Heat transfer tube and heat exchanger

A heat transfer tube comprising:

• first flow paths aligned in the heat transfer tube;
• and
• a second flow path disposed in an inner end part of the heat transfer tube along a first direction parallel with an alignment direction of the first flow paths, wherein
• each of the first flow paths includes:
• a section with a rectangular shape that is elongated in the first direction;
• and
• protrusions disposed on an inner surface,
• the second flow path includes:
• a section with a rectangular shape or a square shape;
• and
• protrusions disposed on an inner surface,
• an end surface in the first direction of the heat transfer tube has a semiarcuate section,
• the section of each of the first flow paths has a long side having a first length and a short side having a second length, where a ratio of the first length to the second length is between 1.1 and 1.5,
• the second flow path has a sectional area that is smaller than a sectional area of each of the first flow paths, where an aspect ratio of the second flow path is less than 1.1, and
• each inner end part of the heat transfer tube along the first direction includes the second flow path.