Airflow Dynamics and Aluminum Coating Oxidation Behavior under Electric-Arc Spraying with Airflow Pulsations

The paper aims to investigate the airflow dynamics of electric-arc spraying (EAS) with airflow pulsation. The study is focused on the dynamic structure of the airflow with an obstacle in the form of crossed electrodes at the steady and the pulsating air supply (with a frequency up to 120 Hz). The work was fulfilled using a computer simulation, the airflow “shadow” photo visualization, and the microstructure characterization of the coatings formed. It was found that when air flows along the crossed electrodes with a gap of 2 mm, a depression zone appears in the flow with a pressure drop from 0.56 MPa to 0.01 MPa. The air pulsation resulted in a change in a flow’s dynamic structure towards an increase in the length of the depression zone, which covers most of the arc, affecting the liquid metal oxidation. It is established that the frequency of a droplet formation should match the frequency of the airflow pulsation to minimize the metal oxidation. With the air pulsating at about 65 Hz, the oxide volume fraction in the aluminum coating was reduced by 3.6 times compared to the steady airflow. EAS with airflow pulsation has the potential for technological cost reduction.

Study the Effect of Air Pulsation on the Flame Characteristics

Pulsating combustion is used in a lot of industrial applications like conveyer drying, spray, boilers of commercial scale because its great role in increasing combustion efficiency and producing environmentally friendly combustion products. This paper evaluates how different frequencies (100, 200, 300, 400 and 500) rad/s applied to air velocity view a lot of improvements in the combustion and flow variables (v, T, NO and turbulent kinetic energy) and the effect of adding cross excess air to air pulsation with 500 rad/s frequency on the same flow variables. The performance of pulsating flames was numerically modulated by using Ansys Fluent 16 commercial package by building a 2D combustion chamber of Harwell standard furnace boundary condition on Ansys geometry and divided it into 61000 elements in Ansys meshing 16. Eddy Dissipation Model (EDM) is used to solve transient numerical combustion equations and Detached Eddy Simulation (DES) as viscous model. Converged numerical results have shown that increasing frequency from 100 to 500 rad/s increase average velocities of combustion products and turbulent kinetic energy by 22% and 80 respectively. The pollutant NO decrease by 60% and the time average temperature decrease from 1900 k to 1000 k.

Coupling Vibration Investigation of Cyclone Separator Interacted With Unsteady Fluid

Gas–cyclone body coupling vibration is one kind of vibration caused by air pulsation. This coupling vibration causes widespread damage and deformation of three-stage cyclone separator used in residue fluid catalytic cracking. After theoretically analyzing the mechanism of the generation of the gas–cyclone body coupling vibration, the numerical simulation of three-dimensional swirling flow the cyclone separator was performed by using Reynolds stress model (RSM). The results showed the existence of precessing vortex core (PVC) in the cyclone separator. The PVC phenomenon and motion of PVC were described in detail. Furthermore, the amplitude and frequency of gas fluctuation in the PVC region at different axial positions were quantitatively analyzed. The simulation results agreed with the experimental results of laser Doppler velocimetry (LDV). Finally, characteristics of PVC in cyclone separator with a novel vortex finder were designed, and the results showed that the novel vortex finder can reduce flow vibration.