Two-Phase Magic
A heat pipe harnesses the enormous energy of phase change to transport heat with almost no temperature drop. When liquid evaporates at the hot end, it absorbs the latent heat of vaporization — about 2,260 kJ/kg for water. The vapor rushes to the cold end at near-sonic speed, condenses, and releases that energy. The wick structure then pulls the liquid back by capillary action. This closed-loop cycle creates an effective thermal conductivity 25–100 times higher than solid copper, which is why heat pipes are inside virtually every laptop.
The Capillary Engine
The wick is the heart of a heat pipe. Its pore structure generates capillary pressure that pumps the working fluid against gravity and viscous resistance. Sintered powder wicks offer high capillary pressure but lower permeability. Grooved wicks provide easy fluid flow but weaker capillary force. Screen mesh wicks balance both. The simulation models capillary-driven flow and shows the pressure balance that determines the maximum heat transport capacity.
Operating Limits
Every heat pipe has a maximum heat transport rate governed by whichever limit is reached first: capillary (wick pumping capacity), boiling (nucleate boiling disrupts the liquid film), entrainment (high-velocity vapor strips liquid from the wick), viscous (insufficient vapor pressure at startup), or sonic (vapor velocity reaches Mach 1). This simulation evaluates all five limits and highlights the active constraint, helping engineers design within safe operating margins.
From Laptops to Spacecraft
Heat pipes cool laptop CPUs, smartphone processors, LED arrays, satellite electronics, and nuclear reactor cores. Variable-conductance heat pipes (VCHPs) use a non-condensable gas to self-regulate temperature. Loop heat pipes (LHPs) separate the vapor and liquid paths for longer transport distances. Pulsating heat pipes use oscillating liquid slugs without any wick. This simulation covers the fundamental straight heat pipe, but the principles extend to all these advanced variants.