NOVELTY - Integrated reactor (10) has two separated channel structures for guiding two streams of fluid. In at least one stream within a reaction area (16), a reaction produces a variation in temperature and at the same time heat transfer between the streams. At least one of the two streams is received in a dosed manner, and the other fluid is distributed throughout the reaction area.    USE - Evaporation of energy and superheating in mobile, e.g. vehicle, and fixed fuel cell systems (claimed), and selective oxidation of carbon monoxide in fuel cell systems (claimed).    ADVANTAGE - The integrated reactor allows the flow of two streams of fluid, one in a dosed manner and the other to be distributed across a reaction area with simultaneous heat transfer between the fluids. It ensures efficient coupling of the heat exchange operation.    DETAILED DESCRIPTION - An integrated reactor (10) has two separated channel structures for guiding two streams of fluid. In at least one stream within a reaction area (16), a reaction produces a variation in temperature and at the same time heat transfer between the streams. At least one of the two streams is received in a dosed manner, and the other fluid is distributed throughout the reaction area. The dosing operation is carried out by a structure comprising a metal or plastic perforated film, or by a porous ceramic structure.    INDEPENDENT CLAIMS are also included for:    (1) a method for conducting in a precise manner a reaction in the integrated reactor;    (2) application of the integrated reactor for the efficient evaporation and superheating in fuel cell systems; and    (3) application of the integrated reactor for selective oxidation of carbon monoxide in fuel cell systems.    DESCRIPTION OF DRAWING(S) - The drawing is a overhead view of an integrated reactor.    Integrated reactor (10)    Fluid distribution area (11)    Reforming gas (13)    Combustion gas (14)    Channel structure (15)    Reaction area (16)    Transverse channels (17)    Feed guidance assembly (18)    Fluid collection area (19)