A heat exchanger and a method for drying a humid medium. In the heat exchanger an internal cross-over passage, allowing a humid medium to double back on itself in a zone delimited by a barrier, is provided. In a first step the heat exchanger cools itself and in a final step the heat exchanger heats itself. Separation areas allow condensation and collection of water within the heat exchanger. The heat exchanger and method enable drying of compressed air within one and the same heat exchanger package.