In Adapt, you can create an adaption register marking cells that have a volume fraction of one phase between 0 and 0.5. Therefore, the iso-min value should be 0 and the iso-max value should be 0.5. With this adaption register, which will be created when you have clicked on “Save”, the wall-zones can be separated. Under mesh/separate/faces, the register can be selected (option: mark). For the separated (wetted) surface, the area-integral can be calculated via Report/Results Reports/Surface Integral.