Super Thermal Conductors (Heatpipes) rely upon an effective capillary action between the working fluid and the internal porous lining (wick structure).
Gravity has a very important influence on the thermal performance.
As can be seen in tables 2, gravitational effect can increase the thermal transmission capabilities of an STC or STX Heatpipe to 2 times that of its maximum thermal transmission capability when operating in a vertical plane; i.e. with Evaporator section lower than Condenser section.
In this orientation gravity assists the return fluid flow.
In the opposing mode, i.e. Evaporator section high, and driving heat downwards, the capillary action must work against gravitational force.
Table 3 shows the influence in this case, which is entirely dependent upon the static height difference between the Condenser and Evaporator section.
For certain applications, where this effect would cause an unacceptable constraint on a system, DAU can offer also special antigravity Heatpipes (Series SSC and SSX) with special capillary wick structures, which have a much reduced sensitivity to effects of gravity.