Numerical Analyses of Fluid Dynamics of an Atomization Configuration
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G. Trapaga Laboratory of Investigation in Materials of CINVESTAV-IPN, Unidad Quertaro, C.P. 76230, Quertaro, Qro., Mexico
N. Yang Organization 8715, Sandia National Laboratories, 7011 East Avenue, P.O. Box 969, Livermore, California 94550
E.J. Lavernia Department of Chemical and Biochemical Engineering and Materials Science, University of California, Irvine, California 92697 (Received 2 November 2000; accepted 29 October 2001)
Computational fluid dynamic techniques were used to analyze the gas flow behavior of a typical atomization configuration. The calculated results are summarized as follows. The atomization gas flow at the atomizer’s exit may be either subsonic at ambient pressure or sonic at an underexpanded condition, depending on the magnitude of the inlet gas pressure. When the atomization gas separates to become a free annular gas jet, a closed recirculating vortex region is formed between the liquid delivery tube and the annular jet’s inner boundary. Upon entering the atomization chamber, an underexpanded sonic gas flow is further accelerated to supersonic velocity during expansion. This pressure adjustment establishes itself in repetitive expansion and compression waves. A certain protrusion of the liquid delivery tube is crucial to obtain a stable subatmospheric pressure region at its exit. The vortex flow under the liquid delivery tube tends to transport liquid metal to the high kinetic energy gas located outside the liquid delivery tube, thereby leading to an efficient atomization.
I. INTRODUCTION
Gas atomization is a material processing technique widely used to produce many types of metallic powders such as aluminum, copper, and iron, as well as their alloys.1–3 During atomization, a stream of molten metal is broken into fine droplets by high-velocity gas jets, and the powder particles obtained are typically characterized by low-segregation and refined microstructure. Under an inert environmental atmosphere, the powder particles are spherical with low oxidation. Recently, gas atomization has been increasingly used to economically produce fine metallic powders, to explore new alloy powders, and to provide a mass source for spray forming. Fine powder particles have many potential applications.4,5 Fine spherical powder particles may be used in powder injection modeling and thermal spraying where flowability is required, and powder particles with a mean size of less than 10 m may be used to produce ferrofluids, magnetic 156
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J. Mater. Res., Vol. 17, No. 1, Jan 2002 Downloaded: 19 Mar 2015
recording tapes, conductive pastes, and conductive plastics. Nickel/metal hydride (Ni/MH) rechargeable battery is an exciting replacement for Ni/Cd battery because of its extended cycle life, enhanced energy storage capacity, and reduced environmental hazard. Hydrogen induced fracture is a critical factor resulting in Ni /MH battery degradation after repeated recharging cycles. Related studies show that fine spherical powder particles produced by gas atomization have advantages of a
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