Modeling of Gas Flows in Near-Nozzle Region

For the delivery of atomization gas, different types of nozzles have been employed, such as straight, converging, and converging-diverging nozzles. Two major types of atomizers, i.e., free-fall and close-coupled atomizers, have been used, in which gas flows may be subsonic, sonic, or supersonic, depending on process parameters and gas nozzle designs. In sonic or supersonic flows, the mass flow rate of atomization gas can be calculated with the following equation based on the compressible fluid dynamics  

The power requirement for pressurizing atomization gas may be estimated using the following expression  

Recently, there has been an increasing number of numerical studies on the gas delivery stage 161 163 324 325 496 608 and some experimental measurements in the near-nozzle region. 160 162 169 170 [177][327][608]-[6io] Extensive theoretical, 611 numerical, 161 and experi-mentah170 175 studies on high-speed gas jet flows in the near-nozzle region have been conducted to investigate velocity profiles, pressure distributions, shock waves and flow structures. 

Over the past decade, a number of numerical studies have been performed to model the liquid metal and gas delivery, spray, deposition, and consolidation stages in spray forming. 18] 51 52] 154] 156] 174] 338] 

On the basis of the experimental observations,l160 169 327 Liu[325] conceived a liquid film-sheet breakup model for atomization of liquid metals with close-coupled atomizers. In this atomization model, it was postulated that atomization of a liquid metal with a close-coupled atomizer may occur in the following sequence (1) formation of a liquid film, (2) conversion of the liquid film into a liquid sheet, (3) primary breakup of the liquid sheet into droplets, (4) droplet 

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