Heat exchanger and method of manufacturing the same

An exhaust gas recirculation cooler configured to cool exhaust gas from an engine, the heat exchanger comprising:

• an inlet configured to receive the exhaust gas from the engine;
• an outlet configured to direct the exhaust gas back toward the engine;
• an exhaust gas flow conduit including
• a first end adjacent the inlet,
• a second end adjacent the outlet,
• a first arcuately shaped side,
• a second arcuately shaped side opposite the first arcuately shaped side,
• substantially flat broad sides extending between the first arcuately shaped side and the second arcuately shaped side,
• a first channel adjacent the first arcuately shaped side and extending between the first end and the second end, the first channel having a first hydraulic diameter,
• a second channel adjacent the second arcuately shaped side and extending between the first end and the second end, the second channel having a second hydraulic diameter, and
• a plurality of third channels located between the first channel and the second channel, each of the third channels having a third hydraulic diameter, the third hydraulic diameter less than the first hydraulic diameter;
• and
• a plate located at one of the first end and the second end of the exhaust gas flow conduit to inhibit the exhaust gas from flowing through at least one of the first channel and the second channel while allowing exhaust gas flow through the plurality of third channels.