The meaning of the expression ''as hell'' according to the free dictionary is to a great extent, or to add emphasis in some adjectives like mad, angry frustrated and so on. I would translate it as: furioso pra caralho, pra cacete, pra merda and other ways. There's another expression similar to this one, that is, ''as f*ck'' and it has basically the same meaning but it's stronger than ''as hell''
sometimes it doesnt make sense the use of '' as hell'' in some sentences like the ones below but it is used anyway.
Ex: It's cold as hell outside the house.
Ex: Esta frio pra caralho do lado de fora da casa.
Ex: This kid is smart as hell he got all the questions right.
Ex: Esse garoto e inteligente pra merda ele acertou todas as questoes.