Abstract During cold dynamic gas spray additive manufacturing, the thermal field within particles is generally simplified by a state of an instantaneous uniform distribution over the particle's media at any position inside and outside the De-Laval nozzle. This paper addresses critical discussions using analytical and computational analysis of the transient heat transfer within the solid particles due to the convective exchange with the flowing gas. An analytical criterion depicts conditions of instantaneous uniform temperature over the range of typical cold spray data including various particle thermal conductivity, particle size range, dragging velocities, gas nature and gas setting conditions. The analytical depiction draws the conclusion that, during cold spraying, the temperature field within particles is mostly instantaneously uniform. The notion of instantaneousness is further investigated via computational analysis of the transient thermal gradient regimes within particles. The phenomenological computations enable to characterize the duration of the transient stage prior to the state of uniform temperature. Comparisons with analytical particle's residence time using various scales of travelled distance give a more relevant notion of instantaneousness. The particle temperature is not strictly instantaneously uniform. However, such instantaneousness prevails for a covered distance unit of 1 mm which is widely enacted in the literature to compute the particles temperature during cold spraying. As conclusive remarks, issues due to this instantaneousness of the particle temperature are reviewed and suitable alternatives for efficiently heating the particles during cold spraying are reported.

中文翻译：

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冷喷涂增材制造过程中固体测微粉末的飞行温度

摘要 在冷动态气体喷涂增材制造过程中，颗粒内的热场通常通过在 De-Laval 喷嘴内外任何位置的颗粒介质上瞬时均匀分布的状态来简化。由于与流动气体的对流交换，本文使用分析和计算分析对固体颗粒内的瞬态热传递进行了批判性讨论。分析标准描述了在典型冷喷涂数据范围内瞬时均匀温度的条件，包括各种颗粒热导率、颗粒尺寸范围、拖曳速度、气体性质和气体设定条件。分析描述得出的结论是，在冷喷涂过程中，颗粒内的温度场几乎是瞬时均匀的。通过对粒子内瞬态热梯度状态的计算分析，进一步研究了瞬时性的概念。现象学计算能够表征均匀温度状态之前的瞬态阶段的持续时间。使用各种移动距离尺度与分析粒子的停留时间进行比较，给出了更相关的瞬时概念。粒子温度不是严格地瞬时均匀的。然而，对于 1 毫米的覆盖距离单位，这种瞬时性普遍存在，这在文献中被广泛制定以计算冷喷涂过程中的颗粒温度。作为总结性评论，