Physics / mechanism
A heat pipe is a sealed evacuated vessel containing a working fluid that transfers heat via phase-change cycling: evaporation at the heat source (evaporator), vapour transport along a pressure gradient, condensation at the heat sink, and capillary-driven liquid return through a wick structure. Thermal conductivity effective values reach 10,000–100,000 W/m·K, dwarfing copper (~400 W/m·K). Key parameters: working fluid selection (water, ammonia, sodium for high-temp), wick permeability, vapour space pressure drop, and tilt sensitivity. State of the art includes sintered-powder and axially-grooved wicks operating at <0.1°C/W thermal resistance; loop heat pipes (LHPs) and oscillating heat pipes (OHPs) push performance in orientation-agnostic or ultra-compact geometries.
Competitive landscape
Competing passive thermal solutions include vapour chambers (2D heat spreading, better for planar sources), solid spreaders (pyrolytic graphite, diamond composites), and active liquid cooling loops. For chip-scale applications, microfluidic cold plates and immersion cooling are increasingly competitive above ~300 W/cm². Adjacent: thermoelectric modules (active, lower COP), thermosyphons (gravity-dependent, simpler). OHPs are gaining ground in space and AI accelerator cooling due to no moving parts and high heat flux tolerance.
Companies using
Connected ideas
Sources
Frontier (open questions)
- To be added.