High Initial Pressure Research Articles

Laminar burning velocity of 2-methylfuran-air mixtures at elevated pressures and temperatures: Experimental and modeling studies

2-Methylfuran (MF), a promising biofuel candidate catalytically produced from biomass-based fructose, has attracted the attention of fuel researchers. However, there is limited data available for the laminar burning velocity, especially at high initial pressure conditions. In this work, the laminar burning velocity of MF-air mixtures at elevated initial pressures (T0 = 363 K; p0 = 0.1–0.4 MPa) was experimentally determined in a spherical outwardly expanding flame. Numerical simulation was also conducted in Chemkin using two detailed chemical kinetic mechanisms at elevated pressures (similar to the experiment condition: T0 = 363 K; p0 = 0.1–0.4 MPa) and elevated temperatures (T0 = 363–563 K; p0 = 0.1 MPa). Data from experimental and modelling studies were compared and discussed. The experimental results showed that at a given T0 and p0 the laminar burning velocity of MF-air mixtures reached peak values at equivalence ratios ϕ = 1.1–1.2, and it slowed down dramatically when the MF-air mixture was too rich or lean. Laminar burning velocity decreased with the increase in p0. The laminar flame speed of MF-air mixture from two chemical kinetic mechanisms exhibited a similar trend with experimental data; however, both the two mechanisms led to overestimation at the most initial conditions. Compared to the Galway mechanism, the Tianjin mechanism better predicted the laminar burning velocity of MF-air mixtures, especially at initial pressures of 0.1 and 0.2 MPa. The current MF mechanism needs further improvement to better predict the combustion of MF at high-pressure conditions.

An investigation on gas hydrate formation and slurry viscosity in the presence of wax crystals

Clarifying the interaction effect between hydrate and wax is of great significance to guarantee operation safety in deep water petroleum fields. Experiments in a high‐pressure hydrate slurry rheological measurement system were carried out to investigate hydrate formation and slurry viscosity in the presence of wax crystals. Results indicate that the presence of wax crystals can prolong hydrate nucleation induction time, and its influence on hydrate growth depends on multiple factors. Higher stirring rate can obviously promote hydrate growth rate, while its influence on hydrate nucleation induction time is complicated. Higher initial pressure will promote hydrate formation. Gas hydrate slurry shows a shear‐thinning behavior, and slurry viscosity increases with the increase of wax content and initial pressure. A semiempirical viscosity model showing a well‐fitting is established for hydrate slurry with wax crystals by considering the aggregation and breakage of hydrate particles, wax crystals, and water droplets. © 2018 American Institute of Chemical Engineers AIChE J, 64: 3502–3518, 2018

An efficient system of compressed natural gas (CNG) secondary filling station based on reducing abnormal refilling behaviors

CNG secondary filling station is a critical infrastructure in CNG industry. By data mining, it is found that there are energy inefficient refilling behaviors with abnormal small volume, higher initial pressure, lower final pressure, or tiny change in pressure. Therefore, an energy efficient system of CNG secondary filling station is provided by reducing these abnormal inefficient actions in this article. The performance of the provided system is measured by analyzing the statics of these abnormal behaviors. It is found that if the abnormal inefficient refilling behaviors were avoided, the efficient system of CNG secondary filling station will be improved by no less than 12.937 percent.

Cerebral Autoregulation in the Prediction of Delayed Cerebral Ischemia and Clinical Outcome in Poor-Grade Aneurysmal Subarachnoid Hemorrhage Patients.

Pressure reactivity index and oxygen reactivity index are used to assess cerebral autoregulation after acute brain injury. The value of autoregulation indices in the prediction of delayed cerebral ischemia and outcome in patients with subarachnoid hemorrhage is still inconclusive. In this study, we aimed to focus on the predictive value of the first 72 hours commonly referred to as "early brain injury" in comparison to the overall monitoring period. Retrospective observational cohort study. Neurocritical care unit at a tertiary academic medical center. Forty-three consecutive poor-grade patients with nontraumatic subarachnoid hemorrhage admitted between 2012 and 2016 undergoing continuous high-frequency monitoring. High-frequency monitoring includes arterial blood pressure, intracranial pressure, and brain tissue oxygen tension. Pressure reactivity index and oxygen reactivity index were evaluated as moving correlation coefficient between mean arterial pressure/intracranial pressure and cerebral perfusion pressure/brain tissue oxygen tension, respectively. Median autoregulation monitoring time was 188 ± 91 hours per patient. Initial pressure reactivity index was 0.31 ± 0.02 and decreased significantly to 0.01 ± 0.01 (p < 0.001) 3 days after admission with a second peak 10 days after admission (0.18 ± 0.14; p = 0.001). Admission oxygen reactivity index was high, 0.25 ± 0.03, and decreased to a minimum of 0.11 ± 0.02 eight days after admission (p = 0.008). Patients with delayed cerebral ischemia had significantly higher overall mean pressure reactivity index values (p < 0.04), which were more pronounced during the first 72 hours, reflecting early brain injury (p < 0.02). High pressure reactivity index during the first 72 hours was associated with poor functional outcome (p < 0.001). No association between oxygen reactivity index and delayed cerebral ischemia or clinical outcome was observed (p = 0.8/0.78). High initial pressure reactivity index, presumably reflecting early brain injury, but not oxygen reactivity index, was associated with delayed cerebral ischemia and worse clinical outcome in poor-grade subarachnoid hemorrhage patients. Our data indicate that autoregulation indices should be interpreted cautiously when used in these patients and that timing is crucial when autoregulation indices are evaluated as predictor for delayed cerebral ischemia and outcome.

Experimental study of flame propagation across a perforated plate

Flame propagation across a single perforated plate was experimentally studied in a square cross-section channel. Experiments were performed in premixed hydrogen-air mixture with different equivalence ratios and initial pressures, aiming at identifying the parametric influence. High-speed schlieren photography and pressure records were used to capture the flame front and obtain the pressure build-up. Four stages for the flame front crossing the perforated plate were obtained, namely, laminar flame, jet flame, turbulent flame and secondary flame front. Following ignition, a laminar flame was obtained, which was nearly not affected by the confinement. This laminar flame was squeezed to pass through the perforated plate, producing the jet flame with a step change on velocity. Turbulent flame was generated by merging the jets, which facilitated the acceleration of the flame front. Secondary flame front induced by Rayleigh-Taylor instability was clearly observed in the process of the turbulent front moving forward. Both velocity and pressure are enhanced in this stage. Parametric studies suggested that the secondary flame front is more obvious in the stoichiometric mixture with higher initial pressure, and characterized by a faster propagation velocity and a bigger pressure rise.

Parametric optimization of the MVC desalination plant with thermomechanical compressor

This article deals with parametric optimization of the Mechanical Vapour Compression (MVC) desalination plant with thermomechanical compressor. In this plants thermocompressor is used instead of commonly used centrifugal compressor. Influence of two main parameters was studied. These parameters are: inlet pressure and number of stages. Analysis shows that it is possible to achieve better plant performance in comparison with traditional MVC plant. But is required reducing the number of stages and utilization of low or high initial pressure with power consumption maximum at approximately 20-30 kPa.

Potential explosion hazard of polyester resin dust formed from a granulation process: Limiting oxygen concentration with different pressures

When polyester resin (PR) is manufactured on an industrial scale, the spreading of the dust cloud is a potential explosion hazard. The maximum explosion pressure and maximum rate of pressure rise were in the range 3.6 bar < Pmax(500) < 9.8 bar and 32 < (dP dt–1)max(500) < 356 bar s–1, respectively, which is more than that of sugar dust explosion. The explosion index Kst = V1/3(dP dt–1)max was in the range 8.86 bar m s–1 <Kst(500) < 96.63 bar m s–1, which belongs to dust explosion class St-1. In addition, the results indicated that the explosion pressure can be significantly lessened with lower LOC. However, the inhibiting effect is not obvious at higher initial pressure. Therefore, the oxygen concentration must be considered as low as feasibly possible at a higher pressure to lessen the explosion hazards in production as well as handling process. Moreover, according to rough set analysis, the most significant factors for explosion intensity (Pmax) are dust concentration and initial pressure. The two parameters should be prudently controlled during the storage, transportation, and manufacturing of PR dust.

Instability of the Phase Transition Front during Water Injection into High-Temperature Rock

Water injection into a high-temperature geothermal reservoir saturated with superheated vapor is investigated. A solution to the one-dimensional problem in the form of a traveling wave is found. It is shown that there exist two types of solutions which correspond to the boiling of water and the condensation of vapor. In the condensation regime with high initial pressure, vapor ahead of the phase transition front is shown to be in a supercooled state. For moderate or law initial pressure, solutions with condensation and boiling are thermodynamically consistent. Linear stability of the phase transition surface between the water and vapor regions is analyzed. It is shown that the phase transition front moving at constant velocity is always unstable.

Visualization for compressed natural gas(CNG) secondary station refilling behaviors

Data visualizations are recently used for providing an access to complex data and information. In this paper, the visualization method is adopted to find possible ways of improving CNG secondary filling station’s refilling efficiency. Based on single attribute of volume, initial and final pressure, the visualization results show that one possible way to improve refilling efficiency is to by avoid abnormal inefficient refilling behaviors with small volume, higher initial pressure or lower final pressure. Based on time, the visualization results, considering the periodic property of refilling behaviors, present another possible way to improve refilling efficiency through reducing inefficient use of time. From the refilling log’s visualization, it is found that there is room for improvement in refilling efficiency and possible improving ways are primary studied. But the reasons of these abnormal actions are needed to be studied in future research.

Effects of in-situ stresses on the fracturing of rock by blasting

Blasting is widely applied in deep rock excavation. The effect of in-situ stresses on the fracturing of rock due to blasting was investigated. A theoretical model was used to explain the effect mechanism of in-situ stresses on crack propagation due to blasting. Four cases with different in-situ stress conditions were numerically investigated. The numerical results indicate that the crack propagation is governed by the blast load in the vicinity of the blasthole while the high in-situ stresses can influence the crack propagation in the far-field. The crack propagation trends towards the direction in which the high initial pressure is applied.

Numerical study of hydrogen–oxygen flame acceleration and deflagration to detonation transition in combustion light gas gun

A large eddy model with detailed chemical reaction mechanism is developed to investigate the interior ballistic process of the combustion light gas gun (CLGG). Flame acceleration and deflagration to detonation transition process with high initial pressure and low initial temperature hydrogen–oxygen mixture in CLGG is numerically studied. Simulation results indicate that the hydrogen–oxygen flame propagation experiences an exponential acceleration stage, a nearly uniform propagation stage and a fast reacceleration stage. Detonation can be triggered through two different mechanisms, which are the amplification between the overlapped shock wave at flame surface, and the elevated flame velocity and shock strength caused by local explosions. Reflected shock waves play an important role in the suppression of the flame propagation when the flame front is close to the chamber throat, leading to a deceleration of the deflagration flame.

Effects of Sodium Carbonate Additive on the Hydroliquefaction of a Sub-bituminous Coal with Fe-Based Catalyst under Mild Conditions

In this paper, the influence of Na2CO3 (NC) on the hydroliquefaction performances of Hongliulin (HLL) coal with an Fe-based catalyst, γ-FeOOH (FC), under mild conditions was investigated, and the properties of the resulting preasphaltene and asphaltene were examined. Results show that the addition of NC to FC-catalyzed liquefaction significantly promoted coal conversion and oil production and reduced water production under mild conditions, especially at high initial H2 pressure. The H2 consumption of mild liquefaction (0.53–1.93%) is much smaller than that of the traditional liquefaction processes, and the addition of NC to FC can enhance H2 consumption, especially the runs with weak hydrogen donor solvents. The addition order of NC and FC is an important factor which can affect the activity of FC and NC binary catalysts. There exists a prominent synergistic effect between NC and FC in HLL coal hydroliquefaction, and the synergistic effect could be ascribed to the combined promotion actions of NC for the ...

Role of hydroxyl production and heat release in the two-zone fuel-rich adiabatic dimethyl ether/air flames at atmospheric pressure

Fuel-rich laminar adiabatic flames of premixed dimethyl ether/air mixtures at a high initial temperature and atmospheric pressure have been studied by numerical simulation and sensitivity analysis. These flames, having two heat release zones, are of great interest as an unusual and little-studied subject. We have investigated the chemical processes occurring in the two zones and analysed the mechanism of heat release in the flame. It has been found that the key reactions that have a significant influence on the flame speed are those involving dimethyl ether and the products of its incomplete oxidation. Calculation of the heat release rate confirms the presence of two heat release zones in the flame. A comparison of the reactions making a major contribution to the heat release with those significantly affecting the flame speed indicates that the main factor determining the flame speed is the formation of hydroxyls, rather than heat release. Analysis of the flame speed sensitivity shows that in the case of a two-zone structure of the flame, its speed is mainly determined by the reactions taking place in the low-temperature zone. That is, the cool zone with a higher temperature gradient is the leading one.

Uso de recursos y costos de hospitalizaciones por insufi ciencia card í aca: un estudio retrospective multic é ntrico en Argentina

Heart failure has a great impact on health budget, mainly due to the cost of hospitalizations. Our aim was to describe health resource use and costs of heart failure admissions in three important institutions in Argentina. Multi-center retrospective cohort study, with descriptive and analytical analysis by subgroups of ejection fraction, blood pressure and renal function at admission. Generalized linear models were used to assess the association of independent variables to main outcomes. We included 301 subjects; age 75.3±11.8 years; 37% women; 57% with depressed ejection fraction; 46% of coronary etiology. Blood pressure at admission was 129.8±29.7 mmHg; renal function 57.9±26.2 ml/min/1.73 m2. Overall mortality was 7%. Average length of stay was 7.82±7.06 days (median 5.69), and was significantly longer in patients with renal impairment (8.9 vs. 8.18; p=0.03) and shorter in those with high initial blood pressure (6.08±4.03; p=0.009). Mean cost per patient was AR$68,861±96,066 (US$=8,071; 1US$=AR$8.532); 71% attributable to hospital stay, 20% to interventional procedures and 6.7% to diagnostic studies. Variables independently associated with higher costs were depressed ejection fraction, presence of valvular disease, and impaired renal function. Resource use and costs associated to hospitalizations for heart failure is high, and the highest proportion is attributable to the costs related to hospital stay.

Effects of high-pressure anaerobic digestion up to 30 bar on pH-value, production kinetics and specific methane yield

The production of biogas for combined heat and power generation represents a common method in Germany. An alternative is the purification of biogas to biomethane and injection into the natural gas grid to decouple gas production from usage in terms of space and time. The concept of pressurized two-stage anaerobic digestion integrates biogas production, upgrading and pressure boosting within one process. The increasing solubility of CO2 in process liquid at high pressures results in high methane contents in gaseous phase and in drop of pH. To investigate the effects of high initial pressures (10, 20, 30 bar) and dissolved CO2 on pH-value, production kinetics and specific methane yields, pressurized batch methane reactors were built up. Additionally, a method for indirect measuring of pH-value was determined. The results of the experiment showed a decrease in pH from 7 to 6.31 (10 bar) and 6.25 (30 bar). Furthermore, neither a significant influence of initial pressures on the pressure increase nor on the degradation of organics and the specific methane yields was observed. However, the results show that anaerobic digestion at high pressures up to 30 bar might be a promising alternative to post purification and pressure boosting applications.

On the detonation propagation behavior in hydrogen-oxygen mixture under the effect of spiral obstacles

Detonation propagation velocity behavior and cellular structure of stoichiometric hydrogen-oxygen mixture in spiral obstacles with four roughness (ξ = 0.133, 0.231, 0.4, 0.625) are systematically examined, at the conditions outside-, near- and within the propagation limits. The experimental results indicate that, at p0 = 10 kPa (outside the limits), spirals with roughness smaller than 0.4 facilitate the initiation of detonation, but ξ = 0.625 spiral causes the detonation quench earlier than that in smooth tube without spiral, and suggests it has prohibiting effect on the detonation propagation. At p0 = 12 kPa (near the detonation limits), spirals with ξ = 0.133 and 0.231 extend the detonation limits and therefore they have the facilitating effect on the detonation propagation, but this positive effect is not obvious in the spiral with larger roughness (i.e., ξ = 0.4 and 0.625). As the initial pressure is higher than 15 kPa, under such condition detonations are well within the limits, the dual effects of promoting and prohibiting of the spiral on the detonation propagation are more obvious, which are confirmed by the cellular structures obtained from smoked foil. The ZND induction zone length (ΔI) analysis confirms ΔI is shorter at higher initial pressure, under this condition detonation is more sensitive and easier to survive from failure as it enters into the spiral section.

A comprehensive study of light hydrocarbon mechanisms performance in predicting methane/hydrogen/air laminar burning velocities

In order to obtain the precise predicted values of methane/hydrogen/air burning velocities from simulations, the performances of GRI mech 3.0, Aramco mech 1.3, USC mech 2.0 and San diego mech mechanisms were systematically studied under various conditions by PREMIX code and compared with experimental data from literature. The conditions where each mechanism gave their good performance are obtained and concluded. The flowrate sensitivity and rate constants of key elementary reactions were analyzed to insight the different behavior of each mechanism. The results showed that all these widely used small hydrocarbon mechanisms could gave reasonable predictions for pure methane and methane hydrogen blends. Nevertheless, they lack sensitivity for rich hydrogen at elevated pressures due to their complex reactions competitions controlled by hydrogen sub model. USC mech 2.0 was found more suitable for being used at low hydrogen contents while San diego mech gained better results at high hydrogen contents. GRI 3.0 gave good predictions for methane hydrogen blends except for high initial pressures. Generally, Aramco mech 1.3 showed the best performance for all testing conditions. Moreover, there was relatively large deviation from the predicted results and experimental data in the transition regime where the hydrogen fractions were between 60% and 80%, it may could be optimized by tuning the rate constants of reactions.

Effects of pore pressure in pyroclastic flows: Numerical simulation and experimental validation

AbstractPyroclastic flows are mixtures of volcanic gases and particles that can be very hazardous owing to their fluid‐like behavior. One possible mechanism to explain this behavior is the reduction of particles friction due to the internal gas pore pressure. To verify this hypothesis, we present a numerical model of a granular flow with high initial pore pressure that decreases with time as the gas‐particle mixture propagates. First, we validate the model by reproducing laboratory experiments. Then, the numerical code is applied to pyroclastic flows of Lascar volcano (1993 eruption, Chile). The simulation reproduces the runout and the morphological features of the deposits, with lateral levées, a central channel, and a lobate front. Our results support the hypothesis of the role of gas pore pressure in pyroclastic flows and explain both the fluid‐like behavior of the flows and the formation of lateral levees.

Maximum transient pressures in a rapidly filling pipeline with entrapped air using a CFD model

ABSTRACTThe aim of this research is to assess the maximum transient pressures in a rapidly filling water pipeline containing entrapped air. A three-dimensional computational fluid dynamics model is used to simulate the rapid filling process and to describe the maximum transient pressures for a given range of initial conditions (i.e. air pocket size and initial pressure differences). Results are compared with experimental data. The air pocket size that leads to the highest maximum pressure (critical air pocket size) has been obtained for each initial pressure difference. Two types of behaviours have been identified at the maximum compression of the air pocket: air compression preserving a clear air–water interface and total air compression with the collapse of the air–water interface. The former typically occurs for small air pockets combined with low initial pressure differences, whereas the latter occurs for large air pocket sizes with high initial pressure differences.

Precipitation of curcumin by pressure reduction of CO2-expanded acetone

In this work, a technique of precipitation by pressure reduction of gas-expanded liquids (PPRGEL) has been utilized to precipitate ultra-fine particles of curcumin. Curcumin is a natural and pharmaceutically viable compound found in Indian spice, turmeric and possesses several medicinal properties. However, it suffers from low bioavailability due to its poor solubility in aqueous medium. Precipitation of ultrafine particles of such compounds improves their bioavailability due to increase in surface area and hence the dissolution rates. The PPRGEL process precipitates ultra-fine particles by generating large, rapid and uniform supersaturation in the solution produced by a sudden and large reduction (40–70K) in the solution temperature in a very short time (as low as 1min). In this work it was found that the particle size, size distribution and polymorphic behaviour of precipitated curcumin particles depends on initial CO2 pressure as well as on the additives used. Curcumin particles mostly precipitated in monoclinic form. However, curcumin particles precipitated at 40bar and with additives such as Tween 80 and PF68 were found to precipitate as a mixture of orthorhombic and monoclinic forms. Dissolution studies show that the precipitated curcumin particles dissolve faster than raw curcumin. Further, a mathematical model was used to estimate supersaturation, nucleation rates, growth rates and average sizes of particles precipitated by PPRGEL. Comparison of experimental particle sizes with the predicted particle sizes suggests that at lower initial pressures, heterogeneous nucleation mechanism dominates the particle formation process and at higher initial pressures, homogeneous nucleation mechanism seems to dominate the particle formation process.