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.

通过冷喷涂工艺成功地沉积聚合物颗粒需要高颗粒温度和低颗粒速度。为了提高粒子温度，一种解决方案是使用相对较长的喷嘴，以增加粒子在喷嘴内的停留时间，并限制超音速流的膨胀。然而，要做到这一点，由于制造限制，必须串联连接几个喷嘴（直到达到所需长度），或者，必须在喷嘴的内部形状中引入不规则性。在这项研究中，我们旨在使用计算流体动力学 (CFD) 分析 240 毫米长喷嘴中心的横截面积减少 20% 喷嘴的效果。在这两个部分的交汇处，会出现几种现象：(i) 阻流器和 (ii) 颗粒在交叉点反弹，导致它们向上游移动。对于直径大于 30 µm 的颗粒，由于惯性和 Saffman 升力的影响较大，有 20% 到 25% 的颗粒在喷嘴内反弹。对于这些粒子，记录到较大的温度和较低的速度。