Heat transfer apparatus

Apparatus comprising:

• a panel having first and second main faces;
• and
• a sealed system internal within the panel and comprising:
• a first manifold cavity at a first end of the panel;
• a second manifold cavity at a second end of the panel;
• and
• plural passages, each of the plural passages extending from the first manifold cavity to the second manifold cavity, wherein
• the sealed system contains a fluid in both gas and liquid states,
• each of the plural passages defines a phase-change portion and a drain portion,
• the phase-change portion and the drain portion are adjacently located and extend along the passage, and
• for each of the passages:
• the phase-change portion is closer to the first main face than it is to the second main face,
• the phase-change portion has a profile that includes:
• one or more protruding features at least one of which extends away from the first main face, and
• first and second ribs, each extending inwardly with respect to a boundary of the passage, wherein the first and second ribs partially close the drain portion from the phase-change portion, and
• the drain portion is closer to the second main face than it is to the first main face, and
• the drain portion has a profile that is absent of protruding features.