Dear professors，
I have try to run the process and it worked without error, but its result seems not right. In the spray region is H2O, which were flowed onto the outside of the bed under the inlet air velocity 1m/s. This seems abnormal.
plate.zip (71.3 KB)
The density is computed automatically based on ideal gas law, using the air and water molecular weights. I am not sure about what you feel is an abnormal result, but your mesh is too coarse to accurately locate the top boundary conditions. The grid spacing in the x-direction is 6mm and the smallest MI is 5 mm wide. You also have inlets and outlet at the same y-location so it may create backflows. Double check the gas viscosity value, it seems a bit high.