Ignition delay times of dimethyl ether (DME) and propane blends were measured in a shock tube at varied DME blending ratios (0%, 20%, 50%, 80%, 100%), equivalence ratios (0.5, 1.0, 2.0), temperatures (1100-1500 K) and...
详细信息
Ignition delay times of dimethyl ether (DME) and propane blends were measured in a shock tube at varied DME blending ratios (0%, 20%, 50%, 80%, 100%), equivalence ratios (0.5, 1.0, 2.0), temperatures (1100-1500 K) and pressures of 20 atm. Mechanism validations were conducted using different chemical kinetic models. A new C5 chemical model with DME sub-model was developed and it can well predict experimental ignition delay times of pure propane, DME and their blends. Experimental and numerical results show that with the decrease of temperature, the ignition delay times increase and the activation energy decreases slightly. With the increase of equivalence ratio, ignition delay times increase for propane and decrease for DME in this study. Ignition delay times decrease with the increase of DME blending ratio and the decrease rates become larger with the increase of equivalence ratio. The peak values of H and OH mole fraction increase with increasing the DME blending ratio, and they promote the ignition of DME/propane blends. Sensitivity analysis shows that the reaction rates of R1 and R353 increase with the increase of DME blending ratio and induces the decrease of the ignition delay time of DME/propane blends.
A novel braking material,C/C-ZrB_(2)-ZrC-SiC carbon fibre-reinforced hybrid ceramic matrix composite,was prepared by chemical vapour infiltration and polymeric precursor infiltration and *** of the microstructure of C...
详细信息
A novel braking material,C/C-ZrB_(2)-ZrC-SiC carbon fibre-reinforced hybrid ceramic matrix composite,was prepared by chemical vapour infiltration and polymeric precursor infiltration and *** of the microstructure of C/C-ZrB_(2)-ZrC-SiC composite showed the homogenous dispersion of three-phase ceramic as the *** frictional properties of the hybrid C/C-ZrB_(2)-ZrC-SiC ceramic matrix composite were measured by a disk-on-disk type dynamometer under dry and wet conditions to simulate the normal landing state of aircraft brake disk friction pairs.C/C-ZrB_(2)-ZrC-SiC ceramic matrix composite has a higher and more stable friction coefficient under wet condition than under dry condition,indicating that the composite has better performance compared with C/C or C/C-SiC braking materials.
Ignition delays of stoichiometric syngas mixtures (H2/CO/O 2) diluted with argon were measured behind the reflected shock wave at pressures of 0.2, 1.0 and 2.0 MPa, temperature from 896 to 1264 K, equivalence ratios o...
详细信息
Ignition delays of stoichiometric syngas mixtures (H2/CO/O 2) diluted with argon were measured behind the reflected shock wave at pressures of 0.2, 1.0 and 2.0 MPa, temperature from 896 to 1264 K, equivalence ratios of 0.3, 1.0 and 1.5. The effect of non-ideal conditions on ignition delays, determined by pressure trace behind the reflected shock wave (pressure rise rate is approximately 4.22%/ms), was used to calculate. Six available mechanisms were selected to simulate the ignition delays of syngas mixtures, the predicted results were compared with the measured ones. These results indicated that there is no mechanism can calculate accurately ignition delays over all testing conditions. The ignition delays predicted with three mechanisms (Davis 2005, USC ver 2.0, NUI nc5-49) are close to the measured ones. Using the Davis mechanism to analyse reaction kinetics, the achieved results showed that the reaction R1 dominates the ignition process of syngas. The reaction R31 plays an important promoted role in ignition process of syngas mixtures.
The structures of two laminar premixed n-heptane/O2/Ar flames (F1.60: F = 1.60, C/O = 0.51, and F1.80: F = 1.80, C/O = 0.57) and one laminar premixed n-heptane/methanol/O2/Ar flame (F1.80 M: F = 1.80, C/O = 0.51) are ...
详细信息
An Eulerian-Lagrangian numerical simulation is performed to study aeolian sand transport in a wind tunnel. The evolutions of three parameters, sand mass flux, decay rate of sand mass flux profile and sand particle mea...
An Eulerian-Lagrangian numerical simulation is performed to study aeolian sand transport in a wind tunnel. The evolutions of three parameters, sand mass flux, decay rate of sand mass flux profile and sand particle mean horizontal velocity with time, are investigated. The results show that: Sand mass flux takes more time to reach the saturated state than the last two parameters. First, we prove the evolution with time in the simulation is similar to the evolution in the length direction in a wind tunnel and then the experimental data from unsaturated wind tunnel can be used in the quantitative comparison with simulated saturated results. Second, detailed comparison is carried out. The tendency of sand mass flux is consistent with the experimental data. Decay rate of sand mass flux profile and sand particle mean horizontal velocity fit the experimental data well especially for cases of small free stream wind velocity, and the deviation is getting larger with the increasing of free stream wind velocity.
Severe slugging, which could induce large-amplitude pressure and flow rate fluctuations, is a major and expensive problem in multiphase transportation systems of offshore oil production system. To avoid such problem i...
Severe slugging, which could induce large-amplitude pressure and flow rate fluctuations, is a major and expensive problem in multiphase transportation systems of offshore oil production system. To avoid such problem is a basic requirement for flow assurance management. This study is an experimental and numerical investigation of severe slugging in a relatively long pipeline-riser system. A series of experiments on two-phase, air-water flow in a flexible Sshaped riser were carried out. The experimental system has a 114m long horizontal pipeline connected to a 19m long pipe which is inclined to −2degree from horizontal, followed by a 15.3m high riser operating at atmospheric end pressure. Four types of flow patterns were found and characterized by the pressure fluctuations at the bottom of the riser. A flow patter map for the prediction of severe slugging was developed based on the experimental results. The detailed characteristics of severe slugging such as pressure fluctuations, liquid holdup, under different gas-liquid superficial velocities were provided. A transient model to predict the flow behavior in the pipeline-S-shaped riser system was developed based on an existing model (OLGA). The modified model, which was tested against new experimental results obtained in this study, showed that the four types of flow patterns observed in the experiment were predicted with acceptable discrepancies. The flow pattern map was obtained using present model, as well as the detailed characteristics of severe slugging. In addition, the reasons for the difference between experimental and numerical results were analysed in this article. The motive of the numerical studies was to identify the areas that could not be reproduced by the present model and to give some suggestions for future models.
The signals monitoring petroleum transmission pipeline in offshore oil industry usually contain abundant information about the multiphaseflow on flow assurance which includes the avoidance of most undesirable flow pa...
The signals monitoring petroleum transmission pipeline in offshore oil industry usually contain abundant information about the multiphaseflow on flow assurance which includes the avoidance of most undesirable flow pattern. Therefore, extracting reliable features form these signals to analyze is an alternative way to examine the potential risks to oil platform. This paper is focused on characterizing multiphaseflow patterns in pipeline-riser system that is often appeared in offshore oil industry and finding an objective criterion to describe the transition of flow patterns. Statistical analysis on pressure signal at the riser top is proposed, instead of normal prediction method based on inlet and outlet flow conditions which could not be easily determined during most situations. Besides, machine learning method (least square supported vector machine) is also performed to classify automatically the different flow patterns. The experiment results from a small-scale loop show that the proposed method is effective for analyzing the multiphaseflow pattern.
Cerebral aneurysm, a local enlargement of an artery caused by weakness in the wall of a cerebral artery, has the high death rate and disability rate, and is a threat to public health. The forming mechanism of aneurysm...
Cerebral aneurysm, a local enlargement of an artery caused by weakness in the wall of a cerebral artery, has the high death rate and disability rate, and is a threat to public health. The forming mechanism of aneurysm is complex, which motivated many researchers to conduct studies in this field. The results indicated that increasing heart frequency can aggravate the oscillation of wall shear stress, and push The growth points of aneurysm along the aneurysm wall, thereby significantly affecting bthe growth and rupture mechanism of aneurysm. In addition, it is found that the curvature of the vessel is the key to induce the secondary vortex in the aneurysm; the secondary vortex increases the magnitude of WSS near the dome of aneurysm, which can cause the rupture of aneurysm dome. there is a linear relationship between the velocity of blood flow and the square root of hear frequency.
The objective of the present work is to investigate the air-water two-phase flow patterns in pipeline-riser system with an S-shaped flexible riser. The test loop with 50 mm ID consists of a horizontal pipeline with 11...
The objective of the present work is to investigate the air-water two-phase flow patterns in pipeline-riser system with an S-shaped flexible riser. The test loop with 50 mm ID consists of a horizontal pipeline with 114 m in length, a downward inclined section with 16 m in length, and an S-shaped flexible riser with 24 m in height when downward section inclined at −2° with respective to the horizontal. The inclination angle of the downward section varied from −2° to −5°. The liquid superficial velocity ranged from 0.03 to 1.5 m/s, and the gas superficial velocity from 0.4 to 6.0 m/s. Identification and characterization of flow regimes were attained by pressure at riser-base and liquid holdup at riser top. Severe slugging I, severe slugging II, transition flow and stable flows are observed to exist. flow pattern maps for each declination are presented and the transition criteria are proposed. It's found that as higher liquid and gas velocity is required for the transition of the flow in the pipeline from stratified to intermittent with increasing the declination angle, severe slugging was observed to occur over a wilder range of flow conditions. The effect of riser geometry and separator pressure on the occurrence of the flow patterns was also examined. It shows that the S-bend tends to suppress the initiation of severe slugging.
暂无评论