Calculation of Laminar Flows of Plasma in the Channel of a Plasmatron with the Self-Adjusting Length of the Electric Arc

A simplified method is suggested for the calculation of the parameters of laminar flows of plasma in the channel of a plasmatron. A new analytical solution of the Elenbaas–Heller equation is derived, which generalizes the channel model of electric arc to the case when the volume radiation makes a significant contribution to the electric arc energy balance. Numerical calculations are performed in order to determine the electric field intensity, the longitudinal pressure gradient, and the heat transfer to the electric arc channel wall depending on the working parameters of the plasmatron in a laminar flow of gas in a stabilized section. In determining the arc length, it is assumed that the electric arc is shifted downstream of the flow and, at the same time, performs random walks over the channel cross section. The walks occur under the effect of vortexes whose characteristic size is of the order of the arc diameter.     

Hysteresis of the current-voltage characteristic of a continuous electron-beam-controlled discharge in a nitrogen flow

A hysteresis in the current-voltage characteristic of continuous electric discharge controlled by an electron beam in a nitrogen flow has been experimentally observed. It is suggested that the transition from a self-sustained glow discharge regime (typical of ionization chamber) to the electron-beam-controlled discharge is accompanied by the transition from the laminar to turbulent boundary layer at the cathode surface.     

Multicriterial Optimization of the Operation and Design Parameters of Electric-Arc Plasmatrons of Linear Circuits

A new method of design synthesis of electric arc heaters by prescribed characteristics is suggested. The method has been applied for multicriterial optimization of the conditions of burning an arc with longitudinal eddy stabilization by an air flow in a plasmatron channel.     

Specific features of wall free convection in a temperature-stratified medium

A flow in the near-wall region with free convection in a temperature-stratified medium is analyzed. A laminar flow in a plane square domain and laminar and turbulent flows near a plate are considered in the cases of linear and nonlinear stratifications. Different nonstationary stages of the flow and a local self-similar regime with criterion for its realization are distinguished. General characteristics for the laminar and turbulent regimes are formulated.     

Laminar and Turbulent Transition of Fine-Grained Slurries

An experimental investigation of flow behavior of fine-grained highly concentrated slurries, i.e., water mixtures of kaolin and fly ash from a fluidic-type combustion chamber produced during the process of desulphurization, in horizontal straight pipes is presented. A pipe loop with hydraulically smooth stainless steel pipes was used to measure the slurry flow parameters. Kaolin slurry has time-independent, yield pseudo-plastic response for volume concentrations higher than about 6%. In contrast, fluidic fly ash-gypsum water mixture is time dependent and showed substantial decrease of flow resistance due to the effect of shearing during the initial period of pumping. An intensive shearing of concentrated fluidic fly ash-gypsum slurry results in a substantial reduction of the hydraulic gradient in the laminar region and in a marked shift of the laminar/turbulent transition point towards a lower velocity value. After shearing in a turbulent regime a reduction in the hydraulic gradient at the transition point reached about 50% of its original value. The transition from laminar to turbulent regime results in an abrupt increase of flow resistance. The flow patterns become fundamentally different for the two regimes. It was found that pressure fluctuation could well indicate the laminar/turbulent transition. The transition from laminar to turbulent flow is very important for accurate and efficient design and operation of dense slurry pipelining. The optimum operational condition is slightly above the laminar/turbulent transition point, where flow conditions are often very attractive from an economic point of view.     

Laminar and Turbulent Transition of Fine-Grained Slurries

An experimental investigation of flow behavior of fine-grained highly concentrated slurries, i.e., water mixtures of kaolin and fly ash from a fluidic-type combustion chamber produced during the process of desulphurization, in horizontal straight pipes is presented. A pipe loop with hydraulically smooth stainless steel pipes was used to measure the slurry flow parameters. Kaolin slurry has time-independent, yield pseudo-plastic response for volume concentrations higher than about 6%. In contrast, fluidic fly ash-gypsum water mixture is time dependent and showed substantial decrease of flow resistance due to the effect of shearing during the initial period of pumping. An intensive shearing of concentrated fluidic fly ash-gypsum slurry results in a substantial reduction of the hydraulic gradient in the laminar region and in a marked shift of the laminar/turbulent transition point towards a lower velocity value. After shearing in a turbulent regime a reduction in the hydraulic gradient at the transition point reached about 50% of its original value. The transition from laminar to turbulent regime results in an abrupt increase of flow resistance. The flow patterns become fundamentally different for the two regimes. It was found that pressure fluctuation could well indicate the laminar/turbulent transition. The transition from laminar to turbulent flow is very important for accurate and efficient design and operation of dense slurry pipelining. The optimum operational condition is slightly above the laminar/turbulent transition point, where flow conditions are often very attractive from an economic point of view.     

Experimental investigation of the spatial displacements of an arc-heated plasma

Oscillations of an electric arc in a plasmatron with the fixed arc in wide ranges of currents and air flow rates have been investigated. The distribution functions of arc oscillations have been obtained for various currents, gas flow rates, and distances from a cathode.     

Electrode self-cleaning in a barrier ozonizer operating in a turbulent gas flow regime

The effect of self-cleaning of the discharge gaps in electric barrier ozonizers featuring a turbulent gas flow is related to the fact that the hydrodynamic forces (separating foreign solid and liquid particles from the electrode surface) predominate over electric forcers (attracting such particles to the electrodes). In this respect, ozonizers operating in a turbulent gas flow regime are advantageous over devices operating with a laminar flow.     

Two-mode model of flow in a plasmotron channel

The characteristics of an electric arc in a turbulent gas flow are calculated on the basis of the concept of laminar flow in the arc zone.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 51, No. 5, pp. 830–835, November, 1986.     

Instability of Quantized Vortices Attached to Oscillating Boundaries in Superfluid 4He

The motion of quantized vortices is studied using a vibrating wire in superfluid ⁴He. A vortex filtering method provides a superfluid practically free of remanent vortices in which the vibration of a wire cannot generate turbulence. Vortex lines are produced by cooling through the superfluid transition and remain forming bridges between a wire and a surrounding wall. Bridged remanent vortices increase the resonance frequency of a vibrating wire: the rate of an increase due to the remanent vortices is constant in a laminar flow regime and steeply increases in a turbulent flow regime with increasing wire velocity. These results suggest that oscillation of the bridged vortices provides a linear contribution to the wire vibration in the laminar flow regime, until instability occurs in the oscillation of the vortices, causing turbulence.      

Turbulent phase distribution during lag synchronization breakage

The distribution of turbulent phases in a time realization of dynamical systems in the regime of intermittent lag synchronization has been studied. A method of determining the duration of laminar and turbulent phases by means of the wavelet transform is proposed.     

On a local predictor of shear instability and the initiation of local turbulence

The stability of a local laminar shear flow and its transition into turbulent flow is considered as a local phenomenon. This transition may remain local, in which case the flow field is partially laminar and partially turbulent, or it may spread and make the whole field turbulent. One of the applications of this analysis is the prediction of local heat-convection rates, which are enhanced by local turbulence. Another application is in heart-lung blood pumps, where excessive shear rates are detrimental to red blood cells.The analysis is Lagrangian, which concentrates on the stability of a fluid particle in maintaining its position in a laminar shear flow. This stability is shown to depend on the magnitude of a non-dimensional parameter, namely the local Reynolds numberRe _L =ha ²/v whereh is the local shear rate,a is the particle radius andv is the fluid's kinematic viscosity. It is shown that when, locally,Re _L > 530, the flow is, locally, unstable. The application of this criterion is simple and direct, and in certain cases it can be shown that the resulting unstable flow is indeed turbulent.Because the analysis relies on an experimental coefficient which has been obtained for a rigid sphere, rather than for a fluid particle, the criterion is introduced at this stage as a conjecture. Several examples are presented which demonstrate the criterion's ability to yield correct predictions for instability.     

Determination of the plasma temperature in a pulsating arc

The distribution functions of arc pulsations depending on the current, gas mass flow rate, and the distance from the cathode in a plasmatron with a fixed arc length have been obtained. The distributions of the plasma emission intensity by the transverse image method have been measured. From these data, the temperature distribution over the arc radius has been determined and the influence of the pulsations on the measurement accuracy has been shown.     

Modern Approaches for Calculating Flow Parameters during a Laminar–Turbulent Transition in a Boundary Layer

We analyze modern methods for calculating heat and hydrodynamic flow parameters in a boundary layer during the laminar–turbulent transition. The main approaches for describing the phenomenon of laminar–turbulent transition are examined. Each approach is analyzed. The manner in which different factors influence the laminar–turbulent transition is studied. An engineering model of the laminar–turbulent transition in a high-velocity flow is presented.     

Experimental investigation of ice slurry heat transfer in horizontal tube

Heat transfer of ice slurry flow based on ethanol–water mixture in a circular horizontal tube has been experimentally investigated. The secondary fluid was prepared by mixing ethanol and water to obtain initial alcohol concentration of 10.3% (initial freezing temperature -4.4 °C). The heat transfer tests were conducted to cover laminar and slightly turbulent flow with ice mass fraction varying from 0% to 22% depending on test performed. Measured heat transfer coefficients of ice slurry are found to be higher than those for single phase fluid, especially for laminar flow conditions and high ice mass fractions where the heat transfer is increased with a factor 2 in comparison to the single phase flow. In addition, experimentally determined heat transfer coefficients of ice slurry flow were compared to the analytical results, based on the correlation by Sieder and Tate for laminar single phase regime, by Dittus–Boelter for turbulent single phase regime and empirical correlation by Christensen and Kauffeld derived for laminar/turbulent ice slurry flow in circular horizontal tubes. It was found that the classical correlation proposed by Sieder and Tate for laminar forced convection in smooth straight circular ducts cannot be used for heat transfer prediction of ice slurry flow since it strongly underestimates measured values, while, for the turbulent flow regime the simple Dittus–Boelter relation predicts the heat transfer coefficient of ice slurry flow with high accuracy but only up to an ice mass fraction of 10% and Re_cf > 2300 regardless of imposed heat flux. For higher ice mass fractions and regardless of the flow regime, the correlation proposed by Christensen and Kauffeld gives good agreement with experimental results.     

A note on the radial wall jet with swirl

Summary The aim of this paper is a determinations of the space flow geometry of turbulent radial wall jet with swirl by means of a similarity analysis. It is assumed that except for a very thin layer near the wall, the flow field of the turbulent radial wall jet is similar. The wall conditions for a Newtonian fluid flow used in a paper by the present authors [11] — and satisfactory only for a laminar regime — are substituted by a suitable condition often employed in 3-D turbulent boundary layer problems. It is assumed that the direction of the shear-stress resultant is the same as the direction of the mean velocity-gradient resultant.With 3 Figures     

Generalization of test data on resistance in tubes with ribbon swirlers

On the basis of identity of the mechanism of fluid motion in tubes with ribbon swirlers and in coils, criterial equations have been obtained for determining the resistance coefficient in a swirled flow in the laminar regime with macro-eddies and in the turbulent regime.     

Heat loss in the channel of a plasmatron

A mathematical model is constructed and a computational experiment is carried out to determine the characteristics of a longitudinally blown electric arc in the channel of a plasmatron under conditions of local thermal equilibrium. A feature of the model is that it makes allowance for radiation transfer in the real spectrum of an electric- arc plasma. An algorithm for solving the problem is presented and the effect of radiation reabsorption on the radiation and conductive heat loss in the plasmatron channel is shown.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 58, No. 3, pp. 505–511, March, 1990.     

Rotating Couette flow of helium II

An experimental study of He II Couette flow is reported. Using second-sound measurements (Doppler effect, attenuation), we show the existence of different regimes and study their dependence on temperature and gap between the cylinders. We propose a simple model which allows a qualitative understanding of our experimental results. According to this model, the transition from laminar to turbulent flow takes place in two stages by a series of instabilities. First, the laminar regime vortex array is disorganized. Then, normal fluid instabilities lead to turbulence of the whole He II.Laboratoire associé au Centre National de la Recherche Scientifique.     

Flow turbulence in a cylindrical channel encompassing an electric arc

The effect of an electric arc on the gas flow in a cylindrical channel is investigated. It is shown that the striking of an arc in a laminar flow leads to its turbulence at the boundary of the arc column. Within the arc column, the flow is rendered laminar by the high viscosity of the arc plasma. However, thermal turbulence may develop in the central part of the arc.Academic Scientific Combine A. V. Lykov institute of Heat and Mass Exchange, Academy of Sciences of Belarus', Minsk. Translated from Inzhenerno-Fizicheski Zhurnal, Vol. 62, No. 4, pp. 601–607, April, 1992.