Properties of acoustic resonance in double-actuator ultra-sonic gas nozzle:numerical study

The ultra-sonic gas atomization （USGA） nozzle is an important apparatus in the metal liquid air-blast atomization process. It can generate oscillating supersonic gas effiux, which is proved to be effective to enforce the atomization and produce narrow-band particle distributions. A double-actuator ultra-sonic gas nozzle is proposed in the present paper by joining up two active signals at the ends of the resonance tubes. Numerical sim- ulations axe adopted to study the effects of the flow development on the acoustic resonant properties inside the Haxtmann resonance cavity with/without actuators. Comparisons show that the strength and the onset process of oscillation are enhanced remarkably with the actuators. The multiple oscillating amplitude peaks are found on the response curves, and two kinds of typical behaviors, i.e., the Hartmann mode and the global mode, are discussed for the corresponding frequencies. The results for two driving actuators are also investigated. When the amplitudes, the frequencies, or the phase difference of the input signals of the actuators are changed, the oscillating amplitudes of gas effiux can be altered effectively.

Simulation and experiment investigations on fabrication of Fe-based amorphous powders by a novel atomization process equipped with assisted gas nozzles

Based on computational fluid dynamics method,the effect of atomization gas pressure on the atomization efficiency of Laval nozzle was studied,and then a discrete phase model was established and combined with industrial trials to study the effect of a new type of assisted gas nozzles(AGNs)on powder size distribution and amorphous powder yield.The results show that increasing the atomization pressure can effectively improve the gas velocity for the Laval nozzle;however,it will decrease the aspiration pressure,and the optimal atomization pressure is 2.0 MPa.Compared with this,after the application of AGNs with the inlet velocity of 200 m s^(-1),assisted gas jet can increase the velocity of overall droplets in the break-up and solidification area by 40 m s^(-1) and the maximum cooling rate is increased from 1.9×10^(4) to 2.3×10^(4) K s^(-1).The predicted particle behavior is demonstrated by the industrial trails,that is,after the application of AGNs,the median diameter of powders d50 is decreased from 28.42 to 25.56 lm,the sphericity is increased from 0.874 to 0.927,the fraction of amorphous powders is increased from 90.4% to 99.4%,and only the coercivity is increased slightly due to the accumulation of internal stress.It is illustrated that the AGNs can improve the yield of fine amorphous powders,which is beneficial to providing high-performance raw powders for additive manufacturing technology.

Effect of gas blowing nozzle angle on multiphase flow and mass transfer during RH refining process

A three-dimensional mathematical model was developed to investigate the effect of gas blowing nozzle angles on multiphase flow,circulation flow rate,and mixing time during Ruhrstahl-Heraeus(RH) refining process.Also,a water model with a geometric scale of 1:4 from an industrial RH furnace of 260 t was built up,and measurements were carried out to validate the mathematical model.The results show that,with a conventional gas blowing nozzle and the total gas flow rate of 40 L·min^(-1),the mixing time predicted by the mathematical model agrees well with the measured values.The deviations between the model predictions and the measured values are in the range of about 1.3%–7.3% at the selected three monitoring locations,where the mixing time was defined as the required time when the dimensionless concentration is within 3% deviation from the bath averaged value.In addition,the circulation flow rate was 9 kg·s^(-1).When the gas blowing nozzle was horizontally rotated by either 30° or 45°,the circulation flow rate was found to be increased by about 15% compared to a conventional nozzle,due to the rotational flow formed in the up-snorkel.Furthermore,the mixing time at the monitoring point 1,2,and 3 was shortened by around 21.3%,28.2%,and 12.3%,respectively.With the nozzle angle of 30° and 45°,the averaged residence time of 128 bubbles in liquid was increased by around 33.3%.

Resonant behaviors of ultra-sonic gas atomization nozzle with zero mass-flux jet actuator

The resonant behaviors of an ultra-sonic gas atomization nozzle with a zero mass-flux jet actuator were numerically investigated with FLUENT software by using a double precision unsteady two-dimensional pressure-based solver. The Spalart-Allmaras turbulence model was adopted in the simulations. Numerical results indicated that the oscillation properties of the gas efflux were effectively improved. Several resonatory frequencies corresponding to different vibration modes of gas were distinguished in the nozzle. With the changing of nozzle geometric parameters, different characters among those modes were elucidated by analyzing the propagations of pressure waves.