Buoyancy effect on heat transfer and surface coking of hydrocarbon fuel in horizontal square channel at supercritical pressures

Heat and mass transfer of pyrolytic hydrocarbon fuels at supercritical pressure has important implications for regenerative cooling technology in advanced engines. Based on the detailed chemical kinetic mechanism of China No. 3 jet fuel (a.k.a. RP-3), the heat and mass transfer of RP-3 in a horizontal square cooling channel under asymmetric heating and buoyancy at supercritical pressure is investigated numerically. The results show that buoyancy induces secondary flow. The secondary flow enhances the heat and mass transfer between the near wall region and the core flow field, which can effectively improve the utilization level of fuel heat absorption capacity and suppress the carbon deposition on the surface of the cooling channel. In the case of bottom heating, the dramatic change in fuel density with fuel pyrolysis induces the strongest secondary flow, resulting in the highest fuel heat absorption capacity and the least carbon deposition. In addition, as the operating pressure increases, the buoyancy effect becomes stronger duo to fuel pyrolysis, which is significantly different from the buoyancy effect in the non-cracking zone. Under the buoyancy effect, the increased operating pressure enhances the secondary flow intensity, which reduces the heated wall temperature and suppresses the carbon deposition on the cooling channel surface. The results of this paper are expected to provide further insight into the design and optimization of regenerative cooling technologies.