Heat exchanger, in particular for exhaust gas cooling system comprising a heat exchanger for cooling the exhaust gas, method of operating a heat exchanger

The invention relates to a heat exchanger, in particular for exhaust gas cooling an internal combustion engine of a motor vehicle comprising a first part heat exchanger (11) having at least a first flow channel (21) for the passage of a medium to be cooled and at least a third flow channel (41) for the circulation of a first coolant, at least a second part of the heat exchanger (12) with at least one second flow channel (22) for the passage of the medium to be cooled and at least one fourth flow channel (42) for the circulation of a second cooling medium, wherein the at least first flow channel (21) and the at least second flow channel (22) are in flow communication and the at least one first flow channel (21) and the at least one second flow channel (22) at least a first specific heat transfer area (23) and at least a second specific heat transfer area (24), wherein the second specific Heat transfer area (24) divided by the first specific heat transfer area (23) a quotient (Ψ) results, wherein the at least one first flow channel (21) has a larger ratio (Ψ) and the second flow channel (22).