scholarly journals Whistler-regulated Magnetohydrodynamics: Transport Equations for Electron Thermal Conduction in the High-β Intracluster Medium of Galaxy Clusters

2021 ◽  
Vol 923 (2) ◽  
pp. 245
Author(s):  
J. F. Drake ◽  
C. Pfrommer ◽  
C. S. Reynolds ◽  
M. Ruszkowski ◽  
M. Swisdak ◽  
...  
Keyword(s):  
Heat Flux ◽  
Thermal Flux ◽  
Mean Free Path ◽  
Transport Equations ◽  
Intracluster Medium ◽  
Sound Waves ◽  
Whistler Waves ◽  
Classical Electron ◽  
Turbulent Spectrum ◽  
Electron Thermal Conduction

Abstract Transport equations for electron thermal energy in the high-β e intracluster medium (ICM) are developed that include scattering from both classical collisions and self-generated whistler waves. The calculation employs an expansion of the kinetic electron equation along the ambient magnetic field in the limit of strong scattering and assumes whistler waves with low phase speeds V w ∼ v te /β e ≪ v te dominate the turbulent spectrum, with v te the electron thermal speed and β e ≫ 1 the ratio of electron thermal to magnetic pressure. We find: (1) temperature-gradient-driven whistlers dominate classical scattering when L c > L/β e , with L c the classical electron mean free path and L the electron temperature scale length, and (2) in the whistler-dominated regime the electron thermal flux is controlled by both advection at V w and a comparable diffusive term. The findings suggest whistlers limit electron heat flux over large regions of the ICM, including locations unstable to isobaric condensation. Consequences include: (1) the Field length decreases, extending the domain of thermal instability to smaller length scales, (2) the heat flux temperature dependence changes from T e 7 / 2 / L to V w nT e ∼ T e 1 / 2 , (3) the magneto-thermal- and heat-flux-driven buoyancy instabilities are impaired or completely inhibited, and (4) sound waves in the ICM propagate greater distances, as inferred from observations. This description of thermal transport can be used in macroscale ICM models.

Particle-In-Cell simulations of resonant interactions between whistler waves and electrons in the near-Sun solar wind: scattering of the strahl into the halo and heat flux regulation.

2021 ◽  
Author(s):  
Alfredo Micera ◽  
Andrei Zhukov ◽  
Rodrigo A. López ◽  
Maria Elena Innocenti ◽  
Marian Lazar ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Heat Flux ◽  
Solar Wind ◽  
Velocity Distribution ◽  
Pitch Angle ◽  
Electron Velocity ◽  
Magnetic Field Direction ◽  
Whistler Waves ◽  
Electron Velocity Distribution ◽  
Particle In Cell

<p>Electron velocity distribution functions, initially composed of core and strahl populations as typically encountered in the near-Sun solar wind and as recently observed by Parker Solar Probe, have been modeled via fully kinetic Particle-In-Cell simulations. It has been demonstrated that, as a consequence of the evolution of the electron velocity distribution function, two branches of the whistler heat flux instability can be excited, which can drive whistler waves propagating in the direction parallel or oblique to the background magnetic field. First, the strahl undergoes pitch-angle scattering with oblique whistler waves, which provokes the reduction of the strahl drift velocity and the simultaneous broadening of its pitch angle distribution. Moreover, the interaction with the oblique whistler waves results in the scattering towards higher perpendicular velocities of resonant strahl electrons and in the appearance of a suprathermal halo population which, at higher energies, deviates from the Maxwellian distribution. Later on, the excited whistler waves shift towards smaller angles of propagation and secondary scattering processes with quasi-parallel whistler waves lead to a redistribution of the scattered particles into a more symmetric halo. All processes are accompanied by a significant decrease of the heat flux carried by the strahl population along the magnetic field direction, although the strongest heat flux rate decrease is simultaneous with the propagation of the oblique whistler waves.</p>

New low-frequency waves and negative mass instability in dusty plasmas

2010 ◽  
Vol 76 (6) ◽  
pp. 929-937
Author(s):  
D. P. RESENDES ◽  
R. BINGHAM ◽  
S. MOTA ◽  
V. N. TSYTOVICH
Keyword(s):  
Electron Temperature ◽  
Free Path ◽  
Collision Frequency ◽  
Low Frequency ◽  
Mean Free Path ◽  
Sound Waves ◽  
Ion Temperature ◽  
Plasma Particle ◽  
Charging Mode ◽  
Dust Charging

AbstractLow-frequency dusty plasma waves with frequencies much smaller than the frequency of charging collisions of plasma particles with dust particles are considered taking into account elastic and charging collisions of plasma particles with dust and neutrals. The usual dust sound waves with an upper frequency equal to the dust plasma frequency are found to be present only for wavelengths much smaller than the plasma particle effective mean free path due to the effective collision frequency. The effectice collision frequency is found to be inversely proportional to the square root of the product of the charging frequency and the frequency of particle momentum losses, involving processes due to elastic plasma particle–dust collisions and collisions with neutrals. It is shown that when the wavelength of the wave is much larger than the mean free path for effective collisions, the properties of the waves are different from those considered previously. A negative mass instability is found in this domain of frequencies when the effective mean free path of ions is larger than the effective mean free path of electrons. In the absence of neutrals, this appears to be possible only if the temperature of ions exceeds the electron temperature. This can occur in laboratory experiments and space plasmas but not in plasma-etching experiments. In the absence of instability, a new dust oscillation, a dust charging mode, is found, whose frequency is almost constant over a certain range of wave numbers. It is inversely proportional to the dust mass and charging frequency of the dust. A new dust electron sound wave is found for frequencies less than the frequency of the dust charging mode. The velocity of the dust electron sound wave is determined by the electron temperature but not the ion temperature, as for the usual dust sound waves, with the electron temperature substantially exceeding the ion temperature.

Convective Heat Transfer in Wall-Bounded Flows Affected by Severe Fluid Properties Variation: A Second-Moment Closure Study

2010 ◽  
Author(s):  
S. Jakirlic´ ◽  
R. Jester-Zu¨rker
Keyword(s):  
Heat Flux ◽  
Dissipation Rate ◽  
Transport Equations ◽  
Moment Closure ◽  
Reference Database ◽  
Turbulent Heat ◽  
Second Moment ◽  
Fluid Properties ◽  
Second Moment Closure ◽  
Near Wall

Different flow configurations subjected to increasingly enhanced wall heating were selected to be computationally investigated by means of a differential, near-wall second-moment closure model based on the solution of transport equations for second moments of the fluctuating velocities and temperature, ui″uj″͠ and ui″θ͠ respectively. Both Reynolds stress model and heat flux model represent wall-topography free formulations with quadratic pressure-strain term and pressure-temperature-gradient correlation. The transport equations for the turbulent stress tensor and the turbulent heat flux are solved in conjunction with the equation governing a new scale supplying variable, so-called “homogeneous” dissipation rate, Jakirlic and Hanjalic (2002). Such an approach offers a number of important advantages: proper near-wall shape of the dissipation rate profile was obtained without introducing any additional term and the correct asymptotic behaviour of the stress dissipation components by approaching the solid wall is fulfilled automatically without necessity for any wall geometry-related parameter. The configurations considered include fully-developed and developing flows in channel (without and with a sudden expansion) and pipe in conjunction with the scalar transport under conditions of variable fluid properties for which an extensive experimental and numerical (DNS and LES) reference database exists.

scholarly journals Excitation of VLF quasi-electrostatic oscillations in the ionospheric plasma

1996 ◽  
Vol 14 (1) ◽  
pp. 27-32 ◽  
Author(s):  
B. Lundin ◽  
C. Krafft ◽  
G. Matthieussent ◽  
F. Jiricek ◽  
J. Shmilauer ◽  
...  
Keyword(s):  
Heat Flux ◽  
Electromagnetic Waves ◽  
Ionospheric Plasma ◽  
Electron Distribution Function ◽  
Collisionless Plasma ◽  
Sound Waves ◽  
Thermal Electron ◽  
Band Emission ◽  
Suprathermal Electrons ◽  
A Current

Abstract. A numerical solution of the dispersion equation for electromagnetic waves in a hot magnetized collisionless plasma has shown that, in a current-free ionospheric plasma, the distortion of the electron distribution function reproducing the downward flow of a thermal electron component and the compensating upward flow of the suprathermal electrons, which are responsible for the resulting heat flux, can destabilize quasi-electrostatic ion sound waves. The numerical analysis, performed with ion densities and electron temperature taken from the data recorded by the Interkosmos-24 (IK-24, Aktivny) satellite, is compared with a VLF spectrum registered at the same time on board. This spectrum shows a wide frequency band emission below the local ion plasma frequency. The direction of the electron heat flux inherent to the assumed model of VLF emission generation is discussed

scholarly journals Slip boundary condition of heat flux in Knudsen layers

2014 ◽  
Vol 470 (2161) ◽  
pp. 20130578 ◽  
Author(s):  
Mingtian Xu
Keyword(s):  
Boundary Condition ◽  
Heat Flux ◽  
Velocity Slip ◽  
Slip Boundary Condition ◽  
Mean Free Path ◽  
Knudsen Layer ◽  
Boltzmann Transport ◽  
Slip Boundary ◽  
The Mean ◽  
Solid Walls

In a Knudsen layer with thickness comparable to the mean free path, collisions between heat carriers and solid walls play an important role in nanoscale heat transports. An interesting question is that whether these collisions also induce the slip of heat flow similar to the velocity slip condition of the rarefied gases on solid walls. In this work based on the discrete Boltzmann transport equation, the slip boundary condition of heat flux on solid walls in the Knudsen layer is established. This result is exemplified by the slip boundary condition of heat flux in nanowires, which has been proposed in a phenomenological way.

HEAT FLUX MEASUREMENT BY USING A HEAT PIPE BASED HEAT FLUXSENSOR

2018 ◽  
Vol 3 (11) ◽  
Author(s):  
Joses Jenish Smart ◽  
Antony Raja S ◽  
D.S. Robinson Smart ◽  
Lindon Robert Lee
Keyword(s):  
Heat Flux ◽  
Heat Conduction ◽  
Steady State ◽  
Heat Pipe ◽  
Thermal Flux ◽  
Heat Flux Sensor ◽  
Heat Flow Rate ◽  
Sensing Element ◽  
Time Duration ◽  
Radiation Mode

Heat flux or thermal flux, sometimes also referred to as heat flux density or heat flow rate intensity is a flow of energy per unit area. In SI units, it is measured in [Wm-2]. Measurements of heat flux are usually derived from temperature measurements. Under a temperature gradient the two thermocouples will be at different temperature and so register a voltage. The heat flux is proportional to this differential voltage. An effective way of measuring the heat flux in furnaces, boilers, ovens and similar other systems for combined convection and radiation mode of heat transfer by a heat pipe based heat flux sensor is described in this proposal. A cylindrical sensing element made out of Copper it is exposed to the heat source. The sensing element is insulated in the cylindrical surface so that one-dimensional heat conduction is ensured in the sensing element. By applying the Fourier law of heat conduction, the heat flux received by the sensing element can be evaluated at steady state by measuring the temperature difference between the two specific points in the sensing element. Since the sensing element is connected thermally to the heat pipe, the whole system will reach steady state in relatively short time duration.

A New Ballistic-Diffusive Model for Heat Pulse Propagation

2012 ◽  
Author(s):  
Yanbao Ma
Keyword(s):  
Heat Flux ◽  
Pulse Propagation ◽  
Dielectric Materials ◽  
Heat Pulse ◽  
Second Sound ◽  
Sound Waves ◽  
Transverse Waves ◽  
Longitudinal Waves ◽  
Diffusive Model ◽  
Diffusive Part

In this paper, we reported a new ballistic-diffusive model for heat pulse propagation in dielectric materials. The internal energy and heat flux are split into ballistic part originating from the boundaries and diffusive part originating from inside medium. The ballistic part is modeled based on analytical solutions while the diffusive part is described by Guyer-Krumhansl equations. To validate this model, heat pulse propagation in pure NaF at low temperature is studied. The observed longitudinal waves, transverse waves, second sound waves, and diffusive waveforms from the experiments conducted in early 1970s are numerically reconstructed. There is qualitative agreement between numerical results and experimental observation.

Dynamics of viscous dissipative collapse with casual approach in string inspired Gauss–Bonnet gravity

2019 ◽  
Vol 34 (10) ◽  
pp. 1950074
Author(s):  
M. Tahir ◽  
G. Abbas
Keyword(s):  
Heat Flux ◽  
Gravitational Collapse ◽  
Bulk Viscosity ◽  
Transport Equations ◽  
Coupling Coefficients ◽  
Dynamical Equations ◽  
Bonnet Gravity ◽  
Viscous Heat ◽  
Theory Of Gravity

In this work, we have studied the effects of dissipative viscous/heat gravitational collapse on the dynamics of collapsing source in 5D Einstein–Gauss–Bonnet theory using full casual approach. For this purpose, the dynamical equations have been formulated by using Misner–Sharp approach in 5D Einstein–Gauss–Bonnet theory of gravity. Using the Müller–Israel–Stewart theory, the dynamical equations have coupled with casual transport equations for the heat flux, the bulk and shear bulk viscosity to determine the effects of heat flux including thermodynamics viscous/heat coupling coefficients. The applications of this work to certain astrophysical situations are discussed.

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