Influence of the nozzle inner geometry on the particle history during cold spray process
Résumé
High particle temperature and low particle velocity are required to successfully deposit polymer particles by cold spray process. To increase the particle temperature, a solution is to use a relatively long nozzle to increase the particle resident time inside the nozzle and limit the expansion of the supersonic flow. However, to do this, due to manufacturing limitations, several nozzles must be attached in series (until the desired length is reached), or alternatively, irregularities must be introduced into the inner shape of the nozzle. In this study, we aim to analyze the effect of 20% nozzle reduction of cross section area at the center of a 240 mm long nozzle using computational fluid dynamics (CFD). At the intersection between the two sections, several phenomena take place: (i) the flow chokes and (ii) particles rebound at the intersection leading them to go upstream. For particles with a diameter larger than 30 µm, 20 to 25% of the particles rebound inside the nozzle due to the larger influence of the inertia and the Saffman lift force. For these particles, larger temperature and lower velocity is recorded.
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