Heat exchanger

A heat exchanger comprising:

• a plurality of flat tubes;
• a first header-collecting pipe connected to an end of each of the flat tubes;
• a second header-collecting pipe connected to the other end of each of the flat tubes;
• and a plurality of fins joined to the flat tubes, the heat exchanger provided in a refrigerant circuit which is configured to perform a refrigerating cycle, and causing a refrigerant to exchange heat with air, wherein
• the first header-collecting pipe and the second header-collecting pipe are in an upright position,
• a plurality of heat exchange sections each of which is constituted by adjacent ones the flat tubes are arranged one above the other,
• the first header-collecting pipe includes therein one communicating space which communicates with the flat tubes of all of the heat exchange sections,
• the second header-collecting pipe includes therein subspaces which correspond to the heat exchange sections on a one-by-one basis and each communicate with the flat tubes constituting a corresponding one of the heat exchange sections, and
• the heat exchanger further includes a discharge accelerator which accelerates discharge of the refrigerant in a liquid state from a lower portion of the heat exchange section which is the lowermost heat exchange section during defrosting in which the refrigerant in a high-pressure gas state is introduced from the communicating space to the flat tubes in order to melt frost having formed on the fins.