MATHEMATICAL-MODELING OF THE ISOTHERMAL IMPINGEMENT OF LIQUID DROPLETS IN SPRAYING PROCESSES

A mathematical representation has been developed and computed results are presented describing the spreading of droplets impacting onto a solid substrate. Problems of this type are of major practical interest in plasma spraying (PS) and in spray forming (SF) operations. While the present study was confined to the fluid flow aspects of the process, information has been generated on both the final splat dimensions and on the time required to complete the spreading process. Through this treatment, it is possible to relate these quantities (the splat size and the spreading time) to the operating conditions, i.e., droplet size and droplet velocity, and material properties. The theoretical predictions were found to be in good agreement with both Madejski's asymptotic solution [17] and with available experimental results. For typical SF conditions (droplet sizes in the 100-mu-m range and droplet velocities in the 100 m/s range), the spreading times were of the order of microseconds, i.e., significantly shorter than the estimated solidification time.