Experimental determination of the relationship between flattening degree and Reynolds number for spray molten droplets

Copper powders were selected to create splats of a regular disk shape by plasma spraying on a preheated flat substrate surface. Copper powders of a small size range with a regular spherical shape were used to ensure a valid mean particle size. The particle velocity and temperature were measured based on the thermal radiation from particle surface. The flattening degrees were estimated using the average diameter of splats and spray particles for different spray conditions. The relationship between the flattening degree (ξ) and the Reynolds number (Re) for the spray molten droplet was examined experimentally using exponential formulas with different power factors as reported in the literature. The results revealed that the equation ξ =1.21 Re^0.125 determined by the experimental data rather than other equations with the power factors of 0.2 and 0.25 to Reynolds numbers is applicable to reasonably estimate the flattening degree of the spray molten droplet in a wide range of the Reynolds numbers. This range, from several hundreds to several ten thousands, covers typical molten metallic droplets and oxide ceramic droplets in thermal spraying.