A molecular dynamics study on thin film phase change characteristics over nano-porous surfaces with hybrid wetting conditions

Liquid-vapor phase change characteristics over nanoporous substrates with different surface morphologies as well as wettability variations have been investigated in the present study. Non-equilibrium molecular dynamics (NEMD) simulations have been performed for a nanoscale domain consisting of argon (Ar) liquid and vapor over a square patterned nanoporous platinum (Pt) substrate. For the nanoporous substrates, three different pore heights and three different base (B)- substrate (S) wetting conditions are considered, namely uniformly wetted hydrophilic surface (BphiSphi), hydrophilic base with hydrophobic substrate (BphiSpho), and hydrophobic base with hydrophilic substrate (BphoSphi). Initially, the whole simulation system is equilibrated, followed by a linear heating of the platinum wall to induce liquid vapor phase change. For all cases under consideration, evaporation, diffusion, heat transfer and adsorption characteristics are evaluated to compare and contrast the phase change behavior among the surfaces. It is observed that the nanoporous structure improves the heat transfer phenomena compared to flat surfaces. Local heat accumulation inside the pore depends on both pore height and wetting conditions, so the initial bubble nucleation and growth pattern depend on these parameters significantly. However, for higher pore heights, both the BphiSphi and BphoSphi surface patterns provide nearly similar transport characteristics.