US Patent 11480394 Heat pipes having wick structures with variable permeability

A heat pipe is provided having a hollow body defining an interior vapor space, evaporator and condenser regions, a wick structure lining an inner wall of the hollow body, and a working fluid disposed in the hollow body, wherein a path for the working fluid in liquid state extends from the condenser region toward the evaporator region or wherein the wick structure extends along a direction from a first end of the hollow body toward the second end, and wherein the wick structure includes first and second regions that extend along the path or direction and that each have wick particles defining respective pore sizes that are different from one another.