Investigation of the coupling characteristics of buoyancy force and fuel endothermic cracking in uniformly heated rectangular channels

With increasing flight Mach numbers, hypersonic vehicles face growing demands for effective heat sinks. Conventional fuels, limited by their endothermic capacity under moderate thermal conditions, can no longer meet these requirements. Hydrocarbon-based chemical heat sinks, utilising deep thermal cracking, offer a potential solution; however, the combined effects of cracking reactions and buoyancy—due to radial density gradients—complicate heat and mass transfer. This study investigates the influence of buoyancy on thermal and chemical transport in uniformly heated horizontal and inclined rectangular channels. Results show that buoyancy increases the outlet fuel temperature by 11 K and reduces the average flow velocity by 0.2 m/s in cracking conditions. It also leads to significant circumferential heat transfer non-uniformity by increasing thermal resistance and reducing heat flux on the upper wall. Buoyancy modifies the wall temperature distribution, suppressing cracking at the top and promoting it at the bottom. Additionally, buoyancy affects coking behaviour, reducing deposition in the inlet region but increasing it at the upper wall and corners, especially under low-pressure and high-flux conditions. These findings inform design strategies for improved regenerative cooling.