Abstract: The invention relates to a heat exchanger (1) for transferring thermal energy from a warm gas flow to a cold gas flow, comprising: a first group of ducts (2) with a first connection and a second connection; a second group of ducts (3) with a third connection and a fourth connection, which group is thermally coupled to the first group of ducts; first supply means (6) for supplying the cold gas flow to the first connection; first discharge means (7) for discharging the cold gas flow from the second connection; second supply means (8) for supplying the warm gas flow to the third connection; and second discharge means (9) for discharging the warm gas flow from the fourth connection, wherein the device comprises alternating means for temporarily and repeatedly alternating in pairs the supply and discharge means on the connections.