Design of micro-channel based actively cooled thermal shields for ultra-high temperature applications

• Design for novel actively cooled microchannel thermal shields is analyzed; • Microchannel design has only minor effect on coolant mass flow rate requirements; • UHTC ceramics optimal due to high thermal conductivity and temperature tolerance; • Liquid water coolant mass requirements might be competitive with ablative shields; In this study, novel designs of high-temperature thermal shields that can be actively cooled by circulating water through a bioinspired internal microchannel network are numerically evaluated. The level of cooling that can be achieved and the thermal stresses developed in the shield material are analysed using computational fluid dynamics and finite element modelling. From the comparative analysis of those results, design guidelines for the development of such actively cooled thermal shields (ACTS) are proposed: (i) channel design plays only a minor role on the coolant mass needed to produce a desired level of cooling but (ii) small channels around the regions of maximum temperature gradient and stress concentrators like sharp corners should be avoided to prevent cracking of the shield material; and (iii) high temperature tolerance and high thermal conductivity are key parameters for the shield material. Thus, ultra-high temperature ceramics (UHTC) such as ZrB 2 appear to be optimal candidates for the additive fabrication of such ACTS elements, provided they can survive the thermal cycling without cracking. Water was confirmed as an excellent coolant for such an application, enabling the development of reusable solutions for aerospace re-entry shields, involving coolant masses that could become competitive against current single-use ablative shields. Similar systems could provide suitable thermal protection or heat exchange solutions in many other demanding industrial applications.