Novel Wick Structures for Improved Heat Pipe Performance

Heat pipes are commonly used for transporting heat over relatively long distances with very low temperature drop. One of the limitations of heat pipes is the capillary limit, which states that the sum of pressure drops of the working fluid cannot exceed the capillary head developed by the wick. Since most of the working fluid pressure drop is incurred in flow through the wick, it is important to reduce the wick resistance as much as possible while still being able to transport the required thermal load. All heat pipes made today have the same wick throughout the heat pipe. This facilitates manufacture, however it causes a great deal more resistance to liquid flow than is minimally required. By breaking the wick up into several different regions in which the wick properties are different, a more optimal stepwise wick is proposed. Preliminary calculations done by the PI indicate that the capillary limit of a heat pipe can be increased by a factor of 2x to 3.5x, depending on the number of discrete steps the wick is divided into. The proposed program aims to demonstrate the improvement in capillary limit experimentally.

Many non-NASA commercial applications would also benefit from more capable heat pipes. Most military electronic systems rely on heat pipes for thermal management. Laptops and desktop computers could make use of this innovation to enable the use of smaller heat pipes that consume less material and therefore weigh less and cost less than current uniform wick heat pipes.

This concept could be applied to any NASA application where conventional heat pipes are used. Radiator panels, reactor cores, electronics thermal management are all candidates to name a few. Heat pipes with higher capillary limits would enable either longer heat pipes, smaller (& lighter) heat pipes, or increased power transport within current SOA weight and volume envelopes.

This is early/mid-stage (TRL 3) — the most realistic path in is NASA SBIR/STTR, which funds small businesses and research institutions to develop technology aligned with NASA's needs (equity-free, phased funding). Check whether a current SBIR/STTR solicitation topic overlaps with this project's technology area, or contact the project directly (above) to ask.

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