| 摘要 |
PROBLEM TO BE SOLVED: To improve heat exchange efficiency of an EGR cooler, by increasing a heat transfer area in an internal/external peripheral surface of a tube. SOLUTION: Relating to this EGR cooler, having a tube 3 and a shell enveloping this tube 3 to supply cooling water 9 to and discharge it from the inside of this shell to additionally make exhaust gas 10 pass through in this tube 3 so as to perform a heat exchange between this exhaust gas 10 and the cooling water 9, ring-state fins 11, as a fin shape increasing a heat transfer area, are formed in multi-steps by a relatively short pitch in an external peripheral surface of the tube 3.
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