Heat Pipe Thermal Resistance & Capillary Limit Calculator
Model electronics cooling heat pipes: maximum capillary heat transport limit (Qmax), thermal resistance network (Rhp), effective length, wick capillary pressure, and vapor core dynamics.
1. Heat Pipe Geometries & Wick Structure
2. Operating Thermal State & Orientation
Pumping Limit & Resistance Results
Internal Architecture & Thermal Resistance Circuit
5 Fatal Engineering Traps in Heat Pipe Thermal Design
1. Capillary Dryout Burnout & Rapid Thermal Runaway
If power dissipation on the evaporator exceeds the maximum capillary pumping limit (Q > Qmax), liquid returns through the wick slower than it evaporates. The porous wick dries out completely. Without liquid to absorb latent heat, evaporator wall temperature surges within seconds by 80°C–150°C, destroying high-power CPUs or GPUs.
2. Adverse Gravity Tilt in Laptop & Vehicle Orientations
Operating a heat pipe with the evaporator physically elevated above the condenser (adverse tilt, ψ < 0°) forces capillary action to fight hydrostatic gravity head (ΔPg = ρl · g · L · sin(ψ)). Grooved or mesh wicks lose up to 85% of their heat capacity when tilted upwards by just 10 degrees, causing unexpected thermal throttling in handheld devices.
3. Non-Condensable Gas (NCG) Blanketing from Aluminum Reaction
Using water as a working fluid inside aluminum tubes creates an electrochemical reaction generating non-condensable hydrogen gas. Vapor sweeps hydrogen into the cold condenser tip, creating an insulating gas bubble that blocks the condensation zone. The effective heat pipe length progressively shrinks until the cooler fails.
4. High-Velocity Vapor Shear & Entrainment Liquid Stripping
At high heat fluxes, high-speed countercurrent vapor rushing past the porous wick surface exerts severe interfacial shear stress. If the Weber number exceeds unity (We > 1), the vapor jet tears liquid droplets directly out of the wick pores and flings them into the condenser, starving the evaporator wick of return liquid.
5. Post-Assembly Pipe Bending & Sintered Wick Delamination
Bending cylindrical sintered heat pipes into intricate shapes around chassis components without precision internal mandrels crushes the vapor space and shears the sintered copper powder off the inner copper tube. Delaminated wick particles float freely, choking capillary flow channels and increasing thermal resistance tenfold.
Capillary Limit & Fluid Transport Formulations (Cotter & Peterson)
Maximum capillary pumping pressure developed by porous wick pores of radius reff:
ΔPc,max = [ 2 · σ · cos(θc) ] / reff
Hydrodynamic pressure balance for continuous steady-state operation:
ΔPc,max ≥ ΔPliquid + ΔPvapor ± ΔPgravity
Liquid viscous pressure drop via Darcy's Law in porous media:
ΔPliquid = [ μl · Leff · Q ] / [ ρl · Awick · K · hfg ]
Maximum capillary heat transport limit (Qmax):
Qmax = [ ΔPc,max - ρl · g · Ltotal · sin(ψ) ] / [ ( μl · Leff ) / ( ρl · Awick · K · hfg ) + ( 8 · μv · Leff ) / ( π · ρv · rv4 · hfg ) ]