Heat exchanger

A heat exchanger comprising:

• a plurality of flat tubes;
• a first header collecting pipe to which one end of each of the flat tubes is connected;
• a second header collecting pipe to which the other end of each of the flat tubes is connected;
• and
• a plurality of fins joined to the flat tubes,
• the heat exchanger being capable of functioning as an evaporator by exchanging heat between a refrigerant flowing in the flat tubes and air, wherein
• the first header collecting pipe and the second header collecting pipe stand upright,
• the first header collecting pipe is provided with one connection port to which a pipe is connected to guide a gas-liquid two-phase refrigerant into the first header collecting pipe, and
• the first header collecting pipe has
• main horizontal partition plates that define a plurality of communication chambers, each communicating with one or more of the flat tubes, by horizontally crossing an internal space of the first header collecting pipe,
• a vertical partition plate that defines a mixing chamber, communicating with the connection port and all of the communication chambers, by vertically running through the internal space of the first header collecting pipe, and
• an auxiliary horizontal partition plate that defines, along with the vertical partition plate, the mixing chamber by being disposed between a pair of the main horizontal partition plates, which are vertically adjacent to each other, and by horizontally crossing the internal space of the first header collecting pipe, and
• the mixing chamber is shorter in height than one of the plurality of communication chambers, which is adjacent to the mixing chamber, with the vertical partition plate interposed between the mixing chamber and the adjacent communication chamber.