High-Temperature Tungsten Liquid Metal Heat Pipes: Applications and Performance

The thermal management of hypersonic leading edges is driven by high heat fluxes and high operational temperature regimes. Multiple approaches including ablative armor, transpiration cooling, fluid loops, and heat pipes are discussed and evaluated for their merits. A focus is laid upon a tungsten heat pipe operating with lithium as the working fluid. A numerical model is developed to characterize the thermal performance of such systems. Numerical results are compared to approximations applying first principles governing equations. Operational points close to the capillary limit and the sonic limit are chosen to highlight the characteristics of a liquid-metal heat pipe configuration. It is found that the average velocities are insufficient for the determination of the sonic limit as they do not account for higher centerline velocities due to boundary layer formation. The specific heat pipe is found to be suitable for operating at Mach 6-7 applications and provides an order of magnitude improved thermal conductivity compared to pure tungsten.