Abstract: A heat exchanger has tubes for performing heat exchange between an internal fluid flowing inside of the tubes and an external fluid flowing outside of the tubes and a tank connected to the tubes. Each of the tubes has projections projecting from an outer surface thereof. The projections are arranged in a longitudinal direction of the tube such that grooves are provided between the adjacent projections as external fluid passage portions. The tank has tube insertion portions defining openings into which ends of the tubes are inserted. Each of the tube insertion portions is configured such that a perimeter surface defining the opening thereof entirely covers at least one external fluid passage portion of the tube.

Abstract: A tube for exchanging heat between inside fluid and outside fluid includes a uniform cross-section portion. The outside fluid flows in an outside passage meanderingly extending in an outside fluid flowing direction. The uniform cross-section portion is disposed at least at each end of the tube longitudinal direction, and has an inside passage and a joint. The inside passage is constructed with a first inner face and a second inner face, which are spaced from each other, and the inside fluid flows through the inside passage. The joint is constructed with the first inner face and the second inner face, which are connected to each other to increase a pressure-resistant strength.