Numerical and experimental modelling of back stream flow during close-coupled gas atomization

Abstract

This paper reports the numerical and experimental investigation into the effects of different gas jet mis-match angles (for an external melt nozzle wall) on the back-stream flow in close coupled gas atomization. The Pulse Laser Imaging (PLI) technique was applied for visualising the back-stream melt flow phenomena with an analogue water atomizer and the associated PLI images compared with numerical results. In the investigation a ConvergentDivergent (C-D) discrete gas jet die at five different atomization gas pressures of 1 to 5 MPa, with different gas exit jet distances of 1.65, 1.6, 1.55, 1.5, 1.45 and 1.40 mm from the melt nozzle external wall, was combined with four melt nozzles of varying gas jet mis-match angles of 0, 3, 5, and 7 degrees relative to the melt nozzle external wall (referred to as nozzle types 1 to 4). The results show that nozzle type 1 with the smallest mis-match angle of zero degrees has highest back-stream flow at an atomization gas pressure of 1 MPa and a gas die exit jet located between 1.65 mm to 1.5 mm from the external melt nozzle wall. This phenomenon decreased with increasing mis-match angle and at higher atomization gas pressure. For nozzle type 2, with a mis-match angle of 3 degrees, a weak back-stream flow occurred with a gas exit jet distance of 1.65 mm from the melt nozzle external wall. For a gas pressure of 1 MPa with a decrease in the gas jet exit distance from the external wall of the melt nozzle this phenomenon was eliminated. This phenomenon was not seen for nozzle types 3 and 4 at any gas pressure and C-D gas exit jet distances.

Review of the Methods for Production of Spherical Ti and Ti Alloy Powder

“…13 The technique of close-coupled gas atomization (CCGA) was developed to increase the yield of fine powder. 23 As shown in Fig. 4b, the melt is disintegrated by the direct impact of high-pressure gas right below the tip of an extended melt guide tube.…”

Numerical and Experimental Investigations of the Effect of Melt Delivery Nozzle Design on the Open- to Closed-Wake Transition in Closed-Coupled Gas Atomization

“…It was established that the results where the mesh containing 11000 elements or more were acceptably mesh independent and these were subsequently used for the simulations reported here. More details of mesh independence study are discussed in Motaman et al [11].…”

“…The SST kmodel has been applied in the results presented here to close the Reynolds stress terms in the turbulence model. The CFD sensitivity to the turbulence model used is considered in more detail by Motaman et al [11]. The molten metal was omitted from the model as the aim of this study is to understand the simplified situation of the high-velocity gas jet flow behaviour around the melt delivery nozzle.…”

Performance Testing and Rapid Solidification Behavior of Stainless Steel Powders Prepared by Gas Atomization

“…The fast fluid velocity, high temperature, and the lack of an effective observation method make it complex and difficult to research. It is generally belbived that the gas atomization process involves four stages [ 6 , 7 ]: (1) the break-up of a liquid column into ligaments; (2) the break-up of ligaments into droplets, which is known as primary breakup; (3) the breakup of droplets into smaller droplets, which is called secondary breakup; (4) the spheroidization and solidification of the droplets into powders.…”

“…Atomization breakup is often studied by computer numerical simulation. Many studies have used computational fluid dynamics (CFD) software [ 8 ], like Fluent of ANSYS (ANSYS, Inc., Canonsburg, PA, USA), to calculate the influence of various parameters on atomization flow fields [ 9 , 10 , 11 ]. There are also some analysis methods based on optical principles for measuring the shape and velocity of particles in a flow field, which is called visualization research, e.g., high-speed imaging, particle imaging velocity field meters, etc.…”