Effects of Molecular Diffusion on the Combustion of Ethylene in Axisymmetric Cavity Flame Holder Scramjet Engines

2020 ◽  
Author(s):  
◽  
Flynn Hack
Keyword(s):  
Molecular Diffusion ◽  
Axisymmetric Cavity ◽  
Flame Holder ◽  
Scramjet Engines

Overview of Fuel Injection Techniques for Scramjet Engines

2011 ◽  
Author(s):  
Wei Huang ◽  
Zhen-guo Wang ◽  
Shi-bin Luo ◽  
Jun Liu ◽  
Zhi-xun Xia ◽  
...  
Keyword(s):  
Fuel Injection ◽  
Mixing Efficiency ◽  
Injection Technique ◽  
Ongoing Research ◽  
Hypersonic Propulsion ◽  
Flame Holder ◽  
Flow Field Characteristics ◽  
Injection Techniques ◽  
Scramjet Engine ◽  
Scramjet Engines

As one of the most promising hypersonic propulsion systems for hypersonic vehicles, the scramjet engine has drawn an ever increasing attention of researchers worldwide. At present, one of the most important issues to be dealt with is how to improve the fuel penetration and mixing efficiency and make the flame stable in supersonic flows. Further, how to reduce the structural weight of the engines is an urgent issue that needs to be considered. The ongoing research efforts on fuel injection techniques in the scramjet engine are described, mainly the cavity flame holder, the backward facing step, the strut injection and the cantilevered ramp injection, and the flow field characteristics and research efforts related to these fuel injection techniques are summarized and compared. Finally, a promising fuel injection technique is discussed, namely a combination of different injection techniques, and the combination of the cantilevered ramp injector and the cavity flame holder is proposed. This is because it can not only stabilize the flame, but also shorten the length of the combustor, thus lighten the weight of the scramjet engines.

The Spread of Pollutants from Harbour Sludge Depots

1984 ◽  
Vol 16 (3-4) ◽  
pp. 623-633
Author(s):  
M Loxham ◽  
F Weststrate
Keyword(s):  
Time Scales ◽  
Molecular Diffusion ◽  
Near Field ◽  
Parameter Analysis ◽  
Migration Patterns ◽  
Long Time ◽  
Dilution Effects ◽  
Short Time ◽  
Harbour Sludge

It is generally agreed that both the landfill option, or the civil techniques option for the final disposal of contaminated harbour sludge involves the isolation of the sludge from the environment. For short time scales, engineered barriers such as a bentonite screen, plastic sheets, pumping strategies etc. can be used. However for long time scales the effectiveness of such measures cannot be counted upon. It is thus necessary to be able to predict the long term environmenttal spread of contaminants from a mature landfill. A model is presented that considers diffusion and adsorption in the landfill site and convection and adsorption in the underlaying aquifer. From a parameter analysis starting form practical values it is shown that the adsorption behaviour and the molecular diffusion coefficient of the sludge, are the key parameters involved in the near field. The dilution effects of the far field migration patterns are also illustrated.

Qxygen transfer in gravity flow sewers

2000 ◽  
Vol 42 (3-4) ◽  
pp. 417-422 ◽  
Author(s):  
T.Y. Pai ◽  
C.F. Ouyang ◽  
Y.C. Liao ◽  
H.G. Leu
Keyword(s):  
Differential Equation ◽  
Partial Differential Equation ◽  
Dissolved Oxygen ◽  
Flow Velocity ◽  
Molecular Diffusion ◽  
Eddy Diffusion ◽  
Partial Differential ◽  
Diffusion Term ◽  
Sewer Pipes ◽  
Gravity Sewer

Oxygen diffused to water in gravity sewer pipes was studied in a 21 m long, 0.15 m diameter model sewer. At first, the sodium sulfide was added into the clean water to deoxygenate, then the pump was started to recirculate the water and the deoxygenated water was reaerated. The dissolved oxygen microelectrode was installed to measure the dissolved oxygen concentrations varied with flow velocity, time and depth. The dissolved oxygen concentration profiles were constructed and observed. The partial differential equation diffusion model that considered Fick's law including the molecular diffusion term and eddy diffusion term were derived. The analytic solution of the partial differential equation was used to determine the diffusivities by the method of nonlinear regression. The diffusivity values for the oxygen transfer was found to be a function of molecular diffusion, eddy diffusion and flow velocity.

Enhancement of catalytic esterification by tuning molecular diffusion in sulfonated carbon

2021 ◽  
Vol 318 ◽  
pp. 111024
Author(s):  
Lili Huang ◽  
Caicheng Song ◽  
Yingcen Liu ◽  
Hua Lin ◽  
Wanyue Ye ◽  
...  
Keyword(s):  
Molecular Diffusion

scholarly journals Molecular Dynamics Simulation on the Interaction between Palygorskite Coating and Linear Chain Alkane Base Lubricant

Coatings ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 286
Author(s):  
Jin Zhang ◽  
Lv Yang ◽  
Yue Wang ◽  
Huaichao Wu ◽  
Jiabin Cai ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Structural Changes ◽  
Molecular Diffusion ◽  
Linear Chain ◽  
Interfacial Interaction ◽  
Dynamics Simulation ◽  
Electrostatic Energy ◽  
Experimental Development ◽  
Practical Applications ◽  
Self Diffusion

Molecular dynamics (MD) simulations were conducted to investigate the interactions between a palygorskite coating and linear chain alkanes (dodecane C12, tetradecane C14, hexadecane C16, and octadecane C18), representing base oils in this study. The simulation models were built by placing the alkane molecules on the surface of the palygorskite coating. These systems were annealed and geometrically optimized to obtain the corresponding stable configurations, followed by the analysis of the structural changes occurring during the MD process. The interfacial interaction energies, mean square displacements, and self-diffusion coefficients of the systems were evaluated to characterize the interactions between base lubricant molecules and palygorskite coating. It was found that the alkanes exhibited self-arrangement ability after equilibrium. The interfacial interaction was attractive, and the electrostatic energy was the main component of the binding energy. The chain length of the linear alkanes had a significant impact on the intensity of the interfacial interactions and the molecular diffusion behavior. Moreover, the C12 molecule exhibited higher self-diffusion coefficient values than C14, C16 and C18. Therefore, it could be the best candidate to form an orderliness and stable lubricant film on the surface of the palygorskite coating. The present work provides new insight into the optimization of the structure and composition of coatings and lubricants, which will guide the experimental development of these systems for practical applications.

Evaluation of the mixing quality of high-viscosity yield stress fluids in a tubular reactor

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Le Xie ◽  
Guangwen He ◽  
Bin Yu ◽  
Shaowei Yan
Keyword(s):  
Yield Stress ◽  
Large Scale ◽  
Molecular Diffusion ◽  
Time History ◽  
High Viscosity ◽  
Cfd Model ◽  
Step Method ◽  
Mean Velocity ◽  
Mixing Quality

Abstract In this study, the mixing quality of high-viscosity yield stress fluid (Carbopol aqueous solution) under laminar and turbulent flow regimes was evaluated through a numerical experimental study. A three-dimensional computational fluid dynamics large-eddy simulation (CFD-LES) model was employed to capture large-scale vortex structures. The proposed CFD model was validated by the experimental data in terms of mean velocity profiles and velocity-time history. Thereafter, the CFD model was applied to simulate the residence time distribution using the tracking technique: tracer pulse method and step method. In addition, the non-ideal flow phenomena caused by molecular diffusion and eddy diffusion were evaluated. The effects of the rheological properties on the mixing performance were also investigated. The presented results can provide useful guidance to enhance mass transfer in reactors with high-viscosity fluids.

scholarly journals Gated Molecular Diffusion at Liquid‐Liquid Interfaces

2021 ◽  
Author(s):  
Lianshun Li ◽  
Huilou Sun ◽  
Mingwei Li ◽  
Yang Yang ◽  
Thomas P. Russell ◽  
...  
Keyword(s):  
Molecular Diffusion ◽  
Liquid Interfaces
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