A device for mixing and for evaporating, and/or for the reaction of, a plurality of fluids, wherein a mixing, evaporating and/or reacting region is formed by the annular gap between concentrically nested cylindrical and/or conical tube sections, which are heated electrically and/or by means of a heat transfer medium, and the plurality of fluids are supplied distributed across the circumference, and/or length, together or successively, such that the plurality of fluids mix with one another, the supply or removal of heat and the mixing location being selected such that the plurality of fluids either do not evaporate, or evaporate before, during or after being mixed.