On electron screening effects in the low-energy 3He(d,p)4He data

We have calculated the screening effects of the two electrons in the atomic ³He gas target on the low-energy³He(d, p)⁴He data. The nuclear degrees of freedom have been described within the microscopic multi-channel Resonating Group Method, while the two electrons have been treated in Born-Oppenheimer approximation deriving the exact screening potential within the Path Integral Monte Carlo method. Our model underestimates the observed screening effects implying the need to consider the coupling of nuclear and electronic degrees of freedom.     

逆向复式射流预燃室燃烧器

预燃室是一种高效、低ＮＯｘ排放很有发展前途的洁净煤燃烧技术。但是，目前由于其体积过大，使它在实际应用中受到限制。本文叙述的逆向复式射流预燃室燃烧器结构简单、体积小、燃烧效率高、煤种适应性强，可望成为符合洁净煤技术要求的高效、低ＮＯｘ主燃烧器。     

Fluid dynamics of slender,thin, annular liquid jets

Perturbation methods are used to obtain the one-dimensional, asymptotic equations that govern the fluid dynamics of slender, thin, inviscid, incompressible, axisymmetric, irrotational, annular liquid jets from the Euler equations. It is shown that, depending on the magnitude of the Weber number, two flow regimes are possible: an inertia-dominated one corresponding to large Weber numbers, and a capillary regime for Weber numbers of the order of unity. The steady equations governing these two regimes have analytical solutions for the liquid's axial velocity component and require a numerical integration to determine the jet's mean radius for inertia-dominated jets. The one-dimensional equations derived in this paper are shown to be particular cases of a hydraulic model for annular liquid jets, and this model is used to determine the effects of gravity modulation on the unsteady fluid dynamics of annular liquid jets in the absence of mass injection into the volume enclosed by the jet and mass absorption. It is shown that both the convergence length and the pressure coefficient are periodic functions of time which have the same period as that of the gravity modulation, but undergo large variations as the amplitude, frequency and width of gravitational pulses is varied.     

Probe measurements in thermal plasma jets

Measurements of composition, temperature, and velocity in atmospheric argon plasma jets are reported, using enthalpy probes. The plasma jets are generated by a commercial type plasma gun and the measurements are expected to be of particular interest for industrial applications such as plasma spraying. Emphasis has been on the central and downstream regions of the plasma flame. The entrainment of air into the jet was found to be very high, even close to the axis of the jet. Gas samples analyzed with a gas chromatograph showed demixing of the air, i.e., nitrogen is more abundant in the jet than at room temperature. The high air entrainment has a strong cooling effect on the plasma, resulting in a rapid temperature drop along the axis. The influence of the argon flow rate and of the arc current on the jet's conditions was parametrically studied. Matching of the quantities measured in the jet with the torch input confirmed the validity of the results, and the relevance of enthalpy probe diagnostics in thermal plasma jets.     

A new nozzle design for dc plasma spray guns

A new design is proposed for dc plasma spray gas shroud attachments. It has been found experimentally that the performance of a conventional conical gas shroud is not satisfactory due to the entrainment of the cold air inside the gas shroud. Numerical simulations confirmed this finding. Parameters such as the cone angle and the main gas flow rate can significantly influence the flow pattern inside the nozzle, resulting in air entrainnient and formation of a circulation zone at the exit region. A new design is proposed which can considerably improve the performance of shrouded nozzles. The superior performance of the proposed design has been demonstrated by numerical simulation. The new design is based on a modification of the conical shape by optimizing the profile of the nozzle from a conical shape with a constant angle to a streamlined configuration. The optimized shape was obtained from an analysis of the streamlines of a fixed angle nozzle.     

Plasma contamination with electrode metal vapor jets

Two mathematical models for the anode and the cathode plasma jets are elaborated. It was possible to calculate the jet parameters and to explain the phenomenon of the plasma disk formation. This was confirmed by spectroscopic measurements of copper atoms density distributions.     

Some perspectives on the modeling of plasma jets

A mathematical representation is developed describing the temperature and the velocity profiles and mixing in a plasma jet discharging into ambient air. In the model, realistic allowance is made for turbulent behavior, the temperature-dependent property values, and also for the boundary conditions, including entrainment. The more precise definition of the boundary conditions, mixing, and entrainment are thought to be important novel features of this work. The theoretical predictions were found to be in good agreement with measurements reported by Vardelle regarding the behavior of a nitrogen plasma, but the agreement was less satisfactory for an argon plasma jet. Possible reasons for the discrepancy are discussed.Notation C ₁,C ₂,C _D constants inK- turbulence model - h enthalpy - H ₁ length of integration region - H ₂ width of integration region - K turbulent kinetic energy per unit mass - m mass concentration of plasma - Q _f mass flow rate of plasma gas for flat inlet profiles - Q _P mass flow rate of plasma gas for parabolic inlet profiles - P _w torch power - r radial coordinate - R ₀ internal radius of torch exit - S source term for dependent variable - S _R radiation loss per unit volume of plasma - T _a ambient temperature - T _m maximum temperature - T _t torch tip temperature - u velocity inz-direction - u _{C 1} velocity at and in the direction of the symmetry axis of the flow - u _m velocity of plasma atr=0 andz=0 (maximum velocity) - u axial direction velocity difference across the width of the mixing region - v velocity in r direction - Y radial width of the mixing region - z axial coordinate - density - , _e, _t molecular, effective, and turbulent viscosities, respectively - dissipation rate of turbulence energy - thermal efficiency of plasma torch - Prandtl/Schmidt number forh, K, , andm Visiting Fulbright Scholar and Associate Professor of Chemical Engineering, on leave from the Institute of Chemical Engineering and Technology, Punjab University, Lahore-20, Pakistan.     

Entrainment of cold gas into thermal plasma jets

There is increasing evidence that the entrainment of cold gas surrounding a turbulent plasma jet is more of an engulfment type process rather than simple diffusion. A variety of diagnostic techniques have been employed to determine the development of turbulence in a plasma jet and to measure concentration and temperatures of the cold gas entrained into atmospheric-pressure argon plasma jets in ambient argon or air. The results indicate that the transition to turbulence causes a rapid drop of the axial jet velocity due to entrainment of the cold gas surrounding the plasma jet. Dissipation of the cold engulfed gas bubbles by molecular diffusion is relatively slow if molecular gases (for example air) are entrained, as indicated by conditional sampling and CARS measurements. Temperature measurements using emission spectroscopy and enthalpy probes show strong discrepancies in the jet fringes.