Hesameddin Safari, Mohammad Hassan Rahimian
University of Tehran,Tehran, Iran
Two-phase gas-liquid flows including phase changes play an important role in many natural and industrial processes. In this work, the multiphase lattice Boltzmann (LB) framework for immiscible and large density ratio flows is extended to include phase change effects. Both liquid and vapor phases are assumed to be incompressible. If evaporation occurs at the phase interface, a new volume of gas is generated. Thus, the divergence-free condition of the velocity field is no longer satisfied. We extend a previous model by a suitable equation to account for the divergence of the velocity field within the interface region. Furthermore, the convective Cahn-Hilliard equation is extended to take into account evaporation effects. Four different distribution functions are incorporated in the model. Two of them are used for recovering the Cahn-Hilliard and momentum equations. Moreover, the temperature and vapor concentration fields are advected by volume averaged macroscopic velocity and!
also computed by two independent distribution functions.
In a first step, a D1Q3 LB model is constructed and validated against the analytical solution of a one-dimensional Stefan problem for different density ratios. Finally the model is extended to two dimensions (D2Q9) to simulate sessile droplet evaporation on a heated substrate. We demonstrate that the results obtained by this new approach are in good agreement with theory. The different modes of sessile droplet evaporation on hydrophobic and hydrophilic surfaces can be captured successfully.