Flame balls stabilized by suspension in fluid with a steady linear ambient velocity distribution

1991 ◽  
Vol 227 ◽  
pp. 407-427 ◽  
Author(s):  
J. Buckmaster ◽  
G. Joulin
Keyword(s):  
Three Dimensional ◽  
Lewis Number ◽  
Stationary Solutions ◽  
Heat Losses ◽  
Energy Losses ◽  
Spherically Symmetric ◽  
Relative Impact ◽  
Central Question ◽  
Stable Solutions ◽  
Combustion Equations

The ignition of lean H2/air mixtures under microgravity (μg) conditions can lead to the formation of spherical premixed flames (flame balls) with small Péclet number (Pe). A central question concerning these structures is the existence of appropriate stationary stable solutions of the combustion equations. In this paper we examine an individual flame ball that is suspended in a fluid whose velocity far from the flame is steady and varies linearly in space. Detailed results are obtained for simple shear flows and simple straining flows, both axisymmetric and plane.Convection enhances the flux of heat from the flame and the flux of mixture to the flame, but because the Lewis number (Le) is less than unity the relative impact on the former is greater than on the latter. Consequently, there is a net loss of energy from the flame to the far field, and if large enough this will quench the flame. For values of shear or strain less than the quenching value there are two possible stationary solutions, but one of these is unstable to spherically symmetric disturbances of the flame ball. The radius of the other solution is unbounded as Pe goes to zero. Examination of a class of three-dimensional disturbances reveals no additional instability when the energy losses are due only to convection, but sufficiently large flame balls are unstable when volumetric heat losses from radiation are accounted for. This last result is in agreement with previous results that have been obtained for zero Pe, albeit with inadequate accounting for the flow field generated by the perturbations.

scholarly journals The time domain numerical method of three-dimensional conductors including radiation with lumped parameter circuit

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Souma Jinno ◽  
Shuji Kitora ◽  
Hiroshi Toki ◽  
Masayuki Abe
Keyword(s):  
Numerical Method ◽  
Time Domain ◽  
Maxwell Equations ◽  
Three Dimensional ◽  
New Formalism ◽  
Vector Potentials ◽  
Lumped Parameter ◽  
Radiation Theory ◽  
Stable Solutions ◽  
The Time Domain

AbstractWe formulate a numerical method on the transmission and radiation theory of three-dimensional conductors starting from the Maxwell equations in the time domain. We include the delay effect in the integral equations for the scalar and vector potentials rigorously, which is vital to obtain numerically stable solutions for transmission and radiation phenomena in conductors. We provide a formalism to connect the conductors to any passive lumped-parameter circuits. We show one example of numerical calculations, demonstrating that the new formalism provides stable solutions to the transmission and radiation phenomena.

Thermal Analysis of Solids at High Peclet Numbers Subjected to Moving Heat Sources

1999 ◽  
Vol 121 (1) ◽  
pp. 182-186 ◽  
Author(s):  
O. Manca ◽  
B. Morrone ◽  
S. Nardini
Keyword(s):  
Thermal Field ◽  
Three Dimensional ◽  
Heat Losses ◽  
Transfer Model ◽  
Heat Sources ◽  
Moving Heat Source ◽  
Motion Direction ◽  
Thermal Fields ◽  
Diffusion Component ◽  
Conductive Thermal Field

A three-dimensional heat transfer model has been developed to obtain the conductive thermal field inside a brick-type solid under a moving heat source with different beam profiles. The problem in quasi-steady state has been approximated by neglecting the axial diffusion component; thus, for Peclet numbers greater than 5, the elliptic differential equation becomes a parabolic one along the motion direction. The dependence of the solution on the radiative and convective heat losses has been highlighted. Thermal fields are strongly dependent on different spot shapes and on the impinging jet; this situation allows control of the parameters involved in the technological process.

scholarly journals Towards the distributed burning regime in turbulent premixed flames

2019 ◽  
Vol 871 ◽  
pp. 1-21 ◽  
Author(s):  
A. J. Aspden ◽  
M. S. Day ◽  
J. B. Bell
Keyword(s):  
Laminar Flame ◽  
Three Dimensional ◽  
Lewis Number ◽  
Reaction Rates ◽  
Turbulent Flames ◽  
Fuel Temperature ◽  
Transport Models ◽  
Eddy Viscosity Model ◽  
Order Of Magnitude ◽  
Number Species

Three-dimensional numerical simulations of canonical statistically steady, statistically planar turbulent flames have been used in an attempt to produce distributed burning in lean methane and hydrogen flames. Dilatation across the flame means that extremely large Karlovitz numbers are required; even at the extreme levels of turbulence studied (up to a Karlovitz number of 8767) distributed burning was only achieved in the hydrogen case. In this case, turbulence was found to broaden the reaction zone visually by around an order of magnitude, and thermodiffusive effects (typically present for lean hydrogen flames) were not observed. In the preheat zone, the species compositions differ considerably from those of one-dimensional flames based a number of different transport models (mixture averaged, unity Lewis number and a turbulent eddy viscosity model). The behaviour is a characteristic of turbulence dominating non-unity Lewis number species transport, and the distinct limit is again attributed to dilatation and its effect on the turbulence. Peak local reaction rates are found to be lower in the distributed case than in the lower Karlovitz cases but higher than in the laminar flame, which is attributed to effects that arise from the modified fuel-temperature distribution that results from turbulent mixing dominating low Lewis number thermodiffusive effects. Finally, approaches to achieve distributed burning at realisable conditions are discussed; factors that increase the likelihood of realising distributed burning are higher pressure, lower equivalence ratio, higher Lewis number and lower reactant temperature.

scholarly journals Time-dependent three-dimensional Oldroyd-B nanofluid flow due to bidirectional movement of surface with zero mass flux

2020 ◽  
Vol 12 (4) ◽  
pp. 168781402091378 ◽  
Author(s):  
Manzoor Ahmad ◽  
Sabir Ali Shehzad ◽  
Asif Iqbal ◽  
Muhammad Taj
Keyword(s):  
Differential System ◽  
Mass Flux ◽  
Three Dimensional ◽  
Lewis Number ◽  
Time Dependent ◽  
Zero Mass ◽  
Homotopy Analysis ◽  
Nanoparticles Concentration ◽  
Bidirectional Movement ◽  
Parameter Values

Unsteady three-dimensional flow of an incompressible Oldroyd-B nanomaterial is reported in this article. The origin of flow is time-dependent surface spreading in lateral directions transversely taking nanoparticles with zero mass flux. The formulated partial differential system is reframed by similarity variables into ordinary differential system. The obtained system is solved by the process of homotopy analysis for dimensional temperature and concentration of nanoparticles. Physical parameter behavior on temperature and concentrations of nanoparticles is examined using graph and tabular data. The surface temperature is also measured and evaluated, and it is found that the temperature is reduced for greater unsteadiness parameter values. We found that the higher [Formula: see text] enhances the curves of nanoparticle concentration and temperature while these curves retard for the incrementing values of [Formula: see text] The increasing nature of Brownian movement [Formula: see text] and Lewis number Le corresponds to lower profiles of nanoparticles concentration.

scholarly journals A three-dimensional laser interferometer gravitational-wave detector

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Mengxu Liu ◽  
Biping Gong
Keyword(s):  
Gravitational Wave ◽  
Laser Interferometer ◽  
Three Dimensional ◽  
Electromagnetic Emission ◽  
Laser Interferometry ◽  
Electromagnetic Spectrum ◽  
Spherically Symmetric ◽  
Directional Response ◽  
Wave Detector ◽  
The Universe

Abstract The gravitational wave (GW) has opened a new window to the universe beyond the electromagnetic spectrum. Since 2015, dozens of GW events have been caught by the ground-based GW detectors through laser interferometry. However, all the ground-based detectors are L-shaped Michelson interferometers, with very limited directional response to GW. Here we propose a three-dimensional (3-D) laser interferometer detector in the shape of a regular triangular pyramid, which has more spherically symmetric antenna pattern. Moreover, the new configuration corresponds to much stronger constraints on parameters of GW sources, and is capable of constructing null-streams to get rid of the signal-like noise events. A 3-D detector of kilometer scale of such kind would shed new light on  the joint search of GW and electromagnetic emission.

MHD three dimensional double diffusive flow of Casson nanofluid with buoyancy forces and nonlinear thermal radiation over a stretching surface

2017 ◽  
Vol 27 (12) ◽  
pp. 2858-2878 ◽  
Author(s):  
B.J. Gireesha ◽  
M. Archana ◽  
Prasannakumara B.C. ◽  
R.S. Reddy Gorla ◽  
Oluwole Daniel Makinde
Keyword(s):  
Thermal Radiation ◽  
Three Dimensional ◽  
Lewis Number ◽  
Nonlinear Thermal Radiation ◽  
Stretching Surface ◽  
Temperature Ratio ◽  
Content Type ◽  
Casson Nanofluid ◽  
Diffusive Flow ◽  
Double Diffusive

Purpose This paper aims to deal with the study of heat and mass transfer on double-diffusive three-dimensional hydromagnetic boundary layer flow of an electrically conducting Casson nanofluid over a stretching surface. The combined effects of nonlinear thermal radiation, magnetic field, buoyancy forces, thermophoresis and Brownian motion are taken into consideration with convective boundary conditions. Design/methodology/approach Similarity transformations are used to reduce the governing partial differential equations into a set of nonlinear ordinary differential equations. The reduced equations were numerically solved using Runge–Kutta–Fehlberg fourth-fifth-order method along with shooting technique. Findings The impact of several existing physical parameters such as Casson parameter, mixed convection parameter, regular buoyancy ratio parameter, radiation parameter, Brownian motion parameter, thermophoresis parameter, temperature ratio parameter on velocity, temperature, solutal and nanofluid concentration profiles are analyzed through graphs and tables in detail. It is found that the solutal component increases for Dufour Lewis number, whereas it decreases for nanofluid Lewis number. Moreover, velocity profiles decrease for Casson parameter, while the Nusselt number increases for Biot number, radiation and temperature ratio parameter. Originality/value This paper is a new work related to three-dimensional double-diffusive flow of Casson nanofluid with buoyancy and nonlinear thermal radiation effect.

Effects of the Heat Transfer at the Side Walls on Natural Convection in Cavities

1990 ◽  
Vol 112 (2) ◽  
pp. 370-378 ◽  
Author(s):  
Y. Le Peutrec ◽  
G. Lauriat
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Numerical Solutions ◽  
Three Dimensional ◽  
Thermal Conductance ◽  
Fluid Flows ◽  
Heat Losses ◽  
Transfer Rates ◽  
Side Walls ◽  
The Difference

Numerical solutions are obtained for fluid flows and heat transfer rates for three-dimensional natural convection in rectangular enclosures. The effects of heat losses at the conducting side walls are investigated. The problem is related to the design of cavities suitable for visualizing the flow field. The computations cover Rayleigh numbers from 103 to 107 and the thermal conductance of side walls ranging from adiabatic to commonly used glazed walls. The effect of the difference between the ambient temperature and the average temperature of the two isothermal walls is discussed for both air and water-filled enclosures. The results reported in the paper allow quantitative evaluations of the effects of heat losses to the surroundings, which are important considerations in the design of a test cell.

Asymptotic analysis of premixed burning with large activation energy

1972 ◽  
Vol 56 (1) ◽  
pp. 81-95 ◽  
Author(s):  
Francis E. Fendell
Keyword(s):  
Laminar Flame ◽  
Lewis Number ◽  
Spherically Symmetric ◽  
Arrhenius Kinetics ◽  
Finite Rate ◽  
Activation Temperature ◽  
One Dimensional ◽  
First Order ◽  
Monomolecular Decomposition ◽  
Kinetics Of

The structure and propagation rates of premixed flames are determined by singular perturbation in the limit where the activation temperature is large relative to other flow temperatures for several basic flows. Specifically, the simple kinetics of an exothermic first-order monomolecular decomposition under Arrhenius kinetics is studied for one-dimensional laminar flame propagation, spherically symmetric quasi-steady monopropellant droplet burning, and other simple geometries. Results elucidate Lewis-number effects, losses owing to fuel gasification processes, and conditions under which the thin-flame approximation is a limit of finite-rate Arrhenius kinetics.

A NOTE ON THE STABILITY OF STATIONARY SOLUTIONS TO A SYSTEM OF CHEMOTAXIS

2000 ◽  
Vol 02 (03) ◽  
pp. 373-383
Author(s):  
TAKASHI SUZUKI
Keyword(s):  
Parabolic Equations ◽  
Original System ◽  
Stationary Problem ◽  
Stationary Solutions ◽  
Slime Molds ◽  
System Of Parabolic Equations ◽  
Variational Structure ◽  
Cellular Slime ◽  
Stable Solutions ◽  
The Stability

In 1970 a system of parabolic equations was proposed by Keller and Segel to describe the chemotactic feature of cellular slime molds. It has L1 preserving property for the first component and in use of this the stationary problem is reduced to a single elliptic problem concerning the second component. This problem has a variational structure and several features of the solutions are derived from it. In this paper we study linearized stable solutions in this sense and show that any of them is stable as a stationary solution to the original system of parabolic equations.

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