A wick, for example a few layers of fine gauze, is commonly used. This is fixed to the inside surface of the tube, and capillary forces return the condensate to the evaporator ( illus. b).

Since the evaporator position is not restricted, the air conditioning heat pipe may be used in any orientation.

One limitation of the basic thermosiphon is that in order for the condensate to be returned by gravitational force to the evaporator region, the latter must be situated at the lowest point.

The air conditioning heat pipe is similar in construction to the thermosiphon, but in this case provision is made for returning the condensate against a gravity head.

If the air conditioning heat pipe evaporator happens to be in the lowest position, gravitational forces will assist the capillary force.

Alternative techniques, including centripetal forces and osmosis, may be used for returning the condensate to the evaporator.