Heat pipe with composite wick structure

A heat pipe comprising:

• a metal casing having an evaporator section and a condenser section;
• a porous major wick structure disposed on an inner wall of the casing, an average pore size of the major wick structure corresponding to the evaporator section being smaller than that of the wick structure corresponding to the condenser section;
• at least one assistant wick structure disposed in an inner wall of the major wick structure, the at least one assistant wick structure defining a plurality of pores communicating an inside of the at least one assistant wick structure with an inside of the major wick structure and a channel in an inner space thereof;
• and
• working medium filling in the casing and saturating the major wick structure and the at least one assistant wick structure;
• wherein vapor in the metal casing flows from the evaporator section to the condenser section via a space between the major wick structure and the at least one assistant wick structure, and condensate in the metal casing flows from the condenser section to the evaporator section via the pores of the major and the assistant wick structures and the channel of the assistant wick structure.