1)is there reicha in microwaves?
2) if yes, does residue on the walls of microwaves present an issue of reicha?
1. If both foods are cooked in the microwave together there will be reicha.
- I am not sure if the small amount of residue on the walls will be an issue of reicha. However it is only theoretical, because the main issue in a microwave is the zeiah, (steam) that comes out of the food when the microwave heats it up. In order to use the microwave you would have to cover the item, and make sure that no drips will get on to the plate underneath it. Therefore if you are going to heat something fleishig in a milchig microwave it would need to be covered, and a fleichig glass under it. When the food is covered there will be no issue of reicha.
See Pischei Halacha –Kashrus pg 232.