Characterization of a spray torch and analysis of process parameters

Visualization studies of the spray from swirl injectors under elevated ambient pressure

In order to further improve the efficiency of spray dust removal in tunnel and obtain favorable equipment parameters, the dust removal performance of high pressure spray atomization particle size was deeply studied. Taking the dust generated in Tiantai Mountain tunnel as the research object and combining with the numerical simulation method. Based on FLUENT pressure-swirl atomization model, in this paper, the mechanism of high pressure spray dust reduction is analyzed. The pressure nozzle is simulated at 4 pressures (2, 3, 4, 5 Mpa) and 3 nozzles (2.0, 1.5, 1.0 mm in diameter). The simulation results show that when the nozzle diameter is constant, the droplet size decreases with the increase of pressure, and the atomization effect is better. When the spray pressure is constant, the droplet size increases with the increase of nozzle diameter. According to the measured results of dust in Tiantai Mountains, it is suggested that the nozzle diameter should be 1.5 mm and the working pressure should be 4 Mpa, which can reasonably and effectively settle the fine particles of dust in the tunnel.

Pulsed high-velocity water jets are of interest for breaking rocks and other materials. This paper describes a straightforward way of generating single water pulse with a hammer impacting a piston that rests on top of a chamber filled with water. This impacting action pressurises the water, expelling it at high velocity through a nozzle. A theoretical investigation is outlined aimed at gaining a better understanding of this system for generating water pulses. A computational model is developed to simulate the pressure dynamics in the chamber based on continuity and momentum equations for a compressible viscous flow. This model is used to optimise the relative sizes of the hammer and piston as well as the height of the water column to produce the highest velocity water pulse. The model was validated by building an experimental apparatus. In these experiments maximum pressures of about 200 MPa were measured inside the chamber over a time period of about 560 μs. This produced a water pulse with maximum velocity of 600 m/s. Experiments were conducted with nozzle diameters between about 1 mm and 4 mm to study the effect of discharge volume on the pressure history. The results illustrate that although the peak attainable pressure decreases with an increase in nozzle diameter, the duration of the elevated pressure remains similar for all nozzles.

Low interfacial tension liquid–liquid extraction with impinging-jets contacting method: Influencing parameters and relationship

The arc root fluctuations at the anode-nozzle of a d.c. plasma spray torch with a special configuration of the electrodes allowing to work with the same gas flowrate with nozzle diameters ranging from 6 to 10 mm were systematically studied. The plasma gas was Ar/H2 (25 vol % H2), the current was varied between 200 and 600 A and the plasma gas flowrate between 24 and 80 slm. After 30–60 mn working the nozzle wall started to be sufficiently eroded to have a stagnant arc spot which lived until arcing created another one. It was shown that the life time of the upstream arc spots were 30–40 % longer than the downstream ones which could play an important role in the electrode erosion. Dimensional analysis allowed to find a relationship between the nozzle diameter D, the arc current I and gas flow rate G and the mean spot lifetime which is closely connected with the difference between D and the electrical diameter of the arc column. The comparison of voltage signal and light emission at a point of the plasma jet close to the nozzle exit on its axis allowed to determine the mean electrical field within the plasma column and the mean position of the arc root. The comparison with the electrode erosion area for well defined conditions showed a good correlation with the calculated arc root position.

Very low pressure plasma spraying has been intensively studied in recent years especially the properties of plasma jet. These properties are affected by plasma generating and working conditions. These operating parameters such as arc power, plasma gas flow rate and chamber pressure have influences on specific enthalpy and temperature of plasma jet. In this work, the measurements under very low pressure were performed using enthalpy probe which was previously modified (increase of the internal diameter and depositing TBC coating (Ni/Al and ZrO2+ Y2O3) on the head). Different parameters, for instance, current intensity, hydrogen gas flow rate and detecting distance were changed in order to point out their effect on the characteristics of plasma jet. The specific enthalpy, temperature and quantity of heat in this situation were obtained.

In the plasma welding, the welding conditions, that is nozzle diameter, composition and flow rate of plasma gas and cover shield gas, welding current and travelling speed, must be selected according to material and thickness of the work. In the plasma arc welding of stainless steel, we discovered that the range of proper welding condition is remarkably affected by the quality of the back. shield gas.To study the effect of the composition of back shield gases on the forming of back beads, we examined plasma arc welding of 304 stainless steel (t=9 mm), with various back shield gases of Ar, N2, CO2, Ar mixed CO2, Ar mixed O2, N2 mixed CO2, and N2 mixed O2.A summary of the results is shown below.(1) When O2 or CO2 is mixed to inert gas as back shield gas, the length of back plasma flame is shorter than in the case of pure inert gas. There is a tendency of the flame be coming shorter according to the amount of O2 or CO2 mixed to inert gas.(2) When we used inert gas that is Ar or N2 as back shield gas, the range of proper welding condition is very narrow. Therefore welding work is very difficult. But the range of proper welding condition is remarkably expanded by mixing of oxidizing gas that is O2 or CO2 to inert gas.(3) By mixing of 10% O2 or 30% CO2 with Ar, the range of proper welding condition becomes maximum. With mixing of over 50% O2, the back bead is severely oxidized, spatter increase, undercut and concave occur at the back bead.(4) Indifferently to the composition of back shield gas, the cross section of welded metal appeared wine cup. And microstructure, hardness and corrosion resistibility of the welded metal were not affected by the composition of back shield gas.

Micronization of cyclosporine using dense gas techniques

Numerical study on flow and heat transfer characteristics of the double-hole jet in flowing liquid

Water cluster ion intensity and distribution is affected by source conditions in direct sample analysis (DSA) ionization. Parameters investigated in this paper include source nozzle diameter, gas flow rate, and source positions relative to the mass spectrometer inlet. Schlieren photography was used to image the gas flow profile exiting the nozzle. Smaller nozzle diameters and higher flow rates produced clusters of the type [H + (H(2)O)(n)](+) with greater n and higher intensity than larger nozzles and lower gas flow rates. At high gas flow rates, the gas flow profile widened compared with the original nozzle diameter. At lower flow rates, the amount of expansion was reduced, which suggests that lowering the flow rate may allow for improvements in sampling spatial resolution.

Numerical analysis was performed on the laminar thermal plasma flow of a constricted cascaded arc plasma generator with a larger ratio of radius and pipe length compared to previously used arc plasma generators. The numerical results concerning plasma temperature and velocity were compared with the experimental data measured using the probes methods. The effects of the mass flow rate of the plasma gas and the supplied current on plasma temperature, velocity, and current at a cross section of the plasma torch are clarified. These effects on plasma temperature and current density are estimated to be small when using a numerical model employing a single flow and a single temperature without taking into account the effects of the collision and dispersion of plasma gas particles. Except for the large mass flow rate of plasma gas, the numerical results for the plasma velocity are almost identical in magnitude to the experimental data.

Impingement and breakup characteristics of free opposed impinging jets with unequal nozzle diameter

Experimental and numerical studies of nozzle effect on powder flow behaviors in directed energy deposition additive manufacturing

<div class="section abstract"><div class="htmlview paragraph">As known, the constant injection mass is a criterion for measuring the thermal efficiency of diesel engines. In this study, the effects of nozzle hole diameter on diesel free-spray characteristics were investigated in constant injection mass condition. The experiment was performed in a constant volume combustion chamber equipped with a high pressure common-rail injector that can change nozzles. Three single-hole axis nozzles with different hole diameters were used. High speed camera and Schlieren visualization set-up were used to capture the spray behaviors of liquid phase and vapor phase respectively. For liquid phase spray, the higher nozzle hole diameter, the higher were the liquid phase spray penetration rate and the saturated liquid phase spray penetration length. The saturated liquid phase spray penetration length wound not grow but oscillate around different mean values at the steady stage. In addition, the increase of nozzle hole diameter increased the saturated liquid phase spray cone angle. For vapor phase spray, the variation laws of vapor phase spray penetration lengths could be divided into nonlinear increase period and linear increase period. The effects of nozzle hole diameter on vapor phase spray penetration rate were negligible in the nonlinear increase period, but the higher nozzle hole diameter, the higher was the vapor phase spray penetration rate in the linear increase period. The higher nozzle hole diameter, the higher were the increase-rate of vapor phase spray cone angles and the saturated vapor phase spray cone angles. The reduction of nozzle hole diameter increased the pure vapor phase spray penetration tip length.</div></div>

Voltage, current, acoustic pressure and light fluctuations from a plasma torch were recorded and analysed by fast Fourier transform (FFT). These measurements were performed for three nozzle diameters, and varying the argon plasma gas flow rate up to 30 l/min. At high flow rates the results confirm the observations depicted in the litterature concerning the good correlation between these different signals. At low gas flow rate a peak in the acoustic pressure spectra which maximum intensity coincide with the laminar-turbulent transition could be used to characterize this transition.