Heat exchange device comprising: - a circulation enclosure delimited by at least two side plates, called external plates (18, 19), - an inlet frame, having at least one inlet, called first inlet, of a first heat transfer fluid in the circulation enclosure, - an outlet frame, having at least one outlet, called first outlet, of the first heat transfer fluid outside the enclosure, the inlet frame and the outlet frame being interconnected by each of the external plates (18, 19) and adapted to allow the circulation of a first flow of heat transfer fluid in said circulation enclosure in one direction, called the main direction of circulation of the first fluid, between the first inlet and the first exit, - a second inlet, between the inlet frame and the outlet frame, of a second heat transfer fluid in the circulation enclosure, - a second outlet, between the inlet frame and the outlet frame, of the second heat transfer fluid outside the circulation enclosure, - a passage, called passage of the second heat transfer fluid, allowing the circulation of a flow of the second heat transfer fluid in the circulation enclosure between the second inlet and the second outlet, - a plate exchanger block arranged in the circulation enclosure so as to be in fluid communication with the inlets and the outlets to allow the circulation of the first heat transfer fluid and the second heat transfer fluid in and through this exchanger block and the transfer of calories between them, comprising at least one stiffening device of said heat exchange device, said stiffening device: - mechanically connecting the input frame and the output frame, characterised in that it comprises at least one reinforcing bar arranged so as to extend between the input frame and the output frame forming a non-zero angle with respect to the main direction of flow of the first fluid, each bar having at least one point of attachment to the inlet frame and at least one point of attachment to the outlet frame, - being adapted to: ∘ increase the stiffness of the circulation enclosure with respect to the translational movements of the input frame and of the output frame relative to each other in a direction orthogonal to the main direction of circulation of the first fluid, ∘ extend through said passage of the second heat transfer fluid without preventing the circulation of the second flow of heat transfer fluid between the second inlet and the second outlet. - a circulation enclosure delimited by at least two side plates, called external plates (18, 19), - an inlet frame, having at least one inlet, called first inlet, of a first heat transfer fluid in the circulation enclosure, - an outlet frame, having at least one outlet, called first outlet, of the first heat transfer fluid outside the enclosure, the inlet frame and the outlet frame being interconnected by each of the external plates (18, 19) and adapted to allow the circulation of a first flow of heat transfer fluid in said circulation enclosure in one direction, called the main direction of circulation of the first fluid, between the first inlet and the first exit, - a second inlet, between the inlet frame and the outlet frame, of a second heat transfer fluid in the circulation enclosure, - a second outlet, between the inlet frame and the outlet frame, of the second heat transfer fluid outside the circulation enclosure, - a passage, called passage of the second heat transfer fluid, allowing the circulation of a flow of the second heat transfer fluid in the circulation enclosure between the second inlet and the second outlet, - a plate exchanger block arranged in the circulation enclosure so as to be in fluid communication with the inlets and the outlets to allow the circulation of the first heat transfer fluid and the second heat transfer fluid in and through this exchanger block and the transfer of calories between them, comprising at least one stiffening device of said heat exchange device, said stiffening device: - mechanically connecting the input frame and the output frame, characterised in that it comprises at least one reinforcing bar arranged so as to extend between the input frame and the output frame forming a non-zero angle with respect to the main direction of flow of the first fluid, each bar having at least one point of attachment to the inlet frame and at least one point of attachment to the outlet frame, - being adapted to: ∘ increase the stiffness of the circulation enclosure with respect to the translational movements of the input frame and of the output frame relative to each other in a direction orthogonal to the main direction of circulation of the first fluid, ∘ extend through said passage of the second heat transfer fluid without preventing the circulation of the second flow of heat transfer fluid between the second inlet and the second outlet. ∘ increase the stiffness of the circulation enclosure with respect to the translational movements of the input frame and of the output frame relative to each other in a direction orthogonal to the main direction of circulation of the first fluid, ∘ extend through said passage of the second heat transfer fluid without preventing the circulation of the second flow of heat transfer fluid between the second inlet and the second outlet.