Numerical investigation of droplet impact on heated surfaces with pillars

This work proposes an improved three-dimensional double multiple relaxation time lattice Boltzmann model that can correctly recover the macroscopic temperature equation. Using this model, the impact of a droplet on a heated surface with pillars is simulated, and the effects of pillar width (w) and distance between pillars (b) are analyzed in detail. Four boiling droplet types are numerically reproduced, namely, deposition boiling, contact boiling, transition boiling, and film boiling. In the deposition boiling regime, no vapor bubble generation is observed within the droplet, but secondary droplets are generated at the periphery of the droplet due to the sharp geometric profile of the pillars and the differences in the rate of evaporation. The difference between contact boiling and transition boiling lies in whether the droplet is always in contact with the surface. For conditions with large w values, contact boiling is not observed, due to the high-pressure peaks from below, while for smaller w, a transition from deposition boiling to transition boiling, then to contact boiling, and subsequently to transition boiling can be observed. Two obvious vortices are found in the center of the liquid film with decreased b, which results in bubble nucleation even at low Ja values. In addition, boiling may take place, in which a stable vapor layer is formed between the droplet and the surface by increasing Ja, which leads to a significant reduction in the heat transfer efficiency. Published under an exclusive license by AIP Publishing.

Automated summary

This work proposes an improved three-dimensional double multiple relaxation time lattice Boltzmann model that accurately recovers the macroscopic temperature equation. The model is used to simulate the impact of a droplet on a heated surface with pillars and analyze the effects of pillar width and distance between pillars. The results show four boiling droplet types, and provide insights into their characteristics and transitions.