Heat transfer to supercritical hydrocarbon fuel in horizontal tube: Effects of near-wall pyrolysis at high heat flux

•An improved kinetic model was applied for pyrolysis in CFD simulations.•Effects of near-wall pyrolysis on the heat transfer were detailedly analyzed.•Nu is decreased for the increased thermal boundary layer effect at high heat flux. Understanding heat transfer to endothermic hydrocarbon fuels (EHFs) with pyrolysis at high heat flux is a challenging issue for the design of regenerative cooling panels in the fuel-cooled thermal management technology of advanced aircrafts. In this work, the convective heat transfer of supercritical EHFs in presence of pyrolysis reactions was experimentally investigated in horizontal tubes at the heat flux up to 1.836 MW/m2 under 3.5 MPa. A CFD model with an improved kinetics (Chem Eng Sci 2019, 207, 202-214) has been developed and extensively validated to get detailed information on the coupling mechanism of heat transfer and pyrolysis. The heat transfer rate can be enhanced by pyrolysis reactions at relative low heat flux (below 400 kW/m2). With increasing heat flux, the rapid and high-degreed pyrolysis near-wall considerably changes the local composition and thus the thermophysical properties, resulting in the significant heat absorption differences in the cross section and local heat transfer deterioration. Typically, Nub decreases from 108.8 to 73.4 (about 30%) when the heat flux increases from 426 to 758 kW/m2. The possible reasons may be attributed to the weakened near-wall turbulence by the increased fluid viscosity in presence of secondary products, as well as the increased thermal boundary layer effect attributed to the high near-wall heat absorption and huge radial property gradient at high heat flux.