Header assembly, heat exchanger and air conditioning system

A heat exchanger, comprising:

• a first header and a second header, wherein the first header and the second header are spaced apart from each other, the first header comprises a first sub-header, the first sub-header comprises at least one header assembly;
• wherein each of the at least one header assembly comprising:
• a first tube comprising a first wall and having a first cavity;
• a first plate at least partially located in the first cavity, wherein the first plate partitions the first cavity into a first sub-cavity and a second sub-cavity;
• a second tube at least partially located in the first cavity, wherein the second tube comprises a second wall and has a second cavity, wherein the second tube further comprises a first communication portion and a second communication portion, the first communication portion is in communication with the first sub-cavity and the second cavity, the second communication portion is in communication with the second sub-cavity and the second cavity, and at least part of the first communication portion is located at the second wall;
• and a first port located at the first wall and in communication with the first sub-cavity;
• and the first sub-header is arranged along a length direction of the first header;
• and
• a plurality of first heat exchange tubes in communication with the first tube and the second header.