Studying the Effect of the Air-Cap Configuration in Twin-Wire Arc-Spraying Process on the Obtained Flow Characteristics
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JTTEE5 24:46–54 DOI: 10.1007/s11666-014-0183-1 1059-9630/$19.00 Ó ASM International
Studying the Effect of the Air-Cap Configuration in Twin-Wire Arc-Spraying Process on the Obtained Flow Characteristics Using Design of Experiment Oriented Fluid Simulation W. Tillmann, M. Abdulgader, N. Anjami, and L. Hagen (Submitted June 11, 2014; in revised form October 6, 2014) The computational fluid dynamics approach is adopted in this work using the design of experiments to reveal the effect of the air-cap configurations on the obtained gas velocity, the shear stresses, the high velocity zone, and the convergence of the obtained spraying plume in the twin-wire arc-spraying process. The parameters, which are revealed to optimize the air-cap configuration, are the throat diameter, the convergence angle of the throat inlet, the throat length, and the distance between the throat outlet and the intersection point of the approaching wires. The throat length is dependent upon the other configuration parameters. Outlet gas velocity, the turbulence in the flow, and the exerted shear stresses at wire tips are directly affected by the dominating flow regimes near the intersection point of the approaching wires. The presence of wires and the contact tips in the gas flow has enormous impact on the obtained flow characteristics. Air-cap throat diameter and the distance between throat outlet and intersection point determine the shape and length of the obtained high velocity zone in the spraying plum.
Keywords
atomization, analytical model, computational fluid dynamics, fluid dynamics, nozzle design, wire arc spray
1. Introduction Thermal and kinetic energy are the main driving forces behind the deposition mechanism of the thermal-sprayed coatings. The main properties of the obtained coating are determined by the parameters, which control the ‘‘particle formation,’’ the obtained in-flight particles characteristics (velocity, temperature, and size) and thus the flattening behavior of droplets on a prepared substrate surface (Ref 1-3) as shown in Fig. 1. The size and shape of the in-flight particles by thermal spraying techniques using powder feedstock (like in plasma and HVOF) is predefined by the size distribution and shape of the used powders. The powder particles are finely divided by means of carrier gas This article is an invited paper selected from presentations at the 2014 International Thermal Spray Conference, held May 21-23, 2014, in Barcelona, Spain, and has been expanded from the original presentation. W. Tillmann, Chair of Materials Engineering, University of Dortmund, Dortmund, Germany; and M. Abdulgader, N. Anjami, and L. Hagen, Institute of Materials Engineering, Dortmund University of Technology, Dortmund, Germany. Contact e-mail: [email protected].
46—Volume 24(1-2) January 2015
as they injected into the flame and subsequently through the flame jet, where a heating and acceleration takes place. In case of twin-wire arc-spraying (TWAS) process, the in-flight particles are initiated out of a melting bath at the
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