Step #1: Match heat source power density to wick type. If power density is below 30 W/cm2, a screen/bundled fiber or grooved wick may be adequate. Anything much above that and a sintered wick is the likely choice.
Step #2: Ensure wick can handle orientation requirements. Grooved and screen wicks offer high Qmax for a given size heat pipe, but they can have dry-out problems if the evaporator is much above the condenser. Sintered wicks work much better against gravity than other wick types.
Step #3: Optimize the wick design for the specific application. Heat pipes only operate as intended when a sufficient amount of working fluid is transported from the condenser to the evaporator in order to prevent wick dry-out. This capillary limit is usually the gating factor in heat pipe operation and is determined by two opposing factors:
- Capillary pressure provides the driving force for the working fluid to move from the condenser to the evaporator through the wick structure, especially when working against gravity.
- Pressure drop opposes the movement of the working fluid and is typically caused by resistance within the wick structure and the internal geometry of the heat pipe
These two factors move together but wick design choices – even within wick types – can optimize the heat pipe for specific applications.
By optimizing wick characteristics, engineers can tune heat pipes for specific application requirements. Typically, this involves changes to pore size and/or wick volume.
