of 1% of the cetane booster, 2-ethylhexylnitrate (2-EHN), to the fuel was found to shorten the measured ignition delay time, as expected. However the presence of 2-EHN can also increase the magnitude of the initial pressure decrease compared to conventional diesel fuel. Detailed chemical kinetic modeling shows that the effects observed in the constant volume vessel can plausibly be attributed to pyrolysis reactions, and that the addition of 2-EHN to the base fuel enhances their influence. The modelling results also imply that the influence of these pyrolysis reactions increases with increasing temperature, pressure, the alkyl chain length of the base fuel, and the amount of any radical initiator in the fuel.

Effect of fully blocked non-rigid boundary conditions on detonation wave

For the past half century, the research on boundary conditions on the detonation wave resulting in a velocity deficit or detonation failure mainly focused on the rough-walled or acoustically absorbing condition in one/two-dimensional models. In this paper, experiments on gaseous detonation propagation are conducted in the tube fully blocked by the non-rigid obstacles, under 20 kPa with the explosive gas of C2H2 + 2.5O2 + nAr. The polypropylene membrane (PET) is selected as the non-rigid obstacle in this paper. The detonation wave behavior is to decelerate, accelerate, and overdrive prior to reaching a stable state once passing through the PET obstacles. When the initial pressure decreases or the layers of PET obstacle increases, the detonation wave will transit from a velocity deficit mode to a failure mode after deceleration occurs. With the PET layers increasing, the velocity minimum decreases continuously from 0.61 vCJ (m = 1) to 0.23 vCJ (m = 8). The propagation mode is associated with the average diameter of the hole after passing through the PET obstacles. The detonation wave will diffract when the average diameter decreases. In addition, the Mach reflection degenerates to the expansion wave and self-ignition ceases. As the shock is reflected from the tube wall, the initial regular reflection changes to a Mach reflection and auto-ignition forms again. For the multi-PET obstacles, the velocity after obstacles fluctuates more violently. The instability is regarded as the critical factor in the deceleration and acceleration.

Effects of Inertization Process in Confined Spaces With Application in the Aeronautical Industry

A long time ago, you have heard about accidents by gas explosions and the destruction that they can cause. To be able to avoid it requires an understanding of what a gas explosion is and what can reduce the frequency and consequences of these events. The upper and the lower flammability limits (UFL and LFL, respectively) are the maximum and the minimum concentration of the fuel in the air, respectively, in which a flame propagate, they are considered key tools in the prediction of fire, evaluating the possibility of explosion and design of protection systems. There is an interest in finding the flammability limits of ethanol mixed with an inert gas at reduced pressure as a safety measure for the future use of this biofuel in aeronautical applications, taking into account the typical altitude of a commercial aeroplane (<40 000 ft.). In this work, the flammability of hydrated ethanol (5,18%vol. Water) was evaluated experimentally and the nitrogen was used as an inert gas. The experimental bench was build according to the norm ASTM E-681. The ethanol was injected using a precision syringe with 1 ml of volume, nitrogen and air were injected using the partial pressure law of Dalton. The method for measure flammability was by visual observation of flame propagation. The results plotted as a function of the additions of nitrogen shows that when the initial pressure decreases, the UFL decreases and both the LFL and the limit oxygen concentration (LOC) increases. In addition, the variation of UFL is more noticeable than the LFL when the percentage of nitrogen increase in the ethanol/air mixture.

The influence of initial pressure on the characteristics of conical bubble sonoluminescence

Based on a conical bubble U-tube, conical bubble sonoluminescence was investigated by using pure water as the working medium. Intense cavitation luminescence can be obtained. With the decrease in initial pressure inside the bubble, the intensity and duration of light emission increased. The spectrum is mainly composed of the spectral bands of H2O at the initial pressure of 1000 Pa. With the decrease in initial pressure, a broad continuum background spectrum that is well fitted by blackbody radiation can be detected, on which several spectral bands emitted by water molecules are superimposed. A higher temperature inside the bubble can be obtained with the decrease in initial pressure. Moreover, the intensity of the continuum background spectrum becomes more dominant compared with that of H2O emission bands. Finally, we conclude that blackbody radiation and molecular emission contribute to luminescence of conical bubble cavitation. Moreover, the initial pressure inside the conical bubble significantly affects the emission mechanism of conical bubble sonoluminescence.

Deep Drawing of Aluminum Alloys Using a Novel Hydroforming Tooling

A simplified sheet hydroforming tooling was designed, fabricated, and tested. The advantage of the new tooling is its simplification of the tools, its requirement of lower hydraulic pressure for forming and decreasing the cost of the process. In this article, a new method of hydroforming deep drawing assisted by floating disk is proposed and investigated through experiments and simulation. Moreover, its advantages, such as simplifying the tools, decreasing the required medium pressure of the forming process, and elimination of some wrinkle due to ironing effect, have been discussed. An aluminum alloy, Al6061-T6, is formed successfully, and the influence of process parameters including the punch nose radius and friction are studied. It is determined that decreasing punch radii and friction, lead to a decrease in initial pressure and an increased safe zone, respectively. Working pressure curves, which guarantee sound workpieces, have been founded by series of experimental results. Wrinkling and fracture modes are studied and predicted in experiment and simulation. The finite element (FE) analysis is carried out. Hill–Swift and North American Deep Drawing Research Group (NADDRG) theoretical forming limit diagram (FLD) models are used to specify fracture initiation in finite element model (FEM), and it is shown that Hill–Swift model gives a better prediction. The simulated results are in good agreement with the experiment.

Measurements of Laminar Burning Velocities and Markstein Lengths ofn-Butanol−Air Premixed Mixtures at Elevated Temperatures and Pressures

Measurements of laminar burning velocities and Markstein lengths of n-butanol−air premixed mixtures was made over a wide range of equivalence ratios at initial temperatures of 413, 443, and 473 K and initial pressures of 0.1 and 0.25 MPa using the high-speed schlieren photography and outwardly propagating flame. Effects of laminar flame thickness, thermal expansion ratio, and flame Lewis number on flame stability response were studied. Schlieren photos of flame propagation are recorded. The results show that laminar burning velocities of n-butanol−air premixed mixtures are increased with the increase of initial temperature, and they decrease with the increase of initial pressure. Markstein lengths are decreased with the increase of the equivalence ratio, and they decrease with the increase of initial temperature, and all these indicate that the flame instability is increased with the increase of equivalence ratio, the decrease of initial pressure, and the increase of initial temperature.

Analysis of combustion and flame propagation characteristics of LPG and Gasoline fuels by laser deflection method

This work is to investigate the combustion characteristics and flame propagation of the LPG (liquified petroleum gas) and gasoline fuel. In order to characterize the combustion processes of the fuels, the flame propagation and combustion characteristics were investigated by using a constant volume combustion chamber. The flame propagation of both LPG and gasoline fuels was investigated by the laser deflection method and the high-speed Schlieren photography. The result of laser deflection method show that the error of measured flame propagation speed by laser method is less than5% compared with the result of high-speed camera. The flame propagation speed of the fuel is increased with the decrease of initial pressure and the increase of initial temperature in the constant volume chamber. The results also show that the equivalence ratio has a great effect on the flame speed, combustion pressure and the combustion duration of the fuel-air mixture.

Investigation of Detonative Combustion Characteristics

The pressure and deflagration-to-detonation transition (DDT) characteristics of acetylene and oxygen flame were studied in a detonation tube. The pressure history and the flame velocity along the tube were measured with high frequency pressure transducers and ion probes. By analyzing the data recorded in the experiment, the detonation wave pressure, post-wave pressure and DDT distance were obtained, together with the effects of the initial pressure varying from 2 104 Pa to 105 Pa, equivalence ration from 0.3 to 1.0, and mixture concentration from 60% to 100%. It was found that the detonation pressure was decreased respectively with the decrease of initial pressure, equivalence ratio and mixture concentration, but the DDT distance was enlarged. The DDT distance was found particularly sensitive to mixture concentration.

Physical modelling of baroclinic development in the lee of the Alps

When baroclinic development is triggered by an obstacle, like an extended mountain range, the so-called lee, or secondary cyclogenesis can develop. The presence of the obstacle exerts a blocking effect on the lower layers of the impinging airflow, forcing them to go round its borders and reach the lee region with a delay. Blocking and delay are both responsible for the initial pressure decrease downwind of the mountain and for the subsequent proper downstream baroclinic development. According to this rather simple scheme, a cyclogenesis episode in the lee of the Alps was simulated in a hydraulic turntable. The results of these experiments showed a good agreement, both from a qualitative and quantitative point of view, with the analysis of an episode of lee cyclogenesis coupled to a cold outbreak in the Mediterranean, which actually occured in Southern Europe downstream of the Alps.

The influence of ammonium persulfate on guinea pig tracheal muscle tone: release of nitric oxide.

Clinical studies have shown that oxidizing substances like hydrogen peroxide (H2O2) and ammonium persulfate used in the hair cosmetic industry may cause airway diseases. In in vitro experiments with isolated guinea pig tracheae ammonium persulfate solutions induced an initial transient relaxation of smooth muscles. This relaxation could be measured by a decrease in isometric pressure in the cannulated trachea instilled with ammonium persulfate at a hydrostatic pressure of 2.5 kPa. In control experiments, saline caused an initial pressure decrease of less than 10% within one minute. In contrast, instillation of different ammonium persulfate solutions (9.10(-5) to 9.10(-2) M) effectively dilated tracheae and resulted in a concentration-dependent drop in intratracheal pressure to 1.53 +/- 0.62 kPa (61% of the instillation pressure). The effect of ammonium persulfate on smooth muscles is obviously mediated by nitric oxide because the relaxation could be blocked by inhibitors of nitric oxide synthase (L-NMMA 40 microM and L-NAME 200 microM). The precursor of nitric oxide, L-arginine (1 mM), the D-isomers of the inhibitors and a mixture of L-arginine and L-NAME did not affect the ammonium persulfate-induced initial intratracheal pressure decrease. The results allow us to conclude that acutely elicited tracheal muscle dilatation by ammonium persulfate is mediated by nitric oxide. However, it is possible that a continuous use of oxidizing substances may lead to epithelial damage and, therefore, reduce the production of nitric oxide, thus facilitating constrictory responses.

Spherical elastic-plastic wave solutions

T wo closed-form radially symmetric elastic-plastic wave solutions, corresponding to spherical cavity loadings, are compared to numerical solutions constructed by a finite difference code. An infinitesimal strain theory, with plastic incompressibility, a Mises yield condition and either perfectly plastic flow or parabolic work hardening, allows wave function representations in both elastically and plastically deforming regions. The solutions examined are for (a) the loading problem in which the cavity wall pressure is raised instantaneously to a value p 0, sufficient to induce plastic yielding, then maintained at P 0, and (b) the unloading problem when the wall pressure is released continuously after the instantaneous step to P 0. In the former case there is a region of continuous plastic loading extending from the cavity wall to the diverging plastic discontinuity front which persists for a finite time until the plastic discontinuity is annulled. In the latter case, provided that the initial pressure decrease rate exceeds a critical value, the region behind the diverging plastic discontinuity front is purely elastic. In both cases the numerical solution smears the plastic discontinuity, and while the maintained plastic loading in case (a) allows the maximum pressure to be attained over a finite distance, this is prevented by the elastic unloading in case (b) and the following release wave is significantly distorted. It is shown that suitable ramping of the applied load produces an excellent analytic-numeric agreement unless the continuous unloading is too rapid.