Liquid-gas coupling cell model based on a single moving superheated droplet and its application to flashing sprays

This study develops a liquid-gas coupling cell model to examine droplet cooling evaporation and motion in flashing sprays, incorporating droplet-droplet interactions and bidirectional liquid-gas coupling through single moving superheated droplet analysis. Experimental validation confirms good consistency, with an error of 17%. The effect of characteristic parameters, such as droplet temperature (T_d0), radius (r_d0), injection velocity (u_d0), ambient pressure (p_a), ambient temperature (T_a), and injection direction, were evaluated. Results show that droplet-droplet interactions significantly inhibit evaporation when the droplet-droplet distance is less than 100r_d0. As evaporation proceeds, the in-droplet heat conduction increases when ε (the thickness of the in-droplet thermal boundary layer) <r_d and decreases once ε=r_d. Latent heat transfer is significant and dominates evaporation. Because of the increased thermal nonequilibrium level, the increasing T_d0 and decreasing p_a enhance evaporation. A 10 K increase in T_d0 increases the evaporation rate by a factor of approximately 1.5 to 3. The decreasing T_a improves evaporation by the increased temperature difference. The enhanced evaporation by larger T_d0 increases the drag force and slows the motion more rapidly. The enhanced evaporation by decreasing p_a results in a smaller drag force. Decreasing r_d0 increases evaporation due to the larger specific surface area and lower thermal conductivity resistance while leading to a smaller drag force. The increasing u_d0 enhances evaporation via enhanced interfacial heat transfer. The injection direction has little influence on evaporation. The droplet travelling upward has a larger deceleration rate and a shorter distance.