A heat exchanger comprising: at least a first plate (12A/B) and a second plate spaced apart from the first plate (12A/B) to define a first gap between inner surfaces of the first plate (12A/B) and of the second plate in which at least a first fluid circulates, with a major portion of the first gap being free of obstructions; a first peripheral wall on the periphery of the first gap, the first peripheral wall having a curved profile inside the first gap; at least one inlet radially positioned with respect to the first gap to inject the first fluid in the gap; at least one outlet centrally positioned in the second plate, for the first fluid to exit the first gap, said at least one outlet being a first pipe centrally positioned in the second plate for the first fluid to exit the first gap, whereby the first fluid circulates in a swirling flow in the major portion of the first gap; characterised by at least a third plate spaced apart from the outer surface of the first plate (12A/B) to define a second gap in which at least a second fluid circulates, with a major portion of the second gap being free of obstructions, the second fluid contacting an outer surface of the first plate (12A/B) for heat exchange with the first fluid; a second peripheral wall on the periphery of the second gap having a curved profile inside the second gap; and at least one other inlet and at least one other outlet being in fluid communication with the second gap to cause a swirling flow of the second fluid in the second gap, said other outlet being a second pipe centrally positioned in the third plate for the second fluid to exit the second gap, whereby the first pipe and the second pipe are concentric. at least a first plate (12A/B) and a second plate spaced apart from the first plate (12A/B) to define a first gap between inner surfaces of the first plate (12A/B) and of the second plate in which at least a first fluid circulates, with a major portion of the first gap being free of obstructions; a first peripheral wall on the periphery of the first gap, the first peripheral wall having a curved profile inside the first gap; at least one inlet radially positioned with respect to the first gap to inject the first fluid in the gap; at least one outlet centrally positioned in the second plate, for the first fluid to exit the first gap, said at least one outlet being a first pipe centrally positioned in the second plate for the first fluid to exit the first gap, whereby the first fluid circulates in a swirling flow in the major portion of the first gap; characterised by at least a third plate spaced apart from the outer surface of the first plate (12A/B) to define a second gap in which at least a second fluid circulates, with a major portion of the second gap being free of obstructions, the second fluid contacting an outer surface of the first plate (12A/B) for heat exchange with the first fluid; a second peripheral wall on the periphery of the second gap having a curved profile inside the second gap; and at least one other inlet and at least one other outlet being in fluid communication with the second gap to cause a swirling flow of the second fluid in the second gap, said other outlet being a second pipe centrally positioned in the third plate for the second fluid to exit the second gap, whereby the first pipe and the second pipe are concentric.