Droplet Deformation and Evaporation on a Hot Surface

Chandra and Avedisian 411] studied the collision dynamics of a liquid (n-heptane) droplet on a polished, solid, stainless steel surface, and on a liquid film created by deposition of a preceding droplet using a flash photographic method. They presented a comprehensive series of clear images of droplet shape, morphology, and structure during the deformation process. In their experiments, the 

In a subsequent study, Chandra and Avedisian13851 investigated droplet impingement on a ceramic porous surface. It was found that the spreading rate of a droplet on the porous surface at 22 °C is lower than that on the stainless steel surface, and for a given temperature the maximum spread diameter is smaller on the ceramic surface 

On the basis of experimental observations (Fig. 3.27), Senda et al.[335h415] proposed six modes for water droplet deformation, and breakup during impingement on a hot surface coupled with heat transfer and evaporation (Fig. 3.28). Each mode occurs under a specific combination of surface temperatures and impact conditions, as described below. 

Type R. This mode corresponds to low impinging velocities at any surface temperatures considered (200-400 °C). A droplet spreads as a radial film after impinging on a hot surface. Then, it shrinks and rebounds from the surface without breaking up. Hence, the mode is called R type. 

Type H. Further increasing droplet diameter and/or impinging velocity from the level in type N, the number of spots where the vapor blows through the radial film increases as compared to that in type N. Small droplets blown by the vapor are distributed even over the radial film, but the blowing-through of the vapor is weaker than in the type N. The pieces of the broken radial film that remain on the substrate surface are similar to those in type N. 

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