scholarly journals Computational Study of Premixed Flame Propagation in Micro-Channels with Nonslip Walls: Effect of Wall Temperature

Fluids ◽  
2021 ◽  
Vol 6 (1) ◽  
pp. 36
Author(s):  
Orlando J. Ugarte ◽  
V’yacheslav Akkerman
Keyword(s):  
Flame Propagation ◽  
Computational Study ◽  
Reacting Flow ◽  
Narrow Channels ◽  
Flow Equations ◽  
Flame Acceleration ◽  
Flame Dynamics ◽  
Micro Channels ◽  
Fuel Mixtures ◽  
The Impact

This investigation evaluates the propagation of premixed flames in narrow channels with isothermal walls. The study is based on the numerical solution of the set of fully-compressible, reacting flow equations that includes viscosity, diffusion, thermal conduction and Arrhenius chemical kinetics. Specifically, channels and pipes with one extreme open and one extreme closed are considered such that a flame is sparked at the closed extreme and propagates towards the open one. The isothermal channel walls are kept at multiple constant temperatures in the range from Tw=300 K to 1200 K. The impact of these isothermal walls on the flame dynamics is studied for multiple radii of the channel (R) and for various thermal expansion ratios (Θ), which approximate the thermal behavior of different fuel mixtures in the system. The flame dynamics in isothermal channels is also compared to that with adiabatic walls, which were previously found to produce exponential flame acceleration at the initial stage of the burning process. The results show that the heat losses at the walls prevent strong acceleration and lead to much slower flame propagation in isothermal channels as compared to adiabatic ones. Four distinctive regimes of premixed burning in isothermal channels have been identified in the Θ−Tw−R space: (i) flame extinction; (ii) linear flame acceleration; (iii) steady or near-steady flame propagation; and (iv) flame oscillations. The physical processes in each of these regimes are discussed, and the corresponding regime diagrams are presented.

scholarly journals Acceleration of Premixed Flames in Obstructed Pipes with Both Extremes Open

Energies ◽  
2020 ◽  
Vol 13 (16) ◽  
pp. 4094
Author(s):  
Abdulafeez Adebiyi ◽  
Olatunde Abidakun ◽  
V’yacheslav Akkerman
Keyword(s):  
Flame Propagation ◽  
Premixed Flame ◽  
Critical Parameters ◽  
Reacting Flow ◽  
Computational Simulations ◽  
Chemical Parameters ◽  
Flow Equations ◽  
Flame Acceleration ◽  
Logistic Regression Algorithm ◽  
Steady Propagation

Premixed flame propagation in obstructed channels with both extremes open is studied by means of computational simulations of the reacting flow equations with a fully-compressible hydrodynamics, transport properties (heat conduction, diffusion and viscosity) and an Arrhenius chemical kinetics. The aim of this paper is to distinguish and scrutinize various regimes of flame propagation in this configuration depending on the geometrical and thermal-chemical parameters. The parametric study includes various channel widths, blockage ratios, and thermal expansion ratios. It is found that the interplay of these three critical parameters determines a regime of flame propagation. Specifically, either a flame propagates quasi-steady, without acceleration, or it experiences three consecutive distinctive phases (quasi-steady propagation, acceleration and saturation). This study is mainly focused on the flame acceleration regime. The accelerating phase is exponential in nature, which correlates well with the theoretical prediction from the literature. The accelerating trend also qualitatively resembles that from semi-open channels, but acceleration is substantially weaker when both extremes are open. Likewise, the identified regime of quasi-steady propagation fits the regime of flame oscillations, found for the low Reynolds number flames. In addition, the machine learning logistic regression algorithm is employed to characterize and differentiate the parametric domains of accelerating and non-accelerating flames.

Understanding the Effect of Capacitive Discharge Ignition on Plasma Formation and Flame Propagation of Air–Propane Mixture

2019 ◽  
Vol 141 (8) ◽  
Author(s):  
Kwonse Kim ◽  
Omid Askari
Keyword(s):  
Experimental Study ◽  
Flame Propagation ◽  
Computational Study ◽  
Plasma Formation ◽  
Operating Conditions ◽  
Propagation Time ◽  
Capacitive Discharge ◽  
Spark Plug ◽  
Discharge Ignition ◽  
The Impact

This work is an experimental and computational study to investigate the effect of capacitive discharge ignition (CDI) on plasma kernel formation and flame propagation of air–propane mixture. This paper is mainly focused on the plasma formation and flame propagation characteristics, pressure rise, propagation time, velocity field, and species concentrations. A conventional ignition system is used for comparison purpose. A constant volume combustion chamber with volume of 400 cm3 is designed for experimental study. This chamber is utilized to visualize the plasma formation as well as the flame propagation induced from two ignition sources. The experiments are performed in a wide range of operating conditions, i.e., initial pressure of 2–4 bar, temperature of 300 K, chamber wall temperature of 350 K, spark plug gaps of 1.0–1.5 mm, discharge duration of 1 ms, discharge energy of 500 mJ, and equivalence ratio of 0.5–1.0. The computational study is performed by ANSYS fluent using the partially premixed combustion (PPC) model having the same conditions as experimental study. It is shown that the average peak pressure in CDI increased by 5.79%, 4.84% and 4.36% at initial pressures of 2, 3, and 4 bar, respectively, comparing with conventional ignition. It could be determined that the impact of combustion pressure in CDI system is more significant than conventional ignition particularly in lean mixtures. Consequently, the flame propagation rate in CDI system, due to the large ionized kernel around the spark plug, can be significantly enhanced.

scholarly journals Analysis of Gaseous and Gaseous-Dusty, Premixed Flame Propagation in Obstructed Passages with Tightly Placed Obstacles

Fluids ◽  
2020 ◽  
Vol 5 (3) ◽  
pp. 115
Author(s):  
Furkan Kodakoglu ◽  
Sinan Demir ◽  
Damir Valiev ◽  
V’yacheslav Akkerman
Keyword(s):  
Flame Propagation ◽  
Premixed Flame ◽  
Dust Particles ◽  
Blockage Ratio ◽  
Two Dimensional ◽  
Analytical Formulation ◽  
Flame Acceleration ◽  
Explosive Materials ◽  
Run Up ◽  
The Impact

A recent predictive scenario of premixed flame propagation in unobstructed passages is extended to account for obstructions that can be encountered in facilities dealing with explosive materials such as in coalmines. Specifically, the theory of globally-spherical, self-accelerating premixed expanding flames and that of flame acceleration in obstructed conduits are combined to form a new analytical formulation. The coalmining configuration is imitated by two-dimensional and cylindrical passages of high aspect ratio, with a comb-shaped array of tightly placed obstacles attached to the walls. It is assumed that the spacing between the obstacles is much less or, at least, does not exceed the obstacle height. The passage has one extreme open end such that a flame is ignited at a closed end and propagates to an exit. The key stages of the flame evolution such as the velocity of the flame front and the run-up distance are scrutinized for variety of the flame and mining parameters. Starting with gaseous methane-air and propane-air flames, the analysis is subsequently extended to gaseous-dusty environments. Specifically, the coal (combustible, i.e., facilitating the fire) and inert (such as sand, moderating the process) dust and their combinations are considered, and the impact of the size and concentration of the dust particles on flame acceleration is quantified. Overall, the influence of both the obstacles and the combustion instability on the fire scenario is substantial, and it gets stronger with the blockage ratio.

scholarly journals Impact of Radiative Losses on Flame Acceleration and Deflagration to Detonation Transition of Lean Hydrogen-Air Mixtures in a Macro-Channel with Obstacles

Fluids ◽  
2018 ◽  
Vol 3 (4) ◽  
pp. 104 ◽  
Author(s):  
Gautham Krishnamoorthy ◽  
Lucky Mulenga
Keyword(s):  
Combustion Wave ◽  
Computational Cost ◽  
Scaling Analysis ◽  
Small Surface ◽  
Flame Acceleration ◽  
System Pressure ◽  
Micro Channels ◽  
Radiative Losses ◽  
Run Up ◽  
The Impact

While there has been some recognition regarding the impact of thermal boundary conditions (adiabatic versus isothermal) on premixed flame propagation mechanisms in micro-channels (hydraulic diameters <10 mm), their impact in macro-channels has often been overlooked due to small surface-area-to-volume ratios of the propagating combustion wave. Further, the impact of radiative losses has also been neglected due to its anticipated insignificance based on scaling analysis and the high computational cost associated with resolving it’s spatial, temporal, directional, and wavelength dependencies. However, when channel conditions promote flame acceleration and deflagration-to-detonation transitions (DDT), large pressures are encountered in the vicinity of the combustion wave, thereby increasing the magnitude of radiative losses which in turn can impact the strength and velocity of the combustion wave. This is demonstrated for the first time through simulations of lean (equivalence ratio: 0.5) hydrogen-air mixtures in a macro-channel (hydraulic diameter: 174 mm) with obstacles (Blockage ratio: 0.51). By employing Planck mean absorption coefficients in conjunction with the P-1 radiation model, radiative losses are shown to affect the run-up distances to DDT in a long channel (length: 11.878 m). As anticipated, the differences in run-up distances resulting from radiative losses only increased with system pressure.

scholarly journals Effect of added struts and intake velocity on flame stabilization in supersonic combustors

2021 ◽  
Vol 9 (1) ◽  
Author(s):  
Akram Mohammad ◽  
Keyword(s):  
Mole Fraction ◽  
Computational Study ◽  
Combustion Process ◽  
Combustion Efficiency ◽  
Single Step ◽  
Flame Stabilization ◽  
Reacting Flow ◽  
Mach Numbers ◽  
German Aerospace ◽  
The Impact

In the present computational study, the impact of strut positions and the effect of inlet Mach numbers on the combustion efficiency are investigated in a strut-based supersonic combustor. An experimentally investigated model combustor developed at the German Aerospace Center (DLR) is simulated and validated. Then, a model combustor with three struts placed at different positions is investigated. Two-dimensional, compressible, reacting-flow governing equations are solved along with single-step chemistry reaction and k-ω SST turbulence model using a commercial CFD code FLUENT. The oblique shock from the struts has a profound influence on the mixing and combustion process. The H2O mole fraction, H2 mole fraction contours, and combustion efficiency of various configurations are compared for finding better mixing and flame stabilization. The combustion efficiency reduces when the two struts are located in farther downstream or placed at the same downstream location. At higher Mach numbers, the combustion is delayed, and the mixing of fuel with the supersonic mainstream is incomplete.

scholarly journals The Prisoners’ Dilemma in collaborative carriers’ request selection

2021 ◽  
Vol 29 (1) ◽  
pp. 73-87 ◽  
Author(s):  
Margaretha Gansterer ◽  
Richard F. Hartl
Keyword(s):  
Computational Study ◽  
Logistics Industry ◽  
Individual Outcomes ◽  
Selection Strategies ◽  
Prisoners Dilemma ◽  
Trading Mechanisms ◽  
And Behavior ◽  
The Impact ◽  
Idle Capacity

AbstractLogistics providers have to utilize available capacities efficiently in order to cope with increasing competition and desired quality of service. One possibility to reduce idle capacity is to build coalitions with other players on the market. While the willingness to enter such coalitions does exist in the logistics industry, the success of collaborations strongly depends on mutual trust and behavior of participants. Hence, a proper mechanism design, where carriers do not have incentives to deviate from jointly established rules, is needed. We propose to use a combinatorial auction system, for which several properties are already well researched but little is known about the auction’s first phase, where carriers have to decide on the set of requests offered to the auction. Profitable selection strategies, aiming at maximization of total collaboration gains, do exist. However, the impact on individual outcomes, if one or more players deviate from jointly agreed selection rules is yet to be researched. We analyze whether participants in an auction-based transport collaboration face a Prisoners’ Dilemma. While it is possible to construct such a setting, our computational study reveals that carriers do not profit from declining the cooperative strategy. This is an important and insightful finding, since it further strengthens the practical applicability of auction-based trading mechanisms in collaborative transportation.

The impact of replenishment parameters and information sharing on the bullwhip effect: A computational study

2008 ◽  
Vol 35 (11) ◽  
pp. 3657-3670 ◽  
Author(s):  
Thomas Kelepouris ◽  
Panayiotis Miliotis ◽  
Katerina Pramatari
Keyword(s):  
Information Sharing ◽  
Computational Study ◽  
Bullwhip Effect ◽  
The Impact

Effect of Inlet Configuration on Moderator Velocity and Temperature Distribution Inside the Calandria of a Heavy Water Reactor

2008 ◽  
Author(s):  
Abhijeet Mohan Vaidya ◽  
Naresh Kumar Maheshwari ◽  
Pallippattu Krishnan Vijayan ◽  
Dilip Saha ◽  
Ratan Kumar Sinha
Keyword(s):  
Temperature Distribution ◽  
Impact Velocity ◽  
Heavy Water ◽  
Computational Study ◽  
Water Reactor ◽  
Heavy Water Reactor ◽  
The Impact

Computational study of the moderator flow in calandria vessel of a heavy water reactor is carried out for three different inlet nozzle configurations. For the computations, PHOENICS CFD code is used. The flow and temperature distribution for all the configurations are determined. The impact of moderator inlet jets on adjacent calandria tubes is studied. Based on these studies, it is found that the inlet nozzles can be designed in such a way that it can keep the impact velocity on calandria tubes within limit while keeping maximum moderator temperature well below its boiling limit.

Nonlinear mixed convective Williamson nanofluid flow with the suspension of gyrotactic microorganisms

2021 ◽  
pp. 2150145
Author(s):  
Shuang-Shuang Zhou ◽  
M. Ijaz Khan ◽  
Sumaira Qayyum ◽  
B. C. Prasannakumara ◽  
R. Naveen Kumar ◽  
...  
Keyword(s):  
Heat Source ◽  
Lewis Number ◽  
Solution Procedure ◽  
Energy Concentration ◽  
Gyrotactic Microorganisms ◽  
Dimensionless Parameters ◽  
Flow Equations ◽  
Fluid Parameter ◽  
Source Sink ◽  
The Impact

This investigation aims to present the thermally developed bioconvection flow of Williamson nanoliquid over an inclined stretching cylinder in presence of linear mixed convection and nonuniform heat source/sink. The activation energy and suspension of gyrotactic microorganisms are accounted with applications of bioconvection phenomenon. Appropriate nondimensional variables are opted to attain the dimensionless form of flow equations. The resulting momentum, energy, concentration and motile density equations are abridged to highly coupled and nonlinear in nature. The numerical treatment is followed for the solution procedure by employing the shooting method. The influence of some relevant dimensionless parameters is discoursed graphically along with physical justifications. Moreover, the impact of several dimensionless parameters on skin friction and Nusselt number is obtained and listed in tables. It is observed that the velocity of fluid shows a decreasing variation for Williamson fluid parameter. The change in unsteadiness parameter and heat source parameter enhanced the nanofluid temperature. The motile microorganisms profile declines with bioconvection constant and bio-convection Lewis number.

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