Controlling Gravity Impact on Diffusion Flames by Magnetic Field

2012 ◽  
Vol 134 (6) ◽  
Author(s):  
Fouad Khaldi
Keyword(s):  
Magnetic Field ◽  
Scaling Laws ◽  
Diffusion Flames ◽  
Combustion Process ◽  
Flame Length ◽  
Dimensionless Number ◽  
Length Variation ◽  
Zero Gravity ◽  
Blue Color ◽  
Gravity Level

The ability to use a magnetic field as a means for controlling the role of gravity buoyancy on the combustion process is demonstrated by applying a strong vertical magnetic field gradient on a laminar gas jet diffusion flame. The confirmation is based on a comparison of flame appearance; in particular, length variation, to both elevated gravity (higher than earth’s gravity) and zero-gravity combustion experimental data. The comparison parameter is the dimensionless number G, defined as the ratio of gravity level generated by magneto-gravity buoyancy to earth’s gravity. The more important results are as follows. First, for G > 1, good agreement between magnetic and centrifuge length scaling laws reveals that the slight decrease of flame length according to L ∼ G−1/8 is the result of increasing artificial magnetically induced gravity strength. It ensues that flame thinning, bluing, lifting, and extinction are produced by similar mechanisms previously identified in centrifuge diffusion flames. Thereafter, at G ≅ 0, the flame assumes a nearly hemispheric shape and a blue color in perfect similarity to nonbuoyant flames under zero-gravity conditions generated in drop towers. Another important fact is that the magnetic field offers the ability to observe the flame behavior at low gravity levels 0 < G < 1. A primary interesting result is that flame length varies strongly, following the scaling law L ∼ G−1/2.

Numerical Simulation of Effects of Gravity on the Micro Jet Flame in the Confined Space

2013 ◽  
Vol 732-733 ◽  
pp. 127-132
Author(s):  
Yun Hua Gan ◽  
Yan Lai Luo
Keyword(s):  
Numerical Simulation ◽  
Flame Structure ◽  
Numerical Data ◽  
Glass Tube ◽  
Flame Length ◽  
Zero Gravity ◽  
Gravity Level ◽  
Confined Space ◽  
Jet Flame ◽  
Ceramic Tube

A microscale ceramic tube was used as a burner jet, and a coaxial jet flame was established in the confined space between the ceramic tube and the outer quartz glass tube. The effects of gravity on the small jet flame characteristics in the confined space were investigated numerically. Comparisons between the experimental data and the numerical data showed that characteristics of the small jet flame structure and temperature field were in good agreement. It verified the accuracy of the numerical simulation. Numerical simulations of flame characteristics at zero gravity level were performed. The results show that the gravity level has a greater influence on the flame width than that on the flame length. The chemical reaction rate is larger under the condition of normal gravity than that of zero gravity.

scholarly journals Influence of DC Electric Field on the Propane-Air Diffusion Flames and NOx Formation

Energies ◽  
2021 ◽  
Vol 14 (18) ◽  
pp. 5745
Author(s):  
Sang-Min Kim ◽  
Kyeong-Soo Han ◽  
Seung-Wook Baek
Keyword(s):  
Electric Field ◽  
Diffusion Flame ◽  
Diffusion Flames ◽  
Combustion Process ◽  
Flame Length ◽  
Nox Emission ◽  
Nox Formation ◽  
Dc Electric Field ◽  
Air Diffusion ◽  
Reduction Percentage

The aim of this research is to investigate the effects of a direct current (DC) electric field on the combustion behavior of a co-flow propane diffusion flame. The flame length and NOx emission were observed and measured. The electric field enhances the combustion process of propane diffusion flame by causing the movement of ions and molecules in the flame, resulting in a change in the shape of the flame. The flame heights decrease with an increase in the applied voltage and polarity, a more dominant effect to be observed with a positive DC electric field. However, for the applied negative polarity, the inner-cone of the propane diffusion flame is shifted by the electric field. Drastic reduction in the NOx emission is observed with an increase in the applied DC voltage and polarity. In the existing system, the reduction percentage of NOx is within the range of 55 to 78%.

scholarly journals Planetary Magnetic Fields and Habitability in Super Earths

2018 ◽  
Vol 27 (1) ◽  
pp. 183-231 ◽  
Author(s):  
Pablo Cuartas-Restrepo
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Scaling Laws ◽  
Thermal Evolution ◽  
Solid Core ◽  
Direct Influence ◽  
Physical Processes ◽  
Planetary Magnetic Fields ◽  
Planetary Magnetic Field ◽  
Planetary Dynamos

Abstract This work seeks to summarize some special aspects of a type of exoplanets known as super-Earths (SE), and the direct influence of these aspects in their habitability. Physical processes like the internal thermal evolution and the generation of a protective Planetary Magnetic Field (PMF) are directly related with habitability. Other aspects such as rotation and the formation of a solid core are fundamental when analyzing the possibilities that a SE would have to be habitable. This work analyzes the fundamental theoretical aspects on which the models of thermal evolution and the scaling laws of the planetary dynamos are based. These theoretical aspects allow to develop models of the magnetic evolution of the planets and the role played by the PMF in the protection of the atmosphere and the habitability of the planet.

scholarly journals Flux expulsion with dynamics

2016 ◽  
Vol 791 ◽  
pp. 568-588 ◽  
Author(s):  
Andrew D. Gilbert ◽  
Joanne Mason ◽  
Steven M. Tobias
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Lorentz Force ◽  
Differential Rotation ◽  
Time Scale ◽  
Scaling Laws ◽  
Dynamical Regime ◽  
Kinematic Evolution ◽  
Flux Expulsion ◽  
The Magnetic Field

In the process of flux expulsion, a magnetic field is expelled from a region of closed streamlines on a $TR_{m}^{1/3}$ time scale, for magnetic Reynolds number $R_{m}\gg 1$ ($T$ being the turnover time of the flow). This classic result applies in the kinematic regime where the flow field is specified independently of the magnetic field. A weak magnetic ‘core’ is left at the centre of a closed region of streamlines, and this decays exponentially on the $TR_{m}^{1/2}$ time scale. The present paper extends these results to the dynamical regime, where there is competition between the process of flux expulsion and the Lorentz force, which suppresses the differential rotation. This competition is studied using a quasi-linear model in which the flow is constrained to be axisymmetric. The magnetic Prandtl number $R_{m}/R_{e}$ is taken to be small, with $R_{m}$ large, and a range of initial field strengths $b_{0}$ is considered. Two scaling laws are proposed and confirmed numerically. For initial magnetic fields below the threshold $b_{core}=O(UR_{m}^{-1/3})$, flux expulsion operates despite the Lorentz force, cutting through field lines to result in the formation of a central core of magnetic field. Here $U$ is a velocity scale of the flow and magnetic fields are measured in Alfvén units. For larger initial fields the Lorentz force is dominant and the flow creates Alfvén waves that propagate away. The second threshold is $b_{dynam}=O(UR_{m}^{-3/4})$, below which the field follows the kinematic evolution and decays rapidly. Between these two thresholds the magnetic field is strong enough to suppress differential rotation, leaving a magnetically controlled core spinning in solid body motion, which then decays slowly on a time scale of order $TR_{m}$.

Gravity Level Influence on a Laterally Heated Ferrofluid Submitted to an Oblique Strong Magnetic Field

2006 ◽  
Vol 220 (2_2006) ◽  
pp. 199-208
Author(s):  
Marcel Hennenberg ◽  
Boris Weyssow ◽  
S. Slavtchev ◽  
V. Aleksandrov ◽  
B. Scheid
Keyword(s):  
Magnetic Field ◽  
Strong Magnetic Field ◽  
Gravity Level

Zur Begrenzung der radial en Ausdehnung des Li chtbogenstromes durch ein axiales Magnetfeld. II. Skalengesetze und Vergleich mit Experimenten / On Limitation of the Radial Extent of the Arc Current by Means of an Axial Magnetic Field. II. Scaling Laws and Comparison with Experimental Results

1972 ◽  
Vol 27 (4) ◽  
pp. 652-670
Author(s):  
O. Klüber
Keyword(s):  
Magnetic Field ◽  
Cross Sections ◽  
Scaling Laws ◽  
Axial Magnetic Field ◽  
Angular Frequency ◽  
Model Calculations ◽  
Simple Geometry ◽  
Radial Extent ◽  
Arc Current ◽  
Field Lines

Abstract In an arc with superimposed axial magnetic field, radial current components cause a rotational motion of the plasma column and produce azimuthal Hall currents and hence electromotive forces such that the arc current is guided by the magnetic field lines. In the first part of this paper the steady-state plasma equations have been solved for a homogeneous plasma in simple geometry, allowance being made for finite viscosity. Here, scaling laws giving the radial extent of the arc current are obtained. In addition, electrodes with finite cross sections are treated. The results of model calculations agree well with experimental data. Generally, the model is applicable, if the angular frequency of the plasma is small compared with the ion gyration frequency.

scholarly journals Numerical Prediction of the Dynamic Behaviour of Turbulent Diffusion Flames

1996 ◽  
Author(s):  
Dieter Bohn ◽  
Gregor Deutsch ◽  
Uwe Krüger
Keyword(s):  
Steady State ◽  
Frequency Response ◽  
Turbulent Diffusion ◽  
Dynamic Behaviour ◽  
Diffusion Flames ◽  
Sudden Change ◽  
Combustion Process ◽  
Turbulent Diffusion Flames ◽  
Time Element ◽  
Flame Behaviour

Environmental compatibility requires low emission burners for gas turbine power plants as well as for jet engines. In the past significant progress has been made developing low NOx and CO burners. Unfortunately these burners often have a more pronounced tendency than conventional burner designs to produce combustion driven oscillations The oscillations may be excited to such an extent that pronounced pulsation may possibly occur; this is associated with a risk of engine failure. The stability of a burner system can be investigated by means of a stability analysis under the assumption of acoustical behaviour. The problem with all these algorithms is the transfer function of the flame. A new method is presented here to predict the dynamic flame behaviour by means of a full Navier-Stokes-simulation of the complex combustion process. The first step is to get a steady-state solution of a flame configuration. After that a transient simulation follows with a sudden change in the mass flow rate at the flame inlet. The time-dependent answer of the flame to this disturbance is then transformed into the frequency space by a Laplace Transformation. This leads, in turn, to the frequency response representing the dynamic behaviour of the flame. In principle, this method can be adapted for both diffusion as well as premixed flame systems. However, due to the fact that diffusion flames are more controlled by the mixing process than by the chemical kinetic, the method has first been used for the prediction of the dynamic behaviour of turbulent diffusion flames. The combustion has been modelled by a mixed-is-burnt model. The influence of the turbulence has been taken into account by a modified k-ε-model and the turbulence influences the combustion rate by presumed probability density functions (pdf). The steady-state as well as the transient results have been compared with experimental data for two different diffusion flame configurations. Although the burner configuration is relatively complex, the steady state results collaborate very well with the experiments for velocity, temperature and species distribution. The most important result is that the heat release which drives the oscillations can be modelled sufficiently accurately. The effect of using different pdf-models has been discussed and the best model has been used for the transient calculations of the dynamic flame behaviour. The results for the frequency response of the flame are very encouraging. The principal behaviour of the flame — higher order time element with a delay time — can be predicted with sufficient precision. In addition, the qualitative results collaborate fairly well with the experiments.

Topological analysis of separation phenomena in liquid metal flow in sudden expansions. Part 2. Magnetohydrodynamic flow

2011 ◽  
Vol 674 ◽  
pp. 132-162 ◽  
Author(s):  
C. MISTRANGELO
Keyword(s):  
Magnetic Field ◽  
Liquid Metal ◽  
Scaling Laws ◽  
Numerical Study ◽  
Topological Analysis ◽  
Metal Flow ◽  
Magnetohydrodynamic Flow ◽  
Sudden Expansion ◽  
Internal Layers ◽  
Flow Topology

A numerical study has been carried out to analyse liquid metal flows in a sudden expansion of electrically conducting rectangular ducts under the influence of an imposed uniform magnetic field. Separation phenomena are investigated by selecting a reference Reynolds number and by increasing progressively the applied magnetic field. The magnetic effects leading to the reduction of the size of separation zones that form behind the cross-section enlargement are studied by considering modifications of flow topology, streamline patterns and electric current density distribution. In the range of parameters investigated, the magnetohydrodynamic flow undergoes substantial transitions from a hydrodynamic-like flow to one dominated by electromagnetic forces, where the influence of inertia and viscous forces is confined to thin internal layers aligned with the magnetic field and to boundary layers that form along the walls. Scaling laws describing the reattachment length and the pressure drop in the sudden expansion are derived for intense magnetic fields.

Combustion Oscillations in Bluff Body Stabilized Diffusion Flames With Variable Length Inlet

2009 ◽  
Vol 131 (5) ◽  
Author(s):  
M. Madanmohan ◽  
S. Pandey ◽  
A. Kushari ◽  
K. Ramamurthi
Keyword(s):  
Heat Release ◽  
Phase Angle ◽  
Bluff Body ◽  
Diffusion Flames ◽  
Combustion Process ◽  
Low Frequency ◽  
Pressure Oscillations ◽  
Pipe Length ◽  
Entry Length ◽  
Low Frequency Oscillations

This paper describes the results of an experimental study to understand the influence of inlet flow disturbances on the dynamics of combustion process in bluff body stabilized diffusion flames of liquid petroleum gas and air. The results show the influence of weak disturbances created by the change in incoming pipe length on the amplitude of pressure oscillations and the phase angle between pressure and heat release. It is seen that the phase delay increases as the entry length increases. The rms value of pressure, however, generally falls with the increase in length. The phase angle is seen to be in the second quadrant, showing that the heat release oscillations damp the pressure oscillations. Therefore, the decrease in the phase angle results in the reduction in damping and hence an increase in pressure fluctuations. The dominant frequencies of combustion oscillations are found to be the low frequency oscillations, and the frequency of oscillations increases with a decrease in the inlet pipe length and an increase in the flow Reynolds number. It is suggested that such low frequency oscillations are driven by vortex shedding at the wake of the bluff body, which energizes the diffusion and mixing process.

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