The product is fed into the pipes which are available with inside diameters starting at a size of 1 mm. The construction of the very small pipe diameters offers the advantage of a very large surface, hence enabling extremely intense and quick heat exchange, in particular for highly exothermic reactions. This heat exchanger can be used, for example, as a downstream pipe reactor for microstructured production mixers and production reactors. The micro heat exchanger can be supplied as a straight pipe heat exchanger or as a U-tube heat exchanger.