  Multiphase flows frequently occur in many important engineering and
scientific applications, but modeling of such flows is a rather challenging
task due to complex interfacial dynamics between different phases, let alone if
the flow is oscillating in the porous media. Using humid air as the working
fluid in the thermoacoustic refrigerator is one of the research focus to
improve the thermoacoustic performance, but the corresponding effect is the
condensation of humid air in the thermal stack. Due to the small sized spacing
of thermal stack and the need to explore the detailed condensation process in
oscillating flow, a mesoscale numerical approach need to be developed. Over the
decades, several types of Lattice Boltzmann (LB) models for multiphase flows
have been developed under different physical pictures, for example the
color-gradient model, the Shan-Chen model, the nonideal pressure tensor model
and the HSD model. In the current study, a pseudopotential
Multiple-Relaxation-Time (MRT) LBM simulation was utilized to simulate the
incompressible oscillating flow and condensation in parallel plates. In the
initial stage of condensation, the oscillating flow benefits to accumulate the
saturated vapor at the exit regions, and the velocity vector of saturated vapor
clearly showed the flow over the droplets. It was also concluded that if the
condensate can be removed out from the parallel plates, the oscillating flow
and condensation will continuously feed the cold surface to form more water
droplets. The effect of wettability to the condensation was discussed, and it
turned out that by increasing the wettability, the saturated water vapor was
easier to condense on the cold walls, and the distance between each pair of
droplets was also strongly affected by the wettability.
