Patent ID: 8544454

Claim:
A flow duct for a heat exchanger, for an exchange of heat between a first fluid, which includes an exhaust gas or exhaust-gas/air mixture or charge air, and a second fluid, which includes a coolant, comprising: a duct casing having an interior space which is surrounded by a duct casing inner side; webs arranged in the interior space on the duct casing inner side, wherein the flow duct has a cross section, which is designed for conducting the first fluid in the interior space and which is configured to be traversed by flow, transversely, with respect to a flow duct axis, and wherein a hydraulic diameter of at most the flow duct, defined as four times a ratio of an area of a cross section which is configured to be traversed by flow to a periphery wetted by the first fluid, is in a range between 1.5 mm and 6 mm, and wherein a ratio of the hydraulic diameter and a duct casing thickness is in a range between 0.8 and 8.