Transpiration cooling of a porous Nb-based alloy in high heat flux conditions

Abstract

High heat flux environments, such as those encountered in atmospheric re-entry and nuclear fusion, impose severe thermal gradients and high local temperatures on structural components. Scalable heat transfer methods need to be integrated with structural designs to manage these extreme heat loads. Transpiration cooling is a potential approach for managing localized heating and maintaining structural durability in these environments. Capillary-driven transpiration cooling shows potential to adapt to dynamic heat flux conditions, but has not yet been investigated under high heat flux conditions. In this investigation, a porous structure was tested with active transpiration cooling under multiple heat flux conditions. Additive manufacturing was employed to produce a specimen with a tailored porous geometry using a refractory niobium-based alloy (C103). Water was selected as the coolant due to the high magnitude of energy absorbed during vaporization. To generate high heat flux environments for testing, an experimental apparatus that employs a high powered laser and corresponding characterization equipment has been designed. Coolant flow through the structure was driven by capillary forces, which enabled rapid adaptation to changes in heat flux from 132–330 W/cm2. Stable coolant flow rates and temperatures were observed under a range of constant high heat flux conditions. The C103 porous sample maintained average surface temperatures below 170 °C while subject to heat fluxes up to 330 W/cm2, indicating the transpiration cooling of the printed structure provided effective heat dissipation in these conditions.