Attempt to answer from 4 years later ...
(1) I think the easiest way is to use a Pipe block. Attach the right amount of thermal mass to the H port to represent the thermal mass of the granules. At the same time, estimate the hydraulic diameter and cross section area of your "pipe" so you get about right area for heat transfer with the granules. Basically, you can treat the granules as part of the pipe wall.
(2) the moist air domain would be more appropriate. At the same time, you'll likely need to write your custom Simscape block or equations to define the water removal process. The enthalpy change on the moist air side is handled automatically if you use a moist source block to add or remove water from the moist air.
