Heat exchanger

A heat exchanger installed on an intake path or exhaust path of an internal combustion engine and configured to transfer heat between gas containing exhaust and refrigerant, the heat exchanger comprising:

• a gas path through which the gas flows;
• and
• a refrigerant path through which the refrigerant flows, wherein
• a water-repellent portion provided with water-repellent treatment is formed at part of a portion that contacts the gas in the gas path, and
• a hydrophilic portion provided with hydrophilic treatment is formed at part of the portion that contacts the gas in the gas path, the part being different from the water-repellent portion and having a temperature lower than the temperature of the water-repellent portion while the heat exchanger is actuated, wherein a portion of the gas path having a temperature higher than a boundary temperature, measured between the water-repellant portion and the hydrophilic portion, while the heat exchanger is actuated is free of the hydrophilic portion, wherein
• the gas path includes a plurality of pipes disposed in parallel to each other in the heat exchanger,
• the water-repellent portion is formed on inner wall surfaces of some of the plurality of pipes,
• the hydrophilic portion is formed on some other pipes of the plurality of pipes, the other pipes being different from the pipes on which the water-repellent portion is formed, and
• the other pipes on which the hydrophilic portion is formed are disposed at a part having a temperature lower than the temperature of a part at which the pipes on which the water-repellent portion is formed are disposed while the heat exchanger is actuated.