In this work the VOF model is used to track interface between the droplet and the air by assuming immiscible fluids.
The momentum equation is used for air and droplet not for substrate. The energy equation is solved for whole domain. Surface tension at free surfaces is modeled using the continuum surface force (CSF) model 14. SIMPLE method is used to solve discretized energy and momentum, a method in which the pressure Poisson equation (PPE) is solved.
The existence of phase change in the numerical calculations poses a challenge because it is a mathematical discontinuity. There are two popular approaches to the solution of this problem: The Stefan approximation, it predicts the precise location of the solid/liquid interface and, the enthalpy method, used when the phase-change front is known to occur within a known interval. Stefan approximation requires the use of a deforming grid or transformed coordinate system. The enthalpy formulation allows a fixed grid to be used in the solution.
Also, it removes the need to explicitly satisfy conditions at the phase-change front, thus making it suitable for use in standard solution procedures