Thermal Plasma Flow Research Articles

Behavior of particulates in thermal plasma flows

Injection of particulate matter into a thermal plasma represents one of the approaches used in thermal plasma processing. The injected particles are usually treated as a dispersed phase, governed by the equation of motion and the rate equations for heat and mass transfer in Lagrangian coordinates. A stochastic approach is introduced to take particle dispersion into account due to turbulent fluctuations by randomly sampling instantaneous flow fields. Three-dimensional effects are also considered which are mainly due to particle injection and the presence of a swirl component. A modified approach for investigating noncontinuum effects on plasma-particle heat transfer is proposed, incorporating both electric and aerodynamic effects on the boundary layer around a particle immersed into a thermal plasma. Comparisons of theoretical predictions based on the present model with available experimental data are, in general, in reasonable agreement.

Experimental study of effective particle heating by a thermal plasma flow confined in a porous ceramic tube

The heating of a single alumina particle (1 mm diameter) was experimentally investigated using a thermal argon plasma flow confined in a tube. Two kinds of tube were used; a porous ceramic tube (PCT) with a transpiration gas and a water-cooled copper tube (WCT). The temperature and velocity of the particle heated in a thermal plasma flow were measured at the exit of the tube by the calorimetric and optical method, respectively. The plasma temperature and velocity at the exit of the tube were also measured. The heating rate of a particle was estimated from these experimental results. According to the results, the heating rate of a particle is higher for PCT with a small flow rate of transpiration gas than for WCT. Therefore, PCT is effective for the particle heating.

Processing of a thermal plasma flow in a tube

Abstract

Nusselt number correlations for heat transfer to small spheres in thermal plasma flows

Seven different equations predicting heat transfer rates to small spheres in plasma flows are examined considering argon and nitrogan as plasma gases from 300 to 21,000 K at 1 atm. For argon there is a general consensus up to 9000 K, beyond which wide deviations in behavior occur. For nitrogen, the seven correlations are in good agreement up to 4000 K, but show substantial deviations beyond this value. Comparisons with the sparsely available experimental data are made for argon from 300 to 17,000 K and for nitrogen up to 5500 K. Disagreement between the various correlations and experiment can exceed one order of magnitude.

The effect of gas injection on a thermal argon plasma flow in a water-cooled tube

The effect of gas injection on an atmospheric thermal argon plasma flow in a water-cooled tube was investigated experimentally and numerically. The injection gas is argon, helium, or nitrogen. The static pressure with helium injection increases greatly because of its high thermal conductivity, while little increase occurs for nitrogen injection because of the dissociation. The increasing rate of the static pressure depends on the ratio of the momentum term to the viscosity term. The heat flux to the tube wall with gas injection changes less than that without injection. The numerical results showed variations similar to the experimental ones.

Heat and momentum transfer to particles in thermal plasma flows

Abstract

Static pressure and heat flux measurements of a thermal argon plasma flow in a water-cooled tube

The momentum and energy transfer phenomena with large temperature difference were investigated experimentally and theoretically, using an argon atmospheric thermal plasma. The plasma was generated by an arc discharge, 4–6 kW, and flowed into a water-cooled copper tube for static pressure measurements and into a copper block with the same size hole (8 mm i.d.) for measuring heat fluxes using a transient method. The argon flow rate was 2.77–8.31×10−4 kg/s. The static pressure of the plasma flow shows a different variation from that of an ordinary flow and does not decrease monotonically. The axial distributions of the numerical calculations are in fair agreement with those of the experiments, and it is concluded that the contributions of recombination and of physical properties play important roles in the behavior of the confined thermal plasma flow.

Behavior of small particles in a thermal plasma flow

In this paper computational results are presented which reveal the effects of the Knudsen number on heat transfer and drag of small particles in a flowing thermal argon plasma. The Knudsen number is restricted to moderate values so that “temperature jump” and “velocity slip” conditions may be employed, and for the governing equations the continuum approach remains valid. It is shown that the ratio of the heat fluxes with and without the Knudsen effect is almost identical to the ratio obtained by the authors for the case of pure heat conduction. This fact is very important for modeling of the behavior of particles injected into an actual plasma reactor when the Knudsen effect has to be taken into account.

Numerical Analysis of Thermal Piasma Flow in a Pipe

Thermal plasma flow in a water-cooled pipe was investigated using numerical calculations for three models for the physicochemical state in the pipe: thermal equilibrium, a frozen state, and an approximately real state. The velocity and energy fields are different from ordinary pipe flow and vary characteristically depending on the state in the pipe and the initial conditions. The velocity along the center line of the pipe increases initially and then decreases, while the mixed-mean temperature and the mixed-mean total enthalpy decrease somewhat differently. The pressure decreases initially and then increases. The longitudinal variation of the heat flux density was examined by calculating the Nusselt number in the conventional way.

A flux preserving method of coupling first and second order equations to simulate the flow of plasma between the protonosphere and the ionosphere

This paper describes a numerical method developed to solve the interhemispheric flow of thermal plasma, heat and momentum along closed magnetic field tubes in the plasmasphere. The essence of our technique incorporates the best aspects of two former approaches into a single unified code. The first is the so-called shooting or searching method, which employs integro-differential equations, and the second involves the solution of second order nonlinear partial differential equations by conventional iterative techniques. The former method attains optimal performance above ∼2000 km, and the latter below this altitude. The combined approach yields a satisfactory solution over an entire geomagnetic flux tube, encompassing two low altitude regimes, in the northern and southern ionospheres, and a high altitude regime spanning the distance between them. We demonstrate that the solution is stable and simulate the collapse of the postsunset ionosphere.

Effects of convection electric field on the thermal plasma flow between the ionosphere and the protonosphere

Dynamic behavior of the coupled ionosphere-protonosphere system in the magnetospheric convection electric field has been theoretically studied for two plasmasphere models. In the first model, it is assumed that the whole plasmasphere is in equilibrium with the underlying ionosphere in a diurnal average sense. The result for this model shows that the plasma flow between the ionosphere and the protonosphere is strongly affected by the convection electric field as a result of changes in the volume of magnetic flux tubes associated with the convective cross- L motion. Since the convection electric field is assumed to be directed from dawn to dusk, magnetic flux tubes expand on the dusk side and contract on the dawn side when rotating around the earth. The expansion of magnetic flux tubes on the dusk side causes the enhancement of the upward H + flow, whereas the contraction on the dawn side causes the enhancement of the downward H + flow. Consequently, the H + density decreases on the dusk side and increases on the dawn side. It is also found that significant latitudinal variations in the ionospheric structures result from the L-dependency of these effects. In particular, the H + density at 1000 km level becomes very low in the region of the plasmasphere bulge on the dusk side. In the second model, it is assumed that the outer portion of the plasmasphere is in the recovery state after depletions during geomagnetically disturbed periods. The result for this model shows that the upward H + flux increases with latitude and consequently the H + density decreases with latitude in the region of the outer plasmasphere. In summary, the present theoretical study provides a basis for comparison between the equatorial plasmapause and the trough features in the topside ionosphere.

Interhemispheric flow of thermal plasma in a closed magnetic flux tube at mid-latitudes under sunspot minimum conditions

The coupled H + and O + time-dependent continuity and momentum equations are solved within a region of the L = 3 magnetic flux tube lying between (and including) the F2-layers of conjugate hemispheres. The method of solution is an extended and modified version of the Murphy et al. (1976) method. The model is used to study the coupling between the F2-layers of conjugate hemispheres during magnetically quiet periods. The results of the calculations strongly indicate that the protonosphere acts as a reservoir, with variable H + content, which prevents direct coupling between the F2-layers of conjugate hemispheres. However there is generally a significant interhemispheric flow of plasma. This flow is caused by conditions in the summer and winter topside ionospheres and it maintains continuity in the plasma concentration within the protonosphere. There are times when the direction of flow is from the winter hemisphere to the summer hemisphere. It is suggested that maintenance of the winter F2-layer at night is not assisted directly by the F2-layer of the conjugate summer hemisphere. It is shown that during the first few days of protonosphere replenishment after a magnetic storm there is an upflow of H + in the topside ionosphere at all times in the summer hemisphere. There is also an upflow of H + during the daytime in both hemispheres. A comparison with the results obtained when the interhemispheric H + flux is held permanently at zero shows that both F2-layers are little affected by the interhemispheric H + flux. Nevertheless both F2-layers are affected by the H + tube content of the protonosphere. When the H + flux at 1000 km in one hemisphere is much greater than the H + flux at 1000 km in the conjugate hemisphere, there is a corresponding signature in the interhemispheric H + flux. The results suggest that there is insufficient time between magnetic storms for complete replenishment of the protonosphere to occur.

Protonospheric-ionospheric modeling of VLF ducts

Numerical simulations of the ionosphere and protonosphere have been used to investigate diurnal and seasonal variations in magnetospheric plasma density enhancements capable of ducting VLF radio waves. During winter and equinoxes, VLF ducts may extend down to 300-km altitude at night but usually terminate above 1800 km during the day. In summer, ducts terminate above 1000-km altitude at all local times. The daytime flow of thermal plasma from the ionosphere into the protonosphere limits the half-life of a VLF duct to about 2 days.

Mid-latitude electron density enhancement in the nocturnal topside ionosphere and its longitudinal inequalities.

A study of data from the cylindrical electrostatic probe and the topside sounder aboard the Alouette 2 satellite reveals the existence of nighttime Ne enhancements at mid-latitudes, at altitudes 1, 000-3, 000km. The peaks seem to approach the equator with increasing altitude, and appear to lie on a specific set of geomagnetic field lines. The intensity and location of these nocturnal Ne peaks, as well as the electron density in the entire low- to mid-latitude range, show a marked dependence on geomagnetic longitude. These observations are interpreted in terms of field-aligned flow of thermal plasma from the protonosphere above 3, 000km in the presence of a westward electric field at L≈2.

Influence of thermal plasma flow on the daytimeF2layer

Previous work on theoretical modeling of thermal plasma flow between the ionosphere and the plasmasphere on the night side of the earth, where photoionization is almost completely absent, is continued to cover ionosphere-magnetosphere coupling in the dayside ionosphere. Results indicate that the daytime plasmapause should be associated with the H(+) trough in the top-side ionosphere, but not with the trough in O(+) density or NmF2. At night the plasmapause can be identified with a trough in both H(+) and O(+) densities.

Effects of photoelectron heating and interhemisphere transport on day-time plasma temperatures at low latitudes

The thermal balance of the plasma in the day-time equatorial F region is examined. Steady-state solutions of electron and ion temperatures are obtained, assuming the ions are O + and H +. The theoretical concentrations of O + and H + and the field-aligned velocity were obtained following Moffett and Hanson (1973), while theoretical photoelectron heating rates of the electron gas were taken from Swartz et al. (1975). The results demonstrate the gross features in the electron and ion temperatures as observed at the Jicamarca Observatory and in the ion temperatures observed on the OGO-6 satellite. The rapid increase in electron temperature above 500 km at the magnetic equator is due to heating by photoelectrons created at higher latitudes and travelling up along the field lines. The rapid increase in ion temperature is due to good thermal contact with the electrons rather than the neutrals. It is shown that field-aligned interhemispheric thermal plasma flows appreciably affect these temperatures, and that, with a net plasma flow from the summer hemisphere to the winter hemisphere, the temperatures are higher in the winter hemisphere. These effects are related to the character of the ion temperature minimum observed by OGO-6 near the magnetic equator.

Ion heating in thermal plasma flows

The general effects of thermal plasma flows on the thermal structure of the upper ionosphere and inner magnetosphere are discussed. In the light of presented results, it is shown that thermal ions in the outer regions of the plasmasphere and beyond may be substantially hotter than previously thought.

Model development of supersonic trough wind with shocks

The time dependent one dimensional hydrodynamic equations describe the evolution of the thermal plasma flow along closed magnetic field lines outside of the plasmasphere. The convection of the supersonic polar wind onto a closed field line results in the assumed formation of collisionless plasma shocks. These shocks move earthward as the field line with its ‘frozen-in’ plasma remains fixed or contracts with time to smaller L coordinates. The high equatorial plasma temperature (of the order of electron volts) produced by the shock process decreases with time if the flow is isothermal but it will increase if the contraction is under adiabatic conditions. Assuming adiabaticity a peak in the temperature forms at the equator in conjunction with a depression in the ion density. After an initial contraction, if the flux tube drifts to higher L coordinates the direction of the shock motion can be reversed so that the supersonic region will expand along the field line towards the state characterizing the supersonic polar wind. A rapid expansion will lower the equatorial density while the temperature decreases with time under adiabatic but not isothermal conditions.