Abstract: A heat-exchange device includes a flow enclosure defined by two external plates, a first inlet and a first outlet for a first heat-transfer fluid, a second inlet and a second outlet for a second heat-transfer fluid, and an exchanger block with plates disposed in the flow enclosure so as to be in fluid communication with the inlets and outlets in order to permit the flow of the first fluid and of the second fluid into and through this exchanger block and the transfer of calories therebetween. Each external plate has at least one hollow. An air-conditioning system may include such device and an aircraft, in turn, can include such air-conditioning system.